i practical electronics - worldradiohistory.com · kenn garroch advertisement manager david bonner...

I PRACTICAL November 1991 £1.50

ELECTRONICSSCIENCE AND TECHNOLOGY

ScreenplayComputer monitorsfor the 90s

Modemmadness

Radio rulesA new RSGB licence

CAD for real

How it worksSuperhet radio

Data sheet

New techroundupSolar cellsOptical discsIn car navigationIn flight video

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November 1991 Volume 27 No. 11

This month...

The bad thing about the Britishsummer, apart from the weather ofcourse, is that everyone goes onholiday. This means that even the bestlaid plans can go astray. In the nextmonth box last month (if that makesany sense) I mentioned that we wouldbe looking at the ION camera fromCanon and the technology behindimage scanners. Unfortunately, due tovarious people being on holiday, noneof the items mentioned were availableso we were unable to look at them -hopefully they will appear in the nearfuture.

Having looked at a number of CADsystems over the past few months, PEseems to have gained something of areputation for being a CAD Mag. As analternative to a straight 'review'Andrew Armstrong describes some ofthe pitfalls that can be encounteredwhen buying a CAD system. Inpractice, these can occur when buyingalmost any kind of software. AsAndrew explains, the trick to avoidingthem is to be aware they exist and notbelieve everything you're told withoutseeing it in action.

Our main feature this monthconcerns computer displays. As ademonstration of what is possible withthe latest technology, the coverillustration was generated entirely oncomputer. It uses the well knownMandelbrot Set as the basis for thepatterns with only the 'artistic'arrangement of the objects being leftto the human touch.

Kenn Garroch, Editor

Next month...

Canon's S-50 SpeakersAdding a new dimension to sound

All I Want For ChristmasWhat are the best electronic gifts?

How It WorksMains communications systems

Build ItGreenhouse monitor

Out on October 3

Features

Technology Update 10

The latest in solar cells, optical discs and transistor technology

The RSGB's New Licence 12

Radio expert Ian Poole describes how the radio waves are nowavailable to everyone

Computer Aided Design 16

Getting into CAD is not as straightforward as it may seem

Computer Displays 25

Will LCDs replace CRTs? Paul Kennedy looks at the basic technology

A Virtual Instrument 43Jason Sumner plugs a card into his PC to turn it into a DMM

Build It

PE Chronos 36Putting together the display board

Rain Gauge 45Measure rainfall the professional way with Owen Bishop's pluviometer

Regulars

Wavelengths 5

Help with old organ components and more on the MOSCODE amplifier

Innovations 6

Westland's Merlin and the world's smallest desktop PC are in the news

Silicon Valley 14

ADCs to beat all the records plus super powered i/o

New Product Developments 20In car navigation and the latest developments in airline entertainment

How It Works 30

The Superheterodyne Radio

Data Sheet 32NS32CG160 32 -bit processor featuring built in graphics commands

Practical Components 34

Inductors

Practical Technology 52Barry Fox on the problems and pitfalls of international electronic mail

Techniques 57

All you need to know about light detecting switches

Barry Fox 623D -TV technologies abound, but are they any good?

Editor. Kenn Garroch Advertisement Manager David Bonner Production Manager: Richard Milner Production Assistant: Dino Digioacchino Office Manager: Laura Esterman Publisher: Angelo Zgorelec

Practical Electronics tetra House 193 Uxbridge Road London W12 9RA Tel: 081-743 8888 Fax: 081-743 3062 Telecom Gold: 87: SQ(1567 Advertisements The Publishers of PE take reasonable precautions to

ensure that advertisements published in the magazine are genuine, but cannot take any responsibility in respect of statements or claims made by advertisers. The Publishers also cannot accept any liability in respect of goods not being

delivered or not working properly. © Intro Press 1991. Copyright in all drawings, photographs and articles published in PRACTICAL ELECTRONICS is fully protected, andreproduction or imitations in whole or in part are expressly

forbidden. All reasonable precautions are taken by PRACTICAL ELECTRONICS to ensure that the advice and data given to readers is reliable. We cannot, however, guarantee it, and we cannot accept legal responsibility for it. Prices quoted are

those current as we go to press. All material is accepted for publication on the express understanding that the contributor has the authority to permit us to do so. Practical Electronics is typeset at Intra Press on Macintosh

computers using Quark Xpress. lmagesetting by Pressgang. Reproduction by Circle Rule. Printing by Andover Press, St Ives plc. Distribution by Seymour Press ISSN 0032-6372

November 1991 Practical Electronics 3

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Letters

WavelengthsIf you have any comments, suggestions, subjects you think should be aired, write to PE

On reading PE October issuepage five, Wavelengths, Mr.F J Trowman requests help

with an electronic organ problem.Might I suggest that he contacts theElectronic Organ ConstructorsSociety, Trevor Hawkins, 23Blenheim Road, St. Albans,Hertfordshire, All 4NS, Tel. 072757344. Send a self stampedaddressed envelope if writing, thesociety publishes a very usefulmagazine a number of times a year.

D J BrownCoventryW Midlands

The society publishes its magazine fourtimes a year and costs £1.50 to joinplus £9.50 for a years membership.

Cover BotherI have noticed that the cover of PEhas been getting a lot more livelyover the past few months. Actually,lively is rather an understatementwhere the October issue isconcerned. What I would like toknow is how they are produced.They are not photographs, as far asI can see, and for pieces of artwork,they are very precise. How is itdone?

L DobbsWorthingEast Sussex

The September cover picture wasdrawn with a CAD art package on aMacintosh computer, in black andwhite. The colours where added withthe aid of a process colour book and theimage placed onto the DTP page layoutalong with the text and logos. TheOctober picture was produced in asimilar way but used a computergenerated background. The currentissue was also produced directly from acomputer but using a fractal program.PE aims to be at the forefront oftechnology not just in its content butalso in the way it is produced - apartfrom How It Works, pretty well all ofthe illustrations are drawn with a CADsystem.

Cable On The Right RoadWhat's all this about cable TV nothappening in the UK? (Barry FoxPE October 91). They have beendigging the road up down mystreet for the past week and thesigns say that the inconvenience isdue to cable TV installation. Inaddition, there are now some prettybig poster ads going up trying topromote the thing. It looks asthough cable is not as dead as it'ssupposed to be.

R J ClarkeLondonSW4

What Diagram?In your article about theMOSCODE amplifier inSeptember's PE, I noticed areference to a Fig. 5. I'm sure otherreader's must have noticed thatthere isn't one so how aboutreprinting it as you obviouslyforgot it accidentally.

K SmithDoverKent

Apologies for missing out the diagram.Unfortunately, it is impossible to put itin now as it is so big (a whole page). Ifanyone would like a copy please writeto PE enclosing a SAE and markingyour letter Amp Diagram. We'll getone to you as soon as possible.

More MoscodeThank you for the interesting andinformative project in theSeptember PE. I'm referring to thehigh power amplifier design. Iwould like to get hold of a full kit ofparts from Hobtek but you didn'tprint their telephone number.Could you help out?

L AshbyKings LynNorfolkHobtek can be contacted on0903 726 083

All Weather VideoAfter reading Barry Fox's "Video'sIn The Rain" in the September issue,I would like to ,make one pointabout video rental shops which heseems to have missed. A number ofthe films I hire are not shown onsatellite and are unlikely to ever beshown. I won't be able to use anyfancy simple button press to viewthem so I suppose I'll have to go outinto the weather and borrow them.J BrownManchesterAs far as I know, BSkyB shows most ofthe new movies as soon as they arefinished with the cinema circuit.Unfortunately, it may not show anyminority interest films or those whichwere never really suitable for showingon the cinema or TV.

Intelligent AddressAs a founder member of therecently formed HyperdyneSynthetic Systems Group (primarilyinvolved in the research anddevelopment of cyborg implantsand whole android systems) and along time admirer of yourpublication, I was very interested tosee Neural Systems appear in yourpages. I was especially interested inthe NT404 NISP developmentpackage from Neural Technologies.I have endeavoured to find acompany contact address or thedistributor of the package, to noavail. Can you help?

Paul BenhamDerryNorthern Ireland

We've had a number of enquiries aboutthis so an address is definitely calledfor. Neural Technologies can becontacted at:7a Lavant StPetersfieldHantsGU32 3ELTel. 0730 60256Fax 0730 60466


Innovations

InnovationsThis month, the Navy's new Merlin helicopter, the world's smallest PC and the future of science.

On the 2ndNovember, theSecretary of State

for Defence, the RT. Hon.Tom King MP announcedthat the British Navy'snew helicopter, theMerlin, was to be theEH101 produced byWestland and Agusta inassociation with IBM.

The EH101 wasoriginally designed byWestland and its Italianpartner Agusta. Aftersigning an agreement in1979 to develop ahelicopter to meet thedemands of the 1990s, theEH101 has now flown1220 hours with some1290 mission flights. Allof the major avionics anddynamics tests have beencompleted and thecommitment from theBritish Government nowmeans that production

The Westland E11101 Merlin in its new role with the Navy.

can get underway.All of the hardware for

the machine will be builtin Europe with 98% of theprogramme being placedwith the UK and Italianmanufacturers. IBM willbe using its previousexperience gained onsimilar programmes inthe US where itdeveloped advancedcomputer simulators,systems proving andoperational trials of anti-submarine systems.

The EH101 is designedto be operated in one ofthree formats, Utilityfeaturing a rear door,HeMiner seating up to 30passengers and the Navalvariant, now known asthe Merlin. All three useadvanced compositematerials and sport threeengines. The rotors aremade from fibrereinforced and metal

components with each ofthe five blades having upto 35% increasedefficiency compared toconventional blades.

On the electronics side,the active vibrationcontrol system uses amicroprocessor controlledactuator to reduceairframe vibration by anaverage of 70%. Theavionics uses digitaldatabuses with anautomatic flight controlsystem offering autopilotand automaticstabilisation. The pilotoperates the aircraft viahigh resolution CRTdisplays that provideinformation on a "need toknow" basis.

Cable TV StetsAnyone who has noticedthe street being dug upoutside their homes will

probably have realisedthat cable TV is here, orwill be soon. Others maybe unaware of thecoming viewingrevolution.

A survey comm-issioned by theIndependent TelevisionCommission (ITC) showsthat awareness is on therise with interest insubscribing expressed bynearly half (48%) of thosequestioned. 10% alreadysubscribe and 38% saythey would subscribe ifthe price were right. Thisis a slight improvementover the 43% interestannounced a year ago.

The survey was basedon a sample 1004 peopleand supplemented by asample of 404 subscribersto cable or satellite whowere asked about theservices they receive.Only 67% of those

6 Practical Electronics November 1991

Innovation=

questioned had heard ofcable TV compared withthe 94% who had heard ofnew television channels.

The main reason givenfor not getting cable TVinstalled was usually thehigh cost. The next twomost popular reasonswere that thosequestioned didn't watchenough TV to make itworthwhile and that theywere satisfied with thecurrent services suppliedby the mainstreambroadcast channels, BBC,ITV and Channel 4.Adding value to the cablepackage proved to besomething of a winner. Ofthose questioned, 34%said that they would bemore likely to subscribe ifa telephone service couldbe provided as well. Themost appealing aspect ofthis service was areduction in telephonebills with guaranteedfault repair in 4 hours,itemised bills and callwaiting (knowing thatanother call is comingthrough) also quitepopular.

45 -

40 - May 1990 CI

35 October 1990

30 May 1991

25

20

15

10

5 - 1.10Cable & ITV Channel 4 BBC 1 BBC 2

satelliteHow viewing figures have changed over the past year.

When asked about the16 different televisionchannels available oncable, only some of whichare available on satellite,the top five wereDiscovery Channel (cableonly) Sky Movies Plus,Sky News, The MovieChannel and CNN (cableonly).

RM On The MoveResearch Machines,makers of the Nimbus PChas just announced thelaunch of a range of

notebook computers. TheRM NB100 is an 8086based machine that is justover one inch thick andweighs 3.51bs. It has a1.44Mb, 3.5in floppy, 1Mbof RAM, a CGAcompatible LCD (640 x200 pixels) and MS-DOSon silicon disk. Priced at£599 it offers a relativelycheap entry into portablecomputing that is PCcompatible.

The RM NB200 andRM NB220 are based onthe popular 80286microprocessor. With a

clock speed of 12MHz,1.9in thick and weighingunder 7lbs with 1Mb ofmemory and a doublesupertwist backlit VGAscreen (640 x 480 with 32grey levels) they are fullyAT compatible.Expansion optionsinclude a VGA monitor,mouse port, serial andparallel interfaces,external keyboardconnector, externaldiskette connector andbus port. Optional extrasare a 20Mb hard disk(standard on the NB220)


Month=

which is suppliedcomplete with Windowsversion 3.

The top of the range,NB340 offers the samefeatures as the NB200 butwith an 80386SXprocessor and a 40Mbhard disk.

Prices start at £1199(£949) for the NB200,£1499 (£1199) for theNB220 and £1699 (£1399)for the NB340 - figures inbrackets are available tofurther and highereducation purchasers.

RM's main market forthe machines is hoped tobe in the education areawhere it is already one ofthe leading PC suppliers.However, the currentwide availability andperformance competitionfrom the many othercompanies producinglaptops could mean thatRM's current prices willhave to fall.

Tiny PCsThe Tiny is the world'ssmallest desktopmicrocomputer measur-ing 210mm x 73mm x133mm. Available in three

formats, the bottom of therange is the TC1 whichsports a 10MHz V30, asingle floppy disk drive,serial, parallel, games,mouse and video ports, 81key keyboard, PALmodulator, CGA Herculescompatibility, DR -DOS 5plus four pieces ofbundled software, MiniWord, Bannerprogramme, puzzle andclock, all for £299. Thenext machine up is theTC2 which has the samespecifications as the TC1but has an extra floppydrive and is priced at£349.

The top of the range isthe TC3 which is the sameas the TC1 and TC2except that it has a 80286running at 12MHz, 1Mbof memory, 3.5in floppyand 40Mb hard diskdrives and is priced at£599.

The manufacturers,Tiny Computers, of 33Ormside Way, HolmthorpIndustrial Estate, Redhill,Surrey, RH1 2LW, Tel.0737 779511, also market arange of building blockcomputers allowingOEMs to make up

The new boolikoinlIPUS.

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machines with a choice ofprocessors - 286,386SX/DX and 486 -video cards and diskdrives. Prices start at £249for the 12MHz BB286 andrise to £999 for theBB486/25 cache.

Public ScienceExtending theunderstanding of scienceto the general public hasbeen the aim of COPUSsince its inception in 1985.The Committee on thePublic Understanding ofScience recentlyannounced its latest fiveyear plan in which itidentifies the followingchallenges.

Persuading fundingbodies to make publicunderstanding of sciencea required and rewardedelement in academicinstitutions.

Encouraging scientistsand engineers to go onmedia training courses.

Extending sciencecoverage in print andbroadcasting media, forexample women'smagazines, chat showsand soap operas.

Working withwomen's groups,recognising that publicunderstanding of scienceissues are particularlypertinent to women.

Developing plans for aScience in Art Festival.

Continuing the ScienceBook Prizes, run jointlywith the Science Museumand now in its secondyear of sponsorship byRhone-Poulenc.

A booklet setting oputthese aims, COPUS LooksForward: the next fiveyears, is available freefrom Jill Nelson, COPUSExecutive Committee c/oThe Royal Society, 6

Carlton House Terrace,London SW1Y 5AG, Tel071 839 5561 ext 226.


The most importantaddition you willmake to yourTOOLKIT

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Technology Update

!Among TowardsThe FutureIan Poole describes some of the latest advances in electronics technology with a look at anew solar cell design, high quality optical discs and microwave transistors.

The poor efficiency of solarcells has always been aproblem making them useable

in small and specialisedapplications. However recent workundertaken in Japan has broughtthe efficiency of their cells up to anew world record level of 16%.Furthermore it is hoped that in lessthan a year this might be improvedto give efficiencies of around 18%.All of this has been achieved byusing polycrystalline siliconcoupled with some new techniques

Normally it was found that apolycrystalline structure wouldonly give a poor level of efficiencybecause of the many boundarieswhich existed within it. Howeverby using a number ofimprovements this structure cannow been used to its bestadvantage.

The first new feature is in theform of form grooves as shown inFig. 1. Although these are producedmechanically they are just over 100gm wide and 50 gm deep. By usingthese grooves the actual surface

area available for conversion issignificantly increased. In additionto this the distance between theelectrode and any point on thesurface is reduced and this meansthat the internal resistance will belower.

Another advantage of thegrooves is that they reduce thereflectivity of the cell. In fact amajor problem in any solar cell isthat any light which is reflectedcannot be converted into usefulelectrical energy.

The reflectivity of the cell isfurther reduced by the addition of anew layer. This is made up frommagnesium fluoride and titaniumoxide and is a great improvementover the traditional single layer as itabsorbs more of the light spectrum.

A final improvement has beenmade by modifying themanufacturing techniques andreducing the size of the frontelectrode to 45% of the surface area.This gives a small but noticeableincrease in the area which canactually collect the light.

Fig. 1. New high efficiency solar cell.

Optical DiscsFor some time the problem of lowdata rates in optical discs has beentheir major drawback. This appearsto be a obstacle of the past now thatSony have introduced their new 3.5inch erasable drive. This can storeup to 128Mb in an erasablemagneto -optical form and canaccess 120Mb from a pre-recordedoptical disc of similar format to thatof a conventional domestic compactdisc.

In order to achieve thisoutstanding performance severaladvances have had to be made. Thefirst is the new heads which areused. They are much smaller thanany used on previous systems andcan detect the polarity of themagneto -optical discs as well as theinformation in CD format onprerecorded discs.

The other major advance is inthe use of a new chip set developedby AMD. It consists of an AM95C96which has been developedspecifically for optical disc controlHowever, the major speed increasehas been achieved by the AM95C94,a specialised error detector. Thisnew chip performs in hardware thespecific error detection circuitryneeded for optical discs. Previouslythis was all performed by softwareand was much slower. This newchip can now correct an erroneousbyte in 100 where the previoussoftware took 0.25 ms.

The disc spins at 3000 rpmgiving a data transfer rate of 625 kbper second with a seek time (thetime taken to reach a specific pointon the disc) of 40 ms.

If prerecorded discs arerequired, Sony is able to make themup from a re -writable master.


Technology Update

Transistor TechnologyIn the past, Gallium arsenide wasthought to be the best material formicrowave semiconductor devices.A new type of transistor may beable to change all of this usingsilicon to take a step forwards inspeed and power capabilities.

The new transistor has beendeveloped in France by the CentreNational d'Etudes desTelecommunications. The firstsamples of the device have ameasured frequency of more than26GHz and computer simulationshave indicated that the sametechniques can be used to obtaindevices with frequencies up toabout 100GHz. In addition to thisthe new transistor can handlecurrents of up to 100mA giving it avery respectable power handlingcapacity.

The new device is a form ofVMOS FET called a Permeable BaseTransistor (PBT). Although it isbased around a conventional Vstructure, a number of alterationshave been made as can be seen fromFig. 3.

In fact the basic concept was firstused in the mid 1960s in the USA tomake bipolar transistors. In thesethe base was replaced with a thinmetallic film to give what wascalled a metal base transistor.However, the problem encounteredin this design was that the electronsused to traverse the base as a resultof their momentum and thisdrastically reduced the efficiency.

The solution was adiscontinuous base and is appliedin the PBT with remarkable results.However, the structure is ratherunusual. The device is made from apiece of N+ silicon which has layers

Fig. 2. Sony's magneto -optical disc.

of N- and then N+ silicon grownonto it. Then a series of parallelgrooves are etched through the topN+ epitaxial layer. After this a thinmetal layer is deposited onto theupper surfaces of the silicon. On thetops of the fingers the metalisationacts as the source and in the bottomof the trenches it forms the gate.The underside of the fingers doesnot receive any metalisation withthe result that there is goodisolation between the gate and thesource. In addition, the metalisationfor both the gate and the source canbe deposited at the same time andwithout any screening. This greatlysimplifies the fabrication process.

The active region of the deviceoccurs only around the edge of the

Typically 0.2iim4->

Typically 0.41.1m

Gatemetalisation100 A thick

Source metalisation

Protectiveoxide

insulation

N+ silicon

Drain

Fig. 3. The structure of a PBT FET.

gate metalisation. As this area isvery small (around 150A) the activeregion is exceedingly small. Theother dimensions of the device arealso fairly small which enables theoverall frequency response to bemaintained.

Apart from the high frequencyperformance and the currentcapability there are a number ofother advantages to this device. Thefirst is the relative simplicity of thefabrication process. Although itdoes need several advancedtechniques to be used, it shouldmean that the prices of PBTs oughtto be very competitive when fullproduction is reached.

The fact that silicon is used asopposed to gallium arsenide alsobrings some advantages. One is thatthe thermal conductivity of siliconis higher than GaAs, and this resultsin a comparatively high powerdevice. The other arises from thefact that the bulk crystal defects insilicon are lower than in GaAs. Thismeans that silicon is capable ofgiving a better noise performance .

Although these devices are stillin the development stages, it shouldnot be too long before they are seenin use. They are still likely to beexpensive, but in view of theirpotential they should be cheaperthan equivalent devices made byother means.


Radio Feature

A New Radio NoviceLicence From The DTIIan Poole describes how, under a new scheme, gaining access to the radio waves is noweasier and cheaper than ever before.

On July 25th 1991 sevenyoung people received thefirst of a new type of

amateur radio transmitting licence.The new licence is called the novicelicence and was launched at thebeginning of 1991. Its aim is toprovide a new way into the hobbyand it is intended for people of allages, although it is particularlystructured to encourage youngpeople into amateur radio.

What Does It Offer?The novice licences give access to awide variety of bands and types oftransmission as shown in Fig. 1.There are two classes of licence,Class A which gives access to all thenovice bands, and class B whichonly allows operation on bandsabove 30 MHz. For both licencespower limits are quite low at 3watts RF output or 5 watts DCinput to the final stage. Even so thisis quite sufficient to make some

U.K. Novice licence BandsFrequency Band (MHz) Types of Transmission Permitted1.950 - 2.000 Morse, Telephony, RTTY, Data3.565 - 3.585 Morse10.130 - 10.140 Morse21.100 - 21.149 Morse28.100 - 28.190 Morse, RTTY, Data28.300 - 28.500 Morse, Telephony50.620 - 50.760 Data51.250 - 51.750 Morse, Telephony, Data433 - 435 Morse, Telephony, Data1240 - 1325 Morse, Telephony, RTTY, Data, Facsmimile, SSTV,FSTV

10 000 - 10 500 Morse, Telephony, RTTY, Data, Facsimile, SSTV, FSTVMaximum power 3 Watts RF output or 5 Watts DC input.Figure 1

respectable contacts especially onthe HF bands below 30 MHz whereintercontinental contacts are quitepossible if a good aerial is used.

There is plenty of scope forexperimentation within the licence.There are no restrictions on havingto buy factory made equipment.Indeed the training for the licence isset up to encourage home

Natasha Weir, callsign 2E1AAE, with her csalloto courtesy of RSGB).

construction. In addition to this awide variety of modes oftransmission are available - Morse,AM, FM, and SSB are all allowed asis data transmission. This is ofparticular interest because of thenew packet radio transmissionswhich are being widely used byamateurs.

Obtaining The LicenceThe object of the training for thenew licence is to learn in a practicalway. Candidates must satisfactorilycomplete a practical course rununder the auspices of the RadioSociety of Great Britain. It consistsof a number of work sheets whichare all designed to teach aparticular aspect of electronics andradio. For example one work sheetmay have a soldering task on itwhilst another may be on making acontact. The course should takeabout 30 hours to complete so it isnot particularly arduous. Theassessment is carried out on acontinuous basis and if one sectionis "failed" then this does not mean


New Radio Licence

that the whole course is failed.Having successfully completed

the course a 90 minute exam has tobe passed. This is set by the Cityand Guilds but it is based on thepractical course.

Having reached this far it ispossible to obtain a class B licence.If a full class A novice licence isrequired then a simple morse test of5 words a minute has to be passed.This too is organised by the R.S.G.B.

Bearing in mind the number ofyoung candidates likely to beapplying for the novice licence thecost is free to people under 21 yearsof age. However for olderapplicants the cost is £15, the sameas the ordinary amateur radiolicence.

CallsignsA completely new set of callsignshave been started specifically forthese licences. Unlike the standardsystem which starts with the letterG (e.g. G3YWX) the new novicecallsigns start with the number 2.This is followed by a letter whichindicates the country: E forEngland; M for Scotland; W for

Wales; I for Northern Ireland;D for the Isle of Man; U forGuernsey and J for Jersey. Thenext character is a numeralwhich denotes the class oflicence. The numbers 0,2,3,4indicate a class A licence whilst1,5,6,7,8 indicate a class Blicence. Following this are threeletters which make the callsignunique and are issued in strictalphabetical sequence. Forexample a class B licence inScotland might be 2M8CCN.

Where To Get ItA number of people havefought long and hard to havethis new licence introduced.Now it has arrived there is thepossibility of many morepeople being able to access theairwaves.

Information about theNovice Licence can be obtainedfree of charge by requesting aNovice Pack from the RadioSociety of Great Britain,Lambda House,CranbourneRoad, Potters Bar, Herts, EN63JE.

1991-1992

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send envelope, minimum size C4 (123/4" x 9"),self addressed with £2.65 stamps affixed ORsend £4 ch/po with request for catalogue,(Export £6) to the address below.Also available for callers.Trade/Industry/Education.Attach notepaper request for FREEcatalogue with trade price lists.

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Robert Cherry, callsign 2E1AAC, makes his first UK Novicecontact (photo courtesy of the RSGB).

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Silicon Valley

TI, Exel And National

SemiconductorThis month's valley looks at quick analogue to digital convertors, safety consciousEEPROMs and clever power drivers.

One of the penalties of highspeed integrated circuits isusually high power

consumption. This is especially trueof "flash" analogue to digitalconvertors (ADC). Able to make 8 -bit conversions at up to 20 millionsamples per second (MSPS), theADC 0881 from NationalSemiconductor, featured in lastmonth's valley is especially powerhungry. An alternative, also fromNat Semi, is the ADC10662/4which, although not quite as fast,offers a conversion of 10 -bits in466ns while dissipating only235mW. Using a patented multi-step architecture, the chips areamong the fastest of their typeavailable.

Aimed at applications thatrequire high speed with low powerconsumption, such as medicalelectronics, portableinstrumentation, disk drives andhigh speed data -acquisitionsystems, the 10662 features twoanalogue input channels (with fouron the 10664), is pin compatiblewith the older 10062 and operatesfrom a single 5V supply. Analoguesignals up to 250kHz can bedigitised accurately without theneed for an external sample/holdcircuit.

Contact NationalSemiconductor, C/O LorenzMinderer GmbH, Att: MrsHumbert, Raiffeisenstrage 10, D-8016 Feldkirchen, Germany.

Safe EEPROMExel Microelectronics recentlyannounced two new CMOSEEPROMS (Electrically ErasableProgrammable Read Only Memory)featuring auto increment and Vcc

lockout plus low power Excel Microelectronics PO Boxconsumption. 49038 San Jose CA 95161-9038 USA.

The lockout protection providesprotection from inadvertent writes.In noisy environments, the Intelligent Powerelectrical nature of the The TPIC2801 is an octal serialprogramming system in an peripheral driver from TexasEEPROM means that spikes in the Instruments. Each output has apower supplies and write, data voltage capability of 30V at 1A withlines make the data unreliable. The a current limit of 1.4A. The built inXL93LCO6 and 46 have built in protection shuts the device downsupply voltage sensors which after an overload of 100µs andprohibit data alteration whenever notification is available from thethe supply is below a safe value. serial data output of any channels

The auto increment feature in trouble.allows the chips to output a Available in a 15 pin kV powercontinuous stream of data in package, the TTL/CMOSresponse to a single read compatible inputs reduce theinstruction. Normal EEPROMs number of connections needed to aneed a read for each address which, microprocessor system by allowingin comparison, is slow, specially the data at the output to be inputwhen a series of consecutive serially.memory locations must be read. The TPIC2801 is initially

The XL93LCO6 has 256 bits of targeted at automotive andnon-volatile memory arranged as industrial systems but should find16 registers of 16 bits each. applications in any area whereOperation is from a single 5V large drive power is needed.supply at a maximum of 2mA in For more information, contactactive mode and 2µA in standby. TI, Freepost, Backhorse Road,

For more information contact London SE4 882.

is

8 -bit latch current limit, saturation detection.

supply

Serial to parallel convertor

The TPIC2801 intelligent power IC.

Serialdata

s,tput


PSST...Powerful Software Saves Time!

ANNOUNCING ISIS DESIGNER VERSION IIOur popular range of schematic capture products has been upgraded to give 'one button'integration to other CAD software. A special script language allows you to add your ownoptions to the menus so that you can, for example, compile a netlist, convert it to thedesired format and then invoke another DOS program all from one menu selection.

Other new features include full network compatibility, sophisticated support for PCB designincluding automatic property assignment and sheet global net properties, improved editingfacilities, a full screen library maintainance tool and much more.

ARES - Advanced RoutingARES £275

A netlist based, multi -layer PCB design package thatcan integrate with ISIS or other schematics softwareIncludes connectivity checker, design rule checker,power plane generator and automatic back -annotator.

ARES AUTOROUTE £475

Our new autorouter uses an advanced, multi -strategyalgorithm to achieve very high completion rates, yetwhen driven from ISIS, there is remarkably littlesetting up to do - Package, Router -Strategy and DRCdata can all be read from the netlist.

Topological Route Editor (another Labcenter innovation)Unlimited user configurable pad, track and via styles.Full surface mount and metric support.10 copper + 2 silk layers.1 thou resolution.30x30 inch max board size.Up to 5000 pins, 50000 trace segments using EMS RAM.Object oriented 2D drawing for silk screen graphics.Drivers for dot matrix, pen plotters, lasers, POSTSCRIPT,Photoplot (Gerber), NC drill (Excellon).Graphics export in IMG, BMP or EPS formats.

ISIS DESIGNER £275ISIS DESIGNER+ £475

Auto wire routing, dot placement and label generation.Powerful editing facilities.Object oriented 2D drawing with symbol library.Comprehensive device libraries provided.Device editor integral to main program .Output to dot matrix, pen plotters, lasers, POSTSCRIPT.Export to DTP packages in IMG, BMP, DXF or EPS formats.Multi -sheet and hierarchical designs held in one file.Netlist output to most popular EDA software.Bill of Materials and Electrical Rules Check reports.DESIGNER+ advanced features include hierarchical design,Automatic Annotation/Packaging, ASCII data import.

Budget Price CAD SoftwareISIS SUPERSKETCH from only £69

Our highly popular schematic drawing program is stillthe only budget package designed specifically fordrawing circuit diagrams. It has all the editing featuresof ISIS DESIGNER and our Graphical User Interfacemakes it exceptionally easy to learn and use.

Diagrams produced with SUPERSKETCH can berendered on all common printers/plotters includingPOSTSCRIPT and graphics export to most DTP andWordprocessing packages is also possible

An extended device library containing TTL, CMOS,Memory, Microprocessor and Analogue ICs is

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An exceptionally easy to use manual PCB draftingpackage offering most of the features of ARES butwithout the netlisting capabilities.

PCB II shares the same user interface as ISISSUPERSKETCH and both packages plus theextended device library are available for just £149.

abcenten 1COMBINATION PRICESISIS DESIGNER & ARES £495

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Getting Into CAD

A Second Look

At CADWhen Andrew Armstrong took up PCB computer aided design in earnest he discovered thatthere were hidden pitfalls for the new user.

Three years ago I came to theconclusion that I neededcomputer -aided design (CAD)

for printed circuit boards tocontinue my work in electronicsdesign. I have little artistic talentand the increasing complexity ofboard designs coupled with shorterproject timescales made it a matterof necessity rather than economics.

A brief survey of the marketsuggested that, other than buying aSun or similar workstation andaround £20,000 -worth of software, agood alternative was a PC -compatible. The exact choice ofcomputer was left until after I haddecided on a software package, tomake certain that the computer wasadequate for the task.

ConnectivityI needed software which wouldallow me to draw a circuit diagramon the screen and transfer thatinformation to the layout, so thatthe tracks would be forced toconform to the circuit diagram.

To transfer the design fromschematic to layout, anintermediate stage - the netlist - isrequired. This is a complete list ofall components present, and whichpins are connected together.Normally, the program will notallow connection of componentgroups not joined on the schematicand will verify that all the requiredconnections have been made.

One other important function isavailable: autorouting. A CADpackage with automatic routingcalculates the proper path of theconnections as well as maintaininga list of what is connected to what.The first advice I had was thatautorouting would be unlikely to

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route the entire track layout, butwould probably be able to do mostit.

I reasoned that (for example) a70% automatically routed boardwould be quicker to complete thanone with no routing. It is interestingto note that a package whichgenerates a netlist from the pin -to -pin layout connections can performautorouting if a suitable softwaremodule is present. It does notmatter that the netlist was notgenerated from a schematic.

In PracticeAfter visiting exhibitions, readingthe literature and attending anumber of demonstrations, I mademy choice. In order to avoid biasingthe reader either in favour of oragainst the package I bought, I shalluse mythical names from now one.This is only meant to be a guide: it'sno good if you don't do your ownresearch! Anyway, I concluded that

RH Layout by Rhamphorynchuswas the most suitable package inmy price range. At the time, Iexpected to need pen -plotted orphoto -plotted artwork forindustrial design, and artworkproduced on a dot-matrix printerfor published projects. Thespecification of RHL stated that itwould work with any Epson -compatible graphics printer. Inpossession of this information, Iwas set to buy it in the fullconfidence that it would drive myNEC P7 Plus, a 24 -pin printerwhich emulates the Epson LQ850.

Unfortunately, I was wrong.Artwork printouts from RHL onthis printer were approximately30% expanded in height. What thespecification meant was that RHLwould drive Epson -compatible 9 -pin printers.

The other snag was that, thoughRHL would provide a pen -plottedoutput, the pen -plotter had to beconnected to the computer at the


Getting Into CAD

time. It could not generate a file ondisk for plotting by a bureau.

I was told that RHL V2 couldgenerate HPGL files (HewlettPackard Graphics Language, usedby most pen -plotters) on disk, andthat a 24 -pin printer driver, thoughnot currently available, was underdevelopment. On the point ofbuying RHL V1, I changed courseand bought V2.

In the event, the 24 -pin printerdriver did not materialise, and myneed for a disk -based pen -plot filelapsed for different reasons. I foundthat industrial design artwork wasbetter photoplotted from a Gerberfile on disk. The cost ofphotoplotting was similar to that ofpen -plotting and the necessaryphotography.

User Friendly...Meanwhile, expecting the 24 pinprinter driver to be ready at anytime, I set about learning to use theCAD package, with a couple ofconvenient small jobs to serve as aneasy introduction.

All did not run smoothly. Firstof all, the mouse would not work. Ihad bought a Tulip computer withbuilt-in mouse interface. Thespecification of the computer statedthat the mouse was Microsoftcompatible, and sure enough therewas a genuine Microsoft chip on themotherboard. The CAD software, ofcourse, was specified to work withMicrosoft compatible mice, bus orserial types.

The man from Rhamphorynchushad the answer: "It won't work

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because your mouse interface is onthe motherboard. If it was on aseparate card, or if you used a serialmouse, then all would be well." Ithappened that the software waswritten to access the hardwaredirectly, rather than using thecomputer's system or BIOS. Anyitem of hardware at a differentaddress from that assumed by theprogrammers would not work. MyTulip mouse worked with everyother piece of software I had tested- but that didn't alter the situation: Ihad to buy a new pointing device.Instead of a mouse I took theopportunity to buy a high qualitytrackerball - which I had intendedto do, anyway, once I startedearning money with software. Nowit appeared as a startup cost.

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delivered by courier the next day,worked beautifully. That was whenmy troubles really started.

I had assumed that CADsoftware would be much like anyother software package I hadlearned to use: do simple jobs withit initially, and learn advancedfeatures gradually as they becomerelevant. I expected documentationwhich was poorly indexed, becausethis is the way of things withcomputer documentation, but Iexpected it to tell me everythingabout the software, eventually.

I found the reality frustrating.Perhaps infuriating would be abetter word. I had never used apiece of fully industrial softwarebefore, nor anything so complex.Nothing worked in what I imaginedto be the logical manner, and themanuals told me what to do, butnot what the action was for.

For example, the manual mightstate that a function key would"enable closely spaced primitives".The same information appeared onthe menu. What it actually meantwould be something like this:"When drawing or modifying acomponent outline, it can bedifficult to select the correct linefrom several in a small area. Thisfunction steps through eachseparate line in an area to permitselection of the correct one."

The people on the helpline atRhamphorynchus UK were efficientand generally well-informed, andtheir help enabled me to make someprogress. The tutorial book was alsohelpful. This put together the basic


Getting Into CAD

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information needed to lay out aPCB, but it did not illustrateanything complex.

Various friends who designsoftware offered me help to makesense of the package. "As user-friendly as a piranha in the bidet",one commented drily. She addedthat the software had been writtenas if for use by softwareprogrammers, rather than byengineers, and that if I approachedit from a different point of viewsome logic would become apparent.

The 24 pin printer drivecontinued to be delayed and I hadto borrow a 9 pin printer from acontact whenever I needed to makea printout - something of a anuisance.

Then, one day when I enquired,the suppliers had discovered thatthe printer driver for RHL2 was notbeing written, and would not beavailable. By this time I had learnedto use the software fairly well, anddid not want to change, so I

suggested that I could be given thenecessary information to write myown printer driver, or failing that tomodify the parameter file for anexisting driver to make a correctlyscaled printout on my 24 pin printerin 9 -pin (reduced resolution) mode.

My suppliers made enquiry tothe overseas parent company and Iwas told that this informationwould be forthcoming. A delay wasexpected because the programmerwas busy with a software update.Then he was on holiday. There wasalways a good reason for delay. Thedelay lengthened. Eventually they

came back to me with the news thatthe information would not be givento me - it was the proprietaryproperty of the parent company,and they could not be expected torelease it.

During our discussions thesupplier had passed on theinformation that other RHL2 usershad asked about a 24 pin printerdriver. I now offered to write aprinter driver and give the rights tothe company, if they gave me theminimum information that wouldenable me to use my 24 pin printer,but they declined.

I was, by this time at, the end ofmy wits and I cast about for asolution. In the end I demanded arefund on the software. I had beenadvised that obtaining a refundfrom a software supplier was next

to impossible, except as a courtesygesture, because the complexity ofindustrial software and thedifficulty of matching the user'sneeds exactly to a proprietarypackage meant that normal groundsfor return of goods and refund ofpayment are very difficult toestablish. In the end,Rhamphorynchus offered me anupgrade to RH Layout V3 at aconsiderably reduced price. RHL3included a 24 pin printer driver -and several other enhancements aswell.

Reasoning that I could obtain nobetter offer and that even if I

obtained a full refund I would haveto spend several weeks learning touse a new software package -possibly an inferior one - I

accepted. I made the condition thatI would only accept delivery andpay for the software when it hadbeen demonstrated to workcorrectly in all respects on myhardware. The demonstrationshowed that it did all work, and Iupgraded to the top of the RHLayout range.

After learning to use RHL2, anddiscovering what I found difficultor unhelpful about it, I waspleasantly surprised by RHL3. Nolonger did I have to draw aschematic as a rats' nest and thenadd right-angle bends and junctionpoints. No longer did wire or trackrouting have to be from pin to pin;joins could be made at any pointalong a connection. Several otheraspects of use were improved and,though many of the principles ofoperation were similar to RHL2, thelogic of the software was more

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Getting Into CAD

along the lines needed by anengineer rather than a softwareprogrammer.

Poorer but wiser, I now had aCAD package fully suitable for myneeds.

In UseSince buying CAD software I havedesigned ever more complexprinted circuit boards, and havepaid for annual upgrade packageswhich have increased theusefulness of the software steadily.Surface mount components arefully supported and "hot keys"permit more rapid switchingbetween functions. I am told that ageneric move function, whichallows you to move whatever youclick the cursor on, is planned. Thiswould considerably speed the finaltidying up of a layout. To return tousing adhesive tapes and die -cutsymbols would now seem likechanging from a word processor toa quill pen.

So long as the circuit diagram iscorrect, it is possible to get a layout"right first time" to the extent thatthe resulting board could besubstantially ready formanufacture.

Designing a board with CAD isquicker than designing it on paper,with the added advantage that oncethe design is done, plot files mustbe written to disk, taking perhapshalf an hour.

The autorouter, which was mosteffective on boards consistingmainly of standard -size digital ICs,has gradually fallen behind currentrequirements. On a recent surfacemount design, it declined to routeany tracks, even in an area

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BENCHMRRK IMOUSE: -40,-820 AVAILABLE RAN ,

McCAD is a system available for the Macintosh

containing only digital ICs. "Boardtoo complex," said the errormessage.

PCB autorouters now form aspecialised field andRhamphorynchus currentlydistributes an autorouter on behalfof another company. The routerruns under Windows 3, and acceptsinformation from RHL3 in a dataexport format. The top of the rangeautorouter package costs about thesame as the full CAD package, towhit around £4000. The level 1software for about £1100 lookedgood on demonstration, but I shallconsider buying an autorouter onlyif I have a job which is nototherwise practicable.

ConclusionCAD software proved to be a heavyinvestment, but it allows me to dowork which I could not otherwiseeconomically undertake. It isbecoming a virtual necessity to use

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some sort of CAD in electronicsdesign.

Looking back, it might havebeen better if I had initially boughta low cost CAD package such as(had it been available at the time)the cheapest version ofBoardmaker. This would havehelped me to discover some of thequestions I needed to ask about anyCAD package before investing in afull -function one. Whether I wouldthen have decided that a fullysuitable package was too expensivefor me, or gone ahead to look forsuch a one, it would have given melonger to survey the market and themarket itself longer to develop tomeet my need. I may then very wellhave chosen RHL3, spending morebut avoiding some of the anguishwith earlier versions of the package.

As for the quality of the packageI am using, it is very high. I haveheard claims that it is the best onthe market in its price range, andthat may be true. Certainly I can doall I need to with it, and so far it hasbeen updated (for a substantialannual maintenance charge) to takeaccount of developments in thefield. Earth plane generation iseasier, surface mount componentsare better supported, significantimprovements have been addedand minor snags resolved as theybecome obvious.

Getting into professionaltechnology is a bit like placingsavings in an investment fund orshares: it's a way of getting yourmoney off you, and it is up to youto use your judgment to ensure thatyou get a reasonable return. If youdo - everybody's happy.


New Products

Taking Control Of TheHome EnvironmentIan Burley's goodies this month include some in-flight entertainment, a new in -carnavigation system for London and a house control system.

Interest in home automation andcontrol has been riding veryhigh in the US for several years.

Unfortunately, not many practicaladvances have been made, thoughthe Electronic IndustriesAssociation (EIA) in the US didformalise a set of home automationstandards earlier this year.

Now we're beginning to seesome progress. The Californian firmGroup III Technologies Inc. haslaunched its SAMANTHA homeautomation system. SAMANTHA,believe it or not, is extracted fromSecurity And MANagementThrough Home Automation. TheSamantha sales slogan is "TheLifestyle You Deserve at the Pushof a Button."

Samantha's heart is a multi -buttoned unit looking at first glancelike a trendy fax machine with itsLCD display and telephonehandset. It can't directly behave likea fax machine, but it can be adaptedto act as an answering machine. Infact Samantha relies on the phonerather crucially. Through this linkSamantha can monitor up to 15rooms and many dozens of sensorsand controllers as well as beaccessible for re -programming orchecking anywhere in the worldwhere there's a phone.

The central unit, which is calleda Personal Home Director (PHD), isbasically a very very smarttelephone. The PHD has anemergency call dialer, rechargeablebattery back-up, audiblesynthesised context -sensitive helpand 64 programmable macrosequences. Up to 15 rooms can bemonitored and controlled by thePHD. In order to do this it mustcommunicate with individualRoom Directors via telephone

extensions. Each Room Director canbe used as an intercom point, butmore importantly they each act as aterminal to the PHD, which can beremotely controlled via the RoomDirector's compact keypad. RoomDirectors can also be fitted with anoptional temperature sensor.

Once you've fitted RoomDirectors you can proceed to installa selection of sensors, sirens, and

appliance control modules. Whereaccess to a phone socket isinconvenient, accessories are linkedvia radio.

Overall, Samantha can monitorthe phone and be reprogrammedremotely from anywhere whereanother phone is available. It cancontrol lighting, domesticappliances - including the centralheating and monitor rooms for


New Products

security. It can dial out and alert theauthorities, act as a paging systemvia the intercom facility. Samanthacan remember pre-programmedmemos and act as a verysophisticated alarm. It can evenforward voice memos nominatedphone numbers. And yes, there is aclock/calendar facility too! Some ofthe example applications suggestedfor Samantha include heating yourmorning coffee, keeping tabs on thekids (they can be required to enter apass -code, say when they get back

from school), summoning thefamily for breakfast via theintercom, and so on.

It's difficult to evaluate such asystem without getting one's handson one, but the specifications makefor interesting reading. How muchdoes Samantha cost? A starter kitretails for $1495 (£950). That maysound a lot, but isn't compared todedicated alarm systems.

Group Three technologies is at2125-B Madera Road, Simi Valley,CA 93065, Tel.(+44) 805 582 4410.

The Boss travels first class,

Fun In The AirVirgin Atlantic has taken the verypositive and forward thinkingdecision to abandon the old videoprojection system it and most otherairlines have used for years to keepbored airline passengers reasonablyoccupied with the odd in-flightmovie. The replacement is apersonal LCD TV monitor, whichcan access a selection of channels,for every single passenger,including economy class. One ofVirgin's 747s, the Shady Lady,flying the Boston or Newark NewJersey to Gatwick route, has alreadybeen fitted out with the newsystem, provided by Philipssubsidiary, Airvision. First classpassengers get a large, by LCDstandards, six inch screen which ismounted on an adjustable arm fromthe seat arm -rest. Economy classpassengers get either four or fiveinch screens which are mounted inthe seat -back of the seat they face.

Reports received from peoplewho have been lucky enough to flythe new Virgin plane are veryencouraging. Picture quality is verygood and the channel selectionmeans you're not stuck with amovie everybody else has to put upwith. Virgin's own researchindicates that 96% of passengers


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preferred the personal displays.A selection channels are

available ranging from a choice ofmovies to pop videos and a kid's

display offers an adjustable mount.

channel. The rest of Virgin's fleet of747s will be refitted with theAirvision system by this time nextyear. So far Virgin is the only airline

to have committed to the newAirvision system, but Airvision'sPieter Souren expects orders to pickup once the recession is over.

More Fun In The AirTrialled on Qantas Airways andlikely to be adopted by progressiveairlines any time is the perfectaccessory for the Airvision videonetwork. It's a direct link into theplane's flight navigation computer.This system has been devised byAsinc Inc. in Tustin California andit's called the Airshow cabin VideoInformation System. It can answerthose burning mid-flight questionslike "How high are we?", "Whenwill we arrive?", "Where are we?"and even "Where do I go to catchmy connecting flight." TheAirshow display is selectable as anynormal inflight channel would be.The default display is a text -onlyread-out of information so:

Time to DestinationWind SpeedOutside Air TemperatureWind DirectionDistance to DestinationAltitude

4:1453 km/h-55'C240 deg1,143 km10,820 m


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The information displayed is real-time, but even more impressive is acolour map display whichhighlights nearby towns and citiesand shows the plane's path over thelast few hundred miles. The attitudeof the plane symbol indicates itsheading. You can watch the planesymbol turn in real time as the realthing manoeuvres on the runwayfor example. Three map resolutionsare selectable to provide longdistance, medium distance and alocalised view of the regioncurrently being over -flown. Withthe latter option you should be ableto recognise coastal outlines andother major landmarks.

Besides real-time inflight data,Airshow can be patched into thedestination airport's departureinformation system so you can seewhether or not you're going to missyour connecting flight. It's evenpossible to select a map of theairport so you know exactly whereto head for once you've arrived.Airlines are also able to incorporatetheir own custom graphics andancillary information.

Although I haven't yet had theprivilege of playing with anAirshow monitor just yet, I'vemanaged .to locate somebody whohas. His opinion was that it wasquite fascinating, though the neteffect of staring at the displayduring the flight was to make itseem much longer than usual,which can't be very desirable onlong -haul flights!

London TransportThe Department of Transport is atan advanced stage in negotiating acontract with GEC Marconi toprovide London with an Autoguidesystem to shepherd hard-pressedmotorists around the Capital'sclogged traffic system. Autoguidewould complement the existingTraffic Master system which iscurrently on offer to motorwayusers.

Autoguide has been in existencein prototype form since 1987. Theidea is that car's are fitted with anelectronic device which gathersinformation from either microwaveor infra -red beacons at strategicplaces all over the capital within theM25 boundary. Another possibilityis to use buried inductance loops,

though it's likely this method willbe rejected on the grounds of costand unreliability.

The beacons act as invisibleelectronic sign posts which the in -car computer can read. The beaconsare connected via phone lines to acentral master computer system.Besides the beacons there willtraffic flow sensors which thecentral computers will rely on tomake strategic decisions advisingmotorists which way to go. Afterlast month's feature on FuzzyLogic, this sounds like an idealapplication of for that technology.The end result is that the in -carcomputer's simple LCD display willflash warnings of impending

problems and advise the driver toturn off his previously desiredheading. A voice -synthesiser isanother option.

The DoT is confident that onceimplemented, Autoguide couldmake a big impact on the Capital'schronic and worsening traffic flowproblems. Trials of similar systemsin Germany have not been sosuccessful, but feeling is thatLondon's road system is an idealcandidate for Autoguide. The targetis to reduce the cost of the in -carunit to a price roughly comparableto a decent radio -cassette player. Inthe long run the system could savemillions of pounds in wasted fueland time.

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BURIED LOOP

ELECTRONICSIGNPOST

Next turn

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ROADSIDE

Signpostupdates

Hazardwarnings

CENTRALCOMPUTER

POUCE

LA'S

The autoguide system.

Destination

Vehicle type

Link time

Trafficdata

CENTRAL

METOFFICE

RAC

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Display Feature

Refreshing TheSilver ScreenPaul Kennedy explains the basics of computer displays from CRTs through gas plasma tothe latest supertwist LCDs.

Probably the most obvioustrend in the computerbusiness is the movement

towards smaller and more powerfulmachines. A number oftechnologies have been developedto allow this to happen, the mostvital being the high resolution flatscreen liquid crystal display.

The first computers usedprinters to display their results andmany mainframes still use thismethod. However, to allow themachine to be used interactively inapplications such aswordprocessors, spreadsheets,computer graphics, indeed, all ofthe things we now take for grantedfrom computer, some sort of highspeed display is needed.

The first, and still most common,form of output device is the VDU orvisual display unit. This is basicallya cathode ray tube that shows amatrix of characters in the, nowfamiliar, row by column format.Early personal computers allowed

alpha -numeric characters only (A toZ and 0 to 9), possibly with uppercase or possibly with an alternativegraphics character set of lines andsquares and pictures made up onan 8x8pixel matrix - the pixel is thesmallest picture element or dot onthe screen (Fig. 1.), unfortunately,they couldn't be controlledindividually. Fig. 2. shows howcharacters on a screen are made upfrom small squares which theviewer's eye joins together whenseen from a distance. What can't beseen is the blurring effect caused bythe phosphors which runs thecharacters together making anygaps invisible. The idea of a bitimage screen was still in the futuresince most machines didn't havethe memory or processingcapabilities to deal with anythingmore sophisticated than a 40x25 orpossibly 80x25 matrix. With theincrease in memory capacity andthe development of specialisedgraphics chips, computers

Enlarged section ofscreen showing pixels

Fig. 1.

A 640x480 pixel screen is able to displayhigh quality text and graphics.

eventually developed rudimentarygraphics capabilities. The advent ofcomputer games which wentthrough a huge developmentduring the same period highlightedthe new capabilities which includedcolour and increased resolution.

Memory To ScreenThe computer image to bedisplayed is always held inmemory somewhere. The formatand method used to transfer it tothe display vary from system tosystem. The commonest characteronly display system holds the 8 -bitnumber of each character (0 to 255)in an contiguous area of RAMstarting with the top left andmoving down in lines from left toright until the bottom right isreached. For a 40x25 characterscreen this means 1000 bytesdevoted to the screen. Fairly simplecomputer programs can be used tomanipulate the memory allowingcharacters to be moved around onthe display. To get a picture of thecontents of the memory, the videosystem scans the appropriate areaof memory converting eachcharacter number into an image,usually on an 8x8 dot matrix, whichis then used to control brightness ofthe electron beam. The devicewhich does all of the work isknown as a CRTC or cathode raytube controller and, at it simplest,transfers memory data to screendata. More sophisticated systemsallow the shapes of the characters tobe defined in RAM and hencealtered. Graphics are also usuallypossible with 8 -bits in memorybeing used to control eight pixels.This requires more memory since adisplay with 320 pixels by 200 lines,


Display Feature

Liquid Crystal Displays

Early LCDs had a number ofundesirable properties. They wereslow, could only really be viewedfrom directly in front and hadrelatively low resolution. Despitethis, they required very little powerand were fairly robust.

The operation of an LCD isbased upon effects produced byspecial materials which exist in astate between liquid and solid. Thematerials which exhibit this unusualstate or phase are organic andhave large rod -like molecules. Anormal liquid has no order orsymmetry in its makeup andindividual elements are free tomove and orientate as they like. Ina crystalline solid, the opposite istrue, there is a definite fixedstructure. Liquid crystals exist inbetween these two and have a mixof the characteristics. The largemolecules are free to rotate to acertain extent but also have anoverall fixed structure.

Liquid crystals are sensitive totemperature, pressure, electric andmagnetic fields, all of which affecttheir optical properties. The normalmethod of controlling the crystals isto use an electric field which actsacross the material and causeslight to be transmitted or polarisedin different ways. There are actuallythree different types of liquid

crystal, nematic, smectic andcholesteric of which the first is themost common.

The twisted nematic structure isshown in Fig. a. This is set up bysandwiching the liquid crystalbetween two grooved plates, thetop one at right angles to thebottom. In its normal, un-electrified,state it has a twist which rotatesany light passing through it by 900.When an electric field is applied,the crystals line up and the lightpassed straight through. To makethis work as a light valve, two lightpolarisors are placed next to theplates with their polarisationdirections the same as theiradjacent plates. In its relaxed state,light passing through the backpolarisor will be rotated through 90°by the crystal to pass through thefront polarisor which is at rightangles to that at the back. Applyingan electric field untwists the crystaland removes the 90"' polarisationand any light attempting to passthrough the sandwich is blocked.

An LCD can operate in two mainways, by allowing light to enter fromthe front and reflect of a back layerand then exit back through thefront. Alternatively, a backlight canbe used with the crystal interruptingit where necessary.

To obtain a useable display, a

number of pixels (picture elements)must be defined and each musthave individual control. The are anumber of ways of achieving this.In theory, each pixel could have itsown electrodes but any sizabledisplay would require a vastnumber of connections. Analternative is to use a multiplexsystem where a row of pixels areserviced by a one single conductorand a column by another at rightangles. By stepping through therows in sequence and applying thecolumn information, the number ofconnections is drastically reduced.The drawback of this is that thecontrast gets worse with anincrease in the number of pixels.

The advent of supertwist LCDtechnology a few years agoimproved contrast and viewingangles, increased resolution andprovided access to a number ofgrey levels. Displays that offer 640x 480 pixels with 32 grey levels arenow becoming commonplace onmodern laptop portable computers.

A supertwist LCD, as its nameimplies, rotates the light by morethan 90'). In fact it rotates it byabout 30,000 degrees permillimetre. To make an display fromthis material, it is sandwichedbetween two very flat glass layersas well as the polarisors. By setting

Anti glare coating

Front vertical polarizer

Blue compensation layer

Glass

Liquid crystal

Glass

Rear vertical polarizer

White light from backlight

The construction of a supertwist LCD display.


Display Feature

the thickness of the crystal layer exactly,a net rotation of 90° can be set up.Unlike the twisted nematic display, thepolarisors on each side of the crystal arethe same way around. When an elementis off, light enters the first polarisor andis given a 90° twist. This goes to the finalpolarisor and in not allowed through.Applying an electric field to the crystaluntwists it removing the 90' twist so thatit can pass straight through the frontpolarisor. The net result is that an onpixel appears black and an off onewhite.

The main drawback with supertwistLCDs is that they don't affect the whospectrum in the same way. Blue light istwisted by a different amount to the restgiving the whole display a bluish tinge.By using a crystal that affects blue morethan other colours, this can be correctedto give a reasonable black and whiteimage. During the scanning process,turning the pixels on and off at highspeed produces different amounts oflight transmission and gives the greylevels.

Fig a. A twisted nematic crystal. Fig. b. The twisted nematic under anelectric field.

Gas Plasma

The nearest thing to a rival for the LCD is the gasplasma display. This uses the fact that in a lowpressure gas. an electric current can be passed thatexcites the gas atoms and causes them to glow.

Normally gasses are relatively good insulators butwhen they are used at low pressures and with highvoltages. breakdown of this insulation occurs andelectrons will pass through. Each electron leaving thenegative electrode or cathode hits a gas moleculewhich then becomes ionised and hasenough energy to hit another gasatom causing an avalanche ornegative particles to stream towardthe anode. The excitation of the gasin this way causes it to glow with acolour that is characteristic of thegas used. The most efficient is neonwhich gives out orange light. Thedisadvantage of the system is that itrequires about 100 to 200 volts tocause the discharge to start.However, low cost and highbrightness means that they findmany uses in applications where aCRT is too bulky, for example,luggable computers - these aregenerally designed to be used withthe mains but transportable fromlocation to location.

As with LCDs, a multiplexingsystem is used to address individualpixels or elements of the display.The simplest system uses a set ofelectrodes on the bottom of the

display at right angles to a set on the top with smallcavities, in the position of each pixel, between the two- see illustration.

Turning on a cavity requires a voltage above acertain threshold level. By setting one of the electrodesto half of this value and then the other to the oppositehalf, only the cavity where they cross will have the fullvoltage and turn on. This means that an array of, forexample. 10 x 10 pixels only needs 20 connections.

Row data

1 1 1 1 1 1 1 1 1 1

1 1 1 1 1 1 1 1 1 1

Top view

Side view

Plasma UpperLower cavity electrode

conductorsThe operation of agas plasma display.


Display Feature

The Cathode Ray Tube

The operation of the CRT was a fairly logical extensionof early valve technology. A heater emits electronswhich are attracted down the length of the tube tosmash into the phosphors at the other end. Thecollisions generate photons of light which are emittedfrom the viewing end of the tube. The electrons can beconstrained into a narrow beam by focussing coils andsteered around the face of the tube either by moreelectric coils or by electrostatic plates. By scanning thestream of electrons across the face of the tube startingat the top left and tracing out horizontal lines until thebottom right is reached, a square picture of raster scan

Exited phosphourwhere electrons hit

Screenphosphours

image can be built up. As the beam moves across thetube, its intensity can be varied by altering the power tothe heater causing the phosphors to emit more or lesslight, giving a monochrome image of varied levels.

To obtain colour, three phosphors are used, one foreach of the primary colours, red, green and blue. Byutilising three electron guns and steering the beam inthe right way, a colour image can be built up.

To make sure that the electron beams hit thecorrect phosphors, a mask is used. This alsodetermines the resolution or number of pixels that it ispossible to display.

Y (vertical)deflection plates

X (horizontal)deflection plates

Glass

Conductive envelope

layer

AnodeGridsystem Cathode Heater

coil

Electron beam

Electricalconnections

which is the same as 40 charactersin 25 rows based on an 8x8 matrix,now requires 8000 bytes - 40 bytesgives 320 pixels and there are 200rows. The addition of colour

increases the memory requirementyet again since additionalinformation is needed. For examplea 320 x 200 display with 16 coloursrequires 320 x 200 x 4 bits (the 4 bits

MEMMEMMEMMEMMEMOMMMEMMEMME IIIMM ME UM

MEM ME ME ME MI IIUM ME ME ME MIMIME MEM MIME

M ME= ME ME ME MIMEME NM ME IM ME =ME ME UM ME

Fig. 2. Characters on a VDU are made up from individual pixels.

allow 16 colours to be defined) or32000 bytes. Modern VGA (VideoGraphics Array) displays used onIBM PCs and compatibles allow 640x 480 with up to 256 colours andhence 300k or so of memory. Thereare other systems which allowfewer colours but select them froma large palette - super VGAprovides 1024 x 768 x 256 coloursselected from a palette of 256,000 -the picture on the front cover of themagazine give some idea of thequality possible.

The future of the computerdisplay still lies with the CRT forthe near future. However, thedevelopment of colour LCDs andother devices such as the PrivateEye, which projects and image ofthe screen directly onto the retina ofthe eye, could see the dream of thebadge sized super computer cometrue.


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of 10 51/4" DSDD £5.00 ref 5P1687.SONIC CONTROLLED MOTOR One click to start, two click toreverse direction, 3 click to stop) £3.00 each ref 3P1377FRESNEL MAGNIFYING LENS 83 x 52mm £1.00 ref BD827TLCD DISPLAY. 41/2 digits supplied with connection data £3.00 ref3P777 or 5 for £10.00 ref 10P78TALARM TRANSMITTERS. No data avaliable but nicely madecomplex transmitters 9v operation. E4.00 each ref 4P81T100M REEL OF WHITE BELL WIREfigure 8 pattern ideal forintercoms, door bells etc £3.00 a reel ref 3P107TTRANSMITTER RECEIVER SYSTEMonginaly made for nursecall systems they consist of a pendant style transmitter and areceiver with telescopic aen al 12v 80 different channels £12.00 ref12P26TCLAP LIGHT. This device turns on a lamp at a finger 'snap' etc.nicely cased with built in battery operated light. Ideal bedside light etc£4 00 each ref 4P82T.ELECTRONIC DIPSTICK KIT.Contains all you need to build anelectronic device to give a 10 level liquid indicator £500 (ex case)ref 5P194TUNIVERSAL BATTERY CHARGER.Takes AA's, C's, D's andPP3 nicads Holds up to 5 batteries at once. New and cased, mainsoperated £6 00 ref 6P367.ONE THOUSAND CABLE TIESI75mm x 2.4mm white nyloncable ties only £5.00 ref 5P181TPC MODEMS1 200/75 baud modems designed to plug into aPC complete with manual but no software £18.00 ref 18P 12TASTEC SWITCHED MODE POWER SUPPLYBOmm x 165mm(PCB size) gives -r.5 at 3.75A, 4.12 at 1 5A, -12 at 0.4A.Brand new£12.00 ref 12P397.VENTILATED CASE FOR ABOVE PSUNith IEC filtered socketand power switch. £5.00 ref 5P190TIN CAR POWER SUPPLY.Plugs into cigar socket and gives3,4,5,6,7.5,9, and 12v outputs at 800mA. Complete with universalspider plug. £5.00 ref 5P167T.CUSTOMER RETURNEDswitched mode power supplies. Mixedtype, good for spares or repair £2.00 each ref 2P2927.DRILL OPERATED PUMP.Fits any dnll and is self priming. £3.00ref 3P140TPERSONAL ATTACK ALARM.Complete with built In torch andvanity mirror. Pocket sized, rag's 3 AA batteries £3 00 ref 3P135TPOWERFUL SOLAR CELL 1AMP .45 VOLTbnly £5,00 ref5P192T (other sizes avaliable in catalogue).SOLAR PROJECT KIT.Consists of a solar cell, special DC motor,plastic fan and turntables etc plus a 20 page book on solar energy,Price is £8.00 ref 8P517.RESISTOR PACK.10 x50 values (500 resistors) all 1/4 watt 2"'metal film. £5.00 ref 5P1707.CAPACITOR PACK 1.100 assorted non electrolytic capacitors£2 00 ref 2P2867.CAPACITOR PACK 2. 40 assorted electrolytic capacitors £2 00ref 2P2877QUICK CUPPA? 120 immersion heater with lead and cigar lighterplug moo ref 3P927.LED PACK .50 red lads, SO green lads and 50 yellow lads all 5mm£8.00 ref 8P527FERRARI TESTAROSSA. A true 2 channel radio controlled carwith forward, reverse, 2 gears plus turbo. Working headlights£22.00 ref 22P6TULTRASONIC WIRELESS ALARM SYSTEMTwo units, onea sensor which plugs into a 13A socket in the area you wish toprotect. The other, a central alarm unit plugs into any other socketelsewere in the building. When the sensor is triggered (by bodymovement etc) the alarm sounds. Adjustable sensitivity. Price perpair £20 00 ref 20P34T. Additional sensors (max 5 per alarm unit)£11 00 ref 11P6TWASHING MACHINE PUMP.Mains operated new pump. Not selfpriming £5.00 ref 5P187IBM PRINTER LEAD. (D25 to centronics plug) 2 metre parallel£5.00 ref 5P166T.COPPER CLAD STRIP BOARD17" x 4" of .1" pitch "vero" board£4 00 a sheet ref 4P62T or 2 sheets for £7 00 ref 7P227STRIP BOARD CUTTING TOOL£2 00 ref 2P35273 1/2" disc drive 720K capacity made by NEC £60,00 ref 60P2TTV LOUDSPEAKERS.5 watt magnetically screened 4 ohm 55 x125mm. £3.00 a pair ref 3P109T.SPEAKER GRILLS set of 3 matching grills of different diameters.2 packs for 22.00 (6 grills) ref 2P364750 METRES OF MAINS CABLE £3.00 2 core black precut inconvenient 2 m lengths. Ideal for repairs and projects ref 3P91T4 CORE SCREENED AUDIO CABLE 24 METRES £2.00Precut into convenient 1.2 m lengths. Ref 2P365TTWEETERS 2 1/4" DIA 8 ohm mounted on a smart metal plate foreasy fixing £2.00 ref 2P366TCOMPUTER MICE Originally made for Future PC's but can beadapted for other machines. Swiss made £8.00 ref 8P57T. Atan STconversion kit £2.00 ref 2P362T6 1/2" 20 WATT SPEAKER Built in tweeter 4 ohm £500 ref5P205T5" X 3" 16 OHM SPEAKER 3 for £1 OOP ref CD213TADJUSTABLE SPEAKER BRACKETS Ideal for mountingspeakers on internal or external corners. uneven surfaces etc. 2 for£5.00 ref 5P207TPIR LIGHT SWITCH Replaces a standard light switch in secondslight operates when anybody comes within detection range (4m) andstays on for an adjustable time (15 secs to 15 mins). Complete withdaylight sensor. Unit also functions as a dimmer switch! 200 wattmax. Not suitable for flourescents £14.00 ref 14P1OT2 MEG DISC DRIVES 31/2" disc dtives made by Sony housed ina 5 1/4" frame 1 2 meg formatted. £66.00 ref 66P1TCUSTOMER RETURNED 2 channel full function radio controlledcars only £8.00 ref 8P200TWINDUP SOLAR POWERED RADIO! FM/AM radio takes NICADbattenes complete with hand charger and solar panel 14P200T240 WATT RMS AMP KIT Stereo 30-0-30 psu required 240.00 ref40P200T300 WATT RMS MONO AMP KIT £55.00 Psu required ref 55P200TALARM PIR SENSORS Standard 12v alarm type sensor will inter-face to most alarm panels £16.00 ref 16P200TALARM PANELS 2 zone cased keypad entry, entry exit time delayetc. £18.00 ref 18P200T35MM CAMERAS Customer returned units with built in flash and28mm lens 2 for £8.00 ret 8P200TSTEAM ENGINE Standard Mamod 1332

uirgine complete with boiler p,ston etc £30


How It Works

How It Works...Supersonic HeterodyneRadio expert Ian Poole describes the operation of the humble radio receiver withillustrations by Derek Gooding.

The transistor radio has to beone of the most commonpieces of electronic equipment

around the home. There is usuallymore than one in each householdand they range from the verycheapest Medium Wave only setsall the way up to Hi-Fi tunerscosting several hundreds ofpounds. As well as being anintegral part of everyday life, thetransistor radio is also one of theoldest electronic gadgets inconstant use.

Back In The WarVirtually all radios operate using atechnique known as superhet. Thisword is derived from the termsupersonic heterodyne which wasintroduced when the principle wasfirst invented around the end of theFirst World War.

From the name it can beimagined that the system involvesthe beating or heterodyning of twohigh frequency signals. Morespecifically, the principle is basedaround the fact that when twosignals are brought together in anon-linear electronic circuit thentwo further signals are producedwhich are at frequencies equal tothe sum and the difference of theoriginal two.

Mixing R UpLooking at the operation of thereceiver, the radio signal enters acircuit called a mixer where itinterferes and "beats" with anothersignal from the local oscillatorwithin the radio. The output fromthe mixer is then passed into anintermediate frequency or IF stage.

This consists of a series of fixedfrequency filters and amplifiers. Togive an example of the operation ofthe system, imagine that the localoscillator is running at 2.0MHz andthe IF filter has a frequency of0.5MHz. In this situation it will bepossible for signals at 2.5MHz and1.5MHz to be converted down tothe frequency of the filter. In orderto prevent signals on the twodifferent frequencies from enteringthe filter some tuning is added tothe radio frequency stages of thereceiver.

Once the signal reaches theintermediate frequency stages it isamplified and filtered. The nextstep is called demodulation andinvolves recovering the audio fromthe radio frequency signal. In thecase of amplitude modulation thiscan be done quite simply using adiode and a few other components.

All that remains is for the audiosignal to be amplified so that it canbe used to drive a loudspeaker or apair of earphones.

Inside The BoxIn virtually all transistor portableradios a ferrite rod aerial isprovided to pick up Medium(525kHz to 1605kHz) and LongWave (150kHz to 285kHz)transmissions. This type of aerial isrelatively efficient for its size andbeing small it can be fitted into thecase of the radio. Essentially itconsists of a tuned coil woundaround a length of ferrite. As thepickup coil is tuned it acts as the RFtuning for the receiver. For FM aseparate extendable aerial has to beused as ferrite rod aerials do notoperate up to the frequencies usedfor FM (47MHz to 216MHz).

On the circuit board for thereceiver there will be a main tuningcapacitor. This has two sections toit. One for tuning the ferrite rodaerial coil and the other to tune thelocal oscillator. These two functionshave to be carried outsimultaneously, otherwise theoscillator and the RF tuning will not"track" together and they will betuned to different frequencies.There are also two small presetadjusters on this capacitor. One foreach section.

In addition to the tuningcapacitor there is also a coil for theoscillator. This is housed in ascreening can. In most cases theactual circuit for the oscillator andmixer is all based around a singletransistor. Whilst this may not seemto lead to the best performance it isnormally quite sufficient fordomestic radios.

The IF amplifier will have tunedcoils to give it selectivity. Generallythe frequency of this amplifier willbe around 455 kHz for AM and 10.7MHz for FM . These coils will all beadjustable so that the amplifier canbe tuned for the optimum results.

The detector normally consistsof a single diode. From here thesignal is passed to the volumecontrol and then into the audioamplifier. In many cases the audiostages will only use transistors. Ifthis is the case then the two outputtransistors can usually be identifiedby the fact that they are larger ormounted on a heatsink.Alternatively if an integrated circuitis used then it will usually havesome form of heatsinkarrangement. In some cases it mayeven use the copper on the printedcircuit board 1111


How It Works

Medium wave coil

Tuningcapacitor

Diodes fordetector

Ferrite rod aerial

Long wave coil

Trimmeradjustments

Localoscillator coil

Wavebandswitch

IF

transformers(adjustable)

Headphonesockets


Data Sheet

111$32CG160

32 -Bit ProcessorThe NS32CG160 is one of NationalSemiconductors' EmbeddedSystem Processors aimed at office

imaging peripherals. Featuring a 16Mblinear external address space and 16 -bit external data bus, the chipincorporates a 32 -bit arithmetic logicunit, instruction pipelining, an eightbyte prefetch queue and a 16 x 16 bithardware multiplier. Special attentionhas been given to graphics supportwith on chip bit block image transfer(BITBLT) which allows images to bemanipulated at the processor levelwith a subsequent increase in speed.There are 18 dedicated graphicsinstructions as well as full support forfloating point calculations via theNS32x81 coprocessors.

Built into the chip are a clockgenerator, three 16 -bit timers, twoDMA channels, 15 levels of interruptsand a power save system.

The architecture provides five maindata types; bit, binary coded decimal,bytes, words and double words as wellas facilities for array processing.

Image TransferBITBLT operations are used to moverectangular blocks of data around thememory area and hence any displaydevice in use. There are seveninstructions associated with thetransfer, six being executed internallyand one operating in conjunction with

MIT Operation0

1

2

3

45

67

891011

121314

an external BITBLT processing unit(BPU). The general purpose registersare loaded with information about thesource and destination of the block tobe moved, the base addresses, shiftamounts, height, masks, warps andwidth.

Since memory is usually bytealigned it isn't possible to directlytransfer data from one bit position toanother - the bits usually relate topixel positions. The get around this,the shift value is used to align to theword boundary where necessary.Unfortunately, the layout of memorydoesn't directly correspond to thelayout of a screen or printout and thewarp value is needed to define thedistance between two lines of theimage in memory (in bits). The baseaddress tells the processor where theimage starts and the height and widthtell it the size.

As well as simply moving bitimages around, various processingoperations can be executed. The logicalfunctions AND, OR and XOR areperformed on the source anddestination data with the result beingplaced at the destination.

BITBLTs are useful in mostcomputer graphics operations fromsimply printing characters onto thescreen or drawing lines, to movingoverlapping windows and fillingareas.

-

Operation performed.0

source AND destinationsource AND - destination

source-source AND destination

destinationsource exclusive OR destination

source OR destination-source AND -destination

source exclusive NOR destination-destination

source OR -destination-source

-source OR destination-source OR -destination

1


Instruction pipeline

Loader

Registerfile

Executionunit

Hardwaremultiplier

Instruction set

Block diagram of th

MOVEs Move a valueMOVQs Move signed 4 -bit constantMOVMs Move multipleMOVZBW Move with zero extensionMOVZID Move with zero extensionMOVXBW Move with sign extensionMOVXsD Move with sign extensionADDR Move effective addressADDs AddADDQs Add signed 4 -bit constantADDCs Add with carrySUBs SubtractSUBCs Subtract with borrowNEGs 2s complement negateABSs Get absolute valueMULs MultiplyQUOs Divide rounding to zeroREMs Remainder from QUODIVs Divide rounding downMODs ModulusMEls Multiply and extend integerDEIs Divide, extend integerADDPs Add BCDSUBPs Subtract BCDCMPs CompareCMPQs Compare quickCMPMs Compare multipleANDs Logical ANDORs Logical OR

Data Sheet

32 bits

8 -byteinstruction

queue

MicrocodeROM

Graphicssupport

logic

NS32CG160.

BICsXORsCOMsNOTsScondsLSHsASHsROTsEXTsINSsEXTSsINSSs

Businterface

unit

Clear selected bitsLogical exclusive ORComplement all bitsBoolean completemtSave condition codeLogical shift left or rightArithmetic shift left or rightRotate left or rightExtract bit fieldInsert bit fieldExtract bit fieldInsert bit field

CVTP Convert to bit field pointerCHECKs Index bounds checkINDEXs Recursive indexingMOVSs Move stringMOVST Move and translate stringCMPSs Compare stringsCMPST Compare and translateSKPSs Skip over stringSKPST Skip translating until/whileJUMPBRBcondCASEsACBsJSRBSRCXPCXPDSVC

Bit blocktransfer

processingunit

DMAcontroller

Interruptcontrol

unit

Timers

> Address anddata

> Control andstatus

JumpBranch relativeConditional branchMultiway branchAdd 4 -bit const bra if NZJump to subroutineBranch to subroutineCall external procedureCall external with descriptorSupervisor call

FLAG Flag trapBPT Breakpoint trapENTER Save regs and set stackEXIT Restore and reclaim stackRETRXPRETTYRETISAVE

Return from subroutineReturn from ext procedureReturn from trapReturn from interruptSave general purpose regs

RESTORE Restore general regsLPRs Load dedicated registerSPRs Save dedicated registerADJSPs Adjust stack pointerBISPSRs Set bits in status regBICPSRs Clear selected status bitsSETCFG Set configuration registerMOVn Move FP valueMOVLn Move and shortenMOVEFL Move and lengthenMOVsn Convert int to std or longROUNDs Round to integerTRUNCns Truncate to integerFLOORns Convert to largest integerADDn Add floatingSUBn Subtract floatingDIVnCMPnNEGnABSnLFSRSFSR

Divide floatingCompare floatingNegate floatingGet absolute valueLoad FSRStore FSR

RO-R7

Adcress

Program counterStack pointersFrame pointerStatic base

IntbaseI Module

Processor states

StatusConfiguration

ConfigurationDMA Controller

DMA statusInterrupt maskDebug status

Device address countDevice address

Block length countBlock lengthMode control

Channel controlBITBLT

Barrel cntlRight maskLeft mask

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POLYnDOTnSCALBnLOGBnNOPWAITBBOR

Interrupt controller

VectorIn Service

Timers

CounterReload AReload BControl

Internal registers.

Polynomial stepDot productBinary scaleBinary logDo nothingWait for interruptBit Align Block Transfer OR

BBAND BABT ANDBBFOR BABT Fast ORBBXOX BABT XORBBSTOD BAB source to destBITWT Bit aligned word transferEXTBLT External BABTMOVMPs Move multiple patternTBITS Test bit stringSBITSSBITPSTBITsSBITsSBITIsCBITsIBITsFFSs

Set bit stringSet bit perpendicular stringTest bitTest and set bitTest and set bit interlockedTest and clear bitTest and invert bitFind first set bit

s determines the integer length B =byte, W = word, D = doubleword. n determines the floating pointlength, F = standard floating, L = longfloating.


Inductors

Practical Components:The InductorInductors can be ranked with resistors and capacitors as the simplest of electroniccomponents.

Inductors are found in manyapplications in electronics andespecially in alternating current

circuits. The way in which theyreact to varying currents isimportant in filters and tunedcircuits.

The action of an inductor comesfrom the interaction betweenelectrons and magnetic fields.

ow It WorksThe magnetic field f cutting throughthe coil at right angles to the frontarea is equal to the flux B times thearea A:

f=BAThe electromotive force (EMF) E

generated in the coil is dependsupon the number of turns, N, andthe changing magnetic field withtime df/dt:

E = -Ndf/dtFrom Ampere's law the

magnetic flux or field strength B isdefined as a constant c times thecurrent I. c depends on the size,shape and number of turns of thecoil. So:

B = clThe interesting point about a coil

is that changing the magnetic fieldwithin it generates an EMF andhence current in the coil. Running achanging current through a coilgenerates a magnetic field. So, achanging current generates achanging field which generates achanging current. The two currentsare opposite so that the coil orinductor resists a changing current.From the above equations,substituting BA for f in E = -Ndf/dtand assuming A is constant:

E = -ANdB/dt

1. The DiscoveryInduction first demonstrated byMichael Faraday (1791 - 1867) in1831. He also laid the foundationsfor the idea of magnetic lines offorce later developed by JamesClerk Maxwell into classical fieldtheory.

Joseph Henry (1797 - 1878), a,US physicist discovered induction

Substituting cl for B and since cis constant, this now becomes:

E = -AcNdl/dtGrouping the constants together

as L, the inductance:E = -Ldl/dtL is therefore dependent upon

the number of turns, area anddimensions of the coil, all of whichare constant for any particulardevice - L is measured in Henries(H).

What this all boils down to is

and self induction but was pre-empted by Faraday who publishedhis results first. Eventually Henrywas honoured by having the unit ofinductance H named after him.

A circuit has an inductance ofone H if the current which flowsthrough it changes at one amp persecond and produces anelectromotive force of one volt.

that the EMF, or voltage, generatedby a coil is dependent on thechanging current and theinductance. For slow currentchanges, the EMF is small. For avery fast changes, it can be prettylarge. A practical example is whenswitching off a HiFi. A thump maybe heard from the loudspeakers asthe current in the coils collapsesvery quickly. Many modernamplifiers turn off slowly to avoidthis happening.

Area of coil A


Inductors

Air cored Ferrite cored Iron cored Variable

GlossaryChoke -a device used to impede theflow of alternating current or pulseddirect current, including spikes, bymeans of self inductance.Core - magnetic material placedwithin a coil to intensify themagnetic field and alter theinductance.Core loss - heat produced in a coreby eddy currents induced into thematerial. It can be minimised bymaking the core from ferrite.Ferrite -a compound of iron (ferric)oxides and ceramic material. Theyretain their magnetic properties butare poor conductors of electricity.Former -a non -reactive, insulatingsupport, usually made from ceramic,

Passing a current through a coilof wire generates a magnetic field.This magnetic field creates acurrent that is in the oppositedirection to the original current.

Inductance depends on thenumber of turns in a coil, its shape,dimensions and whether any metalis near it. The latter effect is used tomake variable inductances. A rodof ferrite is placed inside a coil witha screw fitting so that it can beinserted and withdrawn to changethe inductance.

In electronic circuits, the twomain uses for inductors are infilters and tuned circuits. Since aninductor resists changes in currentand resists them more at highfrequencies, putting the inductor ina series circuit gives a low passfilter. In parallel it forms a highpass filter since low frequenciespass through the inductor ratherthan the load. It is interesting tonote that this is the opposite to theoperation of a capacitor.

card or plastic, around which a coilis wound.Henry - H, the measure ofinductance. One H is present whenone volt is produced by a varyingcurrent of one amp. Named afterJoseph Henry an early researcher inthe field of magnetic theory.Induct - introduce formally intopossession hence inductor, one whoinducts.Inductance - the property of acircuit which opposes any change tothe existing current level.Q - the ratio of the reactance of aninductor to its effective seriesresistance at a given frequency.Reactance - the opposition offeredby a coil measured in ohms.Turns -a number of complete loopsof wire.

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Measurement Project

PE Chronos...

Building The DisplayThe Universal Counter Timer gets its output section this month as Anthony Smith describeshow to build and test the display board.

This month we'll examine theremaining display boardsection, and then build and

check out the board itself. The firstcircuit of interest, shown in Fig. 1, isprimarily intended to drive thefunction and units LEDs, althoughits secondary purpose is to generateseveral control signals required bythe main circuits.

IC27 is a 4 -to -16 line decoderwhich converts the binary code atinputs SO, Sl, S2, and S3 into thecorresponding decimal equivalentat any of the sixteen outputsnumbered 00 to 016. The outputsare active high, and are buffered bythe sixteen invertors of IC49, IC50and IC51 to provide the required toilluminate one of the sixteenfunction LEDs (D64 to D79inclusive).

IC27 is driven by the fourbinary-coded function lines, FO toF3 , generated the function selectioncircuit described last month. Forinstance, we select function 11 suchthat the binary code is 1010; IC27decodes this input, and drives thecorresponding decimal output, 011(pin 20), high(all other outputsremain low). As a result, functionLED 11 (D74) is illuminated toindicate the choice of function.

Units LEDsAs well as driving the functionLEDs, the decimal outputs of IC27are used in many other ways,particularly to illuminate the unitsLEDs. Table 12 lists the unit LEDappropriate for a particularfunction, or group of functions.

Under normal conditions,functions 1 and 2 (frequency A andB) indicate frequency in kHz units;however, when the high resolution

frequency (HRF) mode is selected,the units must be changed to Hz tocater for the increased resolution.Note, also, that function4(frequency ration A/B) andfunction 8 (units A) both makedimensionless measurements, andthus require no units indication.

Driving the MHz LED isstraightforward: 03 of IC27 issimply buffered by IC54e which cansink enough to illuminate D60whenever function 3 is selected.(The 4514, being a standard CMOSdevice, cannot sink or sourceenough current to illuminate astandard LED; hence, the outputsbe buffered by the more powerfulHCMOS devices).

Driving the remaining unitsLEDs is a slightly more complicatedtask. Consider, for example, the usLED: this must be illuminatedwhenever one of functions 5,6,7,9,or10 is selected. Thus, we require asignal described in logic terms as(5+6+7+9+10). This is achieved intwo steps. Firstly, decimal outputs07,09,010 are used to driveinvertor IC51c via diodes D46, D45,and D44, respectively. (The diodes,along with R106, act as a simplediode -resistor logic or network).

Thus, the output of the invertoris (bar all 7+9+10), that is, it is lowwhenever function 7 or 9 or 10 isselected. This output is used ascontrol signal for the main board,and is also used to drive IC51d,such that the output of this invertoris (7+9+10). By combining thissignal with the outputs 05 and 06using the diode -resistor network ofD41, D42,D43 and R107, wegenerate the (5+6+7+9+10) signalrequired to drive the us LED (D59).

The seconds LED (D58) is drivenin a similar manner. Outputs 011 to

016 are configured in anotherdiode -resistor network usingdiodes D49 to D54, such that theoutput of IC52 goes low andilluminates D58 whenever function11,12,13,14,15, or 16 is selected. Theoutput is further inverted by IC54dto provide another control signalfor the main board, namely(11+12+13+14+15+16).

The kHz LED (D61) must beilluminated whenever function 1 or2 is selected, but must be swappedfor the Hz LED (D62) is HRF isselected. This function can beselected either by operating S13 orby a logic high level from theexternal bus.

With the HRF function off, theoutput of AND gate IC57b is low,the output of IC54a is high and D62is reverse biased. Consequentlywhenever function 1 or 2 isselected, the input to IC54b isdriven high via diode D48 or D47,its output goes low and the kHzLED becomes forward biased.

If HRF is selected no, IC54aoutput goes low, removing theforward bias from the kHz LEDwhich is thus extinguished. D62,however, now becomes forwardbiased and is illuminated,indicating that the reading is nowin Hz. At the same time, the highlevel from IC57b is transmitted tothe main board via terminal R. Thissignal is used to bring thefrequency multiplier into play.

Reset CircuitThe remaining sections of the

display board are shown in Fig. 2.Gates IC57c and IC57d form thereset circuit which is active low andoutput to the main board viaterminal S. Resets occur at powerup, the operation of SW15, a signalinput to SK9, a signal from the


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external bus and by a change offunction or range.

Note that diodes D94 and D95provide protective clamping at thegate input to guard againstoverloads.

On the main board, the resetsignal is fed to the bar RESET inputof the ICM7226A (IC24) via theNOR gate in IC45. At the same timeit is also fed to other circuits on themain board, namely the priming,extended time interval, stopwatchand trigger delay circuits.

As with Reset, the Holdoperation can be activated in anumber of ways. Pressing the frontpanel switch, a signal from theexternal bus and a signal at the holdinput are all valid methods.

When using SW14, a toggleaction is used that allows the user tooperate in a "hands free" way witha further press of the buttonreleasing the hold.

In The HoldThere are many instances when it isdesirable that hold be assertedimmediately after a measurement

has been completed so that furthermeasurements (which may happenvery quickly) do not change thereading. This kind of operation isprovided by the one-shot or single -event circuit based around flip-flopIC32b.

In the lower left hand corner ofFig. 2, the bar STORE signal fromthe 7226A is fee to the clock of aflip-f;lop so that its rising edgetransfers the logic level at D to Q.When SW16 is open, the D input isheld low by R12 and Q is thereforealso held low. However, when D ispulled high an the next bar STOREsets Q high and latches hold,capturing the last measurement.Getting out of this hold conditionrequires switching the one-shot offor activating the master reset.

Display connectionsFig. 3 shows how the digit driversand segment outputs from the7226A are connected to thedisplays. Note that although the dp(decimal point) output is shownconnected o the dp pin o displayeight, this is only really true of

displays 1 to 87. For display eight,the decimal point is actuallyreplaced by the overflow LED, D31.

The component layout for thedisplay board is shown in Fig. 4. Aswith the input board and the mainboard, construction begins bychecking both sides of the PCB forshort circuits, broken tracks,missing tracks, and so on.

The first step is to insert thethrough board links and solder terninto place on both sides of theboard. Next come the diodes andresistors, again making sure tosolder on both sides of the board.IC58 and IC59 follow and don't usesockets. They should be soldered tothe ground plane whereappropriate.

The IC sockets go in next, butdon't have their chips inserted, andare followed by the capacitors -take care with the polarity of C108.

The connector plugs P12 to P17should be inserted next, rememberthat they are mounted ion the rearof the board and are soldered on thecomponent side. At the same time,solder the nine veropins into place -these two are located on the rear ofthe board.


PE Chronos

Soldering the LEDs into placerequires a little patience as theymust be located at the correct heightabove the board - all othercomponents should not extendmore than 1/2in above the frontsurface.

The simplest way to install theLEDs is to make use of the frontpanel as a guide. Firstly, screw thefour 1/2in spacers to each corner ofthe board. Next, insert the sixteenfunction LEDs (D64 to D79), thefour range LEDs (D83 to D86), thefive units LEDs (D59 to D62), thegate LED (D22) and the overflowLED (D3). Remember the function,range and units LEDs are standardred 3mm types, the gate a standardgreen 5mm and the overflow a highbrightness 3mm red.

Take great care to locate theLEDs the right way around °- theanodes are marked with an 'a' inFig.4. Next, gently push the LEDstowards the board so that theyextend no more than 1/2in abovethe surface. Now, screw the boardto the front panel and push eachLED slightly away from the boardsothat each one locates into itsallocated hole in the panel.

The LEDs should now be thatthe correct height above the boardfrom the panel and can be solderedon the rear side. When this is done,unscrew the board from the paneland solder the LEDs on thecomponent side. Take care duringthis procedure not to force the LEDsat all, don't bend the leadsexcessively and don't stress thesolder joints.

With all the LEDs in place, theboard should look something likeFig.5. The final step is to solder theminiature display -test pushbutton,SW17) into place using two shortlengths of thin wire.

Checking It OutThe first step is to check the currenttaken by the VHF section (channelC). Temporarily connect the OV and5V termninals of P17 to thecorresponding terminals of P11 onthe main board. Fig. 6 shows theconnections to be made to the rearof the display board. Don't yetmake any connections except thoseto P17.

Connect an ammeter set to the100mA range is series with the 5Vline between P11 and P17. Do notyet insert any ICs in the display

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board or the main board sockets.Switch the mains power and

note the current. This should be inthe region of 50mA. Check for faultsaround IC58 and IC59 if the currentis higher than this. Turn off themain power.

Temporarily connect all theswitches to the display board asshown in Fig. 6. The 5V and OVmain board terminals are thoselocated next to P11 - it is notnecessary to connect the inputboard to the main board duringthese tests.

The display board ICs can nowbe inserted as shown in thecomponent layout of Fig. 4. Takecare with orientation and rememberthat all the chips are CMOS devices.The seven segment displays cannow be inserted although they arenot required by for the followingtests.

With the ammeter still in place,switch on the mains power andobserve the current - it should notbe more than 70mA to 80mA. Ifexcessive current is being drawn,quickly check the temperature ofthe ICs. If no faults are found on theboard itself, check the temporaryswitch connections.

If the current reading isacceptable, operate the illuminatedswitches: the current should rise by20mA or so.

Now turn off the switches, turnoff the mains power and remove theammeter. Replace the temporarysupply connections with a 2 -wayribbon cable link betweenconnectors P11 and P17 - the linkshould be about 12cm long. Noother connections should be made

to the main board.

Function ChecksSwitch on the mains power again.The function 1 LED (D64) and thekHz LED (D61) should come on. Ifsome other function or units LEDlights up, check C67 and R100 at thereset input of IC26.

Now check that SW11 and SW12can be used to step up and downthrough the functions one at a time.If this operation causes one or morefunctions to be skipped, check theswitch debounce circuits.

While stepping through thefunctions, use a voltmeter or logicprobe to check that the correctbinary sequence is being output atterminals B, C, D and E of connectorP14.

Now select function 1 andmonitor terminals Q and R ofconnector P15; they should both below. Turn on SW13 (HRF) ad checkthat the units LED changes fromkHz to Hz, at the same time, bothterminals Q and R should go high.Repeat this procedure with functiontwo selected.

Turn off SW13 and selectfunction 1 or 2. Check that HRF canbe selected by taking high the HRFinput terminal of connector P16.

Remove the high level from P16and connect the voltmeter or logicprobe to terminal M of P14. Nowobserve the logic level at terminal Pof connector P15; this should behigh only for functions 11 to16.Check, next, the level at terminalQ. This should go high wheneverfunction 3 or 11 to 16 are selected.


PE Chronos

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Checks On ResetWith reference to Fig 2, connect alogic probe to terminal S of P15 andpress the reset switch. The level at Sshould go low. Now temporarilytake the reset input low byconnecting vero pin 19 to OV. Sshould again be low. Remove thelow level from the input and applyit to the external bus reset connectorP16. S should go low again. Finally,pressing the range and functionselect switches also makes S go low.

The power up reset an bechecked by observing the Q outputsof flip-flops IC32a (at pin 5) and atIC32b (at pin 9). turn off the power,

wait ten seconds, then switch onagain. The Q outputs should bothbe low - checking this five to tentimes proves that the outputs nevergo high. Check R133 and C73 if thisisn't the case.

Hold OnMonitor terminal 0 of connectorP15; it should below. Now press thehold button SW14 and output 0should latch high. Press the buttonagain and the output should returnto its original low level.

By waiting until the timebasecircuit has been built and tested, the

10MHz clock signal itself can beused to check channel C. Solder aresistor (say 1k) to the inner core ofthe co -axial cable connected to thechannel input. The, connect thisresistor to the 5V clock squarewaveat terminal 2 (main board).

The resistor and 505I inputimpedance of the channel attenuatethe signal such that the actual peakinput input amplitude is given by:

input amplitude = 5 x 50/(50+R)volts.

where R is the resistor value.By increasing the value of R in

suitable steps, there will come apoint where the prescaler will notfunction correctly. At this point, theinput amplitude measured on theoscilloscope or calculated as above,is the sensitivity of the channel forsquarewaves at 10MHz.

Note that although this testprovides a rough value for thechannel sensitivity, it is only reallyintended to check the basicoperation of the VHF amplifier andprescaler.

This completes all the tests onthe display board - the temporaryleads should be left in place as theywill be needed to check the displayin conjunction with the main boardin the next instalment.


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OMNI ELECTRONICSstock a wide range of

electronic components at

174 Dalkeith RoadEdinburghEH16 5DX

TEL: 031 667 2611Open Monday to Thursday

9:15am - 6:00pmFriday 9:15am - 5:00pm

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This includes all the8751 and 8748families, the PICmicrocontrollers,Z8s and EPROMEmulators. Nearly900 devices in all.

All our programmersus in the UK.Programming times are faster than most of our competitors, e.g.using the parallel port of your PC they program 2764s in 4 secondsand take less than one minute to blank check, program and verify 1

Megabit Flash Memories (and this time includes download time).

New devices areconstantly beingadded - ask ifyou want anyprogrammabledevice added toour list

are designed, manufactured and supported by

We also sell Gang Programmers, EPROM Emulators and Erasers and a universal cross -assemblerfor IBM PCs and compatibles

Write or phone today for Free Information Pack:Phone: (0666) 825146 Fax: (0666) 825141

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EXPRESS

Interak 1SINGLE BOARD COMPUTER

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£17.50+ 50p P&P

+ VAT

A computer doesn't have o look like you'd expect a computer to look.It doesn't have to have a keyboard and a screen and floppy disks andso on.

The SBC-1 has the bare minimum of chips a Z80 computer can haveand still be a computer: A 4 MHz Z80 -CPU chip, an EPROM chip (upto 32K), a static RAM chip (up to 32K) and a pair of 8255A I/O (inputoutput) chips giving 48 individual lines to waggle up and down. Thereare one or two additional "glue" chips included, but these are simple"74LS" or "HC" pans.

A star feature is that no special or custom chips (ie PALs, ULAs, ASICsetc) are used - and thus there are no secrets. The Z80A is the fastestand best established of all the 8 -bit microprocessors - possibly thecheapest too!

Although no serial interface is included, it is easy for a Z80A to waggleone bit up or down at the appropriate rate - the cost is a few penceworth of code in the program: why buy hardware when software will do?

Applications already identified include: Magnetic Card reader, miniprinter interface, printer buffer, push button keypad, LCD alphanumericpanel interface, 40 -zone security interface for auto sending of securityalarms, code converter (eg IBM PC keyboard codes to regular ASCII),real time clock (with plug in module), automatic horticultural irrigationcontroller.

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The idea is (if you are a manufacturer) you buy just one developmentsystem and then turn out the cheap SBC-1 systems by the hundred. Ifyou are really lazy we can write the program for you and assemble theSBC-1 cards so you can get on with manufacturing your product, leavinall your control problems to us.

GreenbankFor more details write or phone us:

Greenbank Electronics, Dept PE11 460 New Chester Road, RockFerry,Birkenhead, Merseyside. L42 2AE. Tel: 051-645 3391.


Review

VIP

A Virtual InstrumentJason Sumner plugs another board into his PC and explores the latest in Digital Multi -meters - but, is it all there?

Nearly everyone with aninterest in Electronics nowhas access to a computer of

some sort. Possibly to most popularis the IBM PC compatible machinefor which there is a whole host ofuseful software, from CADpackages to circuit simulators. Thelatest addition to this list is thedigital multi -meter. No longer isthis confined to a small box with asmall display and, sometimes,relatively few functions. The DMMVIP (Virtual Instrument) is a boardthat plugs into the expansion slot ofthe PC/XT/AT/386 with softwarethat provides all of the functionsneeded on the average DMM butusing the computer as a displayand storage system.

All of the usual functions arecatered for, DC, AC volts up to300V, DC, AC current up to 2A,resistance up to 20M52, capacitanceup to 21.1F and dBm up to ±55dB. Allof the controls are accessed via themouse pointer with the variousbuttons being pressed by simplypointing and clicking. The mainreadout is a 4.5 digit LED with theaddition of a chart recorder offeringeight pens.

On switching on and bootingup, the system can be auto -calibrated with the settings beingstored in an on -board EEPROM. Inpractice, these are set-up at thefactory so calibration should nothave to be performed very often.Selecting the various functions isquick and easy although there isquite a lot of room for on-lineimprovement with the addition of ahelp system - other DMMs have tomake do with a short book, the VIPcould have scored some extrabrownie points by putting all of thison-line. Anyone who has used a

DMM before will not have anytrouble using the VIP, apart,perhaps, from the chart recorder.The user interface for this is a littleconfusing and the minimumsample rate of half a second ratherslow, especially when the hardwareis capable of taking samples at 25times a second.

On starting up the chartrecorder a file name is requestedusing a rather badly designeddialogue system - an improvementwould have been to list current logfiles and be able to add to them.Other improvements would havebeen the ability to activate the log atparticular times in fact, the softwarecould have provided a wide rangeof additions not normally availableon a DMM.

The probes connect to the cardat the back of the PC which, formost users who have the main PCbox on their desks, should prove tobe no trouble. However, some

people keep their machines on thefloor with just the monitor andkeyboard on the desk top - theprobe leads are 1.5m long whichmay just be enough. Some form ofextension box with a protectedconnection to the computer andshorter leads would have made thewhole thing a bit neater though,perhaps, defeated the object of anall in one system somewhat.

As it stands the VIP simplyemulates a basic DMM and, apartfrom the data logging system,provides no particularly cleverextras. At the price of £499excluding VAT, a little more couldhave been expected. As it is, muchbetter value can be had by buying astand alone DMM at a far lowerprice.

For more information contactGlobal Specialities, Rackery Lane,Llay, Wrexham, Clwyd, LL12 OPB,Tel. 0978 853920, Fax 0978 854

Global Specialties

0 - 2000 _L. HI_FAST.12RANGE HOLD OFF

DC

REL

MODE FUNCTION 10 CH 0

Global Specialties

.1 P',a,Jaa 1.1.111... Li0-51 1-ciiCHART RUN SET DATUM SAMPLE RATE

PEN DOWN

The GlobalGlobal DMM VIP screen.


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Rain flanne Prnient

Counting The Rain

Drops As They FallThere may not have been very much rain this summer but things are certainly lookingwetter this autumn. Own Bishop's latest gadget finds out just how much.

Call it udometer, pluviometeror just a common -or -gardenrain gauge, the traditional

instrument for measuringprecipitation has not changed forhundreds of years. Even theancient Romans had them. Rain(plus snow or hail, after they havemelted) is collected in a wide -mouthed funnel and later pouredinto a measuring cylinder. Thecross-sectional area of the cylinderis usually one -tenth that of the openend of the funnel. This increasesthe sensitivity of the technique,since the easily measurable depth of1mm of water in the cylinder isequivalent to only 0.1mm ofrainfall.

The funnel and cylinder raingauge is inexpensive and simple touse but has the disadvantage thatits operation is essentially manual.There is no easy way to automate it.

Recording gauges have beendesigned which weigh the waterinstead of measuring its volume,but these instruments tend to bemechanically complex. Nowadaystwo main techniques are used, thetilting bucket and the drop counter.This project is an example of thetilting bucket technique. Themechanical parts of it are relativelysimple to construct and theelectronics requires only a counterand its associated logic. The circuitcan easily be placed undercomputer control and can be readremotely.

A rain gauge should be able tomeasure with a a precision of0.1mm or less. A day of typicallight rain produces five to tenmillimetres. If the gauge is to beread daily it must be able toaccumulate at least the 25mm ofrain which can fall during a singleday of heavy rain.

Plastic bucket

Hole for emptiedwater

Collectedwater

Optional support(see text)

Adhesive

Automatic Rain GaugeAs rain falls it accumulates in asmall balanced container, referredto as the bucket. When the amountof water in the bucket reaches agiven level, the bucket tilts over andempties itself. An electronic circuitcounts the number of times thebucket empties during a givenperiod, usually 24 hours. From thisdata the amount of rainfall inmillimetres can be worked out.

This project has the feature ofautomatically and remotelyrecording the count at a pre-settime. The rainfall day begins at9am (see box), a convenient hourfor the professional meteorologistjust starting a day's work at thestation. For the amateur, whoprobably has to leave home before9am, this can be an awkward time.To get around this, the gaugeregisters the 9 o'clock reading

Fig. 1.The main components of the rain gauge.

Stem of funnel

Narrow tubeSheet aluminium

Counter weightlead strip

Sensor

Magnet

Adjustable counterweight

"Knife edge"Groove


Rain Gauge Project

holding it until the user has theopportunity or the inclination toattend to it. In the meantime itcontinues to count the bucketfuls ofrain that have fallen since thebeginning of the current period.Moreover, the display unit can belocated indoors, so there is no needto get wet when taking a reading.

How it worksFig 1 shows the bucket mechanism.Rain is collected in a wide -mouthedfunnel in order to obtain a sufficientquantity to measure. It runs intothe bucket which has acounterweight to tilt it back at anangle of about 3°. The mechanismis pivoted on a "knife-edge" locatedin a groove in the wall of theenclosure. As the bucket fills, thewater extends further toward itsmouth and eventually overcomesthe counterweight. The mechanismtilts, the water gushes out of thebucket and drains away. As soonas the bucket empties, thecounterweight restores it to itstilted -back position.

Kicking The BucketThere is scope for ingenuity indesigning and building this part ofthe project. The essential points are: Use plastic for all parts that arelikely to come into contact withwater. The bolt -head inside thebucket is protected by coating itwith adhesive or some other water-proof compound. The bucket tilts back at a veryshallow angle, about 3°, but tiltsforward at a slightly greater angle(about 5°). The mechanism must swing

Glued

Top of box

Inverted rim ofsecond funnel

Funnel

Sealant

Narrow tube

Fig. 3. Setting up the funnel.

freely, which is why a knife-edgesuspension is preferred. Althoughthis is referred to technically as aknife-edge, it is simply a rectangleof sheet aluminium. The knife-edge is below the centreof mass of the assembly, so as togive it unstable equilibrium whenpivoting. The distance between the knife-edge and the centre of mass of thecounterweight is less than thatbetween the knife-edge and thecentre of mass of the bucket. Thisallows a relatively small mass ofwater to overcome the moment ofthe counterweight. If the bucket enclosure has walls,a groove is incised in the wall; theknife edge fits loosely in the groove.If the enclosure has groovesmoulded into its walls, use one ofthese but block the ends of thegroove with strips of plastic toprevent the knife-edge from slidingsideways. Some means of finely adjustingthe counter -weighting is essential;use a large nut that may be turnedto move it along the rod; bend thecounterweight (easy if it is made ofsheet lead); move the knife-edgealong the rod. It may be necessary to have asupport to prevent the bucket tiltingtoo far forward when emptying,otherwise it may not return to thetilted -back position. The enclosure must be firmlymounted to avoid shaking by wind. The jet is positioned so that itdelivers the rainwater cleanly intothe bucket, whether the bucket istilted forward or backward. The tube from the funnel must bepartly blocked or fitted with ascrew -clip (aquarium aerator clip)to restrict the maximum drippingrate to 3 drops per second.Otherwise the tilted bucket maynever have a chance to return to thetilted -back position during a heavyrainstorm. Usually the magnet supplied withthe Hall effect device has its south -seeking pole marked with a spot ofpaint. This end should be directedaway from the sensitive area (thedimpled surface) of the device.

The smaller the volume of waterdelivered at each tilting, the greaterthe precision of the gauge. Thebucket of the prototype delivers 3.3cm3 each time, which is a suitablysmall amount.

Sensorboard

Longbolt

Leads tocounter circuit

of box

North poleof magnet

IC1 Counterweight

Knife-edge

n

Bucket

SouthSouth pole ofmagnet

4Babsoex of

_4_, Strip blocksend of groove

Groove

Fig. 2. Top view.

Through The funnelThis is made from two large plastickitchen funnels. A single funnelwill do, provided it is of the correctdiameter. The alternative is to cutthe rim from a second funnel andglue this upside down to the mouthof the first funnel (Fig 3). Thisreduces the likelihood of rain fromsurrounding areas splashing induring heavy storms. It also makesit easier to give the collecting areathe correct radius. Before cuttingthe second funnel calculate what Rshould be, as explained under"Calibration".

Alarm CallReady -built alarm clock modulesare available fairly cheaply but it ismore economical to make use of adigital alarm clock that has begunto show signs of wear. All too oftenthe battery contacts are the first partto become unreliable and the clockis relegated to the scrap box.

The clock is removed from itscase and bolted to a piece ofstripboard. The old battery springcontacts (unreliable) are cut off andwires soldered directly to theclock's PCB (printed circuit board).The control push -buttons (alsounreliable and very fiddly) arereplaced by PCB -mounting push-buttons. It requires a certainamount of close examination of theclock's PCB to work out where tomake the new connections. Theoriginal push -buttons areconductive pads that make contactbetween pairs of copper areas onthe PCB. With a fine -tippedsoldering iron, there is no difficultyin soldering connecting wiresdirectly to these areas. Not all of


Rain Gauge Project

CalibrationFirst establish the amount of water delivered by the bucket eah time it empties.Call this V mmi. One way to do this is to slowly pour 100cm of water into thefunnel and record the count registered so that V=100000/count.

Now decide on what rainfall (depth in millimetres) is to be represented by thisone count. A suitable quantity is 0.1mm, which means the gauge can record up to25.5mm between readings (see box on binary). This is the maximum likely to fallin one day, expect in very rainy areas. If you live in such an area, 0.2mm wouldalso be a suitable, though less precise, amount.

Given 0.1 mm of rainfall as the unit amount. the area A (in mm2) of the top ofthe funnel is to be A and since the volume of water collected (V) is to represent0.1mm then the unit amount is yi0.1.Since the area o[ a circle A =SO A/TE=R and

R=A;(A/Tc)

therefore R = \I(V/0.1n)and R =1.78`'V

As an example, if V = 3300mm3, as in the prototype then R = 1.78 \ 3300 =102mm. The inverted funnel on top of the upright funnel is cut away to give anaperture of exactly 102mm radius.

the original controls are retained;for example, rain gauges to notneed to snooze. The controls foradvancing hours and minutes areretained and the slider switch for"set clock" or "set alarm" replacedwith a single button

The clock was originallypowered by two button cells,connected to give a split supply of±1.35V. This is obtained by using apotential divider, as in Fig 4. Foruse on a 5V supply R14 would bebetter replaced by a 18142 resistor.

The alarm signal is a squarewave, amplitude about ±1V with afrequency of about 1kHz and lastsfor 4 minutes. The value of R18 ischosen to bias TR1 into its on statein the absence of a signal from theclock. When the signal is present,its negative -going excursions turnthe transistor off repeatedly, givinga series of high pulses, the first ofwhich triggers the flip-flop(IC5c/IC5d). The rest are ignored.Capacitor C3 serves as a low-passfilter to remove any voltage spikes

CD

S2

N,-CY

U

R1422k

R1510k

R1610k

IS3

Circuit constructionThe circuit requires about 30mA ofpower and, since it is intended foroperation 24 hours a day, a 6V DC(direct current) mains adaptor isideal. An alternative would be touse four industrial D -type nickel -cadmium rechargeable batteries,which would last for about a week,especially if the LEDs are switchedoff in between readings. A small(1Ah) lead acid battery would lasteven longer. I

Fig 5 shows the layout ofcomponents of the display unit onthe PCB which is shown in Fig 8.For normal operation link 1 andlinks 3 to 5 are connected as shown,as are the unnumbered links. Link0 is connected to the OV rail; omitthe terminal pin at B and simplyinsert a wire link at that point. If aclock with high -pulse triggering isused, insert a terminal pin at B, andwire the clock output to it; alsoconnect link 2, but not link 1.

If connection to amicrocomputer is notcontemplated, socket SKT1 can beleft out. If a micro is to be used,wire a switch in place of link 4, orpossibly omit the LEDs and thecommoned resistors R2 to R9.

The LEDs specified are a speciallow -current type, pre -assembled in

Qsa

Hours Mins

Alarm clock moduleOV Alarm

L_osso__IINC

Time/alarm

Fig. 4. The timer circuit.

R1791k

R18270k

C4 10n

C3100n

Outputto trigger

circuit

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TR1ZTX300

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from the signal that would preventspurious or false triggering.

This account of interfacing theclock to the gauge applies to oneparticular model of clock. Othersmay need different treatment, forexample, the hours and minutesbuttons may have to be connectedto the OV rail, not the positive rail.However a little thought andexperimentation will usually showwhat must be done.

D9

CI I

Si

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L i nkC

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L\< R2 to R9 Common

I

SKT1

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Rain Gauge Project

The ElectronicsThe counterweight of the bucket has asmall magnet attached to it. A Hall -effectsensor is located so that it detects thefield of the magnet when the sensor is inits tilted -back position. In this state theoutput of the sensor (Fig 6. 101) at pin 1is close to OV. While the bucket isemptying the magnet is moved awayfrom the sensor, the output of which risesto about 6V. As the mechanism tilts backagain the output falls, causing the firstcounter of IC2 to increment by one.

IC2 has two counters IC2a and IC2bcascaded together. IC3 acts as a 4 -inputAND gate incrementing IC2b wheneverthe output of IC2a changes from 15 (=1111 in binary) back to zero. Thus 102can register counts from zero up to 255.This 8 -bit binary output goes to IC6 whichcontains eight D -type latches. When theenable input (pin 11) is high, the output ofthe latches follows their inputs. Whenthe enable input goes low the outputs aresaved or latched. These are 3 -stateoutputs; in Fig 6 the control input (pin 1)is shown connected to OV, which makesthe outputs behave normally. When anoutput is high the LED (light emittingdiode) connected to it is lit and the totalcount can be read as an 8 -bit binarynumber. However. if pin 1 is made high.

+6V0

IC1UGN

3020U

IR11k 0

Qt D

1.11 Q2 (2)

N

CV 03 190

R5T 04 (8)

the outputs go into a high -impedancestate. that is to say they are in effectdisconnected from the LEDs. Moreimportant, they are disconnected fromthe 10 -way socket SKT1, making itfeasible for this socket to be directlyconnected to the data bus of amicrocomputer.

The latches are normally under thecontrol of a clock, which can be either aready -built clock module or. as in theprototype, the "works" of an old digitalalarm clock adapted for the purpose. At9 am each day (or at any other time forwhich the alarm is set) a high pulse fromthe clock sets the flip-flop. IC5c/IC4d.There is also an inverting gate providedby IC4b for use should the clock modulebe one which generates a logic low pulseat alarm time. When the flip-flop is set,the output at pin 10 goes low. Thismakes the enable input of IC4 low so thatthe count is latched and held untilsomeone comes to read it. At the sametime the output at pin 13 goes high,supplying current to the flashing LED.This indicates that the display shows thelatched reading, not the current reading.In the meantime, the count in IC2 hasbeen reset to zero and is subsequentlyincremented if it is raining, but this doesnot affect the output of IC3. After the

18

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-IC a

4012

2-5

1 2 31.10930202

To +6V ,233IC2 pin 16 4012

IC3 pin 14IC4 pin 20IC5 pin 14IC6 pin 14

o 01 (1)

To OV (GND)(NI1.11 12

IC2 pin 8IC3 pin 7

10

Q2 (2)

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Micro -controlinput

Clock {inputs

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260

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05Control

latched reading has been taken, the flip-flop is reset by pressing S1. From thenon the display shows the current countheld in IC2.

Another effect of setting the flip-flop isthat a high pulse is passed to IC5a,which inverts it and sends a low pulse toIC6a. IC6a and lC6d are connected as apulse generator which produces a highpulse on a rising edge, that is, at the endof the pulse from IC5a. IC6c and IC6bOR this high pulse with a possible highpulse produced if the reset button S2 ispressed. The output of IC6b is a high -going pulse which resets the counters.Thus the counters are reset either at thealarm time or when S2 is pressed. Theoutput of IC6b is a high -going pulsewhich resets the counters. Thus thecounters are reset either at the alarmtime or when S2 is pressed. Thepurpose of the delay introduced by C1,R11 and IC5a is to allow time for thecount to be latched into IC4 before IC2 isreset.

The sensor (101) is mounted on asmall piece of strip -board (Fig 7). This isheld in position by a long bolt mounted inthe rear of the box. The IC (integratedcircuit) should be close to the north -seeking end of the magnet when thebucket mechanism is tilted back (Fig 2).

+6V line 0 0 --0-0 +5VLink 5

0 DO

12

6

15

co

Link 40

(OV)

L

+12VIC5, IC6 ==> 74HCO2 0

S2 110Reset no

11111,- 100.2

no.

I -I I-. -R12 C21M 100n

R1310k

0D1

OD2

0D3

0D4

0D5

OD6

0D7

GND

rrDl - D8

R2 - R91k

Fig. 6. The electronics.

U)

0


Rain Gauge Project

Rainfall recordsRegular recording of rainfall as beenestablished in Britain for over 200

ars. The first gauge in was in use asing ago as 1675. By the mid 19thntury the British Rainfall Organisationd established a network which hasw grown to over 7000 recordingations scattered throughout theuntry. It is the densest routineservational network in the world.Recording rainfall has a purpose

fferent from that which is usuallysociated with weather

easurements. Wind direction andrength, temperature and changingrometric pressure are the basis ofe nightly TV weather forecasts.infall records on the other hand haveimmediate bearing on what the

ather will be like tomorrow. Insteady are used in long range prediction

d statistics.The collected data can be

ocessed in a variety of ways,onthly, seasonal and annual totalsd averages. There is also the matterrainfall distribution throughout theuntry. Several industries, including

tourist industry are dependent onthis. Statisticians work on the data toestablish its variability, or moreappropriately the reliability, or rainfall inkgiven area, vital knowledge for.mers, the river authorities and thoseo manage the domestic water

supplies. Other derived data includesthe average lengths of sequences ofwet and dry days, the typical duration of

n showers, the number of showersd howers

blocks of four and in series with a1Kohm resistor they take only 4mAeach. Note that the flashing LED isintended to operate on the fullsupply voltage and does not require

C07

CC

CO

0CO

Fig. 7. The sensor board.

L

)

lasting longer than a given period oftime.

The official rainfall day begins at9am. This is the time at which gaugesare officially emptied, the reading takenand the water container replaced underthe funnel to collect its share of the newday's deluge. With continuouslyrecording gauges such as the bucketgauge and drop counter a more usefulrange of data is obtainable. It is suchequipment which makes it practicableto collect such data as shower length,the number of showers per day andother short-term information. Toreduce this data to a form in which it ismore easily comprehended a few termsneed to be defined, such as exactlywhat is meant by "a rainy day".

A rainy spell requires 15 or moreconsecutive days each with 0.2mm ormore, while an officially wet spell musthave at least 1mm on each of thosedays. Conversely, a dry spell has 15 ormore consecutive days with less than1mm of rain, and there must be lessthan 0.2mm of each of those days tomake it an absolute drought.

Although a rainfall measurementhas no immediate predictive value,rainfall and temperature are the twomain indicators of climatic change.Examination of records make itpossible to discern patterns and trends.This can be of great economicimportance, particularly in areas of theWorld where the successive failure ofthe annual monsoons can bring aboutwidespread starvation. In Britain,rainfall reached a peak in the nineteen -thirties. Since then it declined until, in1974, we experienced the worst

the usual series resistor.The PCB is intended to fit

vertically in slots in the side of thebox. The LEDs are on the upperedge of the board, directed upwardwhen the board is vertical. They liejust below a circular hole and a slitcut in the lid of the box. The twopush -buttons, and other switches, iffitted, are mounted on the lid. Thestrip -board bearing the clockmodule is bolted to the bottom of

drought of this century. The productionof hay and silage fell to only 60% ofnormal, and other crops were similarlyaffected. Britain was once a land oflight but frequent rain, an almost idealclimate for the farmer. The currenttrend seems to be toward long dryspells punctuated by periods of violentstorms. Farmers suffer while touristsare delighted. Fortunately this is mainlya matter of the distribution of rainfall intime. The total annual rainfall is only alittle less than it was before, so ourreservoirs remain full.

The past thirty years has seen adecline in the westerlies blowing acrossthe North Atlantic, bringing rain toBritain and Western Europe. As aresult of this the total rainfall hasdeclined slightly in Western Europe. In

Britain there has also been a change indistribution. In western areas of Britainmuch of the rainfall is precipitated asthe moisture -laden westerlies arepushed up over the higher regions ofCornwall, Devon, Wales, the ScottishHighlands and the Pennines(orographic). The decline in westerlieshas therefore reduced rainfall inwestern regions, while eastern areas ofBritain remain relatively unaffected.

Such are the trends that statisticalexamination of rainfall data has madeapparent. Whether these are on -goingtendencies which may become moreextreme, or whether they are part oflong natural cycles that may yetreverse, or whether the trends may bediverted because of new factors suchas the Greenhouse Effect, is still amatter of conjecture.

the box. If preferred, the clock canbe mounted on the lid withapertures cut to allow the display tobe viewed and the clock push-buttons to be reached. This entailsthe use of a larger box and morework in cutting the holes.

In The FieldThe collector unit must be locatedin the open so that the funnel is

Er: I Ifirj0

0


Rain Gauge Project

The Hall effectIf a current is passing through a slice ofsemiconductor material and there is amagnetic field at right angles to thedirection of the current. the chargecarriers (electrons) of the current aredeflected in a direction at right angles toboth current and field. This is anexample of Fleming's left-hand motorrule, but applied to electrons instead of toa coil of wire carrying a current. Theresult is to produce a higher density ofelectrons on one side of the slice than onthe other. In other words, a potentialdifference appears across it. This is theHall effect, which occurs in all conductorsbut is only easily measurable insemiconductors.

A Hall effect device includes the slicein which the effect occurs together withan integrated circuit to detect the voltagechange and to produce a correspondingoutput. Different types of Hall effectdevice have different kinds of output.Linear devices produce an analogue

Magnet

output voltage which varies in polaritywith the direction of the magnetic fieldand varies in magnitude in proportion tothe field strength (the magnetic fluxdensity). Other devices have a switchedoutput. which is either high (close to thesupply voltage) or low (close to OV). Insome of these the switch is turned onwhen the magnetic flux density exceedsa given amount (+25mT (Tesla) in atypical device). It requires a field ofopposite direction (-25mT) to turn it off.In the device used in this project the fieldis effective only if it is positive (enteringfrom the dimpled side) and exceeds agiven value, +22mT. A magnetic fieldbelow +16.5mT turns it off. A reversedfield has no effect, however strong.

Hall effect devices have manyapplications as proximity detectors, as inthis project, and are used in contact -lessbounce -free switches.

Force on electrons

Slice ofsemiconductor

CurrentField

Mo ion

?\11

9r1

Current flow

On The LinksThe circuit board (Fig 5) has a numberof links which allow the gauge to beoperated in various ways:

Link 0 is used to connect the inputsof IC5b to a low logic level, if that gateis not to be used.

Link1 is used if the clock producesa high alarm pulse. It can be replacedby a switch to isolate the clock if thegauge is to be controlled by amicrocomputer.

Link 2 is connected instead of Link1 to allow the use of IC5b to invert alow -going alarm pulse.

Link 3 normally connects the controlinput of 103 to OV, but can be used toput this function under the control of amicrocomputer.

Link 4, if disconnected, disables thedisplay. It can be left open or replacedby a switch. This is an option foreconomising in current, or for when the10 -way socket is connected to the databus of a micro. If the socket isconnected to the user port of a micro, itis not usually necessary to disable thedisplay.

Link 5 is normally open but isconnected if the circuit is to be poweredfrom the +5V supply of a micro. Notethat the 10 -way socket also has a OVconnection to the OV (ground) rail of themicro, which is essential for properoperation of the interface.

exposed to rain from all directions.It is also a good idea not to expose itto strong winds and situationswhere excessive run-off from treesor from blocked gutters mayoccasionally fall into the funnel.The enclosure can be bolted orscrewed to a stout vertical post tohold it firm in the wind and toallow the measured water to drain

freely away. The funnel mayrequire a supporting bracket to holdit in place and to reduce windvibration.

A 3 -core cable passes through ahole in the bottom of the collectorbox and is taken indoors or to anearby shed or greenhouse wherethe counter hardware is situated. Acable several metres long may be

used as there is little risk of itpicking up interference. Terminatethe cable with a plug or plugs to fitSKT2-4.

Before bolting the lid on thecollector box, check that the bucketis operating properly. Also checkthat no more than 2 or 3 drops persecond fall into the bucket.

Components(Excluding those required for the clockmodule)Resistors(carbon 0.125W or metal film 0.6W, 5%,unless otherwise specified)R1 1kR2 -R9 1k, 8 commoned resistors (1 off)R10, R13 10k (2 off)R11, R12 1M (2 off)CapacitorsC1, C2 100nF polyester (2 off)SemiconductorsDl -D8 PCB mounting LEDs, low currenttype. red (Electromail stock no. 590-036)(2x quad LEDs)D9 Flashing LEDIntegrated circuitsIC1 UGN3020U Hall effect IC switch(Electromail stock no. 307-446)IC2 4520 CMOS dual synchronous divide -by -16 counterIC3 4012 CMOS dual 4 -input NAND gateIC4 74HC373 CMOS octal 3 -state latch

IC5, IC6 74HCO2 CMOS quadruple2 -input NOR gate (2 off)Miscellaneous51, S2 panel -mounting push -to -makepush -buttonsSKT1 10 -way printed circuit connector(Electromail stock no. 488-359) (optional)SKT2-4 1mm Plugs and sockets, panel -mounting (3 off)20 -way DIL socket16 -way DIL socket14 -way DIL sockets (4 off)enclosure for collector unit, ABS or metal box,approx 200mm x 110mm x 60mmenclosure for counter unit, ABS box approx.150mm x 80mm x 50mm (Electromail stockno. 508-936 fits the PCB)printed circuit boardstripboard, for clock module and a small scrapfor mounting IC11mm terminal pins (12 off)Large plastic funnel (1 or 2 off)Materials for making bucket, nuts, bolts,plastic tubing etc

Fig. 9. How to connect everything up.Power supply

OV +6V

Sockets onrear wall of

box


SURVEILLANCEPROFESSIONAL QUALITY KITS

No. I for KitsWhether your requirement for surveillance equipment is amateur, professional or you are just fascinated by this unique area of

electronics SUMA DESIGNS has a kit to fit the bill. We have been designing electronic surveillance equipment for over 12 yearsand you can be sure that all of our kits are very well tried, tested and proven and come complete with full instructions, circuitdiagrams, assembly details and all high quality components including fibreglass PCB. Unless otherwise stated all transmittersare tuneable and can be received on an ordinary VHF FM radio.

UTX Ultra -miniature Room TransmitterSmallest room transmitter kit in the world! Incredible 10mm x 20mm including mic. 3-12V operation. 500m range £16.45

MTX Micro -miniature Room TransmitterBest-selling micro -miniature Room TransmitterJust 17mm x 17mm including mic. 3-12V operation 1000m range £13.45

STX High-performance Room TransmitterHi performance transmitter with a buffered output stage for greater stability and range.Measures 22mm x 22mm including mic. 6-12V operation, 1500m range £15.45

VT500 Nigh -power Room TransmitterPowerful 250mW output providing excellent range and performance. Size 20mm x40mm. 9-12V operation. 3000m range £16.45

VXT Voice Activated TransmitterTriggers only when sounds are detected. Very low standby current. Variable sensitivityand delay with LED indicator. Size 20mm x 67mm. 9V operation. 1000m range £19.45

HVX400 Mains Powered Room TransmitterConnects directly to 240V AC supply for long-term monitoring. Size 30mm x 35mm.500m range £19.45

SCRX Subcarrier Scrambled Room TransmitterScrambled output from this transmitter cannot be monitored without the SCDM decoderconnected to the receiver. Size 20mm x 67mm. 9V operation. 100m range £22.95

SCLX Subcarrier Telephone TransmitterConnects to telephone line anywhere, requires no batteries. Output scrambled sorequires SCDM connected to receiver. Size 32mm x 37mm. 1000m range £23.95

SCDM Subcarrler Decoder Unit for SCRXConnects to receiver earphone socket and provides decoded audio output toheadphones. Size 32mm x 70mm. 9-12V operation £22.95

ATR2 Micro Size Telephone Recording InterfaceConnects between telephone line (anywhere) and cassette recorder. Switches tapeautomatically as phone is used. All conversations recorded. Size 16mm x 32mm.Powered from line £13.45

*** Specials ***DLTX/DLRX Radio Control SwitchRemote control anything around your home or garden, outside lights, alarms, pagingsystem etc. System consists of a small VHF transmitter with digital encoder and receiverunit with decoder and relay output, momentary or alternate, 8 -way dil switches on bothboards set your own unique security code. TX size 45mm x 45mm. RX size 35mm x90mm. Both 9V operation. Range up to 200m.Complete System (2 kits) £50.95

Individual Transmitter DLTX £19.95Individual Receiver DLRX £37.95

MBX-1 Hi -Fl Micro BroadcasterNot technically a surveillance device but a great idea! Connects to the headphone outputof your Hi-Fi, tape or CD and transmits Hi-Fi quality to a nearby radio. Listen to yourfavourite music anywhere around the house, garden, in the bath or in the garage andyou don't have to put up with the DJ's choice and boring waffle. Size 27mm x 60mm.9V operation. 250m range £20.95

SUMADESIGNS

UTLX Ultra -miniature Telephone TransmitterSmallest telephone transmitter kit available. Incredible size of 1mm x 20mm! Connectsto line (anywhere) and switches on and off with phone use. All conversation transmitted.Powered from line. 500m range £15.95

TLX700 Micro -miniature Telephone TransmitterBest-selling telephone transmitter. Being 20mm x 20mm it is easier to assemble thanUTLX. Connects to line (anywhere) and switches on and off with phone use. Allconversations transmitted. Powered from line. 1000m range £13.45

STLX High-performance Telephone TransmitterHigh performance transmitter with buffered output stage providing excellent stabilityand performance. Connects to line (anywhere) and switches on and off with phone use.All conversations transmitted. Powered from line. Size 22mm x 22mm.1500m range £16.45

110(900 Signalling/Tracking TransmitterTransmits a continous stream of audio pulses with variable tone and rate. Ideal farsignalling or tracking purposes. High power output giving range up to 3000m. Size25mm x 63mm. 9V operation £22.95

CD4110 Pocket Bug Detector/LocatorLED and piezo bleeper pulse slowly, rate of pulse and pitch of tome increase as youapproach signal. Gain control allows pinpointing of source. Size 45mm x 54mm. 9Voperation £30.95

CD600 Professional Bug Detector/LocatorMulticolour readout of signal strength with variable rate bleeper and variable sensitivityused to detect and locate hidden transmitters. Switch to AUDIO CONFORM mode todistinguish between localised bug transmission and normal legitimate signals such aspagers, cellular, taxis etc. Size 70mm x 100mm. 9V operation £50.95

QTX180 Crystal Controlled Room TransmitterNarrow band FM transmitter for the ultimate in privacy. Operates on 180 MHz andrequires the use of a scanner receiver or our QRX180 kit (see catlogue). Size 20mm x67mm. 9V operation. 1000m range £40.95

QLX180 Crystal Cointrolled Telephone TransmitterAs per OTX180 but connects to telephone line to monitor both sides of conversations.20mm x 67mm. 9V operation. 1000m range £40.95

QSX1110 Line Powered Crystal Controlled Phone TransmitterAs per QLX180 but draws power requirements from line. No batteries required. Size32mm x 37mm. Range 500m £35.95

QRX180 Crystal Controlled FM ReceiverFor monitoring any of the IT range transmitters. High sensitivity unit. All RF sectionsupplied as a pre -built and aligned module ready to connect on board so no difficultysetting up. Outpt to headphones. 60mm x 75mm. 9V operation £60.95

A build-up service is available on all our kits if required.UK customers please send cheques, POs or registered cash. Please add£1.50 per prder for P&P. Goods despatched ASAP allowing for chequeclearance. Overseas customers send sterling bank draft and add £5.00 perorder for shipment. Credit card orders welcomed on 0827 714476.

OUR LATEST CATALOGUE CONTAINING MANY MORE NEWSURVEILLANCE KITS NOW AVAILABLE. SEND TWO FIRSTCLASS STAMPS OR OVERSEAS SEND TWO IRCS.

THE WORKSHOPS, 95 MAIN ROAD,BAXTERLEY. NEAR ATHERSTONE,

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0827 714476

Practical Technology

Comms, ComputersAnd Cock-upsBarry Fox has used portable communications systems all over the world and if hisexperiences are anything to go by, there is room for a great deal of improvement.

0 ver the last ten years I havetravelled a lot, carrying aportable computer with the

intention of sending back news andarticles to magazines for which Iwrite. Some of these magazinesprovide direct access to theireditorial computer system bytelephone line; others are connectedto an electronic mail system, suchas Telecom Gold or Mercury Link7500.

I have used a whole string ofcomputers (from Tandy 100through budget Toshiba to luggableDell) in Europe, North America andthe Far East, with all kinds ofmodems (both acoustic and hardwired, electronic mail and fax)running at data speeds from 300 to2400 baud.

There is only one thing I can saywith certainty, and that is that notwo communications situations areever alike. It has only veryoccasionally been easy and isusually a very difficult andfrustrating waste of time.

Many portables gobble power sorapidly that you cannot run themoff batteries for much more than an

II this colour porta rom Toshiba needs is reliable commun

hour. The paper specification maypromise longer, but only onminimum memory capacity andwith no add-ons, for example aninternal modem.

Nicad cells becomeprogressively less retentive if you

The Cambridge Z88 is ideal for some portable applications.

do what the instruction booksspecifically warn against, but whateverybody has to do in practice -top up half -charged cells.

Not all PCs have a multi -voltagecharger. My Tosh doesn't, so I haveto carry an extra transformer tocope with both 240 and 110 voltsupplies.

I use an external modem (to savedrain on the PC batteries) and thistoo needs either its own mainsadaptor or spare batteries. Themodem will often switch itself on ina suitcase during travel and flattenthe cells.

Some hotel phones in NorthAmerica now have a socket on theside for direct connection of amodem. Elsewhere, especially inEurope, everything possible is doneto deter connection. Phone plugsvary in size and wiring from


Portable Communications

country to country. Often the bestbet is an omnipurpose modem leadwith crocodile clips on the end.Take the telephone or wall junctionbox apart and play trial and errorgames to find the hot wires.

Many hotels (for example inJapan and the US) now haveswitchboards with non-standarddialling tones which an auto -dialling modem will refuse torecognise. The trick here is to dial 9(or 0) manually, then quickly startthe communication softwarerunning and hang up as the modemgrabs the public system dial tone.

The latest spoiler in the USA isto route long distance calls througha friendly AT&T operator. He orshe interrupts the dialled number toask for the hotel room or credit cardnumber. This defeats the auto dialmodem. It makes sending faxesfrom a PC virtually impossiblebecause the fax modem will need toset up the call and exchangehandshakes before sending the text.

The most simple, bomb -proof,approach to email (Electronic Mail)transmission is to use an acousticmodem or coupler. You dial thehost number manually, listen forthe modem reply tone and then putthe handset in the rubber cups ofthe acoustic unit. Even this failed onme once in an American hotelwhich had mock -antique phoneswhich would not fit the cups.

Telecoms people will tell you

Recently Ivowednever againto carry aPC andsuitcase fullof electronicgizmos...

Probably the smallest printer in the world, the Citizen PN413 gives output on the move.

not to try and phone long distanceto a modem, but instead hook into alocal packet switched network (likeTymnet or Telenet in the USA andJapan). This lets you dial a localhost number, which acts as a nodeinto the international packetnetwork and provides a data rideback to the UK and into theelectronic mail services.

For many years red tape madethis very difficult, with travellersobliged to negotiate expensivepassword PSS deals before leavinghome. Now the UK electronic mailservices have made arrangementswith some foreign data services,which let travellers call a foreignnode with billing following later onthe UK service. These have beenvery poorly advertised and not allcountries have PSS nodes withback -home billing arrangements.

Remember to check on the hostnode numbers and what commsstandard they use. Better still get anumber for a foreign helpline; thehost numbers have a nasty habit ofchanging.

The host modems may be auto -sensing and self -adjust to the speedof the calling modem. Or they maybe of fixed speed, with differenttelephone numbers for differentspeeds. Odd things can happenwhen two auto -sensing modems tryto talk to each other. They lock on atdifferent speeds on differentattempts.

Whereas the 1200 and 2400 baudstandards for Bell (USA andelsewhere) and CCITT (Europe andother elsewheres) are close enoughto match (usually), the 300 baud

Bell and CCITT standards arecompletely incompatible. Frombitter experience I must advise that,if humanly possible, travellersshould find out the number of thehost modems in the cities they arevisiting and then try making longdistance calls from the UK to theremote modems to checkconnection. It is always far easier,and cheaper, to struggle withmismatched modems from yourown home or office phone, thanfrom the bedside phone of a far-offhotel when you have just crawled inoff a long haul flight and are dogtired and jet lagged.

Be warned, incidentally, thatsome of the PSS helplines (even inbusiness conscious North America)only work weekday office hours. Ifyou arrive ill -prepared on a Fridaynight you may not be able to makeany connection until Mondaymorning.

Recently I vowed never again tocarry a PC and suitcase full of theelectronic gizmos which may ormay not successfully connect it to aphone line. Security checks atairports harden this resolve. Butdoubtless I shall keep on trying justonce more.

What I do know for sure is thatnext time I see an advert which tellsus all how easy it is to communicateon the move, I shall lodge acomplaint with the AdvertisingStandards Authority, to see how theadvertiser justifies the claim.Nobody should be allowed to writesuch twaddle unless they haveactually tried it for themselves.


Classifieds

Practical Electronics Classified AdsReach thousands of serious electronic and computer enthusiasts - advertise in PE Classified pages:

Rates 20p (plus 4p VAT) per word or £8.50 (plus .EI.49 VAT) per column cm. All classifiedadvertisements must be pre -paid. Send your copy, with remittance payable to Intra Press, (Payment by

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Practical Electronics, Intro House, 193 Uxbridge Road, London W12 9RA.Tel: 081-743-8888. Fax: 081-743-3062

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visit our s/room and bargain store.Prices from £5 upwards!"

Send SAE for lists

Contact: Cooke International, Unit FourFordingbridge Site, Main Road, BarnhamBognor Regis, West Sussex P022 OEB

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Computer Parts

CAMBRIDGE COMPUTER SCIENCE LIMITED

10MByte Winchesters, used, 3 months Wty,......................................£42.00 each5.25" Disk Drives, 80Tk, DSDD £34.00 each5.25" Disk Drives, 80 Tk, DSDD Used, No Wty £15.00 each(The £15.00 drives are sold on a strictly "as is" basis)525" Disks, DSDD, 48tpi, boxes of 10 . .£3.00/boxLockable diskette boxes for 80'3.5" or 100'5.25" (state which).. ..... .....£5.99 eachSmall sized diskette boxes Lockable) .............40'3.5" £4.75, 50'5.25" £4.99 eachPrinter stands (suit 8-/132 cols) Basic £2.99. or with paper catcher...£10.99 eachDigital multimeter, 14 ranges. inc leads & manual £16.00 eachApricot Disk drive PSU £10 00 each5V @ 6A PAU £4 60 each5V @ 10A PSU £6 40 eachNicads AA £0.89, C £1.99, D £2.09, PP3 £4.99, Universal charger .....£5.99 each74LS TTL, pick and mix, buy 10 or more for.........................................£0.12 eachTypes available: '00 '02 04 08 '10'11 '12 '13 14 '15 20 '21 '26 27 '30 '32 33 37'38 '42 '74 '83 '85 '86 '96 '107 '109 '122 '125 '132 '136 '138 '139 '145 '151 '153'157 '158 '160 '162 '163 '164 '165 '174 '191 '193 '240 '253 '257 '260 '298 '353 '365'366'373 '385 '390 '399'670 '68227128 EPROMS (Ex equipment). £1.20 each or £5.00/5256K Byte DRAM Modules, removed from equipment .........................£6.00 each62256-10 NV 32KByte SRAM £5.008K Byte NV RAM chips £3.00 each......................................................£10.00 fourRange of Aluminium and plastic project boxes (ask for list)

Prices include postage. Add 50p (plus VAT) to orders below £5.00All Items new unless stated. Add 17.5% VAT to all prices.

Send an SAE I or our latest list or for more into.Dept PE, 374 Milton Road, Cambridge, C54 1SU

Tel: 0223 424802, 0031 430488 or 0831 430552 (Mall order only)

Manufacturers Original SparesFor Amstrad, Atari, Commodore and

Sinclair computers.Many TV, VCR & Audio Parts also available - Send S.A.E. or Phone0452 526883 fora 'Price and Availability' on your requirementsAtari YM2149F 'Sound' Chip (ST) £10.02Commodore 906114 'PLA' Chip (C64/C) £9.24Sinclair ZX8302 'ULA' Chip (QL) £10.75Membranes: QL-£7.95 Spec. 48K-£4.50 14128K-£7.99Amstrad Original Service Manual (CPC464 a Monitors) £8.49ditto Original Service Manual (PCW8526/8512) £13.89Chips: PEGA1A-£32.72 TEA2000-£4.49 AY38912-£5,74Sanyo/Fisher VCR Belt Kit VTC6500/VBS3500 £2.49Hitachi Replacement Video Head VT11/14/33/34 £26.10Toshiba Power Transformer (22224100) ST -U2 £9.99Ferguson Tuner Control Door 3v35/36/38/39 £1.95The above is just a very small sample of our stock. For a Catalogueplease send 50p CHOIStamps/3x1RC's etc. Please add 95p (UK) P &P to above orders. All items subject to availability.

MARAPET (PEM) 1 Hornbeam Mews, Gloucester GL2 OUE

MAIL ORDER ONLY TEL: 0452 526883

Miscellaneous

AMPLIFIERSA range of 300 watt self

assembly amplifiers for sale£45.00 each + £2.50 P&P

Also: Range of speaker drive unitsand other amplifiers

Call: Andy on(0273) 681257


Classifieds

Miscellaneous

UNIVERSAL PROGRAMMERHi -Lo ALL -03 £295

Take advantage of Asian low labour cost!* Texas Instrument approved. Good quality.* PC based, programs stored into 5 diskettes.* Program most MPU, PLD, EPROM, EEPROM, BPROM.* Adaptors for PLCC devices are available.* 1 year guarantee. Money back if not satisfied.* Price includes postage but not VAT.

Write for free catalogue and price list.

Active Action Industrial LtdRm 1307, Wing Tuck Coml Ctr.

177-183 Wing Lok StreetHong Kong

SOLVE CROSSWORD PUZZLES BY COMPUTER

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CATALOGUE £1.00 + 25P&P

Resistor Pack 85 different E12 values + zero ohm link total content

1000 resistors £8.95

LEDs 3mm or 5mm red/green 6p each. Yellow I 1p each,

Cable ties 1p each £5.95/1,000 £49.50 per 10,000

Stepping motor 4 phase I2V 7.5' step 50 ohms £8.95

SAA1027 stepping motor driver chip £3.95

FM Transmitter kit good quality sound £8.60

High quality photo resist copper clad epoxy glass boards

Dimensions single sided double sided

3x4 inches £ 0.95 £1.07

4x8 inches £ 2.40 £2.68

6x12 inches £ 5.37

I2x 12 inches £10.66

Special Offers

Computer Grade Capacitors with screw terminals 380000 20V £2.50

8700uf 10V £1.95, 68000ttf I5V £2.95, 10000uf 16V £1.50

7 segment Common anode led display 12mm £0.45

LM2931AT5.0 Low drop out 5V regulator T0220 package £0.85

BS250 P channel MOSFET £0.45, BC559 transistor £3.95 per 100

74LS05 hex invertor £10.00 per 100, used 8748 Microcontroller ...£3.50Stereo LW/MW/FM Tuner pre -amp assembly complete with volume/tonecontrols and tuning scale Brand new in maker's carton .£6.95, faulty £3.50

Circuit etc. for above £0.50.Hour counter (used) 7 digit mains 240V AC 50Hz £1.45LCD display 16 digit 7x5 dots dot matrix £2.50Qwerty keyboard 58 key good quality switches new .£5.00

Qwerty keyboard with serial output, no data £5,00

Wide range of CMOS TTL 74HC 74F Linear transistors kitscapacitors, resistors tools etc always in stock.Please add 95p towards P&P - VAT Included

JPG Electronics 276 278 Chatsworth RoadChesterfield S40 2BH

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Components

High Stability ResistorsCarbon Film Resistors 0.5613 to 10M0 E24 sans 1/4W 1 p

100 off per value 75p. 1000 off in even hundreds per value - MOOMetal Film 1/4W 1ORO to IMO E12 series 5% - 2p. 1% E24 series - 3pMixed metal/cartoon film 1/2W 024 series IRO to 10M0 - 1 1/2pMixed rnetecarbon film IW 4R7 to 10M0 E12 series OpBC107/8/9 12p. BCI 82, BCI83, BC184, BC212 0 L versions 10pBFY50.51 8 52 - 20p, 2N3055 - Sop. T1P316,32A - 25p. TIP, 41,42 - 40p

Tantalum bead electrolytics subminiature (Mtds/Volts)01/35, 022/35. 0.47/35, 1.0/35. 2.2/35. 3.3/16. 32/20. 4.7/16 - 14p. 3.3/35, 4.7125.4.7/35 -15p. 6.8/16, 6.8/35 -16p. 10/16. 20/25 - 20p. 10/35, 22/16, 33/10,47/10 -30p.100/6 -30p 100/16 - 50p. 220/6 - 60p

Aluminium Electrolytics (MtdsNolts)1/50, 2.2J50, 4.7/50, 10/16, 10/25, 10/50 - 5p. 22/16 22/25, 22/50, 47/16, 4725.47/50 -6p. 100/16. 100/25 7p. 100/50 - 12p. 220/16 - 8p. 220/25. 220/50 - 10p. 470/16,470/25 11p. 1000/16 - 15p. 1000/25 18p. 2200/25 - 22p

Miniature Polyester Capacitors 250V Wkg. Vertical Mounting.01..015, 022, .033, 047, .068 4p. 0.1 - 5p. 0.15, 22 - 6p

Mylar Capacitors 100V Wkg. Vertical Mounting E12 Series1000p to 8200p - 3p. 0.01 to .068 - 4p. 0.1 - 5p 0.15, 022 - 6p

Subm. Ceramic Plate 100V Wkg. E12 Series Vertical Mounting2% IP8 to 47P - 3p. 56P to 330P - 4p. 10%390P to 4700P . 4p

Plate/disc ceramic 50V. Wkg. Vertical Mount. E12 sales 1P0 to 112000E6 series 1500P to 47000P - 2p. 01 - 3p

Polystyrene Capacitors 63V Wkg. E12 Series Axial Mounting10010 820P ap 1000P to 10,000 - 5p. 12.000P Op.

Diodes2ener dudes E24 series 3V3 to 33V 400fqW - Op. 1 watt - 12p. 1N4148 - 2p 1N4001 -3p. 1N4002 - 3.5p 1N4007 - 5p.1N5404 - 14p. 0091 - 8p. AA143 - 10p. W1305 - 20pWO1 - 25p 1310010 - 6p.L.E.Ers Red, Green 8 Yellow 3mrn 8 5mm - 10p 8mm 35p20mm fuses 015A to 10A quick blow - 5p. 0.1A to 5A Anti Surge - BpHigh Speed drills 0.8mm. 1.0mm. I .3mm. 1.5mm, 2mm 30p'Expo- /Reliant' drilling machines 12V d.c. with improved 3 -jaw chuck - COOWads AA 90p. HP11 - E2. HP2 -E2.20.1.3 05 Universal chargers for all abovebatteries - 06.50Glass reed switches with single pole make contacts - Bp. Magnets - I2p. 0.1' stripboard2.5" X 1"9 rows 27 holes - 25p. 3.75" X E' 24 rows 37 holes - 70p Ionisers list price£16957 year guarani. - El 200. Jack plugs 2.5mm 113 5mm - 14p Sockets panelmtg. - 10pAll prices VAT inclusive. Postage 300 (free over E5i

THE C.R. SUPPLY CO.127 Chesterfield Road,

Sheffield S8 ORN.Tel: 0742 557771

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TechniquesThis month Andrew Armstrong scrutinises light activated switches.

DR Clark of Plymouth writesto ask whether PE hasrecently published a design

for a light activated switch, toswitch on a lamp at dusk andswitch it off at dawn.

No, we have not published sucha design recently, so here are acouple of circuits which should besuitable.

The circuit shown in Fig. 1 is thesimplest approach to this problem.A photo conductive cell is used toshort out the gate drive to a triacwhen the cell is illuminated.Because the resistance of the cell, anORP12, varies with illuminationrather than changing abruptly at aparticular light level, the lamp willfade in and out rather thanswitching abruptly.

The choice of component valuesin this circuit is dictated by themaximum rated dissipation of theORP12. This photo conductive cellis rated at 250mW maximumdissipation so R1 is chosen toprovide the maximum triggeringcurrent consistent with notexceeding the maximumdissipation of the ORP12.

Diacs generally trigger atapproximately 30V and that the

maximum dissipation in the ORP12occurs at a voltage just below thatwhich will cause the diac to trigger.R2 and Cl present a short timeconstant and cause minimalattenuation of the 50Hz waveformso that the voltage on the ORP12 tocause triggering is only just over30V peak. Assuming that the mainsis an exact 240V sinewave, and thatthe diac triggers at exactly 30V, thevoltage across the ORP12 at thetrigger point will be 31.4V peak.This corresponds with 22.019VRMS, and occurs when theresistance of the ORP12 is 3.33k. Atvoltages in excess of 22V RMS, thediac will fire at some stage duringthe cycle, which will remove thetriggering current from R1 andhence reduce the dissipation of theORP12.

To calculate the dissipation inthe ORP12, we need to know itsresistance at the point at which themaximum AC voltage is applied toit. We then use the formula V2/R.Taking the values given above, themaximum dissipation in the ORP12(which only occurs at one specificlight level) is 145mW. This is safelybelow the maximum rateddissipation of 250mW.

In order to make sure that a

Q&A

sufficient trigger pulse is applied tothe triac, Cl is chosen to be as higha value as possible consistent withthe requirements above. Clearly, ifit has too high a value, the timeconstant of R2 and Cl will be longenough to delay the triac triggeringat maximum brightness. As afurther measure to ensure propertriggering, a triac with a guaranteed5mA gate trigger current and a lowholding current is chosen. Thisparticular triac is almost uniquelysuitable for the job and, because it israted at 4A RMS, it could switch alamp load of almost a kilowatt.

A snubber network is providedto protect the triac from the effectsof mains spikes and because thecontroller will pass through a phasecontrolled region, a filter choke anda class x capacitor are provided toprevent interference from beingradiated into the mains. The chokeshould be made by winding 50turns of 0.8 mm diameter wire onan iron dust core type T94-40(available from Cirkit).

The necessity to filter the outputdetracts from what would be a verysimple circuit, making itworthwhile to consider the designshown in Fig.2.

Fig. 1. A simple approach. L

Load

R133k

D1

R2 15kDIAC

L1

R3100S2

220nclass xT1

TRIAC

ORP12LDR1

C122n

C21n

1kV


Techniques

0V

C^,-; IC1b IC1c

IC' d

01BPX25

R4100k

R510k

D4 1N4006 R9 47k 2W

1/0i 7-1R10 470k R11 470k

Rok

03

-12V

MT1

T1TIC206D

MT2

R810012

1n1kV

0Load

-0 L

Zero Level TriggeringIn this design, a -12V power supplyis generated by means of a mainsdropper resistor and a high -voltagediode. The triac is triggered bypulses from this negative powersupply. A negative supply is usedbecause most triacs trigger betterwith negative gate drive than withpositive drive. Some types of triacare not specified to trigger at all ifthe gate drive is positive and thevoltage on MT2 is negative. The TIC206D is rated to trigger with 5mA ofgate drive in quadrants 1 to 3, whilein quadrant 4 (positive gate drive,negative voltage on MT2) it needs10mA.

In the design shown in Fig.2, thepower supply voltage is set by the12V zener D1, and smoothed by C1.Clearly, there will be some rippleon this supply, but that does notmatter in this application.

The DC current available for thepower supply is not, as you mightthink, half the RMS current whichwould flow in R9 if D4 were notpresent. It is in fact Vpeak/pi*R, forreasons which can onlysatisfactorily be explained bycalculus - and which would besuperfluous to the purposes of thisarticle.

Taking into account that somecurrent must flow in D1, 2mA isenough to power the activecircuitry. The CMOS IC itself drawsvery little current, so 2mA isavailable to be shared between the

current through the photo -transistor, and triggering pulses forthe triac.

ICla and IC1b are used togenerate a short trigger pulse ataround the mains zero crossing.Assuming for the moment that theVPX25 is not illuminated: if themains voltage is at OV, then theoutput of IC1a is at logic 1, andtherefore both inputs of IC1b are atlogic 1, which switches the outputof IC1b to logic 0. IC1c is connectedas an inverter, so its output goes tologic 1. Because Q1 is notilluminated, both inputs of IC1d areat logic 1, so the output of IC1d is atlogic 0. This switches on Q2, whichswitches on Q3, which triggers thetriac Tl.

During positive mains halfcycles, while the voltage is highenough to bias pin 2 of IC1a toabove its switching threshold, theoutput of IC1a goes to logic 0,which propagates through toprovide logic 0 on the output ofIC1c. This forces the output of IC1dto logic 1, which switches off thetriggering current to T1. Duringnegative half cycles, while there isenough voltage to pull pin 6 of IC1bbelow the switching threshold, theoutput of IC1b goes to logic 1,which propagates through to switchoff the trigger current as above.

So long as the voltage of pin 12of IC1d remains above theswitching threshold, trigger pulseswill be generated around the mains

zero crossings. A trigger current ofapproximately 11mA flows. This ismore than enough to trigger a triac,so the triggering is clean. Theduration of the triggering pulses isshort enough to draw less than0.5mA average from the powersupply. It is this technique ofcircuitry which keeps thedissipation in R9 to acceptablelevels (approximately 600mW).

Two resistors are used in seriesto supply signal to the CMOS gatesso that the breakdown of oneresistor alone would not destroy thecircuitry. While one resistor wouldnormally be sufficient, the level ofmains spike generated by afluorescent light switching on or offcan be sufficient to cause a normalspiral cut film resistor to breakdown across the turns.

If Q1 is illuminated sufficientlyto pull the voltage in pin 12 of IC1dbelow the switching threshold, thenthe output is forced to logic 1 andtrigger pulses are no longergenerated, so the lamp remains off.

Whichever circuit is used, thephotodetector must be mounted insuch a way that it does not receiveenough illumination from the lampwhich the circuit controls to switchoff the lamp. It is normallysufficient to use a small piece ofopaque plastic to shield thephotodetector from the lamp whileallowing daylight to fall upon it.


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25 Years

PRACTICAL

ELECTRONICSSCIENCE AND TECHNOLOGY

Looking back over the past 25 years, PE hasmade some very accurate predictions.

November 1966In his editorial this month 25 years ago, the editorexplained that without Avionics, modern airlinerswould be virtually impossible. At this time, all-weatherlanding systems were not common and, prophetically,he looked forward to the time when they would be.Looking further ahead, the editorial went on to say thatthe only solution to safe supersonic transport would beto relinquish control to the "free electron". Before theintroduction of microprocessor systems and thedifficulties involved in proving them to be fault free,this must have seemed an attractive idea. However, asthe Shuttle and Airbus have proved, life is never thatsimple.

1976The Semiconductor Update section in this issuefeatured the SC/MP from National Semiconductor. Asthe author predicted, this device was set to take theconstructor market by storm. SC/MP stands for SimpleCost-effective Micro -Processor. It had46 instructionswith an 8 -bit bus and was available in a number of kitsenabling people to get to grips with the comingrevolution in electronics. The SC/MP or Scamp as itwas known has now faded into the mists of time.However, it should be remembered as the chip whichfired the imagination of thousands of enthusiasts.

1981Not all predictions come true, usually because they arebased on false assumptions. The Robots feature in thisissue made it clear that automation could be used toreplace a lot of jobs in manufacturing industries. Whiletrue to some extent, there has never been a wholescalemove towards robotics, probably because they have, sofar, been unable to replace the incredible flexibility andadaptiveness that is innate in a human being. One day,perhaps, we will all be able to put our feet up and leaveeverything to our mechanical servants - on the otherhand, will we want to?

1986The final prediction in this column comes from BTwho, in 1986, said that it would have replace half of itsold electromechanical exchanges for new digital onesby the end of the decade. This actually happened on20th June 1991 when it converted its 3319th exchange. Ifit carries on at the same rate, it will have finished the lotby about the year 2000, a year full of celebrations

NATIONALCOLLEGE OFTECHNOLOGYDISTANCE LEARNING COURSES

The National College of Technology offer a range of packagedlearning short courses for study at home or in an industrialtraining environment which carry national BTEC awards. Studycan commence at any time and at any level, enabling you tocreate a study routine to fit around existing commitments.Courses on offer include:

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Tutor support and BTEC certification are available as optionswith no travelling or college attendance required. These verypopular courses which are ideal for vocational training containworkbooks, audio cassette lecturettes, PCBs, instruments,tools, components and leads as necessary to support thetheoretical and practical training. Whether you are anewcomer to electronics or have some experience and simplyneed an update or certifications, there is probably a distancelearning course for you. Write or telephone for details to:

National College of TechnologyNCT Ltd. PO Box 11, Wendover, Bucks

Tel: (0296) 624270

Advertising Index21st Century Elec 13 Labcenter 15

73 Amateur Radio 55 Limrose 44

Active Action 55 London Elec. Coll 54

ADM 55 Maplin OBC

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Astrofest 92 61 MOP 42

BK Electronics IBC NCT 60

Bull Electrical 29 Number One Systems.24

Cambridge Comp Sci..54 Omni 42

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Speakers Include:Doctor Patrick Moore,

CBE, Editor -in -Chief, Astronomy Now

Professor Arnold Wolfendale,Astronomer Royal

Professor Sir Bernard Lovell,Jodrell Bank, University of Manchester

Professor Malcolm Longair,Cavendish Laboratory, Cambridge University

Professor Peter Willmore,Department of Space Sciences, Birmingham University

Professor Tony McDonnell,Head of Unit for Space Sciences, University ofKent at Canterbury

Professor Andrew Lyne,University of Manchester

Doctor Heather CouperLeif Robinson,

Editor, Sky & Telescope

Doctor John Mason,Deputy Editor, Astronomy Now

The Venue:Royal Borough of Kensington Town HallHornton Street. London W8 7NX ENGLANDFriday 14th - Saturday 15th February 1992

For details of how to exhibit contact the organisers:Peter HaiII & Associates LimitedSuite 75. 49 Hallam Street, London,W1N 5LN ENGLANDTelephone: 071-580 2104Fax: 071-323 3891

Sponsored by:

Astronomy Now

SKY& TELESCOPE

For a copy of the Conference Prograof special accommodation packages,and how to apply for tickets. write to:

The 1992 European AstroFest (Tickets)Intra House, 193 Uxbridge Road,

London W12 9RA ENGLAND

Barry Fox

3D TV...

Not A Pretty SightBarry Fox ltaks a good look at the variety of three dimensional television systems and, afterexamining all the angles, is not terribly impressed.

Oyer the years I have grownweary of 3D TV and videosystems.

In Japan, Toshiba sells a 3D VHScamcorder and playback system.This works like the 3D variant ofJVC's now defunct VHD video discsystem. It displays left and rightimages alternately to the left andright eyes. The viewer wearselectronically switched LCD shutterspectacles. The result is depth butnasty flicker. It would be evenworse in Europe where the displayframe rate is less, 25 Hz for PALinstead of 30 Hz for NTSC.

Anaglyph systems separate theleft and right images by displayingthem in different colours. Theviewer wears differently colouredspectacles and sees depth in tingedmonochrome or oddly balancedcolour.

Colour fringe systems, likeAspex, Vivitar's Q -DOS, and thesystem used by the Sun newspaperrecently for Page 3 models, addcolour to the edges of moving orout -of -focus objects. Again theviewer wears coloured spectacles.There is less depth but the fringingis less offensive to people withoutspectacles.

Polarizing systems, with twosuperimposed pictures viewedthrough polarizing sunglasses, givecolour and depth, but dimmerimages because half the light is lost.

The much hyped Deep Visionclaimed 3D without spectacles.Grand talk about decodersdisguised nothing more exotic thana vertical strip pattern over a TVscreen which was supposed to give3D to viewers without spectacles. Inreality it gave a blurred picturewith very little depth. Deep Visionseems mercifully to havedisappeared without trace - despite

talk of being "inChristmas".

Anyone in Europe with asatellite dish pointed at the Astrasatellite can tune into Germanchannel RTL-Plus and watch thefirst European demonstrations ofanother 3D TV system calledNuoptix.

Nuoptix relies on the Pulfricheffect, many times re -discoveredover the years. The Pulfrich effect isthe optical equivalent of artificialstereo. If the same sound is heardby both ears but the sound to oneear is artificially delayed, the brainis fooled into perceiving a spread ofsound instead of a point source. Ifthe same image is seen by botheyes, but the image available to oneeye is artificially dimmed, the braintakes longer to process it. If theimage is moving, the brain registersdifferent perspectives for each eyeand is fooled into perceiving depth.

Recently John Christian, whoworks for telecommunications giantGPT, won a £3,000 pounds prize inthe BP/Nat West new technologyawards for yet another 3D system.

the shops by (last)

A conventional camcorder sitson a mount with the lens pokinginto a box which has two lensespoking out of the side. These lensesare spaced apart by 50% wider thanhuman eyes and thus "see" slightlyexaggerated left and right eyeimages. These images fall on twomirrors in the box which turn theimages through 90 degrees. Theoptics also reduce the images in sizeso that the tape records twoupended images, of half normalsize, side by side.

When the tape is played back,the image displayed on a TV screenis of course the same non-standardpair of upended half-size pictures,side by side. There are two ways ofgetting 3D from this image pair.

One is to project the image(Christian uses a Sharp LCDprojector) through a mirror boxwhich works in the opposite way tothe camcorder mirror box. It turnsthe two images through 90 degreesand superimposes them on screen.The projected light for each imageis passed through a polarizingfilter. So a viewer wearingpolarizing spectacles sees 3D, butwith smaller and dimmer picturesthan 2-D.

The other way is to display theimage pairs on a conventional TVscreen and look through a viewingbox. This acts like a pair ofbinoculars, turning the imagesthrough 90 degrees and "feeding"one to the viewer's left eye and oneto the viewer's right eye. In thiscase there is no need to wearspectacles. But it is a very awkwardway to watch TV.

Christian's prize-winningsystem may entertain hobbyists but,sorry, it does nothing for me.


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EARBENDERS:- HI-FI, STUDIO, IN -CAR, ETC.

PRICE £73.26 + £4.00 P&P.

ALL EARBENDER UNITS 8 OHMS EXCEPT EB8-50 AND EB10-50 DUAL 4 AND 8 OHM.BASS, SINGLE CONE, HIGH COMPLIANCE, ROLLED FOAM SURROUND8" 50 WATT EB8-50 DUAL IMPEDENCE. TAPPED 4 8 OHM BASS. HI -Fl. IN -CARRES. FREQ. 40Hz FRED, RESP, TO 7KHz SENS, 97dB PRICE £8.90 + F2.00 P&P.10" 50 WATT EB10-50 DUAL IMPEDENCE, TAPPED 4 8 OHM BASS. HI-FI, IN -CARRES. FRED, 40HZ FREQ. RESP. TO 5KHz. SENS. 99dB .PRICE C12.00 + C2.50 P&P.10" 100 WATT EB10-100 BASS, HI-FI, STUDIORES. FRED, 35Hz FRED. RESP, TO 3KHz. SENS. 96dB PRICE £27.50 + £3.50 P&P,12' 60 WATT EB12-60 BASS, HI -Fl. STUDIO.RES. FR EQ, 28Hz. FRED, RESP. TO 3KHz. SENS. 92dI3 PRICE £21.00 + £3.00 P&P.12" 100 WATT EB12-100 BASS, STUDIO. HI-FI, EXCELLENT DISCORES. FRED. 26Hz FRED. RESP, TO 3KHz SENS. 93dB PRICE £32.00 + £3.50 P&P.FULL RANGE TWIN CONE, HIGH COMPLIANCE, ROLLED SURROUND51/4" 60 WATT EB5-60TC (TWIN CONE) HI-FI. MULTI -ARRAY DISCO ETC.RES. FRU), 63Hz FREQ, RESP. TO 20KHz SENS. 92dB. PRICE £9.99 + £1.50 P&P.61/2" 60 WATT E136-60TC (TWIN CONE) HI -Fl. MULTI -ARRAY DISCO ETCRES. FRED, 38Hz FRED, RESP, TO 20KHz SENS. 94dB PRICE £10.99 + £1.50 P&P.8" 60 WATT EB8-60TC (TWIN CONE) HI-FI, MULTI -ARRAY DISCO ETCRES. FRED, 40Hz FREQ. RESP. TO 18KHz SENS, 89dB PRICE f12.99 + £1.50 P&P.10" 60 WATT EB10-60TC (TWIN CONE) HI -Fl. MULTI -ARRAY DISCO ETCRES. FREQ. 35Hz FREQ. RESP. TO 1 2KHz SENS, 8646 PRICE £16.49 + £2.00 P&P.

TRANSMITTER HOBBY KITSPROVEN TRANSMITTER DESIGNS INCLUDING GLASS FIBREPRINTED CIRCUIT BOARD AND HIGH QUALITY COMPONENTS

COMPLETE WITH CIRCUIT AND INSTRUCTIONS

3W FM TRANSMITTER 80-108MHz. VARICAP CONTROLLED PROFESSIONAL PER-

FORMANCE. RANGE UP TO 3 MILES. SIZE 38 123mm, SUPPLY 12V 0.5AMP

PRICE £14.09 + £1.00 POP

FM MICRO TRANSMITTER (BUG} 100-108MHz VARICAP TUNED COMPLETE WITH

VERY SENS FET MIC RANGE 100-300m, SIZE 56 46mm SUPPLY 9V BATT. PRICE

£8.62 + £1.00 P&P

3 watt FMTransmitter

POSTAL CHARGES PER ORDER £1 00 MINIMUM. OFFICIAL ORDERS WELCOME FROMSCHOOLS COLLEGES GOVT BODIES, ETC PRICES INCLUSIVE OF v A T SALES COUNTER

VISA ACCESS ACCEPTED BY POST PHONE OR FAX ttttttttttttt-VISA

MP VARISPEED TURNTABLE CHASSIS.

OPTIONAL MAGNETIC CARTRIDGES

* MANUAL ARM * STEEL CHASSIS * ELECTRONIC SPEED CON-TROL 33 8 45 * VARI PITCH CONTROL * HIGH TORQUE SERVODRIVEN DC MOTOR * TRANSIT SCREWS * DIE CAST PLATTER4NEON STROBE * CALIBRATED EIAL WEIGHT * REMOVABLE HEADSHELL * CARTRIDGE Fl XINGS * CUE LEVER * POWER 220240V5060Hz * 390 305mm * SUPPLIED WITH MOUNTING CUT-OUTTEMPLATE

PRICE £59.99 + £3.50 P&P.

STANTON AL500 GOLDRING G850PRICE £16.99 + 50o P&P PRICE £6.99 + 50o P&P

OMP MOS-FET POWER AMPLIFIERS,HIGH POWER. TWO CHANNEL 19 INCH RACK

THOUSANDS PURCHASEDBY PROFESSIONAL USERS

NEW MXF SERIES OF POWER AMPLIFIERSTHREE MODELS:- MXF200 (100w + 100w)

MXF400 (200w + 200w) MXF600 (300w + 300w)All power ratings R.M.S. into 4 ohms.

FEATURES: * Independent power supplies with two Toroidal Transformers * Twin L E Q. Vu meters * Rotaryindended level controls * Illuminated on off switch * XLR connectors * Standard 776mV inpUts * Open and shortcircuit proof * Latest Mos-Fets for stress free power delivery into virtually any load * High slew rate * Very lowdistortion * Aluminium cases * MXF600 Fan Cooled with D C Loudspeaker and Thermal Protection

USED THE WORLD OVER IN CLUBS, PUBS, CINEMAS, DISCOS ETC.

SIZES:- MXF 200 W19 H31/2 (2U) DllMXF 400 W19 His'/, (3U) D12MXF 600 W19 H5V) (3U).. D13

MXF200 £171.35PRICES: MXF400 £228.85

MXF600 £322.00SECURICOR DELIVERY £12.00 EACH

OMP LINNET LOUDSPEAKERSTHE VERY BEST IN QUALITY AND VALUE

MADE ESPECIALLY TO SUITTODAY S NEED FOR COMPACTNESS WITH HIGH OUTPUTSOUND LEVELS. FINISHED INHARDWEARING BLACK VYNIDEWITH PROTECTIVE CORNERSGRILLE AND CARRYING HANDLEINCORPORATES 12" DRIVER PLUSHIGH FRED HORN FOR FULL.FRED RANGE 45Hz-20KHz BOTHMODELS 8 OHM. SIZE H18' W15

D12

CHOICE OF TWO MODELS

POWER RATINGS OUOTED IN WATTS RMS FOR EACH CABINET

OMP 12-100 (100W 100dB) PRICE £159.99 PER PAIROMP 12-200 (200W 102dB) PRICE £209.99 PER PAIR

SECURICOR DEL.:- £12.00 PER PAIR

PIEZO ELECTRIC TWEETERS -MOTOROLA

OMP SLIDE DIMMER1K WATT & 2.5K WATT

CONTROLS LOADS UP TO !KW & 25KWSUITABIE FOR RESISTIVE AND INDUCTIVF I DADS Si ACK ANODISED CASEREADII V FLUSH MOUNTED THROUGHPANFI CABINET CUT-OUTS ADVANCEDFEATURES INCLUDE-

* FUI 165mm SI iDFTRAVEI

* NEONMONITOR INDICATORa El ASH OVERRIDEBUTTON HIGH & I OW L EVAPRESETS

Ful I Y SUPPRESSEDTO BS BOO

SIZES-1KW H128 WAO 055rnrn25KW H128 ' W76' 079rnm

PRICES:- 1K WATT £15.992.5K WATT £24.99 60p P&P

PIEZO ELECTRIC TWEETERS - MOTOROLAJoin the Piezo revolution The low dynamic mass (no voice coil) of a Piezo tweeter produces an improved transientresponse with a lower distortion level than ordinary dynamic tweeters. As a crossover is not required these units canbe added to existing speaker systems of up to 100 watts (more if 2 put in series). FREE EXPLANATORY LEAFLETSSUPPLIED WITH EACH TWEETER. 'TYPE 'A' (KSN2036A) 3" round with protective wire

mesh, Ideal for bookshelf and medium sized Hi-fispeakers. Price £4.90 each + 50p P&P.TYPE 'B' (KSN1005a) 3'," super horn. For generalpurpose speakers, disco and P.A.. systems etc. Price

F B £5.00 each + 50p P&P.TYPE 'C' (KSN6016A) 2" x 5" wide dispersion horn. Forquality Hi-fi systems and quality discos etc. Price £6.99each + 50p P&P.TYPE '0' (KSN1025A) 2".6" wide dispersion horn.Upper frequency response retained extending down tomid range (2KHz). Suitable for high quality Hi-fi systemsand quality discos. Price £9.99 each + 50p P&P.TYPE 'E' (KSN1038A) 33/4- horn tweeter with attractivesilver finish trim. Suitable for Hi-fi monitor systems etc.Price £5.99 each + 50p P&P.LEVEL CONTROL Combines on a recessed mountingplate. level control and cabinet Input lack socket85 x 85mm. Price £3.99 + 50p P&P.

TYPEA

TYPE rI

TV, T IT

STEREO DISCO MIXERSTEREO DISCO MIXER with 2 x 5 band L& Rgraphic equalisers and twin 10 segment L.E.D.Vu Meters. Many outstanding features 5 Inputswith individual faders providing a useful com-bination of the following: -3 Turntables (Mag). 3 Mics. 4 Line including CDplus Mic with talk over switch Headphone Monttor. Pan Pot L. & R. Master Output controlsOutput 775mV. Size 360 x 280. 90mm. Supply » A --4r--220-240v.

Price £134.99 £4.00 P&P

B. K. ELECTRONICS Dept PEUNIT 5, COMET WAY, SOUTHEND-ON-SEA, ESSEX. SS2 6TR

TEL 0702-527572 FAX: 0702-420243

i practical electronics - worldradiohistory.com · kenn garroch advertisement manager david bonner...

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