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CESIZECITEE

APRIL 1976

Features

VOL 5 No 4

CA31 30 . . . .

More circuits and applications

SPACE ENVIRONMENTPhoto -feature on spaceflight

TELEPHONES..The centenary of Alexander Graham Bell's historic achievement

MICROFILE ..What's on the chip?

CMOS - PART 3This month we look at counters

ELECTRONICS - IT'S easy . .

-if you take it logically!'

FEED IT FORWARD .......The 1926 principle behind current -dumping

Projects

17

30

36

45

59

65

68

STOPWATCH /CALCULATORStopwatch into calculator will go!

NOISE GENERATORGenerates white or pink noise

AUDIO MILLIVOLTMETERSensitive Instrument for audio noise and signal measurements

5V SWITCHING POWER SUPPLYUseful design illustrates interesting technique

Data Sheet

10

22

54

THE SP8505, an ECL counterTHE TBA570, an AM /FM RECEIVER IC

News & Information

51

EDITORIAL AND ADVERTISEMENTOFFICE36 Ebury StreetLondon SW1VV OLWTelephone: 01-730 8282

HALVOR W. MOORSHEADEditor

ROBERT C. EVANSAdvertisement Manager

STEVE BRAIDWOOD, G3WKEAssistant Editor

LES BELL, G4CFMRON HARRISEditorial Assistants

JEAN BELLProduction

INTERNATIONAL EDITIONSCOLLYN RIVERSEditorial Director

AUSTRALIAModem Magazine Holdings LtdRyrie House, 15 Boundary StreetRushcutters Bay 2011Sydney, Australia.

FRANCEDENIS JACOBEditor in chiefCHRISTIAN DARTEVILLEEditorElectronique Pour Vous international,17 Rue de BuciParis, France.

Electronics Today International is normally published52 on the first Friday of the month prior to the cover date.

NEWS DIGESTSECOND CHANCE ON THE EXELAR WATCH OFFER.ETI BOOK SERVICEPREVIEW OF MAY ETI ........ETI SPECIALSELECTRONICS TOMORROWTECH -TIPSPULSAR

Index

69

344067707273

TECH -TIPS & DATA SHEET, 4 year Index

Special Offer

PUBLISHERSModern Magazines (Holdings) Ltd36 Ebury Street, London SVV1W OLW

DISTRIBUTORSrgus Distribution Ltd

RINTERSGB Newspapers Limited, Colchester

READERS' QUERIES These can only be answered if:hey relate to recent articles published in the magazineRarely can we supply information in addition to thatpublished Written queries must be accompanied by astamped addressed envelope. and telephone queriesmust he brief, not before 4pm and can only beanswered subject to the availability of technical staff.

42 BACK NUMBERS Back numbers of many issues areavailable for 40p each plus 1 5p postage.)SUBSCRIPTIONS. Great Britain CL5.00 per annumOverseas L5.50.

MARSHALL'S CMOS & TTLEnormous discounts

39

Our cover this month shows the calculator/stopwatch, featured on p10, inaction at the ETI 'Yard of Ale' contest, held by courtesy of the landlord of theVictory in Pinner.

COPYRIGHT All material is subject to world wideCopyr'ght protection All reasonable care is taken in thepreparation of the magazine to ensure accuracy but ETIcannot be held responsib'e for it legally Where errorsdo occur. a correction will be published as soon as-possible afterwards in the magazine

READER StRVICES See page 82 fordetails of all ETI Reader Services and otherinformation

1

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-

000

OUR PRICE ONLY -

High quality modules for stereo, mono andother audio equipment.

PUSH-BUTTON

STEREO

\\N- FM TUNER£19 95 Fitted with Phase Lock -loop Decoder

-,4=

The 450 Tuner provides insiant program selection at the touchof a button ensuring accurate tuning of 4 pre -selected stations,any of which may be altered as often as you choose, by simplychanging the settings of the pre-set controlsUsed with your existing audio equipment or with the BI -KITSSTEREO 30 or the M K60 Kit etc Alternatively the PS12 can,b2 used if no suitable supply is available. together with theTransformer T461.The S450 is supplied fully built. tested and aligned The unit iseasily installed using the simple instructions supplied

* FET Input Stage VARI-CAP diode tuning* Switched AFC* Multi turn pre-sets* LED Stereo Indicator

Typical Specification:Sensitivity 311 voltsStereo separation 30dbSupply required 20-30v at90 Ma max.

STEREO PRE -AMPLIFIER

A top quality stereo pre -amplifierand tone control unit The sixpush-button selector switch pro-vides a choice of inputs togetherwith two really effective filters forhigh and low frequencies, plus tapeoutputMK. 60 AUDIO KIT: Comprising2 x AL60's 1 a SPM80. 1 xBTM80. 1 x PA100 1 front panel

and knobs 1 Kit of parts to includeon/off switch, neon indicatorstereo headphone sockets plusinstruction booklet. COMPLETEPRICE £27.55. plus 62pTEAK 60 AUDIO KIT: postageComprising Teak veneered cabinetsize 163/4x 1 1 %/2"x33/4 otherparts include aluminium chassis.heatsink and front panelbracket plus back paneland appropriate sockets Zetc KIT PRICE £9.20/'plus 62ppostage SPECIFICATION:

Frequency Response + 1 dB 20Hz20KHz Sensitivity of inputs1 Tape Input 100mV ,nto 100K ohms2 Radio Tuner tOOmV into

100K ohms3 Magnetic P U 3mV into

501< ohmsP U Input equalises to R 1 AA curve with1 dB from 20Hz to 20KHzSupply - 20.35V at 20mA

Dimensions299mm x 89mm x

35mm

PA100OUR PRICE

£13.50

ALM20-30

AMPLIFIER MODULESThe ALIO. AL20 and AL30 unitsare similar in their appearance andin their general specificationHowever, careful selection of theplastic power devices has resultedin a range of output powers from 3to 10 watts R.M.SThe versatility of their designmakes them ideal for use in recordplayers. tape recorders, stereoamplifiers and cassette and car-tridge tape players in the home

Harmonic Distortion Po=3 watts f=1KHz 02.5%/ Load Impedance 8-16ohm Size: 75mm x 63mm x 25mm

110 Frequency response ±-3dB Po= 2 watts 50Hz-25Hz Sensitivity for Rated 0/P - Vs=25v. RL=8ohm f =1K Hz 75mV.R MS

AL1O AL20 AL303w R.M.S. £2.30 5w R.M.S. £2.65 lOw R.M.S. £2 95

AL 60 25 Watts (RMS)* Max Heat Sink temp 90C. * Frequency response20Hz to 100KHz * Distortion better than 0.1 at 1KHz *Supply voltage 15-50v * Thermal Feedback * LatestDesign Improvements * Load - 3,4,8, or 16 ohms *Signal to noise ratio 80db * Overall size 63mm. 105mm.13mm.Especially designed to a strict specification Only thefinest components ',aye been used and the latestSolid-state circuitry incorporated in this powerful littleamplifier which should satisfy the most critical A Fenthusiast 3.95

MPA30

Enjoy the quality of a magnetic cartridge withyour existing ceramic equipment using the newM.P.A 30, a high quality pre -amplifier enablingmagnetic cartridges to be used where facilitiesexist for the use of ceramic cartridges onlyIt is provided with a standard DINinput socket for ease of connectionFull instructions supplied.

VATADD25%

POSTAGE &PACKINGPostage & Packing add25p unless otherwiseshown. Add extra forairmail. Min. £1.00

STEREO 30COMPLETE AUDIO

7 + 7 WATTSR.M.S.

P & P 45p

£15.The Stereo 30 comprises a complete stereopre -amplifier, power amplifiers and power supply. This,with only the addition of a transformer or overwind willproduce a high quality audio unit suitable for use with awide range of inputs Le high quality ceramic pick-up.stereo tuner, stereo tape deck etc Simple to install,capable of producing really first class results. this unit issupplied with full instructions, black front panel knobs.main switch. fuse and fuse holder and universalmounting brackets enabling it to be installed in a recordplinth, cabinets of your own construction or the cabinetavailable Ideal for the beginner or the advancedconstructor who requires Hi-Fi performance with a

minimum of installation difficulty (can be installed in 30mins)

TRANSFORMER £2.45 plus 62p p &pTEAK CASE £3.65 plus 62p p & p

1Frequency Response 20Hz-20KHz(-3dB). Bass and Treble range12dB. Input Impedance 1 meg ohm.Input Sensitivity 300m V. Supplyrequirements 24V .5mA. Size 152mmx 84mm x 33mm.

Stabilised Power Supply Type SPM80SPM80 is especially designed to power 2 of the AL60 Amplifiers,up to 15 watts (R.M S.) per channel simultaneously With theaddition of the Mains Transformer BMT80, the unit will provideoutputs of up to 1.5A at 35V. Size 63mm. 105mm 30mmIncorporating short circuit protectionTransformer BMT80£2.60 + 62p postage £3.00

PS12

NEW PA12 StereoPre -Amplifier com-pletely redesignedf or use with AL1 020/ 30 Amplifier

Modules. Features include on' off volume.Balance, Bass and Treble controls. Complete

with tope output

6.50Power supply for AL10/20/30,PA12, SA450 etc

Input voltage 1 5-20v A C Output voltage 22-30v D COutput current 800 mA Max. Size 60mm x 43mm x 26mmTransformer T538 £2.30 OUR PRICE E1 20

131 -PAMP.O. BOX 6, WARE, HERTS.

is

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

11E115 digestNO STRINGS (GUITAR?) POWER

Designated the AL250, a new 125Wrms amplifier rose to our noticerecently from Bi-Pak Semiconductors,63a High Street, Ware, Herts. Retailingat under £16 the amplifier has a verygood specification, (see below) thatwould suit it perfectly for use as aguitar amplifier, assuming a suitablepre -amp.

The unit is protected against short-circuit and low loading of the output,and should be, therefore, fairly ruggedin use. Bi-Pak state on their sheet thatthe unit is suitable for 'background'

music. Background at 125W rms?Amen to that! Details from Bi-Pak.

SPECIFICATIONOutput Power (4E2 load) 125WrmsSensitivity (for 100W at lkHz) 450mVInput Impedance (at 100kHz) 331,S2

T.H.D. 50W into 4S2 0.1%50W into 8E2 0.06%

Signal to Noise Ratio(at 1/2 power) >80d B

Power Bandwidth (-3dB) 2 0 Hz -2 5 k HzDamping Factor (8E2 load, at lkHz) 65Size 190 x 205 x 40mm.

SINGLE CHIP LON COSTTEMPERATURE CONTROLLERThe new National SemiconductorLM3911 IC will control temperatureover the -250C to +850C rangebetter than 1/100C stability. Includedon the chip is the calibrated temperature sensor, voltage reference andop -amp. All that is needed for thecomplete control system are set -pointresistors and a power control device.The sensor Is calibrated directly indegrees Kelvin at 10mV/0K and initialaccuracy is +100K, but can beimproved externally. Applications forthe LM3911 range from home thermo-stats to precision temperature baths.The low cost makes it attractive touse as fire alarms or overtemperaturedetectors in electronic circuitry. Forexample, an LM3911 could beincluded in MOS memories to speedclock rate as temperature increased.

NAVY WIRED FOR VISIONMuirhead Ltd, have recently deliveredwire photo equipment to the Navy.Photo transmitters are located onboard ships in areas where incidentsmay occur and photographs taken arethen sent back to a receiver locatedin Whitehall. In this way Governmentofficials have photographic informat-ion available to support verbal reportsof the incident. This equipment was inregular use recently on board theNaval Frigates supporting Britishtrawlers in the Cod War.

111111111=111M11111.11.11

NEW LUX TURNTABLE

41111,_0,

Aimed at the very top of the marketthe PD282 is the first venture intoturntables for the Lux Corporation.The device is direct drive with aunique bearing system. No furtherdetails are available at present, butwatch for it, as it is due to be releasedhere very shortly. (For a while SMEhad the only one in the country.) Theprice will be very high; the PD282 sellsin France for 1664Fr (£168).Distributor: Howland West Ltd.,3-5 Eden Grove, London N7 8E0.

TANDY LISTS

We have just received the new Tandycatalogue, listing their ranges of hi-fiand electronic components. Whilst thehi-fi ranges offer only questionablevalue for their price, the cataloguedoes include some hard -to -obtaincomponents e.g. strobe tubes. Theprices are high, but if you can't findit elsewhere, try Tandy.

FAIRCHILD TO ENTER TV GAMESMARKET

Fairchild's Consumer Division areplanning to launch a wide variety ofTV games in the US during the latterpart of 1976.

The basic unit providing threegames is expected to retail for aboutE. 100 in the US but Fairchild haverecognised that one quickly tires of alimited choice of games, so the unitwill have a slot into which 'cassettes'can be inserted to increase greatly thegame choice. Each cassette will enable3 extra games to be played. Theseinclude sophisticated race track andwar games. Cassettes are expected toretail for S 15.

Plans to market the units in the UKhave not been finalised but it is hopedto launch the range in Britain during1977.

APOLLO-SOYUZ PULSAR

Not, as you would think, the ETIclock taking to space, but the firstextra-galatic pulsar star. It was dis-covered by the Apollo spacecraftduring the link -up last year. Lying inthe Lesser Magellanic Cloud it forms abinary pair with a blue giant, circlingit every 3.89 days. Designated SMC-X1the star is ten times as powerful as anyin our own galaxy.

HOWS DAT!

Maplin Electronic Services produce aregular news sheet as a cataloguesupplement and frequenctly liven thisup with cartoons. Main 'feature' ofthe February 1976 is the ETI DynamicNoise Filter covered in the Februaryand March issues; Maplin are doing akit for this.

We were especially taken with theaccompanying cartoon done for themby Sid Parker of the SouthendEvening Echo and reproduce it belowby kind permission of the artist andMaplin

"I AM FINDIN' DIS DE BEST WAY0' GEDDIN' RID 0' DE WHITENOISE"

75 WAS BAD YEAR FORSEMICONDUCTOR COMPANIES

Last year was a bleak one for the USsemiconductor industry according toan analysis by the Chase ManhattanBank. This had been widely predictedbut only now are the facts comingout.

In the US, the sales of consumerelectronic products was 20% down'audio equipment was down a stagger-ing 30%: Microwave ovens were one ofthe few products which inproved.

The falling sales of consumer pro-ducts led to a 20% drop in semicon-ductor sales but in the last monthsof 1975 a distinct improvement wasunder way. Traditionally the trendsin the US are followed about sixmonths later in Europe and Japan.If this follows on this occasion we canexpect an improvement elsewhere inthe world within a few months.

Digital watches 'took off' last year,cushioning the blow to somecompanies: sales topped 3 millionunits in 1975.

NATIONAL CALCULATOR IC

National Semiconductor offer a new,low-cost six digit floating decimal cal-culator circuit, MM5777. The deviceuses a metal -gate P -channel MOSprocess - a tried and tested processthat gives low end -production cost.

To assemble a complete four -function, six -digit calculator thecompany offer: -

NSA 1161DS 8977MM 5777

LED display stickDigit driverCalculator chip

9V Battery and keyboard to choice

The MM5777 is a 24 -pin, Epoxy -BDI L package, and gives leading andtrailing zero suppression to conservebattery power. It operates with alge-braic notation, and features floatingpoint input and output and chainoperations.

SCHOOL FOR TEACHERS

Essex University will be holding itsElectronics Summer School forteachers during the week July 12-16.This year three courses will be runsimultaneously, Linear Circuit Design,Digital Circuit Design and SmallComputer Systems. This is a newcourse which should be of interest tomathematics teachers as well as thoseinterested in electronics: Furtherinformation from R. J. Mack at theDepartment of Electrical EngineeringScience, University of Essex,telephone Colchester (0206) 44144extension 2408 or 2299.

BOUNCING METERS

Western Instruments have released anew VOM series, one major feature ofwhich is their 'invunerability'. Allfive models in the 660 series aredrop -proof and feature a custom

rugged self -shielded taut -band mech-anism, diode -protected meter move-ment, temperature compensation,pluggable circuit board assemblies,

external fuse replacement, and can berecalibrated without removing fromtheir case. They are warranted, inwriting,to operate after being droppeda height of five feet. (So if youre asmall clumsy engineer - your troublesare over!). Details from ElectroplanLtd, P.O. Box 19, Orchard Road,Royston, Herts. SG8 5HH.

CLOCK UP AN INCH

Two new multiple -digit, PCB mountednumeric LED displays have been intro-duced by Litronix. Each incorporatefour 7 -segment numeric LED displaymounted on a PCB within a red filter.A digit height of the 4520A is '/2in.,and of the 4120A, 1 in. -- the largestnumeric LED display currentlyavailable.

Design principally for applicationsin 12 -hour or 24 -hour electronicdigital clocks, the displays includecolons for a.m., p.m. and Alarm Set

indication, and feature excellentcharacter definition at viewingdistances in excess of 60ft.

Typical electrical characteristics ofthe DL -4520A are: forward voltage of1.8V (at 20mA per segment);luminous intensity of 1.0 mcd; theDL -4120A has a typical forwardvoltage of 3.6V (at 20mA)., luminousintensity of 2.0 mcd.

Production prices are anticipated tobe £4.80 for the DL -4520A, and £5.50for the DL -4120A, in quantity.

news digestFAIRCHILD WATCHESThe Savoy Hotel recently lent itshallowed halls to the launching of yetanother range of digital watches. Theculprits on this occasion are theFairchild Corporation. Two differentlines are being introduced to the UKat present (although a third is

apparently possible in the future).The more expensive of these will carrythe Fairchild name, for distributionthroygh 'fine jewellers' only, withdiscounting a forbidden practise. Theother is marketed under the Timebandname, and is intended for the massmarket, with prices ranging from£19.95 up to £32.95. Prices for themore expensive Fairchild line run from£44 to just below £100. All watchesemploy the same circuit module, anduse LED display. Price differencesare accounted for by styling, braceletand case.

A great deal of work has obvioslybeen expended on the ladies ranges,and here Fairchild have a head start onthe rest of the market. The mensmodels, however, seem little differentto the vast majority of those alreadyon sale in the "UK marketplace"(Fairchilds phrase). Circuitry is alsoalong standard lines and uses a 32kHzoscillator to derive the timing pulses.

The watches are five function, and areoperated by a single pushbutton.

One point perhaps worth notingis that batteries are not userreplaceable and return to the retaileris advised. An obvious question ishow happy are the 'mass market'retailers going to be about carryingout this time consuming operation?Perhaps all digital watch manufact-urers should consider this aspect moreclosely in the future. Availability atpresent is zero, but immediate ship-ments are being arranged by thecompany.

NEW CBM SCIENTIFIC

CBM introduce Greenline SR1800scientific calculator at £29.95 includ-ing VAT, with the optional extra ofa rechargeable cassette and mainsadaptor/charger which come togetheras a rechareable kit for an additional£6.00. This give gives 3 -way powerwith disposable battery, mains and

1?3,i5S lit_12

responsibility will be taken for peorilecontracting 'button mania' from theanimal. We are so intrigued by theSR419OR that we have arranged toreview it more fully in the next issue.

TEXAS RECALCULATE

Texas Instruments announce pricereductions to six of their electroniccalculators. Models affected are asfollows:Model New Price Old PriceTI 1200 £ 8.95 £ 10.95TI 1250 £ 9.95 £ 13.95TI 1500 £14.95 £ 19.95TI 5050 £94.95 £109.95SR 50A £44.95 £ 59.95SR 51A £64.95 £ 89.95

rechargeable cassette. The machineuses algebraic logic and is fully guaran-teed for 1 year. A 12 -digit greendisplay gives 8 -digit mantissa and 2 -digit exponent plus signs. The funct-ions of the calculator are.Accuracy Calculates to 10 digits

while displaying 8 inthe mantissa.

EE EEC EEt Exponent entry andexponent shifts.

Memories Two independentmemories plussummation key tomemory 1.

Parenthesis Single level bracketfacility.

TRIG Sin, Cos, Tan, Sin -1,Functions cos -1, tan -1.LOG Functions Ln ex, log, 10x.Powers Vx x2, x\AT, yx.Conversions Polar to rectangular

coordinates, degreesto radians.Mean and standarddeviation.

change sign, 1/x,

Statistical

OtherFunctions

DANGER: 90 FUNCTION CALCULATORESCAPES FROM CBM!

Also from CBM comes a newscientific with an awe-inspiring 90functions. The beast is called anSR419OR and can be bought for£59.90, but at your own risk; no

Prices include VAT.

TWA USES COMPUTER TO SAVEFUEL

Computer -assisted flight planning andrelated techniques helped Trans WorldAirlines save more than 70 milliongallons of expensive jet fuel in 1975.Flight operations use an IBM System/370 Model 168 to calculate flightplans in order to pinpoint the lowestcost route. The powerful systemconstructs nearly 1,000 flight plansdaily for TWA's world-wide operationsplus countless alternative plans.

The computer calculates threepossible plans: Federal AviationAdministration (FAA) approved; freesearch and minimum cost. Free searchmeans that the system examines everypossible route from origin to destin-ation for the best route. In some casesthe best route may be longer (becauseof bad weather) but is chosen toprovide a smooth ride.

A flight dispatcher creates a plan byentering information into thecomputer via a visual display terminal.Information includes payload, fuelrequirements, allowable takeoffweight, flight time, distance andvarious altitudes and weather data.Stored in the computer's memory isinformation on factors such as aircraftperformance and route.

A dispatcher can request the systemto search up to five altitudes for thebest one. The system figures the bestrouting on the first altitude, then thenext and so on. Using informationfrom the dispatcher, the Model 168simulates each altitude/route combin-ation. Fuel consumption, flight timeand cost is developed for comparisonby the dispatcher who recommends anoptimum plan to the flight captain forhis concurrence.

DIGITAL CLOCKMATCHED CHIP & DISPLAY

DISPLAYOnly Price

£6.36Inc VAT

CHIPOnly Price

£5.50Inc VAT

£9.56Inc. VAT. Post & Packing

FUTABA 5-LT-01. 7 SEGMENTPhosphor Diode. 12.5mm DigitAM/PM and colon

CALTEX CT7001. MOS LSI28/30/31 Day Calendar24 -hour ClockSnooze AlarmClock Radio FeatureEasily Settable Counters

TRANSFORMER - £2.50 INC. VATPayment with order

IMTECH PRODUCTS LTD.IMP HOUSE, ASHFORD ROAD, ASHFORD, MIDDX.

Telephone: Ashford 44211Telex: 936291

it

ELECTROHWTEthe good components service

with a still more up-to-date catalogueIn relatively few years, Electrovalue has risen to aposition of pre-ertinence as mail-order (and industrial)suppliers of semi -conductors, components, accessories,etc. There are wide ranges and large stocks to choosefrom as well as many worthwhile advantages to enjoywhen you order from Electrovalue

CATALOGUE 8 ISSUE 2Second printing now ready. revised and up -dated on prices. etc

.

144 pages. New items. Opto.electronics. Diagrams ofcomponents, applications. I.C. circuits. Post free 40p, includingvoucher for 40p for spending on order over £5 list value.

DISCOUNTSOn all C.W 0 mail orders. except for some items markedNETTimp/ on orders list value

1 0°A r15orodrers listre value,i.:10 or more

FREE POST & PACKINGOn all C.W 0 mail orders in U K over l2 list value. If under. add15p handling charge

PRICE STABILIZATION POLICYPrices are neid and then reviewed over minimum periods of 3months. next review due April 1st

QUALITY GUARANTEEOn everything in our Catalogue - No manufacturer's re,ects,seconds or sub -standards merchandise

ELECTROVATTE LTDAll communications to: Section 5/4, 28 ST. JUDE'S ROAD, ENGLEFIELDGREEN, EGHAM, SURREY TW2O OHB. Telephone Egham 3603 Telex 284475Shop hours 9-5 30 daily, 9.1 p.m SetsNORTHERN BRANCH: 680 Burnage Lane, Burnt,. Manchester M19 INA.Telephone (061) 432 4945. Shop hours daily 9-5 30 p.m.9-1 p m Sats

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

-IERE IS A PHOTO OF THE WATCH IN LASTMONTH'S OFFER (FOR TECHNICALREASONS WE WERE UNABLE TOPUBLISH IT LAST MONTH)THE OFFER IS OPENUI'TIL 31st MARCH1976,

To: EXELAR WATCH OFFERETI Magazine,36 Ebury Street,London SVV1W OLW.

Please find enclosed my cheque/P.O.ti for £14.95 payable to Electronics Todayto I International (Exelar Offer). IMPORTANT:

Please write your name and address on thefc Iback of your cheque and P.O's.

CIL

00 .3'

(4-Ric I ADDRESS

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4c 422

OFFER CLOSES MARCH 31st 1976es z-tWIFFICE4.3 01.15 FOR

(.% -4 USEpc Igo, 0 pc

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CALCULATOR=7.7: i 534

An inexpensive calculatormodified to provide one -hundredthof a second timing.

FOUR -FUNCTION calculators are

now available for as little as £5.00. Atthose prices, it is cheaper to buy acalculator and throw away the partsthat you don't need, than it is to buy akeyboard, display, or calculator chipseparately.

Having this in mind we were veryinterested to receive an applicationnote from National Semiconductorwhich detailed how to modify one oftheir calculators for use as a

stopwatch, We therefore decided todevelop this idea to a full project for acalculator/stopwatch which providestiming with one-hunctredth of a secondresolution for a cost as low as £10.00(including the calculator).The NOVUS 650 calculator is a

simple four -function machine whichhas a fixed decimal point between thesecond and third (RH) digits. Thecalculator does not have floatingpoint, and only works in wholenumbers, the decimal point being anindicator only. These featureshowever, whilst detracting from theusefulness of the machine as a

calculator, make it ideal formodification, without difficulty, foruse as a stopwatch.Stopwatch operation is made

possible by the fact that if '1' is

entered into the calculator and the '+'key is continually pressed, thecalculator will add '1' to the numberdisplayed each time the '+' key is

pressed. Thus, as a stopwatch, the '+'key must be 'pressed' electronically100 times per second. (If a

floating-point calculator were to beused, 0.01 would have to be addedeach time the key was pressed and thisof course is much more difficult to do).

The 100 Hz timebase, required forthe key -pressing function, needsto be supplied by means of a crystaland a divider chain or, by some othersimple but stable oscillator such as aPUT. For most applications the PUT(programmable unijunction transistor)is quite accurate enough and this,coupled with the fact that the crystaland its dividers are bulky andrelatively expensive, led to us choosingthe PUT oscillator.

STOPWATCH

The additional electronics for thestopwatch is all mounted on a separateprinted -circuit board which is a verytight fit in the calculator. Soldering tothe pins of the calculator IC is alsorequired and unless you have previousconstructional experience, especiallywith soldering, do not attempt thisproject.

CONSTRUCTIONDue to the unusual nature of this

project the constructional proceduregiven is much more detailed thanusual. The constructor is well advisedto follow the following steps carefully.

(a) Dissassemble the calculator byremoving the battery and the fourscrews that hold the case together.

(b) Remove the external powersocket and disconnect the leads fromit to printed -circuit board. Take note

SPECIFICATION

Maximum Reading 9999.99 sec (2 hours 46 mins 39.99 secs)Resolution 0.01 secsAccuracy (typ) ± 0.2%Mode - accumulating type, single button start/stop, separate buttonfor clear.Calculator.Six digits, four functions, reverse Polish fixed point.

10'ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

of the position of these leads as theymust be replaced later.

(c) The new pushbutton for thestopwatch must now be mounted intothe back cover. The photograph showsthe approximate location of thisbutton. Note that the web of plastic,between the battery compartment andthe calculator housing, must be cutaway on the right-hand side so that thepush button may be fitted. Todetermine the correct position,temporarily reassemble the calculator,without screws. The correct locationcan now be determined as the buttongoes between the display board, thecalculator board and the battery (yesthere is space!)

(d) Due to the curved case of thecalculator we did not use the normalmounting method for the push button,but just drilled and filed a hole justlarge enough to allow the push buttonto cut its own thread in the plastic. Itmay also be necessary, however, toepoxy the button into position.

(e) Assemble the printed -circuitboard, ETI 534, as shown in thecomponent overlay. The componentsmust be positioned as shown, as theboard fits between the calculatorboard and the keyboard and space isvery limited

(f) Attach thin insulated wires to thepoints shown on the overlay and leavethem about 75 mm long.

(g) To obtain a little more space,trim all component leads on the backof the calculator board, includingthose of ;the calculator IC, as close tothe board as possible. Now cut theprinted -circuit track on both sides ofpin 1 of the M M5736 calculator IC(pin 1 is the pin next to the mark)Using a single strand of flexible wirerejoin the tracks on both sides of pin 1,leaving pin 1 isolated.(h) Position the control board, ETI

534, alongside the calculator board(see photo). Due to space limitationsthe wires from the control board haveto soldered directly onto the pins ofthe calculator ICs.

(j) Check very carefully the point towhich each wire must be connected,cut it to length (not too long), andsolder it directly to the specified pin.The ICs are numbered anticlockwisefrom the 's' mark.

(k) Reconnect the power wiringfrom the external socket.

(I) Connect the push-button switch.(m) Check the calculator before

final assembly as follows: -Connect the battery and switch on.Clear the display and check all keys

and calculator functions.Clear the display

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ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 , 11

CALCULATOR STOPWATCH

Fig. 2. Printed circuit board layout. Full size64 x 52mm.

Marshalls are supplying a kit of partsfor this project (less calculator andPCB) at a price of 0.50+ VAT.

CI 1

ITO PIN17 IC 3

TO PIN18 IC3TO PIN4 IC 3TO PIN3 IC3

TO PIN3 IC4

TO PIN10 IC 3

Fig. 3. Component overlay.

PIN11C3

PARTS LIST - ETI 534

R9 Resistor 15 k ./. W 5%R10 47k " "R1,7 " 100 k " "R2,3,4,5 1M " "R6,8,11,12 ., 1M " "R13* part of calculatorRV1 Trim potentiometer 20 k 20 Turn

type 84 (Morganite)

C2,3 Capacitor 0.00471.1F polyesterC6,8 0.0082 liF '

C5 ,, 0.0681./FC1,4 1 /IF Tag tantalumC7 22 pF 16 V Tag

tantalum

D1-07 Diode 1N914 BA318 or similar

Q1 Transistor 2N6027 or similar

1C1 Integrated Circuit 4011 (CMOS)1C2 " 4016 (CMOS)

Small push buttonPC Board ETI 534Calculator NOV US 650

PCB from Ramar at 68p inc.V

TO PIN14 1C3

Fig. 4. The calculator as modified and before final assembly.

12

PUSHBUTTON

Press the push button.. once. --Thecalculator should now count up byones at 100 times per second.

(n) If a frequency counter or anoscilloscope is available connect to thejunction'of R11 and C6 and adjust for100 Hz. If an oscilloscope is used syncthe cro from the mains and beat the100 Hz against that.

(p) Fold the control board on top ofthe calculator board making sure thatnone of the leads is on top of any ofthe ICs thus preventing the board fromgoing right down.

(q) Cut a small hole in the side ofthe case to allow access to RV1.

(r) Assemble the calculatorcompletely again making sure that theleads do not foul anything and thatthe calculator fits together withoutneeding to be forced.

(s) Check the accuracy of thestopwatch by timing, over a longperiod, using a known accurate source(eg telephone time service) and makesuccessive adjustments of RV1 to givecorrect results.

USING THE STOPWATCHThe conventional stopwatch has a

single button which starts, stops, andresets, the timing. The ETI stopwatch,on the other hand, uses the sidebutton for start/stop and the existingCE/C key for reset.

This configuration allows thestopwatch to be used for applications

For example where three separate runsmust be timed for a total time, thestopwatch is not reset between runsbut merely started and stopped foreach run.

A further advantage is that timingmay be commenced from a readingpreset by the keyboard. This is doneby first clearing the display and thenentering the starting time inone -hundredths of a second. If the '+'button is now pressed before starting,the stopwatch will count up from theentered time, whereas if the '-' buttonis pressed the stopwatch will countdown from the previously enteredtime to zero.

When using the stopwatch be carefulto hold it in such a way that accidental -pressing of keys is avoided, as spuriouskeyboard entries will result in an

erroneous reading.

As a service to readers havingdifficulties obtaining the Novus 650calculator used as our stopwatch, wehave decided to supply, direct. Theprice is 1:5.00 inc, and orders shouldbe sent to ETI Novus 650 Sales 36Ebury Street. London SW1W OLWPlease allow 21 days for delivery

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

IA

D.75492 DualInLina Package

I?

A GMO

TOP vliri

4011

2N 6027

DIGIT 4

DIGIT I

KEYBOARDSCAN

INPUTS

SEGMENT

SEGMENT I

SEP, NT p

SEGMENT

A

CONTROL

CONTROL

11

0

O

III

13

El

Dual InL ale Package

TOP VIEkh

4016Fig. 5. Component connections. 4066

Or1:1 2

DIGIT 3

DIGIT S

DIGIT 6

SEGMENT

SEGMENT.

SEGMENT,

CONTROLA

CONTROL

HOW IT WORKS.With the standard calculator the

keyboard controls a three -line bysix -line matrix, that is, a calculatorkey when pressed joins one of threepins, of IC3, to one of six other pins.This gives a maximum of 18 possiblecombinations of which only 15 areused. The 6 lines are both input andoutput of the IC, that is they drivethe display via IC4 as well as passingkeyboard commands to thecalculator.

The stopwatch is controlled by anadditional push button, which ineffect stops and starts the calculator,whilst reset is performed by thefront -panel 'clear' key. The pushbutton operates a flip flop formed byIC1/1 and IC1/2. The capacitorsaround the flip flop change it from anormal RS type to a toggle type.Diode D3, capacitor C4 and resistorR5 set the flip flop into the stopcondition on initial switch on. Theoutput of IC1/1 is at zero volts in the`stop' state and at +9 volts in the`run' state.

When the output of IC 1/1 goeshigh capacitor C8, together withR12, provides a 10 ms pulse to thecontrol input of IC 2/1. This is ananalogue switch across the '1' key.Thus the closure of this switch isequivalent to pressing the '1' key.When the switch closes capacitor CSbegins to charge via R7. When it

reaches about 6 volts (set byR9/R10) the PUT switches on, andC5 is discharged rapidly to a lowvoltage, the PUT turns off, allowingC5 to recharge. This action takes atplace at 100 Hz. The diode D4 isused for temperature compensation.When the PUT fires, terminal 'ag'drops to a low voltage whichdischarges C6 via D4 and D6. And,although the PUT is on for only ashort time, diode D6 isolates C6allowing it to charge slowly (5 ms)via R11.

The pulse from the PUT is squaredby IC 1/3 and is then used to controlIC 2/2, which is across the '+' key.The pulse thus causes one to beadded to the displayed number 100times per second.

To operate the calculator, at therate of 100 pulses per second, it isnecessary to disable the calculatordebounce circuitry. This is done byIC -2/3, IC 2/4, IC 1 /4 and D7. Thedebounce is disabled only in the 'run'mode, and is still functional innormal calculator operation.

Diode D5 and capacitor C7decouple the control circuitry fromthe calculator, as the high peakcurrents drawn can result in atwo -volt ripple, on the nine -voltsupply, which otherwise would upsetthe timing.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

BUILD THE

TREASURETRACER

MK IIIMETALLOCATOR

AS SEENON BBC -1& BBC -2

TV

Genuine S silicon transistor circuit.does not need a transistor radio tooperate.Incorporates unique varicap tuningfor extra stability.Search head fitted with Faradayscreen to eliminate capacitiveeffects.Loudspeaker or earphone operation(both supplied).Britain's best selling metal locator.kit. 4,000 already sold.Kit can be built in two hours usingonly soldering iron, screwdriver.

- pliers and side -cutters.Excellent sensitivity and stability.Kit absolutely complete includingdrilled, tinned, fibreglass p.c. boardwith components siting printedon.

Complete after sales service. Weighs only 22oz; handle knocks

down to 17" for transport.Send stamped, self-addressed en-velope for literature.

Complete kitwith pre -builtsearch coil

Plus 85p P & PPlus £1.00 VAT (8%)

2.50

Built, tested

£11.50and Guaranteed

Plus 85p P & PPlus £.1.40 VAT (8%)

MINIKITS ELECTRONICS,6d Cleveland Road, South Woodford,

LONDON E18 2AN(Mai order only)

13

9

TELETYPE 28 for £20 onlyMust go due to lack of space

Information supplied. Carriage £2.50 VAT 8%

Solartron 0-12V lamp £7.Solartron 12-2V 1 amp £12.Solartron 1 5-13.5V 1 amp £8.Roband 21.27V 3 amp £10.Roband 9-12V 5 amp £10.

SELECTION OF STABILIZED POWER UNITSCoutant 35V 2 amp £16.Coutant 28V 2 amp £14.Roband 4-14V 3 amp £8.Coutant + and -- 10-12V 3 amptwice £22.

Venner 10V 1 amp £6.APT 12-15V 2 amp £15APT 22.27V 3 amp £10.Farnell 0-12V 2 amp £8.Coutant 20V 2 amp £12.

BUNKER-RAMO 240V inputOutputs + 1 2V 5 ampminus 3.8V 25 ampminus 24V 25 amp

Price £45 each

ALWAYS A LARGE QUANTITY OF TEST EQUIPMENT,SPECIALISED UNITS, CHASSIS, ETC. CALL AND SEE

Ex -Ministry Pye Receiver R3129£6 ea.

Ex -Ministry VHF Receiver R7303Multichannel £8 ea.Ex -Ministry STC HE Receiver Unitswith Plug-in coils £7 ea.Ex -Ministry Marconi Radio Jammertype HG 10. Battery operated £12.Multi Range Millivoltmeter by Airmec Sensitivity down to 1OmV fullscale £7 ea.Marconi Sensitive ValvevoltmeterTF1100 £12 ea.Rohde & Schwarz 10-280MHZ HighGain Wide Band Amplifier £15 ea.

Marconi Calibrator Scopes etc TF345£15 es.Pulse & Bar TV Waveform Generator£15.Airmec Counter 6 digit Standard240V input. Large bright display

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ELECTRONICS TODAY INTERNATIONAL APRIL 1976 15

LYNX ELECTRONICS (LONDON) LTDDIGITAL DISPLAYS ik LED'sDL704 99p DL747 1 7S

DL707 Up DL750 1 752 RED LED ONLY 13pGREEN CLEAR 15I)

TransistorsAC126 1SpAC127 UpAC128 13pAC128K 25pAC141 lapAC141K 21pAC142 lipAC142K 21pAC176 16pAC176K 25pAC187 18pAC187K 25pAC1138 18pAC188K 25pAD140 50pAD142 50pAD143 46pAD149 4SpAD161 35pAD162 35pAL102 95pAL103 93pAF114 20pAF115 20pAF116 20pAFI17 20pAF118 50pAF139 33pAF239 37pBC107 14pBC107B 16pBC108 13p8C109 14pBC109C 16pBC117 19pBC125 18pBC126 25p'BC141 20pBC142 23pBC143 23pBC144 30pBC147 9p*BC148 9pBC149 9pBC152 25p'BC153 lip'BC157 9pBC158 9pBC159 9pBC/60 32pBC161 38pBC16813 9pBC182 11pBC182L 11p

BC183 10pBC.L 10p.BC184 IlpBC164L IlpBC20713 12p'13C21% 11pBC212I1L 11 p8C213 12pBC213L 12pBC214 14p'BC214L 14pBC237 16pBC238 11pBC300 34pBC301 32pBC323 60pBC327 18pBC328 16p'BC337 17p'8C338 17pBCY70 12pBCY71 18pBCY72 12pB0115 55pBD131 36pBD132 40pBD135 36p80136 39p80137 40p130138 45pBD139 ipBD181 UpBD182 92p130183 97pBD232 60p.130233 48pBD237 55p

,BD238 60).BD184 £1.20.BDY20 lOpBDY38 60pBDY60 611pBDY61 6.5pBOY62 55pBF178 211pBF179 31pBF194 10pBF195 lipBF196 12p8F197 12pBF224J.BF244 17pBF257 30p8F258 35p

BF337 32p CRS1-10 25pBFW. 17P CRS1-20 35pBFX29 26p CRS1-40 40pBFX30 30p CRS1-60 65pBFX84 23p CRS3-05 34pBFX85 25p CRS3-10 45pBFX88 20p CRS3-20 SOPBFY. 20p CRS3-40 60pBFY51 lip CRS3-60 85pBFY52 I9p MJ480 KbPBFY64 35P MJ481 £1.05BFY90 6Sp MJ490 90PBR100 20p MJ491 El 15BRY39 40p MJE340 40p'BSX19 lip MJE371BSX20 lap MJE520 45pBSX21 20p MJE521 SipBSY95A 12p OAS 50PBT. £1.00 0A90 Sp13T107 £1 60 0A91BT108 £160 0C41 15pBT109 £1.00 0C42 15PBT116 £1 00 0C44 12p4.105 El .10. 0C45 10pBU105, OC70 10p

02 £1 90. 0071 10pBU 126 £1 0072 22pBY206 15p 0084 14p8Y207 20p' SC40A 73pBYX36-300 SC408 81p

12p SC4OD 98pBYX36-600 SC4OF 659

15p SC41A 65,B Y X36-900 SC41 B 70,

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300 UpBY X38-

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serieszeners IlpC106A 40pC10613 4SpC106D 50pC106F 35pCRS1-05 250

ST2 20pTIP29A 44pTI P30A 574)TI P31 A 54pTIP32A 64pTIP34 £1. 05TIP41A iipTIP42A 72pN2069 14pN2070 16pN4001 4pN4002 SpN4003 6pN4004 7p'N4005 ip'N4006 9pN4007 10p2N696 14p

2N697 12p2N706 10p2N929 14p2N930 14p2N1131 15p2N1132 16p2N1304 20p2N1305 20p2N1711 lip2N2102 44p2N2369 14p2N2369A 14p2N2484 16p2N2646 50p2N2905 lap2N2905A 22p2N2926R 10p2N29260 9p'2N2926Y 9p2N2926G 111p2N3053 1Sp2N3054 40p2N3055 50p2N3440 56p2N3442 £1.202N3570 110p2N3702 10p2N3703 10p2N3704 10p2N3705 10p2N3706 10p2N3707 10p2N3714 £1 052N3715 £1152N3716 £1252N3771 602N3772 £1602N3773 £2102N3819 Up2N3904 lip'2N39062N4124 14p2N4290 12,2N4348 £1202N4870 35p.2N4871 35p'2N4919 70p'2N49202N49222N49232N50602N50612N50622N50642N5496

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THYRISTORS -BA(T092)

50 2$100 25200 27400 38600

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TRIACS- (PLASTIC TO -220 PKGE, ISOLATED TAB)- 4A 6.5A 85A 10A ISA

(a) (b) (a) (b) (a) (b) (a) (b) (a) (b)100 V 0.60 0.60 0.75 0.70 0.78 O. "TS 0.13 0. 03 1.01 1.01200 V 6.. 0.64 0.75 0.75 0. 17 0.87 6.17 0.87 1.17 117400 V 0.77 0.78 0.10 0.13 1.57 1.01 1.13 1.19 1.70 1.74600 V 0.90 0.99 0.17 1.61 1.21 1.21 1 .42 1.50 2.11 2.17N.B. Triacs without internal trigger disc are priced under column (a).Triacs withinternal trigger diac are priced under column (b). When ordering please indicateclearly the type required.

74 TTL mixed prices1-24 25-99 100+

7400 14p 12p 11p7401 I4p 12p 10p7402 14p 12p 10p7403 15p 12}p 10p7404 16p 13p 11p7403 16p 13p 11 p7409 18p 13p 11p7410 16p 13p lip7413 29p 24p 20p7417 27p 22ip 20p7420 16p 13p lip7427 27p 72Ip lip7430 16p 13p lip7432 27p 22}p 16p7437 27p 22}p It.7441 75p UP SOp7442 65p 55p 43p

1-247445 $5p7447 11 p7448 75p7447A 95p7470 31p7472 25p7473 Up7474 Up7475 47p7476 32p7482 75p7485 £1.347486 32p7489 L2927490 49P7491 &Sp

25-097Ip75pUp83p2Sp21p25p211p19p26pUp

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£2.10

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74194 £1 64 £1.34

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£1 .9090p90p119p

LINEAR IC's301A 8 pin DIL 35307 55309K iSe380 14 pin DIL 90381 14 pin DIL 1-i0Matching charge 20p per pair. P 6 P 20, -Overseas 80p. CA3045

3900 14 pin DIL 70709 8/14 pin DIL741 8/11 pin DIL 28 748 8 pin DIL 31555.8 pin DIL 45

565 14 pin DIL L2-00.566 1 pin OIL £1 50.567 8 pin DIL £2.1141

CA3046 14 pin DIL 5085.

NATIONAL CLOCK CHIPSmms314 ..... £3.75(Basic clock chip giving 6 digit display)

MM 5316(Sophisticated device includingalarm, similar to CT 7001)

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16 ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

MORE11

014 THEThe following article providesgreater, detail, of a device firstfeatured in ETI Data SheetNovember 1975, and lists severalapplications for the amplifier notcovered therein.

PHASECOMPENSATION

TAB.

OFFSETNULL

INV.I/P

NON-INVI/P

STROBE

V- AND CASE

0/P

OFFSETNULL

Fig. 1. Functional diagram of the CA3130,

The CA3130 series of operationalamplifiers combines the advantages ofboth CMOS and bipolar transistors ona single monolithic chip. A specificat-ion and description of package optionsavailable were given briefly in the DataSheet referred to above. These will notbe repeated here, and the circuitsfor voltage regulator, pulse generatorand function generator given therewere sufficiently clear to make theirinclusion herealso superflous. Insteadwe shall consider in detail the circuitof the device, and give several furthervery interesting applications.

< 1

E

4:- 12

Z 10wccccJU

-1

U)

wU)

3

0

OUTPUT VOLTAGE (V0)V- = 0LOAD RESISTANCE (RL) - (.5 7

V- = 0 I - !!r_i

ran

-1-

6 8 10 12 14 16 18

TOTAL SUPPLY VOLTAGE (V+) -V

Fig. 2. Supply current against total supplyvoltage.

--1rS o ..0 0,

-1

, 0.

,orTOS

.0

-T°'

CD,

1.1.0,

0

T

°

^-,

--J...s

L

OS

0J 1_ ._J L

NC,r. moor,r,too.

0

Fig. 3. Schematic diagram of the CA3130.

CIRCUIT DESCRIPTIONThe output circuit consists of a

complementary -symmetry MOS (COS/MOS) transistor pair, capable ofswinging the output voltage to withinmillivolts of either supply voltageterminal (at very high values of loadimpedance).

The CA3130 Series circuits operateat supply voltages ranging from 5 to16 volts, or ±2.5 to ±8 volts whenusing split supplies. They can be phase.compensated with a single externalcapacitor, and have terminals foradjustment of offset voltage forapplications requiring offset -null capa-bility. Terminal provisions are alsomade to permit strobing of the outputstage.

The input terminals may be oper-ated down to 0.5V below thenegative supply rail, and the outputcan be swung very close to eithersupply rail in many applications.Consequently, the CA3130 Series

circuits are ideal for single supplyoperation. Three Class A amplifierstages, having the individual gaincapability and current consumptionshown in Fig. 3, provide the total gainof the CA3130. A biasing circuitprovides two potentials for commonuse in the first and second stages.Term. 8 can be used both for phasecompensation and # to strobe theoutput stage into quiescence. WhenTerm. 8 is tied to the negative supplyrail (Term. 4) by mechanical orelectrical means, the output potentialat Term. 6 essentially rises to thepositive supply rail potential at Term.7. This condition of essentially zerocurrent drain in the output stage underthe strobed "OFF" condition can onlybe achieved when the ohmic loadresistance presented to the amplifier isvery high (e.g. when the amplifieroutput is used to drive COS/MOSdigital circuits in comparator appli-cations).

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976 17

THE CA3130OPERATIONAL AMPLIFIERINPUT -OFFSET -VOLTAGE (Vie)

It is well known that thecharacteristics of a MOS/FET devicecan change slightly when a dcgate -source bias potential is applied tothe device for extended time periods.

-The magnitude of the change is

increased at high temperatures. Usersof the CA3130 should be alert to thepossible impacts of this effect if theapplication of the device involvesextended operation at high temper-atures with a significant differential dcbias voltage applied across Terms. 2and 3.

OFFSET NULLING

Offset -voltage nulling is usuallyaccomplished with a 100,000 -ohmpotentiometer connected acrossTerms. 1 and 5 and with thepotentiometer slider arm connected toTerm. 4. A fine offset -null adjustmentusually can be effected with the sliderarm positioned in the mid -point of thepotentiometer's total range.

HANDLINGThe CA3130 uses MOS field-effect

transistors in the input circuit. BecauseMOS/FET's have extremely high inputresistances, they are susceptible todamage when exposed to extremelyhigh static electrical charges. Tominimize the possibilities of damagingthe input stage transistors, Q6 and 07, -the CA3130 utilizes a protective diodenetwork in the input stage.Nevertheless, it is good practice thatprecautions be observed during hand-ling, testing and actual operation ofthe CA3130 devices to minimizepossible damage (see ETI November74 Handling CMOS).

WIDEBAND NOISE

For low -noise performance theCA3130 is most advantageous inapplications wherein the sourceresistance of the input signal is 1

megohm or more. In this case, thetotal input -referred noise voltage is

typically only 23 pV when a

test -circuit amplifier is operatedat a total supply voltage of15 volts. This value of totalinput -referred noise remains essentiallyconstant, even though the value ofsource resistance is raised by an orderof magnitude. This characteristic isdue to the fact that reactance of theinput capacitance becomes a signifi-

cant factor in shunting the sourceresistance. It should be noted,however, that for values of sourceresistance very much greater than 1

megohm, the total noise voltagegenerated can be dominated by thethermal noise contributions of boththe feedback and source resistors.

VOLTAGE FOLLOWERS

Operational amplifiers with veryhigh input resistances, like theCA3130, are particularly suited toservice as voltage followers. Fig. 4

shows the circuit of a classical voltagefollower, using the CA3130 - in a

.split -supply configuration. Thedigital -to -analog converter (DAC)circuit, described in the followingsection, illustrates the practical use ofthe CA3130 in a single -supplyvoltage -follower application.

PEAK DETECTORS

Peak -detector circuits are easilyimplemented with the CA3130, asillustrated in Fig. 5. It should be notedthat with large -signal inputs, the band-width of the peak -negative circuit is

much less than that of the peak -positive circuit. The 'second stageof the CA3130 limits the bandwidthin this case.

Negative -going - output -signal ex-cursion requires a positive going signalexcursion at the collector of transistorQ11, which is loaded by the intrinsiccapacitance of the associated circuitryin this mode. On the other hand,during a negative -going signal ex-cursion at the collector of Q11, thetransistor functions in an active"pull -down" mode so that the intrinsiccapacitance can be discharged moreexpeditiously.

+7.5V

BW (-3 dB) = 4 MHzSR = 10V/µS

Fig. 4. Voltage follower circuit with split supply of plus and minus 7.5 volts. Thiscircuit allows low impedance loads to be driven from a high impedance source.

6V p -p INPUTBW (-3 dB) = 1.3 MHz0.3V p -p INPUT;OW (-3 dB) - 240 kHz

10k

=1_

+7 5V

IN914

la) PEAK POSITIVE DETECTOR CIRCUIT

+ DCOUTPUT

Fig. 5. Peak positive detector circuit. Detectors such as this are ideal for buildingaccurate ac voltmeters.

18 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

'9 -BIT COS/MOS DAC

The circuit of a 9 -bit Digital toAnalog Converter (DAC) is shown inFig. 6. This system combines theconcepts of multiple -switch COS/MOSIC's, a low-cost, ladder network ofdiscrete metal -oxide film resistors, aCA3130 op -amp connected as a

follower, and an inexpensive mono-lithic regulator in a simple singlepower -supply arrangement. An ad-ditional feature of the DAC is that it isreadily interfaced with COS/MOSinput logic, e.g. 10 -volt logic levels areused in the circuit of Fig. 6.

The circuit uses an R/2Rvoltage -ladder network, with theoutput potential obtained directly byterminating the. ladder arms at eitherthe positive or the negativepower -supply terminal. EachCD4007A contains three "inverters",each "inverter" functioning as a

single -pole double -throw switch toterminate an arm of the R/2R networkat either the positive or negativepower -supply terminal. The resistorladder is an assemply of one per centtollerance metal -oxide film resistors.The, five arms requiring the highestaccuracy are assembled with series andparallel combinations of 806,000 -ohmresistors from the same manufacturinglot.

A single 15 -volt supply provides apositive bus for the CA3130 followeramplifier and feeds the CA3085voltage regulator. A "scale -adjust"function is provided by the regulatoroutput control, set to a nominal10 -volt level in this system. Theline -voltage regulation (approximately0.2%) permits a 9 -bit accuracy to bemaintained with variations of severalvolts in the supply. The flexibilityafforded by the COS/MOS buildingblocks simplifies the design of DACsystems tailored to particular needs.

SINGLE -SUPPLY, ABSOLUTEVALUE, IDEAL FULL -WAVERECTIFIER

An absolute -value circuit, using theCA3130 is shown in Fig. 7. Duringpositive excursions, the input signal isfed through the feedback networkdirectly to the output. Simul-.taneously, the positive excursion ofthe input signal also drives the outputterminal (No.6) of the invertingamplifier negative such that the 1N914diode effectively disconnects theamplifier from the signal path. Duringa negative -going excursion of the inputsignal, the CA3130 functions as a

normal inverting amplifier with a gainequal to -R2/R1. When the equalityof the two equations shown in Fig. 12,is satisfied, the full -wave output is

symmetrical.

0-

10V LOGIC INPUTS

+10.010

LSB9

o9

07

94

8 7

16 (r3

CD4007A"SWITCHES"

13

8

806k1%

402k1%

12

200k1%

14

11

25 4

1)3 110

CD4007A"SWITCHES"

13

8

100k1%

806k1%

VOLTAGE+15V REGULATOR

Fig. 6. Nine -bit digital -to -analogueconverter uses CMOS digital switchesand the CA3130.

1 12

806k1%

806k 750k1% 1%

OUTPUT0

LOAD

REGULATEDVOLTAGEADJ.

2

i3M SB

CD4007A"SWITCHES"

806k1%

12

(8)806k1%

PARALLELEDRESISTORS

+15V 10k0

100kOFFSET

= NULL

7

CA3130

"\AA/'0.1,IF 2k-If

3

VOLTAGEFOLLOWER

2

56pF

REQUIREDBIT RATIO MATCH1 STANDARD2 ±0.1%3 ±o.rh.4 ±0.4%5 ±0.8%6-9 ± 1% ABS

ALL RESISTORS IN OHMS.

Fig. 7. An absolute value fulrwave detector provides the average of the input waveform:This is useful for converting dc meters. eg digital voltmeters to read the average of the acinput signal.

Ni4k

R2 R3GAIN . -Ni R 1+R2+R3

R3 RI (1 +;2)

20pF

2k R2FOR X = 0.5 - =Qk R1

0.75R3 = 4k . 6k

0.5

R22k

100kOFFSETADJUST

20V p -p INPUT 8W (-3 d8I - 230 kHz.DC OUTPUT (AVG) - 3.2V

1V p -p INPUT : 8W (-3 de) . 130 kHz,DC OUTPUT (AVG) - 160mV

/VW\

5.1k

PEAKADJUST2k

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 19

THE CA3130OPERATIONAL AMPLIFIER

OPERATION WITH OUTPUT -STAGE POWER -BOOSTER

The current -sourcing and sinkingcapability of the CA3130 output stageis easily supplemented to providepower -boost capability. In the circuitof Fig. - 8, three COS/MOS.transistor -pairs in a single CA3600E ICarray are shown parallel connectedwith the output stage in the CA3130.In the Class A mode of CA3600Eshown, a typical device consumes 20mA of supply current at 15Voperation. This arrangement booststhe current -handling capability of theCA3130 output stage by about 2.5.

The amplifier circuit in Fig. 24employs feedback to establish a

closed -loop gain of 48 dB. The typicallarge -signal bandwidth (-3 dB) is 50kHz.

/1

Fig. 8. A CMOS transistor array maybe connected as a power booster for theoutput stage of a CA3130.

1 F

INPUT 2k

l F

Av JCL, = 48dBLARGE SIGNALBW (-3dB) = 50kHz

510k

+15V

11

L___

IRS =1002'(P0 = 150mWAT THD = 10%)

0

500p F1 2

_J

NOTETRANSISTORS p1, p2, p3 AND ni, n2, n3 AREPARALLEL -CONNECTED WITH 08 AND 012RESPECTIVELY, OF THE CA3130

6 -Digit Digital Clock Kits 12/24 HOUR 50/ 60 HERTZ BRIGHT DISPLAYS SLOW TIME SET FAST TIME SET TIME HOLD 95*

+90p Airmail p&p

If you have been considering buiding a digital clock kit but were discouraged by thehigh prices, we have just removed your last excuse. Why pay over £12 when you canget one for about half that price?

KIT COMPRISES:1 - National MM5314 Clock Chip, 12/24 hour, 50/60 Hz option6 - Bright red common cathode displays, 0.2 7" character height7 - NPN Segment driver transistors6 - PNP Cathode driver transistors9 - Carbon resistors5 - Diodes2 - Disc caps1 - Electrolytic filter cap3 - Switches for time setting functions2 - Etched, drilled and plated p.c. boards1 - Illustrated assembly instructions manualAll you provide is a 9-12v ac/ 200 m /a Transformerand case of your choice

OPTIONAL JUMBO DISPLAYSYou can have 6 - 0.5" Jumbo displays with a suitableboard instead of the 0.27" types. Clock kit with 6 jumbodisplays £10.95' + 90p airmail p&p

* ORDERING INFORMATIONThe above prices shown in British £s are approximateequivalents of the following U.S. Dollar prices and shouldbe used as a guide onlyClock kit with 6 - 0.27" displays U.S. $16.50 post paidClock kit with 6 - 0.50" displays: U.S. $24.75 post paidRemittance by BANK DRAFTS or INTERNATIONALMONEY ORDERS IN U.S. FUNDS. SENT ANYWHERE INTHE WORLD

NO ELECTRONICS KNOWLEDGE REQUIRED TO BUILD THESE KITS

sabtronics P.O. Box 64683, Dallas, Texas 75206, U.S.A.

ELECTRONICS TODAY INTERNATIONAL-APRIL 197620

Call in and see us 9-5.30 Mon -Fri 9-5.00 Sat

Trade and export enquiries welcome

A Marshall (London) Ltd Dept ETI42 Cricklewood BroadwayLondon NW2 3ET Tel 01-452 0161/2Telex: 21492& 85 West Regent St Glasgow G2 200Tel: 041-332 4133& 1 Straits Parade Fishponds BristolBS16 2LX Tel 0272 654201/2& 27 Rue Danton Issy Les MoulineauxParis 92 Tel 644 23 56Catalogtie price 25p

Top 500 Semiconductors from the largest range in the UK25456254564254574

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0.350.350.35

bc.2Cd

BC2088012K

v27O1I016

BF16089163

8F166

0.230.320.40

LM309KLM5T1LM380

1.881.500.98'

2549025491

4.004.38

253392253393

0.150.15

255457255458

0.290.26

AF118AF124

0.350.30

SC212,BC2141

0,60.18

8F1678F173

0.250.27

LM381LM702C

2.070.75

25492 5.00 2N3394 0.15 255459 0.29 AF125 0.30 BC237 0.16 8F177 0.29 LM709T099.8011.

0.4825493 5.20 253402 0.18 255492 0.58 AF126 0.28 8C238 0.15 89178 0.35 0.3825696 0.22 253403 0.19 255494 0.58 AF127 0.28 BC239 0.15 89179 0.43 1401L 0.402N697 0.16 253414 0.20 255496 0.61 4F139 0.65 8051 0.25 89180 0.35 .1,4710 0.4725698 0.82 ,253415 0 24 256027 0.45 AF1R6 0.46 BC253 0.25 BF181 0.36 LM3900 0.612569925706

.0.590.14

253416253417

0.210.29

7N577735128

0.450.73

A970049239

0.650.65

13C257

8C258U.150.16

/0182BF 1 g3

0.350.55

LM 723C1M7417099

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25 7064 0.16 253440 0.59 315139 1.42 A9240 0.90 HC259 017 87184 0.30 8DIL 0.402570825709

0.170.42

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3514035141

1.000.81

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0.700.79

8C261BC262

0.250.25

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0.300.12

14011LM747

0 381,00

25711 0.50 253638 0.15 35200 2.49 AL102 1.00 BC263 u.25 BF 195 0.12 0,7488011. 0.44214718 0.23 2536384 0.15 40361 0.40 ALI 03 1.00 BC300 0.38 89196 0.13 LM7805 1.88257184 0.28 253639 0.27 40362 0.45 BC107 0.14 8C301 0 34 BF197 0.15 14DIL 0.7325720 0.57 253641 0.17 40363 0.88 BC108 0.14 BC303 0 54 89198 0.18 LM7805 2 502591425916

0.220.28

253702253703

u.110.12

4038940394

0.460.56

BC1098C113

0.140.15

80307BC3084

0.170 15

89200892251

0.400.23

LM7812LM7815

1.991.99

25918 0.32 /53704 0.15 40395 0.65 BC115 0.17 8C309C 0.20 89744 0.21 LM7824 1.9925929 0.25 253705 0.15 40406 0.44 BC 116 0.17 BC317 0.12 89245 0.45 MC1303 1.502N930251302

0.260.19

253706253707

0.150.18

4040740408

0.350.35

8C11.BC117

0.180.21

BC3188C337

1391460.20 89247

0.580.65

MC1310MC13300P

2.500.90

251303251304

0.190.26

253708253709

0.140.15

40409404 10

0.520.52

BC1113BC119

0.140.29

BC338BCY30

0.200.80

89254BF 255

0.190.19

MC135IPMC1352P

0.800.80

251305251306251307251308

0.240.310.300.47

2537102537112N3712253713

0.151,151.201.20

4041140594405954060

2,.250.740.840.67

BC121BC1258C126BC/32

0.350.160.230.30

5CV318C932FICY338CY34

0.851.150.850.79

89257892588975969839

0.470.530.550.24

MC1466MC1469ME0402ME0404

3.502.750.200.13

251309 0.47 2N3714 1.38 40602 0.61 BC134 0.13 BCY38 1 00 189879 0.24 ME0412 0.18251671 1.54 253715 9 50 40603 0.58 BC135 0.13 8CY39 1.50 69521A 2.30 ME4102 0.112516714 1.67 253716 1.80 40604 0.56 BC136 0.17 BCY40 0.97 89 578 1.04 ME4104 0.112516718 1.85 253771 2.20 40636 1.10 8C137 0.17 BCY42 0.28 89561 0,27 MJ480 0.95251711 0.27 253772 1.80 40669 .1.00 BC140 0.68 8CY58 0.30 ,B9598 0.25 MJ481 1.20251907 0.60 253773 2.65 40673 0.73 BC 141 0.68 BCY59 u.32 59729 0.30 MJ490 1.05252102 0.60 253779 3.15 AC126 0.20 8C142 0.23 KYR) 0 17 BF X30 0.34 MJ491 1.45252147 0.78 253790 2.40 AC127 0.40 80143 0.25 BCY7I 0.22 69X84 0.30 MJ2955 1.00252148 0.94 253791 2.35 AC128 0 35 EIC147 0.14 BCY72 0.15 89X85 0.35 MJE340 0.48252160 0.90 253792 2.60 AC151V 0.27 BC148 0.09 ,80115 0 75 89787 0.28 MJE370 0.65252218A 0.47 253794 0 10 AC152V 0.49 BC149 0.15 80116 0.75 89588 0 30 MJE371 0.75252219 042 253810 0.37 AC153 0.35 BC153 0.18 80121 1.00 BFX 89 0.90 MJE520 0.60282219A 0.52 253820 0.29 AC153K 0.40 BC154 0.18 80123 0 87 BFY50 0.23 MJE521 0.70252220 0.25 253823 1.58 AC154 0.25 13C157 0.16 BD124 0.67 BFY51 0.23 MJE2955 1.20252221 0.18 253904 0.19 AC176 0.41 BC158 0 16 80131 0.40 89Y52 0.21 MJE3055 0.75214222 IA 0.21 253908 0 19 AC176K 0.40 BC160 0.78 80132 0.50 89,53 0.18 MP8111 0.32252222 0.20 254036 0.67 AC187K 0.35 BC 1678 0.15 ,80135 0.21 89 590 0.75 MP8112 0.402142222A 0.25, 2N4037 0.42 ACIBBK 0.40 8C1688 0.15 .80136 0.22 BRY39 0.38 MP8113 0.47252368 0.17 254058 0.18 ACY18 0.24 8C168C 0.15 B0137 0.24 BSX20 0.28 MPF107 0.302523694 0.22 254059 U.15 ACY19 0.27 BC16911 0.15 80138 0.26 BSX21 0.30 MPSA05 0.25252369 0.22 254060 0.15 ACY20 0.22 8C 169C 0.15 '80139 0.71 BU104 2 00 MPSA06 0.312N2646 0.55 254081 0.15 ACY21 0.26 BC170 0.15 80140 0.87 BUM 2.25 MPSA12 0.35752647 0,98 254062 0.15 ACY28 0.20 8C171 0.16 80529 0.80 C1060 0.65 MPSA55 0.25252904 0.40 254126 0.21 ACY30 0.58 BC172 0 12 80530 0.80 CA3180A 0.85 M P54.56 0.312524044 0.45 254289 0.34 AD142 0.57 BC 177 0.19 89839 0.24 .3020A 1.80 MPSUO5 0.65252905 0.47 254919 0.95 A0143 0.68 80178 0.18 BFR79 0.24 CA3028A 0.79 MPSUO6 0.58252905A 0.50' 254920 1.10 AD14W 0.74 BC/ 79 0.21 BDY20 1.05 CA3035 1.37 MPSU55 0.63252906 0.33 254921 0.83 40150 0.63 BC182 0.12 8F115 0.29 CA3052 1.62 MPSU56 0.80252906A 0.42 254922 0.83 413167 0.69 ,BC187L 0.12 8,17 0.55 CA3046 0.70 NE555V 0.702,42907 0.22 254923 1.00 40161 0.64 8C183 0.12 89121 0.35 CA3048 2.11 NE556 1.30252907A 0.24 255190 0.92 40162 0.69 BC183L 0.12 .123 0.35 CA3089E 1.96 NE560 4.48752924 0.20 255191 0.96 AF106 0.40 BC184 o.13 89125 0.35, .30900 4.23 NE561 4.48252926 0.20 255192 1.24 491098 0.40 BC 1841. 0.13 69152 0.20 LM301A 0.48 NE566A 4.4825 3053 0.25 255195 1.46 49114 0.35 BC186 0.25 .6153 025 LM308 1.17 0023 1.35253054 0.60 255245 0.29 BC187 0.27 89154 0.16 0028 1.48253055 0.75 255294 0.48 89159 0.27

0C35004200450071007200810083091912R53SL414ASL610CSL611C51.612CSl620CSL611C5L62359640C51641C5576003NSN760135SN76023N$576033NST2144300.TAA263TM 350TAA550TAA611CTAA611TAA661BTBA6418TBA651TBA810TBA820T8A920Ti L209TIP294TIP300,TIP3 1 ATIP32ATiP33ATIP34ATIP35ATIP36ATIP4 t ATIP42ATIP29cTIP30c519.31cTIP32cT1P33cT1P34cT1P4 1 c111,42cTiP49T1P535192955Ti 93055

- 11543/TX300155301ZTX302ZTX50027550175X5022Tx530

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TTL Integrated Circuits - Quality & Prices you can't beat"S574174. 0.99SN7495 0.68 55741 75 0.701557400 0.16 5574,0 0.16 SN7432 0.22 5h/451 0.16 557481 100 SN7496 0.68 ZNN77441:3 00.6688 sr, 75 1.14557401 0.16 657411 0.20 SN7437 0.28 SN7453 0.16 Sh7482 0.65 , 557410() 1.10 S574154 120 §N74440 1.1055740145 0.29 SN7412 0.22 557438 0.28 557454 0 16 557483 0 82 S574107 0.30 S574155 0.78 S574181 1.95S57402 0.16 557413 0.28 557440 0.16 S57460 0.16' 557484 0.95 5574118 0.85 5N74157 0.76 S574190 1..6S57403 0.18 SN7416 0.28 557441AN 0.68 $57470 0.29 SN7485 1.00 SN74 t 19 1.75 I S574160 0.88 5574191 1.86557404 0.19 SN7417 0.28 557442 0.65 SN7472 0.21 S57486 0.29 5574121 0.32 5574181 0.88 1.15557405 0.19 SN7420 0.16 557445 0.78 557473 0 31 S57490 0 42 5574122 0.42 5574162 0.88 §,,,

557406 0.36 557423 0.23 SN7446 0.84 SN7474 0.31 5/17491 0.75 5574123 0.65 5574163 0.88 5N74, 96 1.60557407 0.36 557425 0.23 SN7447 0.80 S57475 0.45 557492 0.45 5574141 0.75 S574164 1.60 5574,97 1.58557408 0.19 557427 0.23 SN7448 0.90 S57476 0.30 557493 045 SN74145 0.72 S.74165 1.60 $574198 1.80$57409 0.18 SN7430 0.15 S157450 0.16 SN7480 0.42 SN7494 0.25 SN74150 1.20 5574167 3.30 ,N74199 1.80

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ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

MULLARDRADIO MODULES

RF IF AMPLIFIERLP 1173LP 1181STEREO PRE AMPLIFIERLP 1183/2LP 1184/2FM/IF AMPLIFIERLP 1185FM TUNERLP 1186LP 1400

6.683.94

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5.56

6.887.22

P.C. MARKER PEN DALO 33PC0.87. ZENER DIODES 400MW0.11. 1W 0.17. 2 5W 0.35. ICSOCKETS 8DIL 0.10, 14011 0.14,16DIL 0.13. RESISTORS ,W0.02 (100 per value 0.013). 1/2W0.03 (100 per value 0.014)SCORPIO CAR IGNITION KITE12.50. JUMBO 7 -SEGMENTDISPLAYS E2.00. DL 707 E1.75.MINITRON £1.55. LED. REDYELLOW. GREEN 16d1a 0.31,20d.a 0.33

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.88

,f.)4018 .88C04019 .52004020 .98C04021 88CD4022 85C04023 180134024 .72CD4025 19CD4027 .43CD4028 .83C1340291.06C04030 .52C04031 1.98CD4037 88CD4041 70

Veroboard

CD4042 .70CD4043 .83C04044 .77CD40451.30CD40461.20C04047 95C04049 .45C.050 .45CO45101.25co451, 1.94C.5161.25CD45181.87C045209.87

Coup*, Plain0 1 0.15 0.1 0.15E. fp Ep

2 5.3,,,n 36 26 172.5.5. 40 39 193,4:3%. 40 39311.5. 45 47 - 323,17. 1.61 1.26 1.00 1.92P1NSa36 30 30

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Potentiometers

Single DoubleRotary Pots 25p 75pRotary Switched 55pSlIders 45p 75pFu/1 range of Capacitors stocked. Seecatalogue for detail.

Presets Horizontal or VethcalM/ Elp 3W 10p

MICRO -MIN SWITCHES 2P 2W60p. 1P 2W 50p. SUB MINSWITCHES IP 2W 55p. 2P 2W60p- 2P 2W CENTRE OFF 6 Op. 1PON OFF 45p.

MAIL ORDERALL PRICES EXCLUDE VATPOSTAGE & PACKING 25p

21

AUDIO NOISEGENERATOR^I:7 441

R156k

cl'25µF

25V

R25k6

C2

WHITENOISE

C325p F25V

R339k

R6 R7100k 18k

C6820pF

0.00511F 0.003,uF

Q1 --Q3 ARE TYPE 8C108

Fig. 1. Circuit diagram of the noise geneidtor.

R85k6

PINK

+111----°N°ISEC71pF

03

0v

PARTS LIST - ETI 441 C4 0.005pF polyesterC5 0.003pF polyester

RI Resistor 56k 1/2W 5% C6 820pP ceramicR2 5k6 1/2W 5% C7 1/IF 25V electrolyticR3 39k I/2W 5%R4 11VI 112W 5% Q1 -Q3 Transistor BC548, BC108R5 390k I/2W 5% or similarR6 100k 1/2W 5% PC board ETI 441R7 18k I/2W 5% CASER8 5k6 /2W 5% BATTERIES

OUTPUT SOCKETSCI Capacitor 25V electrolytic North America: Use any NPN transistorC2 1 25V electrolytic with a gain of 100 or more (such as theC3 2 J./F 25V electrolytic Radio Shack RS2013s)

22

Simple circuit generates bothwhite and pink noise.

NOISE is generally an undesirablephenomena that degrades theperformance of many measurementand instrumentation systems. Ittherefore seems strange that anyoneshould want to generate noise, but thisis often the case.

Noise generators are often used toinject noise into radio -frequencyamplifiers in order to evaluate theirsmall signal performance. They arealso used to test audio systems, and asrandom signal sources for wind -likeeffects in electronic music.

There are two commonly used noisesource characteristics, 'pink' and'white'. White noise is so calledbecause it has equal noise energy inequal bandwidths over the totalfrequency range of interest. Thus, forexample, a white noise source wouldhave equal energy in the band 100 to200 Hz to that in the band 5000 to5100 Hz.If white noise is filtered or modified

in any way it is referred to as colourednoise or, often more specifically, as'pink' or 'grey' noise. The term pinknoise should be restricted to the noisecharacteristic that has equal energy perpercentage change in bandwidth. Forexample with true pink noise theenergy between 100 Hz and 200 Hzshould equal that between 5000 Hzand 10 000 Hz (100% change in bothcases).

Pink noise therefore appears to havemore bass content than does whitenoise, and it appears to the ear to havea more uniform output level in audiotesting. To change white noise to pinknoise a filter is required that reducesthe output level by 3 dB per octave(10 dB per decade) as the frequency isincreased. The ETI 441 NoiseGenerator is designed to provide bothwhite and pink noise as required.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

HOW IT WORKS - ETI 441In the days when vacuum tubes

were in common use the mostcommonly used form of noisegenerator was a vacuum -tube diodeoperated in the current saturationmode. Nowadays noise generatorsmay be very complex indeed. Highlycomplex digital generators whichproduce psuedo-random digital noisemay cost many thousands of poundsAn example of a simpler type ofdigital noise source may be found inour synthesizer design (seeInternational Music Synthesizer 4600ETI March 1974). However foraudio work of a general nature themost commonly used, and thesimplest, method is to use a zenerdiode as a noise generator.

Transistor Q1 is in fact used as azener diode. The normal base -emitterjunction is reverse -biased and goesinto zener break -down at about 7 to8 volts. The zener noise current fromQ1 flows into the base of Q2 suchthat an output of about 150millivolts of white noise is available.

The `zener', besides being the noisesource, also biases Q2 correctly, andthe noise output of Q2 is fed directlyto the White Noise output.To convert the white noise to pink

a filter is required which provides a3 dB cut per octave as the frequencyincreases. A conventional RCnetwork is not suitable as a single RCstage gives a cut of 6 dB per octave.Hence a special network of Rs and Csis required in order to approximatethe 3 dB -per -octave slope required.Since such a filter attenuates thenoise considerably an amplifier isused to restore the output level.Transistor Q3 is this amplifier andthe pink noise filter is connected as afeedback network between collectorand base in order .to obtain therequired characteristic by controllingthe gain -versus -frequency of thetransistor. The output of transistorQ3 is thus the pink -noise requiredand is fed to the relevant outputsocket.

CONSTRUCTIONConstruction is relatively simple and

almost any of the common methods,such as Veroboard or Matrix board,may be used if desired. For neatnessand ease of assembly it is hard to beata proper printed -circuit board and forthis reason we have provided details ofa suitable board.

Almost any type of NPN transistorwill do for the generator provided thatthe one used for Q3 has a gain of 100or more.

For use as a separate instrument ingeneral experimentation the unit willneed to be powered by a pair ofnine -volt batteries. However if the unitis to be built into some other piece ofequipment, as is often the case, anysupply within the equipment whichhas an output of between 15 and 30volts dc will beisuitable.

Cci `c li(:r TT

0

Bruel & Kist

+ 0 C2

R2

R8

007

0

Potentiometer Range dB Rectifier: _

0

Printed circuit layout. Fullsize 67 x 49 mm.

Fig. 2. Componentoverlay.

OV

WHITENOISE

+Ve

PINKNOISE

_ Lower Lim. Freq. Hz W. Speed mm/sec.

-Awe., . id.3-7-,,

4 21)

Measuring Obi.-

_ , .. __

--

._ ."N_

- --- ,

1

--

.. -

nu-

__AVIALrALIT__ -11

. 0.7..., 1I.. .

I. .-- .

- - - --- ---..`J '4.`n-'4. 1.

-

- - -. -- 201-10 - .._--

--.1

-

...., a

: I

.....

-,

- -- --=-=:----...-:.--1.-......._.--- ..:11.]

.

_-,--- - -7"-..._-

_....-

Rec. No,Date.

- _----

oil1

mum

___-,--

- - -- ----Sian ._ 0 0.OP 1124

10 20 Hr 50

Multiply Frequency Scale by

Bruel & Kjoer Potentiometer Range S.015 S 2 ,rairreil

Cooenhogen

8 d8

3060

adlirr d8IdOr

401.20,

Measuring Ob,

-45 301-.

A wino,u-,10 S Et 7.13I

100 200

dB Rect,e,

500 1000

Zero Level:

Lower 1_,m Freq

2000 5000

Hz Wr Speed

10000 20000

(1612/2112)

mm/sec.. 11 V . I

4.1.5

Roc NoDate

0 Sign20 Hr 50 100

OP 1124 Multiply Frequency Scare by

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

500 1000

Zero Level.

2000 5000 10000 20000

(1612/21121

23

The Black Watch kit£1425!

* Practical -easily built byanyone in an evening'sstraightforward assembly.

* Complete -right down tostrap and batteries.

*Guaranteed. A correctly -assembled watch isguaranteed for a year. Itworks as soon as you put thebatteries in. On a built watchwe guarantee an accuracywithin a second a day -butbuilding it yourself you may beable to adjust the trimmer toachieve an accuracy within asecond a week.

Touch and tell

f., 12 15

The Black Watch by Sinclair is unique.Controlled by a quartz crystal, andpowered by two hearing aidbatteries, it uses bright red LEDs toshow hours and minutes, andminutes and seconds. And it'sstyled in the cool prestige Sinclairfashion: no knobs, no buttons,no flash.The Black Watch kit is unique, too.It's rational - Sinclair havereduced the separatecomponents to just four -and

' it's simple: anybody who canuse a soldering iron can assemble

a Black Watch without difficulty.From opening the kit to wearing the

watch is a couple of hours' work.

Press here for hours and minutes... here for minutes and seconds.

15 31

The specialist features of the Black WatchLarge, bright, red display -easily readat night. Touch -and -see case -no unprofessional buttons.

Smooth, chunky, matt -black case,with black strap. (Black stainless -steel bracelet available as extra -see order form.)

Batteries easily replaced at home.

Runs on two hearing -aid batteries(supplied). Easily re -set using specialbutton -no expensive jeweller'sservice.

24 ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

The Black Watch -using the uniqueSinclair -designed state-of-the-art IC.The chip...The heart of the Black Watch is aunique IC designed by Sinclair andcustom-built for them usingstafe-of-the-art technology -integrated injection logic.

This chip of silicon measures only3 mm x 3 mm and contains over2000 transistors.The circuit includes

a) reference oscillatorb) divider chainc) decoder circuitsd) display inhibit circuitse) display driving circuits.

The chip is totally designed andmanufactured in the UK, and isthe first design to incorporateal/ circuitry for a digitalwatch on a single chip.

...and how it worksA crystal -controlled reference is usedto drive a chain of 15 binary dividerswhich reduce the frequency from32,768 Hz tot Hz.This accuratesignal is then counted into units ofseconds, minutes, and hours, and onrequest the stored information is .

processed by the decoders anddisplay drivers to feed the four7 -segment LED displays. When thedisplay is not in operation, specialpower -saving circuits on the chipreduce current consumption to onlya few microamps.

LED display

Complete kit

4E14.95!The kit contains1, printed circuit board2. unique Sinclair -designed IC3. encapsulated quartz crystal4. trimmer5. capacitor6. LED display7. 2 -part case with window in

position8. batteries9. battery -clip10. black strap (black stainless -

steel bracelet optional extra -see order form)

11. full instructions for buildingand use.

All the tools you need are a finesoldering iron and a pair of cutters.if you've any queries or problems inbuilding, ring or write to Sinclairservice department for help.

Quartz crystal

2000 -transistor silicon integrated circuit

Take advantage of this 17: Sinclair Radionics Ltd, FREEPOST, St Ives, Huntingdon, Cambs., PE1748171no -risks, money -backoffer today!The Sinclair Black Watch is fullyguaranteed. Return your kit in originalcondition within 10 days and we'llrefund your money without question.All parts are tested and checkedbefore despatch -and correctly -assembled watches are guaranteedfor one year. Simply fill in the FREEPOSTorder form and post it -today!Price In kit form: £14.95 (Inc. blackstrap, VAT, p & p).Price in built form: £24,95 (inc. blackstrap, VAT, p&p).SinclairSinclair Radionics Ltd,London Road, St Ives,Huntingdon, Cambs., PE17 4HJ.Tel: St Ives (0480) 64646.Reg. no: 699483 England. VAT Reg. no: 213 817088.

Please send me

.... (qty) Sinclair Black Watchkit(s) at £14.95 (inc. blackstrap, VAT, p&p).

..... (qty) Sinclair Black Watch(es)built at £24.95 (inc. blackstrap, VAT, p&p).

(qty) black stainless -steelbracelet(s) at £2.00(inc. VAT, p&p).

Name (please print)

Total

I enclose cheque for £made out to Sinclair Radionics Ltdand crossed.

Please debit my Barclaycard/Access/American Express accountnurfiber

Address

Signature

FREEPOST- no stamp required.1111041 t wrneraMINININI=Onlidi

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

ET I/4

* Delete as required

1

25

AU 1111 MILLIVOITMETERSensitive instrument for 'A' weighted audio noise and signal measurements.

128AN ACCURATE and sensitive acvoltmeter is needed for many audioequipment measurements.

Whilst for example, maximum poweroutput is readily measurable with a

conventional multimeter, morecomplex instrumentation is requiredfor measuring noise output (a

measurement required when checkingsignal/noise ratio).

Even signal levels as high as 100 mV,typical output of most pre -amplifiers,are not readily measured withaccuracy on a conventional multimeter.

The ETI 128 Millivoltmeter isspecifically designed for suchmeasurements whilst also being usefulas a general purpose ac/dc voltmeter.The lowest range, of 300 microvoltsFSD, allows measurements to 80 dBbelow one volt, whilst other rangesallow measurements up to 30 volts acor dc. These ranges cover most of themeasurement requirements of audiowork.

When measuring noise levels accountmust be taken of the non-linearcharacteristics of the ear. For thisreason a network has beenincorporated which tailors the meterresponse -versus -frequency to matchthe subjective response of the ear.Such a network is known as an 'Aweighting network' and its useprovides a measurement which is

realistically related to what is heard.When measurements are made usingthis network the results must bequoted as being 'A weighted'.Typically this is done by quoting dBArather than just plain dB.

CONSTRUCTIONThe meter is a highly sensitive

instrument and for this reason theconstructional method given should befollowed closely if noise and humpickup are to be minimized.A diecasi box is used to house the

meter as this provides excellentshielding against external signals. The

The meter used in the prototypemeasured 100 x 82mm but required tobe resealed. Any similar meter may beused as long as it has 100 microampsensitivity.

The ac/dc and Flat/'A' weightswitches are four -pole types althoughonly the outer two poles are used. Thecentre two poles are earthed in orderto reduce the capacitance between thetwo outer poles. Such precautions arenecessary to prevent any possibility ofinstability on the most sensitiveranges. The metal bracket whichsupports the printed -circuit board alsoacts as a shield between the metercircuitry and the input stages.Commence construction by

assembling components to theprinted -circuit board, makingabsolutely sure that all are mounted inthe correct position and with the

correct polarity. This should becarefully done - once the meter isfully assembled, it is very difficult tochange components.

Assemble the front panel, fitting allswitches with the exception of SW3,LEDs, potentiometer, input socket,meter, and the shield. The shieldpasses between the centre twocontacts of the 'A' -weighted switch.

Solder a tinned copper lead to eachof the 12 contacts on the rear wafer ofswitch SW3 (about 25 mm long). Feedthese wires through the holes providedin the printed -circuit board (lb to 11 band Wb) making sure that the wipercontact on the switch goes to Wb andthat the other wires are inserted insequence. Do not solder as yet.

Assemble the printed -circuit boardonto the shield and the rotary switchto the front panel. We used a 3 mm

RANGESdc (FSD)

ac (FSD)

ACCURACYMINIMUM READING

Open circuitTerminated 47 k

POWER SUPPLYVoltageCurrentBattery life

SPECIFICATION

10, 30, 100, 300 mV, 1, 3, 30 V.auto -polarity, LED indication.0.3, 1, 3, 10, 30, 100, 300 mV, 1, 3, 10, 30 V0 dB = 1 mW into 600 ohms (0.775 V)weighting curves, ac only, flat, 'A' weight± 3% nominal

-76 dB-85 dB

+6 and -6 volt (batteries)approximately 12.5 mAapprox 100 hours (8 x 1015 cells)

26 ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

C3fc1200pF

%." SW2a

FLATSWla -r R11 0-0

820kC7 -0

2-24pFC2 T--00.1pF R12

82k

0-0

--O

0C51 R13 R14

180 180k

C4120pF R15 R16

18k 18k

C6- R1715000pF

1k

R1 R23k3 270

Cl+2200j_ 6V

R7220k

SW 3a

R18100k

2

-V. RV1$100k

1

R1910k

C9F33pF

8

C1CA3130

R20 RV210k 220k

ATSW2b

C10

0.056R21 pF47k

6

O.3 mV

SW3b

1 mV

03 mV

10 mV

30 mV

100 mV

300 mV

IV

3V

lOy

30V

CB10pF

A wt?C1212.018

R23NF

27kC12

R22

4k7720

.pF

TO PIN 7IC1,2,3

+ e 4 C17ne,Fi 6V-

BATTERY--1

TO PIN 4IC1,2,4

0I.C18

33p F4. 10y

-Ve

-r 6V' --BATTERY-L

R24270k

-Ve RV31 100k

R2810k

C13F3,3pF

18

IC2CA3130

R25330

9C

R26390

R2910k

5

C14

AC

SW1b

6

R271k2

Fig. 1. Circuit diagram of themillivoitmeter.

D5IN914

R311k

RV45k

stack of washers to space the switchback from the front panel so thecontrol knob would sit down closer tothe front panel. Remove any slack inthe tinned -copper wires, connectingthe switch to the printed -circuit boardand then solder them to the board.Now remove the printed -circuit boardand switch assembly from the frontpanel. The switch will now be rigidlyheld onto the board, and the front

wafer can now be wired to the boardvia further tinned -copper links. Makesure that none of these wires is

touching.Add leads to the printed -circuit in

the locations shown on the overlayand reassemble the board and switchassembly to the front panel. Thecomponents on the front may now beconnected to the board by these leadswhich should be kept as short as

possible without placing undue strainon the wires. The only exception tothis rule is the wire from SW1a toSW2a which should be kept reasonablywell clear of the second pole of SW1O.This is best done by running the leaddown the front panel along thebottom and then back up to SW2a.Shielded wire should be used wheredesignated on the overlay and wiringdiagrams, and this should preferablybe of the low capacitance variety.

The LEDs are connected in parallelbut in anti -phase, the actual polaritiesmay be determined later if necessaryduring the calibration procedure.

CALIBRATIONBefore commencing calibration,

check that the meter performs as itshould on all ranges by applyingknown voltages and checking that a

HOW IT WORKS - ETI 128

The millivoltmeter may beseparated into several sections inorder to simplify the explanation ofits mode of operation. These are: --(a) Input attenuator.(b) 'Input amplifier.(c) 'A' -weight network.(d) Meter drive circuitry.(e) Polarity detector.The input attenuator consists of

resistors R11 to 17 and capacitors C4to 7, and gives division ratios of 1,10, 100 and 1000. The capacitors arerequired to ensure that the divisionremains accurate at high frequencies.

The input amplifier is a CA3130operational .amplifier where the gainis selected by SW3b. Gains of 190,60, 19, 6 and 1.9 are available whichtogether with the input divider ratiosprovide the 11, ranges required. Thehigh gain ranges of 190, 60 and 19are ac coupled, as the temperaturestability of the CA3130 will notallow voltages of less than 10 mV dcto be used. The output of thisamplifier is 60 mV when the meter isindicating full scale on any range. Apotentiometer, RV1, is provided to

adjust the offset voltage on theCA3130 and thus acts as a zero -setcontrol. Since the offset voltage isaffected by temperature this controlis available externally.

When measuring noise in audiosystems a weighting network is oftenused to give a measurement which isrelated to the non-linear response ofthe ear. The most commonly usedweighting is known as 'A' weight andthis facility is built into the meter.The 'A' weight curve is produced bya network that has a three -pole,high-pass filter and a single -pole,low-pass filter. The main section ofthis filter is formed by CIO, C11,C12 and R22, 23, and R24 (twopoles). The third pole is due to C3and the one megohm combinedresistance of R11 to RI/. This latersection prevents saturation of theinput amplifier at low frequencies.Since this filter introduces some lossat I kHz, RV2 is incorporated toprovide the same loss in the 'flat'mode.

The second IC acts as a meteramplifier. Th input signal is rectifiedby the diode bridge DI to D4 whilst

the amplifier effectively compensatesfor the diode drops. A preset foroffset adjustment, RV3, is providedfor this IC. Calibration is performedby adjustment of the shuntingresistance, R31 and RV4, across themeter. Due to the full -wave action ofthe rectifier the meter when on thedc ranges reads uni-directionallyregardless of dc polarity. The outputof 1C2 will however will either be atover one volt positive or one voltnegative (voltage drops across thediodes) depending on whether theinput voltage is positive or negative.This is compared by IC3 against zerovolts and, depending on polarity,either LED 1 or LED 2 will beilluminated. With an ac input bothLEDs will be on. These LEDs aretherefore the polarity indicators.Capacitor C19 removes any highfrequency components which couldbe coupled into the input, as theLEDs are located next to the inputsocket.

Due to the difference between theaverage and the RMS values of asine -wave a slight change in gain isnecessary in the ac mode and, thischange is made by SW1b.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 27

AUDIO MILLIVOLTMETER

SW2a

COM

C4-r=k--L

C -r rs

A T kr --{ R13 1-i -4 R16 1.4..

C7 { R14 r

07a 10a4108a 9a8b

9b

rs,

-1 R15 )-

7b11a

00

6a 6b

5a

Fig. 2. Componentoverlay.

5 b

4b

4a 403b 2 bo

la 3.1 4,2a

R5 4 R3

10b

11b

-I R6

V'Vbe VValb

-r RI 1.

'T44144

0cc

`r 2

-r

SW2b OV SW2bN/O

_

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II

1

-I- R19 f.I;Ryalc

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RV2

ciiB C12

(-)N

cc

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C83 5 I 1110/-4-

I ORV1b

-1 R21

ll

II

I

II +L ..0

KENIII

W IRES MARKED" SHOULD BE SHIELDED WIRE

S

C13

Ve SVV2bCOM

+Ve

E

C15 f,i)

-4 R30 TO LEDs8

IcaF

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H SWlb--{ R25 HN/C

C14

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RV4Immr

C16

4.46

T

N M4

TOMETER

3b (3a) 2b (2a)

4b (4a) li lb (la)

5b (5a)

6b (6ai

7b (7a)

8b (Eta)

REAR WAFER ONLY SHOWNFIGURES IN BRACKETSCORRESPOND TO FRONTWAFER

INPUT

9b (9a)

F

Wb (Wa)

lib Ilia)

10b (10a)

0 VC

Fig. 3. Interconnection diagram.

PARTS LIST - ETI 128R2 Resistor 270 ohm 2% 1/4W C8.14;15 10 pF CeramicR25 330 ohm 2% V4 W C9,13 33 pF CeramicR26 390 ohm 2% 1/4 W C4 120 pF CeramicR4 820 ohm 2% W C5 180 pF CeramicR17R6R10 R15,16R21R8

1k2k78k218k47k68k

2%2%2%2%2%2%

1/4 W

1/4 W114Wide W44 W1/4W

C12 820 pF CeramicC3 1200 pF PolyesterC6 1500 pF polyesterC11 0 coapF polyesterC10 0.0561JF polyester

R13,R14 180k 2.4 vs W C? 0.11.4F polyesterR11 820i4 2% 1/4w C19 4.71JF non polarisedR30.31 RettsturR9.27RI

1k1k23k3

5%5%5%

W1/4 W1/4 W

electrolyticC16,17,18" 33pF 10V electrolyticCI 2201.IF 6V electrolytic

R22 4k7 5% 1/4 W IC1.2 Integrated Circuit CA3130R 19.20 10k 5% 1/4 W IC3 LM301R25.29 10k 5% 1/4 W D1 -D5 Diode \ IN914 BA318 orR 3,23 27k 5% 1/4 W similarR5,12 82k 5% 1/4 W LED 1,2 TIL209 or similar with panelR18 100k 5% .ht W mountingR7 220k 5% ./4W SW1,2 Toggle switch 4 pole 2 positionsR24 270k 5% 1/4W SW3 Rotary switch 2 pole 11 positionsRV I Potentio- SW4 Toggle switch 2 pole 2 positions

meter 100K lin rotary MI Meter 100/LA FSD * see textRV2 220k preset PC Board ETI 128RV 3 100k Die cast BoxRV4 5k Two knobsC7 Capacitor 2-24 pF beehive

trimmerOne phono socketEight 11/2v batteries

2222 808 00006 Shield to Fig. 7

28

.1411.40KN

Fig. 4. Curve of 'A' weight response.

deflection of roughly correspondingmagnitude is obtained. Also check thatthe 'A' -weighted switch appears towork as it should.

1. Short the input, select the 3 mVrange and switch on.

2. Allow about 5 minutes for theinstrument to stabilize thermally and

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

M5111.111=1.5211b3SWVIMIM

Fig, 5. Printed circuit layout. Full size 170 x 87 mm.

This internal view of the meter shows on the right, how the range switch is wired tothe printed -circuit board. Note also the shield.

0

O

L_

0

0

eti 12830 AV/ i0l inv ,00 mV-30.111 -le dle Aid i vflied. lid,

r 3., 3VA -sees . ie de

I vs, 10V2 -led, .2* Oa

V elidVL -711011

10V38

0 0" 0 + 00 A .1

ZERO INPUT

Fig. 6. Front panel artwork.

.I.1Alt wall DA.allp 12.r ON

All A.4..0.1..1A..1,11AVA.AAA.A.

Fig. 7. Details of shield -support bracket.

Note how the shield passes between theearthed, centre contacts of the 'A' weightswitch.

then adjust RV3 to zero the meter.3. Select the 10 mV range, dc, and

'flat', and adjust the front panelcontrol RV1 to zero the meter.

4. Remove the short from the input,select the 300 mV range and apply aninput having a frequency of less than500 Hz and a level which gives a

convenient indication, eg 0 dB. Changethe frequency to somewhere between10 kHz and 50 kHz making sure thatthe input level is the same in bothcases, and adjust capacitor C7 so thatthe meter reads the same in both cases.

5. Apply an ac input signal andswitch between ac and dc. The readingon ac should be about 10% higher thanon dc. If it is 10% lower the leads toswitch SW1b should be reversed.

6. In the ac mode select 'A' -weightand apply a 1 kHz signal of sufficientlevel to obtain a 0 dB indication onthe 1 volt range. Vary the frequency.over the whole audio range and checkthat the response as shown in Fig. 4 isobtained.

7. Go back to 1 kHz and check thatzero dB is indicated in the 'A' -weightmode. Now select 'flat' and adjustRV2 to obtain the same reading.8. Apply an accurately known

voltage with the instrument set to theflat and ac modes and adjust RV4 togive the correct reading.

9. Apply a dc input of knownpolarity and check that the correctLED illuminates. If not, reverse theleads to the LEDs.This completes the calibration and

the instrument should now giveaccurate readings on all ranges and atall frequencies within the specifiedrange.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 29

BRUCE SIBLEY CONSIDERS

SPACThe capsule has to providethe astronaut with a com-fortable biosphere despitethe hostile conditionsfound in space.

HOME FROM HOME

Spacecraft are essentially minuteversions of our own planet. Not onlymust they provide air, water, food,tight, similar climate, and protectionbut they must also provide a meansof disposing of our waste products

SPACE TEMPERATUREPROBLEMS

Probably one of the most interestingeffects met in space concerns thecontrol of temperature within thecraft. A surface exposed to emptysunless space would soon freeze.whereas the opposite side facingdirectly towards the sun wouldcook

Without the sun the temperatureof. objects in interplanetory spacewould theoretically fall to absolutezero. - 273 Centigrade or 0'Kelvin. Providing it carries nointernal heating of its own any

ifI

CRAFT

ABOVE Skylab ecewmen Kerwin and Wertztraet for that mission in a mockup of the

station al Houston To the left is thewardroom to the right is the wastemanagement area A forward compartmentconiairks aCkittional experiments and storage.

Stafford and Afeksey Leonov'-xlether for the recent Apollo-Soyuz

The module was to permit the crews-4.sS !O each others craft

An Apollo modulo in lunar orbit TheRCS can be clearly seen to the left of ther:.an motor

AR RIGHT Part at Skylab is reflected in the-elrner of Jack Lousrna as he works outside:ne craft Two members of the crew were-mployed in 'replacing a damaged heat

SJuolO

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

ENVIRONMENTobject will stabilise close to thistemperature

COMPLICATIONS

Had this been the entire problemfacing American space science, lifewould have been relatively simple.Heaters and thermal shields couldhave been installed in the spacecraftto ensure that a living temperaturewas maintained for ship and crew.Needless to say, this is not thewhole story. The solar thermalradiation having travelled 90million miles, delivers the equiva-lent of 1400 Watts per squaremetre in the vicinity of the earth.

Our temperature problem is

hence that one side of a metalspacecraft will be heated to a

temperature of perhaps 160' Cwhilst its opposite side reaches atemperature of --160 C. resultingin a large temperature gradient.Such a difference of temperatureacross the extremities of the samematerial could result in the destruc-tion of the whole structure.

In addition to the threat of solarheating there are other serioussources of infra -red radiation. Thefirst of these is the rocket motors.Present day spacecraft employ onemajor engine at the rear of the

ELECTRONICS ToDA \e INTERNATIONAL- APRIL 1976

space vehicle and several smallerengines, 'reaction control systemengines' (RCS). which look likeclusters of miniature trumpets. RCSengines are located all over the hullof the space vehicle and are used inmid -course manoeuvers and dock-ing, They fire the exhaust in severaldirections to orient the craft; thusthere is a good chance that some of

'the hot exhaust gases will -dust-parts of the spacecraft or communi-cations equipment. Such impactscould send the temperature soaringto 800°C in a matter of seconds.

HOT BODIES

The other source of thermalradiation is the planets. The innerplanets - Mercury, Mars. Venus,and Earth /Moon - whilst by nomeans as hot as the sun, arenevertheless hotter than surround-ing space. Broadly. these interplan-etary bodies are in thermal equili-brium with each other and with thesmaller bodies that exist within thesystem. Each planet exchangessolar radiation between itself and itsnearest neighbours - includingspacecraft and satellites. In fact, -two types of heat radiation areemitted by planetary bodies. Thefirst is known as the 'albedo' and isthe re -radiation of solar energy; the

SPACECRAFTENVIRONMEsecond is due to the planet's ownheating system, its molten core. Inthe case of the moon, only thealbedo is present. About 1 2% moreheat will be generated by thisprocess and all astronauts operatingon the lunar surface will encounterthis.

THE ABSORBING TRUTH

Not all materials absorb heatequally. A white car for instanceremains much cooler than a blackone when left in the sun all day. Thereason for this is that thermalradiation is confined to a spectrumof 0.8-3.0 Microns and white paintabsorbs very little energy at ,thesewavelengths (it is reflected). We'see' at wavelengths far shorterthan those which correspond to'heat'.

MATERIAL CHOICE

Numerous substances exhibit dif-ferential absorptive and reflectivebehaviour to radiation of differentwavelengths. So we can manufac-ture filters and protective coatingsto weaken or reflect unwantedthermal radiation. These 'protectivecoatings help control the externaland internal temperature of thespacecraft and spacesuits.

SURGICAL COATING

These coatings are usually in theform of extremely thin films, yetthey have considerable effect. Greatcare has to be taken assemblingequipment to ensure that thesefilms are not damaged (one oftensees photographs of people assem-bling equipment dressed like sur-geons performing an operation).Every speck of dust represents ahazard.

PROBLEMS WITH ULTRA VIOLET

We are all familiar with the effectsof the sun's ultra -violet lightradiation; the paint on a door or

32

ABOVE The link -up mission module is checked out by Lenov and Slayton in the mannedspacecraft center

BELOW The spacesuit is the astronauts miniature craft, It provides him protection whilstoutside the capsule.

RIGHT Skylab photographed from the astronauts as they pull away Atop the near end is theemergency solar shield deployed by the second crew A solar power panel matching the one atright foreground was lost during the launching At the far end is the Apollo telescope mountwith its paddle -wheel power panels

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

window frame discolours afterbeing exposed to several months ofdirect sunlight. Our bodies become'tanned' if we stay in the sun.Above the earth's protective atmos-phere the intensity of this UV lightis much greater and the discoloura-tion process is speeded up. Fortun-ately, substances called 'Ferro-cenes' (organic,metallic com-pounds) offer great resistance to UVradiation. At the same time theypermit the thermal coatings beneaththem to continue reflecting thethermal energy incident upon them.A series of layered protectivecoatings is thus formed, the layersof which function at differentportions of the electromagneticspectrum. Without ferrocenes andother similar substances, the sun's

UV radiation would quickly degradethe thermal coatings.

EXHAUSTING PROBLEMS

As mentioned earlier, the exhaustgases emitted from RCS enginescan greatly raise the temperature ofparts of the craft in,a few seconds. Itis essential, therefore, to avoidplacing important communications.equipment - antennae, radar,altimeters, radiation probes, etc, inthe path of exhaust plumes. Severaltechniques are employed to preventoverheating of any equipmentplaced outside the protective skin ofthe craft. Each section of an

antenna, for example, is thermallyinsulated from the next minimisingheat conduction.The materials themselves, mainlymetallic in nature, are chosen fortheir high temperature characteris-tics. Caught in a sudden surge ofheat radiation their molecular struc-ture remains intact and does notdeform, an essential characteristicwhen using precision microwaveantennas. Extra thicknesses offerrocene coatings are also used,and have been found . entirelyadequate in all but the most severeexposure to rocket exhaust.

METEORS

Throughout interplanetary spacethere exist millions upon billions of

fragments of planetary debris,called meteors, or micro -meteorites.The size of these fragments can varybetween the size of a grain of sand'to that of a football or a small island.Any spacecraft unfortunate enoughto encounter the smallest of thesefragments encounters a severehazard. If large numbers wereencountered all at the samemoment the experience becomessomewhat akin to passing through asand blasting machine. Largermeteors will wreck the spacecraftwith a single direct hit. However,astronomical data already collectedby deep space probes, together withearlier information built up from

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

earth based observations, suggeststhat the likelihood of such collisionsoccurring is extremely small indeed.There are, however, regions with avery high population of thesefragments, such as the Asteroid Beltbetween Mars and Jupiter, anduntil space vehicles are built aslarge as skyscrapers (like Star Trek'sEnterprise) there will be obviousdanger for any vessel probing outinto space through these regions.

THE DANGERS OF 'NOTHING'

The gas pressure in space is lessthan 10-12mm of mercury. Thisvacuum, the solar thermalinfluence, tcgether introduce somerather bizarre problems.

Sublimation of materials is ana-logous to evaporation of a liquid.The metals zinc and cadium,commonly used in electronic sys-tems, will sublime at the rate of 1

millimetre per year in the vacuum ofspace. Little imagination is -requiredto see what could happen to wiring,and switch contacts, etc., whenmetals re -deposit themselves acrossa supposedly open circuit. Thus theelectronic systems utilised in space-craft must employ metals that donot sublime readily. In additionElectronic circuits are usually pres-sure sealded as a module, usinginert gases.

OVER -ATTRACTION

A further aspect of vacuum andsolar heat is 'cold welding'. Metallicsurfaces devoid of grease and gasfilms can very easily weld togetherby mere impact under the correctconditions. A switch contact couldbecome permanently closed, or a

relay fused. The designers musttherefore select materials which donot easily succumb to the effect.Coatings or films can assist with thisproblem, but generally it is over-come by the choice of materials.

It is obvious then that explorers inspace have many different hazardsand dangers to overcome. The factthat so many space missions havebeen successful is a great tribute toAmerican scientists.

Photographs supplied by NASA.

33

TECHNICAL BOOKS

FROM ETIAUDIO/HI-FIAUDIO ON WHEELSV. C.Installing and operating incar entertainment equipment currently available

AUDIO TECHNICIANS BENCH MANUALJ. EarlDeals .with test tnstruments. tuner tests disc playing equipment

ELECTRONIC MUSICAL INSTRUMENTSN. CrowrhuretFrom baste 'Ample ampltfication to total music generation

EXPERIMENTING WITH ELECTRONIC MUSICR. &ownEverything ts in thts single volume for today s generation of music bulls

HI-FI LOUDSPEAKERS AND ENCLOSURESA. D. CohenExplains advances in stereo sound including three element stereo and all In one enclosure

MODERN RECORDING TECHNIQUESR. AutumnExplains equ pment controls and techntques in the modern stud.

SERVICING ELECTRONIC ORGANSM. ApplebaumInforms on the various electronic Circuits. how to locale and correct defects

PUBLIC ADDRESS HANDBOOKV. Cap&Best, ponciples microphones planning reliability. fault finding

TAPE RECORDERSH. W. Hedy..Guide to the purchaser, what to look for and 10 asStst in maintaining equipment.

TAPE RECORDING FOR FUN AND PROFITW. SalamGetting the most out of your tape recorder PluS equipment

CALCULATORS99 WAYS TO KNOW AND USE YOURELECTRONIC CALCULATORL. Frenzel

SCIENTIFIC ANALYSIS ON YOUR POCKETCALCULATORSmith

COMPUTERSBEGINNERS' GUIDE TO COMPUTER LOGICG. StapletonGrasp quickly computer Codes. dtgetal ;Owe ODs and switching circuttS

COMPUTER CIRCUITS AND HOW THEY WORKB. WetsBecome acquainted with the various parts of a computer end itS technology

COMPUTER TECHNICIANS HANDBOOKB. cardThis giant volume compares to a 1 000 hour course on computer mechanbs

CONTROL ENGINEERINGN. M. MorrieThis is the 2n0 edition of a highly Successful book. keeping fully abreast of develOpmentsas control engineering

DIGITAL ELECTRONIC CIRCUITS AND SYSTEMSN. M. MorrieThe ideal book for the enthusraSt Confused by legit and dived techniques

INTRODUCTION TO DIGITAL LOGICA. PotionUp to dale hook ustog integrated circuits with emphasis on practical design methods

ELECTRONICSACTIVE FILTER COOKBOOKD. LancasterEverything you need to know to build and use &Clive filters

ELECTRONIC ENGINEERS REFERENCE BOOK -4th EDITIONL. W. TumorA completely new and up.todate reference book for all engineers and Students

BASIC MATHS COURSE FOR ELECTRONICSH. Jac °gown:Quick short cut way to learn the language of maths as applied to electronics

BEGINNERS GUIDE TO ELECTRONICST. L. SquiresShort cut for those ...shim) to obtain a gurCk acquaintance with modern electronics

BEGINNERS GUIDE TO TRANSISTORSJ. A. Redd:houghCovers the basic theory and practice of modern transistors

DESIGNING WITH TR. INTEGRATED CIRCUITSTexas instrumentsCovers the enure family of TTL and practical applications of circuits in dig.' systems

34

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Since the ETI Book Service started about nine months ago, it hasachieved enormous popularity with readers. The books includedin the list are selected for their likely appeal to ETI readers. Thelist includes many 'standard' works as well as the latest titles.

This month we are listing about three times the normal number to introduce readers to some less well-known titles andspecialist books.

It is our policy to quote an all-inclusive price in every case,there is nothing else to pay.

ELECTRONIC CIRCUIT DESIGN HANDBOOKBEEMAGCircutt designers cookbook coniatnIng 639 winning designs

ELECTRONIC MEASUREMENTS SIMPLIFIEDC. HallmarkCovers lust about every concetvable test or measurement you will need

ELECTRONICS POCKET BOOKP. McGoldrick

ELECTRONICS AND PHOTOGRAPHYR. BrownPractical circuit protects devoted to photography

ELECTRONICS SELF TAUGHTJ. Ash.Covers basic principles of electronics includes a large number of simple circuits

ESSENTIAL FORMULAE FOR ELECTRICAL ANDELECTRONIC ENGINEERSN. M. MonisHandy reference book Includes a section on SI units. resistor colour codes and preferred values

HOW TO BUILD ELECTRONIC KITSV. Cap&Instructs the kit builder on how to check components how to assemble and how to cure faults

FIRE AND THEFT SECURITY SYSTEMS6. WeisSelection and inetellation. home maintenance and business Security devices

HANDBOOK OF IC CIRCUIT PROJECTSJ. Ash.From hilt orCuittl to complete digital counters in a single package.

HOW TO READ ELECTRONIC CIRCUIT DIAGRAMSB. BrownEverything you need to know from basic circuit components to integrated chturtS

HOW TO BUILD PROXIMITY DETECTORS ANDMETAL LOCATORSJ. ShieldsA practical doloyourulf book

HOW TO USE IC CIRCUIT LOGIC ELEMENTSJ. StreatorHelps those unfarrithar with digital logic circuits

INTEGRATED ELECTRONICSJ. MillmanUsing an IC approach this text leads the reader step by step from sembOnductor physics todevbes, models. circuits and systems.

INTEGRATED CIRCUIT POCKET BOOKR. C. HubbardTechnology and fabrication of urupolar and bipolar IC s are dtscussed digital and linear IC'scovered from a Circuit point of view

IC OP -AMP COOKBOOKW. Jung £7.50Covers the basic theory of IC op amps in great detail, also includes 250 practical circuit applications

INDEXED GUIDE TO MODERN ELECTRONICCIRCUITSR. GoodmanPractical Schematics with concise theory and troubleshooting information

INTRODUCING AMATEUR ELECTRONICSI. R. SinclairThe book lot the complete novice of any age

INTRODUCING ELECTRONIC SYSTEMSI. R. SinclairProvides a baste insight into what makes etectromcs lick

INSTALLING AND SERVICING ELECTRONICPROTECTIVE SYSTEMSH. SweatierCovers installation and servicing of all elecoonrc security systems

LINEAR ELECTRONIC CIRCUITS AND SYSTEMSG. BishopIllustrates the use of the op amp in many different applications

LINEAR INTEGRATED CIRCUIT APPLICATIONSG. ClaytonA practical approach is emphasised throughout encouragrng the reader to try out devices himself

LINEAR IC PRINCIPLES EXPERIMENTS ANDPROJECTSE. M. NollAn trmoductron to one of electromcS most exciting devices

110 OPERATIONAL AMPLIFIER PROJECTS FOR THEHOME CONSTRUCTORR. M. Marston £2.85Outlines the essential charactenstiCs of op amps and presents useful protects

110 SEMICONDUCTOR PROJECTS FOR THEHOME CONSTRUCTORR. M. Marston £2.85Introduces the r Bade, to FET 5, SCR s and IC s wort lull construction details or many oselL,t circuits

£5.00

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ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

110 COSMOS DIGITAL IC PROJECTS FOR THEHOME CONSTRUCTORR. M. Marston

110 INTEGRATED CIRCUIT PROJECTS FOR THEHOME CONSTRUCTORR. M. MarstonAll the projects have been devised. built and fully evaluated by the author

110 THYRISTOR PROJECTS USING SCR'sB. M. MarstonA companion to the author s previous books

OPERATIONAL AMPLIFIERS DESIGN ANDAPPLICATIONS (Burr Brown)G. To,Covers the entire field of operational amplifiers

PIN POINT TRANSISTOR TROUBLES IN 12 MINUTESL. Garner £2.85Complete information on cocci operations. trOubteShooting charts and service procedures

PRACTICAL TRIAC/SCR PROJECTS FOR THEEXPERIMENTERR. FoeThyristor theory and practice! circuits with low cost SCR TRIACs and 01ACs

PRINCIPLES OF TRANSISTOR CIRCUITSB. Amos £4.40Generally accepted as being a standard textbook on fundamental principles underlying the designof circuits us, tran3istors

RAPID SERVICING OF TRANSISTOR EQUIPMENTG. KingA systematic guide to the servicing of transistor redo. television, tape and hi fi equipment

SEMICONDUCTOR CIRCUIT ELEMENTST. D. TowersGives readers an account of all semiconductor devices commercially available. for each deviceit covers a general description. circuit diagram symbols and working principles

SOLID STATE CIRCUIT GUIDE BOOKB. Were!Step by step instructions to design circuits to your own specifications

TRANSISTOR CIRCUIT DESIGNTease

TRANSISTOR POCKET BOOKR. HibbardComprehensive guide to the characteristics and uses of various types

TTL COOKBOOKD. LancaatorComplete and detailed guide to M. how it works. how to 000 it and practical applications

UNDERSTANDING ELECTRONIC CIRCUITSR. Sinclair £4.00Describes various circuits encountered today with a strong emphasis on fault finding and servicingprocedures

UNDERSTANDING ELECTRONIC COMPONENTSR. Sinclair £4.00Explains about components and bridges the gap between elementary textbooks end unapproachableadvanced treatments

UNDERSTANDING CMOS INTEGRATED CIRCUITSR. Metan £3.30Begins with basic digital IC's, covers semiconductor physics. CMOS fabrication technology and des,

UNDERSTANDING SOLID STATE CIRCUITSN. Crowbar.Written to service the interests of anyone at sub.angineering level

RADIO

BEGINNERS GUIDE TO RADIOG. KingThis book will give a bes,c understand, of how and why radio receivers work

COMPLETE SHORT WAVE LISTENERS HANDBOOKH. SamoanComplete and authoritative guide ever published on shortwave listen.,

FM RADIO SERVICING HANDBOOKG. KegServicing guide intended for home constructors experimenters and Service engineers

FOUNDATIONS OF WIRELESS AND ELECTRONICS(New 1975 edition)M. G. ScroggieCovers the whole basic the., no previous technical knowledge is assumed

NEWNES RADIO ENGINEERS POCKET BOOKH. MoorsNaadAn invaluable compendium of radio facts figures and formulae

PRACTICAL AERIAL HANDBOOKJ. KingImportant and up-to-date guide to radio and TV receiving aerials

RADIO CONTROL MANUALE. SaltordFor all hobbyists and modellers

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

£3.10

£2 \.85

£2.85

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RADIO SERVICING POCKET BOOKV. CopalA practical book for the radio serviceman.

SERVICING TRANSISTOR RADIOSL. DAiroComplete guide giving theory analysis and servicing techniques

WORLD RADIO TV HANDBOOK - 1976This year includes .How to listen to the world.

SEMICONDUCTOR DATAINTERNATIONAL TRANSISTOR SELECTORT. D. Tows.If it takes you longer than One minute 10 find Out all about transistors. then you need a copyof this book.

POPULAR VALVE/TRANSISTOR SUBSTITUTIONGUIDESubstitution data for both valves and transistors in one new volume

RADIO VALVE AND SEMICONDUCTOR DATAA. M. BallCharacteristics of 1.000 valves. cathode ray tubes. transistors. diodes. rectifiers and optical semi -

£2.15 conductors. This new edition (1 9751 is right up to date and over 450.000 copies have been sold

TRANSISTOR EQUIVALENTS DATA BOOKDIODE EQUIVALENT DATA BOOK

TEST EQUIPMENT AND OSCILLOSCOPES

BASIC ELECTRONIC TEST PROCEDURESI. M. GottliebShows how to get accurate measurement with VOMo meters end oscilloscopes

ELECTRONIC TEST EQUIPMENTH. Knottier, £5.00Explains the principles and requirements of particular typos of test equipment including typicalcircuitry

£2.15 HOW TO TROUBLESHOOT AND REPAIR ELECTRONIC

£2.85

£6.00

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£3.45

TEST EQUIPMENTM. Horowitz

£5.75 Packed with practiCal data on repair of all types of instruments

HOW TO TEST INSTRUMENTS IN ELECTRONICSERVICINGF. SchunArnanThe all -in -one test instruments aPPItcalicin handbook

HOW TO USE VECTORSCOPES, OSCILLOSCOPESAND SWEEP SIGNAL GENERATORSS. Prent.saA practical guide that tells how 10 use modern TV test instruments

HOW TO USE YOUR VOM VTVM AND OSCILLOSCOPE£1.85

Tremendous value in helping to select instruments best suited to individual needs

THE OSCILLOSCOPEG. ZwickStarts from the first principles and takes the 'eerier to an advanced level

PRACTICAL TEST EQUIPMENT YOU CAN BUILDW. GroanFor technicians. radio/ TV service operators and serious experimenters

£1.90 RADIO, TV AND AUDIO TEST EQUIPMENTG. KingA practical guide to test instruments and applications concerned largely with the oscilloscope

TEST INSTRUMENTS FOR ELECTRONICSM. CliffordBony modifications to your VOM/VTVM and scope with the a, of this book

WORKING WITH THE OSCILLOSCOPEA. SaundersIncludes workshop test protects with large size drawings

SERVICING WITH THE OSCILLOSCOPEJanuary 1976)

G. KingIncludes a unique series of photographs showing oscilloscope traces to be lound in normaland faulty equipment. Stare° radio. colour TV Circuits servicing is dealt with

£3.65

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£2.45

-£4.70

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HOW TO ORDERAll prices are correct at the time of going to press but are sub-ject to alteration without notice. All prices include postage.Please print your name and address clearly and list each title andprice separately. Cheques and postal orders should be made pay-able to ETI Book Service. Books are sent on seven days' approvalagainst a ft..11 cash remittance, plus postage. Book stock is notheld at ETI s London offices and orders should be sent to: ETIBOOK SERVICE, 25 COURT CLOSE, BRAY, MAIDENHEAD,BERKS.

35

These words were sent, and received, on thetelephone shown above, on 10th Morch 1876The telephone was made byAlexander Graham Bell and theworld's first telephone message watsent by him to his assistant,Thomas Watson, in Boston, Mass.,a hundred years ago.

Twenty-seven years earlier a tele-phone, believed to be the first, wasbuilt in Havana by Antonio Meucciof Florence. This instrument was

TELEPHONE

BOXESThe first public call -box wasopened in New Haven, Conn. on1st June 1880. Payment was to anattendant. Regular callers couldbuy a key to enable calls when theattendant was off duty.

The first coin -operated telephonewas installed in Hartford, Conn, in1889. It was not until 1906 thatthe Post Office opened their firstcoin -box telephone at the LudgateCircus P.O.

never patented or demonstratedpublicly.

The first publicly demonstrat-ed phone was built in 1860 byJohan Philipp Reis near Frankfurt.It was made from a violin case, abarrel bung and a sausage skin.Listeners claimed to be able torecognise music but messages were

,unintelligible.

Prepayment phone boxes werenot introduced until 1925.

The first outdoor kiosks inBritain were erected n 1908. Mostof the kiosks were made of wood,but in dockland areas they weremade of galvanised iron to with-stand the agression of dockers wholose their money.

In 1912 the Postmaster Generalapproved the provision of doodlingpads to discourage callers fromdefacing walls. These were aband-oned during the first World War.

The first standard kiosk designwas introduced in 1921 - a con-crete frame with red wooden doorand metal glazing bars.

1879 First telephone exchange in Englandwas opened in London, by the TelephoneCompany Ltd.1896 National Telephone Company's trunkservice was taken over by the Post Office.1912 All National Telephone Companyexchanges had been taken over by the PostOffice.1915 Archangel submarine telegraph cablewas laid.1925 Prepayment coin -collecting boxeswere introduced.1927 London - New York radiotelephoneservice commenced.1929 Hand micro -telephone was introduced(combined transmitter and receiver in onehand -set).1932 "Telex", "Printergram" and privatetelegraph services were introduced.1937 First submarine coaxial telephonecable opened to Holland carrying 16channels. "999" service introduced inLondon.1943 First submerged repeater laid inthe Irish Sea.1949 London -Birmingham television radiorelay link opened.1951 Telephone Act passed, enablingthe Postermaster-General to fix retailcharges by Statutory Regulation.1956 Opening of the TransatlanticTelephone Cable.1958 First subscriber Trunk Diallinginstallation opened at Bristol.1962 First telecommunications satellite(Teistar) launched. Experimental electronicexchange opened at Highgate Wood.1963 International Subscriber Dialling (ISO)introduced, from London to Paris.1964 Datel services introduced. 4 FirstCrossbar exchange opened to public service.1965 London Post Office Tower opened.1968 Inauguration of first pulse codemodulation (PCM) switching centre.1973 World's first experimental Inter-national Confravision link -up betweenLondon and Sydney.1975 ISD extended to 26 countries. PostOffice's new Research Centre opened atMartlesham Heath, Suffolk at a cost of£111/2 million.

THE FUTURE

Next month's ETI will feature anarticle on VIEWDATA. In this systemsubscribers will be able to call upinformation from a central computerusing their telephone line.

Other developments being research-ed uy the Post Office include sendingsignals down glass fibres. The cap-acity is fantastic - half a millionphone calls can be transmitted downa "cable" of glass fibres!

36 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

THE WORLD'S FIRST INTELLIGIBLE PHONEMESSAGE WAS SENT 100 YEARS AGO

ha.TELEPHONE

EXCHANGESThe first telephone exchange was advertised inOctober 1877 by Isaac Smith, for the New EnglandTelephone Company. Within a month he had 17subscribers. The first in Britain was the GlasgowMedical Telephone Exchange built in 1879. Unlimit-ed calls where allowed for a fee of £12.

The photo above shows a lady operator in anEdwardian telephone exchange.

The first automatic exchange was patented in1889 by Almon B. Strowger, a Kansas City under-taker. Strowger had previously been losing customwhen the wife of a rival undertaker became anoperator of the manual exchange.

The first Strowger exchange was opened 1892 inthe US; the first in Britain opened in London in1892. The early telephones did not have dials - thesubscriber has to tap out the number on 3 keys(hundreds, tens and units).

TELE-

PHONEDIAL

The first telephone dials wereused in 1896. Projecting vanesdivided the sectors of the dial -the use of holes was a laterdevelopment. Today the push-button dial is common and soonit will be standard.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

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Now we bring you...

TOP PROJECTS No.3WHICH INCLUDES ...

41,14. ler

STEREO FM TUNER

LIGHT DIMMER

AF METER

LINE AMPLIFIER

DIGITAL DISPLAY

PLUS MANY MOREAvailable from your newsagents or directfrom ET!. Please send £1.20 to covercost plus postage and packing. Makecheques and P 0.'s payable to ET IMagazine and please write Top ProjectsNo. 3 and your address on the back ofyour cheque.

TOP PROJECTS No. 3ET! Magazine,36 Ebury Street,London SW1W OLW

ON SALE AT YOUR NEWSAGENTS MID -MARCH: R1.00ELECTRONICS TODAY INTERNATIONAL APRIL 1976

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ETU/Marshall'sSEMICONDUCTOR OFFER

ETI and Marshalls have again teamed up to bring our readers this chance to stock up on IC's andpower transistors at very special prices All devices carry Marshalls usual guarantees. and arebrand new (as usual!) straight from the manufacturers. There are large stocks of everything in the

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7400 .16 II 7451 16 11 74190 230 1 70 40004E .18 12 4028 83 60 1M747 8011 40 .287401 .16 .11 7453 .16 II 74193 1.15 15 18314E .18 12 3035 140 90 10748 8161 60 .397402 .16 .11 7454 ..16 11 74196 1 60 1 00 40324E 18 12 4049 45 36 11101310P 250 1.957403 .16 .11 7474 .31 18 4006 .99 73 8E5558 69 407404 19 12 7490 42 24 4007 .18 12 263055 65 457410 .16 II 7492 45 24 4008 .82 63 /412955 1.00 757413 .28 16 7493 .45 .24 4009 .52 35 /4462955 1.20 907416 28 .16 7496 .68 .44 4011 .15 .12 MJE3055 75 EC

7420 .15 II 74107 30 .24 4012 .18 .12 80135/5 PE" 1.10 .757423 23 .14 74121 .32 .20 4013 .45 34 80139/413 Pr 1.58 1.007430 .16 II 74150 1.20 .61 4016 .45 34 50Y56 1.50 987440 16 .10 74153 .68 .24 4018 .88 667442 65 45 74154 1.20 .70 4019 .52 387446 84 55 74755 .78 .35 4023 18 .12'450 16 II 74180 1.10 35 4024 72 50 Devices marked' VAT at 25% Al others at 8%

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6413 28 16 4016 45 347416 28 16 4018 88 167420 16 II 3319 52 387423 23 14 4023 18 12

7430 16 11 4024 72 .507440 16 10 4028 83 607442 65 45 4035 1.40 937446 84 55 4049 .45 367450 16 11 110741 8011 40 28

7451 15 11 LM748 8011 60 397453 16 II 61C 1310P 2.50 1.95

7454 16 II 15555V 69 407474 31 18 793E55 .65 457490 42 24 0J2955 100 157492 45 24 61E2955 1 20 907443 45 24 NUE3055 .75 6074% 68 44 80135,6 Pr 1 10 7574107 X 24 9313140 Pr 1.58 1 BO74121 32 20 80155 , 150 , .9874150 120 61

74153 68 24 SUB TOTAL74154 120 7074155

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I C INSERTION TOOL WORTH 60pCOMPLETELY FREE OF CHARGE IDEALTOOL FOR ALL ENTHUSIASTS

39

electronics todayMAY ISSUE ON SALE APRIL 2nd -30p

VIEWDATAThe Post Office's Viewdatasystem has received surpris-ingly little publicity despitethe enormous implications.What is it? Use your existingtelephone line and TV set tosummon up a vast store ofinformation from a centralsystem. A special report inETI.

OFFERON

CASSETTESHigh quality C90 audio cassettes ata sensationally low price - that'sthe offer in next month's ETI. Fulldetails in the May issue.

CONETAIAn unusual project designed toour normal high standard -expand or compress the dynamicrange of any audio signal toincrease fidelity or intelligabilitydepending on the application.

FROZEN

SIGNALSStorage scope tubes have opened.up the analysis of non -repeatingfast signals, yet how they work isnot widely known and is veryclever.

TEMPERATURE

METER

An inexpensive project using awidely available sensor -a silicondiode! Can be calibrated for C or Fand designed for easy coupling to adigital display.

WILL WE GET 9IT IN TIME

Two weeks before the next issuegoes to press, a really exciting IC isdue for release which will be ofespecial interest to the homeconstructor. ETI has been pro-mised the first sample: if we get it.- you'll know about!

MAKE SURE OF YOUR COPY

ETI's sales increased in 1975 byover 34% (Dec 74 -Dec 75) - thatresulted in a lot of disappointedpotential readers despite consider-able increases in print run. Be sureof your copy - place a regularorder with your newsagent - he'llhe glad to reserve you a copy.

Features mentioned here arescheduled for the May issue. How-ever, circumstances, includingtopical articles, may affect thefinal contents.

TOUCH SWITCHNew Technolgies have made thetouch switch thoroughly practical- next month we present a pro-ject with endless applications.

40

DATA SHEET SPECIAL:AUDIO AMPLIFIER ICsWe've gathered together data onboth common and less well knownaudio amp ICs for this special. Itcovers from milliwatts to 100W

and will save you hours ofresearch when you next tackle anaudio project.

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

P.E. CAR CLOCK KIT AVAILABLESend s a e for details/prices. etc

ADVANCED ALARM CLOCK KITComplete kit including attractive slim case with perspex panel for 6 digitalarm clock with bleep alarm, snooze and automatic intensity control highbrightness display driving. uses MK50253 IC and Jumbo 0 Stn LEDs Kitalso includes PCBs. active and passive components. IC ski min.transformer switches, flat cable, loudspeaker mains cable and plug. Fullinstructions Crystal control /battery back-up and touch switch snooze andalarm are optional add-ons £27.31

SIMPLE & ATTRACTIVE 4 -digit CLOCK KIT.As featured in January Everyday Electronics) Ideal kit lor the lessexperienced constructor. kit includes IC pleasing r,3ii green display withcolon. PCB miniature transformer slim white case with perspex frontpanel, and all other components except mains cable and plug Fullinstructions £15.69

CRYSTAL TIMEBASE KITAll components including PCB (47mm x 59mm) to provide 50cps for clock(Cs giving time accurate to a few seconds a month Kit includes PCB.32 768 kHz miniature watch crystal, trimmer. 3 CMOS ICs and sockets.Cs. Rs

. £6.28

STOPWATCHComplete Kit for Stopwatch (as in December ET1). choose 6 digit rangefrom tens of hours to milliseconds Contents Verocase 75, 1410J redperspex front panel. Manganese batteries. clips. transistors diodes, wiringpins screws sockets, pin -header. CMOS. resistors, capacitors. 5 12MHzcrystal trimmer PCBs 6 x MAN3M displays With instructionscomponent layout, etc .. £31.80STOPWATCH WITH ONE LATCH: As above hut kit also includesfacility to repeatedly freeze one set of displays with count continuing on theother set £47.71ADO VAT et 8% to ell Prices in this advertisement. 1 Sp P&P nn orders under t 3Free on orders over t 3 Orders sent by 1st Class Post Exports No VAT 35p (Europe)1 (Overseas) for Air Mail PgP any excess refunded) Full Price List and Data with any

order or on request (phone or send s a e.)Official Orders welcomed, written phoned or felesed from Yinfsrs PO 00 Nat IndsGoon Departments Companies etc Fastest Delivery for R&D.

SINTEL53a Aston Street, OxfordTel. 0865 49791Telex: 837650. A B ELECTRONIC OXFD

CMOSCMOS fr ifif the leading manufacturers only

CD40004 0.17 CD4028A 0.74 CD4053A 0.77 C040868 0.590040014 0.17 CD4029A 0.94 C040544 0 95 CD4089B 1.27CD4007A 0.17 C040304 0 46 0040554 1 08 CD409313 0.660040064 0.97 CD4031A 1.82 C04056A 1.08 CD4094B 1.53C040074 0.17 CD4032A 0.88 CD405 /A 20.35 C040956 0.86CD4008A 0.79 CD4033A 1.14 C04059A 10.64 CD40968 0.86C04009A 0.46 CD4034A 1.58 CD4060A 0.92 C040998 1.50CD40104 0.46 CD4035A 0.97 CD4061A 16 43 CD4502B 0 98C0401 ;A 0.17 CD4036A 1 82 C040624 7 33 C0451013 1.120040124 0.17 CD4037A 0.78 CD40638 0 90 C045115 1.28C040134 0.46 CD4038A 0.88 0040664 0.58 0845148 2.56C040144 0.83 CD4039A 2 86 0040618 2.95 CD4515B 2.56C040154 0.83 CD4040A 0.88 CD406813 0.18 0045165 1.12C040164 0.46 C040414 0.69 CD40698 018 CD45185 1.03C04011A 0.83 CD4042A 0.69 CD40 /UB 0.18 C045205 1.03C040184 0.83 0040434 0.83 0040718 0.18 CD45278 1.30004019A 0.46 CD4044A 0 77 CD407213 0.18 C045328 1.16CD4020A 0.92 CD4045A 1.15 CD40 738 0.18 CD45558 0.74CD4021A 0.83 CD4046A 1.10 C040758 0.18 C045568 0.74CD4022A 0.79 C04047A 0 74 CD4076B 1.27 MC14508 2.37C04023A 0.17 C040484 0 46 CD40778 0.18 MC14528 0.86CD4024A 0.64 CD4049A 046 CD407813 018 MC14534 6.04CD4025A 0.17 CD4050A 0.46 CD4081B 0.18 MC14553 4.07CD4026A 1.42 CD40514 0.77 C0408213 0.18 MC14566 1.21CD402 74 0.46 C040524 0.77 CD4085B 0.59 MCM145S2 8.05

RCA 1975 CMOS Databook: 400 pages of data sheets and 200 pages ofLircuits. applications and other useful information E2.67 (Add noVAT -post free)Motorola McMOS Databook (Volume 5 Series A)

CLOCK ICs

£2.77 (Add no VAT -post free)

DISPLAYS VEROCASESMK50253 £5.60 OL704E 85p 75, 1410) £2.64MK50250 £5.00 FN0500 £1.02 1205 x 140 x 40mm)MM5314 £4.44 FND5000 95p 75 141 10 £2.94AY51202 £4.76 MAN3M 48p ,205 x 140 x 75mmlAY51224 E3.66 bLT01 E5.80 Flat CableMK5030M Et 2.50 LCD £9.40 20 -way £1 per m.

DISPLAY PCBs (each fits neatly into Verocase J) for clock with 6 x

FND500. for clock with 6 x DL704. for counter with up to 8 x FND500. forcounter with up to 8 x OL704 these four are £1.35 each, for clock with 4x FND500 90p.IC SOCKET PINS. Lowest cost sockets for CMOS. TTL. ICs, DisplaysStrip of 100 pins for 50p, 400 for £2, 1 000 for £4, 3 000 for £1 0.50.

POTENT KNOING

SUNINFita [TWThe tried, tested, proven, reliable, complete,professional, capacitive discharge,

Spark nte" was voted best of 8 systems tested byPopular Motoring Magazine

ORDER NOWTO' ELECTRONICS DESIGN ASSOCIATES DEPT. ETI 4

82 Bath Street. Walsall. WSI 3SE. Phone 33652

PROM Nom

Adams

Oh

SPARKEITE MK 2 OIT MaraMy ilia (IOU

SPAREESTE ME 2 Marty EMS %pg. sena e LI3 OE

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Electrnnir iff....z...

manutacturersannouncement

ElectronicsDesign

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,WILL BE,CHARGED,,,AT

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years ......

HOWEVER .."..

gush unit £13 86 incl V A T post and packing Moth to fit all'1 I Y assembly Int E10 9? inn V A t

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vehicles gosh coil rdfstrtbutor grim. up to 8 cylinders I

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ALL ORDERSRECEIVED

BEFORETHIS DATE

atter

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RPM limiting control C2 42 inci V A T post and peckingTHE KIT COMPRISES EVERYTHING NEEDEDReady defied pressed steel case Waked in man black epoxy ref f nrreds drftwe base and neataink Top duality 5 year guaranteedf ',dormer and components cables coo connectors wonted

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

CALLEN; WELCOME

41

TECH -TIPSINDEX

AC to DC Converter, Precision DecActive Band Pass OctActive Tone Control OctAGC, Simple AugAlarm, Basic AprAmplifier, Economy Feb

FArtificial ull-Wave Rectifier AugAssist that Zener AprAudio Amplifier JanAudio Amplifier OctAudio Clipper, Precision HanAudio Doubler JulyAudio Leads, Universal AugAudio Mixer, One Transistor MarAudio Rejection Filter NovAudio-RF Signal Tracer Preamp JanAudio Trafficator Indicator JanAutomobile Rev Counter/

Tachometer JulyAuxiliary Battery Adaptor Feb

Back-up Failure LampBalanced Regulator, SimpleBandpass Filter, ActiveBattery CheckingBattery LifeBattery SnapsBattery TesterBattery TesterBeeper, TransistorisedBlown Fuse indicatorBoost your Mains'Bucket' RegulatorBurglar Alarm, How not to

Design

Cartridge & Rumle FilterChopper SimpleClipper PreampClock Generator, MultiphaseCMOS ClockColour Coding ComponentsCompressor, SimpleConstant Current CircuitConstant Current SourceCoolant Level WarningCrackle -Free Pot. Opto-Isolator JulyCrossover, Simple SeptCrystal Checker JanCrystal Check -Up MayCrystal Earpieces JuneCrystals, Uncritical AugCurrent Limiter SeptCurrent Limiting JulyCurrent Source, Temperature

Stable Mar

NovAugSeptJulyJuneMayDecJanMayMayAprJan

Jan

Capacitance Multiplier, Variable MarCapacitor, Electronic OctCar Warning Flasher System Sept

MarJanSeptJanFebJanMarMarAprAug

DC to DC/AC InverterDC -DC ConverterDigital Capacitance ProbeDigital Comparator, Low CostDigital DieDigital Tape AdaptorDigital VoltmeterDIL DrillingDiode Adjusts Zener VoltageDiode Checker

SeptMayJulyNovDecJulyJulyJanNovApr

73 8074 6674 6673 8275 6675 6874 6675 6475 6675 6576 4472 8375 6575 6674 6776 4475 64

Diode TesterDiode Tester GO/NO-GODisco AutofadeDoorchimes DelayDouble Precision RectifierDual Polarity Power SupplyDummy Load for High Power

Amps

Electronic FuseElectronic Fuse, BetterElectronic SwitchFET RadioFET Square Wave GeneratorFilament ConnectionsFilter, Active

74 66 Finishing Front Panels75 68 " Warning

Fire Alarm, SimpleFishcaller, TransistorisedFlash Slave DriverFlasher CircuitFlasher TransistorisedFloodlamp Power ControlFluorescent Starting, Flicker -

FreeFour -Way Flasher AdaptorFrequency Meter, Simple

AccurateFuse Failure IndicatorFuzz BoxFuzz Box

74 6775 6472 8074 6674 6674 6275 7376 4975 6775 6874 6676 48

75 68

75 6874 6774 6676 7476 5175 6576 4675 6776 4674 6375 6674 6774 6675 3974 6776 4675 6674 6773 8274 6775 41

76 74

75 6575 6675 3872 8175 7475 4575 4276 5274 6772 84

Sept 74 66Aug 73 82May 75 68Jan 76 45Jan 75 67Mar 75 67

Oct 75 66

Apr 75 66Sept 75 66June 75 64Dec 74 67Feb 75 68June 73 81Jan 74 77Feb 75 66Mar 75June 75 64June 75 65Oct 74 67Nov 75 74Dec 74 66Dec 72 86

Jan 76 45June 75 65

Mar 76 73July 74 66Apr 75 67Oct 75 66

Gain Controlled Amplifier June 73 81GO/NO-GO Diode -Transistor

Tester Jan 76 44

Half Charge Rate for CarBatteries

Half -Wave Rectifier, FastHeadlamp Dipper, AutomaticHeat Sinks, Avoiding InsulatedHigh Impedance AmplifierHigh Impedance Bridge

Amplifier

High Impedance VoltmeterHigh Input Impedance AmpHigh -Power Zenered Votlage

from Low Power SourcesHigh Voltage Constant Current

SupplyHigh Voltage ElectrolyticsHigh Voltage from a BatteryHum Stopper

IC Stablised P.S.Identifying 74 SeriesImproving UJT LinearityIncreased Sensitivity for Heavy

Current ThyristorsIncreasing Noise ImmunityInformation TransferIntruder AlarmInverter, Transformerless

JFET Test, Quick

Feb 76 70Sept 72 86Feb 76 70Apr 75 66Jan 74 77

Sept 75 65

Nov 74 66Nov 74 66

Jan 76 45

Feb 75 69May 74 62Oct 73 82Nov 75 72

Aug 75 66July 75 43May 74 62Apr 75 66July 75 44July 75 38Jan 76 49Jan 76 47

Apr 75 67

LDR, Homemade Jan(Warning: this idea is danderous,

attempt)76 47

do notLED Changeover Circuit Nov 75 73Light Coupled Voltage to

Frequency Converter June 75 64Light -Flasher (Ultra -Simple) July 74 66Light Level Indicator Aug 75 66Light Show Circuit June 74 67Lights -Out Alarm June 74 66LM381 Applications Oct 74 66Lock, Electronic Jan 76 50Logic Analyser Mar 76 73Logic Probe Nov 75 74Loudspeaker Checking June 74 67Loudspeaker Microphone May 74 63Low temperature Alarm June 74 66Low Frequency Extender Mar 76 72Low Regulated DC Voltages July 73 82Low Voltage Stabilisers Mar 75 67

Making Slow Logic PulsesAudible Jan 76 52

Measuring High Resistance withMultiMeter Sept 73 82

Measuring Micro -AmmeterResistance Apr 75 66

Measuring RMS Value of ACwith DC DVM Jan 76 48

Memory that Learns July 75 40Meter Protection with Zeners July 72 83Mixer, Good (RF) Mar 74 63Model Train Speed Control June 75 65Monostable Multivibrator Dec 74 67Multiplier Efficiency, ImprovingJune 72 84Multiplier/Op Amp Circuit

Detectors True RMS July 75 44Multivibrator, Improved Mar 76 74Multivibrator, Unusual Aug 75 65Multivibrator, Wide Range Dec 72 86

Neon Flasher Warning July 75 41Neon, Low Voltage Transistor

Drive Apr 73 89Neon Tube Flasher May 75 67Ni-Cad Discharge Limiter Jan 75 66Noise Limiter Sept 75 66Noise Rejecting SCR Trigger Jan 73 77Noise Source, Simple June 73 81

Op -Amp Radio Dec 74 66OP -Amps as Photocell Amp Dec 72 86Optical Pulse Conditioner Jan 75 66Oscillator, Simple Dec 75 72Oscillator, Wide Range July 72 84

Peak Detect & Hold Circuit Apr 75 67Phase Lock Control Circuit Feb 73 86Phase Locked Loop,

Economical Aug 75 65Photo Electric Relay Feb 75 69PLL AM Receiver Sept 74 66Plop Eliminator Mar 75 66Positive Peak Detector Jan 74 77Power Supplies, Adjusting Sept 75 64Power Supply or Battery? Apr 74 66Power Supply, Variable gives

+ve or -ve output Mar 75 67

42 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

DATA SHEET

INDEXAY -5-1224AAY -5-3507AY -1-0212 & AY -1-5051CA3130ERG303DM252NE540L

DecFebFebNovDecJanNov

75767675757675

42424142436441

SL415A & SL414ATBA810TCA208ATCA210TDA1054ZN1034E/IA 7800 Series

JanOctJanDecOctNovOct

76757675757575

,2386141394337

Product Detector, Transistor Apr 72 84 Temperature Control System Jan 75 66Protecting IC's Against Shorts Nov 74 66 Temperature Sensor May 74 63Pulse Count to Speed Converter Apr 72 83 Temperature Switch Oct 74 67Pulse Delay, Economical Oct 72 81 Temperature Sensor, Remote Aug 75 64Pulse Generator Dec 74 67 Thermistor Oscillator July 75 38Pulse Generator, Simple Aug 73 82 Thermocouple Thermometer Oct 75 64Pulse Timer June 72 84 Thermostat, Low Differential Jan 76 43

Timer, 741 Jan 76 52Tinning with Solder Wick Jan 76 44Tone Control Circuit July 75 39Touch Controlled Doorbell Dec 72 86

RC Oscillator, Stable Dec 74 66 Touch Sensitive Switch May 75 68Reaction Comparator Sept 74 67 Touch Triggered Bistable June 74 67Recording Pickup Oct 73 82 Transformers in Reverse June 74 66Reduced Ripple at Low Current Nov 75 73 Transformer -Inductor Tester May 74 62Reference Voltage Supply Apr 75 64 Transistor Current Gain Tester Feb 76 71Regulator, Variable, High Transistor Identification June 74 66

Voltage Jan 76 45 Transistor Phase Shifter Apr 73 89Replacing Soldering Iron Bits May 74 63 Transistor/SCR Tester Oct 74 67Resistor Values, Odd Aug 74 67 Transistor Socket May 74 63Resistors In Parallel July 75 45 Transistor Tester, Basic Sept 73 82RF Amplifier Protection Apr 74 66 TTL Mains Interface Apr 74 66RF Attenuator, Variable Apr 74 67 TTL Probe Jan 76 51RF Dectector Sept 75 66 Twilight Switch, Automatic July 75 41RF Indicator, LED Feb 76 72 Two Control Signals DownRF Preamplifier Sept 75 64 One Wire Aug 74 67RF Voltmeter, Sensitive Jan 76 47

Variable Brilliance Lamp Oct 75 64

Saw -Tooth GeneratorSaw -Tooth Generator, Simple

MarAug

7573

6882

Variable Duty Cycle OscillatorVariable Frequency Multiple

Waveform Generator

Dec

May

74

75

66

67Schmitt Trigger without

HysterisisSCR Control, Full -Wave

SeptJuly

7275

8641

Varicaps, ChrapieVCO, SimpleVery Low Output Impedance

AprJulyMay

747272

678484

SCR Crowbar Protection July 75 42 Video Power Amplifier Aug 72 85Screw Starter July 75 45 Voltage Controlled Monostable Aug 74 66SCR Tester Nov 74 66 Voltage Divider, Precision Dec 75 74Self -Triggering Timing Circuit Jan 75 67 Voltage Divider, Regulated Sept 75 64Sequential Closing of Relays May 74 62 Voltage Doubler, Modified June 73 81Sequential Timer Nov 72 81 Voltage Multiplier July 75 39Shaft Position Digital Voltage Processor June 74 67

Transducer May 72 84 VR Tubes, Boosting Apr 72 84Sharing Diode Load Apr 75 65Shaver Adaptor July 75 39Shutter Saver Mar 75 66Signal Tracer May 74 62 Waa-Waa Circuit Feb 75 66Signal Track and Hold Circuit Oct 75 64 Warbling Alarm Dec 75 73Sine/Square Wave Converter Apr 75 64 Water Level Alarm Aug 74 66Single Ended Power Supplies, White & Pink Noise Generator Jan 75 68

Coverting June 73 77 White & Pink Noise Generator Apr 75 65Siren Circuits for Toys Feb 76 71 Wideband Amplifiers July 74 67Siren, Toy Feb 75 66 Wiper Delay, Universal Dec 75 72Siren, Simple May 75 66Solder -Flow Problems June 74 66Soldering IC'sSound Effects Generator

JulyOct

7575

4366 Zener Boosts Output Voltage

Sound Effects Generator Jan 76 48 of Regulator Jan 76 46Sound Operated Two Way Zener Diode Check July 75 46

Switch Nov 75 72 Zener Diode Lifts CapacitorSpeed Control for Models Apr 75 65 Rating Apr 74 66

" Errata June 75 Zener Diode Noise Generator Mar 75 68Speeding up Darlingtons July 74 67 Zener Diode Variable Jan 75 68Square -Wave Generator July 73 82 Zener Diode, Variable Mar 75 68Square -Wave Generator, Fast Zener Diodes, Increasing Power

Edge Nov 75 73 Rating Feb 75 66Square -Wave Generator, Variable

DutyStabilised Power SupplyStabilised Power Supply,Meter-

MayDec

7275

8373

Zero -Crossing Pulse GeneratorZero Crossing SwitchZero Crossing Sync CircuitZN414 Power Supply

JuneFebDecJuly

74737374

66868067

ing Mar 76 72Step Frequency Oscillator April 75 64Strength Tester July 75 43 12V-9, 7.5 or 6V ConverterStrobe, Low Frequency Feb 76 71 (Auto) Jan 75 67Suppressed Zero Meter July 72 83 30V Regulators Jan 76 43Suppressed Zero Voltmeter for 100kHz Marker Sept 75 64

car Apr 75 65 5000 Second Astable Aug 74 67Sweep Generator, Linear May 72 83 100.000Mohm DC Proble? Jan 76 52

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

TECH -TIPS AND

DATASHEET INDEX

Tech -Tips has been runningin ETIs since the first issuefour years ago. It is an ideasforum and we cannot supplyfurther details on any ofthe circuits. In this indexsome item's titles have beenrearranged to facilitate search-ing.

Datasheet is a relativelynew series ( 6 months old)and so far has covered onlyICs. For more informationcontact the manufacturerwho can supply full data.

BACK

NUMBERSThe table below shows which of our backissues are available from our offices. Wecharge 40p per issue, plus 15p (for thefirst) then 10p (each subsequent issue) forpostage and packing. Cheques should bemade payable to Electronics TodayInternational and order should be sent to:

Back Issues Department,ETI Magazine,36 Ebury Street, London SW1W OLW.

April 1972 NOMay 1972 NOJune 1972 NOJuly 1972 NOAugust 1972 YESSeptember 1972 YES

1

October 1972 YESNovember 1972 NODecember 1972 NO

January 1973 NUFebruary 1973 NOMarch 1973 YESApril 1973 YESMay 1973 YESJune 1973 YES

(July 1973 YESAugust 1973 YESSeptember 1973 YESOctober 1973 YESNovember 1973 NODecember 1973 YES

January 1974 YESFebruary 1974 YESMarch 1974 NOApril 1974 YESMay 1974 YESJune 1974 YESJuly 1974 YESAugust 1974 YESSeptember 1974 NOOctober 1974 YESNovember 1974 NODecember 1974 YES

January 1975 NOFebruary 1975 YESMarch 1975 YESApril 1975 YESMay 1975 YESJune 1975 NOJuly 1975 YESAugust 1975 NOSeptember 1975 NOOctober 1975 YESNovember 1975 NODecember 1975 YES

January 1976 YES0

43

MAINS TRANSFORMERSPri. 240v. sec. 2 / /0/27v at 800 m/a,£2.25. P.P. 50p.Pri. 110/240v sec. 50v at 10amps.£10.00. P.P. £1.50.Pri. 110/240v sec. 20/21 /22v at 8 amp,£6.00. P.P. £1.50.

110/240v sec. 23/24/25v at 10 amp£7.00. P P. £1.50.Pri 110/240v sec_ 24/40v at 11/2 amp.£1.90. P.P. 60p.Pri 240v sec. 2O/40/60v at 2 amp,£3.00. P.P. 70p.Pri 240v sec. 20v at 2'/2 amp, £2.00. P P50p,Pri. 240v sec. 18v at 1.5 amp and 1 2v at 1

amp, £2.25. P.P. 50p.Pri 240v sec_ 18v at 1 amp, £1.00. P P30p

S.C.R. (NEW. MARKED)1 amp 400 p

i v 35p. 5 amp 400 p i v40p.

PRINTED CIRCUIT KITNo frills, alt value kit containing 4 pieces 8" x7" formica laminate, 1 pce 6" x 6"fibre -glass laminate, 1 lb. etching crystals. 50ccs resist -ink with instructions £2.30. P P50p

CIRCUIT BOARDPCB. 1 /16, 1 oz. COPPERFORMICADim. 8 4 x 7.7 in 3 pcs , 75p.Dim. 9.4 x 8.1 in 3 pcs., 90p.Dim. 10.1 x 7.9 in 3 pcs., £1.00Dim. 13.1 x 9.4 in 3 pcs.. £1.20.Dim. 17.0 x 9.0 in 2 pcs., £1.20.Post & Packing 30p each pack

BARGAIN PACK10 pcs. 10.1 x 7.9 in. Plus free 1/2 lbetching Xtals, £2.80. P P 45p

FIBRE GLASS P.C.B.Dim. 6 x 6 in, 35p each.Dim. 12 x 6 in, 60p eachDim. 12 x 12 in, £1.00 each.Equals less than 1 p sq. in.Post & Packing 5p per sheet.

EDGE CONNECTORS 54 WAY1 vero size etc can easily' he cut to any

length 55p. P.P 10p

RESIST COATED P.C.B. FIBRE GLASS6 x 6 in, 50p ea.12 x 6 in, 90p ea.12 x 12 in. £1.50 eaPost & Packing 10p per sheet

FERRIC CHLORIDE ETCHING XTALS1 lb - 1 litre pack, 60p. P.P. 15p5 lb - 5 litre pack, £1.95. P.P. 55p.

S-DECS AND T-DECSS -DEC £1.90. Post & Packing 20p.T -DEC £3.60. Post & Packing 30p.U -DEC A £4.20. Post & Packing 20p.U -DEC B £6.90. Post & Packing 40p.

OVERLOAD CUT-OUTSPanel mounting 800 WA. 1.8 amp. 10am 55p pea

HIGH CAPACITY ELECTROLYTICS250mfd 63 volt 20p. P.P. 8p.1000mfd / 100 volt, 70p. P.P. 25p.2200mfd/100 volt, 90p. P.P. 25p.4700mfd/ 25 volt, 65p. P.P. 20p.6800mfd/ 16 volt. 50p. P.P. 15p.10.000mfd/25 volt 75p. P.P. 25p.25,000mfd/40 volt. £1.25. P.P. 30p.47,000mfd/40 volt, £2.00. P.P. 50p.100.000mfd/10 volt. £1.50. P P. 50p.160,000mfd /10 volt £2.00. P P. 50p.

10.7 M.H.Z. CANNED I.F.sSize 1 x1/2 x'/2 in. 65p. P P 10p.3 Gang Tuning Capacitor, 8.5pf to 320pf,80p. P.P. 20p.

SIEMENS MINIATURE RELAYS6v 4c.. o with base, 65p ea24v 2c/o with base. 50p ea

MINIATURE METERS500 micro -amp (level -stereo beacon. etc.).scaled half black/half red. Size 1 x 1 in, 65p.P P 15p.

MAINS RELAY 240v3c/o 10 amp contacts, 95p with base.

MINIATURE RELAYS(138.1'/4x'/2) 24v 4c/ o 40p.

RIBBON CABLE8 way. 8 colours. Bonded flat side by side.10 Metres, £1.90..100 Metres. £12.50.

GARRARD PLINTH & COVERFor Zero -100, etc. Finished in brushedaluminium and black, with hinged smokegrey perspex lid, £11.00.

BLUE P.C.B. INKEtch resist, use with any pen, much cheaperthan ready -loaded pens 50ccs. Price 55p.P.P. 10p.

10 NELMES WAY, HORNCHURCHKINNIE COMPONENTS ESSEX RM11 202

HORNCHURCH 45167MAIL ORDER ONLY. PERSONAL CALLERS BY APPOINTMENT

tecItnowledgey in consumer ICs - and their applications.SGS Audio ICs

1-

The much heralded TDA2020to make sure that you don'tSGS application test circuit15 + 15 (RMS) Hi Fi amplifier.

Prices : IC

,.....i.-'

.--

,

/

VIII i ..

is here. And justgo wrong, so is thePCB for a stereo

AUDIO DISCRETES

We've movedTo accomodate expanded R & Dfacilities, AMBIT has moved salesand administration to 25 High St.Brentwood. The existing 37 HighStreet premises are retained for theengineering activities.One of the first products of thismove has been the development ofa TV sound tuner, from an "offBe system, using its own varicapUHF TV tuner, with ICIF am-plifiers and block filters by TOKO.And then one of our best evercircuits - an electronic touch tuner,

and facilitiesscanning mode,with7004for 6 preset stations. The unit issuitable for use with FM, and nowAM of course, and offers a com-plete tuner system without anymoving parts. Selection is by meansof touch tuning in all cases, withmanual scan and preset switchingautomatically interlocked.

Our R&D tacilities are available forgeneral consultancy to OEMs furtherdetails on application. Standard projectestimation fee. including project evalua-lion comment data is £15.00 payable inadvance.

Modules & KitsNew modules:

8011 Totally touch tuned varicap controller built £14.99.8005 Larsholt tunerset accesory unit, with pilot tone filter

and audio stages, rectifier. IC stabilizer, meter drivercircuits, £4.99 (kit)

8001 55kHz low pass filter Imps birdy filterl E2.35 built£1.75 (kit)

2001 Stereo scratch and rumble filter, with continuously

£4variablekt)operating frequencies. E5.80 (built)

.60 (3000 Stereo control preamp - a wide dynamic range, low

distortion AF preamp, with vol, bal, bass and treblecontrols. kit £5.78

2020k The TDA2020 stereo amp kit photographed on theleft. £7.85

7700 TV -off air UHF sound tuner - bu.lt £26.00(4 preset stations)

9000 kit AM/FM moo tuner chassis, with mech. tuner £17.50kit MW/LW varicap tuner module, nc. ferrite rod £9.95

7252 HiFi MOSFET FM tuner module by Larsholt £24.007253 HiFi FET FM tuner module inc decoder £24.005600 Hi 0 MOSFET varicap tunerhead by TOKO £11.25EC3302 FET tunerhead from TOKO £5.00Complete FM Tuner kits, inc case, for use OM Me abovemodules: details SAE please. Prices range from £40 - EEO.

Amongst our various accessories for entertainmentelectronics is a range of FM tuning, frequency andsig. strength meters with 12v, 50mA bulb. £2.50 ea.

--..- -

TBA810AS +HS 1.09TCA940E +HS 1.80TDA2020 2.99

FM LINEAR ICS

ZTX107/8/9 ' 14pZTX413(LN) 17pZTX212/3/4 16pBD 535 rip ril 7A/60v 52p

MC1350 0.70CA3089 +QC 1.94TBA120

1.00

MPX LINEAR ICS

80536 pnpl 53pBD377 nprla 3A/50v 29pBD378 pit 32pBD515 npnl 2A/45v 27p8D516 pnrd 30p

We 4 160 Oa 5 ; ; r*, i Z 5mc1310P +LED 2.20CA3090AQ +LED 3.75

BD609 npni 10A/90v 70102ppBD610 pnial

ambit25 highessex.

._ or_d_

international,aale Kan

street, brentwood,tel: (02771 216029cm14 4rhi. tlx: 995194

Free price li t with an SAE, catalogue of modules and parts40.. inehrdi tg postage and VATGeneral Terms: CWO please, official bodies and companiesplease note min. invoice £7.50. PP for CWO orders 22p perorder. (UK and Eire). Overseas customers please include suffi-cient for postage. VAT is not included, and must be addedat 25%, In stock orders despatched within 48 hours.

44 ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

eta microfileMICROBIOLOGYIN WHICH IS DISCUSSED theinternal operation (biology?) of themicroprocessor. Last month wediscussed the general organisationof a microcomputer: this month weshall focus on the heart of this unit- the microprocessor. We shallstart by reviewing a few basicconcepts - incidentally a goodintroductory course if you haven'tdone much digital work is Cam-bridge Learning Enterprises' 'De-sign of Digital Systems', which isadvertised elsewhere in this issue.By the time you complete Vol 6,microprocessors won't give you any,trouble!

NUMBER SYSTEMS

In everyday life, people count intens, which is fairly logical whenyou consider that you have 10fingers. However, if fate haddecreed that the human race shouldhave only eight fingers, it is veryprobable that we should be count-ing in eights, and it is doubtful thatwe should ever find this to be adisadvantage. Now, a digital com-puter has no fingers and in fact theonly change of state it can 'per-ceive' is the presence or absence ofa voltage. (See 'Electronics - It'sEasy' for a refresher.)

Consequently, it is convenient to

represent these two states as a '0'and '1' respectively. This countingto the base two is known as binaryarithmetic and is the system thatvirtually all digital computers use.Just as the digits in a decimalnumber represent varying powers often, e.g. 365 is 3x102 + 6x101 +5x10°, so in a binary number thedigits represent powers of two. Forexample, the binary number11010 equals 1x24 + 1x2'' +0x22 + 1x21 + 0x2° i.e. 16+8+2which is 26,. The decimal number391, can simply be converted tobinary by various methods - thesimplest to use for such a lownumber is to find the highest powerof two which can be subtractedfrom it and then attempt to subtractdescending powers from it. In thiscase the highest power of two whichcan be subtracted from 39 is thefifth (25=32) leaving 7 remainder.

We 'write down a one as the firstfigure of our result. The next lowestpower is the fourth (24=16) whichcannot be subtracted from 7, so wewrite down a nought. Two to thethird, which is 8, cannot besubtracted from 7 either, so wewrite another nought, but 2 squaredor 4 can be taken away, to leave 3,subtracting 2 leaves 1 and takingaway 1 leaves zero, so we can writethe final three ones to give our finalanswer of 100111 . There arewell-defined methods for convertingbinary to decimal and vice versa,

111

LISTEN! - WITH A DEDICATED MPUDOING THE COMPOSING AND AN-OTHER THE PL4YING. . . .WHO NEEDSMIKE OLDFIELD?

but it is not proposed to go intothese here as they have been dealtwith so often elsewhere, including'Design of Digital Systems'..

Now, as we've said already, mostmicroprocessors have an eight bit(B/nary dig/i) word length, and so itcan be seen that the lowest numberthat can be represented is00000000 and the highest is11111111, or 0 and 255 ,

respectively -Negative numbers canbe represented in either of twoways, by making the first bitindicate the sign of the number or

7

7

15

ACCA

0

ACCB

0

Ix

15

PC

15 0

SP

7 0

H z C

Fig 1. MPU Registers.

Accumulator A

Accumulator B

Index Register

Program Counter

Stack Pointer

Condition CodesRegister

LCarry (From Bit 71

Overflow

Zero

Negative

Interrupt

Half Carry(From it 3)

ProcessorControl

DBE TSC BA Halt NMI Reset

Accumulator A Accumulator B

Index Register

Stack Pointer

Program Counter

8 Bit 16.8.Data AddressBus Bus

Fig. 2 Control lines.

H N Z V C

IlR/W VMA

1 -I

02

IRO +5 V 02 Reset

BusControl

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976 45

11

microfileby taking the two's complement.Once again, we do not propose togo into this in any detail as it hasbeen adequately covered else-where.

Writing out binary numbers infull takes up a lot of space and thenumbers are difficult to memorise;consequently a number systemcalled hexadecimal is used tosimplify matters. In hex thenumbers 0 to 9 are numberedconventionally and 10 to 15 arenumbered A to F. This is particularlyconvenient as 15 equals 1111, thehighest four -bit binary number; andhence an eight -bit number can berepresented by two hex digits asfollows:

0000=0 1000 = 80001=1 1001 = 90010 =2 1010 = A0011=3 1011 = B0100=4 1100 = C0101=5 1101 = D0110 =6 1110 = E0111=7 1111 = FHence, the eight -bit number

10010101 would be representedas 95. For a 16 -bit number, as willbe found on the address bus, thesame system applies except that 4hex digits will be required - e.g.1110010110111101 is E5BD inhex.,

To simplify the handling ofdecimal numbers in computers stillfurther, yet another system exists,known as Binary Coded Decimal(BCD). In this system each decimaldigit is directly converted into afour -bit binary number. To take anexample 49 would become01001001 as shown:

4 9

0100 1001

Equally simply, BCD numberscan be converted to decimal bytaking 4 bits at a time andconverting each group separately toa single decimal digit, e.g.01101000 becomes 68.

Some expertise in handling thesenumber systems is virtually a

necessity if you want to programcomputers of any kind. In order toget the "feel- of them we suggestthat you read up a bit and then try afew exercises in binary addition,etc.

You will soon discover, forinstance, that if you try to add;together two BCD numbers as ifthey were straight binary, you just

1

2

3

4=

Vss

Halt

01

180

0 Reset

TSC

N C

02

= 40n 39

38

37

5 VMA DBE 36

6 NMI N C 35

7 BA 34

8 VCC DO 33

9 = AO 01 M 3210 Al 02 31

11 A2 03 30

12 A3 D4 29

13 A4 D5

14 45 06 27

15 AS 07 76

16 = A7 415 = 2517 48 414 24

18 A9 A 13 23

19 A 1 0 412 22

20 A 1 1 VSS 21

Fig 3. Pin Layout

don't get a correct answer. Thereare ways round this, however, asyou'll discover later. We've alsotreated all these systems as thoughthey represent only numbers, how-ever they also represent theinstructions that the MPU uses as aprogram. For instance, the hex code8B will cause the M6800 micro-processor to add a number frommemory to one of its accumulators,or hex 97 would instruct it to storethe contents of an accumulator inmemory. There are 197 differentinstructions (72 basic types) whichthe MPU uses - we'll cover manyof these in depth when we discussprogramming.

WHAT'S INSIDE?

The M6800 MPU is a 40 pin DILintegrated circuit which containsroughly ten thousand components.The NMOS technology used permitsa very high gate density and gener-ally speaking makes the whole thingpossible. There are one or twobipolar microprocessors about, suchas the Am2901 , but these aregenerally 4 -bit devices which havebeen arranged so that they can beparallelled up to permit longer wordlengths (this is known as bit -slicearchitecture).

If you part with around £27 ofyour cash to buy a 6800 micro youare getting around 3000 logic gateswhich is pretty cheap, if you ignorethe fact that they won't do anythingwithout quite a lot of other hardware,not to mention software (programs)However, at the projectedend -of -'76 price of under £8 thismust be value for money and if by1980 the price drops to the expected

£1 mark you just won't buy CMOS orTTL for most projects!

Obviously, circuitry on the actuallump of silicon is extremely complex- the only sections the programmercan actually get at are the sixregisters which are connected to thedata and address busses, and viacertain pins he can 'get at' someparts of the logic to handle interruptsand data transfers etc. Most of thelogic is inaccessible' for example thearithmetic circuitry around the accu-mulators is 'transparent'; instructthe MPU to add and it will do so,automatically and there is no waythat the function can be modified.Fortunately, one would almost neverwish to alter the way in which theMPU operates It is completely a'general purpose' chip and instruc-tions are built into it to handleeverything you could reasonablywish.

The six registers mentioned aboveare the most important part of theMPU_ They are.

1 Accumulator A (ACCA). One of thetwo 8 -bit working registers of theMPU.

2 Accumulator B (ACCB). Theother 8 -bit working register.

3 (The Condition Codes Register(CCR) which contains various bitsof information about the contentsof the accumulators It is an 8 -bitregister, but only 6 -bits areactually used.

4 (The Program Counter (PC) is a

16 -bit register which usuallygives the address of the instruc-tion the MPU is currently execut-ing.

5 The Stack Pointer (SP) is used insetting up areas of memory forstorage of intermediate resultsand also in handling interrupts.Also 16 -bit in length.

6 The Index Register (IX) is used inspecial addressing modes to letthe MPU jump around in memoryto subroutines etc. Again, this is a16 -bit register.By means of various instructions

one can shift data into, and out of,the accumulators and memory, alterdata, add numbers, and test resultsof operations. At this point, the CCRbecomes of importance. It containssix bits, HINZV & C, as shown in fig1. H is a Half -carry bit which is setwhen a carry is generated from bit 3of the accumulator and is of specialrelevance in BCD calculations. The Ibit is an Interrupt mask bit, which isset if the MPU is to ignore interruptrequests from other devices. (Sorryabout continually mentioning inter-rupts without explaining them, butthis stuff has to be covered first.). Nis a Negative bit and is set if the

46 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

esult of a calculation is negative. Zsimilarly, is set when the result iszero. V is set if the result overflowsfrom the register as a result ofcalculation involving the 2'scomplement representation ofnegative numbers. C is a carry bitwhich is set if the result has greaterthan 8 bits.

The Stack Pointer and IndexRegister can be loaded, increment-ed, decremented, and stored bysimilar instructions. The ProgramCounter is altered by other instruc-tions such as JSR (Jump toSubroutine). All of these instruc-tions will be considered in detailwhen we discuss programming.

PIN CONNECTIONSFig. 2 shows the signals which

let the MPU, communicate with theother parts of the microcomputersystem. The 8 -Bit Data Bus is

bi-directional, that is the MPU caneither send data out on the bus or itcan input data from other devices.The reception of data from memoryis termed reading, whilst transmis-sion of data for storage is calledwriting. The MPU will normallyindicate to the other devices justwhat it is doing by putting theRead/Write (R/W) line low when itis writing and high when it isreading. The MPU will also put outon the Address Bus, the address ofthe memory location it is reading orwriting to or from. However, someambiguities could arise when theMPU is changing the address beingoutput on the bus, and so anothersignal, Valid Memory Address,(VMA) is used which only goes highwhen the Address Bus has stabilisedand read/write operations can takeplace

The Interrupt Request signal(IRO) is used by peripheral equip-ment to signal to the MPU to stopwhatever it is doing in order toperform a more urgent task. Whenthe IRQ line goes low, the micro willcomplete the current instruction,store away the Current contents ofthe registers at a location given bythe stack pointer, and then go to aninterrupt service program. When ithas finished executing this pro-gram, it will reload its registers andstart again from where it left off. Ifthe Interrupt Mask bit of the CCR isset, however, it will ignore aninterrupt request, unless the Non-Maskable Interrupt line is pulledlow. as this bypasses the 1 bit of theCCR and the MPU has to respond tothis request. This ability of the microto be interrupted is phenomenallyimportant, as it all happens soquickly the MPU seems to be doingtwo things at once.

415 A,. 413 411 All 4;0 A9 48

25 74 23 27 20 19 /6 7

t t t t t t t t411,

47 04 AS A4 A3 A: At AOIr. .1 12 11 10

t t t ttt t

0100 01 3

011101 02 3.-41441154, 40 --- Oro,.,. or ern

NO. !Woo. EAmervp, 6 --IP14.1 2 -494

Cow..

InNrr a9/ 11-Apiteal 4 --OA910,9<012A

04909. 514,4 SIMCPow.. Ao.nte,

sun C991,2. 39*Ad

CAnt,co

04,4 6. f Asow -41. ,9eve 4914910 4-- F149989, 949.414r

0.1,4 914,99.7 adres AI-,$144929.9.84 34 .41/- 41-11.""11140,11

V00. 26 I 20 79 308.n. 1,2102 06 05 04 03

Con04.on

31

023701

3300 Fig 4. Internal logic structure.

For example, the MPU canexecute a program, while simultan-eously inputting data from a tele-printer keyboard. The micro canexecute an instruction in a couple ofmicroseconds, while a teleprintercan input a character every 100milliseconds for example, so that itdoes not make sense for the microto hang around spending most ofits time waiting for a character to beinput. Instead it can be executing aprogram until an interrupt stops it toinput the character and store it.when it can return to the mainprogram again until it is once moreinterrupted.

Data Bus Enable (DBE) andThree -State Control (TSC) are bothinputs which cause the MPU to gointo a high -impedance state and,effectively, disconnect itself fromthe busses so that other devices canuse them without affecting theMPU. The Halt instruction alsoforces the MPU into its three -statemode. Bus Available (BA) will gohigh when this happens to indicatethat the MPU has stopped and theaddress bus is available.

Reset is used when the MPU isstarted up. A positive going edge onthis input will cause the MPU toexecute a special restart sequencewhich will initialize outputs andprevent the entire system fromgoing randomly haywire.

0.1 and 02 are the two phases ofthe systems clock, which canoperate at up to 1MHz, at whichspeed it can execute the shortestinstruction in 2p.S. 01 and 02 arenon -overlapping square wavecomplements and are the onlyinputs to the MPU that are not atstandard TTL levels. All data

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

transfers take place during the .Li2

clock cycle, and so this signal canusually be used to drive DBE andalso to enable memories andinterfaces.

The final two inputs to the MPUchip are the earth connection andthe +5V supply.

THE INSTRUCTION SET

We have discussed how certainpins are used to control the MPU,but of course the essential basicconcept of the microprocessor is thatits operation is, for the most partdictated by patterns of O's and l'son the data bus. There are 197 suchpatterns, which are variations on abasic set of 72 instructions. Forinstance, the binary pattern10001011 (or hex 8B) will causethe MPU to perform an addition inthe following manner: If, whileexecuting a program, the MPUincrements the Program Counter toread out the next program step andthen reads in the code 8B, whichmeans in human terms 'Add thefollowing number to what is alreadyin ACCA', it will increment the PCso that it can read in the contents ofthe next location in memory andadd that number to the contents ofACCA. Thus the complete instructiontakes up 2 bytes (eight -bit words) ofmemory and takes 2 clock cycles toexecute. Each clock cycle has twohalves - during 01 the address busis being changed, and the internallogic of the MPU is in operationwhile 02 is used to read /write datawhile everything is (hopefully!) sta-ble.

All of the instructions are exe-cuted in a basically similar manner.

47

microfileFor instance, if the instruction in theexample above had been BB, theMPU would have read in theinstruction, which is a similar addi-tional instruction, and would thenhave read in the contents of the nexttwo bytes of memory. This wouldgive it an address in memory whichit would go to to find the actualnumber which should be added toACCA. We shall return to thisprinciple of addressing, which is ofkey importance, later.

The operation 'add to ACCA' isgiven a shortened, mnemonic formto assist in the writing of programs.Similarly 'add to ACCB' is given themnemonic ADDB, 'load accumula-tor A' becomes LDAA, 'increment'is INC and so on. A complete list ofoperations and their mnemonics isis given in Table 1. Before discuss-ing them in detail, we shall divertbriefly to look at addressing modes.

ADDRESSING MODES

"We've already looked briefly attwo different types of ADD instruc-tion, (i) immediate mode, where thevalue to be used follows theinstruction in the body of theprogram, and (ii) the extendedmode, where the two bytes follow-ing the instruction give an addresswhere the MPU can find thevalue to be used. In fact, there are5 different addressing modes, or6 if you include the case where no

address or value is given, such asCLRA, which clears ACCA.

In the immediate mode, the bytefollowing the instruction is the valuewhich is to be added, subtracted,loaded etc. This is useful forhandling constants in a program.

Direct addressing contains an8 -bit address in the byte followingthe instruction and hence can onlyaddress memory locations 0through 255, so that this area canbe conveniently used for scratch -pad storage. Extended addressinguses the two bytes following theinstruction to give a 1 6 -bit addressso that the MPU can read data fromany address.

Indexed addressing uses theindex register in combination withthe address following the instruc-tion. If the processor encounteredthe instruction LDAA 05 in theindexed mode it would look in theaddress given by the value of theindex register plus 05 and then loadthe contents of this location intoACCA. The indexed addressingmode is particularly useful forjumping about in a program sinceinstructions such as LDX, INX, DEXprovide ways of altering the indexregister value.

The relative mode is used onlywith branch instructions and enable

the processor to branch ± 127locations relative to the presentvalue of the Program Counter.These instructions are particularlyuseful in setting up loops anditerative processes, as well assubroutines.

Detailed information on theinstruction set and addressingmodes is contained in the M6800Systems Reference and DataSheets, and is far too detailed to gointo in any great depth here.However we have made arrange-ments for a data pack to be madeavailable to our readers for 50pto cover postage and packagingfrom Cramer Electronics, 16Uxbridge Road, Ealing, LondonW5 2BP. This will include theSystems Reference & Data Sheets,EXORciser Data Sheets, and assort-ed information including a wallchart giving pricing information.

In the next Microfile we shalllook at the other components whichmake up the memory and input/output parts of the microcom-puter.

If you do not wish to cut out thecoupon, please print your name andaddress clearly on a piece of paperso that it can be used as a label tosend you the information.

To: Cramer Electronics Ltd. 16 Uxbridge Rd., Ealing, LONDON W5 2BP.Please send me an M6800 information pack. I enclose Cheque/P.O. for 50p. to coverpostage and packing.

NAME . .

ADDRESS . . .................. er- ...............

ABAADCADDANDASLASR

BCCBCSBEQBGEBGTBHIBITBLEBLSBLTBMIBNEBPLBRABSRBVCBVS

CBACLCCLI

Add AccumulatorsAdd with CarryAddLogical AndArithmetic Shift LeftArithmetic Shift Right

Branch if Carry ClearBranch if Carry SetBranch if Equal to ZeroBranch if Greater or Equal ZeroBranch if Greater than ZeroBranch if HigherBit TestBranch if Less or EqualBranch if Lower or SameBranch if Less than ZeroBranch if MinusBranch if Not Equal to ZeroBranch if PlusBranch AlwaysBranch to SubroutineBranch if Overflow ClearBranch if Overflow Set

Compare AccumulatorsClear CarryClear Interrupt Mask

CLRCLVCMPCOMCPX

DAADECDESDEX

FOR

INC

INSINX

JMPJSR

LDALDSLDXLSR

NEGNOP

ORA

PSH

ClearClear OverflowCompareComplementCompare Index Register

Decimal AdjustDecrementDecrement Stack PointerDecrement Index Register

Exclusive OR

IncrementIncrement Stack PointerIncrement Index Register

JumpJump to Subroutine

Load AccumulatorLoad Stack PointerLoad Index RegisterLogical Shift Right

NegateNo Operation

Inclusive OR Accumulator

Push Data

PUL

ROLRORRTIRTS

SBASBCSECSEISEVSTASTSSTXSUBSWI

TABTAPTBATPATSTTSXTXS

WAI

Pull Data

Rotate LeftRotate RightReturn from InterruptReturn from Subroutine

Subtract AccumulatorsSubtract with CarrySet CarrySet Interrupt MaskSet OverflowStore AccumulatorStore Stack RegisterStore Index RegisterSubtractSoftware Interrupt

Transfer AccumulatorsTransfer Accumulators to Condition Code Reg.Transfer AccumulatorsTransfer Condition Code Reg. to AccumulatorTestTransfer Stack Pointer to Index RegisterTransfer Index Register to Stack Pointer

Wait for Interrupt

Table I. IVE800 Instruction set

48 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

KEY TO CIRCUIT COMPONENTS

DESIGN IDEA: M6800 SINGLEINSTRUCTION CAPABILITY

The evaluation kit ME K6800D1comprises an MPU, some RAM, ROM,I/O ports and a terminal interface. TheROM (MCM6830-L7) contains an'Executive' program called MI Kbugwhich enables users to load and runtheir programs but does not haveany built-in single-step facility.

This circuit (fig. ) makes use ofthe 6800's interrupt routines bygenerating a non-maskable interruptafter the first cycle of eachinstruction. In response to theinterrupt, the MPU completes thecurrent instruction and stores thecontents of the MPU registers onthe stack. The MPU then jumps,via ,the interrupt vector, to the startof an interrupt service routine inMI Kbug.This loads the index registerwith the address of the firstinstruction of the user's program.This address was previously storedby the user at a predeterminedlocation.

The MPU then goes to the firstinstruction of the user's interruptroutine and executes it. This routinecould, for example, print out thecontents of the stack, which nowholds the MPU internal registercontents applicable to the user'sprogram.

The final instruction in the user'sinterrupt routine (RTI) will handback control to MlKbug. When the-system is instructed to execute thenext instruction, the MPU's registerswill be loaded from the stack and thesequences will repeat.

HARDWARE OPERATION

The circuit relies on the fact thatthe RTI instruction executed justbefore the next step of the user'sprogram is stored at a known addressin MlKbug. A comparator, comprisingfour MC7242 ICs, is connected to the6800 address bus to recognise whenthe address of the RTI instructionis on the bus. The output of thecomparator is ANDed with the VMAand 02 signals.

When the RTI instruction addressis detected, flip-flop A is set and theMC14526 counter, which has beenpreset to 11, begins counting down

1 clock pulses. When it reaches zero,flip-flop B is set, the NMI line is

taken low (hence true) and theMC14040 counter is enabled. Whenthe 14040 has counted 32 02 clockpulses, flip-flops A and B are resetand the interrupt pulse is terminated.

The 11 and 32 cycle delays ensurethat the interrupt pulse occurs at theright time and is of the necessarylength.

(1)(2)

MC7242MC7400

Exclusive NOR gate (4 CM')NAND gate ( 1 off )

(3) MC7479 Flip -Flop (i off )(4) MC14526 Counter (1 oft).(5) MC14040 Counter (1 off)(6) MC7420 AND gate (1 off )(7) MC7401 NAND gate (I oft)

The evaluation kit has an MCM6810128 byte RAM, situated at "the baseaddress A000 (hex), which is usedby the M I Kbug program. However,locations from AO4A to AO7F in thisRAM are not normally used and canbe employed for the user's interruptprogram (see below).

The STS SP instruction is onlynecessary when the program under testuses the stack pointer. If not, theMlKbug stack print routine can bestored directly in memory locationsA006 and A007.

When the 'print contents of stack'routine at address El 1F in MI Kbug

has been executed, a jump is madeto the MI Kbug control program.This means that the user can pressthe 'G' key to execute the nextinstruction in his program, or hecan use any of the other facilitiesoffered by MI Kbug.

The interrupt service routine can bewritten to suit the needs of the userand may include printing out thecontents of memory locations thatmight be changed by the user'sprogram.Design by Marc Bonzon, senior

applications engineer, MicroprocessorSystems Engineering, Motorola Geneva

Memory Address Machine Code Mnemonic Comment

A006 AOA007 4A

AO4AA048AO4CAO4DAO4EA04 F

BFAO087EEl1F

STS SP

JMP PRINT

Address of user'sinterrupt routine

Save user's stackpointer.

Jump to MI Kbug'print contents ofstack' routine.

NEWS AND PRODUCTSSoftware for the AMI S6800 micro-

processor family is now availablefrom the CSS network, which hascomputing facilities available inLondon, Paris and Bonn. This softwareincludes the S6800 Assembler,Relocating Loader and MicroprocessorSimulator, for use in microprocessorsoftware development.

The AMI Assembler is compatiblewith the Motorola assembly languageand offers a number of additionalfeatures including relocatable objectcode, macros, conditional assemblyand local labels.

The Relocatable Loader and Micro-processor simulator offer a widerange of file management and programdebugging facilities.

Also from AMI is a new 512 by 8 bitUV -erasable PROM which is speedcompatible with the S6800 micro-

processor family. Reprogramming is

effected by first erasing the existingbit pattern by exposing the chip toan ultraviolet light source through thetransparent lid for around ten minutes.A new pattern can then be prog-rammed byconnecting a -55V sourceon a single program pin, and standardTTL levels on all additional pins. Lessthan 1 minute is required to programthe full 4096 bits. The S6834 alsofeatures 3 -state outputs and a typicalaccess time of 500nS. This chip is

expected to find wide applications inROM program debugging, and variousapplications where mask -programmedROMs cannot be justified.

AMI Microsystems Ltd., 108ACommercial Road, Swindon, Wilts.

microfileELECTRONICS TODAY INTERNATIONAL-APRIL 1976 49

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These courses were written so that you could teachyourself the theory and application of digital logic.Learning by self -instruction has the advantages ofbeing quicker and more thorough than classroomlearning. You work at your own speed and mustrespond by answering questions on each new pieceof information before proceeding to the next.

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50 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

ETI DATA SHEETSP8505 ECL +10 COUNTER PLESSEY

The SP8505 is a high-performance ECL+10 counter. With sinewave input, thecounter is specified over a 40MHz to250MHz range, using a square wave input,the lower frequency limit for the device isextended down to DC.

It is expected to find application infrequency synthesisers and low cost countersand timers.

1/P

,/P 12BIAS

FIG. 1 BLOCK DIAGRAM 0 VCC

REF

0 TYPEF/F

0

TYPE

F/FREF

a

0 TYPE

F/F

130BIAS

O 0/P

VEE

+200mvimiN,Ov-

INPUTSIGNAL

10

iso

SP8SOS

+ 3 2V

2.0V

-r-

Fig. 2. Direct -coupled input signal.

OUTPUT

ABSOLUTE MAXIMUM RATINGS

Power supply voltage, IVcc.- VEEInput voltage, VINDCInput voltage, VINACOutput current, louTOperating junction temperatureStorage temperature

OPERATING NOTES

8V

Not greater than supply2.5V p -p

15mA+150°C-55°C to +150°C

It is recommended that a positive ground plane isused to prevent damage to the circuit if the outputemitter follower is inadvertently short-circuited toground. The signal source is normally coupledcapacitively to the input, but DC coupling can be usedwith suitable arrangement of the power supplies orbiasing of the input.

The dynamic range of the device can be improved bydecoupling the internal bias chain to ground; suitabledecoupling points are brought out on pins 1 2 and 1 3. Alow inductance capacitor should be used.

With a sinusoidal input of below 20MHz, the circuittends to self -oscillate because the slew rate of the inputis not high enough. The device will operate down to DCwith a square wave input, however, provided that thesquare wave has a slew rate greater than 100V /µs.

ELECTRICAL CHARACTERISTICS

Max. input frequencyMin. sinewave

input frequencyMin. squarewaveinput slew rateOutput voltage swingOutput levels

highlow

Power supply drain

- 450MHz

- 20MHz- 30V /gs

- 7 50mV (typ)

- 7 50mV (typ)- 1 500mV (typ)- 70mA (typ)

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976 51

TBA 570 INTEGRATED AM/FM RADIO RECEIVER CIRCUIT MULLARD

The TBA 5/0 is a monolithic integratedcircuit for use in A.M. and A.M./ F.M.receivers. It incorporates signal detector, I.F.amplifier, mixer, local oscillator and a.g.c. forA.M. limiter, complete i.f. amplifier andfront-end bias stabilization for F.M. and adriver and preamplifier for audio.

It is adapted to operate in conjunctionwith hybrid I.F. block filters and it can befitted with a tuning indicator.

The TBA 570 is able to drive output stagesup to 3W with A.C. 187/188 transistors or5W with AD 161/162. It can also be used in

complete tuner kits, the 500mV a.f. outputsatisfying DIN 45 500 hi-fi standard.

The data given here is for a completea.m./f.m. portable receiver (including shortwave) driven from a 6V supply and having a1W audio output. Voltage swing at pin 11

(a.f. driver) is about 5.5V. A swing of 1 8V isallowable however for mains and car -radioapplications.

103

E io2a.)

0100

O

10-1

-Vp =6 V; - - -Vp 3,6 V

typical valuesfo= 100 MHz; Af =± 15 kHzfrii = 1 kHz

-_:j a.f. signaland noise

26 dB - 54 dBLI

1

noise

10 102 103 104 105 Vi (µV) 106

Fig. 1. Typical S/N curves at FM reception.

MAXIMUM RATINGSVoltages with respect to pins 9 and 16

Total quiescent currentexcept TR31 collector current, f.m. front-endand discrete output stages; Vp = 6 V 10, 5 mA

Pins No. 1 and 7 voltage 18V Vp = 9 V 14, 0 mA

Pin No. 4 voltage 8V Total power dissipation at pin 8Pin No. 8 voltage 8V (excluding TR31) at Vp = 9 V; V816 = 7, 8 V 100 mW

Pin No. 3 voltage 3V Applicable supply voltage range of receiver 6 to 18VPin No. 5 voltage 4VPin No. 14 voltage 1V

Base bias voltage for f.m. front-end 1, 2V

Pin No. 11 voltage 18VSaturation voltage of TR31

at lc = 50 mA;18 = 2, 5 mA V sat 1, 0 V

Currents (Tolerated minimum: 0 mA) Collector breakdown voltage of TR31 (pin 11)Pins No. 2, 6, 12, 13, 15 current 80 [LA at lc = 25 mA; R8E = 71(52 18 V

Pin No. 10 current 5 mA D.C. current gain of driver stage TR31

Pin No. 11 current 50 mA at Ic = 50 mA hfe 25

2,

0011

TRI TRI

S20

R24.61.

TR7

.1,111

9.2.

T 5

T IR/87.1811

TAP

0)

O

TR2

iconR23

non

OS

Fig. 2. Circuit diagram TBA 570.

R2S

s'nR282,7

TR23

)1170

kr,

TR.{ FTR27

R79

non

*vs

02711,1

R/9/0.91.21

TR70

012

010

18011RT 11

TR71

017

52ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

cn

VJE

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I. F

. ban

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ass

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CO

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Q0

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TB

A 5

70.

SWITCHINGREGULATOR SUPPLYIn I

irllw BFIMAMAS

Drive those TTLcircuits withthis 5 volt10 amp (max)supply.

WHILST the introduction of CMOShas lowered the power requirements ofdigital equipment using it, many largescale systems, because of cost andavailability, are still designed aroundTTL logic. For such systems a five -voltsupply having a capability of up to 10amps is often required.

The choice of power supply for asystem depends very much on theoutput requirements. In very lowpower applications a shunt regulatorconsisting of a series resistor and azener may be entirely adequate. Formedium power systems however aseries -pass transistor regulator is

normally used.Whilst the series pass regulator is very

good with regards to ripple andregulation the specification of thetransformer is critical if the supplyefficiency is to be above 50%. In a

larger system this can be a veryimportant factor.

With a switching regulator therequirements on the transformer aregreatly relaxed and an efficiency of70% or more can readily be obtainedwith mains -input variations of from160 to 260 volts.A fourth type is the switch -mode

supply where the mains voltage is firstrectified and filtered. The rectifiedmains then drives a high -frequency

54

inverter which employs a ferritetransformer. Regulation is obtained bycontrolling the inverter and by thismeans very high efficiencies may beobtained. Nearly all the components insuch a system work at mains voltageand hence for safety reasons thisapproach was not used in our project.

CONSTRUCTIONAll components, with the exception

of the transformer and the choke arebest mounted on a printed -circuitboard such as the one specified. Thechoke should be wound as detailed in

Table 2 with four layers close woundof 16 swg wire. Due to the dccurrent in the choke an air gap isnecessary to avoid saturation. Theeasiest method of adjusting this gapfor best performance is to run thesupply at the maximum currentrequired and adjust the gap byinserting that thickness of insulationbetween the cores which givesminimum ripple voltage. We foundthat a 3 mm gap was required at 10amps for a ripple of 50 mVpeak -to -peak.The prototype was mounted in a

TABLE 1Comparison of typical series and switching regulators

SERIES

Output Voltage 5 VOutput Current 10 AEfficiency

240 V in 50%260 V in 40%

Ripple Voltage <5 mV p -pRegulation 0-10 A <0.05 VInput Voltage 240 ± 10%Transformer Secondary 8.5 V @ 12 ADiodes Required 10 AFilter Capacitor 33 000 pFShort Circuit Current 15 A

SWITCHING

5V10 A

70%70%50 mV p -p0.3 V160 to 260 V20 to 30 V @ 80 VA3A2 200µF15 A

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

I -z

pLi.i. w0 tto I- t0- C6 D _.1- LL,D 0Z a0-32,_,<1 0° D -J V/ 0 ..- LtCI ,

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<0 E CC .- LL1 2 ,03 '-o <---v.) i.u2

c/),,<11/ OW Z > LLIIii- CC LIJ CO Qcc

i_)(.3cr--tzt-cc i CDZ.- CO - -- - r --ODCcsti 00 i:C-() cc-

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c,

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

19

die-cast box which acted as theheatsink as well as a shield to preventthe radiation of RFI generated by theswitching action of the supply. Ifanother form of box is used a heatsinkmust be added to the transistor -diodebracket for cooling.An external LC filter will reduce the

ripple even further if required. Forexample a series choke of 20 turns of1.6 mm wire on a 10 mm ferrite rodand a parallel combination of 1000µF electrolytic and 0.47 polyestercapacitors external to the box willprovide considerable extra rippleattenuation.

PARTS LIST - ETI 119

R14 Resistor 0.0 S2 RI1,13 ::R12

33 1W 5%47 I/2W 5%

R3,171 ", loci li1/2W5%220 ',2W 5%

R7,18 390 S2 lirw 5%11< 1/2W 5%R6,8,9 1k1 k 1/2W 5%

R2,4,5R I

61(6 1/2W 5%47 k V2W 5%

RV I Trim Potentiometer 100 11C4 Capacitor 470 pF ceramicC3,5,6 " 0.001 i/F- polyesterC2 0.11-1F polyesterCI " 2500 /IF 50 V electroC7 " 5000 pF 6V electro01-04 Diode 3 Amp 100V IN5408or similar

D5 " BYX50-200ZDI Zener Diode 3.3 V or 3.9 V400 mV

Q1 Transistor 2N2646 or similarQ2,3 " 2N2221A or similarQ4,7 " BC147 or similarQ5 " 80140 or similarQ6 " BOY92 or similarLl choke see Table 2

20V - 30V (J.60VA (7.5 Amp output)75VA (10 Amp output)

SW I Toggle switch 2 pole 240 Vrated.

Heatsink bracket to Fi9.3Diecast Box 6157PPC Board ETI 119Insulation kit for Q6 and 05

RI4 is made out of 4 strands ofelectric fire element each 40mmlong.

A complete kit of transistors anddiodes for this project Is availablefrom Marshalls of Cricklewood for£7.75 including VAT and P & P.

- 8074 - 6

2 HOLES 4mm 01A----

!".-- 6815

-I. 2 0

10-a

5mmDIA

4 HOLES 344mm DIA

0 143

MATERIAL 1 6mm ALUMALL DIMENSIONS IN MILLIMETRES

Fig. 2. Transistor/diodemounting bracket.

55

SWITCHING REGULATOR SUPPLY

D5 AND 06 MUST BEINSULATED FROMBRACKET

HOW IT WORKS - ETI 119

IN a conventional series regulatorpower supply the resistance of aseries transistor is controlled in orderto maintain the correct outputvoltage. The series transistordissipates considerable power andtherefore at very high load currentsseries regulators are quite inefficient.In the switching regulator a Aeriestransistor is still used but does notoperate in its linear range. Instead itswitches ON and OFF at high speedsuch that the load is alternatelyconnected and disconnected to a

supply voltage that is higher thanthat required across the load. Bycontrolling the ratio of ON to OFFtime we effectively control theaverage voltage as seen by the load.For example if it is on for 25% of thetime the average output voltage willbe 25% of the input. Thus bycontrolling the ON/OFF ratio theoutput voltage may be stabilizedwhilst dissipation in the seriestransistor is very greatly reduced.

However since most loads do notlike their supply to be in the form ofa square wave an LC filter is usedbefore the load to pass only the decomponent.

Referring to the main circuitdiagram we see that transistors Q5and Q6 are used as the series switch.LI and C7 form the output filter.Due to the inductance of the choke aflywheel diode is required, not onlyto protect the transistor, but toprovide proper operation. %hen theswitch is on, the load current flowsthrough the transistor, the choke,and into the capacitor and the load(Fig. A). When the switch is openedthe load current must continue toflow through the choke and this isdone via the flywheel diode D5 (see

Fig. B). The current through thechoke will thus rise during the onperiod and fall during :ate off period.The current never falls to zero exceptat very low load currents and theaverage is the same as the loadcurrent.The operating frequency is set by

the UJT Q1 which runs about20 kHz; the higher the operatingfrequency the lower the ripplevoltage on the output. However asthe operating frequency goes up soalso do switching losses in bothtransistor Q6 and diode 05. The20 kHz was chosen .s a compromise.It is high enough not to be audiblebut low enough to keep these lossesto a minimum.

When the UJT tires the pulsegenerated is coupled into the base ofQ4 by C4 turning Q I on. This, inturn,turns on Q2 and the switch Q5/6.When Q2 turns on Q4 also turns onand both latch on. If the currentthrough Q6 rises above about 12 to14 amps Q3 will turn on robbingcurrent from the base of Q2 allowingboth it and Q4 to turn off. This alsoturns off the output switch Q5/6.This is the current protectioncircuitry.

A voltage proportional to theoutput is provided by RV I to 07 forcomparison to the voltage of ZDI. IfQ7 is turned on sufficiently it willalso turn on Q3 thus unlatching Q2/4and turning off the output switch.Once the supply has stabilised thisaction will control the on time of theswitch in each cycle of the 20 kHz,such that the output voltage is

maintained at a voltage as set by RVIin a smooth and even manner.

We used a 240 V to 30 V 2 .A

transformer, which is adequate forsupply currents of up to 7.5 amps,

however any transformer having anoutput of 20 to 30 volts and a powerrating of 60 VA would do. If up to10 amps output is required then atransformer with a rating of 75 to tiOVA would be required.

It is also possible to supply theregulator from a de supply of 10 to40 volts. If the voltage available isless than 20 volts R2 should bereplaced by a link to ensure that theUJT operates correctly.

Fig. A. Current paths with switchingtransistor on.

LOAD

Fig. S. Current paths with switchingtransistor off.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

Fig. 4. Printed circuit -board layout. Full size. 178 x 78 mm.

TABLE 2 Choke winding details.CORE Philips E core 4322-020.

34720 two requiredFORMER Philips 4322-021

31830 or 4312-02123622 one required

Four layers close wound of 1.6mm wire core gap 3 mm (seetext).

CHOKE COMPONENTS

We have, as yet, been unable to find a source of supply to the amateur of the chokecore and former. However the value of this component is not critical and is, in anycase, the subject of experimentation in the adjustment of the airgap. We would there-fore suggest that, although we haven't tried this, the laminations and former of a6.3V ac heater transformer may be of suitable dimensions. It may be, in fact, thatthe secondary of a heavy-duty heater transformer may serve without modification,although we recommend that a 1k resistor be connected across the primary toprevent the effects of a build-up of induced voltage. Please note that this is a matterfor experimentation.

SUBSCRIPTIONS

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who's built an Eli Synthesiser....

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ELECTRONICS TODAY INTERNATIONAL APRIL 1976

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March 1976L

57

Exetron Time Ltd. offer this

unique transformerless designat a substantial saving on re-tail price. The kit is compl-ete less mains lead - all yourequire is a soldering iron,

Solder, and screw driver toassemble your oven digital

clock.

The*A Complete Kit

*or fully built.

'MISTRAL" Digital Clock

Kit £12.50 OW) Built £18000.

0 Pleasant green display () 24 Hour readout

() Silent Synchronous Accuracy <> Fully electronic

O Pulsating colon o Push button setting

" Building time 1Hr 0 Attractive acrylic case

O Easy to follow instructions 0 Size 10.5x 5.7x 8cm

Ready drilled PCB to accept componentsEXETRON (Dept ETI)Regal House,Penhill Road,LANCING, Sussex.

Payment : CWO, Cheque, Access,Barclaycard. (Muote Number)

8ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

C(117*. 11()SIJPART THREEFLIP-FLOPSOur next subject is flip-flops - andwe shall assume that the reader isfamiliar with the working of thesedevices and so the discussion willbegin with the pinout diagrams infig. 1. The first two are standarddual edge triggered devices with"D" and "J -K" type data inputsrespectively. No doubt it is knownthat the "D" variety will divide theinput frequency by two if "0" isconnected to "D- whereas the"J -K" type toggle, as this beha-viour is called, when both "J" and"K" are held high. The set andreset inputs operate asynchronously(ie. independently of the clock)forcing the device into the "0" = 1and "0" = 0 states respectively.These inputs operate when takenhigh in contrast to most TTLbecause TTL inputs rest high whendisconnected whereas CMOS inputsmust never be allowed to -float"anyway. Both the 4013A and the4027A will operate up to about8MHz.

The last device in fig. 1 (the4042A) is a quad data latch of thesort often used for temporarystorage of BCD digits in applicationslike frequency meter displays. If thepolarity input is held low then the"0." output follows the "D" inputin each latch when the clock is alsolow but on the rising edge of theclock pulse the outputs are isolatedand retain the data present at thatmoment. When the polarity input ishigh all this works the other wayround. The clock inputs to all thesedevices should have rise times of5ps or less (at V.. = 10V).

Flip-flops on their own have usesin control circuitry and counters. Ifyou wish to produce a counter tocount through an odd sequence (aGray code for example) it isadvisable to find out about Kar-naugh maps and associated tech-niques which aid the design processconsiderably. The standard form forsuch counters is a sequence of

4013ADUAL 0 FLIP FLOP

SET RESET

BEFORE CLOCKPULSE

AFTER

CLK O

I 0

4027A 4042ADUAL J-K FLIP FLOP QUAD D-LATCH

SET RESET

Vss-8

BEFORE CLOCK PULSE AFTER

CLK J - 0 u

_.1- ° 0

5 0 1 0 1

j-- 1 0 1 0

--I '1 1 1

. NO CHANGEI CHANGES STATE

Fig. 1. Three common flip-flop devices.

11N

ti,,,/2

CK O

1t,,,,/4 0

CK

D 5

O

0,

D2

11

01

01

k- 02L2

02

- 03L3 - 03

0404 L4

-154CLOCK - 5

POLARITY = 6VDD '16 Vss -8

CLOCK POLARITY 0

0 D

0 LATCH

D

LATCH

CLOCK IS COMMON TOALL LATCHES

CK 0

D 5

Fig. 2. Basic binary counting chain used for frequency division.

TY'

CK

'D"

CK

0

CK

0CLOCK

Fig. 3. Principle of shift register. The content of each "cell' is shifted one place to theright on the .rising edge of the clock pulse.

flip-flops whose inputs are derivedfrom the outputs of the others by afew simple logic gates. As far assimple binary is concerned, the:required set-up is shown in fig. 2.but we shall have a lot more to sayon the subject of counters in generallater.

The other main application offlip-flops is in shift registers. A shiftregister is a sequence of flip-flops sointerconnected (see Fig. 3) that ona clock pulse the content of eachdevice is transferred to the next one

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

down the line. The register soformed is referred to as a staticdevice because, unlike some MOSdevices available, data is not lost ifit is not shifted for some length oftime. One modification to the basicdevice is to provide inputs andoutputs to individual flip-flops in thechain and in this form, shiftregisters have many applications inserial to parallel and parallel to serialdata conversion. This though isanother subject which must waituntil a little later in our discussions.

59

C SCOUNTERSOur main subject this month is

counters. It might well be true tosay that the range available (com-pared to TTL) reflects the advanceswhich have been made in otherbranches of electronics, particularly'display technology. BCD countersare conspicuous by their absence asthey have generally been replacedby seven segment decodedcounters. One disadvantage is a

need in many cases for externaldrivers for LED displays but this willbe eliminated when Liquid Crystaltechnology is more advanced and,hopefully, cheaper.

BINARY COUNTERSAs usual we will start with the'

less glamorous devices in the rangewhich, in the present instance, are.the straight -forward binarycounters. First we should mentionthe general operating conditions:required for all CMOS counters. Thelclock input rise and fall times should'be less than 5,uS and the operatingfrequency limit is about 2.5MHz atV = 5V rising to 5MHI at 10V. Asfar as the problem of drive current isconcerned, it is advisable to consult.the full data sheets for the device inquestion but it is reasonable toassume that no trouble is likely tobe experienced if the requirement isless than 0.25mA with a 5V supplyor 0.5mA with 10V.

Fig. 4 gives the pinout diagramsfor CMOS seven, twelve andfourteen stage binary counters. Theoutputs are labelled B, with Bo themost significant bit (i.e. givinggreatest frequency division). It willbe noted that three of the lesssignificant bits are not available asoutputs on the 4020A and thislimits its usefullness in "divide byN" applications as we shall seelater. The greatest division of theinput frequency is 128 for the4020A, 4096 for the 4040A and16384 for the 4020A. In all casesthe counters step on the negativetransition of the clock pulse and thereset input sends all stages tological zero independently of theclock when it is taken high. There isalso a twenty-one stage counter (the4045A) which produces two out -of -phase pulses at separate outputsfor every 20971 52 input pulses. It

60

INPUT.

RESET

BO

B1

82

83

vt.,

,STAGE BINARY COUNTER Vss

12.STAGE BINARY COUNTER

Fig. 4. Three CMOS binary counters.

VDD

Bs

82

84

83

RESET

82

B1

00

08

89

INPUT B10

011Vn

...STAGE BINARY COUNTER

VOO

161

OUT

OUT

Fig. 5. (a) Basic crystal oscillator using CMOS for the active components.(b) Simple analogue amplifier using a CMOS inverter.

IIN

Fig. 6 (a and b) Thetwo reset modes for"divide by N"counters. The out-put is a pulse inboth cases.

Ibl

fIN 0

COUNTEROUTPUTS

RESET

INPUT

1 BINARYCOUNTER

LOGICNETWORK,OUTPUT GOESLOW WHENCOUNTER ISAT "O"

!BINARYN! ? R K ,401 3ACOUNTER OT

H

WHENINPUT C

RESETIS AT 'N

LOGICNETWORKOUTPUTGOESHIGHWHENCOUNTERIS AT

POUT

-f INN

0 fOUT,INN

Fig. 7. A divide by3600 counterusing the firstreset mode.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

is intended for producing onesecond pulses from 2.097152 MHzcrystals for driving clock circuitryand similar applications. Anyoneinterested in using this deviceshould obtain data from a manu-facturer.

While we are on the subject ofhuge frequency division chainsperhaps we should consider crystal.oscillators very briefly. Fig. 5(a)shows one common set-up and it isworth noting that the configurationin Fig. 5(b) is the standard way ofproducing a simple analogueamplifier from a CMOS inverter.

DIVIDE BY N COUNTERS

There are times when it isrequired to divide a signal by otherthan some power of two and byusing a 4024A or 4040A we maydivide by any number from 2 to128 and 4096 respectively, alth-ough extra components arerequired. Fig. 6 shows two ways ofachieving this end. The circuit in (a)has the binary counter feeding a

system of logic gates, the output ofwhich goes high when the counterreaches N-1 (where N is the numberthe input- frequency is to be dividedby). This happens on the fallingedge of the clock pulse because thecounters are negative -edge trig-gered. On the next rising edge theflip-flop Q output goes low andwhen the clock goes low again theoutput goes high, generating a

pulse of length equal to one half ofthe clock period which resets thecounter. It is interesting to draw 'atiming diagram for this circuit andprove it works. It should be notedthat although the actual output is apositive going pulse, a similar pulseof twice its length (i.e. one clockperiod) is available at the Q outputof the 4013. A divide by 3600counter which will provide onepulse an hour from a 1 Hz input isshown in Fig. 7 as an example ofthe technique.

The second mode has theadvantage that the -N- count andnot the "N-1" count is detected,but two logic networks are required;one to decide when the counter hasreached "N" and another toidentify the "all zeroes- state andreset the output. It is also a

disadvantage in some applicationsthat the counter spends a briefperiod in the "N" state. It is againinteresting to draw a timing dia-gram and it is worth noting thecross -coupled NOR gates used as anR -S flip-flop. As an example a divideby twenty four counter is shown inFig. 8 to produce one pulse per dayfrom the one per hour output of Fig

Fig. 8. A divide by 24 counter using reset.mode two. Note the simplicity that may beachieved in the logic networks -- one NANDgate serves to identify "24".

OUT -5

OUT -1

OUT -0

OUT -2

OUT -6

OUT -7

OUT -3

vSS

vDD

RESET

CLOCK

INHIBIT

CARRY OUT

OUT -9

OUT -4

OUT -8

Fig. 9. Pin -out diagram of the 4017Adecimally decoded decade counter.

Fig. 10. A switch programmable divide by N counter for N = 2 to 99. Extension to higher Nis obvious.

7. The circuit dissipation of both thecounters would be very low (lessthan 1 mW) at this low operatingfrequency and the only note ofcaution to be sounded is that thecounter and flip-flop should notboth be triggered from the sameedge of the clock pulse (i.e. oneshould be positive and the othernegative edge -triggered).

A DECIMAL -DECODED DECADECOUNTER

All the old hands at TTL willdoubtless be familiar with the 7490decade counter and 74141 decimaldecoder driver. The 4017A com-bines the count and decode func-tions in a single package but has thedisadvantage of low output drivecapability. Buffering the outputswith 4049A inverters will raise theavailable output to about five or tenmilliamps at supply voltages of fiveand ten volts respectively. The pindi4gram is given in Fig. 9 and thecounter advances one on thepositive clock transition providedthat the inhibit is held low. The resetoperates asynchronously whentaken high as usual. "Carry -out -may be used to clock the next stagein a multi -stage counter. This devicehas fairly obvious applications incontrolling switches in multiplexingequipment as one and only- oneoutput is high at any one time. It is

ELECTRONICS TODAY INTERNATIONAL --APRIL 1976

fairly clear also that we may extend'the techniques of divide by N

counters to cover these devices withthe added bonus of them beingswitch programmable. Fig 10 shows

.this idea realised using reset modetwo because of the ease of switch-ing for N rather than N-1. This

'circuit has lost an inverter comparedwith Fig. 6b, this being the changenecessary to adapt the circuit forcounters and flip-flops which oper-ate on the same clock transition.The sequence of counters couldclearly be extended to any desiredlength and it is an interestingthought that seven of thesecounters (4017As) and theattendant gates could, when fedwith a 1 Hz input, generate pulses atany interval from two seconds to

;over three months! On a morepractical note, used in a phaselocked loop circuit a most versatiledigital frequency synthesiser wouldresult. Remember however that theoutput is a pulse and it would needsquaring (one more flip-flop) beforemost phase comparators wouldaccept it.

SEVEN SEGMENT DECODEDCOUNTERS

We mentioned earlier that CMOSIC design reflected the changes indisplay technology. Two particularexamples of this phenomenon arethe 4026A and 4033A decade

61

Ccounters with seven -segment out-'puts. The pin -out diagrams for thesedevices are shown in Fig 11 and, as;one might guess, the counters are.identical with the exception that the4026A has a display enable func-.tion for use in multiplexing digits.and an ungated C -segment output,'whereas the 4033A has ripple,blanking and a "lamp -test" facility.1We shall consider the use of these'special facilities when we have'discussed the features common toboth. The devices are positive edgetriggered and advance only whenthe clock enable is low. The resetoperates when taken high as usualand the segment outputs go highwhen they are active. Just as in the.4017A the signal at the "'carry out"terminal may be used to clock thenext stage in multi -decode applica-tions.

In the same way as we haveconsidered for other counters, the!seven segment outputs may belidentified by logic gates and the;counters made to divide by any.number. Fig. 12 gives the informa-tion necessary and it should be.noted that the "N-1 and flip-flop"method is used because the othermethod does not count throughzero. If anyone wants to strike ablow for freedom against LSI wehave covered most of the devicesnecessary for designing a CMOSdigital clock. Now we will have toconsider the interfacing of displayswith our seven segment counters.LEDs like the MAN -3 which have a.low current will interface directly ,with the outputs of the 4026A or.4033A and give a tolerable bright-ness with the available drive current(about 5mA), provided that V00 ismore than 9V. If we drop the'voltage down to between 4 and 9Vthen NPN transistors should beinserted as shown in Fig. 13a and if -the supply drops even lower, theaddition of inverting buffers is.recommended. The seven transis-tors needed are generally thecomponents of a single IC. Theattention of the reader is drawn tothe discussion on current limitingresistors to follow.

MULTIPLEXING

Life is never as simple as wemight want and there are tworeasons for complicating the cir-cuitry by using digit multiplexing

VDD

RESET

LINDA TED

Spb

.1

oN

soo

CLOCK

CLOCKEIVASLE

RIPPLEB LANK IN

RIPPLED t.AN,

OUT

CARRYOUT

SMI

VOO

RESET

LAMP TEST

Sp 0

sw

.1d

Fig. 11. Pin -out diagram for the 4026A and 4033A seven segment decoded decadecounters. The labelling of the segments is also shown.

.1 LOEIC NETWORKS

10 tallOtTD, E,R, COUNT 00 REWIRE. EirMORK

CARRYOUT K X

PROtCARRY OUT

bo.o

Fig.12(a) How to produce direct seven segment divide by N counters, (b) logic networksto identify each digit. The extension to a multi -decade version is simple.

OD.0W. 421.

Oft

Fig. 13. Driving MAN -3 type displays (al at intermediate supply voltages and, (b) atlow voltage.

LK /I CA

exam

CL.

DISPLAY EMAilf.RrLIrE

VG 6016AIOCKHNV1RTW40WIPERS

V.4D17A

CQ-V.]WIXOM

411.0111/LIMOCLOCK

Fig. 14.A three decade counter for a 3 -digit multiplexed display. Extra buffering of thedigit lines may be necessary for some displays.

62 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

(i.e. each. digit is displayed for afixed period, usually between about10 and 30% of the time). These arethat to do so is more efficient interms of power consumption andsecondly that most multi -digitdisplays reduce the number oflead -outs (by giving just one set ofseven segment drive lines for thecomplete display and one digit driveline for each digit).

This is the reason why the4026A has a display enable inputwhich, although the counter con-tinues to function, cuts off thedisplay when it is held low. The,display enable output gives a replicaof the input and may be used toenable other counters which are tobe "on- during the same period. Italso explains the presence of the"ungated C -segment" output whichis used for producing some divideby "N" configurations which oper-ate when the display is disabled.The basic arrangement of a threedecade counter is shown in Fig. 14and attention is drawn to the notethat additional buffering may benecessary on the digit lines. It isalso worth noting the use of a 4017divide by three counter (using theflip-flop reset mode) to. control thedisplay.

Other sorts of displays which areoften used are higher current LEDssuch as the MAN -1 which is, incontrast to the MAN -3, a commonanode device. This means it must bedriven by inverting buffers asshown in Fig. 15a. We have beenrelying here on the output currentlimit of the CMOS chip to limit theforward current in the LEDs. Parti-cularly when transistor drivers areemployed it may be necessary toadd current limiting resistors in thesegment lines. The calculation ofthe value is simple given therequired segment current and

;voltage drops (see Fig. 15(b)). Inmultiplexed displays the limitingresistors should, of course, be put inthe common segment lines and it isworth noting that a considerablesaving in resistors in non-mutli-plexed displays may be achieved byputting a single resistor in thecommon line to each digit. The payoff is that the display brightnessvaries with the digit. Fig. 15(c)shows the technique for interfacingwith "Numitron" and similar dis-plays.

The ripple blanking facility is forblanking leading and trailing zeroesin the display and it works asfollows. Take the ripple blankinginput (RBI) of the most significant4033A on the integer side of thedisplay low. Then take the rippleblanking output (RBO) of the IC and

connect it to the RBI of the nextcounter and so on until the positionof the assumed decimal point isreached. Follow exactly the sameprocedure from the least significantcounter in the fractional part of thedisplay backwards to the decimalpoint (see Fig. 16(a)). Of course, ifthe assumed decimal point is at oneend of the display then half theprocedure would be unnecessary. Ifnon -significant zeroes in the placeseither side of the decimal point areto be displayed (so that 7 and .6appear as 7.0 and 0.6) then theRBI's of the two counters concernedshould be taken to V (as in Fig.13(b)). Finally on these two ICs, thelamp -test facility on the 4033A just

:forces all segment outputs highwhen it is taken high.

0I AY

LEO

NI

VDO -VFILID/ - MOIF (1101 OUTPUT

V.10.7 V711.101. LSO IF (Lg.)

Vv - 3.11 -IV b. DI42000 Ty...Mr... 1/7 CA.1041 ol.ihe

Fig. 15. Driving others displays:- (a) MAN -1type (b) example of calculation of limiting;resistor (c) Numitron type incandescentdisplay.

0

la,

tb,

INTEGER PART

ClO

RBI RBO

CLK C/0

RBI

DEC. PT. FRACTIONAL PART

C/O

RBI

CLK C/O

RBI

CLK C.

RBI

CLK

RBO RBI

CLK C/O

RBI

CLK

RBI

VDD VDD

Fig. 16. Four digit counters using the 4033A with non -significant zero supression(a) in all positions (b) in first and last position only.

DATA

J2

52

at

03

J3

VSS

Fig. 17.Pinouts of the4029A and 4018A.

CK CK CK

0) 02 03 a4

0

0

0

0

Fig. 18. Circuit diagram and counting sequence for a four stage Johnson or "twistedring" counter.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 63

C STHE 4029A AND 4081A

We shall conclude our discussionof counters by looking briefly at twomore devices. The 4029A is a

general purpose counter which, atthe price that a 7490 was a year ortwo ago, has most of the features ofthe more exotic TTL devices. Briefly,the device is positive edge triggeredand advances when the clock and,preset enables are both low. Furth-,ermore it counts in binary when theBinary/decade input is high and'BCD otherwise, a high signal at theup/down input persuades it tocount up and a low input forces it tocount down. As though this werenot enough, when the preset enableinput is high, the Q counter outputsare forced to follow the J (-Jam-)inputs. The suffix "4- in both casesindicates the most significant digit.The pinout diagram is given in Fig.17 along with that for the 4018Apresettable divide by N counter.

There are two basic ways ofproducing counters. Firstly there isthe chain of flip-flops each of whichhalves frequency produced by theone before it. This was the principlebehind the binary counters, whichwe considered at the beginning ofthis month's discussion, and also ofthe 4029A. The second method isknown as a Johnson counter and itis basically a shift register consistingof a chain of flip-flops (see p59)with the Q output of the last counterconnected back to the data input. Alittle patience and a pencil andpaper will soon show that such a

'counter will divide the input fre-quency by 2N where N is thenumber of stages. The countingsequence for a four stage counter isshown in Fig. 18 and the reader willnotice that if the counter starts with

contents not in the countingsequence (e.g. 1010) then thecontents are always nonstandardthereafter. Thus some special gatingis required. The simplified internaldiagram of the 401 8A in Fig. 19 isnot complete. Also the Jam inputs'and preset enable (which work inthe same way as in the 4029A)together with the reset (which zerosall stages (01 - Q5 = 1) have beenomitted for clarity. Fig. 20 showsthe way to connect the 4018A todivide by all numbers from three toten. Just as an example of howversatile this device is one applica-tion will be considered in a totallydifferent field from counting. Bydisregarding the clock the Jaminputs and inverted data outputs (Q)can be used as a five data latch fortemporary storage, the outputsbeing updated to the inputs whilethe present enable is high. Nextmonth we will conclude the seriesby considering several differentsubjects.

Continued next month

Fig. 20. Connection of the 4018A as a'divide by "N" counter Input to clock,output waveform from DATA input issymmetric when N is even, almost sowhen N is odd.

oo.a.

n.

0,

6.1.

-) >0.--

6.

to

OCLOCK

0DATA

CK

a,

Fig. 19. Simplified internal diagram of the 4018A.

a,

a_

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64 ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

'ELECTRONICS PART 26it's easy! More complex logic

The exclusive OR gate is morecomplex than the other gates discussedlast month because it contains morethan one basic gate - it is a small logicsystem in itself. Fig. 1 shows howtwo inverters, two AND gates and oneOR gate can be interconnected toachieve the exclusive OR requirement.

A second example is given byconsidering a function

Z=(A.B)+(C.D.E)+(F.G.H.)+(l.J.)The problem might be to realise a

logic network that performs thislogical task - imagine trying todescribe it in words! Brackets are usedto ensure that sub -connections aremade in the correct way; as in linearalgebra operations in brackets ale dei.ltwith first as individual units.

The first step in realising thenetwork is to form the dot ANDfunctions of Z. We need two two -inputAND gates and two three -input ANDgates. (It matters not if a gate hasmore inputs than needed - the unusedterminal is ignored). The outputs ofthese four AND gates are then fed intothe inputs of a four input OR gate sothat the function under the negationbar is achieved. At this point we could'select an OR gate followed by anINVERTER or make use of a NORgate direct.

When drawn as a sy:iem rat

interconnected schematic blocks itappears as in Fig. 2a. Also given inFig. 2b is how a 14 pin dual -in lineIC would appear that performs thisfunction.

As a third example the exercise is

to devise a logic network that willadd (in binary system) two binaryinputs producing the binary sumoutput plus a carry output. Thisfunction called the half -adder, formsthe basis of digital computation withbinary numbers.

Back in Part 5 the concept of thebinary number system was introducedshowing that the counting base is 2

instead of the more commonlyencountered 10 of the decimal system.At any digit position in the binarynumber, the value can be only 0 or 1

so addition of two binary numbersgives a value at each digit position thatalternates as 0 1 0 1, etc., as countingprogresses. When 0 and 0 are added weobtain 0; when 0 and 1 are added weget 1. When 1 and 1 are added wecannot have 2 in a binary system so it

Fig. 1. Logic network providing exclusive- OR function.

returns to 0 with a carry of 1 going tothe next higher digit position. Fig. 14illustrates this idea - try adding thetwo numbers! A half -adder does thisoperation for one digit position. Thetruth table for the half -adder is,"ierefore, as given in Fig. 4a.

The sum column shows we need anexclusive -OR to provide the sum value- hence its importance in computerdesign. A carry is to occur when bothA and B appear so an AND gate is

needed. From these we can developone form of the half -adder system -

F

H

Z = (A.B ) + (C.D.E ) + (F.G.H) + (I.J)Fig. 2. (a) Logic network for functionZ = (A.8) + (C.D.E) + (F.G.H) + (I-11(b) same logic packaged in IC flatpack. Fig. 2(b).

A

B

1 0 1 1 0 0 1

0 1 0 1 1 1 0

10 0 0 0 1 1 1

A .IMOST SIGNIFICANTDIGIT M.S.D

LEAST SIGNIFICANTDIGIT

CARRY OF 1TO NEXT HIGHESTDIGIT

Fig. 3. Addition of two binary numbers proceedswith a carry as for decimal arithmetic but with onlytwo states 0, 1 in each digit.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 65

ELECTRONICS -it's easy!given in Fig. 4b. Note how thecomplexity is growing. Such a circuitrequires around 30 or more passiveand active components and hundredsof such circuits are needed in a digitalcomputing circuit. A version of thesame circuit only constructed usingNAND gates is given in Fig. 4c. Notethat NAND gates 1 and 2 have bothinputs tied together, they thereforeperform the NOT function. Try yourBoolean on this as follows - .

SOME LAWS OF BOOLEANALGEBRA

When devising systems of logic thesituation soon arises which calls forknowledge of the rules formanipulating Boolean expressions.Possible reasons for this may be that alimited range of logic functions areavailable, so conversion of an.expression is needed, or that a largeexpression may not be in its simpleststate. Reduction to its non -redundantstate means use of less elements.

A number of axioms (truths basedon experience) exist for relationshipsbetween Boolean statements. There is)little point in dwelling on theirindividual proofs and historical-develoment - for that see the reading;list. The following relationships are,

summarized to assist when needed:

de Morgan's rule 1 : A + 6 =

MINIMIZATIONTo save components the network

first realised by inspection from a validtruth table may well not be in itssimplest or so-called minimal form. Insimpler cases, application of the aboveBoolean algebra laws by a well -practiced person can often come upwith simplifications.

Beware, however, of applying linearalgebra rules of factoring. It is quitewrong to cancel or subtract equalterms in both sides of a Booleanequation.

Unfortunately, no direct way is

known with which to arrive at a

minimal network by a routinelydeclared simple procedure. The nearestwe can get to this is by means of aKarnaugh mapping procedure whichwe do not discuss in this course as fewreaders will be required to be expert inthis facet of digital electronics.

An example will show how a simplesystem can be minimized byinspection. Consider the expression Z= (A + B) . (A + C) . (A + D). This isreadily seen to be the logic network.given in Fig. 16a. From thedistributive laws given above this canbe rewritten as Z = A + B.C.D which

de Morgan's rule 2 : A.B = A + BCommutative laws : A + B = B + A

A.B = B.A

Associative laws : A.(B.C) = (A.B).0 = A.B.0A+(B+C)=(A+B)+C=A+B+C

Distributive laws : A.(B + C) = A.B + A.0A.0 + A.D + B.0 + B.D - (A + B) . (D + D)

This is as for linear algebra but withextra cases: -

A + B.0 = (A + B) . (A + C)and (A + B) . (A + C) . (A + D) = A+ B.C.D

Absorption laws : A + (A.B) = AA. (A + B) = A

Double negation : not A = A

Universe class laws A + 1 = 1A.1 = A

Null class laws : A + 0 = AA.0 = 0

Complementation laws : A + A = 1A.T = 0

Tautology laws : A + A = AA. A = A

Expansion laws : (A + B) . (A + B) = A + B(A.B) + (A.B) = A.B

represents the logic 'configuration ofFig. 16b. This minimal form requirestwo less gates (provided a three inputAND gate is available).

THE VENN DIAGRAMIn the early days of logical algebra

development, John Venn developed asystem of overlapping circle diagramsas an alternative way with which toexpress the concepts contained in thetruth table. Venn's diagrams consist ofoverlapping circles contained in a

rectangular box. Each circle representsone of the required number ofindependent input variables - A, B, C,etc. If the output variable Z is a 1(assuming that is the conventionchosen) the appropriate area of thecircles is shaded. The rules are thatinside a complete circle its variable isnot negated, outside it is negated.Overlapping area of common circlesrepresents their AND combination.,The examples given in Fig. 17

illustrate -the use of Venn diagrams invarious simple logic situations. Theconcept extends to as many circles,that is, inputs as are needed.

LIMITS OF BOOLEAN

There are a number of limits to theuse of Boolean algebra. In the logiccombination we have considered sofar, there has been no mention of time

INPUTS OUTPUTS

A B CARRY RECORD

0 0 0 0

0 1 0 1

1 0 0 1

1 1 1 0

(a) TRUTH TABLE OFHALF -ADDER

AND CONDITION EXCLUSIVE -OR -CONDITION

Fig. 4(a). Truth table for half -adder logic.

CARRY

(b) IMPLEMENTATION OFHALF -ADDER

RECORD

Fig. 4(b). One form of half -adder logic network.

Fig. 4(c). The half adder using NANO gates only.

66 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

A+B

(a)

Z = (A+B). (A+C). (A+D)

(b)Z = A + B.C.D

Fig. 5. Logic network realising Z + B).+ C). + D)

(b) Simplified network.

or of any feedback around the circuit.In practical systems, time delays always"occur and, further, other elementssuch as counters, multivibrators andmemory devices are generally presentwhose state depends, not only on thelogical inputs at any given time but, on.what has happened previously!Boolean algebra is unable to deal withsuch situations.

In addition, if a function isminimized by means of Boolean itdoes not follow that the derivedcircuit is the cheapest possible. Theminimized circuit may call for 3 -input

Fig. 6. Venn diagrams represent logic statesin topological form. Some people find theseeasier to use than truth -tables.

AND gates, say, but it could well becheaper to use the more readilyavailable NAND gates - even if moregates are required to achieve the samefunction.

Thus it can be seen that Booleanalgebra is far from an infallible meansof arriving at the cheapest possiblesolution. In fact it may not give anysolution at all! Engineering skill andingenuity are still the most important

FURTHER READING

Most books on digital computerdesign include a chapter on Booleanalgebra and binary arithmetic.

"ElectronicSimple",Basford,1967.

Computers - MadeH. Jacobowiti and L.W.H. Allen, London,

"Electronic Instrumentation Funda-mentals" A.P. Malvino - McGraw-Hill, 1967.

"Numbers" R. F room, ElectronicsToday International, Oct. 1973; p.62 --65

For the historical development ofcomputers and other data processingequipment see

"A Computer Perspective" C and REames, Harvard University Press,Massachusetts, 1973.

factors in efficient logic design. It is ofvalue however, and does give a goodinsight into the function ofstraightforward gate circuits.

In the next part we will look atpractical circuitry of logic gates andintroduce several other basic digitalcircuit building blocks. We will then beready to discuss digital systems insome degree of depth.

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ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 67

FEED IT FORWARDMAINAMPLIFIER

DIRECTIONALCOUPLER

AT TENIJATOR

DELAYLINE

AUXILIARYAMPLIFIER

MIXER

IN 1924, Black, working at Bell Telephone Labora-tories , discovered the principle of feedforward. In1929, he discovered feedback, which was destined tobecome one of the many developments of that mostremarkable research institute to sweep the electronicsworld. The 'sweeping' took some time; probably nomore than a handful of professionals had heard of theprinciples of feedback in the thirties, and it was theintensive development of electronics during the warwhich spread the news around a bit. It did, however,become the hottest property in amplifier design in theearly 1950s, and appears in all but the humblest ofbooks on electronics.

Feedforward was rather less fortunate, and but forthe work of Seidal, also at Bell Telephone, in the latesixties, would have become as obscure 'as the "talkingflame" method of modulating a spark transmitter. As sooften happens, however, old ideas take on a newsignificance when new requirements appear, andfeedforward may very well be due for a rather belatedappearance in everyday electronics.

A LOOK BACK AT FEEDBACK

Let's refresh our memories about feedback. In a

feedback circuit, a fraction of the output of an amplifieris fed back to the input and compared with the inputsignal at the input. The difference between input signaland the feedback signal is then passed through the'amplifier again in such a phase as to act as a correctingsignal, if the feedback is negative. Since positivefeedback is seldom used in amplifiers deliberately, weshall stay with negative feedback. For example, if a

positive going spike appears in the output, and is notpresent in the input, negative feedback will ensure thatthis is fed to the input in a polarity which will cause anegative going spike at the output, thus cancelling outthe distortion of the signal. The amount of cancellationwould be complete only if the amplifier had infinitelylarge gain, but can be made great enough for verysatisfactory results.

IAN SINCLAIR

INVENTED BEFORE FEEDBACK, THEPRINCIPLE OF FEEDFORWARD CORRECTIONHAS MUCH TO OFFER MODERN DESIGNERS.

Negative feedback of this kind has some advantagesbut also some disadvantages. On the plus side there is avery considerable reduction in distortion caused insidethe amplifier, coupled with a reduction in gain and anincrease in bandwidth. Any changes in the characteris-tics of the transistors or other devices used cause verysmall changes in the. characteristics of the amplifier.The amplifier, however, may suffer from stabilityproblems, caused by the phase of the feedback varyingwith frequency. The problem region may be outside thenormal bandwidth of the amplifier, so that an amplifierhas to be designed for a much greater bandwidth thanis used. In addition, the amplifier, which is stable with aresistive or inductive load may be unstable with acapacitive load.

A SEPARATE AMPLIFIER

Feedforward, by contrast, samples a fraction of thesignal at the output and compares it with a sample ofthe signal fed forward from the input. The difference isthen amplified in a separate amplifier, and added to theoutput in such a phase as to correct for errors. Theseparate amplifier is the clue to the long time thistechnique has been ignored; in the days of valve ortransistor amplifiers this made the technique unecono-mic. The use of ICs puts rather a different complexionon it, since two amplifiers can be put on one chipalmost as cheaply as one.

Oddly enough, the technique was not revivedbecause of the easy availability of ICs, but because ofdistortion and noise in microwave amplifiers usingtravelling -wave tubes.

In any microwave tube amplifying a signal whichmay be in the region of 10GHz (10000MHz), the delaytime of the signal - the time which it takes to pass fromthe input of the amplifier to the output - is severalcycles, perhaps about 50. In such amplifiers, feedbackcannot be used because it is not possible to make thefeedback appear 50Hz earlier than the signal whichcauses it! Feedforward can, however, be used by takingthe input signal and splitting it so that one part goesinto an amplifier and another part is delayed andcompared to the output. The difference is thenamplified in another microwave amplifier and added inantiphase to the output. Figure 1 shows the type ofcircuit used. The coupling methods used must oermitsignal flow in one direction only, and some allowancemust be made for the time delay caused by eachcoupling, amplifying, or mixing stage.

For such an amplifier, this is the only possiblemethod of distortion reduction, and it has several other

68ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

advantages over negative feedback.There is, for example, no reduction in gain. apart

from that caused by the couplings and mixers, yet anincrease in bandwidth is possible if the auxiliaryamplifier has a greater bandwidth than the mainamplifier. This is because the reduction of gain at theedge of the band acts as a distortion of signal and iscompensated by the auxiliary amplifier just as any otherdistortion is compensated, assuming the auxiliaryamplifier is able to cope. The delay in the amplifier iseasily compensated for by time delays in the couplingto the auxiliary amplifier, and the distortion of the mainamplifier may be reduced to as low a factor as desiredby making the auxiliary amplifier better. The wholearrangement is stable under all conditions, and at allfrequencies, and there is no need to worry about whatthe amplifiers are doing outside the band of interest.

DRAWBACKSAll of these advantages make this a circuit technique

well worth looking at for other applications . . . therehas to be a snag somewhere! It lies in the auxiliaryamplifier, which decides how good the main amplifierwill be. Unlike the case of negative feedback, this is nota closed loop circuit, and changes in the auxiliaryamplifier are not compensated for in the circuit, unlessthe auxiliary amplifier is itself a feedback amplifier. Ifthe gain of the main amplifier is to be controlled towithin 3db or so over a given bandwidth, then the gainof the auxiliary amplifier has to be controlled to a smallfraction of this, the fraction being roughly the stepdownratio at the output which enables us to compare it withthe input. It is this requirement for the auxiliaryamplifier which has kept feedforward from becoMingbetter known.

AREAS OF APPLICATION

Having established these principles, however, weare left with a fascinating -field for experiments, a

challenge for those who say that there is nothing left forthe amateur to discover. Lets toss around some ideas.

For one, we can easily make voltage amplifiers ofhigh gain, good linearity, stability, and low noise. Wecan, if we like use feedback in their construction. Wecan also make rather cheap and nasty power amplifierschurning out many watts at high gain. Combine the twoin a feedforward circuit, and we could have a good highpower, high gain amplifier, stable under all conditionsin which the auxiliary amplifier was stable. The outputof the auxiliary amplifier need not be very high, since itexists only to correct the distortion of the mainamplifier. Might this technique enable us to saygoodbye to crossover distortion at low power levels?

Taking another field altogether, consider timebases.It is easy to generate a linear sawtooth of a few volts,more difficult to generate one of amplitude close to theamplitude of the power supply available, or to preservethe linearity in an inductive load. Why not generate asmall amplitude linear timebase and use it as thereference in a feedforward amplifier to correct anothertimebase?

On another trail now, the distortion of an amplifier towhich feedforward is applied is easily measured, it issimply the correction signal at the output of thefeed -forward stage. All in all, there seem to bepossibilities for this old idea now in the field ofwideband amplifiers, transmitter. modulation, crosstalkreduction, control of signal strength and goodnessknows what else. We may be seeing some feedforwardcircuits in ETI before long!

FREE Brochure

on New KITSWhether-professional,

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CROFTON ELECTRONICS LTDDept. C, 35 Grosvenor Road, Twickenham, Middx. 01-891

1923

ETI PCB's

out PROJECT

NOISSUE

MOONO

TOTAL

11. TITLEMan

NOISSUE

90000NO

TOTAL

IICL

M. SW.. Isl. 25 Oct. 1975 M. 25 f421 Taps SIM 513 Tap Flatlet 02625 wets/dma

lisirNo 2

.ol Pow So.Po 105 APT. 1972 014 £1.46 1/iplfial.Slap W. 520 Jac 1974 52ffi f2.05elk Nose 107 Top Protact 922 El 69 5200 5011

Matte Na.1 klcassic Or Are 529 Sost. 11115 5290 E2.32IE. Pow SalaryTbarasca. attar

III 249 1973 III 21.43 Belli 52995296 f2.32113114

O.. 1.3Oct. 1914

113114

11.57El . 'N.' ........41111roor

530S32

Me. 1975SW. 1975

530532

050ppOW Ws Areplor........., us Jou 1975 115 mai ......01, 533 Oct.19715 5330 Ea,

Iltit , , , Oct 1975 1174

117168.69p Radar It. Nana 702 has 1175

Apr 1975

5339

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filoEl 1 3

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213 as.r

Wale MoreINsitul Plarro Tie

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No 2Sispar Sam 410 Top Pro. 025 f 1.51

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N. I 4140414C

f 1.5211 52 we have stocks of all the

Slip Alcor 414 .10, 1975 4140414E

E1.69

ELIO above boards. Allow 7/10NH,' 111,lateraelcomi 420Four Wool

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Ni,76p

f 1 I I

days for delivery by post.Boards also available for

Pea 4201 £121 other published designs at 6pOsiers. ..0W 4219 Jul 1974

4200

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U a sq. inch + VAT and P&P.Id. an Stun Amp 422 Ass. 1974 422 f297 Large stocks of components50 watIvOlnaPita Two ANS ea

aw.... Amp423 Not 1974 . Illp also available.

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CROFTON ELECTRONICS LTD.Dept. C, 35 Grosvenor Road, Twickenham, Middx. 01-891

1923

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976 69

LECTROAICSTOMORROW

by John Miller -Kirkpatrick

There is a saying that goes some-thing like 'It all comes to he whowaits,' well, the waiting is over atlast, a chip manufacturer has comeout with the true electronic timeswitch. The AY -5-1230 from Gen-eral Instruments is a four digit clockchip based on the successfulAY -5-1200 series with the additionfeatures of having an alarm outputwhich can be programmed to switchon at a given time and also switchoff at another given time. Theoutputs from the chip will drive amultiplexed fluorescent display,such as the Futaba 5 -LT -01, or LEDsvia interface circuitry or a TV displaychip if the optional BCD outputs areused in place of the seven segmentoutputs. The chip was designed todrive the AY -5-8300 series of TVdisplay chips and is intended toallow automatic turn -on and turn-offof the TV at predetermined times. Ifno off -time has been set then theswitch output will automaticallyturn off 10 minutes after turning on;this is a safety aspect to ensure thatthe TV set is not automaticallyturned on and left on.

Apart from the application it wasdesigned for, this chip hasnumerous other obvious applica-tions such as central heatingcontroller, tape recorder switching,'anti -burglar lights etc. The turn -on /turn-off sequence can be optional2ly operated once or cycled to repeatin each 24 hour period; the outputcan be altered by a simple push-button or the timing can becancelled for a complete period withanother switch - all without thenecessity of altering the time of dayor the two alarm times. There arethree outputs from the chip forcontrolling switching, the first is theswitch output, which is intended todrive a relay or SCR (sinks 30mA),the other two outputs are intendedto act as status indicators to showthat an on time and/or off time hasbeen set and will thus become

active at the appropriate time.A very well designed little chip

with tons of applications, you couldparallel two or even more chips ifyou wanted to switch the same ordifferent circuits several timesduring a 24 -hour period, as thedisplay outputs can be wired in

parallel and individually switchedon you could wire up several chipsto operate the same display.

AND NOW AND/ORSome months ago (and also above )I mentioned the AY -5-8300 seriesof TV display chips and commentedthat they are possibly the mostversatile of the range of TV displaychips now on the market. They willaccept time input from chips otherthan the AY -5-1200 series, eg theCT7002 (or HCM 7002 as it is nowrknown). GI have now announcedthe 8320 chip which gives the

16 TT, 191/

jL

HOP,SNC

P

220.

option of time and channelnumber display; whereas the 8300is channel only and the 8310 istime or channel. As the channelnumber system is not used in theUK the multiplexed inputs fromwhich the channel number isgenerated could display tempera-ture, humidity, etc, or could be usedin TV studio systems to identify thesource of the video displayed oneach monitor. I have only onecomment to make to GI and thatconcerns the number of digitsdisplayed in the time mode. GI onlyproduce four -digit clock chips andthus have not considered it neces-sary to provide for six -digit displayon the 8300 series, National makesix -digit clock chips but havedesigned their MM5841 to acceptinput only from their MM5318chip. I know that GI, Mostek andNational are competitors butwouldn't it make more sense todesign a chip that can interface withyour own or your competitors chips?Can we hope to see an AY -5-8330or MM5842 which will accept

.multiplexed input from most of thechips on the market. possibly alsowith optional input of seven seg-ment or BCD inputs?

IT'S CHEAPER TO GO THE OTHERWAYHaving just mentioned optionalinput of seven -segment or BCD itoccurred to me that the immortal7447 decoder has been with us forsome time now at prices of aboutE1.00 each; several decoders towork the other way have beenproduced but not very well publi-cised, thus making them expensive

1 CD4001

224 /101 330

22K

BACKGP0,40 0/P 221

44111 S,NC i/P"U 22K

250

CHAPACT ,F1 0,P10 CR T CATHODE

4104

81259

Al 5-1203A

0SET HT, SOHr--/____. SE I MIN

AT 5 8320

18K

CLOCKDISPLAY

elloo

2

Fig. 1. The AY -5-8320 interfaces with the 1203 or 1230 clock chips.

2'

70ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

A

8

D

2)

= 74002 = 74028 = 7408

and making them difficult to obtain.In applications where cost is a moreimportant factor than space andpower you might be interested inthe circuit below for convertingseven -segment to BCD. It workswith numbers 0-9 including tailedsixes and nines but not tailed sevensor representations of numbersgreater than 9. The inputs requiredare those produced by 7447s; someclock chips and the 7448 decoderhave inverted signals and thesewould require a set of invert gatesbefore the seven -segment to BCDdecoder circuit. As CT7002s werenot available for about a year I

designed this circuit to work from7001s where a BCD input wasrequired. it is in fact cheaper than a7447 decoder. If anybody has anysimilar circuits that use fewer chipsor which will accept tailed sevensand/or the characters produced by7447s for numbers above nine thenI would be interested to hear fromthem.

MORE NEW CHIPS AND WHATTO DO WITH THEMThe MK50396 and MK50397 fromthe Mostek stable are now availa-ble. If you remember these are thehours/minutes/seconds andMinutes/Seconds/ .99 versions ofthe MK50395 multi -purpose coun-ter chip. This family has the featuresof six decades of count and displaywith presetting of counter andcomparator registers, display latch,equal and zero outputs, BCD inputsand BCD and seven -segment out-puts. Recently I have used these

Fig. 2. Seven Segmentto BCD converter.

mrinneminuillillifIMI' 0 0 0 0 o 0, 0 0 0 0 0

1 111 0 0 0

t: 0 0 1 0 1 I 0 0 1 0

_, 0 0 I 0 i l 0 A 3,,

,

r

1 0 0 1 0 0

S 0 1 0 0 1 0 0 1 0 1 0 5

f , t 0 G

El0 1 0 0 0 0 0

0 0 0 1 1 1 1 1,i i u

H 0 0 0 0l:! 0 0 C 1 0 0 1 9

..71 10 0 1 3 10 10 C 1 010 1 9

TRUTH TABLE

chips in several applications whichhave been very varied and havecome up with some fascinatingtricks that they will do. If you do notwant to use BCD switches or TTL toload the counter or comparator thenyou can use the chip itself. Oneapplication uses the MK50396 asan up/down counter of minutesand seconds; the counter is alwaysstarted from zero and counts upuntil an external action takes place.This action causes the counter tolatch the display and also totransfer the BCD output into thecomparator register. the display isthen de -latched (the counter hasbeen going all of the time) until asecond action causes the counter tostop. A second sequence is thentimed from zero and compared tothe first by simply comparing thefirst signal from the sequence withthe comparator equal output fromthe chip. If the first sequence wasfaster than the second then theequal will occur before the outsidesignal and vice -versa. If the secondsequence was faster than the first

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

,then this could cause the compara-tor to load a new time for compa-rison. After a sequence of theseevents the comparator would con-tain the fastest time for the group asany that were slower would notaffect the comparator and any thatwere fa-ster would have recalibratedthe comparator. This system couldbe used as a stopwatch in racemeetings where competitors wouldknow if they had beaten the recordby finishing before hearing a bell. Inthe original application no digitalreadout was needed as we onlyneed to know the fastest sequenceand not the actual time of thatsequence, the cost of the systemwas less than £20, if a digitalreadout was required then it wouldadd about f_10 to the cost.

Another application requiredtime of day to he loaded into theMK50396 at regular intervals andthis to be used in conjunction withthe comparator this time withanother external time. The applica-tion was to check the accuracy ofquartz and mains clocks by regular-ly checking the variance from a

known good source - a quartz -dri-ven MM5318. Approximately onceper hour a button was pushed bythe operator; this caused the time tobe loaded from the master 5318and all of the 531 8s under test intothe 50396 and 50397 comparatorregisters. All of the 50397s nowstarted counting at 100Hz until thecounter was equal to the compara-tor. This caused the equal signal tochange state and this in turnstopped the count and held the datain the counter. Any counter whichhad not stopped within one minutewas assumed to have been countingin the wrong direction (ie clock wasgaining not losing) and a flip-flopwas reset to cause down counting atthe next test. The whole system wasthen checked manually at leisureand the fast or slow difference ofeach clock under test was read outand the clock adjusted accordingly- it hasn't been built yet but itproves that you can do a lot morewith some of these LSI chips whenyou start putting them piggy -backstyle. Look into the 50395 seriesthey are almost up to micropro-cessor standard in complexity andability.

Data:GI chips: General Instrument Mi-croelectronics, 57-61 Mortimer St,London W1N 7TD.Mostek: Mostek (UK) Ltd, 240Upper St, London Nl.GI and Mostek chips are availablefrom Bywood Electronics, 68 Eb-berns Rd, Hemel Hempstead.

71

tech -tiA HIGH IMPEDANCE BUFFERAMPLIFIER

This circuit has a voltage gain of justless than unity, but its power gain is

very large indeed. It makes an idealpreamplifier for a high impedancesource signal. The input impedance isabout 800k with the FET specified,but if a FET without a built in gateprotection diode is used, the inputimpedance will be largely controlledby the gate resistor. The circuit has asmallsignal output impedance of about10 ohms and is capable of deliveringabout 7mA p -p into a capacitively -coupled 25 ohm load. The low -frequency breakpoint is about 240Hz,the upper breakpoint is in excess of1M H z.

The principle of operation is

1,F

1.2M

ML10113

6801?,

C182L

simple. The circuit employs a FETfront end to obtain the high inputimpedance, but the transconductance

+12V

of the FET is too low to be useful onits own, and so it is boosted by theoutput transistor, the BC182L.

(COURTESY LIGHT EXTENDERAND HEADLAMP REMINDER (+VEEARTH)

With the ignition switched off, an

earth from the passenger or driversdoor causes C to discharge, the relayto operate and the courtesy lamp to

HEADLIGHTSWITCH

ye

DRIVERSDOORSWITCH

I

light. The relay is operated throughtransistor T2 which is biased on by Ti.T1 and T2 remain on once the door isshut until C is recharged, hence givingapproximately 15 seconds delaybefore the courtesy lamp extinguishes.Operation of the ignition inhibits thedelay switch by biasing T1 off. i.e.courtesy lamp only alight whendoor open. D2 and D3 must be

HEAD ye

LAMP

BUZZER

D1

D2

I PASSENGERDOORSWITCH It

D3

IGNSWITCH

capable of carrying full courtesy lampcurrent.

The headlight reminder operatesonly when the headlights are left onand the drivers door is operated,thereby allowing departure of pass-engers without disturbance.

For --ye earth diode polarities andcapacitor C should be reversed andtransistor types changed.

COURTESYLAMP

72 ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

BARGAIN SALEIdeal for students, mathematicians and scientists

ACCURON897

Scientific

Main Features8 digits. LED displayBasic Arithmetic Functions (+ - ,x. -) plus

V. lixTrig and inverse trig functions

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Logarithms (LN 'LOG e..Change sign key (CHS)Free floating decimal pointBattery saving deviceDegree.'Radian selectionReverse polish notationError indicationIndependent memoryCancel last memory

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Main Features8 digits, green displayBasic Arithmetic

Functions( + -ix -) plus% and V

+ I- change signAutomatic constantFree floating decimal

pointChain calculationsCE cancel last entry keyOverflow indication

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ACCURON 877(Desk Top)

Main Features8 digits, green dis

playbasic Arithmetic

Functions(+ X -(plus`,key

Low power consumption

Automatic constantfour keys memoryChain calculationsOverflow indication

PRICE:

I enclose my cheque for tto cover the cost of my0 897 0 861 0 877 calculator

(please tick)

Name

Address

ORDENDALE LTD. Tel: 01-723 0243367 Edgware Road, London, W21BS

PULSAR,E13.95WE ARE REPEATING OUR SPECIAL OFFER ON THIS DIGITALALARM CLOCK WHEN WE RAN IT LAST YEAR IT PROVED TO BEONE OF OUR MOST SUCCESSFUL OFFERS EVERI OUR PRICEINCLUDES VAT AND POST & PACKING

Full size = 5in across and 3'hin deep.

Pulsar shows the time 0.7in high on brightPlanar Gas Discharge displays (there is a

brightness control on the back). The dot onthe left of the display shows AM/PM, andthe flashing (1 Hz) colon shows that thealarm and clock are working.

A bleeper alarm sounds until the clock istipped forwards. Then the "snooze" facilitycan give you 5 minutes sleep before thealarm sounds again, and then another 5minutes, etc, until you switch the alarm off.The clock also features a mains -failureindicator.

We have a large number of units in stock forthis offer but please allow 28 days fordelivery.

PULSAR OFFERETI MAGAZINE36 Ebury Street,London SW1W OLW.

I enclose cheque/P.O. for £13.95 (pay-able to ETI) for a Pulsar Alarm Clock.

Those not wishing to cut their magazinemay order on their own notepaper.

tech -tipsTAPE HISS REDUCTION CIRCUIT

The circuit in Fig. 1. is used to eitherboost or cut frequencies. When makinga recording, point X is wired to pointR so that treble signals are boosted by10dB, and then during playback, pointX is wired to point P so that the signalfrom the tape, including the hiss,has the treble cut by an equivalent

' amount. The circuit values are such

3.3k

that the overall frequency response,from record through playback, is flatover the range 2.0Hz-20kHz. Thus theoutput signal after playback is

identical with the input signal beforerecording, but the hiss is cut by 10d8.

R V1 sets the gain of the circuit tobe unity at low frequencies (<500Hz);RV2 is adjusted so that the collectorvoltage of Q3 is half the positiverail voltage. When this is set, thecircuit will function without apparent

0 047,1F

-OR

4.7k

P

68052

T

5.6k

distortion with an input voltage ofup to 1.5V r.m.s.

If monitoring during record is notrequired, the same circuit may be usedfor record and playback, with X

switched between P and R as

necessary. If monitoring during recordis required, two circuits are needed,one with X wired to R and the otherwith X wired to P.

For stereo, two circuits are

required.

4ARV25k

PRESET

LOUDSPEAKER PROTECTIONUNIT

The following circuit will protectloudspeakers against overload if thecorrect components are used.

Operation of the circuit is quitesimple, Diode D1 rectifies the signalacross the speaker, which developesa fluctuating DC voltage across C1.When this voltage exceeds a certainlevel, the relay contacts open, whichdisconnects the lodspeaker and ifrequired puts a resistor across thesignal. In the case of valve amplifiersit is usually necessary to keep a loadon the output when there is an inputsignal present, therefore R2 will have

to be included in the design. Withmost types of transistor amplifierstoday, the resistor R2 may be omitted.

INPUT SIGNALTO SPEAKER

O

!D11N4001

R1

(see text)

T ---c15°PF

R1 is adjusted to give adequateprotection at whatever power is beingused. Resistor R1 value should be

selected according to the power atwhich the speaker will need to be

R2

PROTECTEDLOUDSPEAKER

RELAY 18512(Contacts normally closed)

limited and of course the impedanceof the speaker. In my case the resistorR1 was made 220R but this may be

too low for very high power applic-

ations.

74 ELECTRONICS TODAY INTERNATIONAL APRIL 1976

V

INTRODUCTORYPRICES

In addition to National, NI ostek and Caltex clock chips, we are now selling a range ofGeneral Instruments chips.

Until 30th April, 1976, we are pleased to offer the following special prices:AY -5-1202 + Futaba 5LT01The AY -5-1202 chip interfaces directly with the5LT01 to provide the basis for a very simple electronicclock. The hours and minutes can be in 12 or 24 -hourformat and 50 or 60 Hz can be used as the timingsource. The rest of the circuitry is very simple and lowin current requirements - a 100mA transformer witha 20v winding will be adequate.

Special price £9.50

AY -5-1230 + Futuba 5LT01Basically this chip is similar to the 1202 but has manyadditional features. Mainly it has an ON /OFFprogrammable alarm which can be used in sevensegment mode to drive the 5LT01 or in BCD mode todrive logic or TV display chips

Special price £10.00MK50253 + Futuba 5LT0112 or 24 -hour 6 -digit alarm chip. Snooze facility

Special price £10.50

COME AND SEE US AT SEMINEXMarch 22nd -26th. Stand 11. Imperial College, SW7

Please send SAE for free ticket and new catalogue.MISTRAL CLOCK KITUses AY -5-1202 + Futuba 5LT01. Complete kitincluding case £11.58

PRICE LISTCLOCK CHIPS

NATIONALMM5309 7 seg + BCD with resetMM531 1 7 seg + BCDMM5312 7 seg + BCD 4 digit onlyMM5313 7 seg + BCDMM5314 7 segmentMM5315 7 seg + BCD with resetMM5316 Non-mpx alarm clockMM5318 7 seg + BCD (external digit select)MM5371 Alarm clock 50HzMM5377 Car clock, crystal controlled. LCDMM5378 Car clock. crystal controlled, LEDMM5379 Car clock, crystal controlled. Gas dischargeMOSTEKMK50250 Alarm clock (12Hr +60Hz/ 24Hr+ 50Hz)MK50253 Alarm clock (12Hr+ 50Hz / 24Hr + 50Hz)MK 50204 Stopwatch/ CalculatorMK50395 UP/DOWN Counter -6 DecadeMK50396 UP/DOWN Counter-HHMMSSMK50397 UP/DOWN Counter-MMSS.99CALTEXCT7001 Alarm/calender 7 segmentCT7002 Alarm/calender BCDCT7003 Alarm/calender 7 seg. Gas dischargeCT7004 Alarm/calender 7 segCT6002 LCD/CMOS Clock/ watch chip

MHI-5309MHI-531 1MHI-5314MHI-5318MHI-5378MHI-50250MHI-50253MHI-50204MI11-50395

MHI CLOCK KITS1-9

7 357 356.607.35

15 108 358.35

14 0019.50

CHEVIOT ALARM CLOCK24 -hour 4 -digit alarm clock, 0.5" green display, tilt tosnooze. Finished clock - not kit £21.85

ALL PRICES EXCLUDE VAT AT 8%

1-95.695.694.885.694.885.69

10 173.368.147 216.736 73

5.605 60

11 1914 5014.5014.50

7 307.307 307.30

15.00

MHI-50396 19 50MHI-50397 19.50MHI-7001 10 00

MHI CASE Please include 25p post+ packing) 2.95

SOCKETS18 pin 0.6024. 28 or 40 pin 1 00Soldercon strip sockets 0.30

DISPLAYS

1.9 FUTABA PHOSPHOR DIODESLITRONIX 5LT01 5 80DL707, 704, 701 1 48 5LT03 5 80DL727, 728, 721 3 75DL747, 746, 750 2 45 FILAMENTARY DISPLAYS

Minitron 3017F 2 00Itoka 2.5" 8.00

LITRONIX CLASS 11 PRODUCTS Itoka 5" 24.80DL707E. 704E 0 70DL727E, 728E 1 80DL747E, 750E

MHI-707/4 (digit) 0 3"MHI-707/6 0.3"MHI-727 /4 0.5"

LIQUID CRYSTAL1 50 Swarovski 31/2 digit watch disp10 00

MHI DISPLAY KITS

1.96 609.508.50

MHI.727/6 0.5"MHI-747/4 0.6"MHI.747/6 0.6"

12 009 80

14 70

PAYMENT TERMSCash with order. Access. Barclaycard (simply quote your number and sign)Credit facilities to accredited account holders. Pro -forma invoices can be issuedissued.

Please send 20p for post and packing.

ALL PRICES EXCLUDE VAT AT 8%

13YELIDEEBYWOOD ELECTRONICS

68 Ebberns RoadHemel HempsteadHerts HP3 9ORCTel 0442 62757

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976 75

tech -ti STech -Tips is an ideas forum and is not aimed at the beginner.We regret we cannot answer queries on these items.

ETI is prepared to consider circuits or ideas submitted byreaders for this page. All items used will be paid for. Draw-ings should be as clear as possible and the text should prefer-ably be typed. Circuits must not be subject to copyright.Items for consideration should be sent to ETI TECH-TH.6Electronics Today International, 36 Ebury Street, LondonSW1W OLW.

TOUCH FLIPFLOPCMOS IC's have many advantagesover TTL, one being the high inputimpedances. In Fig. 1, two NOR gatesare cross coupled to form a flipflop.If plate S is touched ambient noisecasuses an alternating voltage toappear at G1 input. During the firstpositive cycle G1 output goes negativesetting the flipflop and turning RLA1on. It remains on until the R plate

TOUCH PLATES

0A90

is touched. R1 and R2 must not beomitted since they discharge any

potentials remaining on the platesafter they have been touched, thusallowing the flipflop to have its statechanged rapidly. R1 and R2 alsoprevent any static charges building up,thud damaging the IC, while thesupply is disconnected. 22Mohmresistors are difficult to get so two10Mohm resistors in series may be

used.The unit may be left on continually

as a milliameter indicates no currentflow at all in the off position. If RLA1is omitted TR 1 collector becomes aTTL output with a high fan out.Connect the inputs of G3 and G4 toground if they are not to be used. Thetouch plates can be placed several feetfrom the IC provided screened cable isused for them.

+Vcc (5-12V)

22M52.R1

2 5

22MSZR2

16

RLA1310052

CD4001AECMOS

6k8

HOUSE EARTH

TR1BC108

OV

IC TAPE -HEAD PRE -AMP

This circuit is suitable for a tapespeed of 3.75 inches/sec. and providesa risin@ gain at low frequencies (about40 dB below 100 Hz) a minimum gainof about 15 dB around 2-3 kHz and a6 dB boost (to about 21 dB) above 10kHz for reasonable compensation. Alow noise op -amp is used.

76ELECTRONICS TODAY INTERNATIONAL APRIL 1976

oiP

Complete the coupon andwell sendyou

ourcomplete,newcatalogue.

The new Heathkit catalogueis now out. Full as ever with exciting,new models. "I make building aHeat hkit even more interesting andsatisfying.

And, naturally, being Heathkit, every kit is absolutelycomplete. Right down to the last nut arid bolt. So you won'tfind yourself embarrassingly short of a vital componenton a Saturday evening --when the shops are shut.

You'll also get a very easy to understand instructionmanual that takes you step by step through the assembly.

Clip the coupon now (enclosing a 10p stamp for postage)and we'll send you your copy to browse through.

With the world's largest range of electronic kits tochoose from, there really is something for everyone.

Including our full range of testequipment, amat cur radio gear,equipment and many generalinterest kits.

So, when you receive yourcatalogue you should have hours of pleasant reading.

And, if you happen t o be in London or Gloucester, callin and see us. The London Heat hkit Centre is at 233Tottenham Court Road. The Gloucester showroom is nextto our factory in Bristol Road.

At either one you'll be able to see for yourself t heone thing the catalogue can't show you.

Namely, how well a completed Heat hkit performs.Heath (Gloucester) Limited, Dept.ETI - 36 Bristol Road,Gloucester, GI2 GEE. Tel: Gloucester (0452) 29451.

Digital IC tester. Digital electronic stop watch.

r

II-

IME

FREESOLDERING IRON

WORTH

Sa50with all orders over £30

ISO

4,1

Heathkit Modulus. A new era in Hi-Fi.

The newHeathkit catalogue.Out now. FREETo: Heath (Gloucester) Limited, Dept.ETI-46,Gloucester,G1.2 6EE.Please send me my Heathkit catalogue. I enclose a 10p stamp for postage.Name Address

NE AIN

Schturnberger

Postcodenimer.-- Full details in the catalogue. Offer available finr limited peri xi only.

ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

Mr

77.

news digestSCIENTIFIC ANALYSIS ON THEPOCKET CALCULATORby Jon M. Smith, Wiley-Interscience

Virtually all of our readers own pocketcalculators and many of them areprofessional engineers and scientists.It is for these readers that we haveintroduced this book to ETI BookService. It is aimed at the engineer/scientists who has to perform sophist-icated numerical analysis on anycalculator from the Novus 650 to anHP -65. The author in fact stresseshow much analysis can be performedon a simple, 4 function machine,and gives routines for calculatingsin x, cos x 'etc. (Personally, I think it'seasier to look up the tables, but ifcan't find them it's nice to knowyou're not completely stuck.) Thebook scores a big plus on the followingpoints: It is authoritative, compre-hensive, and forces the reader tothink about what he is doing. Thecontents range from elementarytabularanalysis of data, through suchtopics as Bessel Functions, FresnelIntegrals, Fourier Analysis, NumericalIntegration methods, Linear SystemsSimulation, Approximation byChebysher and Rational Polynomialsand Statistics, with a very good finalsection on the Programmable Calcul-ator. As can be seen, this is not a bookfor the mathematical novice, nor is itlight reading. Equally well. it is

perhaps a little awkward to use forquick reference. Overall, however, thisis THE book for calculator users whowould like a bit of intellectual exercisewhich will pay off in giving them anorder of magnitude increase in valueof their machines.

MINI-FETSThe Siliconix J401/406 and J410/412series of monolithic n -channel dual-JFETs are presented in 8 -pin MiniDIP package. The J410/J412 are forgeneral applications while the J401 to

J406 offer a high performance forOp Amp front ends. The J401 featuresCMRR >95dB; offset 5mV (max) anddrift 10µV/0C (max): Details fromSiliconix Ltd, 30A High Street,Thatcham, Newbury, Berks RG134JG.

78

SWEEPING RADARDEVELOPMENT

Ferranti have designed and built aradar system which fits inside therotor blades of a helicopter, andutilises these as the aerial. This enablesa very narrow beam to be produced,giving a very high resolution picture.This means, amongst other things,that the helicopters will be safer tofly in poor visibility conditions, andsurvivors in heavy seas can be detectedwith vitual certaintly. Flight trialsbegin early this year.

HP CALCULATOR BONUS

HP -45 OWNERS who are feeling a bitpeeved following the introduction ofthe HP -25 calculator by HewlettPackard can take heart from the factthat the HP -45 can be used as a stop-watch and 12 hour clock.

It's a little bit tricky, but becomeseasy with practice. To trigger the beastinto 'stopwatch mode' you press RCLand then simultaneously press thekeys R STO and CHS. The displaywill then appear as four pairs of zerosrepresenting hours, minutes, secondsand hundredths (from left to right).

Pressing CHS will stop and start thetimer, EEX will blank out the hund-redths, and CLX will reset the display.The unit can be switched back to'calculator mode' in two wayspressing ENTER t clears the display,while pressing the decimal point keywill reformat the display toH.MMSSloo in either FIX4 orFl X6 (depending on whether hund-redths were displays).

Time splits may be stored bypressing the desired register numberwhile the timer is running; pressingthese keys while it is stopped willrecall a time to the display. Pressing 0accesses the LASTx register and recallsthe time at which the timer wasstopped. Times may be entered asabove and the calculator switched to'stopwatch mode' to use the times asstarting values.

Now here's the catch: it's wildlyinaccurate, since the clock rate is notcrystal controlled However,as the chip is the same (we believe!)as in the HP -55 this problem could beovercome by the few daring peoplewho may be willing to rummagearound inside it. We apologise to HPfor ever having mentioned this, as weunderstand that they prefer not toknow about it!

Continued from page 8

KEEP AN EYE ON THE PUPILS

After almost 10 years of workHoneywell scientists have produceda device that promises to becomean important teaching tool.

The development - called a remoteOculometer - focusses a beam ofinfra -red light on a subject's eyes, anda special TV camera records theminute changes made by the eyes'movements. This information is fed toa signal processor, which calculates theeye movements and makes it possibleto produce a television picture onwhich a black dot shows the exactmovements the subject's eyes makewhile looking at a scene.

It is believed that the Oculometercan play a major role in the field oflearning disabilities. Scientists areworking to enable a paralysed personto use his eye movements to activatetypewriter keys.

FREEHAND WITH COMPUTERS

A device called CHIT (CHeap InputTerminal), invented by NationalPhysics Laboratory, makes it easierand cheaper to have computing com-plexes recognise handwriting. Whenlinked to character recognition system,it is possible to doodle into computers,and have them understand it! Thismeans that ordinary pencils/pens canbe used, and places like banks andshops can now have a viable signatureverification system.

Chit operates from two resistivestrips at right angles, spaced by a smallair gap. As a pen moves across thetablet, the pressure causes the twostrips to meet. A current is passedthrough them, and the voltagedeveloped is an analogue representat-ion of the pen position. Switchingbetween strips, to sample the voltagedeveloped, gives x and y outputs.This is done very rapidly, and theoutput fed to the computer in binaryform.

National Research DevelopmentCorporation, Kingsgate House, 66-74Victoria Street, London SW1E 6SL.

TTLs by/400 13p7401 149.7g0,2 14p

41 it::7405 16p7406 38p7407 36p7408 14p7409 20p7410 13p7412 2397413 32p7414 6097416 3397420 14p/ 422 18p7423 34p/425 30p7427 37p/430 74p7432 25p/437 25p7440 1497441 6597442 60p7447 75,37448 713p

7450 15p7451 161)7453 16p7454 16p7460 1Sp7470 27p7472 25p7473 30p7474 30p7475 45p7476 3097480 50p7481 9S,7482 709

TEXAS7483 80p7484 95p7485 120p

;::: 270p7490 40p7491 75p7492 4597493 40p7494 7597495 65p7496 78p74107 30p74121 30p74122 40p74123 68P74141 65p74151 72p74153 85p74154 150p74155 76p74156 76p74160 99p74161 99p74162 99974163 99p74164 120p74166 126p74174 120974175 85p74180 100974181 298p74182 82p74185 135p

-24190 144974191 14.4p74192 120p74193 120974194 108p74195 75p74198 198p74199 1809

C-MOS LOGIC

I.Cs NEW

LOW PRICES

CD4000AE 19pC040014E 19pCC:140024E 19pCD4009AE

679C04011AE 19pCD40124E 19pC040134E 559C040164, 50pC04017AE 120CD401/34E 175pC040204E 250pCD4022AF 1709C1340234E 19pC040244E 120pC040254E 19pC0402641 196pCD4027AE 75pCD40284E 140p00402974 175pC040304E 5SpCD40424E 137pC04043AE 202p

.0040464E 140ACD4047AE 154pCD4049AE 63pCQ40544E 196pC0405541 196p034056/LE 135PC1340604E 2290C040694E 37pCD4071AE 27pCD4081AE 'tapC040824E Z7pC045104E 130PC04511AE 200pC045284E 120p

i ._ AMPS1458 D-i, OP Amp '1 Come *1 P.^ OIL lop3014 Et Comp to pin Wt. 3593130 03SmOS , fli Pow, MosFet 8 pc DIL

10...0P3900 Clued Op Amp 14 pin OIL ',OP367 PET Op Amp

709 Pet CompTO 99 275p8 1, p,r, DIL 3pp

741 Ini . Comp 8 14 p.. Dil 25p747 Dual 741 14 pin OIL 22p748 E.1 Comp Rpm OIL 3P776 Programmable Op Ainp TO .5 1409

AC126 12pAC127 12pAC128 11pAC141 18pAC142 189AC176 11pAC187 13pAC188 12pA0149 43p

TRANSISTORSBF 182 33pBF184 22pBF185 22p

'13F194 10p'BF1 95 9pBF196 14p".197 151,BF200 32p

25697 13p2N698 3092N706 12p25708 1892N918 40p2N928 2092N930 lap251131 18p

2N41231.1,3,,f 44218%6 210,8p ,,,

254347130p.2N4348160p.22NN44440.1 3300pp

40360 40P40361 38p

'OA90 7p.00AA99,1 7p

7p04200 8p.0A202 10p.:NN491,448 .ip4p

LINEAR I.C.s A0161 36p ; SF257 32p 251132 18 40362 40p RECTIFIER__

.T1.0 25pCA3028 OM Cascade Amp 105 90pCA3046 5 Transistor Array 14 pin OIL 509

Clued Low Noise Amp 16 pm OIL 200p.CA3089E FM IF System 16 pin OIL 200p'CA3090E FM Stereo Multi Dec 16 pin DIL 160P

la80380C VCO Fun Gen 14 , OIL 2759LM380 2W Audio Amp 14 pm DIL 90PLM381 Stereo Neamp 14 pm 011 160PM252 Rhythm Generator 16 pin DIL 900PMC131OP FM Stereo Dec 14 p. OIL 175pMC1312MC1314 SO Quad Dec 14 pin DIL 1100pMC1315MC1495 Mulhplier 16 , DIL 3.71)MC1496 Sal Mod/Demod 14 pin OIL 100p.wcAuccie 1. 4W Audio Amp PCB S°PMFC.6040 Eieciroruc Atienuator PC8 9C.NESS5 Tmer 8 p,r, OIL 40p253823

0E556 Dual 555 14 pin OIL 100p'NE561 PLL with AM Deena! 16 pin DIL 325pNE562 PLL v.., VCO 16 pin DIL 325956563 PLL FM / IF Demod 16 pin OIL 300p5E565 PLL 14 pm OIL 2009NE566 PLL Fun Gen 8 pin OIL 150pNE567 P11 Tone Dec 8 pin OIL 15092567 Dual 567

stu72733 Video Amp14 pin DIL 370p

-784800 5W Audio Amp14 pm OIL 120pOIL..2225N51322.99,22366GY,784/310 7W Audio Amp OIL

90,"°9134820 2W Audio Amp OIL 80p

XR2240 Pro, Timer ,C.ounier 16 pin OR. 370915414 TRF Radio Receive, 10,8 110p

..

40162 36pAPI 14 lapAF115 18pAF116 189AFT 17 189AF139 33pAF239 38p8C107 9p

BC108 9pBC109 10pi3C109C 12p

13C147 7pBC148 7pBC149C ap 1

'80157 lipBC158 10,3 '

:80159 11pBC169C 12pTUNNEL8C177 18pBC178 1798C179 18p

.BC182 10p8C1 83 10p8C184 lipBC187 30p

BC212 11pBC213 10p

'U839 30p1BFR40 30pSFR,. 30PBFR80 ' 309BFR88 309BFX30 30pBFX84 26p8FX85 25pBFXB6 25pBFX87 20pBFX88 24pBFY50 16pBFY51 15pBFY52 16pBRY39 34p85X20 189

"BB..110085 2154.4

.1E340 45pMJE295599pMJE305565p

,V1PSA06 30p hAPS412 SOpNAPSA56 32pMPSUO6 62pMPSU56781.0C28 65p

25130421p2N1305 21p25130628p251307 289251.308 28p2N1309 28p251613 20p251711209251893 30p252218 21p252219 20p252220 191,252221 20p252222 20p252369 149252484 30p

252905252904 2200pp

252906 20p2529260. 7p25292613 7p2N29260 8p

2N 3054 45p2N3055 50p

40364 120p40409 55p40410 55p40411 2259

40595 85p

FETs.

PM F102 30pMPF103 30p-sAPF104 30p-MPF 105 30p253819 22p'253820 50p

50p255457 30p

.225555445580 330opp

MOSFETs

35140 85,35128

3N 141

120p40603 58p40673 58p

8Y726 12p8Y127 12p

BYZ10 459

.7, , P44 657

154001 5p

815'40307 457ppp

ZENER3.3V 10 33V400mW 9p1W 18p

AEY1 I 659

VARICAP25p

NOISEZ5J 100pVOLTAGE REGULATORS FIXED PLASTIC - 3 Terminal

Amp Ve 200mA (105)5V 7805 140p 790500V

12V 7812 1409 7912 2009 7812 99p15V 7815 140p 7915 2009 7815 99918V /818 140p 7918 200p - -24V 7824 140p 7974 2009 _ -.15VARIABLE Data sheets on regs723 "l,. PIN L.:, 45p at 10p each + s.a e

TRIACS OTHER400V 500V 40430 99p

3 Amp 85p 120, 1509 40486 9996 Amp 88p i 50p leo, 40669 99,

10 Amp 109p 180p 195p BR 10QAmp 145p 210p 250p pt., 21p

BC214 149 0C35 55p13C478 30p 0C36 60pBCY70 .p 0041. 2 1596CY71 229 :0c0C475, 151,80123 100p 20p80124 65p TIP29A 40P

TIP3OA 489

253439 67p2534421409.253702 lip:252703 11p253704 11 P

'2N3705 lip253706 109

..,...T1,43 27p BRIDGE252160 809 RECTIFIERS2N2646 38p2548/1 30p 254 100V2Op

1A 50V 22pPUJTSCR-THYRISTORS BIAn°7001: Strrd 140p

C10613lA 50V 10514100V 105

40p 44/400V Plastic 55942p MCR101

1A400V 705 S2p 054.15V 1092 25p14600V 105 70111 2N352534100V Stud 49p saia0ov 10.66 90p34400V Stud 750 25444474100V TO5 + 05 84p SA 600V

Piasi.c 1859

80131 36pBD132 40p

80135 43pgcit 3g 63781:1140 70p8F115 22pBF167 23pBF 170 23p13F173 25p

TIP31A 52pTIP32A 58pTIP33A 90pTIP34A 11 5p119354 225pTIP36A 270pTIP41 A 65pTIP42A 70p

253707 lip753708 Sp'253709 9p253773

2209253866 90p2N3903 lap2N3904 20p

to 100V 24p'2N6027 48p I A 400V 27pDIODES IA 600V 30p

SIdNAL 2A 50y 30p0A47 7p .24 100V 35p

.0A 70 9p 4A 100V 60p.0481 Elp, 6450v 6090485 lOpi 6A 100V 65p

OPTO-ELECTRONICSOCP70 30o SEVEN SEGMENT DISPLAYSOCP71 1209 3015F 0 3 in Olt 120pORP12 SOp MAN3M 0 127.e PC8 110pORP60 75p 01704 0 3 rn OIL 1359ORP8 1 85p 01707 0 3 in Oil 1359255777 40p 01747 0.6 .. DR 2259

LEDS: TiL209 Red 14p TIL21 1 Green 30p744009 705 + FIS 909 255060BA 50V Plastic 130p 0 BA, 30V 10.92 34p

124400V Plastic 1600 .255062,6A i00v Pus. 1609 0 84, 100V 70.92 37p164400V Plastic 1809 '705064164600V Plastic 220p 0 84,200v 70.92 40p

Minimum Order £2 All first grade devicesP&P 209 Visitors by appointmentPlease add VAT to 'total Gov' Colleges

BFI 77 26p TIP2955 70pBF , 7B 2ap .2TX108 10pB,, 79 339 .ZTX300 13pBF180 33p 1TX500 15p8F181 33p ZTX502 18p.

welcomeetc orders accepted

253905 18p'2N3906 20p'254058 1Sp'254059 10p2N4060 13.

TECHNOMATIC54 SANDHURSTTel. 01.204 4.333

VAT RATESALL ITEMS AT 8, EXCEPTwhere marked which are rated

t 2596

LTD.ROAD, LONDON, NW9

LOW PROFILE OIL SOCKETS BY TEXAS8 pin 13p, 14 p.n 14p. l6 pin 115p, 24 pin 50p.

IN LA R + TO.

Fully branded devices by Texas. -RCA-Motorola National Mullard etc

Functional featuresof the system include

Basic arithmetic + - x. ,Trig functions (sin. cos, tan)Inverse Trig functions (sin -1. cos -1. Ian 11

Logarithms (1n. log) (Anti -logs (e x. 10 x)Exponentiation (yCombinatorial functions (n1. (:). (n) tdNormal Distribution function (Pr(x))Gamma function (f(c))Arithmetic mean. standard deviation.rt of sum of squares. normGroup operations (1.:-1, o. 7 ,o

Group controls (kJ .CL GRPConvenience functions (1 x. x7 ,/x tr)Flexible memoryinntrol (STO. RCL.Factor reversal (XY)Degree/Radian selection (Trig or Inverse Trig)Automatic error detection and displaySeparate Clear operations (CE. CL. CLF. CLGRP

SC60 ADVANCEDSCIENTIFIC

The SC60 is the most advancedscientific and statistical calculator inits price range.

O 3 memoriesO 50 functionsO 66 keyboard commandsOperating Femur*.Alciebraic (node entry Two nestedparentheses levels Number entry ,nfloating point or scientific notation Automatic selection of current notationfor result display (scientific or floatingpoint) 10 digit mantissa; 2 digitexponent Sign selection and display(mantissa and exponent) Full chainCalculation with any function sequence Three user addressable memories 'Protected' memory group includes -

Sum memory - Sum -of -squares memory- Index memory

variance sq

MEMORY three addressable memoriel which can also bs used automatically for statistical lunclio.. with suemanor, turn of squares memory and lodes memory plus index registerACCESSORIES is ior .4 sciRntic

SC60.10 MEMORYAlso available is the SC5010 which hat 10 operator accessible memories with protected group memory whichincludes lam Mer110ry. SUM 013,1211111memory. and inlet memory £64.95 inc. VATp. p.

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

SC44 SCIENTIFIC(1) Operating features of the system

Number entry in floating point orscientific notation

Automatic selection of correct nota-tion for result display (scientific orfloating point)

Algebraic problem entry Two parenthesis levels 8 digit mantissa 2 digit exponent Sign selection and display (mantissa

and exponent). Full chain calculation with any

function sequence

1 YEAR WARRANTY

ACCESSORIES INCLUDENicol rechargeable batteries. A/C adaptor: chargerleatherette carry case, instructions. 1 year guaranteeweight 330 grams

We repair most makes of calculators. send s.a e forquotation

r please send me SC60 - E.54 inc VAT, p &por SC60 10 - E64 95 in VAT, p &pOr SC44 E34 56 Inc VAT. p &p

£34.56inc.

VAT & pp.p.

ADDRESS

Orders to KRAMER & CO., 9 October Place, Holders Hill Road,London NW4 1EJ. Tel 01-203 2473 Telex 888941 attention KRAMERRegistered No 1797716. Export orders invited

79

MINIADS FOR DETAILS ON ADVERTISING INMINIADS, OR ELSEWHERE IN ETI,

CONTACT BOB EVANS, 01-730 8282

PRINTEDCIRCUITS

ad

HARDWAREReadily available supplies of Construc-tors' hardware, Aluminium -sheet andsections, Printed circuit boards, top

-

quality for individual designs.

Popular E.T.I. boards always in stock.Prompt service.

Send 15p fC.r catalogue.

RAMAR CONSTRUCTOR

SERVICESMASONS ROAD

STRATFORD-ON-AVONWARWICKS. Tel. 4879

CABINET FITTINGSfor Stage Loudspeakers and Amplifier Cabs_

Fretcloths. Coverings. Recess Handles. Strap Handles.Feet. Castors. Locks and Hinges. Corners. Trim,Speaker Bolts, etc.. etc

Send 2 x 81/2p Stamps for samples and list.

ADAM HALL (E.T. SUPPLIES)Unit CL, Stadine Works, Grainger Road

Southend-on-Sea, Essex

TREASURE HUNTING! Amateurs andProfessionals world-wide enjoy success withC. Scope Metal Detectors. Simple to operate,

- lightweight, ultra -sensitive. Prices from£26.24. Tel. Ashford 29141 now for fulldetails.

The Proprietors of British Patent No. 1043741,for -Method and apparatus for producing smallelectrical components- desire to negotiate forthe sale of the patent, or for the grant oflicences thereunder. Particulars from Marks &Clerk, 57.60 Lincoln's Inn Fields, LondonWC2A 3LS.

RELPAK TESTED DEVICESLow Cost Bargain Components NO EXTRAS

50. 100-82009W Resistors 75p IC Socket Pins -100. al 75p50. 11,81,21),W Resistors 75p /emus. 2.330-400mW 9p50. 101,82KITAW Resistors 75p 114001 509 IA 6p

50.1.-8200,W Resistors 75p 194002 1009 IA 7p

Egan Pots Lin. 11(.2M2 ea. 16p 194006 8009 IA 13pBridge Recs 509 %A ea. 14p 194148 Signal Diode 4

Bridge Rocs 509 2A et. 37p MJE305.5 MPN 70pV1414IC Radio. en. E1.36 kiJE2955 PRP 99p292646 Unitunction. ea. 55p 6 Led, 01 299 75p

TECHNICAL DATA AND ASSISTANCE FOR YOURPROJECTS

MONEY BACK GUARANTEE -- SAE for LISTSRELTRAN LIMITED (Dept. ETI)P.O. Box 18, Camberley, Surrey

CMOS. Gates 4001, 4011 17p. Counters4017 83p; 4040 86p. 8 -pin DIL ICs 74124p; 555 44p. TRIACS (Plastic) TAG 250400V/ 10A 67p (34- 64p). DIAC 19p. MiniMains TRANSFORMERS 100mA 6-0-tV85p; 12-0-12V 95p. 2N6027 (PUT) 30p;2N3055 36p; 1N4004 6p; 13x8C14880p*; 10x8C158 80p'. P&P 15p ADD 8%VAT (-25%) T.K. ELECTRONICS, 106Studley Grange Road, LONDON, W72LX.

P.C.B.s andCOMPONENTS forE.T.I. PROJECTS

P.C.B.'sActive CrossoverActive CrossoverLogic ProbeLogic PulserLogic Tester50+50W Power ModuleSimple CMOS TesterSimple CMOS Tester . .

Tone Burst Generator .

ETI 433AETI 4338ETI 120ETI 121ETI 122ETI 422ETI 123a

ETI 124Exposure Meter ETI 951Audio Level Meter ETI 438

88p86p35p35p

£1.85£3.00

70p

83p35p75p

New protects available at 1.25p per sq. cm. forsingle sided or 1.5p per sq. cm. for doublesided (min. 35p).

COMPONENTSETI 120 £3.68ETI 121 £2.30ETI 123 £4.88ETI 124 £8.67

ETI 951 (inc. case)£3.15

ETI 122 £17.00ETI 438 £8.80

Prices inc. VAT and postageSend s.a.e. for full list of boards andcomponents available.Mail orders, please, to: D.B.M. Products

Unit 14, Southern Road. Aylesbury,Bucks.

Greenbank ElectronicsFREE!

Data and suggested circuits for AY -5-1 224 and MK 50253 clock chips,details of PCB's and component kits for AY -5-1224, data sheets forLED 0.3" and 0.6" displays.

NEW!PCB TO SUIT AY -5.1224 clock chip 95p

4 DIGIT KITSKit includes: PCB, AY -5-1224 chip, 4 LED digits, transistors, diodes,resistors, capacitors, solder pins (success guaranteed), with 0.3" digits£9.95 (0 6" high digit version also available)

CLOCK CHIPSAY -5-1224 4 digit1.2,124 hour £3.66MK 50253 4/6 digit alarm clock £5.50

" LED DISPLAYS (ECONOMY TYPES)"DL -704E 0.3" common cathode ..... . ........ 85p

DL -747E 0.6" common anode £1.70

Add 8% VAT to all prices, post, etc. 10p + VAT per order.GREENBANK ELECTRONICS (Dept. T12E)

94 New Chester Road, New FerryWirral, Merseyside L62 5AG

Tel: 051-845 3391

PRECISION'POLYCARBONATE CAPACITORS

440V- All High Stability - Extremely Low LeakagekANCE:D(S-IENSIONS ,VALIX . (rem), .. P.CC .. . ,

Fl L 13V Raeie; 1% 2% 5%

e'. 3- .27 - 11) -.7 5 Ifs,' 0.47aF 67p 59p up0.22aF 33 16 64pr 71.0µF 82p 82p 521)

0.25,, 33 16 87p '2.2,, 913p 75p nip

.0.47,, 33 19 80p4.7, £1.12 f3.13 94t,

0.5,, 33 19 87p' 16.8,, £1.96 E1..38 £1.13

0.68aF 50.8 19 93p 10y, .,40 £1.95 01.64

1.0µF 50.8 19 E1.03"15,F £3.22 C2.79 C2.24

2.06F, 50.9 25.4 C1.44 .22,1' £4.28 C3.68 t3.06

'TANTALUM BEAD CAPACITORS - Values available: 0 1. '

0.22, 0.47, I O. 2.2. 4.8, 6.iµF at 15V/25V or 35V; 10,, at 160 /20vor 2.5V; 22.0µF at 6V or 16V; 33.0,., at 6V or 10V; 47 00, at 3V or6V; 100.0,S at 3V. ALL at 10p each, 10 for 95p.50 for £4.TRANSISTORS & I.C.'s

ACI28 14p1 BC268A/384 lapACI76 Illp. BC547/558A 12p

ADI49'30p BBCDY712

12p

AFI78 13 /132 39p

BC107/8/938,,,' 22p

24pAF239

12p 28p

:BC:i45.3174154/9 10p 81184 22p

BC157/8/912p 5F194/185, 12,12p BF196/197. 12p

18p BF200 27p

BCBCV872/183L lip BF262/263. OpBC183/183L I 1p 13,50/51/52 20p

..13CBC2'412/121"12LL 14p14 irk8584/'-/' 2,1,'P13C213/213L -1Ip 136101 41p

'BC211/214i. I I p GFT872 25p

0071 12p

252926G 12p

2529260 I Ilp2N2926Y 11p

2N3054 63p

2N3065 50p2N3702/

3704 lip'

TiP30A 52pTIP3IA 55pTIP32A 64pTIP3055 55p.

MPUI31 49pNE.5.5.5 61p741C 32pZN414 C1.15.SN76013ND

8C267 0C44/0045 14p

POPULAR DIODES-IN914 6,8 for 45p. 18 for Sep; I N916 8p,6for 45p. 14 fcr 90p; 1S44 5, 11 for 50, 24 for C1.00; 154148 5p, 6for 27p, 12 for 48p; 1N4091 5,sp; 002 6p; 003 (Pip; 004 7p; 006 lip;007 Pap.LOW PRICE EENF.R DIODES-400MW. Tol. ±5% at 5mA.Values available 3V. 3.3V, 3.6V, 4 7V, 5.1, 5.6V, 6.2V. 6,8,7.5V, 8.2v, 9.IV, 10y. II, 12V. 13V, i3 I5V. I6V, 18V, 20,,22V. 24V. 27V, 30V All at 7p each; 5 for 33p; 10 for 63p. SPEC IA LOFFER: 100 Zellers for C6.00. RESISTORS -High stability, low noise carbon film 5,..AW at40'C. ,SW at 70.C. Ell series only -from 2.20 to 2.2M1). ALL at1p each, 9p for 10 of any one value. 70p for 100 of any one value.SPEC!AL PACK. 10 of each value 2.20 to 2.21101730 resistors),ES.

SILICON PLASTIC RECTIFIERS -I.5 amp. brand new wireended 0027; 100 P.1 V. 7p (4 for 26p). 400 P.I.V. Sp (4 for 30p).BRIDGE RECTIFIERS -2, amp. 200V 40, 350v 43p, 60(W Sip."SUBMINIATURE VERTICAL PRESETS-0.IW only. ALL atSP each; 500. I./ 2200, 4700. 6800. 1k0. 2.2k0. 4.7k17. 6.8k0,

15k0, 22k0, 47k0. 68k0. 1000. 250k0. 680k0. IMO.2.5M0.9,40.PLEASE ADD I5p POST AND PACKING ON ALL ORDERSBELOW E5. ALL EXPORT ORDERS ADD COST OF SEA/AIRMAILPLEASE ADD 8% VAT to all items except those marked with

which are 25,Send S.A.E. for lists of additional ex.stock items

Whole.le price lists available to bona fide companies_

MARCO TRADING(Dept. D3)

The Old School, Edstaston, Nr. Wern, ShropshireTef.-WhixalliShropshire) (STD 094872) 464/5-,

(Propos. Minicost Trading Ltd.)

LOW-COST I.C. MOUNTING for any size DILpackage. 100 Soldercon sockets 60p. 7 and8 hole plastic supports 5p pair. Quantityrates. SAE details and sample. Trial pack60p. (P.&P. 10p/order). P.K.G. ELEC-TRONICS, Oak Lodge, Tansley, Derby-shire DE4 5FE.

SEA,500Capacitor

,sc Discharge

IGNITIONII MAXIMUM PERFORMANCEIMMAXIMUM ECONOMYMEASY COLD START

SYSTEM IProfessional photoelectric ignition using L.E.D. light source and reflective disc. Thismachined aluminium disc gives a timing accuracy far superior to other methods and issimple to fit. Unit housed in diecast box x x Price E18.80 (Kit £16.801State car/model/measurement across cam lobes.

SYSTEM IIContact breaker model as above less sensor. Price £12.80 IKit 00.801 IVI/C Twin unitPrice £15.00. S.A.E. for descriptive leaflet - ALL UNITS IN STOCK Mail orders toCOI Electronic Systems Ltd, 275 Vale Road, Ash Vale, Aldershot, Hants,Demonstration/Callers to Hillside Motors, 292 Carshalion Road. Carshalton. Surreytelephone 01-642 9973.

80ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

s 0 12, - 0.2 I INFRA Pm

LED RED 16p551,15

1OP Seal lead 49p27p up 1 5mW ELIO

6.'W £1.55Pan. . Gi Ycl, 1pOR . 27p 3.3p 1 ow', 55p

OPTO-ISOLATORSIL4 1.5kV 150kHz El035025kV 5MHz E2.25

sots 50V 100V 400V10514 25p 271, 46p1066 3A 27p 35p 50pTRIAC T05 2A 400V 60p

Data Boa with all OPTOAC125/ 6/ 7/815PAD161/162 40PAF117 24AF124,5/6. 7

3'1P8,107/6 9 9P8C109C 12P1.47' .9 113P8C157/8 9 I 1p9C167/8/9 11p

8C1&98/9 17p12p

8

8C182/3/4,L1lpBC186/7 30p8C212/3/41. 12p1Icy70/71 .7713p1,4194,5 12p8F196/7 14p.400808,50/51 16pBFX29 30pBFX84 24pBSX19/20 16p0071 10p75706 10p2N1711 20p252219 20p252904/5/6/7

1511252904, 5/6418p252926(R) 7p

2N2926(G) 12p2N3053 15p2N3054 45p2N3055 41p253702/3,4 12p753903/4 ,I. 6

16p2N2646 35pMPF102 40p253819 25p253823 30p

VOLTAGE REGS.5V 7805 Plastic

12V 7812 1 Amp15V 7815 all18V 7818 E1.50723 DIP14 50p'-BRIDGE RECTS.2A 50V 30p2A 100V 36p2A 200V 41p24 4COV .6,

8R100 D.ac 21p-,15914 3p154001 5p154002'3 6pIN 4004/5 7p

13p154148 4P,0A47 ..0470 0A79 8p0A81 0490 7p049/ 0495 6p04200 6p04202 .

ZENERS UM2.7 33v 9p

NE565V 609,E556 (1.10LM380 E1.00Z5414 El 107400 16p

D.I.L. SOCKETSr.8.p. 12p

14.pm 13If16., 14pMica , bushesT031.066 SpDale Pen 70P

OP. AMPS .709 all 25p741 8 pin 29p748 0 I L 36,

PRICES INCLUSIVE + 15p F. SP (1st class)

ISLAND DEVICES. P.O. Box 11. Margate. Kent

TURN YOUR SURPLUS capacitors, transistors,etc., into cash. Contact COLES-HARDING &CO., P.O. Box 5. Frome, Somerset. Immediatesettlement.

START YOUR OWN BUSINESS REWINDINGELECTRIC MOTORS

This unique instruction manual s'iows step by step howto rewind motors. working part- or full-time, withoutprevious experience Everything ylib need to knoweasily explained, including where to obtain materialshow to get all the work you need, etc etcA go(dmine of information and knowledge Only £3.65+ 28p P&P from Magnum Publications. Dept ET5Brinksway Trading Estate, Brinksway. Stockport. SK3OBZ Overseas Distributors wanted

GLASS FIBRE P.C.B.s. Send 1.1 masterand 30p per board plus 7p per sq inchtinned or plus 9p per sq. inch drilled andtinned Send for quotation on double sidedboards Discount for quantityPROTO DESIGN, 4 Highcliffe Way,Wickford, Essex, SS11 8LA.

DETECTOR PRODUCTSManufacturers of the popular "SolInvictus" Metal Detectors. Sup-pliers to Trade throughout the

United Kingdom and Abroad.

Trade and Retail EnquiriesWelcomed.

Or call at our showrooms at58a KING ST., BLACKBURN

LANCS.Tel. 62561 or 54105

XL, cic TD. P.O. BOX 34,CANTER BU RY.CT1 ITT

ALL PRICES INCLUDE P&P AND VAT.

ANTEX SOLDERING IRONS,with slide on 8. off bits) 5W 'C' miniature irons3/32';1/8'; 3/16'bits-each'C Elements18W 'G. miniature irons3/32'; 1/6'; 3/16"bits-each'G' Elements15W' .CN'Low leakage irons3/32", 1/8'; 3/16')as-each'CCN' Elements.,5W'X25' Low leakage irons3/32'; 1/8'; 3/16"bits-eachX25. Elements

'SK2',SolderingKi,

£2.30£0.45£1.10£2.50£0.45£1.35£2.70£0.45£1.50£2.30

ST3 Stands -for all models £1.10SOLDER in Bib dispenser £0.45WIRE STRIPPERS CUTTER £0.85HAND DRILLS Leytool precision,coi-noact , 5/16" chuck £3.99AERIALS Extend 15-120cm £1.50CASSETTE 'Head Demagnetisers'Shaped pole -saves time £3.65EARPHONES Stethoscope £1.25MICROPHONES Dynamic £2.15PRINTED CIRCUIT KITS -Allitems for producing p.c's £3.99

£0.47 SIGNAL INJECTOR -Audio through£1.15 video signals,self contained £4.250.85 SPEAKERS -75mm di? 8n. £1.00

PLEASE MENTION EllWHEN REPLYING TO

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INDEX TO ADVERTISERS

Ambit p.44AndromedaElectronics . . p.16B.H. Components . p.83B.I.E.T. p.15Bi-Pak pp.4 & 5Bi-Pre Pak p.83By wood p.75Cambridge Learning p.50C.D I MiniadsChiltmead p.14Chromasonics p.2Crofton Electronics p.69E.D A. p.41Electrovalue p.9Exetron p.58Fordendale p.73Greenbank MiniadsHeathkit p.77

Henry's Radio p.15lmtech Products . . . p.9Island Devices . MiniadsKinnie Components p.44Kramer & Co .. p.79Lynx Electronics p.16Maplin Electronics p.84Marco Trading . MiniadsMarshall's p.21Metac p.37Minikits p.13Ramar MiniadsR.F. Equipment .. p.82Sabtronics p.20Sinclair... . pp.24 & 25Sintel p.41Technomatic p.79Vero MiniadsWilmslow Audio .. p.64

ELECTRONICS TODAY INTERNATIONAL -APRIL 1976

THE SCIENTIFIC WIRE CO.Copper - Nickel Chrome - Eureka - Manganin

WiresEnamelled - Silk - cotton - Tinned Coverings

No minimum charges or quantitiesTrade and Export enquiries welcome

S.A.E Brings List

P.O. BOX 30, LONDON, E4 98W

8C1078C1088C109TIP3055TIP2955LTX300ZtX304ZT X500ITX50425305515914154148

10p10p10p49p69p15p25p15p25p49p

154002 4p154003 4p154004 5p154007 6p34 '800V Rec. 15pBRIDGES15 200V2A. 600VDIL

Spin4p 555 Toner

26p33p

25p49p

JVAT INC PB,P 20p I

LEDS W. clip. 0.125"IlL209 (Red) 17pMV5I 74 (Orange) 22pMV5274 (Green) 22pMV5374 (Yellow) 22pCAPACITORS10mfd '12V IO 20p

'00 ElI °mid 70V22mta /50v 10 30ploomte n 6V 1..E1.50.100Ornici .6y

AUDIO -OPTICS, 19 MIDDLEWAY, CHINNOR,OXONTel. Kingston Blount 52683

SUPERB INSTRUMENT CASES by Ba-zelll manufactured korn heavy duty PVCfaced steel Hundreds of people andindustrial users are choosing the cases theyrequire from our vast range, competitive'prices start at a low 75p. Over 400 Modelsto choose from. Prompt despatch Freeliterature (stamp would be appreciated)Bazelli, 'Department No 27, St WilfredsFoundry Lane. Halton, Lancaster, LA2 6LT

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The easiest, fastest way ofconstructing your electroniccircuits. 0.1" x 0.1" or 0.15" x0.15" Matrix, 15 sizes.

New catalogue available (price 10p + S.A.E. at least 7" x 9")Vero Electronics Limited, Retail Dept.,Industrial Estate, Chandler's Ford, Hants., S05 3ZRTelephone: Chandler's Ford 2956 (STD 04125)

81

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We reckon ETI is worth keeping: and our surveys indicate that astaggering 97% of readers keep their copies for at least threemonths. Now we can offer you a binder which holds 12 issueswhose quality befits the magazine: excellent. Send £2.00 (whichincludes VAT and postage) to:

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Epoxy -Glass PCBsTypical prices INCLUSIVE of VAT & post

Audio Level Meter. _ET' 438 Mar '76 100pCMOS Tester ETI 123A Feb '76 90pCMOS Tester _____ETI 12 38 Feb.76 90p50+50W Power Module Ell 422 Jan. '76 270pActive Crossover 2 Way ETI 4334 Oec '75 90pActive Crossover 3 Way ETI 4338 Oec. '15 90p100w Guitar Amplifier ETI 413 Top Proh 1 140pLogic Probe_ _

ETI 120 Oec.'7 60plogic Pulser. ETI 121 Oec."75 60p

logic Tester. ETI 122 Jan. '76 _ ____ .150 p

International 25 ETI Int.25 Oct '75 _375pSend 10p for full lists of PCBs and Kits for all ETI and many

other published project PLUS low cost COMPONENTS

NEW BURGLAR ALARM KIT complete with CASE and 5

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TTL74 0 0_ II p 7474 25p74 01_ 11 p 7493 37P741 11 p74 1 6_ _20p74 20 II p7430 II p7437 11p7440 II p

LINEARSCA 3046NE 5 5 5pA 74 1BC107,108,109

50p50p27p

9p

SPECIAL OFFERSMiniature glass encapsulated REED SWITCHES .10 for 50pSolid TANTALUM BEAO Capacitors 2 2uF & 47uF only_ _8pGlass Tin Oxide '2w Resistors 22K 33K 39K .2pBulk Offer 33K only 50- 75p _100-120p

Mail Order Only. C.W.O. P & P 15p Prices V.A.T. inclusive

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82

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reader servicesSUBSCRIPTIONSThe annual subscription to ETI for UK readers is £5.00. The current ratefor readers overseas is £5.50. Canadian subscription rate is $10 per year.Send orders to ETI SUBS Dept.

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ELECTRONICS TODAY INTERNATIONAL-APRIL 1976

FROM BI-PRE-PAK

Stirling Scund productsBECAUSE OF DEMAND AND RE -ORGANISEDPRODUCTION, THE SUPERB

SS.125 HI -FIDELITYPOWER AMP

NOW COSTS £6.25 inc. Postage & VATOUTPUT25 watts R.Pil S. into 11S2 using 501122 watts H.M.S. into 4)) using 330(Low imp. not less lhan

DISTORTIONLess than 0.05% al all power levels(from 10Hz to 10KHZ)

FREQUENCY RESPONSE1dB 15 K2 to 30 KHz (4)))IdB 0(t to 30 KHz (K2)

HIGH Z INPUT100 Kohms (4018 gain/100x)

INPUT SENSITIVITY150mY for 25W.R.M D out

SIZE(inc heat -sink type mountingplatform( x 3" o s' high (120076022mm)

Not only is this Stirling Sound's best audio amplifier yet;it rightfully qualifies as one of the best of its kind yetmade available to constructors. Intended above all forhigh-fidelity, the characteristics of the SS.125 are suchthat it can be used in many other applications wheredependability is the prime consideration. The SS.125integrates well with other S.S units as well as those ofother manufacturers. Incorporates new circuitry using acomplementary long-tailed pair input and full comple-mentary output circuits to give standards of performance.Designed and made for constructors who appreciatequality and value!

MORE STIRLING SOUND MODULESVVith easy to follow instructions

F M TUNER UNITS

SS 201 Tuner front end Ganged geared variable tuning88.108MHz A F C facility E5.00

SS.202 I F amp A meter and!or A F C can be connected(size 3" x 2") E2.65

SS.203 Stereo decoder for use with SS 201 and 202 orany good F M tuner A LED beacon may beattached (3" x 2") £3.85

SS.105 5 watt amplifier to run from 1 2V (31/2" x 2" x 1/2") £2.25SS.110 Similar to SS 105 but more powerful giving 10VV

into 4ohms £2.75SS.120 20 watt module when used with 34 volts into 4

SS.140 Delivers 40 watts R M S into 4 ohms using a45V '2A supply such as our SS 345 the power andquality of this unit are superb two in bridgeformation will give 80 watts R M S into 8ohmsSize 4" x 3" x Va"

SS.100 Active tone control, stereo, ± 15d8 cut and boostwith suitable network

SS.101 Pre -amp for ceramic p u radio & tape with passivetone control details

SS.102 Stereo pre -amp with R I A A equalisation. magp u tape and radio in

SS.300 Power Supply Stabiliser. Add this to yourunstabilised supply to obtain a steady workingvoltage from 12 to 50V for your audio systemworkbench etc Money saving and very reliable £3.25'

TERMS OF BUSINESS:VAT at 25% must be added to total value of order except for items marked or (8., whenVAT is to be added at 8% No VAT on overseas orders. POST & PACKING add 22p for UKorders unless marked otherwise. Minimum mail order acceptable - El Overseas orders, addET for postage. Any difference will be credited or charged. PRICES subject to alteratiohwithout notice. AVAILABILITY All items available at time of going to press when every effortis made to ensure correctness of information

£3.00

£3.76'

Et .60

£1.60

£2.25

Order your Stirling Sound products from

BI-PRE-PAK LTDCo Reg No 820919

222 224 WEST ROAD. WESTCLIFF ONSEA. ESSEX SSO 90F.TELF.PHONE: SOUTHEND(0702)46344

SS. 125£5.20

VAT

POST PAID

And5 NEW STIRLINGSOUNDS POWER

SUPPLY UNITSRobustly designed units in each of whicn is a sta.'s,'take -off point to provide for tuner. pre -amp and controlstages Size - 51/2" x 3" x 21/c" high (P P add 50pany model)

SS 312 1 2V 1A £3.75'SS 318 £4.15'

SS 334

18V/ 1A£4.60'

34V/ 2ASS 324 24V/ 1A

£5.20'SS 345 45V/ 4A £6.25'

Transformers for SS334 and SS345 are supplied withtransformers separate from PCBs Add 50p for P P any model

A new Stirling Sound C.D.I. Unit for your car.Super Shark Mk. 2Lven better than the original version thousands of which are inuse saving motorists appreciable time and money for petrol Veryeasy to install The Stirling Sound model incorporates switch forinstant change to conventional ignition. instant adaption to posor neg earth return anti.burglar immobilising switch pre setcontrol for rev limitation There are no exposed parts. the uniton pc b being housed in strong enclosed metal box Withinstructions and leadsSire 7," x 4," x 2," ex switches (193 a 1 1 7 x 54rnm)(P,P

add 50p) BUILT &KIT £7.95 TESTED £10.50A NEW X -HATCH GENERATOROperates at R F level

For colour and mono TV Plugs into aerial socket of set Operateswithout need for transmissions, 4 push button operation Runson 4 self contained penlite type batteries Will lit into a largepocket Strong plastic case BUILT £27.50' KIT £25'

A USEFUL CATALOGUE - FREESend us a large S A E with 10p stamp and we will send you theiatest Bi-Pre Pack catalogue free by return Packed with usefullines IS a real money saver

ri0 STIRLING SOUNDI SEA ESSEX SSO OOF

IPlease send

Inc VAT

NAME

ADDRESS

181 PRE PAK) LTD 222 WEST ROAD WESTCOEF-01

1

for which I enclose t

FACTORY -- SHOEBURYNESS ESSEX

More than

PROJECTS FOR YOU TO BUILD4 -digit clock, 6-Gigit clock, 10W high quality poweramp., High quality stereo pre -amp., Stereo Tuner,F.M. Stereo decoder, etc., etc.

CIRCUITS . . . Frequency Doublers, Oscillators, Timers,Voltmeters, Power Supplies, Amplifiers, CapacitanceMultiplier, etc., etc. ..Full details and pictures of our wide range of components,e.g. capacitors, cases, knobs, veroboards, edge connectors,plugs and sockets, lamps and lampholders, audio leads,adaptor plugs, rotary and slide potentiometers, presets,elays, resistors (even 1% types! ), switches, interlockingpushbutton switches, pot cores, transformers, cable and

keyboards, L .E.D. s, 7 -segment displays, heatsinks,transistors, diodes, integrated circuits, etc., etc., etc. .

The 3600 SYNTHESISERThe 3600 synthesiser includes the most popular features of the4600 model, but is simpler Faster to operate, it has a switchpatching system rather than the matrix patchboard of the largerunit and isparticularlysuitable for liveperformanc,and portable

Please sendS.A.E forour priceIrst

GRAPHIC EQUALIZERA really superiorhigh quality stereographic equaliseras described inJan. 1975 issueof ETI. We stockall parts (exceptwoodwork )including all themetal workdrilled and printed as requiredto suit our components and PCB'sS A E for price list or complete repent of article price 15p

The 4600SYNTHESISER 00'4

We stock all the parts for this brilliantly designed synthesiserincluding all the PCBs. metalwork and a drilled and printed frontpanel, giving a superb professional finish Opinions of authorityagree the ETI International Synthesiser is technically superior tomost of today's models. Complete construction details in ourbooklet available now. price El 50. or S A E please forspecification

ELECTRONIC ORGANBuild yourself an exciting ElectronicOrgan. Our leaflet MES51, price 15p,deals with the basic theory of electronicorgans and describes the construction ofa simple 49.note instrument with a singlekeyboard and a limited number of stops.Leaflet MES52, price 15p, describes theextension of the organ to two keyboardseach with five voices and the extensionby an octave of the organ's range.Solid-state switching and new footaues along with a pedal boardand a further extension of the organ's range are shown inleaflet MES53 priced at 35p (pre publication price 1 5p

NO MORE DOUBTS ABOUT PRICESNow our prices are GUARANTEED (changes in VAT excluded) for two month periods We'll tell you about pi ice changes in advance forjust 30p a year (refunded on purchases). If you already have our catalogue send us an s.a e and we'll send you our latest list .of

GUARANTEED prices. Send us 30p and we'll put you on our mailing list - you'll receive immediately our latest price list then everytwo months from the starting date shown on that list you'll receive details of our prices for the next GUARANTEED period before theprices are implemented, -- plus details of any new lines, soecial offers, interesting projects and coupons to spend on components torepay your 30pNOTE The price list is based on the Order Codes shown in ourcatalogue so an investment in our super catalogue is an essentialfirst stepCall in at our shop, 284 London Road. VVestclift on Sea. EssexPlease address all mail to

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