uk £1.60 ir £2.35 (incl. vat) - worldradiohistory.com...wordstar handbook e11.95 dbase-ii for the...

THE ELECTRONICS MAGAZINE WITH THE PRACTICAL APPROACHUK £1.60 IR £2.35 (incl. VAT) May 1989

Radio data system decoderAnalogue multimeterCode converter for printersA closer look at the transputerFunction generatorTAXIchir ICsS -VHS to RGB converterForecasting flickers in the field

Dual -tone multi -frequency (DTMF) system decoder

f 1

I

ca

1nt 15001'

R13 F115471a 1 5GM

F114

00

06cli

c 1N4002

/I

CO

In 11500v

1----- ---,/, /C6

O 00125V

7812

C10

10p16y

disable

()e11.4Ie

0000 II

connected

1 333.58141-4z

ae-,

N3

12V

100 r

L9 7702 68 M 00

5

CD

12V

0

DTMF data

1

12

t_U

IR w1 u13 10

0ICS4511

15a

1,124

-1- Lr t H c 0

___N 4. = = 4.093Si

Please mention ELEKTOR ELECTRONICS when contacting advertisers

BBC Micro Computer SystemARCHIMEDES310 bas c £695 (a)440 bas:: £2049 (a)

ask for fut details on add-ons andsoftwareBBC MASTER SERIES:AMB15 BBC MASTER 128K.. £356AOCO6 Turbo (65C102) Card. £115ADF10 Econet Card £49ADJ22 Ref. Manual I E14A0J23 Ref. Manual Part II E14UPGRADE KITS:1.2 OS ROM £15ONES ROM £19BASIC II ROM 1880 8) E22.50ADES ROM £261770 DES Kit £49Econet Kit (B&B + ) f55ACORN ADD-ON PRODUCTS:Torch ZEP 100 E229512 2nd Processor £249IEEE Interface E265Teletext Adapter £9532016 Co Proc £949X25 Gateway £2.175

(a)(d)(dl(c)1c)

(dl(dl(d)(dlId)(dl

(a)lb)lb)fb)(a)la)

Ask for full detals on our fire range of software

WORD PROCESSOR ROMs:VIEW 2.1 £35 (d) VIEW 3.0 .. E48 (c)Speernaster £49 (dl VIEW INDEX £12 (dlWORDWISE E24 (dl WORDWISE+ E38 (dl

SPELLCHECK IIIWYSIWIG÷ E21 £31 (dlINTERWORD £46 (dl EDWORD II £43 (a)LANGUAGE ROMS:Micro Prolog E62 (c) Microtext E52 (elISO PASCAL £51 (c) LOGOTRON (55 (c)LOGO E46 Icl MACROM E33 IdlLISP 139 (dl COMAL E43 fd)

Oxford Pascal E36 (c)COMMUNICATIONS ROMS:TERMULATOR E25 IdlMASTER TERMULATORCOMMSTAR IIMODEM MASTERCOMMAND

- E34.75 (dIE28 (c11£11 (dlE34 (dl

UTILITY ROMs:DOTPRINT PLUS for FX1F1X compatiblesDOTPRINT DUAL for MX rangeAcorn Graphics Extension Rom E28 (d)Merin with 57 disc utility commands100 page manual £37.50

MULTIFORM Z80 2nd Processor for the BBCThis calque Z80 2r.o Prc:essor running 051.tr. a _ a -1-s: any standard CP M soft-ware on the BBC micro. It is suppled with a _ _ . :P %1 formats and includes autility to configure it to read other formats_ This Ls a.., ,s environments where com-puters with different CP '.' 'ormats are used and the data cannot be easily exchanged betweenthem. Mains powered Pocket Wordstar & MSrDOS RW utilty) E249 (b)MS:DOS Read±Write E49 (c)

META Version 3 ASSEMBLERAssembles 17 of the popular processors. Over 70K long program on two roms and a disc andprovides complete Editing and Assembly facilities. It uses appropriate mnemonics for differentprocessors. Fully nestable macros. nestable conditional assembly (IFTE1SEENDIF). modularsource code, true local and global labels, 32 bit labels arid arithmetic. 30 ways to send objectcode and 50 directives.A powerful editor with many features. Send for detailed leaflet. £145 (b)

BBC DISC DRIVES5.25" Mrigle Drive:1 x 400K 40180T DS: TS400 E80 (b) PS400 with psu5.25" Dual Drive:2 x 400K 40180T DS: TD800 _ _ E165 la) PD800 with psu2 x 400K 40/80T DS with psu and buet in monitor stand PD800P3.5" Drives:1 x 400K 80T DS 1S35 1 E69 lb) PS35 1 with psu1 x 4001C 801 DS with psu TD35 2 E126 (b) P035 2 with psu

Combo drives (5.25" & 3.5"1:P0853 with integral PSU E180 (a) PD853P with integral PSU

E90 101

£175 la)E189 (a)

E95 (b)E139 (b)

£205 lal

EPSON PRINTERS£155 (a,(£219655 TKir:_i...,X,A14,15P6815 :80 col)LX800E275 (a,FX800

FX1°5°£349 (a) BROTHER HR20 E349 la;

EX800 £399 fa) STAR LC10 £179 (ail :aa

EX1000GO 3500 Rased £1249

(a) STAR LC10 Colour £E222755

£1249 (a) STAR LC24-1010500 E265 (a) JUKI 6100 (Daly Wheel) .... £295 laL085 (80 toll E415 (al INTEGREX (Colour) E629 laL01050 (136 col) £569 la) NAT PANASONIC KX P 1081. £145 la.We hold in stock a large variety of printer attachments, interfaces and consurnabk,s.tease write or phone for deta:rs.

3M FLOPPY DISCSIndustry standard floppy discs with a life time guarantee. Discs in packs of 10:

5% DISCS 3'h DISCS40T SS DD £6.50 (dl 40T DS DD. £7.00 ;di 80T SS DO £10.00 (dl80T SS DD£12.00 (d) 80T DS DD .E11.00 (dl 80T DS DO £11.75

PLOTTERSHitachi 672 x D A3 4 col HPGL E479 (a,Plotmate A4S E379 (a); A3M £549 (aRoland 880 A3 flat bed 8 col E575 la;Variety of Plotter pens and accessories in stock. Larger plotters available pleaseenquire.

DISC ACCESSORIESSingle Disc Cable £6 to) Dual Disc Cabe E8.50 (dl10 Disc Library Case £1.80 Ic) 30 Disc Storage Box £6 fcl40 Disc Lockable Box £8.50 (Cl 100 Disc Lockable Box E13 (c)Roppictene Drivehead Cleaning Kit with 20 disc: s -:::e cleaning kits 5h" £14.50 (dl; 314" £16 (dl

ACCESSORIESBUFFALO 32K Buffer for Epson printers E75 Id); FX8O plus sheet feeder E129 Ibi:EPSON Serial Interface: 8143 £30 (b); 8148 with 2K buffer E65 (b).EPSON Paper Rol Holder E17 (Dl; FX80/80 +MI5 Tractor Attach £37 (b); RX/FX80Dust Cover E4.50 (dl; LX80 Tractor Unit E20 (c); L0800 Tractor Feed E47 (b).EPSON Ribbons: MX/RXTX130 E5; MYJRX/FX100 £10 (dl: LX80 £4.50 Id);JUKI: Serial Interface E65 Id); Tractor Attach. £149 (a): Sheet Feeder £219 (a),Ribbon E2.50 (al; Spare Daisy Wheel £14 Idl.BROTHER HR20: Sheet Feed E229; Ribbons - Carbon or Nylon £3; Tractor FeedE116 Ill(; 2000 Sheets Fanfold with extra fine pert. 9.5" - E13.50: 15" £17.50 (b).BBC Parallel Lead £6; Serial Lead E6 Parallel Lead (2m) E12

BT APPROVED MODEMSMIRACLE TECHNOLOGY WS Range

WS4000 V21/23.(Hayes Compalibie. Intefvgent. Auto Dfat.Auto Answer) E129 lb)WS3000 V21123 ProfessionalAs WS4000 and with BELL standards andbattery back up for memory £244 (b)WS3000 V22 ProfessionalAs WS3000 V21123 but with 1200 baud fullduplex £379 (al

WS3000 V22 bill ProfessionalAs V22 and 2400 baud full duplex E495 (a)WS300018BC Data Lead £10 (dlWS2000 V21N23Manual Modern E92WS 2000 Auto Dial Card E27 (dlWS 2000 Auto Answer E27 (dlWS 2000 SIC1 Kit £5 (dlWS 2000 User Port Lead £5 (dl(Offer &Mod to current stocks)

SPECIAL OFFEREPROMs/RAIVIS

2764-25 £2.80 (dl27256-25 16.00 (dl27512-25 £9.00 (d)6264LP-15 £6.00 (d)27128-25 (12.5 Vpp) £4.50 (d)27128-25 (21.0 Vpp) £6.00 (d)

MONITORSMICROVITEC 14" RGB TAXAN Supervision 620.... E269 (a1431 Standard Resolution [175 (a) TAXAN Supervision 625.... E3191451 Medium Resolution E225 (a) TAXAN Supervision 770+1441 Hi Res E359 (with swivel stand) E449 (a'MICROVITEC 14" RGB/PAL & Audio1431 AP Standard Resolution £199 (a)1451 AP Median Resolution E219MICROVITEC 20" RGB/PAL/Aucfo2030 CS std Res E380 (a)2040 CS Hi Res £675 fa)ntsubishi 14" RGB Med Res 1813C (BM)

E219 (a)

12" MONOCHROME MONITORS:PHILIPS:

7502 Green Screen E 72 fa,7522 Amber Screen E 79 la,7752 E BS (a

Philips Monitors supplied withswivel sta-i

PROJECTS:Junior Computer Kit £86 (b)Housekeeper kit £58 (b)Elekterminal Kit (1980) . 150 (b)ASCII Keyboard kit £75 (b)J C Books 1, 2, 3, & 416.90 (c) eaUniversal Terminal (6502) Kit £75 (b)Elekterminal Kit (1983)... £70 (b)

BOOKSNo VAT on books; Carriage (c)

LANGUAGES: View 3.0 User Guide6502 Assy Lang Prog £19.95 Viewstore8086 Book £23.95 Yiewsheet

E15.00 Wordwise PlusAcorn BCPL User GuideAcorn FORTH E7.50Acorn LISP E7.50Acorn ISO Pascal Ref Manual. £10.00Intro to COMAL E10.00Intro to LOGO £7.50Micro Prolog Ref Manual E10.00Introduction to Turbo Pascal... £14.95Prog the Micro with Pascal ....E8.50The UNIX Book £7.50

£9.00£9.00£9.00E9.95

SOUND & GRAPHICS:Mastering Music E6.95DISC DRIVE SYSTEMS:Advanced Disc User Guide .. _ .E14.95Disc Book E3.50Disc Programming Techniques £7.95Disc Systems E6.95File Handing on the BBC £6.95

Unix User Guide £19.95 APPLICATIONS:Understanding Unix E18.45 interfacing Proj for BBCBBC MICRO GUIDE BOOKS 813C and Small BusinessBBC User Guide Acorn £15.00BBC Plus User Guide £15.00Drawing your Own BBC ProgramsE6.95Inside Information £8.95Math Prog in BBC Basic £7.95Toolbox 2 £10.95VIA 6522 Book 450PROGRAMMING/UTRITYAdvanced Sideways Ram UserGuide £9.95Advanced User Guide (BBC) ...E12.50Applied AssAang on the BBC88C Micro Sideways ROM's RAM's£9.95Guide to the BBC ROM E9.95Beginners Guide to W.P E7.95

E6.95£5.75

PROFESSIONAL SOFTWAREWordstar made easy £16.95Introduction to Wordstar E17.95Wordstar Handbook E11.95dBase-II for the first time user (16.95Understanding dBase-Ill £22.95Multiplan Made Easy £18.95Multirnate Complete Guide £16.95ABC of LOTUS 123 E17.451-2-3 for Business £16.95Adv Tech in dBase IIAII E22.95Mastering CPIM £17.95CPIM BibleIntroducing CP/M on BBC & 280 £9.95MSIPC DOS Prompt £10.95

PROGRAMMED ROMS FOR ELEKTORPROJECTS

503-N Jnr. Computer Monitor 516 T.: -; Dice 2716 £ 7.302708E 4.80 521 Cr.-..zen & Video Routine for

504 Disco fights 2708 E 4.80 DOS Jana .. 2732 + 2716 £16.40522 CharGen & video; Routine for ex-tended junior 2732 + 2.2716£24.00523 Char. Generator .. 2732 E 9.00524 Ouantisner 2732 E 9.00525 Universal Term 2732 £ 9.00526 Wind Dir Ind 2716E 7.30527 Elabyrinth 2716 £ 7.30530 Daisywheel (face 2 2716 E11.00

505 Chess Intelekt 2 x 2716 E14.60506 J C Tape Monitor . 2716 f 7.30507-61J C Printer Mon & PME

2716 E 7.30508 J C Bus Control 82523. 4.80510 150 MHz Freq Meter 2 x82523

£ 9.605.14 Dark Room Computer 2716 £ 31.

Please add carriage 50p unlessindicated as follows:

EXCLUDE VAT falfB lb1f2.50 felt -1.50 allt-1.00

ALL PRICES

SEE OUR PAGE 5 ADVERTISEMENT FOR COMPONENT PRICES

TECHNOMATIC LTDTECHNO HOUSE, 486 CHURCH LANE, LONDON NW9 8TQ

(Tel 01 205 9558, Fax 01 205 0190. Telex 922800)305 EDGWARE ROAD, LONDON W2, Tel: 01 723 0233

PLEASE ADD CARRIAGE AS PER CODE & 15% VAT

(Export: no VAT. p&p at Cost)Orders from Government Depts. & Colleges etc. welcome

Minimum telephone order £5.Detailed Price list on request.Prices subject to change without notice 1*

ELEKTOR ELECTRONICS MAY 1989

In next month'sissue:

In -circuittransistor testerIn -line RS232monitor

Guitar amplifier CMOS switches

for audioapplications

MIDI keyboard Diodes and

their uses Disconic

antenna Echo Unit

Front coverThe Dual -Tone Multi -frequency Decodershown hereunderneath a stan-dard telephone set isa state-of-the-artdesign based onTeltone Corporation'ssingle -chip receiverType M957.The DTMF diallingscheme for telephonenetworks wasdeveloped by BellLaboratories and in-troduced in the UnitedStates in themid -1960s as analternative to pulsedialling. Offering in-creased speed, im-proved reliablility, andthe convenience ofend -to -end signalling,DTMF has since beenadopted as standardand recommended foruse by telecommuni-cation organizationssuch as CCITT. CEPT.NTTPC and manyothers around theworld.

Comment

11 Britain in the RACE; Sound future for SMT

12 Electronics Scene

Application Notes50 Get off the bus with TAXIchipTm devices

Components

30 Practical filter design (5)by H. Baggott

39 A closer look at the transputerby Pete Cho'.vn

Computers

54 PROJECT: Code converter for Centronics -compatible printersby N. \Villmann

General Interest

16 PROJECT: The digital model train (4)by T. '.Nigmore

Intermediate Project

14 Sine wave converterby K. ).Valters

Radio & Television

32 PROJECT: Radio Data System (RDS)demodulatorby J. Bareford

57 PROJECT: Super VHS to RGB converteran ELV design

Science & Technology

26 Forecasting flickers in the fieldby Dr. Bill Stuart

Telecommunications

45 PROJECT: Dual -tone multi -frequency decoderby Robert Krijgsman PE1CHY

Test & Measurement

18 PROJECT: Analogue multimeterby T. Giffard

Information

Events 44; Readers' Services 65

Guide Lines

Switchboard 66; Buyers' guide 64; Classified ads 74;Index of advertisers 74

The digital model trainp. 16

Analogue multimeterp. 18

Radio Data System Demodulatorp. 32

A closer look at the transputerp. 39


1 0'9_713374r.17.1I 4 1

-2971 3... 695 "3,P. 6 950.5..:1.733EGA 2_233576737. 120292020.0.20 1057

2,4.0009 7.4003273027 15505.2522730 220E.174104 0161-0.74319 0230471929 3:71.2420048111.132637022 1 t 0U19E3202 2 7:...-.6.-.. 937189767534 I04

L''''' "'U522022.1 0 7712200207.24 0 2112.5111021 0652220558 4-211-1-713307 2309212926. 1,5505023014 1.70

W599202 2925002250 17,551,12.0 33:E.72.345.22 573520 )..-6- 745727010106115717 1572701110511 57.-, 232281 2 5.5.7:7007 3 72

_ 2 826224770 2 31_, :09165 9 37'

--""'' '"-70614- . .. 0

. ....... _ . _ 77.- _ r r r _ : r r

-- - ' . -91:. r - - -5112.03: - - 7 :31205212 . . 731246717 7.7 . 1 170030740.- - ' : 740674e-- 2 73,.4122:45--- , 520.0043, '37672672255 17226034059 340ZW4 0937 5 07251005126 12.637 7-777 10922E8511511N 03E128601012i 6 99

01037522. 5

.. r . 2 32551.-2g-690

711 175 25211d5526720

. 11101, 1393

. . .2 10 5633

. r ' : :6765 5265

523220205 3530'''''''' "'05425.5.123 2301'003035 3214".5.2 77001 1506-77-13129 8.06

' r 775 3155...... 1209

9E577 52.52159274 76.7075290 3871P8222 22_99nz33-70 z23322-401232 29176520 4.655.50.22 49515522.5.9 7020E232 59305421 92205057 0 55Reec277 1279602192 52322502122 5472232772 11.125C72075702560

11352:3265113.24

6.462252E7 122 1200

1226SC7267 LEC1440

36250.231.67151574

925254.7661537128

9.1157-5266203120

7.0393-%W.11[1910

6347115M.71.51 018

02262 300

''''DnCl""IS27-6507027264-12716

2120221.77C620-15270

50316227200-10-210

202274. 1 710-23"027.20'"'"' 630

1.041-37.763.20 2101330

1.50u312 2025 7.10tra1.93767V.2. 20

73310215460/ 320710 6-72245.9 630915.614 25 11407(2.35 5.10 9_2482724.035 18_5382120 10 1696810025 St 500202337 106.40

1.1775022 0.35

2.53(0=1:33 -2X-r 00.727S

020032 056L1J1131X7 056047310T 016U.11719,4-63 001.142812122 075

L11,710 A10 1-,Z1'?.41 C'1.7105

92.739313 1.100173932202 1901717621382-5 22402950315 2221.21033122 9202.07801480 0.65WC 275316.122 020IC 724.52C9 0351-036.02.372 7 5"2.076.0932 .10764.22122 --1075.1282 571032. 12027 obi14232974.22 0.6014279.2640T7.072120507 1.201.157-41.336C7 27372227607782 1362.0731-11292 120/028115537 36301-72112C3 32361626175C7 36310419412 30075.11703601 165n727202 1 35-

71.721587 111Tt7703101 11511 27300W4C 2.18117001-930 2_1821280.1.360 7.18.7.4722-04C 112763 786753 1 23732.30200 1_5877.70200 1.581217613.21.2 128LA7010370 75119.17.114. 158us.7206.12C 10_131.2.73432.84C 11360273302721.4 062987827011C 1391247010ECICC 1_33115103109015 73910781.2263,C 100.27911500 1391.117220201C 7231117060.0 20412177064.E4. 202017309310 2011.247312C2C 209447515E3E 207usn,ssrc zos5.7124720 20971.73315025 1511.5.79.41242C 9211.173.715CLE 711150-360270214 321(35431&7450[ 1251.2.70.1.24.09C 121

TEL 01-471 9338 TLX: 929709 VICOM G FAX: 01-552 0946DIGITAL INTEGRATED CIRCUITS SPECIALISTS

23272071070 630`r.1.1721763411 3a.so-227-2124.118010.2...273 927757, 526.5

'"" 26.27227.3,9 0.10mammas700 022/sal . 0127501 02131401 0.15702 025

s377

0207 0337 039208 0.157533 0207310 0.157213 035

0-312fAti 3073747.I'4130

7'10811 030713 0.197227 07437 024'332 47.29737 0931412 0-357142 04051.25706217 000700 cum7517.51 02025727471 60074727374 0307475 01571.7617.29701 02071n1433

00.4°

7.1010 03011% 92974837422 OAS2.15... oss

" ' T ' ' 0 32,... 07 3 5 0 327412,21 032785132 0_3270(57350 32785137 127670408 031702113 031745745 0767s.5117 ass78522.9 WV&

rs:sisi ass7,,3753 030785734 00470303 0_23722156 040702767 0257045758 230749528. 0063,5165 0 44-R5752 ass70974, 24080333 030-40.33 00063,..3.03 Oho.3.43.0103 0 ..78510 010744003 0345,5,3 033705171 0_367,, 033705131 6506,8,,E2 740703132 1003,7433 1007,447.07,,,,,,-, aia344373,3 0 ....s7,133 030702193 046705155 05033,30 004203137 ase7435227 050

"...217 3 2-30701620 2 207462627 2-364:5522 2.2005E23 70585540 09985641 0.90096477 1304(5647 1.1003542-1 2_50413241 190026132 2.50836.3 1.10

71456431 24042643 1.7044.5605-7 33004646 560125527 56002342 56012E0 1. 0083521 03244552 5 00195653 56085351 56005633 5_2545E29 618.756'7 0 6815673 3_20

...5474 12082-22 210445554 2_4105607 2_40412600 24082420 2_30.1.12237 2 60

.741.2118 1257.15793 3267535734 329785722 1407.1-57_1.55 7.10

241-5'n TAO712733 12602.-°°^2 303

. - . : 3. 0027 0-333 7 3378745073 140700351 039

0.750355 457420525 0.34720365 061700347 03670070 0367420373 04574.27.1. 0 40700371 0 527420377 024700332 020740390 05570-0-03. 0.50700123 065700023 068700231 0_6270050 072740241 0_72700533 066700651 0_667403573 0227220571 0.70750855 57272205507420572 0.83700123 720700255 0.61700522 044700620 1.707590323 170700610 0-907006.3 0373740645 015700216 730700648 1307.60531 17073015.2 1.1071006 3_367.2.21-59 3.367.20924 336700553 326

73.37132 007307s 33 0 57703.-7753 03674017E4 1707407157 0_557201156 07075eCT 760 0.797401162 044700062 0 95105062 0 86740/125 0457.40022 1.107.6:7125 1.107407173 080705.2717.7 0777062175 0727007101 3_20700102 1357022123 126700201 1_05740201 1557022793 7.367007123 7337007795 15574207221 13275201237 1_2574.01230 0987407203 0637007241 063737072.2 1_107002243 1.207005245 0707002245 0707507751 8807101253 0 007.a.crn7 a so7.203726 12574305203 1.5017

7401223 073201263 1.X.7.4cira3 1.407001293 2.357001354 1 SS1001356 1.6*

. , ..., 1407522 6-607010,4 665751015 BM75763). 730751673 11207,576-M 8307517275173 37075124 1.9075175 320251765 225751775 3.31

757708 2_43751739 3437.15275103 "" -751E2 06075129 CIAO751096 03075117 30770212 317752.73 12775115 33275326 27270361 3.33, 7,a- 23275372 65575431 1.2275433 16270333 13276534 1_2272.20 3_337-372.5.2 72475.3251 5.1075-.7ce 7 Si76.31165 22276447 2287510 2'1675442 72576462 023734520 16472451 0.6TU51 0.45

21722298 2370227-2290.5 22204873222. 14 a,32397227mA 772203026;3,3 7.3 20

0276559A 025011715623 1052347 1_031.9367 030-1132111 025

0003431.2 0.53113SM.IA3265 2_75tr-411371 0369241 225 3309E0104 090970,5 ass2.4.902 0_93

'2" .L0.22.07 7,65

56

353,1-r223r1.,-'11`

2163311, 055Un32°11

0200.0031 0.70033702 3331.03111 0231.11217T 1.3551.10-160 135.1.011.5 1,201.7.1-noi 0.4504330 215111M1117 92131343312 1.1013.335.2 1_2S...703B 1.221.327.7 11541222r7142 2--5 ' -0*1152333 30 114510332a 1-5°107.335 0-.°.573331'/6.3061.13420 056

0020-P202E22065

2220322 17-32M,21° .77067-W7 340

220320

.---1-1. 7 320er.-5-2 390''''''. 4,50

50.745- .2 1590cals7 a 31.2323222-022 11334-.24......,--- 13.2356704 4329055.33005-12

022206329 212068

G352W2212 7.289063919P 10.401-3363.WLV 9_10

2409 .0214550009000

7606 0357606 0357436 as73637013 0507875 0.407018 0.407224 0,40755-6 0_357372 040722 0201318 0407574 050332172 347147059-2 29994710345 233192305 2231.82225 2237.407 3-351.1271 22194303 2.73I. 7125-2 027treacv 0263.7-4009 0_739701202 0.671.7678-V 067276004 0736.0404 02677e230r 0730622.202 0921301202 0103.7n1scv 090tresvacy 129

02647557555 1.23(7sascv an572333-5 0209721200 0.73(975[5 073373004 02.337720CY ossf 7.24,1 0607.701517 8210497/36.5111-24

20 229018801-12 20222114023215 627254143-3/1-5 60202222.7 1E0van -3075 2231.1122333-0 2.090093 1 7000230.52 202W1-33123_0 0 63606307 49502421-1 16217829502175975

2260.239473C72 7 0236.02,, 5-529032237-21 5531.21-31C--71.11 238274317312 2_49.v3202,3 0.499123dX-5 8212423232.12 0235.332].2-15 6531413202,5 0.4391232d42-72 2_3311025922-15 26417123137-12 277-04702- . 277103201.5 277,-1.M.--.111-- "4L1.3-2-1.°2 1°28(2.325 6121125-n32 8.51133.33i 155116.332-5 1.70L1334011-12 7-27013400-15 222u13302175 22291.1.2402 9.7 62758340495 6.47L3214.17 5 647W3+-0[,12 2933121-700. 0 7270224210-5 227.1.11182 -12 157.340480 15 2471.30.93112 5 237,..u. 5712 1.10*Ult.'"? 75 7.10u93405325 1_109123421 11 0.221-223.°2- 14 0-52736-4671-5 002623457 17 078921377275 078163417-5 03100422 17 1.16(30419..5 01638343320 1 721134505 74 1.54733557 042112117600-7 052314747221 0_2235579549.31 2292117924.82 0330379.120224 2291.3.029178.34 03902]81714% 8393879.13404 72911.172.0.82 0.33

05203.22081 Icy

1832 0 fa10{4= 02042167 1_25

7400/5 1255120. 4_20653299 54055277220053y. 6_7505517 6 4092271 1039429 31055421 920SW-. 040EZ17217 320E.1 2508151R 25001-53 2-9S82520 340879-3. 3.9502C3313159 5_909350273!5 4904555536 3554, 44434e0d2.40443-101ge 45422-2022.4. 5 0_740W01-0707 6,72cosisluP es?2492037 sn12117.7044031 93002102339 725002721113-10 11.5601/265121000

245702223272 277004333'./012 257

4 33397161: 1 27

0.72-7726 557172-21005 2 Z07-2.0.230 37'0228607 20 3 '67-541Z2 50 1.331211 6 1-1051112 5 5-:0073.3. 30 0 -34414E3675 1 2530057 23 34145.1......., 5 sa08.770 3 7524,....2737 4 252029.107 5 3251:71.3733 5629931,20.0 434.074287E2 426.082260 10.13590,20 39014660.04 806,,,,,,-, 9227838547-5 44 20032378494 4160250102 392033273 31430654E9 362102615911-6 70207-0221. 8.45200102 2.179060-29 3110E81623 3_5920030214 42901271700 mei031703- 6_3760202-118 5.53o454024:._ 11220.6.371727 5.97210433- 99915351501 1210,46 r -.0. 2.10.5 ' ' ' .1- 1013

- 11107.09

77.. _ . s 12_25..1.,: .. .. . .. 11521....... - 5 16_260 a - - . -_ 129

_ _

tr.: - .. - 1 32.3tn: ....-:...:- 25411:3'0' 8 2.1.2243.0.7 4224455,5455. ass0082.2 99113:02762 11331.15727 1,001713214.1014402011237 6785 33722.0.932 7 7445 122412300785 375712241292772 364106101556:5 6_071/5.12107295 3_987.1773355104

4261723.96225175

325t05,75,,:-1.55

452

506906739 10.402063507- 14.30.42341£027.10

18209360220196

50541921131150

2020300012 7123172>210007 9 an1137-33X17 S2S706229 3365053555 5.76069.3- 60003309323 4020,zza,ccoxpa

2441:,292200CP/13

7030..coa,coosn 3

27302.5.5,022.5576

17242.0327011/03 71200329020

109-2025217...65 0 338#32,..,-650 2.30963033,0 3565753647756 59007.3321-204-712

I_ 2271.13.262. 3 -

1210

/772172. 95 592113733:21:. 3.1211.27241572 33602091790 15.1571922-0316/ 434153031.02. 1337117:0553757 1037WM00 2 .6LOft252: 3-54595.2.31X 3.71.i2° -.712.S 301570.28v11-1-370 4.37tow:am oar579730714 6 601.4073103 16.3719072250 2774112376210 70592001500 3.37L405154452 447121731W.770 171772527782 562- --223614 2.22

27000 267..77-.77: 2 .0

. -71 298r - 1 3_60

- . - - -.. 244.- , , 1C3 274. r70432 376

7 . :-... 210 2.10Z,....-427.2.21 5 10367.649.0 5052204-210 2231006.570 1752801-513 1 5461101202 59070657[ 3 40005507 572.722-20 102008-20 7_4128820156 103323133006 1029263[41350 22.4323812.65 2243762-01 1020ZE-0224 8.05

7001 04471707 0,07011 0302715 30075119 1.107021 03075122 03073123 02073125 0407406 04274128 00271100 020: 2951 00374163 06474167 0.1418 0001402. an74245- , A,70E5 04074279 02574233117033 244.753678 020:73.36211 ass

21-52' 0 0637445241 05170_5247 aSD742243 0557.157.4 016754...45 04622247 046742246742242 0737115251 028745253 0207125255 0557453257 0317.222.A 020782253 13..W742763 0.36755W25 0367442273 0507522275 0377445240 :0343,3, 056742120 0.33711.53 0.30702255 0257115233 025

MIMMEMEM74003 0.14750332 0 14740004 0.747.40230742004 07574901934 024742.1.6 43674048 02274010 020745011 0,,742034 03370020 03073C31 0207479737 om70033 03075403274032 03078051 0.3370153 512870/73 020343,34 03074075 0301411076 0.20745077 030700r r 033

."4557 51°_0521366720877 260711161376 6 10

2.237.320122 503700233 164740128 0901. "Sr 720114206:91 1207151-627 1.10750613 12070006 126711-1[5.7 126700606 124700629 1257.3c4032 025740407 030700097 0207001722 0.40701[3321 0347404020 040730405D 0.3473C101,-, 038700837 0_33700863 022

744414755 0157 0.7870121737 2747042362 OW7102373 0707002311 0.707401377 1.4820293390 03570249-2253 096710033 1357401234 135700040 0927002541 0937042203 02074212324 02070015737001771 0W740250 7407007223 4.20711{1640 1.10700930 7107007646 1_40702[703] 1.407001651 EC700252 120

7r.-457572433675452724037384 13157P.sso724E00467733627516172363

_

75205 44675463 436701727377777-372._ -- :

r ...

02512S018an0-211161,057.101.10122416

2 Er 2

'':- -

'

-

'

75

11.135811 0261 1.13621 23051536017 120Issami 110Z.5

1.123201 0Lua:^7.3 tsa21/15122 LW91418104 535023237 370112317.7 3001.1r42211 260,113.9501-1 1.262173365-3 1-&7901100 . 166.7.222712 320.'73573.1 32027351 2_107.1W24 120 33170 133... 23160 2.20

.63274 190

.12.3.367 020.13334 0551,002 3 70

_0330 720

00.10,00115247.55

064800855,..-,.....,-..-4,33. 478279 .....2.2221 1St0,70, 2.15L.3,-.,--, 2_35,;:--93734-3,, 468i.43., 6..,..,54,,c 25.09L337. T-,., 1034012 172.-5111.

2221L4,334027.2

731345023332213,3x3_, 592,.037-_-....7.7 5 4518062 192

721,....30.v4.5-738

118223170-5:773 436(23779, 40433.07 83 05304,91730- 1224,5 /.. 1_4591.23337 79100317 82293.73322.1 13_461.173317.22011

16_24(14337`.2 1.47003702 12633,,,,,, 2a3(833524.722,

10_720132.52-57 2253.43....7 5623,1136 1033833. 30030,23:51 10343,033 303L5673 -x3; 0_703401 52598223.2- 5934936, 4,, 33.3Lp2257c, 3023002,32. 3306,666,,, 5 5,333-033,4 1331175.3C5C 35511272326 012o.37634 122z475-7-.4-7- 1270u.273.77- 62 1937

570143.02922 6_1005746801439 029103220, .4 75906931090

29-3354:9207w, 1,3412332375 3657tnr..7e79-3s

23.400,33-3,.-.03464

2/2247222.53335

1.22210.7 75-25 25

7-572261W-4.253952

1.02A..-6. 174.3

lEZI=E51200 09,r 7.14502 0.1471332 0,470203 06.,744504 on711622 0.1470626 0.4371007 04278508 03478509 0.15742510 0.14

74sszas sso200,21 0097405777,33.7_, _11.,6,,,,,,, 52074133n 1321742357 020.74,0,..3 0407495363 sso15333 130705355 0307155368 035

707 ' '039

74,, - - 03174,, . , 03,2.,,... _ 0372,,..., .. _.,7/0771 036700725 0-3474,.0733. 03474.001 ass34,733 4330

740133 0_357411[137 *51

700862. 028709[1053 095716177.4000 092709E4057 1.727004500 0332°7°1°22 0-327--.'e°T5. 02674-c4074 0322.-C.....°. 0-307001511 076_7'5454: 322'.8'.. 7 . tie

708-1570 1.757 12)55W2 2.767417C14002 0_427013-74315 12070012016 3907....-1.4077 1.15701,7750, 7 0307040123132 3202..:T.0703 31074.0740104 236-20"r174'°7°2 282

71127.. 3.0.1-7503 3.175494 3-567-6433 7-58735:21 203.215010 8-0A7'7",-"A 1022700125 4220070 L'1470530 132375425733 256755125334 256

,..--_,5-,a, 0351.170202 1_25..1.17101.0 0 20turn°. 0 sa3333.33o, 033[274101 0.243117411557 03511174711 0627.317.22 035437303 04563.3755775 366,,,,,6£, 390

785u 014741-512 0.14704.503 022

7495357 0337412358 035742373 0550

707<139 036700233 1124740127 044

210<45"0830-°82.2r-.52°

22.22.°- 0-"=MGM=75103 045731074 119

2.-124-5 '22 3077-0103 173

013-26.07 32313210/, 063

2.23.570. 2301.7073.6.......10

16.1513744-37-0022

355951177 ....217.5

613772.11.&.:224.1

2901.957590-0735

5.078820016,5

1580us320ceoe 379639-32315136 418-1703203256 23_5010372233-3 St 031.536007: 11.605465025-1 7_0922.293024 152329331 7_202205281 2937200560 49059053194 12.388220231132

11_22=ES -900337 79

5914_73

7-31965697

1022. r ' . ' 921

12.77r. .266

4207_ 31.2527031.2

5,4021.2152380024.011125_- 70422235710324.07051.

31931842.220102-12

34 751,s2:,:t...-:,:,7E..

5222

74514 0.23753515 02578520 01578521 023'6_$22 0.12709524 ass25526 0.1529527 8162223 0.15

0.452232 an

0.16-4237 0.7673233 01770930 016

785371 050702375 05.27392377 042741330 an78013 1.1075 1.-A2 563715522 2.4678202 04570 2-7-0, 0437.4 9741 441785335. 0.78utsa.s.s 1.7070 1-247412122 an749503 122

71140 42 04024140151 03474140153 034200754 09674E0153 0 53740157 036700125 0367470160 04434397101 044740162 0 44700 Tw 05474220763 014700 10r 05737416122 o ss740173 0_54

2°.C.S.3 ola.20C22°,.. 0 063._,77 'X° 0692.422" 13°:'''C..._rxe 2-10' '''''' C'C'' 0"7.-.°2°I. 1771147075 1417507076 2107...°"58 ...5°'1107}42 0 76741C 7734 17-76"7'Ca31673 0 ""---'-'",'-, 0 s=

7002 Tss751M 0.W003737464 166751CW 1 13575112 1 SO701004 2177500 08075004 93333,12 2.7575112 1.4075)13 105'.12025.5.7)7504 1337505 13075116 40475117 401

I=0.73

91155 250555 0_2055'002 0.90558E1105 74070331. 03074101 01671505 02032202.2/ 39.74

123052574523 24202157422D 41.003058131 5409259320 16E8

140137122 1301107327 0.702141413 065001155 015um 7 45a 013101463 290441401 06014.1485 0.60031154 620-4[1745 265507456 065U1C1M-7 21070303 (9700332.0 t103503 060

r- 114i57"

.2,2.'5 3044.03.72-. 2504243017 7204720075 2.0.2.7050540 720,,,-2e.4,...52 240

m3=12=20822 20 1.-,,8 -3 201.6268275 201503116112103 210C3153232415.

20_2_

1723083303 3 4076.92225227 0

1.1.:'73.04.31.6-1070

70312 02178347 ass7090 052153535 0 64785511 09570563 01570256 0.17741573 02671271 020741.272 0_25741216 026731277 0.75145711 026741.5*2 00704555- 020741266 0-2578530 0_2270931 026724292 03578593 028733585 045744536 0567435107 03374.5109 030749502 0.30744203 11.307525114 030785122 0.3870.5123 031

785350 502785423 502185160 5637455461 4411854514 19974205 135785467 190745454 2227.4-5469 499711.54251 59973202 1227824318 6_47712224 3_1E8

38520 095785511 0_95785246 455702547 425782236 420245546 42074555e 045705067 4_6374L5504 1_9574L5563 1377046_2 3618785570 1.56742227 1527085322 1557315622 1537295624 135

700173 0.31710175 0_3870021 120740152 0.40700190 0267410151 0.567410192 0347111[193 0_42700134 0_42734005 0_46700211 an700237 0507340713 030740740 0.42700141 027700243 0347570343 020700244 044100115 548700251 0.2517715253 0357450257 05070-0358 020700269 0.35700765 024700773 04471145279 036700320 864700193 044

1011M121=0E.700701 032740502 0.=730703 0.347410104 0.3,75002 0-12700710 0.3271145111 032740174 054700110 0_34740121 0.327120127 12.361320730 6.36700732 0-22700142 0687430133 029700774 0.55700575 02170006 076750786 834700:93 0 902501707 0.S47.00280 054710971117 0747420110 0712.0-4-1125 001700026 083700103 0457001737 042

7-118 4017510 40475102 12975122 12075123 1.727512. 21575122 12575131 59775729 12575123 42275130 76775175 13175132 50975140 2.7675141 11575142 166767425 52375133 16075104 42522146 262157W 1.007515, 33575722 5007523 36525720 1057015.2 19075157 33575756 32375155 170

1329252 13.1640707.5 sso.3757721 21_691.9123874 35_7307-500 122003707-310 11.72C174 63G 0104.04-6-5 000CA329 1 1_20CA30207 338117-930 2_1014131101 130C331451 2_.2001.1162 135CA.328 135C27.72C6 205Da023530731 29.5M-3717. 202817015 2.536633070 292251260255 37015,05093 5 5_952.0 274402 436020710 199330710005 52501770815 6964272055_ 1729537126041. 6950747135[37 1171

40332322 0200023202725 3_1075231 1950234 1.70

. 120020322 1_507125332 190.3330 522.8006 "

4E213 '52655605E5.Z.5615E25778530 T

5137110032 0 10010702 1 200612.557 0.7065.530565 795575.4131 7 610512052-2 125037301711 900101122-910. 4141131 02015.771 0_7537773 56514'13 7001,0.7175n, 1__

OUR( 90932.2.2

.°T127- .1°.17.0

0.12120 000 S7.10'

1520 Mr=nr.M.- ; '- := 2 2'

514- 1, 7614-77150

=27245 8W273/35-15 220275156.5. 23 73027033220 3157

72027025620 211

690275.721,60 , S 793773226-15 730

POOGIUM111/61106161A9 0224. ,

7 ..Please contact us for 4000 series or see the September issue of Elektor Electronics.

VI EWCOlvi ELECTRONICS PLEASE ADD 70p P&P and then 15% V.A.T.OFFICIAL ORDERS from Govt. & Educational Establishments are

77 UPPERTON ROAD WEST accepted. OVERSEAS orders, postage AIR/SURFACE charged at

PLAISTOW LONDON E13 9LT cost. V.A.T. not applicable for EXPORT orders. Stock items by re-, turn of ost.

PLEASE PHONE/WRITE FOR ITEMS NOT LISTED N.B. Prices subject to change without notice & stock availability.


-AA

Editor/publisher: Len SeymourTechnical Editor: J SuitingEditorial offices:Down HouseBroomhill RoadLONDON SW18 4JQEnglandTelephone: 01-877 1688 (National)or +44 1877 1688 (International)Telex: 917003 (LPC G)Fax: 01-874 9153 (National)+44 1874 9153 (International)Advertising: PRB Ltd3 Wolseley TerraceCHELTENHAM GL5O 1THTelephone: (02421 510760Fax: (0242) 226626European offices:Postbus 756190 AB BEEK (LiThe NetherlandsTelephone: +31 4490 89444Telex: 56617 (elekt nilFax: +31 4490 70161Director: M.M.J. LandmanOverseas editions:Publitron Publicacoes Tecnicas LtdaAv 1piranga 1100, 9° andarCEP 01040 Sao Paulo - BrazilEditor: Juliano BarsaliElektor sariRoute Nationale; Le Seau; B.P. 5359270 Bailleul - FranceEditors: D R S Meyer;G C P RaedersdorfElektor Verlag GmbHSusterfeld-StraGe 255100 Aachen - West GermanyEditor. E J A KrempelsauerElektor EPEKaraiskaki 1416673 Voula - Athens - GreeceEditor. E XanthoulisElektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (ElBombay 400 007 - IndiaEditor: Surendra lyerElektuur B.V.Peter Treckpoelstraat 2-46191 VK Beek - the NetherlandsEditor: P E L KersemakersElectro-shop35 Naseem PlazaLasbella Chrp.vkKarachi 5 - PakistanManager: Zain AhmedFerreira & Bento Lda.R.D. Estetzlnia, 32-1°1000 Lisboa - PortugalEditor: Jeremias SequeiraIngelek S.A.Plaza Reptiblica Ecuador2-28016 Madrid - SpainEditor: A M FerrerElectronic Press ABBox 550514105 Huddinge - SwedenEditor: Bill CedrumDistribution:SEYMOUR1270 London RoadLONDON SWI6 4DH.Typeset & composed in theNetherlands by GBS, Beek (L).Printed in the Netherlands byNDB, Zoeterwoude.Copyright IP 1989 Elektuur B.V.

ABC

Britain in the RACEThe award of almost £80 million worth of orders to British firms in the finalphase of the European Research into Advanced Communications Equipmentprogramme is encouraging news. It means that British companies have gainedmore than a quarter of the last allocation which covers some 40 differentprojects. The total budget for the research programme amounts to almost £900million.

Since the programme is a cost -shared one, the latest award means that the 40 -odd British companies involved have to invest a combined sum of close to £80million in the various research projects. Virtually all the important telecommu-nications companies in the United Kingdom, such as STC, GEC, Plessey,British Telecom, Philips, BICC Cables, and a host of others are among those toreceive a share of the funding.

A recent report on the likely effect of the programme on the British telecommu-nications industry says that full exploitation of the results of the researchprojects would require the participating companies to invest an amountexceeding £300 billion during the last ten years of this century.

Sound future for SMTAlthough there are still some who doubt the viability of Surface MountTechnology, there is ample evidence that the use of surface mount componentsis growing rapidly throughout the industrialized world,

None the less, there remain a number of problems of which the most serious isprobably the absence of agreed international standards of assembly andinspection. Another is the difficulty of visual inspection (automated inspectionsystems can not - yet - take over completely from the human inspector),which stretches human capabilities to their limit (think, for instance, of thethousands of solder joints on a single Eurocard).

However, the first step to the solution of a problem is recognition of theproblem and it is widely accepted that most pitfalls associated with surfacemount technology have been recognized. In any case, the worldwide growth ofSMT speaks for itself. If it were not a viable production method offering manyadvantages, it would have died a natural death by now.

Change of addressFrom 3 May 1989 our editorial address will be

ELEKTOR ELEC1RONICS (Publishing)Down House Broomhill Road LONDON SW18 4JQ

Telephone 01-877 1688 Telex 917003 Fax 01-874 9153

Our European (production) Offices remain at

P.O. Box 75 6190 AB Beek (L) The NetherlandsTelephone +31 4490 89444 Telex 56617 Fax +31 4490 70161

OF TIE Amer6,-P.F.L OF ORCIAATPCF1S


ELECTRONICS SCENE

Satellite broadcastingThe current and future state of satellitebroadcasting will be the focus for discussi-on at the sixth annual European SatelliteBroadcasting Conference to be held on22-23 June at the Queen Elizabeth IIConference Centre in London. It will bringtogether the leading problem solvers andstrategic planners in this volatile andrapidly expanding business.Further information on the event may beobtained from the organizers: BlenheimOnline Ashill Drive PINNER HA52AE Telephone 01-868 4466.

Ethernet transceiverThe Ethernet Transceiver from RinglanComponents is approved to IEEE 802.3

The unit incorporates a NETSCAN facilitythat allows fault diagnosis without disrup-tion to users on the network.Full details from Ringlan Components 58Burkitt Road Earlstrees Industrial Estate Corby NN I7 2DT Tel. (0536) 400517.

Airline videosThe world's first in-flight personalizedvideo systems are being evaluated byBritish Airways on board its Boeing 747aircraft. The systems allow passengers thefreedom to decide what they want towatch, when they want to watch, and givesthem the control to start, stop, rewind andview again. The aircraft will have a libraryof about 50 video cassettes on board, ran-ging from comedy to drama, classics ordocumentary.

New test centre for System XTelecommunications administrationsthroughout the world will benefit from anew 1,858 rn2 test facility being establis-hed by GEC Plessey TelecommunicationsThe centre, which is due to come into ope-

ration later this year, will house ten feasi-bility model System X digital telephoneexchanges, making it the largest of its kindin the United Kingdom and one of the lar-gest in the world.

Automatic announcersAn announcing system in which solid-state electronics are used to reproduce'real' voice has been introduced by P ACommunications.The `Parva' announcers may be used as asingle -line telephone answering system,for multiple -line answering, or forannouncements in railway stations. Eachannouncer can be linked to up to 100telephone lines.Full details from P A Communications Ltd 10 Darin Court Crownhill MiltonKeynes MK8 OAD Tel. (0908) 567248.

Call -alert adaptor for cellular phonesDrivers with cellular telephones can bealerted to incoming calls while away fromtheir vehicles by an adaptor that switcheson a warning device.The 'Call -alert Sounder' from ACC-CELL, is driven by pulses from a current-

sensing adaptor actuated by an incomingcall. It is intended for use with cellulartelephones that do not have an in-builtcall -alert facility.The unit is produced by ACC -CELL Ltd Apex House Kingsfield Lane LongwellGreen Bristol BS15 6FL Telephone(0272) 352261.

The CT1 module in the 'Modicom' range oftraining boards from LJ Electronics is forhands-on instruction of student electronicsengineers and technicians in digital com-munications. There are three units in therange, each of which is available separatelywith individual user manuals or as a packa-ge with complete study curriculum.LJ Electronics Francis Way BowthorpeIndustrial estate -Norwich NR5 9JA.

Mini aerial for satellite receptionMr Patrick May, a senior lecturer in theengineering science department at ExeterUniversity has perfected a new small aeri-al and simple frequency changer that pro-mises to replace many of the large andunsightly dish aerials used to receive satel-lite TV programmes.The aluminium tube antenna can be eithera 'V' shape, typically 609 mm tall, orrhombic. It is of the 'travelling wave' typecapable of receiving transmissions over awide range.

Video standards translatorA translator that makes the transfer ofvideo signals between VHS and Umaticrecording machines possible has beendeveloped by Midlands Video Systems.The TT -880-P converts the commandsfrom a Sony RM-440 Umatic editing con-troller into commands recognized by aPanasonic industrial VHS recorder.Signals fed back from a Panasonic machi-ne are translated into Sony commands.Midlands Video Systems Ltd 3aAttenborough Lane ChilwellNottingham NG9 5JN.

Secure voice communicationsThe 'BA 1772' narrow -band secure voiceunit from MEL offers secure voice com-munication on HF, VHF and UHF radionetworks. It consists of a voice coder(vocoder), an encryption unit and amodem.

Suitable for use with backpack, mobile orfixed radio stations, it operates on a con-ventional voice channel with no modifica-tion of the transmitter -receiver, and willoperate over all types of transmission path.MEL Manor Royal Crawley RHIO 2PZTelephone (0293) 28787.


Fax sent direct by computersAn electronic interface from Hasler allowstext and diagrams to be translated into thesignals sent by a fax machine without theintervention of a scanning device. Itallows text images sent by a computer tobe received by any Group 3 facsimilereceiver or by another computer similarlyequipped.The 'Hasler Fax Unit' is said to offer amuch clearer image than that from a scan-ning fax transmitter since the image istranslated direct by the interface.Hasler (Great Britain) Ltd CommerceWay Croydon CR0 4XA Telephone 01-680 6050.

Computerized film and TV makingA complete range of computerized moti-on -control equipment together with acustom design and manufacturing serviceis available from Mark Roberts FilmServices. The company's range of productsincludes computer systems, model rigs,special-purpose rostrums, fade/dissolvecontrol units, automatic focus units, came-ra/projector motors and custom designs.The company can also update and compu-terize existing systems or it can design,supply and manufacture complete systemsto customer specifications.Mark Roberts Film Services BirchesIndustrial Estate Imberhome Lane EastGrinstead RH19 1XZ Tel. (0342) 313522

Digital speech recorder and analyserA digital recording system that makes thetranscription of recorded speech easier,quicker and more accurate has been pro-duced by Racal Recorders. The systemmakes it possible to extract the intelligiblespeech from faint or crackly distant radioor telecommunications transmissions. Thevoice information is recorded digitally onto hard memory disks. With the aid ofadvanced software any point on the diskmay be indexed precisely so that it can bereturned to and repeated as often as requi-red. The use of digital recording ensuresthat there is no loss of fidelity throughoutthe record / replay process.Racal Recorders Ltd Hardley IndustrialEstate Hythe Southampton SO4 6ZH Telephone (0703) 843265.

Cable -end systemA multicore-cable termination that enablesusers to assemble cable ends on their ownpremises with the minimum of tooling isavailable from lcore. 'Optimum 11' solves

the problem of joining multicore cable tomultipin connectors and is easy to install.It replaces the last few inches of multicorecable with a flexible conduit. This avoidsthe installation and vibration problems thatoccur when the normally stiff cable istransferred into the back of a multipin con-nector.Icore International Ltd Leigh RoadSlough SL1 4BB Tel. (0753) 74134.

Compact telex testerThe 'T 300 Telex Analyser', a new testequipment for the engineer in the field.from Componedex is compatible with SPCand Strowger systems. It is able to decodeBaudot, Hex, and ASCII protocols and isdesigned to cope with the higher speeds ofthe next generation of telex machines - upto 300 baud. It incorporates in a single unitfunctions that have hitherto required sepa-rate items of test equipment, and it willtest power levels, establish contact with aremote terminal and discover its identity(handshaking), and locate breaks in theline between base and exchange.Componedex Ltd 21 Alston Drive Bradwell Abbey Milton Keynes MK139HA Telephone (0908) 322177.

ELECTRONICS SCENE

New method of 'turning around' liveradio material

BBC engineers have devised a new met-hod of using digital technology to record,store and replay incoming live materialwith just one machine. This developmentpaves the way for a more efficient meansof 'turning around' live radio material

Wideband fibre optic linkThe first ultra-wideband fibre -optic link inEurope has been produced by Marconi.The 2-20 GHz. I km long transmissionline represents a new technology offeringvastly superior bandwidth and insertionloss compared with existing coaxial cableor waveguide, and also gives immunity toelectrical interference.Bandwidth capability is equivalent to 3000television channels or six million telepho-ne conversations transmitted simultaneou-sly down a single strand of optical fibre. Inaddition, many optical carriers can be mul-tiplexed down the same fibre on slightlydifferent wavelengths.

FIBER OPTIC COMMUNICATIONS COMPONENTS

MARKET IN EUROPE - 1993

Cabled Fiber $476M

Test Equipment S123M

Splicers/Kits $28M

TDM Units $33M

CouplersINDM S28M

Connectors $56M

TxiRxiModems $167M

z

777SOURCE: =cost and Sullivan, ltd. 0

Report #EI012

1/ f/50 100 150 200 250 300 350 400 450 500

$Million

According to a report from Frost & Sullivan, there is enough fibre optic cable in Europe tocircle the earth twice - 90,000 km. A new study by the company forecasts that sales of fibreoptic components will double between 1988 and 1993.


14

L\TERMEDIATE PROJECT

A series of projects for the not -so -experienced constructor. Although each article willdescribe in detail the operation, use, construction and, where relevant, the underlying theory

of the project, constructors will, none the less, require an elementary understanding andknowledge of electronic engineering. Each project in the series will be based on inexpensive

and commonly available components.

3b. Sine wave convertorby K. Walters

The simple triangular -to -sine wave converter described herecomplements the basic signal source described last month.

A function generator is not completewithout an output that supplies a stable,sinusoidal, waveform of adjustable fre-quency and amplitude. Fortunately. asinusoidal signal is fairly simple togenerate from a triangular signal. whichis supplied by the basic function gener-ator module described in last month'sinstalment of the Intermediate Projectseries. As already mentioned there, thefunction generator is a user -configu-rable design, to which we are now aboutto add a further module: a triangular -to -sine wave convertor.

presence of a silicon diode in the circuit.One of the basic features of a diode isthat it starts to conduct at a forward volt-age, th, of about 0.6 V, and passes morecurrent, Id, as the voltage increases (seethe U -V curve in Fig. 2). A reasonableapproximation of a sine wave would,therefore, be achieved by applying atriangular signal to a circuit as shown inFig. 3.The actual convertor is formed by RI andanti -parallel diodes Di -D2. Opamp ICIfunctions as a buffer to prevent the sinewave being distorted by the load imped-

Fig. 1. The sine wave converter translates a triangular input voltage (left-hand photograph)into a sinousoidal waveform (right-hand photograph).

First attempt: the diode limiterThe differences between a triangular anda sinusoidal signal are apparent from theoscilloscope photographs in Fig. 1 (thevertical sensitivity of the scope is set to1 V per division). The signals shown aregenerated by the present convertor.Looking at the curves, it would appearthat the sine wave is simply a triangularsignal with rounded, rather than sharp,inflection points. There is virtually nodifference between the signals aroundthe zero -crossing. The curve of the sinewave, however, becomes rounded whenthe instantaneous amplitude rises above0.8 V or so. This can not but point to the

ante. as will be seen later.Series resistor RI and diodes Di -D2 forma special type of potential divider (p.d.)for the positive and negative excursionof the input voltage. The output voltageof the p.d. is a function of the currentpassed by the diodes. This current in turndepends on three factors: the instanta-neous input voltage, the value of 12i, andthe U -I characteristic of the diodes used.Since the input voltage rises and fallslinearly, and RI is constant, the U -I char-acteristic is the main factor to determinethe current that flows as a result of theinstantaneous input voltage. Hence, thecharacteristic determines to a large ex-

tent the shape of the output voltage.

The above operation is ideal, and onlyachieved in the theoretical case wherethe p.d. is not loaded. In all other cases,the load draws current from the p.d., sothat the current through RI becomes

0.6U Ud

896005X-12

Fig. 2. Basic voltage -current (V -I) charac-teristic of a silicon diode. Note that Id risessharply above 0.6 V.

Fig. 3. The basis of a triangular -to -sinewave converter is formed by a voltage -de-pendent potential divider and a buffer.


greater than the forward current througheither diode. The additional currentchanges linearly with the input voltage,giving rise to a triangular voltage on Ri.Obviously, this voltage causes severedistortion of the sine wave.The opamp connected to the p.d. has aninput current of almost nought. so that itsupplies an output voltage that is vir-tually identical to the ideal voltage ob-tained from the p.d. The opamp soobviates load effects on the p.d. and atthe same time provides sufficient drivepower.

Feedback does itThe above discussion could lead to theassumption that the circuit of Fig. 3 isthe perfect sine wave convertor. Unfor-tunately, this is not the case.

Fig. 4. The waveform obtained from thebasic circuit of Fig. 3 can hardly be called asine wave.

The scope display in Fig. 4 shows thewaveform supplied by the circuit ofFig. 3. The signal has flattened tops andresembles only vaguely a sine wave. Ap-parently, the voltage is limited too se-verely by the diodes.A better sine wave is obtained by extend-ing the circuit of Fig. 3 with a secondpotential divider that provides feedbackof a portion of the output voltage. Thepractical circuit is shown in Fig. 5: thefeedback arrangement 'raises' theground reference of the diodes, and ef-fectively reduces the voltage appliedacross them to a level that results in lesssevere limiting.The operation of this circuit is basicallyas follows: an increasing output voltagegives rise to a voltage between the wiperof Pi and ground. The voltage betweenRi and ground will, however, not changemuch with respect to the situation inFig. 3, so that a smaller voltage is ap-plied across the diodes. These are, as aresult, operated over a relatively smallpart of their U -I characteristic. With Padjusted correctly, the diode voltagewill not rise very far above the conductlevel around 0.6 V. The use of feedbackresults in a sine wave with acceptabledistortion, as already shown in Fig. 1.A low-pass filter, R3 -C3, is provided atELEKTOR ELECTRONICS MAY 19S9

896005X-13

Fig. 5. Circuit diagram of the triangular -to -sine wave convertor, the second module in thelow -budget function generator.

the output of the triangular -to -sine waveconvertor. This filter suppresses har-monics and helps to improve the shapeof the sine wave. Feedback resistor R2 isincluded to stabilize the opamp.

Building and testingThe component mounting plan of Fig. 6shows that the sine wave convertor oc-cupies only half the available surface onUniversal Prototyping Board Size -1(UPBS-1) used for most circuits dis-cussed in this series of articles.Construction should not present prob-

Fig. 6. Construction on board UPBS-1.

lems because relatively few componentsand wire links are used.

The circuit is connected to a symmetri-cal 8 V supply (or two 9 V PP3 bat-teries). Set Pi to the centre of its travel.Connect the input to the triangular waveoutput of basic generator module de-scribed last month. Connect the outputof the convertor to the input of an oscil-loscope. Watch the scope display whilecarefully adjusting Pi until a reasonablyshaped sine wave is obtained. If a dual -beam scope is available, the sine wavemay be compared with the secondaryvoltage from a mains transformer.

The last two modules in the functiongenerator, the output amplifier and thepower supply, will be described in aforthcoming instalment of the Inter-mediate Project series.

Parts list

Resistors (±5%):Ri;1:12.10KR3=2K2R4=470RP1=1K0 preset for horizontal mounting

Capacitors:Ci:C2=100nC3=1n0

Semiconductors:Di;D2=1N4148ICI=CA3130

Miscellaneous:8 -pin IC socketPCB Type UPBS-1 (see Readers Servicespate).

16

THE DIGITAL MODELTRAIN PART 4

by T. Wigmore

Universal signals and switching decoder

The points (turnout) decoder described inPart I of this series (Ref. 1) is a circuit thatprovides short pulses to its output that maybe used for the control of turnouts (points)and other electromagnetic elements of themodel railway. That decoder does not pro-vide a momentary but a continuous con-tact. It is really a remotely controlled four-way toggle switch with change -over con-tacts.

Although the decoder described in thisinstalment enables all kinds of element tobe switched, the design is aimed primarilyat (non -electromagnetic) light signals. Itprovides separate switched outputs towhich LEDS or conventional light bulbsmay be connected. If desired, it is possibleto mount relays on the PCB. These would,for instance, enable switching the trackvoltage at the same time as the signals, ineffect providing the basis for hardware -

based block protection.

Four sets of light signals may be connec-ted to a decoder. If relays are used, it is

possible to switch circuits that are of ne-cessity electrically isolated from the track.

The present decoder uses the same addresslocation as the points decoder. It is suita-ble for use with the Marklin HO systemand the "Elektor Electronics Digital TrainSystem - EDiTS" to be published in futureinstalments in this series, commencingnext month.

Circuit descriptionThe circuit diagram of the decoder, seeFig. 28, shows some similarity with that ofthe points decoder in Fig. 4. Use is madeagain of the N1C145027 to analyse the serialdata emanating from the rails into adressesand control data. The trinary address,At-A4, is set with the aid of jumpers orwire links. A5 is an address bit, but since itis permanently connected to ground it isalways logic 0. None the less, provisionhas been made to give this bit anothervalue in the future to make it possible. ifrequired, to give the present decoder a dif-ferent address location.The four data bits

am available at outputs D6-D9.Three -to -eight decoder 1C2 generates a setor reset signal for one of the R-S bistables.To obviate critical races, a set or resetpulse is passed on only after the Valid-Transmission signal has become active.The last switching position of the fourchannels is stored by 1C3, a quadruple R-Sbistable.

The output stages are based on Type ULN2004 darlington arrays. The signal lightsmay be connected direct to the darlingtonoutputs, which are switched with respectto the positive supply line (about 20 V).For convenience, series resistors (R7 --R to)have already been provided in the com-mon lines, so that signals using LEDS maybe connected without further work. If con-ventional light bulbs or other elements areto be connected, the value of the resistorsmay be adapted as appropriate or they maybe replaced by wire links to ensure that theconnected element is provided with thecorrect voltage.

6

DS

1N4148

C65V6

K1

At

2

A2A2 11-.-0 3 0--A34 0 61 0-03-43A.

44 ---06170-C4 Cri De .11-0 p 0--

03

251/T2206 5066v3 00

rn'N

CL2

5 65

4 R2/122Cl

0

IC 1

CoMC 07

145027 08

RI o

09

16

0ro 315Y I 0s4r2 Du

coz74 Y4'11

HC y5 D0GI 138 va Dg

N7 0.7:12A 66. 026

IC 2

6

7 61 9

RS

a45

S

/11...N4 = IC 4 .4069D1...04= 1N4935Ra1...Re4 =12V

16

4

67

12

11

IS

0 EN03

113

SO

RI lc 3t

R2404462

R3

53

01

02

C3

3

1436

K2a

0 0

91

*14e text

a

135

cs

IC 6II

ULN2004

ti

03020106070604

2

15

.9_10

n.. Rn

2 C

K5a

K3a

0 0 0

a

C

C

2

0 0

K4a

1112

RI3

614

K4b

KSb

67291 4- 10

Fig. 28. Circuit diagram of the universal signals and switching decoder.


Parts list

Resistors:R1 = 12 kR2-R4 =100 kR5 = 270 kR6 = 3k3R7-R9 =1 k*R11-R14 = 150 R

Capacitors:Cl = 1n8C2 = 3n9C3 = 1 nC4 = 220 µ/25 V radial typeC5 = 220 pi6V3 radial typeC6 = 100 n

Semiconductors:D1-D4 =1N4935**D5 =1N4148D6 = 5V6/400 mWICI = MC145027IC2 = 74HC138IC3 = 4044IC4 = 4069IC5; IC6 = ULN2004

Miscellaneous:Rel-Re4 =12 V relay for PCB mounting

with single change -over contact

K1 = 3x4 terminal block for PCBmounting with 4 shorting plugs

PCB 884012

*If light bulbs are used instead of LEDs,the value of these resistors must beadapted as appropriate.

**Other types in the 1N493X series mayalso be used

The maximum current drawn by 105 andfc6 is 1 A (actually limited by the recti-fier). Each separate channel may switchnot more than 500 mA. If higher currentsare required. or if the particular circuit isto be electrically isolated from the rails,relays must be used. These relays mayalso serve to provide automatic control oftrains if the present decoder is used for theoperation of signals.

The usual freewheeling diodes for therelay coils are contained in the darlingtonarrays. Resistors 1211-1214 serve to limit thecurrent drawn by the relay coils. This isnecessary because the supply voltage(18-20 V) is a little high for 12 V relays.

If the supply is interrupted (for instancebecause of a short-circuit between therails), the last data will be retained for20-30 seconds thanks to c5. As long as thesupply is restored fairly quickly, operation

Fig. 29. The printed -circuit board for theuniversal signals and switching decoder.

of signals and other connected elementswill be recommenced from the operationalcondition that existed immediately prior tothe supply interruption.

Taking the decoder into useTerminals B and R are connected to the railthat is supplied by the brown and redwires respectively of the digital system(Marklin colour coding).

Low -current (<500 mA) elements, such assignals, may be connected direct to the 'a'(darlington) outputs. The total currentdrawn by such elements must not exceed 1A at any one time. If LEDs are used, seriesresistors 127-1110 must be fitted.

When the red button on the keyboard ispressed, outputs marked '2' are active andthe relevant relay is energized.

Take care that signals controlled by the

Fig. 30. Illustrating the manner in whichsignals with three lights may be con nected

present decoder are isolated from the rails.Signals with three lights should be con-nected in accordance with Fig. 30.Elements, whether electrically isolatedfrom the rails or not, that draw a currentexceeding 500 mA must be connected tothe 'b' (relay) outputs. The switching cur-rent should not exceed 1 A. These outputsmay also be used for block control.

Address settings are as given in Table 1(Ref. I). A closed DR- switch in that table

Fig. 31. Numbering of the jumpers or wirelinks on connector K I .

corresponds to a jumper or wire link in thepresent decoder. The numbering of theselinks is shown in Fig. 31.No jumper orlink needs to be placed for address 5,because a wire link to ground has alreadybeen provided on the PCB.

References:Elektor Electronics, February 1989, p. 42

Next month we commence with the Elek-tor Electronics Digital Train System.


18

ANALOGUE MULTIMETERby T. Giffard

An advanced electronic multimeter with no fewer than 80ranges and easily reproducible accuracy.

An important consideration with homeconstruction of test equipment is invari-ably the achievable accuracy and the de-pendence thereof on the calibrationprocedure. The analogue multimeter de-scribed here has no alignment pointssimply because its accuracy is derivedmainly from close -tolerance (0.1%) re-sistors. These components have longbeen outside the reach of the hobbyist,but are now gradually becoming avail-able in small quantities and at reason-able cost. The 0.1% resistors used in thepresent meter may be replaced with lessexpensive 1% types at the cost of someaccuracy.One feature that makes the analogue

multimeter a particularly interesting testinstrument is the large number of rangesavailable for measuring voltage, currentand resistance: there are no fewer thaneighty.

Analogue versus digitalThe choice between a digital and ananalogue multimeter is often made onthe basis of personal preference. Al-though digital multimeters are now com-monly found in almost any electronicsworkshop, the analogue meter holds itsown thanks to its ability to show thetrend of a measured quantity. This fea-ture is especially useful for alignment

purposes, since it is easier to observe themovement of a needle than to resolvefour or more rolling digits and, possibly,a shifting decimal point on a digitalread-out. Another benefit of the anal-ogue meter scale is that it allows asimple way of indicating tolerance andhigh/low ranges in coloured areas on themeter scale.

Probably because of the 'absolute' dis-play indication, digital multimeters areoften, but in most cases wrongly,credited with better accuracy than anal-ogue meters. Many electronics enthusi-asts are convinced that any type ofdisplay, whether LED or LCD -based,rules out read-out errors because the in-dication itself is not liable to misinter-pretation. They forget, however, that thefinal accuracy of both the digital and theanalogue multimeter is determined bythe electronics inside, not the read-outonly. In fact, the additional error intro-duced by carefully reading the measuredvalue on a good analogue instrumentwith a class -1.5 or better mirror -typemoving -coil meter is nearly alwayssmaller than that introduced by any com-ponent with 1% tolerance. As examples,3 V is easily resolved on a good anal-ogue scale of 300 V, and 0.1 V on a scaleof 10 V.

Combined R -V -I measurementThe design of the analogue multimeter isbased on a voltage meter with a basicfull-scale deflection (f.s.d.) sensitivityof 1 mV. There are several ways of mak-ing such a meter circuit: either a separatevoltage amplifier could be added for the1 mV range, or the entire instrumentcould be designed such that all rangesare scaled down to the most sensitiverange of 1 mV.The multimeter discussed here is basedon the latter principle. The main reasonto opt for a common range of 1 mV is,perhaps surprisingly, a very practicalone: it is the use of a 12 -way rotary rangeswitch with one pole. From a point ofview of design, a double -pole 12 -wayswitch might have been a better choice.Such a switch is not used here, however,because of its higher price and the re-quirement for additional components.

Voltage measurementThe voltage ranges are created conven-


19

tionally with the aid of a switchable volt-age divider as shown in Fig. la. Thevoltage divider is designed such that ascale factor of 10 dB (approx. 3 times or41o) is obtained. The analoguemultimeter has 12 voltage ranges fromI mV f.s.d. to 300 V f.s.d. The fixedvoltage divider ensures that the meterhas a constant input resistance on allranges. This means that range switchingdoes not affect the measurement as itdoes on many non -electronic analoguemultimeters (with non -electronic wemean: not using active devices such asFETs, bipolar transistors or opamps).

Current measurementA shunt resistor translates measured cur-rent flow into a proportional voltage asshown in Fig. lb. The shunt resistor hasthe ideal value of 1 S2 so that themeasured voltage can be taken to repre-sent the measured current without theneed of a correcting factor.

Resistance measurementResistance can be measured by incorpor-ating the unknown resistor, Rx, in a volt-age divider as shown in Fig. lc. Thesecond resistor is- an adjustable refer-ence type that forms part of the voltagedivider. The voltage across this resistoris proportional to the value of themeasured resistor. Resistance measure-ment with this method has the disadvant-age of requiring a non-linear scale, butis still attractive because it is simple tocombine with the V (voltage) and I (cur-rent) ranges of the multimeter.The voltage divider is supplied with abias voltage of 10 mV. This limits thevoltage measured across the referenceresistor to a maximum of 10 mV, andrequires the sensitivity of the basic mil-livolt meter to be lowered from 1 mV to10 mV for resistance measurements.

Seven sub -circuits: onemultimeterCombining the three previously men-tioned measurement principles, showingthe internal configuration of the 1 mVmeter amplifier, and adding a power sup-ply to the whole results in the circuitdiagram of Fig. 2.Rotary switch S2 selects between R, Vand I measurement.The principles illustrated in Fig. 1 arefairly simple to recover from the circuitdiagram. The adjustable voltage dividerof Figs. la and lb, and the adjustableresistor of Fig. lc, are formed by rotaryswitch Si and resistors Ri through R14.The resistors serve the double functionof voltage divider and references for theCI ranges. This arrangement not onlysaves resistors, but also allows a single -pole rotary switch to be used. RI throughRya and all other 0.1% resistors arestandard values from the E96 -series. Inmost ranges. the final accuracy of the

Analogue Multimeter

SPECIFICATION

Voltage measurement:Direct voltageAlternating voltage: effective value of sinusoidalwaveforms (ACrms)

Alternating voltage: average value (ACAv)

Input impedance:Frequency range:Protection:

1 MilDC...20 kHzmax. 300 Vrms

Ranges:1 mV; 3 mV; 10 mV; 30 mV; 100 mV; 300 mV; 1 V; 3 V; 10 V: 30 V: 100 V: 300 V

Current measurement:Direct current (DC)Alternating current: effective value of sinusoidalwaveforms (ACrrns)

Alternating current: average value (ACAv)

Internal resistance:Frequency range:Protection:

1 flDC...20 kHzfuse 3.15 A slow

Ranges:1 mA; 3 mA; 10 mA; 30 mA; 100 mA; 300 mA; 1 A; 3 A

Resistance measurement:Test voltage: 10 mVProtection: none

Ranges:3 11; 10 11; 30 Li; 100 11; 300 Q; 1 kil; 3 kil; 10 kil; 30 kil; 100 Ica; 300 kf2; 1 Mfg

Signal level measurement:-60 to + 50 dB in decades (0 dI35775 mV -1 mW into 600 f2)

Accuracy:Voltage ranges:Current ranges:Resistance ranges:

dB ranges:

Power supply:Supply voltage:Current consumption:

±(2% of f.s.d. + 0.5% of measured value)±(2% of f.s.d. + 1.5% of measured value)all ranges from 10 Si to 1 MCI:

±[2%(2+x+1 / x)+0.4%(1+x)]in 3 Q range:

±[2%(2+x+1 / x)+1.3%(1+x)](x = centre-scale/measured value)±(0.18 f.s.d. + 0.002 dB measured value)

6 V (4 penlight batteries)25 mA

Fig. 1. Basic measurement techniques applied in the analogue multimeter: voltage (a);current (b) and resistance (c).


20voltage divider is determined almost ex-clusively by the tolerance of the resis-tors, since the error introduced by theratio of their values alone is of the orderof a few hundredths of a per cent. Thiserror is, however, slightly higher in the100 V, 300 V, 10 SI and 3 S2 ranges be-cause the values of R12 and R13111214 arethen so small that the resistance of thesolder connection becomes significant.There is, therefore, little point in using0.1% resistors for RI3 and R14. None the

less, the deviation caused by the bottomresistor in the ladder is made as small aspossible by connecting R13 and RI4 inparallel and so ruling out additional de-viation caused by an incorrect nominalvalue.Another composite resistor, Ri-R2. isseen at the top of the ladder network. Inprinciple, a single 681 kS1 resistor wouldhave been all right here, but the maxi-mum permissible input voltage of themultimeter, 300 Vr. results in a peak

value across (R1+R2) of 20042:4:282 V.This is close to, and in some cases over,the maximum voltage that may existacross most types of 0.25 W or 0.33 Wresistor. The required 'high -voltage' re-sistor is. therefore, made from twoseries -connected resistors with aboutequal values and a total equivalent valueof 681 ki.2. In the worst case, each ofthese resistors thus carries only abouthalf the maximum anticipated voltage.Input coupling capacitor Ci serves to

R2

R3

R4

Rs

RE

R7

R8

R9

R13

811

R12

813

-C;1-

A COM

El

3A15

O

R141

12

1%

8 A

R16 R16

1%

533

9

RAM

C9 C14. 6 100 n

6V

R21 R22

6V

6V

03

IC2

OP16

D8...011 =BAT85

823

6V ix 50

6V

6V

AC6

Sib

R30

825 R26

ck 1%

"o8

09

0-3S45

642

-rBT

lop ,6V10V

=.11',14148

Al, A2 =1C3 = TL062CP, LF412

All resistors 0.1 %unless ettwwi se noted

890035-12

Fig. 2. Circuit diagram of the analogue multimeter.


remove DC components when alternat-ing voltages are being measured. Thealternating voltage across CI is negli-gible at most frequencies, and the directvoltage across it is 300 V at the most.The capacitor drops some alternatingvoltage at input frequencies below10 Hz only. Fortunately, a measured al-ternating voltage of this or a lower fre-quency will rarely have an amplitudethat causes the 400 VDC specification ofCI to be approached or exceeded.The voltage source of Fig. lc is foundback in the circuit diagram as sub -circuitAI -PI -R27 -R28. Preset Pi allows the out-put voltage of Ai to be adjusted such thatthe instrument indicates 0 S2 with short-circuited input terminals. Fluctuationson the battery supply voltage are thuscompensated. The 0 f adjustment alsoprovides a convenient 'battery -low' in-dication: as soon as Pi has to be turnedalmost fully counter -clockwise toachieve the 0 Q indication, it is time toreplace the battery pack.

Power supplyThe heart of the power supply is formedby voltage inverter 1C4. The TypeICL7660 comprises an oscillator and avoltage doubler which are used here togenerate a negative supply voltage toobviate a second set of batteries. Rippleon the negative output voltage is sup-pressed by networks Li -C6 and Cs -L2 -C7.The operation of these filters is backedby the special lay -out of the printed cir-cuit board. Diodes Ds and D6 protect theoperational amplifiers in the meter cir-cuit from permanent damage when theirsymmetrical supply voltages do not riseat the same rate when the instrument isswitched on with S41.

Input amplifierThe function of the millivolt amplifier isthe conversion of the voltage at junctionSI-Sze-Ris into a proportional currentflow through moving -coil meter Mi.This is done in two steps by two sub -cir-cuits: an input amplifier and a V -I con-verter.The input stage around ICI is a non -in-verting amplifier with a voltage gain of50. The accuracy of this amplifier is0.2% within the nominal bandwidthwhen 0.1% tolerance resistors are usedin positions R17-Ris-R19. Deviationsbecome greater, of course, outside theamplifier's pass -band: at the 3 dB roll -off frequency, for instance, the voltagereduction is 29%. Ergo, the input ampli-fier must be dimensioned for a band-width much greater than that strictlyrequired for reasonably accurate meas-urements. Allowing an error of 1%(0.08 dB), for instance, means that anamplifier bandwidth is required of aboutten times the -1% frequency. A 1% -bandwidth of 20 kHz then correspondsto a -3 dB -bandwidth of 200 kHz. Inpractice, the bandwidth has been re-

duced here to about 185 kHz by the ad-dition of C2.Potentiometer P2 compensates off -set in-troduced by the relatively high amplifi-cation of ICI, and the fact that this is setup as a direct -voltage amplifier. Seriesresistors R21 and R22 are added to narrowthe otherwise unwieldy range of P2. Pro-duction tolerances on the resistors andthe operational amplifier may, however,call for the control range to be shifted alittle until minimum off -set is achievedwith the potentiometer set to about thecentre of its travel. The control range isshifted empirically by correcting thevalues of R21 and R22: a lower value forone necessitates a higher value for theother until minimum off -set is achievedwith P2 set to the centre of its travel.Constructors less inclined to experi-menting with this adjustment may re-place P2 and the series resistors with asingle 100 Id/ multi -turn preset.The off -set compensation alone is notsufficient to guarantee stable operationof the sensitive input amplifier: theopamp itself, ICi, must be a type withlow off -set drift to rule out the need forfrequent corrections in the setting of P2.The Type OP -17 from Precision Monoli-thics used in position ICI guaranteesvery low drift over a wide temperaturerange. The operating temperature of thedevice should be allowed to settle, how-ever, for a minute or so after switchingon the multimeter.

Overload protectionThe input amplifier is protected againstoverloading by network R ts-R16-Di-D2.The diodes make it impossible for theamplifier input voltage to exceed +0.6 Vor -0.6 V. Any excess input voltage isshunted away via RI5 and Rib. The diodesform a high resistance, and R15 and Ribhave no effect, as long as the input volt-age remains within the nominal range.This means that the protection circuitdoes not normally affect the accuracy ofthe measurement. It does, however, af-fect the termination resistance of pin 3of the opamp, which is sensitive to noisebecause of the high input impedance.The sensitivity to noise is, in fact, sohigh that the PCB track carrying the out-put signal of ICI is carefully screenedfrom the input circuitry to prevent oscil-lation. Recalling that the input amplifierworks with very small signals (max.I mV), it will not come as a surprise thatthe carefully designed lay -out of theready-made printed -circuit board is es-sential for correct operation of themultimeter. The excellent stability of theanalogue multimeter is a feather in thecap of the Elektor Electronics PCB de-sign staff.It should be noted that the high imped-ance between input terminal and + inputof ICI causes the capacitance of Di andD2 to become significant in the 3 mV and3 mA ranges and, therefore, to reduce

Fig. 3. How to make a shunt from a con-ventional power resistor.

the amplifier's bandwidth to some ex-tent.

V -I converter/meter driverThe amplified output signal supplied byICI is fed to two sub -circuits. The firstof these to be discussed is a precisionV -I converter and associated meterdriver set up around opamp IC2.The moving -coil meter, MI, is current -driven to achieve maximum accuracy.The meter current, depends on twofactors only: input voltage Ui availableat pin 3 of IC2, and the resistance be-tween the - input of IC2 and ground (R23,R2411R2s or R26). For the switch positionshown in the circuit diagram. and assum-ing that IC2 provides very high gain:

/rti = Ui / R23

showing that the accuracy of the volt-age -to -current conversion depends onthe accuracy of R23 only.Moving -coil meter MI forms part of adiode bridge circuit that rectifies themeter current. This results in MI indicat-ing the average value of the rectifiedcurrent, whether this is generated by adirect or alternating voltage or current,and irrespective of the polarity of thedirect voltage or current. Schottkydiodes are used in the rectifier becausethey have a lower on -resistance than sili-con types. This allows the gain of IC2 tobe reduced slightly, resulting in a higherattainable bandwidth.The bandwidth of the V -I converter is afunction of the measured value. The rea-son for this lies in the fact that the inter-nal resistance of the diodes in the bridgeis a function of the forward current,which is, in turn, a function of themeasured value. Fortunately, the effectsof this annoying variable are practicallyunnoticable by virtue of a suitablydefined bandwidth of the input amplifieraround ICI.The V -I converter around IC2 is com-pleted with three switch contacts, ameter overload protection, D7, and a sta-bilization capacitor, C3. Switch contactSob short-circuits the meter coil when theinstrument is turned off. This helps to


Parts list

4! 01111111100(-)

0/1 IOSOU

(-)

C meesuie.

1

0.ill MI

IMO

es(-)08888800

esse

Resistors:(all 0.1% tolerance. E-96 series', unlessotherwise noted)

Ri=357KR2=324KR3=215KR4=68K1R5=21K5Rs=6K81R7=2K15R5=681 RRs=215RRio=68R1Rit=21R5Ri2=6R81R13=3R16: 1 %1314-845R; 1 %R15:1=116;R21:R22=47K5; 1%Rt7=1K54Ria=32R4Rie=1K05R2o=82R; 5 %R23=1K00FI24=909RR25=95K3; 1 0/0R26= 10K0F127=180K: 50/0R2a=100R; 5%R29=330R; 5%R33=5K6; 5%R31=1RO; 10 W; 1%P1=470R linear potentiometer.P2=4K7 linear potentiometer.

ElectroMail. telephone (0536) 204555.

Capacitors:C1 =220n; 400 VDCC2=560pC3=68nC4:C5=.10p: 10 V: radialC6:C7=47p: 10 V; tantalumCs:C5:Cio;CI 1:C12:C13:C14=100n

Semiconductors:;02;D3:D4;05:a6;07=1N4148

Ds:Ds:Dio:D11=BAT85ICI=OP-17 (PMI)IC2=0P-16 (PMI)IC3=TL062 (Texas Instruments)1C4=ICL7660 (Intersil)

all integrated circuits in 8 -way dual -in -line(DIL) enclosure.

Miscellaneous:L1;L2= 15 mH inductor with ferrite core(R<25Si= single -pole 12 -way rotary switch forPCB mounting.S2= 4 -pole 3 -way rotary switch for PCBmounting.S3= 3 -pole 4 -way rotary switch for PCBmounting.S4= double -pole toggle switch.Bi= 4 penlight batteries plus holder.Mi= 50 pA moving -coil meter: R<5 kil; de-flection angle 86': dimensions: 110x83 mm(e.g. Monacor Type E -11B: order no.29.0200).M2= centre -zero moving -coil meter _-L.100 pA:dimensions: 14:-:35 mmFi= fuse 3.15 A delayed action: with panel -mount holder.PCB Type 890035 (double -sided: notthrough -plated: available ready-madethrough the Readers' Services).Front -panel foil Type 890035-F (availableready-made through the Readers' Services).

Fig. 4a. Lay -out of the component side (above) and the solder side (below) of the PCB forthe multimeter.


PC.13( 04 05-l ril3n10 0

CI

til C3 I10000 t .a.001 toC14

CU

a

52

o -

L

0-1-2 CB

0+nnocs .c1C4

C101:31

C4+C=3

L0) C2 CA R2010 0 92I, omorRi7 jo 0021 )O 0)1.-...- Lr,nein ,.9. AI t0ic1 2.

,-I is a ucwo T15-.9i-N- _L_

02 01 02----1

1R14 K. si(R13 0

1310

1;

M1J

.ffld

Fig. 46. Component mounting plan. The dashed lines indicate the positions of the screens.

protect the coil and the needle from tak-ing damage during transport.The other two switch contacts, S2d andS3b, set the ratio Im / Ui in accordancewith the selected measurement. ResistorR23 is used with DC and ACAv measure-ments. Measurement of sinusoidal alter-nating voltages require the meter toindicate a 1.11 times higher value. Thisis achieved by selecting R241IR25, whoseequivalent value is 1.11 times smallerthan that of R23. As already noted, thesensitivity of the meter must be reducedto 10 mV for resistance measurements.This is accomplished by selecting R26with switch contact S2d.

Indicator circuitThe second signal path from ICI leads toan indicator circuit around opamp A2.This drives a small centre -zero moving -coil meter that indicates the polarity ofthe measured signal. When M2 deflectsto the right, the V -S1 or A input terminalis positive with respect to the COM ter-minal. Similarly, when M2 deflects to theleft, the V -L2 or A input terminal is ne-gative with respect to the COM terminal.Meter M2 does not deflect when alternat-ing voltages and currents are measured.Opamp A2 is set up as a non -invertingamplifier whose gain depends on thelevel of the input signal. This is achievedwith diodes D3 -D4, whose equivalent re-

sistance is a function of forward current.The gain of A2 is inversely related to theinput signal amplitude. This results inhigher sensitivity around the centre -zeropoint of the meter, so that the polarity ofrelatively small signals is indicated re-liably. It should be noted that M2 ismerely an indicator - off -set compen-sation with P2 should, therefore, alwaysbe carried out for the main read-out.meter Mi. The response of M2 around thecentre -zero point may be improved byreplacing the TL062 with a LF412 whichhas a lower off -set and off -set drift, buta slightly higher current consumption(5 mA more than the TL062).

Shunt resistorResistor R31 is the shunt for convertingmeasured current into a proportionalvoltage. The resistor used is a 10 W typewith 1% tolerance. It is not, strictlyspeaking, a shunt resistor because thisnormally has four terminals. The twoextra wires are created by solderingthem to the existing leads where theyleave the resistor body. This creates ashunt with sense wires, exactly as indi-cated by the relevant symbol in the cir-cuit diagram. Fuse F1 protects R31 fromdestruction when a too large current ispassed. It also prevents the value of R31changing gradually as a result of occa-sional. light, overloads.

ConstructionAs already stated, the printed -circuitboard designed for the multimeter is es-sential for correct operation. It is. there-fore, not recommended to build thecircuit on stripboard or prototypingboard. Also, when you plan to etch yourown PCB, remember that the quality ofthe board supplied through the Readers'Services is hard to match with simplematerials and tools.The PCB is double -sided but notthrough -plated. Screening is fitted asshown on the overlay in Fig. 4b. Com-mence the construction with making the9 through -connections on the board.Then fit the power supply parts andcheck the presence of the correct supplyvoltages at a number of relevant pointson the board.Proceed with the mounting of the resis-tors in the input attenuator. The resistorsshould be fitted about 2 mm above theboard surface to minimize stray capacit-ance. Resistors R15 and R16 are mountedlikewise for reasons of safety.Circuit ICI must be soldered direct on tothe PCB: do not use an IC socket! For theother ICs, sockets may be used.The screening boxes may be installedwhen all components have been fitted.The piece of tin-plate that screens thesolder side of the board is the easiest tomake. Short-circuits are prevented byspraying the screen with plastic at thePCB side. The plate must be fitted asclose as possible to the PCB - the maxi-mum distance is 2 mm - and is, ofcourse, soldered all around to the groundplane.The screens at the component side of theboard are a little more difficult to install.The locations are indicated by thedashed lines on the overlay. The heightof the screens equals that of the bodiesof the switches (that is, excluding thethreaded shaft). All compartments are,finally, closed with a lid that must, how-ever, be simple to remove.The components not accommodated onthe PCB are connected to it withscreened cable. The cable screening issoldered to the ground plane or the tinplates only: at the other side of the cable,it is not connected. The shunt circuitforms an exception: the wires betweenterminal A to the fuse, between the fuseand the shunt, and between the shunt andthe COM terminal should have a cross-sectional area of at least 1.5 mm'- be-cause they must be capable of carryingcurrents up to 3 A. The sense connec-tions from the shunt are, of course, madein screened cable (see Fig. 3).

The enclosure is given an attractive ap-pearance with the front -panel foil andthe meter scale shown in Fig. 10. Thecompleted scale is carefully cut out andfitted in the meter.The scale of the polarity indicator must


24be replaced with a home-made one: cuta piece of paper or light cardboard tosize and provide on this the marks - (tothe left of the scale), + (to the right ofthe scale) and - at the centre (do not usea 0 here because the meter is incapableof indicating the true zero -point).

Practical useAlthough the day-to-day use and oper-ation of the analogue multimeter isstraightforward and similar to other me-ters of this type, it is. none the less,

worth wile to note a few particulars.

After switching on, allow a minute or sofor the instrument to warm up. The off-set -compensation potentiometer is thenadjusted for minimum meter deflection,which is not necessarily the same asmoving the needle to the 0 -indication.Only then may the moving coil meter benulled mechanically with the plasticscrew provided for this purpose. Elec-tronic nulling should always be carriedout by indication of the main meter, notthe polarity indicator.

Fig. 5. The first phase of the construction has been completed: thepower supply and voltage divider parts are installed on the hoard.

56Lit (3,

e i444tt131.00 Co to co kO l9 t9 t9 41st.

IT121 11111111111W

The multimeter is protected againstoverloading in the DC/AC/ACAv ranges.but not in the SI ranges. Do not, there-fore, use these longer than strictlynecessary, and make a habit of checkingthe selected range and quantity beforemaking any measurement.The DC/AC/AC:v., selector should beoperated with due care. The DC positionallows measuring both direct and alter-nating voltages and currents, or directvoltages superimposed on an alternatingvoltage. The important thing to remem-ber in all cases is that the meter indicates

Fig. 6. Phase two: reads for fitting the screens...

Fig. 7. Phase three: ready for mounting the top plates on thescreens...

Fig. 8. The top plates must not be omitted: the front -panel is toofar away to achieve proper screening otherwise.


Fig. 9. This front -panel foil is available ready -made through the Readers' services. Themeter scale is cut out for mounting inside the moving -coil meter (foil shown 76% of true size).

the average value of the rectified volt-age.The AC position enables measuring thealternating component only. Any bias orsuperimposed DC levels are blocked bya capacitor. The meter shows the aver-age value of the full -wave rectified volt-age multiplied by 1.1d. This means thatthe AC position allows reading the effec-tive (r.m.s.) value of sinusoidal inputvoltages. The ACAv position is used fornon -sinusoidal voltages. It is essentiallyequal to the AC position without thefactor 1.11, so that the average value isindicated.It is often necessary to check whether adirect voltage measurement is valid ornot because there may be an alternatingcomponent as, for instance, in the caseof an oscillating amplifier. When an al-ternating component is measured, thismar invalidate the measured direct volt-age. This need not be so in all cases,

however, since the correctness of thedirect voltage indication depends on theratio of the direct voltage to the peakvalue of the alternating voltage. The pre-viously taken DC measurement is incor-rect if this peak value is greater than thedirect voltage.It is possible to use the multimeter as anammeter and a voltage meter simulta-neously, but only if one terminal can beconnected to a common junction in thecircuit under test. This is the case in, forinstance, resistance measurement to thecurrent -voltage method. Current andvoltage can then be measured separatelyby switching between A and V with S2.This useful feature is available becausethe shunt circuit is not broken, and theVS2 terminal is not disconnected.

Moving -coil meterThe design of the scale supplied with the

front -panel foil for the multimeter isbased on the Monacor moving -coilmeter stated in the Parts list. This meterhas an indication angle, tp, of 86°. Othermeters may be used provided these arecapable of covering an angle of 86°.Also, the gain of ICI may have to beadjusted by changing the equivalent re-sistance of parallel combination Ris-R19according to

= R rap /1.50(86-01

When selecting resistors for Rig and Rigon the basis of the calculated value, it isbest to decide on one with a slightlyhigher value than calculated, and selectthe other for the best possible approxi-mation of the required equivalent value.The actual value so obtained must bewithin 0.1% of the calculated value.

How accurate?The way the analogue multimeter is spe-cified in the shaded box on the first pageof this article is perhaps not too com-mon, but not unusual. The data given arepresented in a way analogous to thatcommonly used for specifying the per-formance of a digital multimeter. Thedigits specification is, however, re-placed by a corresponding percentage ofthe full-scale deflection (% f.s.d.).The error calculation applicable to theresistance ranges is rather elaborate andtherefore often omitted altogether in ma-nuals supplied with analogue multime-ters. A brief description is, however,given here.The centre of the scale is taken as aconvenient starting point for the errorcalculation because the extremes(nought to the left and infinite to theright) are difficult to work with mathe-matically. This is why the centre -scaleresistance value, rather than the moreusual scale multiplier, is printed near therange selector.Even a brief analysis of the way themeter error is introduced already leadsto a rule of thumb. The measurementprinciple adopted here results in a non-linear scale, and the minimum measure-ment error is four times the class of themoving -coil meter plus the error causedby the measurement circuit. A class -2moving -coil meter can not, therefore,measure resistance with an accuracy bet-ter than 8%. This minimum value is com-monly found as the only specification ofmany analogue multimeters. However,the error increases exponentially to theleft and the right of the centre indication.Fortunately, the meter described herehas no fewer than 12 resistance ranges,so that a reading as close as possible tothe centre indication is nearly alwayssimple to achieve by operating the rangeswitch.


SCIENCE & TECHNOLOGYForecasting flickers in the field

by Dr Bill Stuart, Geomagnetism Research Group, British Geological Survey, Edinburgh

Rapid and hitherto unpredictable fluctuations in the Earth'smagnetic field have for centuries been a problem to navigators

and, in more recent times, for operators of cable, radio and radarsystems. Spacecraft become subject to changes in atmospheric

drag that may affect their orbits and re-entry glide paths bymany tens of kilometres. Automation of geomagnetic data

collection and processing has now made immediate informationabout the field available to laboratories on a national scale and

will make it accessible to professional users internationally. Aglobal mathematical model enables field values to be

calculated with good accuracy for any part of the world andgives forecasts for some years ahead.

"I saw an aurora to the South and notedsimultaneously a great movement of themagnetic needle. When I announced thisto Professor Celsius he said he too hadnoticed such a disturbance but had notmentioned it in order to see whether Itoo would light on the same speculation.Professor Celsius had, by letter, re-quested Mr Graham in London to ob-serve his own needle for several days.The magnetic needle at London had justsuch an unusual motion at the same timeas here at Upsala."That was how, on 1 March 1741, a stu-dent of Andreas Celsius confirmed ob-servations made some 20 years earlier byGeorge Graham that a finely pivotedmagnetic compass was subject to sud-den, unexplained disturbances, andadded that the disturbances occurredsimultaneously in London and Upsalaand that they related, in some way, todisplays of bright aurora. On 20 October1746, Celsius measured a disturbance of4°10' of air in the compass. (On 7, 8 and9 February 1986 compass deviationsreached over 10° during a severe mag-netic storm that lasted for 42 hours.)A century later Baron Alexander vonHumbolt wrote letters to the RoyalSociety (23 April 1836) and to the RoyalGeographical Society (10 January 1838)proposing that Great Britain, with itsworldwide colonial influence, shouldjoin in a scheme to establish geomag-netic observatories using the standard-ised instruments and measuring tech-niques devised by Carl Friedrich Gauss,and participate in a worldwide study of

geomagnetic disturbance. He worte: "Ithink the subject is not without import-ance to seamen."

Record prizeBy 1841, 50 geomagnetic observatorieshad been established where compassneedles were observed by hand and eyeonce an hour or sometimes every fiveminutes. The Admiralty offered a prizeof £500 for the invention of magneticself -recording arrangements. It was wonby Charles Brooke, who used a lightbeam reflected from a mirror attached tothe end of the compass to magnify thecompass movements, and recorded thebeam's motion on a sheet of photo-graphic paper attached to a slowlyrotating drum. Co-ordinated measure-ment of the Earth's magnetic fieldthroughout the world had begun.Graham and Celsius used only a sensi-tive compass to detect changes in thedirection (D) of the geomagnetic field inthe horizontal plane. Gauss devisedsuspensions that responded to changesin the strength of the horizontal compo-nent (H) and the strength of the verticalcomponent (Z); he used a torsionsuspension and counterbalanced pivotrespectively. In that way variations of thefull vector field could be recorded. Suchvariometers record only field changesabout an arbitrary zero, or baseline. Toconvert their records to actual fieldvalues, absolute measurements must bemade and compared with the variometer

record to calibrate its scale and ascribean actual value to the baseline. Gauss in-

devised techniques for making absolutemeasurements using standard magnetsto create deflections at fixed distancesand for measuring their oscillationperiod.Although very effective, such essentiallyanologue instruments are not compat-ible with digital logging systems andcomputer control. An electronicmagnetometer, known as a fluxgate, wasdeveloped in World War II for airbornesubmarine detection and is still an essen-tial part of Nimrod's airborne tacticalsystem. It has been adapted for use ingeomagnetism. In the instrument, analternating electrical current in awinding around a core of ferromagneticmaterial magnetises the core to satu-ration at each half cycle. An ambientmagnetic field along the core producesasymmetry in the cycle of magnetisationand causes -second harmonic distortionin the voltage induced in a secondarywinding around the core. The amplitudeand phase of the second harmonic is ameasure of the magnitude and sense ofthe ambient field.Because a fluxgate sensor is a single -axisdevice, sensors arranged at right -anglesare used to obtain the geomagnetic vec-tor. The inherent instability of electroniccomponents used for amplification andrectification in the instrument meansthat it, too, has to be calibrated againstprecise absolute measurements fromtime to time.


Proton magnetometersModern absolute measurements makeuse of the fact that atomic particles havea magnetic moment, by virtue of theirelectrical charge and their spin or orbitalangular momentum, which causes themto precess in a magnetic field in ananalogous way to that of a gyro underthe influence of gravity. Normally, in-dividual precessions are randomlydistributed in phase and cannot bedetected. But if a very strong magneticfield is applied in a direction perpen-dicular to the ambient field the pre-cession takes place about the axis of thefield and the atomic particles become, ineffect, aligned in that direction. If theadded field is removed suddenly the par-ticles begin to precess about the remain-ing ambient field from that directionand are, therefore, in phase coherence;that is, they all do it in unison. Theirprecession can be detected by the voltagetheir combined magnetic moments in-duce in a coil around the sample. Its fre-quency is a measure of the ambient field.Water, or a hydrocarbon, provides a con-venient source of protons in thehydrogen nuclei, and proton precessionmagnetometers have become the stan-dard for geomagnetic field measurementbecause of the precision (one or twoparts in 106) to which their fundamentalconstants are known, and because theyare portable and easy to operate.Proton magnetometers measure thestrength of the field without providinginformation about its direction. Formeasuring directional components ofthe field they are adapted by applyingcontrol fields, generated in what arecalled Helmholtz coils, arranged tocancel out all but the component whichis to be measured. The simple example isa coil assembly with an axis arrangedhorizontally in the geomagnetic merid-ian. The generated field is adjusted tocancel H, leaving Z to be measured.

Core of the earthThe main geomagnetic field is caused byelectrical currents flowing in the fluidpart of the Earth's core, driven by mech-anical forces from the Earth's rotation,the heat and pressure of depth, radioac-tive decay and by chemical changestaking place in the core itself. The mainfield changes continuously with time.For example, the direction of magneticNorth in Britain moves eastward at a rateof one degree every five years, and thestrength of the main field decreases byone per cent every ten years. One reasonfor this so-called secular change is thatthe core fluid is a perfect electrical con-ductor and lines of magnetic field whichcross its surface are frozen in relation tothe fluid. So the movement of field linesmeasured on the Earth's surface is adirect representation of the motion ofthe surface fluid of the core. Recentstudies reveal that abrupt changes occurin the rate of secular change, causedperhaps by inner processes of mountainbuilding within the core itself.One task of co-ordinated geomagneticmeasurement is to chart the main fieldand secular change for studies of theEarth's deep interior. It is also necessaryfor navigation, which uses geomagneticreference as much now as at any time inthe past. Modern navigational charts arederived from a mathematical modelwhich fits a dipole, quadrupole andhigher magnetic multipoles to the globalset of measurements. Such mathematicalmodels are ideal for incorporation inflight -deck computers of aircraft andmissile guidance systems.The main field extends outward intospace where it comes under the influenceof the solar wind, a stream of protonsand electrons boiling off from the Sunand flowing into interplanetary space.The geomagnetic field creates a bubblein the solar wind that is called themagnetosphere, preventing it from

........----.

a.re

AkAr-r.jD.r.a.rten

IllSt::,-.

r.:' a3' co ce Er) OS. C.) 1C0 "6 00 7e.'10

(MERSA. TV& Pus)21.00 2..t 0)

Examples of daily magnetograms showing the most common range of disturbance.ELEK'TOR ELECTRONICS MAY 1989

reaching Earth directly. In themagnetosphere, the geomagnetic field iscompressed on the sunward side anddrawn out in an extended tail on thenightside in a dynamic state of balancewith the forces of the solar wind. Theshape of the magnetosphere and itsbalance are maintained by electrical cur-rents flowing in a well-defined networkof circuits within the magnetosphere andin the ionosphere. It is the magnetic ef-fect of these currents which createsgeomagnetic disturbance. Because thereis a great deal of variability in the solarwind it is very blustery, so geomagneticactivity is erratic and sometimes ex-tremely intense.

Automatic techniquesIn 1987 the three standard geomagneticobservatories in Britain, now operatedby the Geomagnetism Research Group(GRG) of the British Geological Survey(BGS), finally dispensed with photo-graphic recording of geomagnetic ac-tivity and adopted automatic methodscontrolled by a central computer inEdinburgh.A microcomputer at each observatory isprogrammed to sample the field ex-perienced by each fluxgate sensor every10 seconds, to transfer these data to storeand to perform routine computations onthem. Minute values are computed usinga filter to exclude very high frequencyfield fluctuations from the final data set.Mean hourly values are computed at theend of every hour. The range of distur-bance (maximum value minus minimumvalue) for each component of the field isalso computed, at the end of each hour,for the preceding hour and three hoursin conformity with international conven-tion. These ranges are converted into astandard index of magnetic disturbance,known as K values, which is compatiblewith those derived from handscaling theold magnetograms. When the processeddata are transferred to Edinburgh ananalogue record is plotted, correspond-ing with the old photographic dailymagnetogram.All the prepared information is availablefor use a fraction of a second after theend of each hour. In practice it is storedon cartridge tape and awaits instructionsfrom the computer in BGS's Edinburghoffice. The Edinburgh computer is con-nected to each observatory by the publictelephone network using auto -dialmodems. The eventual aim is for thecentral computer to call up each obser-vatory on its own initiative and retrieveand process the data into the final formsthat users need. This means that self -checking procedures have to be devel-oped to replace the manual tests tomaintain veracity and quality control.These tests, often subjective, are crucialto maintaining the high quality of oper-ation expected of a standard geomag-

28netic observatory. In the meantime,while automated quality control is beingtested, the procedure is for operators tocall up data every working day so thatthe processing is supervised.

Getting it rightThe most important quality controlmeasure is to compare the fluxgatereadings with precise absolute measure-ments. Most magnetometers, fluxgatesand suspended magnets are subject todrifts of calibration and baseline. Inclassical observatories absolute measure-ments are made weekly and variometerbaselines are adjusted to take account ofthe differences between variometerreadings and measured values. Manualabsolute measurements take a relativelylong time, some 10 to 15 minutes, and onoccasions when the geomagnetic field iseven only slightly disturbed the errors intiming often exceed the real differencebetween variometer and absolute value.The automatic system used by BGS usesproton precession magnetometers incarefully aligned coils which produce thecontrol fields for vector information toperform baseline reference measure-ments (BRMs) every hour in an auto-matic sequence. The BRMs aresynchronised with the minute valuesfrom the fluxgates and are comparedwith them 'on the hour' to produce acontinuous baseline for the variometers.BRMs are absolute measurements withbut one exception: the coils can becomemisaligned or the pillars on which theyare placed may tilt gradually. In such cir-cumstances the control fields may in-troduce errors in the absolute valuemeasured. So manual absolute measure-ments are still needed, but now only twoor three times. a year to correct for thegradual and very small changes in theBRMs. The synchronisation of BRMcomparisons virtually eliminates errorsdue to geomagnetic disturbance.Apart from being technically satisfyingto those engaged in the work, the devel-opment of BGS's Automatic RemoteGeomagnetic Observatory System(ARGOS) makes geomagnetic dataavailable to users in science and com-merce in a form that can be handled bycomputer. It does so a great deal morerapidly than did the classical techniques.Photographic charts used to be changeddaily: they had to be developed, fixedand dried; manual scalings had to be in-dependently verified and eventuallytyped into a computer to be put intodigital form. At a single observatory thatprocess took a day or two, and whenregional or global data are needed thedelivery time took weeks, months oreven years.

Editing and availabilityWhen the ARGOS data have been called

In the magnetosphere, the solar wind is deflected about Earth by the geomagnetic field. Onthe day -side, solar wind pressure compresses the magnetic field lines while electromagneticfriction drags the night -side field lines into a long tail. Shaded areas near Earth represent theradiation belts where high-energy protons and electrons are trapped in geomagnetic field lines,creating dangerous conditions for astronauts and equipment in spacecraft.

Equatorialring current

Ay:roralelectrcei:

Field -alignedcurrents

Cross -tailcurrent

Skeleton representation of electrical currents brought about by the solar wind's deformationof the magnetosphere, maintaining the balance between the pressure of the solar wind andthe magnetic pressure of Earth's field. It is the magnetic fields of such currents that causegeomagnetic disturbances.

up to Edinburgh and verified to be cor-rect, they are screened for spikes, whichare errors caused by transient inter-ference, and for drop -outs, which arelost data bits. Such errors are almost en-tirely caused by noise on the telecom-munications line. They are edited outand the analogue record is plotted forquick reference. Data are stored for com-putation of daily, monthly and annualsummaries, but are also transferred tofiles on BGS's mainframe computerwhere they are available to users, withother data maintained by GRG in its roleas a World Data Centre for geomagnet-

ism, through JANET, the JointAcademic Computer Network. JANETis accessible by research workers in allUK universities and research institutesand, via commercial networks, to otherusers in the UK, Europe and around theworld.

The BGS Geomagnetic Information andForecast Service (GIFS) holds historicaldata sets from the world's observatories.It also carries simple indicators of solaractivity relevant to forecasting geomag-netic disturbance levels, and it providesaccess to:


29

(a) Annual mean values of the geomag-netic field components from 511 obser-vatories, dating back to 1813.

(b) Hourly mean values of the three fieldcomponents for the three UK obser-vatories over the previous 12 months; thefile is updated daily.

(c) Hourly and three -hourly values ofthe range of activity, and the index basedon it, for the previous 12 months, alsoupdated daily.

(d) Files of the local activity index forthe three UK observatories, extendingback to 1940.

Files of planetary activity indices andwhat is known as the geomagneticcharacter figure, back to 1932, with filesof daily sunspot numbers and solar10.7 cm radio flux. These historicalrecords will be extended back to about1850 in the near future.

(e) A program that enables local valuesof the geomagnetic field components tobe calculated from a global field model,known as the International Geomag-netic Reference Field.

(0 A forecast of geomagnetic activity forthe next 24 hours and, with less con-fidence rating, for the following 26 days(the next solar rotation). The forecast in-cludes current and predicted values ofthe solar 10.7 cm flux.

Forecasting space weatherThe power of GIFS lies in combining thehistorical record of geomagnetic andsolar activity with current data and theactivity forecast. Forecasting spaceweather, which is what geomagnetic ac-tivity means, was not worth while whenthe most recent data available were daysor weeks old.A forecast of space weather is extremelyvaluable for people engaged in hightechnology because it has to do with howmuch and what type of particle radi-ation is reaching Earth's magnetospherethrough the solar wind. Its bearing onthe magnetosphere includes radiationhazards to astronauts making spacewalks and electrostatic charging of thespacecraft themselves, which can causeelectronic components to burn out orcircuits to be falsely triggered, spuriouscommands and the black -out of com-munication. Raised ionospheric tem-perature and density increase at-mospheric drag at altitudes from 100 toseveral thousand kilometres and affectthe orbits of low -flying spacecraft usedfor defence, navigation and commercialpurposes. The re-entry glide path of thespace shuttle is shortened by 75 km attimes of geomagnetic disturbance.Ionospheric temperature may increaseby 1000 °C and its density increases byELEKTOR ELECTRONICS MAY 1989

up to 50 per cent at times of geomag-netic disturbance; these figures corre-spond with 5 °C and 0.5 per cent re-spectively for a serious storm in thelower atmosphere. During geomagneticdisturbance ionospheric winds reachmany thousands of kilometres per hour.One of the main applications of spacescience during the next 30 or 40 yearswill be observation of Earth for econ-omic and ecological planning from long -life low -altitude platforms such as thespace stations planned in the Columbusprogramme. Managing such spacecraftdepends heavily on knowing flight con-ditions and having advance warning ofmajor changes.One important application of knowingspace weather lies in monitoring the or-bital decay of spacecraft whose life isover. Since 1957 oer 30 000 artificialsatellites have been launched for civiland military purposes. All will eventu-ally fall back to Earth, and most do notburn up completely as they re-enter theatmosphere. It is especially important tobe able to predict the landfall of thosepowered by nuclear reactors. This appli-cation and techniques for predictinglandfall are likely to become more andmore important.Key military targets (weapons silos, com-mand centres and so on) are protectedagainst nuclear attack by especially thickand reinforced concrete. Certain longand intermediate range ballistic missilesare designed to have an accuracy of bet-ter than 50 metres to be effective againstsuch `hardened' targets. The weaponsare rendered useless if precise and up -to -the -moment information about the dragand deflection they might experience infalling through the ionosphere is notavailable.Defence experts also need space weatherinformation for the sort of telecom-munication that depends on the electrondensity in the ionosphere. Reliable use of`over -the -horizon' radars depends onknowing the effective heights of theionospheric layers and their distribution.Geomagnetic disturbance itself causeselectromagnetic induction in the groundand in long conductors such as pipelines,telephone or television cables, railwaysignalling systems and power lines. InFinland recently a magnetic stormgenerated a transient surge current of160 amperes in a power line rated at 350amperes and carrying a standing load of300 amperes.None of these needs for informationcould be satisfied before automatic op-eration of observatories came into being.Other countries have modernised theirgeomagnetic observatories, notablyCanada which led the way 15 years agowith digital recording, but none has yettaken the important step of full auto-mation with central control and process-ing. There are about 200 geomagneticobservatories around the world and

more than two-thirds of them still use in-struments and methods based onGuass's techniques and Brooke'sphotorecording of 1841.To provide global information in therapid time needed for useful forecasting,BGS and the US Geological Survey(USGS) are promoting a co-operativeprogramme called INTERMAGNET,through which geomagnetic obser-vatories around the world will transmitreal-time data by satellite to three or fourcommunication centres which will col-lect and process the data for users. Apilot scheme is under way, supported bythe Air Weather Service of the US AirForce, in which six USGS geomagneticobservatories are being equipped withautomatic recording equipment andtransmitters. The three UK observatorieswill have transmitters fitted to ARGOSand receivers will be sited at the USGSheadquarters at Golden, Colorado andthe BGS observatory at Hartland,England. The two sets of observatorieswill send data to GOES, a US Depart-ment of Commerce satellite, which willbeam the information to the two receiv-ing stations. In Britain the data will betransferred from Hartland to Edinburghby dedicated telephone line and will bemade immediately available on GIFS. Inthe US the information will be relayeddirectly to the Air Weather Service.USGS and BGS have invited all theworld's observatories to participate inthe programme. Already Canada,France, India, Japan, South Africa andthe Soviet Union have made firm com-mitments. It is expected that over 100observatories using standardised equip-ment will be linked together by INTER -MAGNET by the end of the century.Observatories using classical measuringtechniques have to employ many highly -skilled people, so it is hardly surprisingthat they are found mainly in the moredeveloped countries. There is notenough coverage in the southernhemisphere and almost none in theoceans, and that bias is reflected in fieldmodels. Areas that produce no data aremodelled by using information fromareas where there are plenty of data. IN-TERMAGNET includes plans to set upunattended instruments in countrieswhose priorities and resources cannotjustify their maintaining a programmeof geomagnetic research, and on oceanicislands from which geomagneticmeasurements have never before beenavailable. Through this, models of themain field and secular change will be-come a great deal more accurate andmore rapidly available.

30

PRACTICAL FILTER DESIGN (5)by H. Bae;gott

Last month we discussed the design of wide band-pass filters. This month'sinstalment in the series deals with narrow band-pass network

Not only the gradient of the skirts of aband-pass filter, but also its relative band-width, B, is important - see Fig. 26. Steepslopes and a narrow pass band are twoconflicting requirements, so that the filterdesign is really a compromise.

Fig. 26. Characteristic curve of a band-pass filter:the bandwidth, B, is the section between the-3 dB points

The bandwidth of a band-pass filter is clo-sely associated with the Q -factor. which isthe ratio between the centre frequency, fc,of the pass band and the -3 dB bandwidth:

B =fn-ft

pass filter with a centre frequency of 1000Hz. a bandwidth of 250 Hz and an attenua-tion of not less than 40 dB at 400 Hz and3000 Hz. The frequency corresponding to400 Hz at the other side off is calculatedas follows:

400f2= 1000', so that

12= 10002/ 400 = 2500 Hz,

that is, an attenuation of 40 dB at 400 Hzis already achieved at 2500 Hz. If wechoose an attenuation of 40 dB at 3000Hz, the corresponding frequency at thelow -frequency side of the curve will be:

11= 10002/ 3000 = 333.3 Hz.

This does not give the required attenuationand, therefore, we must choose the firstsolution.

The gradient of the slopes of the curve iscalculated from the ratio of the bandwidthat two equally attenuated frequencies andthe pass band:

[31] gradient = (2500-400) / 250 = 5.25.

The centre frequency of the filter is not thearithmetic mean of the -3 dB frequenciesbut is calculated from:

f,= Nififh (321

If the Q -factor is higher than about 10, forall practical purposes

= +/h) / 2 [33]

The computation of a band-pass filtershould be based on a symmetrical design.If. for instance. a given attenuation is wan-ted at a number of frequencies that lie out-side the pass band (indicated by fl and f,in Fig. 26). it is necessary to calculate withthe aid of the formula fc2= 11 1, at whichfrequency the most stringent requirementsoccur. All further computations must thentake account of these findings.Assume that we want to design a band -

It then becomes a question of looking upthe frequency curves that will bepublished in one of our forthcoming issuesand finding a filter that has an attenuationof not less than 40 dB at a normalized fre-quency of 5.25. This is, of course, thesame method as used for low-pass andhigh-pass filters.

Passive band-pass filtersThe first and simplest way of designing apassive band-pass filter is computing

appropriate low-pass and high-pass sec-tions and connecting these in series as des-cribed in the previous instalment. In thecase of narrow band-pass filters, it is.however, necessary, to retain correct impe-dances at the input and output of the com-posite network, and this is achieved by in-serting a T- or rt-attenuator as shown inFig. 27. The attenuation should be of theorder of a few decibels.

A rather more sophisticated band-pass fil-ter may be designed by first computing alow-pass section and then transforming theresults. This is rather simpler than itsounds: capacitors are replaced by a paral-lel network of a capacitor and inductor,while an inductor is replaced by a seriescombination of an inductor and a capacitoras shown in Fig. 28. The formulas for cal-culating the components are:

L = 1/C(2 ELY [34]

C = l/L(2 Irfe)2 [35]

An example of a practical design is givenin Fig. 29. Here again, we first determinethe gradient of the slopes' and then compu-te a low-pass section. The various compo-nents are calculated for a low-pass filterwith a bandwidth equal to the -3 dB passband of the band-pass filter. The valuesare then recalculated with the aid of for-mulas [34] and [35]. This method is fastand gives good results.

The operation of passive filters is stronglyinfluenced by the Q -factor of the inductorsused. The Q(uality) of an inductor is deter-mined by the ratio of its impedance to itsd.c. resistance:

Fig. 27. When two filters are cascaded, it is necessary to insert an impedance -correcting attenuator.


_Lc

L

TFig. 28. Illustration of the manner in which thevalues of components calculated for a low-passsection may be transformed into those requiredfor a band-pass filter.

Q=coLIR 1361

If care is taken to ensure that the Q -factorof the inductors is several times largerthan that of the filter, deviations from thetheoretical curves will be minimal.

Active band-pass filtersWe shall discuss the design of active band-pass filters on the basis of two fairly sim-ple circuits. The first is a design with mul-tiple feedback paths as shown in Fig. 30.With this design it is possible to start withavailable (standard) values of capacitorsand then calculate the values of the resist-ors. This is a worthwhile advantage if it isremembered that the computation of aband-pass filter can be pretty complex.Each pole requires a separate filter, so thata design quickly becomes fairly large. Afourth -order filter, for instance, consists offour sections.

Fig. 30. Computations for an active band-pass fil-ter with multiple feedback paths remain relative-ly simple. This type of filter may be used for Qvalues of not greater than 25.

To determine what type of filter and whatslope gradient are required for a givenapplication, it is necessary to start with thecalculations indicated at the beginning ofthis instalment. The results will enable thepole characteristics of the wanted filtertype to be found in the tables, after which

Fig. 29. Practical realization of the transformations

the specific calculations to arrive at thecentre frequency and Q of each sectioncan be carried out. In the case of a pair ofcomplex poles this is done as follows:

C = ce+ 13= [37]

Qs= 1.1({ C+4Q2+Qq[(C/Q)2+16Q2--8ce+8132] I / 8ce) [38]

D = [ota+V(aVs2-Q)] IQ [39]

iso=felp [40]

fsb= Dfc [41]

where fs, andfsb are the centre frequenciesof the two band-pass filters: they have thesame value Q5.

For a real pole, the calculation is some-what simpler:

Qs=Q1a [42]

The centre frequency of a real -pole sectionis equal to the central frequency of the en-tire band-pass filter.

The amplification, A5, of each stage con-tained in the filter is:

A5= AN/ [11-Q,2(f, /fc-fc ifs)] [43]

where A is the overall amplification, f, isthe resonant frequency of the section andfc is the centre frequency of the completefilter. It is prudent to distribute the overallamplification equally over the sections.Once all these computations have beencompleted, three parameters of each sec-tion are known: Qs, fs and A.

After a suitable value has been chosen forcapacitors C, the value of the resistors canbe calculated:

R3= Qs irf,C [44]

illustrated in Fig. 28.

/21 = R3I 2A,

R-,= R3 / (4Q52 -2A5)

1451

(461

The amplification, A5, must not be greaterthan the amplifcation of the multiple -feed-back path circuit 2Q,2. At the same time, itshould be noted that the open -loop ampli-fication of the opamp must be much grea-ter than 2Q52.

If Q -factors greater than 25 are required,the design of Fig.31 should be used: itenables Q -factors of up to 100 to be achie-ved. The component values are calculatedwith the aid of the following formulas:

R3= R4 =1 2nf,C [47]

R1= (2Q8R3) I A,

= RIA,/ (2-A,)

[48]

[49]

I0

636008 - 16

Fig. 31. This design, based on two opamps is sui-table for filters that need a Q -factor between 25and 100.

The maximum amplification of this confi-guration is 4W-.

Next month we will start with a review ofthe various filter tables.


RADIO DATA SYSTEM (RDS)DEMODULATOR

sources: European Broadcasting Union; Philips Componentsdesign: J. Bareford

After several years of study and practical tests, the Radio DataSystem (RDS) is currently implemented on all BBC/IBA VHF FM

broadcast transmitters in the United Kingdom. Other countries inEurope are following now that all technical and functional

specifications of the system have been finalized by the EuropeanBroadcasting Union (EBU). The primary aim of the RDS system is topermit the realization of automatic tuning features in car radios.This article provides an introduction to the operation of RDS, andpresents a demodulator as a basis for experimental reception of

this new service.

Most motorists are wellaware that reception of VHFFM signals is troublesomein a moving car because ofsignal reflection, the limitedrange of the transmitters,and noise induced by theengine and other movingparts. The Radio Data Sys-tem should alleviate some ofthe plight motorists suffer intrying to stay tuned to a par-ticular programme duringthe trip. Especially in hillycountryside, and in areaswith a high transmitter den-sity, continued reception ofa particular programmemeans frequent retuning ofthe car radio and a possiblehazard for the motorist.If so programmed, a RDS-compatibleradio tuned to, say, BBC Radio -1, willproduce this programme irrespective ofthe whereabouts of the car in thecountry. During the trip it is automati-cally tuned to the strongest signalavailable from a VHF FM transmitterthat carries the BBC Radio -1 pro-gramme.In addition to automatic tuning, RDSprovides a host of other facilities whichare of great significance in view of theincrease in road traffic and the economiclosses caused by traffic jams. Becausethey are linked by a microwave network,local radio stations such as Radio Kentcan relay traffic information and emerg-ency calls to `RDS-compatible' motor-ists listening to a national service such asBBC Radio -1: when the traffic an-nouncement is broadcast, the car radiois automatically tuned to the frequencyused by the local station.

RADIO DATA SYSTEMFeatures of RDSThe Radio Data System has been de-signed for use throughout Europe, andwith future extensions in mind. Thisdoes not mean, however, that all techni-cal features listed in Table 1 are availablein a particular country.

Primary featuresThe Programme Service (PS) name andthe Programme Identification (PI) arethe most important of the primaryfeatures of RDS.

PI information enables the receiver todistinguish between countries or areas inwhich the same programme is trans-mitted, and the identification of the pro-gramme itself. The code, which is not in-tended to be displayed, enables the re-ceiver to search for the strongest trans-

mitter signal available forproviding a particular radioprogramme in the car. Thecriteria for re -tuning the re-ceiver would be the avail-ability of a better signalhaving the same PI code.

PS information is a textconsisting of a maximum often alphanumeric charactersthat form the station nameor a meaningful abbrevi-ation thereof, e.g.RADIO MERC for RadioMercury.

Further important primaryfeatures include:

AF (alternative fre-quency list)

A list of up to 25 frequencies of VHFFM stations broadcasting the same PIcode in one area or adjacent areas maybe transmitted. The list can be loadedand stored in the RDS-compatible re-ceiver.

TP/TA (Traffic Programme/TrafficAnnouncement)

These are essentially on/off codes thatindicate whether a particular transmittercarries traffic information or not. Thesignal may be used for interrupting acassette or compact -disc player, turningon a lamp or another signalling device inthe car, or be taken into account duringautomatic frequency search.Secondary featuresA number of so-called secondaryfeatures are available for broadcasters.Again, not all of these may be actuallyimplemented, although most are in theUK.


ON (Other Networks)This code supplies information on pro-grammes available on other networks. Itmay be used in conjunction with the AFlist and the PI code to switch the receiverautomatically from, say, BBC Radio -I toa station broadcasting traffic an-nouncements, say, Radio Kent.

CT (Clock Time and date)UTC time codes are transmitted for con-version to local time in the receiver.

IN PTY (Programme Type)This code identifies the programme typewithin 31 possibilities. Examples of PTYcodes are: 00001 = News; 00101 = Edu-cation; 01110 = Folk Music. The PTYcode may be used for search tuning.

IN PIN (Programme Item Number)This code enables receivers and recordersto respond to preselected programmes orprogramme items. Use is made of thescheduled programme time.

RT (Radio Teletext)Text transmissions are primarily in-tended for suitably equipped homereceivers. In a car, however, they presenta possible hazard, and are therefore in-tended for controlling a speech syn-thesizer.

TDC (Transparent Data Channel)This oddly named code refers to the useof displays and computer equipment fordownloading text or short computer pro-grammes supplied by the RDS decoder.

Table 1.Features of RDS CEBU Recommendation)

Primary features

PI Programme identificationPS Programme service nameAF Alternative frequenciesTP/TA Traffic programme/traffic

announcement

Secondary features

ON Other networksCT Clock time and datePTY Programme typePIN Programme item numberRT RadiotextTDC Transparent data channelDI Decoder identificationMS Musicispeech switchIH Inhouse information

Additional features

RP Radio pagingTMC Traffic message channel

tsigncllevel

monosignal

L + R

pilottone

stereo difference R DSSigner subcarrier

L-R

15 19frequency kHz kHz

23kHz

ME38

kHz53 57

kHz kHz

880209-11-11

Fig. I. Spectrum of the baseband transmitted by a VHF FM broadcast transmitter modulatedwith a conventional stereo multiplex signal plus associated pilot tone, and the RDS datastream.

DI (Decoder Identification)These 4 coded bits indicate which of 16possible audio processing modes (Dolby,surround -sound, HighCom, CX, and,possibly, de -scrambling) is applicable tothe received programme.

IN MS (Music/Speech)When used, this 4 -bit code allows the re-ceiver to distinguish between music andspeech, and to control the volume accor-dingly.

IH (In -House)This code is provided for use by thebroadcasting authority only. Appli-cations include identification of trans-mission origin, remote switching of net-works or local transmitters, and pagingof staff. Standard RDS receivers ignoreIH codes.

Additional features:In addition to the primary and second-ary features discussed above, the relevantEBU recommendation lists two 'ad-ditional features':Radio Paging, RP, may also be im-plemented as a separate feature of RDS,i.e. independent of IH codes. SimilarlyTMC, Traffic Message Channel codes,may be used independently of TP codes.

Technical description of theRDS signalThe RDS datastream is available con-tinuously on a subcarrier added to thebaseband transmitted by a VHF FMbroadcast station. This baseband, whichwas formerly called the multiplex signal,already comprises the stereo differencesignals L-R and L +R plus the associ-ated pilot tone at 19 kHz (CCIR rec-ommendation 450-1).The RDS system uses a subcarrier fre-quency at 57 kHz, which is locked eitherin phase or in quadrature on to the thirdharmonic of the 19 kHz pilot tone. Theresulting baseband spectrum is shown inFig. 1.The RDS subcarrier is suppressed andamplitude -modulated by a so-called bi-

phase coded data signal, whose structurewill be reverted to below. The modu-lation system for RDS is thereforedouble-sideband with suppressed carrier(DSSC). Alternatively, it may bequalified as two-phase PSK (phase shiftkeying) with a phase deviation of 90°.Provision has been made to ensure thatthe RDS system does not interfere withthe ARI (Autofahrer Rundfunk Infor-

Fig. 2. Basic differential encoder made froma D -type bistable and a XOR gate.

Fig. 3. Biphase-modulated symbols gener-ated by logic is and Os are composed of apositive and a negative half -cycle.


34

Odataclock

0 data

differentially0 encoded

data

biphasepulses

biphase°modulation

signal

0 0 1

1 1 0 1

0 1

O 0

O 0

_irrO 0

EZa2C9 - -14

Fig. 4. Timing diagram illustrating the generation of the RDS datastream.

mation; Broadcast information formotorists) which has been in use for anumber of years already in FederalGermany. The ARI system shares the57 kHz subcarrier with the new RDSservice.

The bandwidth occupied by the RDSsidebands in the baseband spectrum cor-responds roughly to the rate of thedatabits, 1187.5/s. The data clock(signal 1 in timing diagram Fig. 4) is ob-tained by dividing the subcarrier fre-quency, 57 kHz, by 48.Before it is applied to the RDS modu-lator, the datastream is coded differen-tially to reduce the overall bandwidth, to

minimize power waste by the subcarrier,and to ensure optimum reliability of thesystem. The basic layout of the differen-tial encoder used is shown in Fig. 2. Thiscircuit, based on a D-bistable with XORlogic feedback, is fed with the data clocksignal and the NRZ (non -return to zero)data signal (diagram 2 in Fig. 4.). ANRZ signal remains logic high withsubsequent logic high input pulses, andtoggles only on the high -to -low or low -to -high transitions. The differentiallycoded signal is shown in diagram 3 inFig. 4: the output state of the bistablechanges only when the input bit is logicI. The differential logic signal is thenbiphase-coded as shown in diagram 4 in

Group -4 blocks .104 bits

Block 1 Block 2

1

Block 3 IN Block.

Block =26 bits

J Information word

Information word .16 bits

Cirectrword [offset .ord

,a---Checkword=10 bits

cilt-71`61`.51`,1`31`21c,frat

880209 -11-15

Fig. 5. Structural analysis of the RDS data format (courtesy European Broadcasting Union,Brussels).

Fig. 4. In pure biphase coding, a logic 1in the source data results in a positivehalf cycle followed by a negative half cy-cle (see Fig. 3). For a logic 0, the orderis reversed. In practice, RDS uses aslightly different method based onbiphase pulses instead of half -cycles (seethe inset waveforms to the right ofdiagram 4 in Fig. 4). A logic 1 then cor-responds to a positive pulse followed bya negative pulse. The opposite applies toa logic 0 in the source data.After shaping and filtering to reduce theoverall bandwidth, the biphase-codedRDS signal is modulated as shown indiagram 5 in Fig. 4.In an RDS-compatible receiver, the bitclock and the NRZ data are recoveredfrom the baseband by a specialdemodulator. In fact, filtering and shap-ing of the data spectrum is split equallybetween the transmitter and the receiverto ensure maximum noise immunity.Thanks to the differential coding, data isalways decoded correctly irrespective oflogic inversion in the receiver.

Coding structure of the RDSdatastreamRDS data is subdivided in 16 -bit words,accompanied by a 10 -bit checkword. TheMSB (most significant bit) is alwaystransmitted first. The data andcheckword bits together form a 26 -bitblock (Fig. 5a). Four of these blocksform a 104 -bit group. Since all data istransmitted continuously without gapsbetween the blocks or groups, the grouptransmission time is 87.5 ms.The 10 -bit checkword enables the re-ceiver to detect and correct errors whichmay occur when reception is impaired ormarginal. This checkword, composed ofbits c'n (Fig. 5) is of the so-called CRC(cyclic redundancy check) type. The 10-bit CRC word is obtained by multiplica-tion of the 16 -bit information word witha matrix polynomial, and subsequentXOR-ing with an off -set word. Afterthese operations, the checksum is ap-pended to the information word. Thecheckword is transmitted MSB-first.There are 5 off -set values, A, B, C, C'and D, appended to blocks 1, 2, 3, 3 and4 respectively. These off -set values en-able the receiver to synchronize with thereceived datastream and thus to processthe groups and blocks separately.

Gro ti p typesEach group contains data that marks itsstatus. This type -marking is achievedwith the first 5 bits (MSBs 15 through11) in block 2 of the group. The firstfour bits, 15 through 12, indicate thegroup number, the fifth bit the type, Aor B. The group types so obtained carrythe features listed in Table 1. All grouptypes comprise the complete 16 -bit


Program Identification (PI) code in thefirst block, which thus has the highestrepeat rate, and is received at 87.5 -ms in-tervals. Similarly, the PTY (ProgrammeType) code and TP (Traffic ProgrammeIdentification) bits are assigned fixedpositions in the second block, whose bit -order is basically as follows. Startingwith the MSB (bit 15) the bit -order is:

the 4 -bit group number (0 to 15); group type (1 bit) A or B;; TP flag (1 bit);

PTY (5 bits); M/S flag (1 bit); DI (1 bit); decoder address (2 bits).

Alternatively, the last 3 bits indicatewhich of the eight PS characters are con-tained in the 2 bytes of the fourth blockin the group. In the B -version of allgroups, blocks 1 and 3 contain PI data.This state is marked with off -set word C'instead of C. In the A -version of group0, the third block contains sixteen AFbits.

Although bound by EBU recommenda-tions, broadcasting authorities are inprinciple free to decide on the order andrepetition rate of the groups. The use ofthe bit positions reserved for PTY andM/S is optional, and dummy bits may betransmitted when these services are notused.

Towards a decoderApart from RF and AF circuits, anRDS-compatible radio requires the fol-lowing modules:

an RDS demodulator that recoversthe NRZ data and the bit clock from thebaseband; a decoder capable of (I) recognizingthe block structure by synchronizingwith the off -set masks, and (2) error cor-rection; an alphanumerical display unit; an interface for controlling RF andAF sub -circuits in the radio.

Table 2. RDS Group Types

group typel information bits

OAOB

1 A/B2A/B3A/B4A5A/B6A/B

1 5B

-PI, PTY, TP, TA, DI, MS, PS, AFPI, PTY, TP, TA, DI, MS, PSPI, PTY, TP, PINPI, PTY, TP, RTPI, PTY, TP, ONPI, PTY, TP, CTPI, PTY, TP, TDCPI, PTY, TP, INHPI, PTY, TP, TA, DI, MS

bandfilter

212n.c.

20 19 19 17 16 15 1.1

SDA1000

2 3 4 5 7

*CBS 456 F 11**optional external data litter

01.1s

SK

DK.BK

DK

Data

13 12

a 9

L. J. 1f.Clock

Fig. 6. The RDS concept proposed by Siemens is based on two chips for demodulation(SDA1000) and processing (SDA1010) of the composite RDS signal. The serial output of theSDA1010 supplies a data signal suitable for feeding to the system processor in the (car) radio.

The first module, the demodulator, isdescribed further on in this article. Forevident reasons, this demodulator takesits input signal from a point ahead of thede -emphasis circuit.A number of semiconductor manufac-turers, including Siemens and Valvo(Philips Components West -Germany),have recently released integrated RDSdemodulators. The use of one of these,the SAA7579T from Valvo, is describedin an application intended for furtherexperiments with RDS. Meanwhile,Siemens have announced a two -chip set,the SDA1000-SDA1010 for RDSdemodulation and partial decoding (seeFig. 6). The final link, an intelligent,that is, programmable and error -correcting, display driver with radio in-terface, however, does not seem to beavailable from any manufacturer as yet,leaving ample room for experiments anddevelopments with software in generaland single -chip microcontrollers in par-ticular.

For your experiments: anRDS demodulatorThe Type SAA7579T is a CMOS RDSdecoder in surface -mount technology.The chip is manufactured by PhilipsComponents. The circuit proposed herediffers from the standard applicationsuggested by the manufacturer. Forvarious reasons, this application wasfound to give unsatisfactory results, sothat a better configuration wasdeveloped.The function of the RDS demodulator isthe recovery of the clock and datasignals from the encoded RDSbitstream. As already discussed, theserial RDS signal is first coded differen-tially and then converted to biphasesymbols that are modulated on to a57 kHz subcarrier. The suppressed RDScarrier and the sidebands caused by the

modulation process are broadcast by aVHF FM transmitter, together with thestereo multiplex signal.In a receiver, the multiplex signal isavailable at the output of the FMdemodulator. From there, it is fed to thestereo decoder and the parallel -connected RDS decoder. The RDSdecoder has a bandfilter that extracts theRDS sidebands at 57 kHz from the base -band. A synchronous demodulator isthen used to recover the biphase RDSsignal and the subcarrier. Next, thebiphase symbols are decoded andrestored to their original bit format withthe aid of a differential decoder.This brief description covers the basicoperation of the hardware required fordemodulating and decoding the RDSsignal. The remaining functions ofword -synchronization, group and blockrecognition on the basis of off -set wordevaluation, error correction, data pro-cessing and interfacing to the radio anddisplay require the use of a microproces-sor and, of course, a suitable controlprogram.

SAA7579T: functionaldescriptionThat the SAA7579T comes in a surface -

mount assembly (SMA) package is notsurprising because the chip is intendedfor applications in car radios. The func-tional structure of the chip and its pinn-ing are shown in Figs. 7 and 8 respect-ively.The SAA7579T works from a singlesupply voltage of 5 V, and draws only1.6 mA (typ.), The pre -filtered RDSsignal is applied to input pin 15,designated mux. A so-called Costas-loopwith associated 4.332 MHz crystal oscil-lator demodulates the signal synchron-ously, and also supplies the regenerated57 kHz subcarrier. The presence of anARI signal is flagged by a high level atpin I.


36

6 7 6 5

9 10 11 12 13 IL 15 6

ARI

TQ2

TQ1

T57

T1

OSCI

OSCO

USS

UDD

MUX

T2

T3

RESET

QUAL

RDDA

RDCL

880209-1-12

Fig. 8. Pinning of the SAA7579T RDSdemodulator in a 16 -way surface -mount en-closure.

The Costas-loop supplies the regener-ated 57 kHz subcarrier and the demodu-lated RDS signal, which is a synchron-ous stream of biphase-coded symbols, ata rate of 1187.5 Hz. The regeneratedsubcarrier is divided by 48 to supply thedata clock signal, RDCL, which has a fre-quency of 1187.5 Hz. Synchronizationto the data in the biphase bitstream isachieved by controlling a programmabledivider. The process of data recovery iscontinued in a biphase symbol decoderand a subsequent differential -phasedecoder.The use of differential encoding makesthe demodulation process independentof the absolute phase of the modulationsignal, which results in a high degree ofimmunity of the system to inversion ofthe signal in the receiver/demodulator.The RDS datastream is synchronizedwith the clock signal and then fed out topin 10, marked RDDA. The signal isdigitally compatible to simplify direct in-t9rfacing to a microprocessor system.The same applies to the auxiliarysignals, the clock, RDCL (pin 9), and thequality bit, QUAL (pin 11). The RDS datashould not be processed when QUAL islogic low.Relative to the clock, data are valid for417 pts after a clock transition, irrespec-tive whether referenced against thepositive or negative pulse transition.

Table 3. Pinning of SAA 7579T

Pin Signal Function

(1) ARI ARI indication output (ARI = H)(2) T02 Test output 2(3) TQ1 Test output 1(4) T57 57 kHz test output15) T1 Test input 116) OSCI Oscillator input17) OSCO Oscillator output18) Uss Ground (0 VI(9) RDCL RDS clock output

(10) RDDA RDS data output(11) QUAL Signal quality indication (H = o.k.)(12) RESET Reset input for test logic(13) 13 Test input 3(14) 12 Test input 2

(15) MUX RDS input (MUX; clamped and filtered)(16) Ut,J +5 V supply voltage

This forces data changes, i.e., toggling ofthe data signal (RDDA), to take place 4 Asbefore a clock transition (positive ornegative).

Application circuitsThe application circuit for theSAA7579T developed by Philips Com-ponents is given in Fig. 9. Transistor Tiforms an amplifier with relatively highinput impedance. The high -Z inputamplifier ensures that the FM demodu-lator in the receiver is not excessivelyloaded. The amplified baseband is takenthrough a 4 -stage bandfilter with induc-tors from Toko. The frequency responseand group delay characteristic of thisfilter are shown in Fig. 10. The RDSsignal at the output of the filter is ap-plied to a Type TBA120U which func-tions as a limiter/amplifier. Buffer T2

raises the composite RDS signal to adigital level so that it can be applied toinput mux of the SAA7579T.

The above application circuit for theRDS decoder was tested and sub-sequently modified. The final versiondeveloped in the Elektor Electronicslaboratory is shown in Fig. 11.The amplification of the first stage is ad-justable with preset Pi. Good selectivityat 57 kHz is achieved with a three -stagebandfilter based on fixed inductors withparallel, partly adjustable, capacitances.Potential divider R6 -R- provides the DCbias for emitter follower T,. This stageensures that the bandfilter is only lightlyloaded while driving the input of fastopamp ICI with sufficient signal ampli-tude. Diode Di compensates tempera-ture drift of the transistor's UWEparameter. The opamp, a Type LF357, isset up to provide an amplification of101. Series network RI 1-D2 forms aclamping circuit to limit the outputsignal of the opamp to digital levels (ap-prox. 0 V/+5.5 V). The component con-figuration around the RDS decoder chip

IL= U's

a

6

cosy -Van ab

fixed Chide(

Eo - phasesyrrbol decoder

Oscillator

ARI defector

Sync & forregen

ifferential

SAA 7579

Cuality- bitfrfieratOf

1117.91,

RCM

QUA

Test logic endGLOW signal selector

O

RES 7

5 3 6

72 11 7,22 TQ1 751 880209- I - 1 1

Fig. 7. Block schematic of the SAA7579T (courtesy Philips Components).ELEKTOR ELECTRONICS MAY 1989

Uotpx 120pF

C14

150k0

68kR

1R6

R7

BC 548

1800 RI CI LIC7

L2C2

1110pF

240R2

0 .8,5V

loon----t

I 0,1µFCS

1110pF3.30

R822pFC1S

L3 21.10C3 R3 C4

3.3nE

I

R4

O.lpFCt2

9

10

11

12

13

30

20-

C13

COO

IMPF I II"C19 C18

BC 558

880209 - I - 14

Fig. 9. Original application circuit for the SAA7579T. The Toko inductors in the four -stage band-pass filter tuned to 57 kHz are Type126ANS/A3561HM.

5V

NI...N6 =1C4 = 4050

3

a

12V

IC2 a» 1>

SAA FL/14

7579T Foci.,t23>4--(3- CURLN1 2

2

4332kHz220.232 -13

is standard and identical to the originalPhilips Components application. Alloutputs of the SAA7579T, and theregenerated 57 kHz signal, are bufferedwith a CD4050 to enable driving a mi-croprocessor port.The RDS decoder chip and the inputstage around Ti are fed from aregulated +5 V rail provided by on-board regulator IC3. The opamp mustbe powered from a higher, but alsoregulated, voltage, in this case +12 Vavailable at the input of the regulator.The total current drain of the circuit islower than 100 mA.

Alignment and applicationLittle needs to be said about the align-ment of the demodulator. The amplifi-cation of the input stage is adjusted withPi until an oscilloscope shows that D2starts to clip the signal. This happens

.35

tp.s1

.25

.15

. s

-5

I . `//

/ pass -band \yI \

7 \

/ group delayfil 4

1

-25kliz

0

148)

-2

-4

-a

-100 Ai 2.5kHz

57kttz

Fig. 11. Circuit diagram of the RDS demodulator.ELEKTOR ELECTRONICS MAY 1989

Fig. 10. Pass -band characteristic and groupdelay plots of the 4 -stage band-pass filter.

38

Parts list

Resistors (±6%):R1;R13=220KR2;Fl1o=100KR3 = 6K8

R4;Re=4K7135;Rs=Re;117;R1 ;R12= 2K2121=100K preset H

Capacitors:Ci;Ci2=10nC2;C7;Cio=40p or 45p trimmer capacitorC3;Cs;Ci1=47p; polystyreneC4=47p; 16 VC5;C13;C19=100nC6=2p7Cs=4n7C14;C17;C18=1p0; 16 VC15=100p; polystyreneC16=18p; polystyrene

Inductors:11;12;13=68 mH radial inductor with ferriteencapsulation

Semiconductors:Dl;D2=1N4148

=BF451T2=BF494ICt =LF357IC2=SAA7579T (Philips Components)IC3 = 78105IC4=4050

Miscellaneous:Xt = quartz crystal 4.332 MHz; parallel

resonance.PCB 880209 (not available through the

Readers Services).

when the opamp supplies a signal with aswing greater than 10 V. The trimmers inthe bandfilter are adjusted for maximumamplitude of the signal at the emitter ofT2. The QUAL bit indicates whether validdata are being received or not. The ARIbit will not go high in the UK since thereare no transmitters broadcasting this ser-vice.The signals are then ready to be appliedto a microprocessor -system running anappropriate program. How aboutdesigning such a system as your final -year course project? Let us know!

For further reading:

I. EBU Technical Document 3244-E:Specifications of the radio data systemRDS for VHF/Fill sound broadcasting.European Broadcasting Union, Brussels,March 1984.

2. EBU Technical Document 3260:Guidelines for the implementation ofthe RDS-system. European Broad-casting Union, Brussels, January 1988.

3. Parnall, S.J., Lewis, A.R., and Robin-son, J. (BBC): The technical realizationof a new broadcast service. Paperdelivered on the occasion of IBC 1988,Brighton.

n(J -r-

0 0 2.0

Q S2. -413 A AIV A C.)

sap 8

64 0--01010a)?0-14-9 010

2.4

I- 0lY IT IF CH Fej

C BN

E7()°(-

JC +

10, rg_08 +o ro

Fig. 12. Track layout and component overlay of the printed -circuit board designed for the ex-perimental RDS demodulator.


39

A CLOSER LOOK AT THE TRANSPUTERby Pete Chown

The transputer is probably the most powerful microprocessoravailable today; ironically, it is also one of the least used. It is a

RISC chip and a very powerful one. Its power stems mainly fromits ability to join transputers and use them as a single unit, thusmultiplying the power. The fastest transputers available today

have a speed of 15 MIPs (millions of instructions per second) and2-4 Mflops (millions of floating points operations).

If you built a computer with a transputer, same time.it would be about the fastest desktop com-puter you could buy. It would be several The transputer is a complete computer ontimes faster than a vAx 11/780. if you used a chip: it incorporates 2 or 4 K of memory,four of these devices, your (still desk-top) computer would be faster thansome mainframes with a speed equalto about 1/10 of a Cray -I. If you usedfifty of the devices you would reachthe bottom of the supercomputerrange (remember that these could stillfit under a desk). A thousand of thedevices would form the fastest com-puter ever built, at a cost around thatof a small mainframe.

Remember the Mandelbrot plots thattook 3 hours on a BBC Micro? Onetransputer would do this in 20seconds. Fifty transputers would do itfast enough to zoom in and out andmove in real time!

Transputer architectureIf this all sounds too good to be true,there is a catch. The transputer is verydifficult to program, because youmust tell it explicitly which parts ofyour program may be run at the sametime on different transputers. Thisinevitably leads to the other problem:that programs written on one compu-ter can be hard to make run on a dif-ferent one, because there are differentnumbers of transputers available. Toget round this problem, the transputerhas a feature whereby more than oneconcurrent process may be run on onetransputer. This means that you can splityour program into a lot of processes. Thenif there are a lot of transputers available,the processes are run on separate ones,otherwise on the same one. You are, how-ever, still left with that extra level of com-plexity in having to decide which parts ofyour program may be run at the

microprocessor and interfacing and it ishere that the next problem arises. If youadd external memory, as you obviouslyneed to do, the speed will be about halved.This still, of course, leaves it faster thanmost other microprocessors. You can alsoadd additional transputers if maintainingthe speed is vital.

Inmos (who make the transputer; not to beconfused with Intel. who make the 8086series processors) have provided a langua-ge for programming it, called Occam,

which has the facilities for parallelprocessing (that is, running processesat the same time on different transpu-ters). Unfortunately, it is awful. Togive you some idea, the level ofindentation at the left margin is signi-ficant in determining when statementblocks end. To fill the gap, therefore,conventional languages have beenproduced with parallel constructs.How good these are remains to beseen: Occam forces you at everystage to think about possible parallelprocessing, but the others, such asparallel-C, may not and may allowyou to avoid really having any paral-lelism to speak of, not by choice butjust by not thinking.

The transputer, like any microproces-sor family, comes in a variety ofspeeds and bus widths. Basically, theT212 series has a I6 -bit bus width,the T414 a 32 -bit one, while theT800 is the same as the T414, butwith a floating-point processor builtin. Table 1 lists all the processorswith their speeds that are currentlymade.

The Inmos link systemObviously, with many transputersworking on a problem at the same

time, communications is needed. Equallyobviously, it can not be by a conventionalnetwork, because the more transputers thatare added, the longer the delays will beco-me.

Inmos therefore decided to have seriallinks that join either two transputers or atransputer and an t/o device. These links


40are bi-directional and operate at 5 or10 MHz; 5 MHz is the standard, butmany of the devices have an option torun faster. There are 4 links providedfrom each transputer and one on eachi/o device.

Interfacing to i/o devices is muchsimpler with the links than with con-ventional memory -mapped t/o. Un-fortunately, four links are seldomenough and so a memory -mappedsystem must be used as well. Thereare specialized interface chips for thetransputers as with any microproces-sor family and these allow links to

Processor Bus MIPs Floatingpoint

IMS T212A-G17S 16 -bit 8.75 noIMS T212A-G2OS 16 -bit 10.00 no

IMS T414B-G15S 32 -bit 7.50 noIMS T414B-G2OS 32 -bit 10.00 no

IMS T800C-G17S 32 -bit 8.75 yesIMS T800C-G2OS 32 -bit 10.00 yesIMS T800C-G3OS 32 -bit 15.00 yes

Table I. Transputers and selected characteristics currently inproduction.

beinterfaced to a bus on another micropro-cessor, or to control a printer port. Someof the support devices c,..n be programmedin their own right and are used for control-ling discs or other devices needing com-plex controllers.

Transputer networksNetworks of transputers may be built up,so that a message can travel from onetransputer to another; although there maynot be a direct route, it gets there throughseveral other transputers. It might seemthat designing an efficient network wouldbe difficult, but in fact the difference inperformance between the best and theworst is usually only about 10%. In verylarge systems, it becomes more important,but as long as a reasonable configurationis chosen, there is unlikely to be a pro-blem. Some common arrangements areshown in Fig. 1 and Fig. 2.

Programming in parallelOccam has been designed from the outsetwith parallel processing in mind. In eachstatement block, you must decide whetherthe statements are to be executed one afterthe other, at the same time, or whether thefirst statement to become possible is to beexecuted. The last sounds somewhat use-less, but is. in fact, used when, for exam-ple, a program is displaying a menu and atthe same time it is spooling to a printer.Here it is possible to say that if a key ispressed first, it will be acted on, whereas ifthe printer buffer becomes empty. new textwill be supplied. The program in thisexample would then loop back to dealwith the next key press or requirement fortext.

Four other languages exist for parallel pro-cessing: assembler; parallel -Pascal; paral-lel -C; and parallel -Fortran. Assembler onthe transputer is very complex and its usecan not be recommended. There is littlepoint in using Fortran since it is rather out-

dated. Parallel -Pascal and parallel -C arethe best, but it is dubious whether either ofthem is worth using for reasons alreadystated: programs will tend not to incorpo-rate as much parallelism as they otherwisewould.

Interfacing the transputerInterfacing should be carried out if possi-ble through Inmos links. If there are notenough links, memory -mapped i/o couldbe used, but Inmos standard devices wouldnot work and devices with sufficient speedfrom other manufacturers are hard to find.

The basic interface device is the IMSC011A. This provides a means of interfa-cing it to bus systems and also controls the

Tramsleg

Fig. 1. A node of transputers that leaves four linksfree and is useful for small systems. It can alsoincrease the size of a network if each transputer isreplaced by a n node of them.

Fig. 2. A hypercubic network, which is usedwhere there are rather more transputers. It doesnot, however, leave any spare links, which may bea problem.

more basic i/o pons. The ImsM212Bprovides a more sophisticated inter-face for discs and other peripheralsthat normally need dedicated con-trollers. This is programmed bydownloading a program into its linkon power -up. It then uses a fairlystandard transputer instruction set.

External memory will be needed inall but the simplest applications (anarithmetic processor for your micromight not, and it would be a lotfaster than any other on the mar-ket!). External memory is added by

a simple bus structure. This is multiplexedin almost the same way as the 8086 bus,except that it has 32 -bit data and addres-sing.

Many of the current transputer systemsuse an interface to a bus system, more spe-cifically to an 8086 -type bus. The deve-lopment system supplied by Inmos plugsinto the expansion bus on an ims-compati-ble PC. More recently, another system hasappeared, which is the fastest desktopcomputer ever built. It is also an IBM-COM-patible that can run PC -DOS and os/2 pro-grams. This is not its main application.however, and it relegates its 80836 proces-sor to an unaccustomed back seat!

It is interesting to note how the clocks areprovided. Distributing high -frequencyclocks produces problems of crosstalk andr.f. interference. Consequently, a single 5MHz clock is sent to all transputers,regardless of speed. and an internal reso-nator steps up the clock speed to the17-30 MHz required for the internal ope-ration of the parts.

Transputers do not have an interruptsystem like a more conventional micropro-cessor. Instead, they have an event line. Asingle process inside the transputer can betriggered by the event line at any one time.When the process has started, thetransputer offers a high output on its eventacknowledge line. This then allows theprocess to determine the cause of the eventand to act on it.

Starting a transputer on power -up is diffe-rent from doing it with other microproces-sors. You have a choice of two ways ofdoing it: you can have the BootFromROMline low, in which case the transputer willdownload a program from a link and startup, or you can have BootFromROM high,in which case the transputer will commen-ce executing two bytes before the end ofmemory. This would then contain a back-


41

ward jump to the start of the program inROM.

OccamThe language Occam is the closest Inmosrecommend that you should get to assem-bly language. Generally, Occam state-ments compile almost exactly into machi-ne code instructions, but this is not alwaysthe case. One notable exception is the flo-ating-point operations on transputers with-out a built-in floating-point processor.There is one exception to Inmos's recom-mendation that you should not program inassembly language and this is for compi-lers: they do not advocate languages com-piling into Occam.

The transputer is so completely differentin its parallelism from what has gone be-fore that it is necessary to develop comple-tely new languages to deal with it.Ultimately, languages such as Prolog maybe used, but Prolog has not had longenough to evolve to become really usable,except for some particular types of pro-blem.

AII,SEQ, and PARALT, SEQ, and PAR form the Occam equiva-lent of Pascal's BEGIN and start a statementblock. Statements following them that arein the statement block must be indentedand the block is concluded by having astatement that is outside the indentation.

sEQ is the most easily understood Occamblock statement. It tells the compiler thatthe statements in the block are to be exe-cuted in sequential order. This would seemobvious as far as a conventional computeris concerned, but must be specified withtransputers.

PAR is the equivalent of SEQ but tells thecompiler to excecute all the statements inthe block at the same time if this wouldhelp to improve efficiency. They will notnecessarily be executed at the same time.because if there are not enough transputersto allocate one per statement, one transpu-ter may swap between them as concurrentprocesses.

ALT is a statement peculiar to Occam thatis not really parallel in nature. It has someanalogue in the asynchronous traps thatcan be used on a vAx to restart a processon a particular event occurring, or perhapson the interrupts that can be trapped onmicros, but it goes far beyond either ofthese. What it does is to suspend executionof the current process until one of the sta-tements in the ALT construct can execute

(they will begin by being unable to execu-te because they will all be waiting forsome kind of input, a buffer to empty, theevent line to be asserted, or some othersimilar occurrence). When one can execu-te, it runs, but all the others are abando-ned. It is thus possible to have a processrunning, but not consuming any processortime unless some input occurs that must bedealt with by it. In the mean time, fore-ground tasks may continue as normal.

ChannelsAn Occam channel is the means of com-munication between processes running onthe same transputer, or processes runningon a separate but linked transputer. Theydo not handle routeing across a networkby themselves: this would be handled bythe operating system in a complete trans-puter system.

Channels are declared by the statement:

CHAN OF (type) (channel name):(process)

They are then valid for the process imme-diately following the declaration. To use achannel, one process created by the pro-cess following the declaration (with a PARstatement) would write into the channel. Itwould then be suspended until the valuehad been read out of the channel again byanother process. It could then carry on andpossibly write another value in.Conversely, a process might attempt toread the channel first, and in this instanceit would be suspended until another pro-cess had written a value in it, and it couldthen proceed.

Channels can also work across transputers.In this case, the channel declaration ismade to refer to the link instead of to aword in memory. This is not difficultbecause the links are memory -mappedwithin the transputer chip. Generally, thiswould not be done until run-time: in thiscase, the same program could run on amicro or a supercomputer, and all thatwould be changed would be the number ofprocesses running on any one transputer.

It is possible to ensure that certain proces-ses run on different transputers, for exam-ple to guarantee that a minimum level ofperformance is provided: there is no pointin running a simulation of the aerodyna-mics of a rocket (the type of problem forwhich the Cray -I was developed) on acomputer consisting of a single transputer.If the outermost PAR construct in a pro-gram is replaced by PLACED PAR, each of

the component processes will be run onseparate transputers. It will then be an er-ror if there are more processes than trans-puters.

It must be emphasized that ways of alloca-ting processes to transputers, and commu-nicating between processes and transpu-ters, are very much in the formative stageand, although the hardware is present,there are as yet no established softwaretechniques for it. This is one of the greatproblems with transputers today, andindeed with any parallel processingmachines, but no solutions seem to beforthcoming. Any solution would be infi-nitely preferable to no solution, but theemphasis appears to be on finding a per-fect solution, rather than simply finding ananswer that works, which is what every-one wants!

Variables, loops and proceduresIt seems almost surprising that Occam hasanything as mundane as variables, loopsand procedures, but it does, although theloops are like nothing seen before.

The variables are declared for each pro-cess: they can then be accessed by anysub -process. The declarations take theform:

(type) (variable name): (process)

The permitted types are:

BYTE

INT/INT32

trrr64

REAL32

REAL64

BOOL

TIMER

numbers 0 to 255numbers -80000000 hexto +7FH-H-1-1- hex

numbers -8000 hex to+7FEE hexnumbers-8000000000000000hex to+7H-i-i-i-H-H-i-Htit hex32 -bit lEE real (8 -bitexponent)64 -bit LEE real (11 -bitexponent)Booleanrefers to the real-timeclock on any transputer

An example of a variable declarationwould therefore be:

INT x:

SEQ

Instructions referring to variable XInstructions NOT referring to variable X.

Loops in Occam are arranged by creatinga large array of parallel processes for a


42loop where each iteration is performed atthe same time, or by creating one processat a time for loops where the iterationsmust be done one after another. Examplesof both these loops are easy to find.Suppose you were trying to find a squareroot iteratively: you would then need touse your result from the first time aroundthe loop in the second. You would thus usea sequential loop to ensure that the rightintermediate result was used. If. however,you were plotting a large number of pointson the screen, it would make sense to dothem at the same time. It is worth notingthat sequential loops are slightly faster ifthere is nothing else to choose betweenthem, for example. if there was a choicebetween a sequential loop and a parallelloop where the intermediate results werepassed on via channels. Note that WHILEloops are always sequential for obviousreasons.

Loops are started as follows:

SEQ = 0 FOR nsequential FOR type loop

(statements in loop)(statements NOT in loop)

PART = 0 FOR n

parallel FOR type loop(statements in loop)(statements NOT in loop)

WHILE (condition)sequential WHILE loop

(statements in loop)(statements NOT in loop)

Before we consider procedures, it is worthconsidering how to avoid procedures.Remember that a procedure called onlyonce is basically inefficient and would beincluded only to make the program morereadable. To get around this, the Occameditor provided with the transputer deve-lopment system incorporates a system offolds. This means that the listing you editcan be folded so that you only see the pre-sent level that you are working on. Levelsbelow that (i.e., lower down in a top -downapproach) are replaced by explanatorytext. If you wish to see them for debug-ging. you press a key and move down alevel. It may well be that Occam programstend to be less procedural than other lan-guages.

There will, of course, be times when theuse of a procedure is desirable and Occamprovides procedures for these situations.They are declared by something like:

PROC square (tNT x)x: = x*x

The name is used to call the procedure. forexample:

square (n)

Functions are also provided in Occam.The following factorial calculation willgive some idea of the construction ofOccam as well as of the use of functions.

LNT FUNCTION factorial n)tN pVALOF

SEQ

p : = ISEQ i = 1 FOR n

13:=1)*iRESULT p

Note that a sequential loop was used, notbecause it would be impossible to use aparallel loop, but because the extra over-heads of a parallel loop were not justifiedby the small amount of processing beingcarried out inside it.

Notice that a colon follows the functionand procedure declarations in the sameway as it does variable declarations. Thisis because procedures and functions areregarded as being merely certain variabletypes.

Introducing machine codeAs mentioned earlier, Inmos do notrecommend the use of machine code otherthan for writing compilers. Many peoplehave disregarded their advice, and a macroassembler is now available for the trans-puter development system. Transputerassembly language is no different fromany other: programs will run more quickly.but development time will be far longerand programs may bog down more easilyand become impossible to debug. Unfor-tunately, this happens more easily on thetransputer. Suppose a location in memoryis being corrupted. This type of bug maybe nearly impossible to find in a conventi-onal microprocessor. If hundreds of pro-cesses are going on at the same time whenthe corruption occurs, finding the correctone will be a hopeless task.

Actual machine code programming is be-yond the scope of this article. but it is pos-sible to give some idea of the way thetransputer's instruction set works.Basically. the transputer uses reverse

polish notation, in the same way as Forth.This means that all operations take placeon a stack, and there are instructions toload the stack and save results.

There are three registers in the transputerthat form its arithmetic stack. There is nostack pointer. This means that the stackmay never exceed three words, and it mustnever be allowed to under- or over -flow,since undefined effects will then occur: itis not detected as an error.

The transputer also has a workspace poin-ter that points to the local variables. It al-lows access to all the variables in a typicalsystem because it would be arranged sothat the variables declared at the lowestlevel immediately followed the workspacepointer, followed by the next lowest levelof variables, and so on up to the globalsfurthest from the pointer.

There are also PC and operand registers.The operand register is used to constructliterals and input addresses. This is becau-se all transputer instructions are singlebyte. Consequently, literals will takeseveral instructions: most literals, how-ever, are small and positive or small andnegative. The transputer can produce thesewith a minimum of instructions. Instruct-ions that expect an operand have space fora parameter of 0-15 to be specified. Themost common is LDC, which pushes avalue on to the arithmetic stack. Someexamples are the best way of understan-ding how the literals are coded (the # signmeans hex):

LDC #02: LDC can take a single nibble as aparameter, so this can assemble directly to#42

LDC #12: this becomes PFIX #1 LDC #2,generating it in two stages; the code is#21: #42

LDC #-12: this is negative, so it becomesNFIX #1 LDC #2; the code is #61; #42

If larger positive or negative numbers arerequired, additional prefix instructions areadded. For negative numbers, only oneNFIX is required and the rest can be PFIXinstructions.

There are many other instructions that takean operand in this way. Some of these areshown in Table 2.

The last instruction is very important foraccessing instructions that do not fall intothe one -byte -with -operand category listed


43

Instruction Hex Mnemonic0 OX

1 1X Idip2 2X pfix4 4X ldc6 6X nfix8 8X adcF FX opr

Namejumpload local pointerprefixload constantnegative prefixadd constantoperate

Table 2. Some instructions that take an operand

above. Sixteen instructions are availablewith no operands: #F0 through #FX: lesscommon instructions are then obtained byusing those instructions together with PFIXinstructions. All the instructions may beobtained by the use of not more than onePFIX instruction. The full instruction set isvery complex and only a few extracts willbe given. The floating-point instructionshave not been included and neither havethe basic arithmetic logic operations, sincethese are only necessary if you were towrite in assembler. Instead, I have concen-trated on those instructions that showaspects of the processor which are diffe-rent from established ones. The opcodesquoted in Table 3 must be converted eitherin to a prefix followed by an opr or an opron its own.

The first group of instructions is of interest

Opcode Mnemonic Name

22 ldfirner2B tin4E tali51 taltv, t

07 inOB outOF outwordOE outbyte

OD startp03 endp15 stopp

load timertimer inputtimer alt starttimer alt wait

input messageoutput messageoutput wordoutput byte

start processend processstop process

Table 3. Opcodes grouped according to theinstructions.

because it illustrates the operation of theALT construct described above; when anALT construct contains a reference to thetimer to wait, it will use those instructions.The second group refers to channels thatare used to pass information between pro-cesses. The last group is used to controlthe starting and stopping of processes;stopp is an abnormal end, while endp is

the normal exit from aprocess.

Transputer applicati-onsFor many years thetransputer was a soluti-on looking for a pro-blem, because its usewas not standard andparallelism was hard toimplement and programfor. For some reason it

was never used, and is still not used in anyproduct, simply as a fast RISC chip. Iwould have liked to add to the list ofapplications of transputers by giving onehere, perhaps as a programmable arithme-tic processor for a Pc (Mandelbrot plots in20 seconds!), but unfortunately the highprice tag (£70-£300, depending on speed)and the difficulty of programming themwithout a proper development board pre-vented it.

Some of the existing transputer applicati-ons are very exciting. One of the newest isa graphics workstation, which, althoughnot cheap (£20,000), is far less expensivethan the large mainframe that would havebeen required without the transputer. Itoffers a way of manipulating solid shapes,with shading depending on light direction,containing thousands of individual poly-gons. These can be rotated and zoomed inand out in real time. By contrast, anothercompany produces 3D computer graphicssequences, admittedly on a cinema -sizescreen, with conventional technology: aCray supercomputer that takes about anhour to produce one second of film!

Atari are also producing a transputerworkstation. This will have a price tag ofabout £3,000, depending on the number oftransputers selected. It can have up to 13,which would give it a performance equalto a present-day mainframe costing about£400,000.

The futureThe transputer does seem to be catchingon after a long period of stagnation. Inmosmoved into profit (about £5 million) intheir latest financial year and, if anything,this means that the transputer is here tostay with us!

However, as far as the fairly long-termfuture is concerned, there are already devi-ces likely to outperform the transputer.Intel have announced recently that theyhave succeeded in putting a supercompu-ter style vector processor on to a chip.

Although this may take a long time co-ming and will not be capable of parallelprocessing, it will render the transputerobsolete, because it would be able to out-perform several hundred transputers.Having said that, it may be as well to besceptical: perhaps, because of the con-straints of putting the vector processor ona chip (preventing high-speed logic beingused), it will turn out to have a similarspeed to RISC processors around today orRISC processors that have been developedby the time it is ready.

The transputer itself continues to be deve-loped. of course. The T800 is a fairlyrecent arrival, so that possibly the transpu-ter may have moved another step ahead bythe time the competing devices are readyfor sale.

ReferencesThe two major texts that can be referred toOn the transputer are

Transputer Reference ManualISBN 0 13 929001 XPrentice Hall (£19.95)

and

Transputer Instruction Set -a CompilerWriter's GuidePrentice Hall

There are numerous other technical papersor Inmos documents referred to in theTransputer Reference Manual, but theseare in the main of interest to specialistsonly.

Editor's note.During the final processing stages of thisarticle, Intel announced that later this yearit will release a chip, code -named N10,that can perform 150 million instructionsper second (NitPs). which makes it about10 times faster than the fastest transputeravailable today.All that is known of the NIO at themoment is that it is manufactured in Intel's1µ CHNIOS process, that its one milliontransistor design incorporates integer andfloating-point add and multiply units onthe same die, and that it includes a 4Kbyte instruction cache and an 8 Kbytedata cache.


44

IEE Meetings1-3 May - Command, control, communi-

cations and management information.3 May - Of ships, mips and microchips.4 May - Satellites and the ISDN.12 May - The needs of mature engineers.16 May - Packet video.18 May - Current issues in neural net-

work research.23 May - Managing the design of com-

plex space systems.23-26 May - Acoustics, speech and sig-

nal processing.24 May - Highly elliptical orbit satellite

systems.24 May - Superconductors.24-26 May - UK teletraffic.26 May - Applications of ultrashort pul-

ses for optoelectronics.26 May - The new "Electricity at Work"

Regulations.

Readers are also advised that each year theIEE organizes a range of conferences,vacation schools, technical seminars andworkshops on subjects within the fields ofelectrical, electronic and control engineer-ing. and computing.

The purpose of an IEE conference is toallow those engaged in research. develop-ment, manufacture, application, teachingor training in a specific area to meet otherssimilarly engaged, to discuss develop-ments and improvements in the state-of-the-art.

Vacation schools are designed to provi-de an intensive course of study in a narrowor specific area of electrotechnology forengineers recently graduated or with someyears' experience in an organization follo-wing the completion of engineering educa-tion.

Technical seminars and workshops aredesigned to allow specialists to describetheir recent work to others in a particularrapidly developing field of endeavour.Some workshops contain a large elementof practical 'hands-on' teaching to allowengineers to familiarize themselves withsystem and sub -system usage.

Further information on these. and manyother, events from IEE Savoy Place London WC2R OBL Tel. 01-240 1871.

The 1989 Defence Components &Equipment Exhibition will take placefrom 9 to 11 May at the National Exhibi-tion Centre, Birmingham.

The exhibition focuses attention on thesuppliers of components, sub -systems andservices. The only exhibition of its kind inEurope, its concentration on this vital sec

EVENTS

tor of industry has proved highly success-ful in the past.

Full details from Industrial & TradeFairs Ltd Radcliffe House BlenheimCourt Solihull West MidlandsB91 2BG Telephone 021 705 6707.

World Telecommunication Day, celebra-ted annually on 17 May, commemoratesthe founding of the International Telecom-munication Union in 1865 under the name"International Telegraph Union" by theplenipotentiary representatives of 20 statessignatories of the International TelegraphConvention - the first intergovernmentaltreaty for the regulation of internationaltelegraphy.

Software Futures and OS/2, a seminar,will take place at the Churchill Hotel,London on 3-4 May.

Biotech '89, a conference and productdisplay, will be held at the Tara Hotel,London on 16-18 May.

Software Measurement & Estimation, aseminar, will be held at the ChurchillHotel, London on 18-19 May.

Procurement of Software IntensiveSystems, a conference, will take place atthe Tara Hotel. London on 24-25 May.

Full details of these events may be obtai-ned from Blenheim Online BlenheimHouse Ash Hill Drive Pinner HA5 2AE Telephone 01-868 4466.

Frost & Sullivan are organizing a numberof seminars on Information Technology,Data Communications and Telecommuni-cations. Full information from Frost &Sullivan Sullivan House 4 GrosvenorGardens London SW1W ODH Tel.01-730 3438.

Communications '88 will be held at theNational Exhibition Centre, Birmingham,from 10 to 13 May.Details from Cahners Exhibitions LimitedChatsworth House 59 London Road Twickenham TW1 3SZ Tel. 01-891 5051

The Computers in Manufacturing exhi-bition will be held at Doncaster on 17-18May. The event is organized by Indepen-dent Exhibitions, Tel. (0372) 372842.

Calls for papersThe deadline for papers to be contributedto the Fifth International Conference onMobile Radio and Personal Communi-cations at the University of Warwick on11-14 December 1989 has passed.

An International Conference on Auto-mated Test and Diagnosis will be held atthe Bournemouth International Centrefrom 9 to 12 April 1990. Papers for thi,event are now invited.

The Eighth International Conference onVideo, Audio and Data Recording is tobe held at the University of Birminghamon 23-26 April 1990. A synopsis of about300 words of possible contributing papersshould be sent to the IEE by no later than30 June 1989.

An FEE International Conference onExpert Planning Systems will be held inBrighton from 27 to 29 June 1990. Any-one wishing to offer a contribution shouldsubmit a synopsis of about 1000 wordsbefore 5 May 1989.

The Fourth International Conference onTelevision Measurements will be held inMontreux, Switzerland on 20-22 June1991. Papers will be sought in the fields ofcable television, terrestrial televisionbroadcasting and direct broadcasting bysatellite.

Information on all the above papers shouldbe addressed to Conference Services IEE Savoy Place London WC2R OBLTelephone 01-240 1871 Ext. 222.

WE ARE MOVING!

Please note that from3 May 1989

our address will beElektor Electronics

(Publishing)Down House

Broomhill RoadLONDON SW18 4JQ

Telephone 01-877 1688Telex 917003 (LPC G)

Fax 01-874 9153


45

DUAL -TONE MULTI -FREQUENCYDECODER

source: Teltone Corporationdesign: Robert Krijgsman PE1CHY

The dual -tone multi -frequency (DTMF) dialling scheme fortelephone networks was originally developed by Bell

Laboratories and introduced in the United States in the mid -1960sas an alternative to pulse dialling. Offering increased speed,

improved reliability, and the convenience of end -to -endsignalling, DTMF has since been adopted as standard and

recommended for use by telecommunications organizationssuch as CCITT, CEPT, NTTPC, and others around the world.

The versatile DTMF decoder described here is a state -of -the artdesign based on Teltone's single -chip DTMF receiver Type M957.

The DTMF system has been designed toconvey dialling information from a sub-scriber to his local exchange. Since theDTMF keypad is not disabled during thecall, the tones may also be sent after thecall has been answered. This makespossible a number of interesting applica-tions related to remote signalling andcontrolling via the telephone network.Sending DTMF signals is simple with apush-button type telephone, althoughcredit-card like tone senders are avail-able for the older, rotary dialling, tele-phone sets. After dialling, the miniatureloudspeaker in the card is simply held infront of the microphone in the receiver,so that DTMF signals are transmitted tothe called subscriber.Most local telephone exchanges acceptcalls from both DTMF and pulse -diall-ing telephones. Especially in areas withrelatively few subscribers, however, the

local exchange may be compatible withpulse -dialling only. Fortunately, thisdoes not make DTMF-based signallingto the called subscriber impossible be-cause the signals can be sent after estab-lishing the connection by means ofpulse -dialling. Special dual -mode tele-phone sets are available for this purpose:after pulse -dialling. the DTMF keypad isenabled for sending control signals tothe called party.

Background to DTMFWhen pressed, each of the 16 keys on theDTMF keypad generates a signal com-posed of one frequency from a high -fre-quency group, and one frequency from alow -frequency group. The high and lowfrequency groups are arranged in rowsand columns as shown in Fig. 1. Press-ing key number 5, for instance, causes

the telephone set to transmit two tonessimultaneously: one of 770 Hz (row;low -frequency group) and one of1336 Hz (column; high -frequencygroup). This 16 -digit scheme is oftenreduced to 12 -digit because signals inthe 1633 Hz column are reserved forspecial non -dialling purposes. Manytelephone sets in Europe do not havekeys A, B, C and D. The DTMF decoderdescribed here supports all 16 codes,however.The two frequencies that form a DTMFsignal are carefully selected for non -har-monic relationship (that is, incidentally,the reason why they sound so ugly).

Signal level considerationsTo ensure reasonable communicationquality for all subscribers, telephoneauthorities like British Telecom have

Column

es

;)

697 2 3 A

770 4 5 6 B

Row

852 7 8 9 C

941 0 D

I equencies in H )

890060-11

Fig. I. A DTMF signal is composed of twofrequencies selected by pressing a single keyon the telephone set.


46

Oda(1.000V) -

-&IB(0.398V)-

signal-level

-18dB(0.126V)

-2Ed B10.050V1

calling slation

localline

trunkline

localline

called station85.0050 - 12

Fig. 2. Graph showing typical attenuation of a signal carried over the telephone network(courtesy Teltone Corp.).

drawn up specifications for the maxi-mum signal levels within a particularfrequency spectrum transmitted by atelephone set. The same applies to thetermination and source impedance,which must be 600 LI in most countries.A standard telephone set has a transmitlevel of -11 dBm or 220 mV. for tonesfrom the low -frequency group, and-9 dBm (275 mV.) for tones from thelow -frequency group (0 dBm equals1 mW into 600 a). This simple way ofachieving pre -emphasis is required tocompensate the high -frequency attenua-tion introduced by the telephone linesand the amplifiers. A tolerance of 2 dBmis allowed on both transmit levels, whichare defined for a nominal termination

impedance of 600 LiLosses inevitably occur as signals arecarried from a transmitter to a receivervia the telephone network. Figure 2shows an example of how telephonelines reduce the effective level of thesignal as it is carried from the calling tothe called subscriber. From this it will beclear that any DTMF decoder must beable to handle a wide range of inputamplitudes. The DTMF decoder de-scribed further on in this article meetsthis requirement by handling signalsdown to -40 dBm correctly.Signal attenuation is. unfortunately, notthe only problem DTMF receivers haveto cope with. Background noise. pulseinterference and. of course, voice sig-

nals may be present on the line as shownin the example spectrum of Fig. 3. Be-cause all these signals may contain to.iefrequencies similar to those representingDTMF digits, high noise immunity andgood selectivity are prime design aimsfor any DTMF receiver.

Teltone's M957 DTMFdecoderThe Type M957 is one of a family ofDTMF encoder/decoders and relatedproducts manufactured by Teltone. Theinternal schematic of the M957 is shownin Fig. 4. When connected to a telephoneline, radio receiver, or other DTMF sig-nal source, the receiver filters out mains -

induced noise, dial tones from theexchange, random noise and other inter-ference. It then separates the compositeDTMF signal into its high- and low -fre-quency group components, amplifiesand limits these, and digitally measureszero -crossings over averaging periods toachieve digit decoding. With 4 outputbits. 16 binary combinations are avail-able, representing codes 1 through 16 or0 through F hexadecimal.The only external components requiredto put the M957 to work are an inexpens-ive NTSC quartz crystal (3.579 MHz),one resistor and two capacitors. The chiphas a sensitive analogue input with aremarkably wide drive margin. Thestrobe output indicates validity of thedata on the 4 digital outputs. The OE(output enable) input allows switchingthe digital outputs to high -impedance.The strobe output and the OE input makeinterfacing the decoder to a micropro-

18 c333Hz

VAUD LEVELS AHDFREOUEUCIES FOR DIUF

665 Hz !659A - 22 cS

*0 Hz 460 Hz

SIGNALLEVEL(dBm)

LOWGPO uf, GRO

A ,6

TOLERABLE LEVEL FORINTERFERING S-Gt.IALS

A aB

340+3 Hz

Fig. 3. High noise immunity is a prime design consideration for any dual -tone multi -frequent} I DTNIF) decoder (courtesey Teltone Corp.)


cessor port or bus simple. The logic le-vels applied to inputs A and B of theM957 define the sensitivity of the anal-ogue input amplifier (see Table I).

Table I.

Input sensitivity at Ub=5 V

A B min. typ. max. unit

0 0 -32 -2 dBm1 0 -35 - -5 dBm0 1 -38 - -8 dBm1 1 - -40 dBm

Circuit descriptionThe circuit of the DTMF decoder withdigital output interface is shown inFig. 5. The decoder works automat-ically: it waits for ring pulses, acceptsthe incoming call, and then checks thetelephone line for valid DTMF signals.The DTMF code sent by the calling sub-scriber is shown on a 7 -segment LEDdisplay and made available in binaryform on a 4 -bit output.

Capacitors CI, C5 and C6 block the directvoltage of about 50 V on the telephoneline. Resistor R9 does not pass currentbecause relay contact ret is still open.When the subscriber is called, the ringvoltage of about 75 Vpp/25 Hz causes acurrent through CI, RI and the LED inopto-coupler IC7. The phototransistor inthe opto-coupler conducts and causes C2to be charged slowly via R2. Two or threering pulses are required to fully chargeC2. Schmitt -trigger inverters ICI. andICI, then toggle, so that monostable IC2is started via D2. Relay Ryi is energized,LED D5 lights, and relay contact ryi isclosed so that R9 terminates the tele-phone line: the call is answered.Meanwhile. C2 is discharged via Q (IC2)and D4 to restore the stand-by conditionof the ring detection circuit. The callingparty can now start sending DTMFcodes. When these are received andfound valid by the M957, the strobe out-put, pin 18, goes low briefly, and thedecoded digit is fed to the digital outputsand to display driver ICs (remember thatthe digital signal swing is determined bythe supply voltage of the decoder chip).The received DTMF digit (0-F) is indi-cated on a high -brilliance 7 -segment dis-play.Monostable IC! keeps the line relay en-ergized because it receives a new triggerpulse from the strobe output via D3. Therelay is de -energized when IC! is nottriggered within 10 s from the lastDTMF code.Switch Si is included to prevent theDTMF decoder automatically acceptingincoming calls. The switch thus allowsELEKTOR ELECTRONICS MAY 1989

SIGNAL -

DIAL TONEREJECTION

HIGH GRG.:

LOW GROt

-F

Fig. 4. Internal structure of the M957 single -chip DTMF decoder from Teltone. The anal-ogue signal is converted to a digital code by means of a digital zero -crossing detector (courtesyTeltone Corp.).

Fig. S. Circuit diagram of the DTMF decoder with an auto -answering function and digitaloutputs for remote control applications.

48

Fig. 6. Track layout and component mounting plan.

the circuit to be disabled without havingto unplug its input cord from the tele-phone socket.

ConstructionThe printed -circuit board shown inFig. 6 greatly facilitates the constructionof the DTMF decoder. All the parts aresimply fitted in accordance with theoverlay on the board and the Parts List.The decoder is conveniently poweredfrom a 12 VAC/250 mA mains adaptor.Voltage regulator 106 must be fitted witha small TO -220 style heat -sink. Alterna-tively, it may be bolted to the enclosurepanel with an insulating washer in be-tween. Capacitors C5 and C6 must havethe specified voltage rating of1500 VDC to prevent any chance of an

C4=4µ7; 63 V; radial Universal SemiconductorParts list Gs;C6=1n0 1500 V Devices Ltd.)

C7=10nCige.-33p Miscellaneous:

Resistors (±5%): Cii101).; 16 V Si= miniature SPSTRi=2K2 Cii=1000g; 25 V switch.R2=100K Rei= 12 V PCB -mountFt3;Fls;REI;f117,-1M0 Semiconductors: relay; eg. SiemensR4=100K Di=1N4007 V23037 -A0002 -A101.R5=4M7 D2;133;134;Dic1 N4148 Xi= quartz crystal 3.579Ri=33K Ds= red LED MHz (Cricklewood Electro-R.27OR Os...Ds incl.=1N4002 nics Ltd).Rio;Rii;Riz=470K Ti=BC547B LDi= HD1107-0 (Sie-Ris;Ria;Ri6=47K C1=4093 mens; ElectroValue).

56K C2=4047 TO -220 style heat -sink forR18...R24 incl.=1K0 Ca=CA3140 ICs.

C4=M957 (Teltone) PCB Type 890060 (seeCapacitors: C5=4511 Readers Services page).Ci ;C3;Ciz;C13;Cia-=100n Cs=7812C2=4}17; 63 V; axial C7=CNY21 (listed by


49

Fig. 7. The completed DTMF decoder is a compact and reliable unit. The 4 -bit strokedoutput simplifies interfacing to a wide range of digital equipment, including PCs and oilierhome computers.

external voltage being applied to thetelephone line. Along the same lines, thestated optocoupler meets the require-ments for minimum insulating voltage.Digital output signals A-D and thestrobe signal are available on a 10 -waypin header and may be used for drivinga digital circuit via a short flat -ribboncable. An external level shifter such asthe Type 4050 is required to obtain TTL-compatible pulses. It is, however, alsopossible to feed the decoder from a 5 Vsupply, obviating the need for a levelshifter.

ApplicationsThe DTMF decoder provides reliablecode transmission via many media,whether telephone lines, local controlnetworks, industrial wiring systems. orradio equipment. Computer owners mayring up their own system at home andturn the mains to the machine on with aparticular DTMF code that controls arelay. The AUTOEXEC.BAT file maythen start a particular programme, whosecourse is determined by bit -combina-tions supplied by the DTMF decoder.One code must be reserved, however, toshut the system down.Remote control of coffee machines, cas-sette and video tape recorders and otherequipment is also possible by reservingtwo codes to turn each device on and off.The LED display always shows the lastreceived code.The remote control system can be eivensome security by fitting non-standard.but matching, quartz crystals in theDTMF sender and decoder. In the proto-ELEKTOR ELECTRONICS MAY 1989

type, PAL crystals (4.433 MHz) fitted ina DTMF sender and the decoder de-scribed here resulted in acceptable rejec-tion of the standard (3.579 MHzderived) tones.Other applications of the DTMF decoderinclude selective calling for mobileradios and tape control for slide presen-tations.

Source: Teltone Application GuideSC1: Applications far DTMF and pulse

dialing access and control.

Teltone Corporation P.O. Box 657 10801 120th Ave. N.E. Kirkland WA USA 98033-0657. Telephone: (206)827-9626.

Teltone Corporation 7A Hill Avenue AMERSHAM HP6 5BD. Telephone:(0494) 728099.

UK distributor is Chesilvale Ltd. 10Woodland Road CLIFTON BS8 IHQ.Telephone: (0272) 736166. Fax: (0272)736516.

Note: the DTMF decoder described hereis not type -approved by British Telecomand may not be connected to the publicswitched telephone network (PSTN). Incountries other than the UK, the relevantPTT authorities should be contacted forinformation on type -approval.

50

APPLICATION NOTES

The contents of this article are based on information obtained from manufacturers in theelectronics industry, or their representatives, and do not imply practical experience by

Elektor Electronics or its consultants.

GET OFF THE BUS WITH TAXICHIPTM DEVICESThe Am7968 TAXIchipTm transmitter and Am7969 TAXIchip receiver

chip set from Advanced Micro Devices is a general-purposeinterface for very high-speed (4-12.5 Mbytes/s) point-to-point

communications over coaxial or fibre -optic media.

In the past, high-speed datatransfers required the use ofparallel buses. Sending lots ofbits simultaneously was fasterthan sending them one -bit -at -a -time. But this solution wasmessy: multiple data pathsadded cost and bulk to a sys-tem. Performance issuescropped up, too. Parallel buseswere only practical over rela-tively short distances; trans-mission speed was limited bycross -talk and radio inter-ference (RFI) considerations.Also, reliability suffered as thenumber of wires and connectorpins increased.

Advanced Micro Devices(AMD) has developed TAXI-chipTm (Transparent Asyn-chronous Xmitter-receiver/nterface) devices that provide

IIIinisgmasi".%Weeeeees%

ADVANCED Z1CALL AaTHDAntittDA/A PAM 31AfAits

100,14A.ALtam

TAXI CO.

the performance of multiple -path design without all the drawbacks.Serial communication links are easy

with the high-speed Am7968/Am7969chip set. These ICs enable communica-

lion engineers and designers toreplace parallel buses with aserial link, while maintainingthe performance of the old par-allel system. The bulk, weightand cost of parallel ribbon ca-bles and associated connectorsare eliminated without reducingdata throughput and withoutchanging the system architec-ture.

Speed up datacommunications...The 100 NIbps effective datathroughput rate of the TAXI -chip set is 10 times faster thanthe data rate of conventionalRS -422 line drivers and recei-vers - the fastest point-to-po ink communications standardin existence today.The versatility of theAm7968/Am7969 chip set

allows top performance to be achievedwith lower hardware cost and minimal

GET OFF THE BUS WITH TAXIchip DEVICES

32-B1 .410TA'fret,

A -z1

TrnmgLOVC

32 -at Mainframe 850101 - 12

TAXI:ftoRe:eye/

High Speed Pnme


be programmed to select one of three bitmodes of operation:

a

o'

Tama:*

890101 - 13

The TAXIchip set offers a data throughputrate higher than any of the currently usedinterface standards.

8 data and 4 command bits;9 data and 3 command bits;10 data and 2 command bits.

For wider parallel inputs, TAX Is can becascaded to squeeze multiple -bytewords into a single serial link. Flexiblebyte -width and the option to cascadeTAXI chips give freedom to move amaximum amount of data with a mini-mum number of components.

The TAXIchip transmitterThe AM7968 transmitter has 12 parallelinputs, segregated into data and com-mand lines. Normal message traffic issent over data lines. Supervisory control

DATA COLIIJAtiD

I I/Fib*, doaz°Pik CableLink

Am7968Transmitter

DATA COLILIAND

890101 - 14

Typical basic applications of the TAXIchipset from AMD.

RFI effects. Coaxial cable can be can bedriven direct by TAXIchip products, andis the lowest -cost media for short -to-moderate distances. Optical Data Links(ODL) are also simple to interface to thechip set, affording all the advantages offibre -optic communication. These bene-fits include long-distance coverage, im-munity to Electromagnetic Interference(EMI) and RFI, wide bandwidth andelectrical insulation.

...and increasecommunications distanceAs Am7968/Am7969-based designscommunicate over a serial link, distan-ces are not limited by the same con-straints that plague parallel buses.Cross -talk and bit -to -bit skew are notproblems with TAXI -based connections.And since the Am7968 and Am7969were designed specifically to interfacewith high-speed optical data links, fibreoptic cable may be used to cover distan-ces up to several miles.

Accommodates all bus widthsThe Am7968 TAXIchip transmitter andAm7969 TAXIchip receiver form a flex-ible interface solution for high-speedpoint-to-point data communications.The TAXIchip set operates much like asingle parallel register. Data is loadedinto one side and read from the other,which is separated by a long serial link.TAXIS have 12 parallel interface pinsdesignated as either Data or Commandbits. Data represents the normal messagetraffic between host systems. Com-mands may originate from the communi-cation control section of a host; theyoccur at a relatively infrequent rate buthave priority over data. Each TAXI can

TAXIchip devices

10 times faster than conventional RS -422Data throughput up to 100 Mbps (12.5Mbytes/sec)Direct drive of coaxial cables, or interfacewith fibre -optic linksProgrammable byte widthTwo priority levels for information trans-ferCascadable, for buses 16, 32 or more bitswideComplete on -chip PLL and crystal oscil-latorSimple strobe/acknowledge handshakeStraight -forward TTL parallel bus inter-faceSingle +5 V supply

information is handled by commandlines. The DATA MODE SELECT pin maybe tied low, high or left open to deter-mine the mix of data and command pins.The transmitter sends data if all of thecommand lines are logic 0 when the de-vice is strobed; command information issent if any of the command lines arelogic 1 when the transmitter is strobed.

Parallel information is captured in theinput latch on the rising edge of a strobepulse. An acknowledge signal is thensent back from the transmitter when it isready to accept the next byte. Informa-tion is transferred to the encoder latchfirst and then through the data encoderand into the shift register, on two suc-cessive byte clocks. Encoded patternsthen come out of the shifter and through

Strobe

Ack

X1

StrobeAcknowledge

ti

X2Clock 4---ta

Data ModeSelect

SerialInput

Oscillatorand

Clock Gen.

Data Command

4Input Latch

4,Encoder Latch

Serial Interface

Data Encoder

Shifter

Cascade Local Select

MediaInterlace

Internal block schematic of the Am7968 TAXIchip transmitter

-*Serial Out-*Serial Out -

890101 - 15


the media interface one bit at a time.Voids between transmitted data or com-mand bytes are filled with special syncpatterns which keep the Am7969 PLLsynchronized, and define byte boun-daries. As data does not have to be sentevery byte cycle, parallel data through-put in bytes/s can be slower than theminimum specified transmission rate(40 MHz: 32 Mbps) would seem to indi-cate.

The data rate is set indirectly by an ex-ternal quartz crystal which oscillates atthe byte rate. An internal PLL multipliesthe byte rate by 10, 11 or 12 (dependingon whether the TAXIs are programmedto be in 8. 9 or 10 -bit mode) to arrive atthe serial transmission rate. TAXIs use4B/5B and/or 5B/6B encoding schemes,essentially expanding each byte by two

Serial In

Serial In -Media

Interface

Violation

Shifter

Decoder Latch

Data Decoder

Oscillatorand

Clock Gen.

a

PLLClock Gen.

xi

X2

Output Latch4

Data Command

tByte Sync

Logic

Internal block schematic of the Am7969 TAXIchip receiver.

Data ModeSelect

Catch NextByteI GotMine

-4. Clock

DataStrobe

Command-1" Strobe

890101 16

bits.

The SERIAL INPUT pin allows transmit-ters to be wired in parallel to funnel verywide data paths into one high-speedchannel.

The TAXIchip receiverDuring reception, the Am7969 acceptsmessage patterns into its shifter. In thenext byte clock -cycle, the pattern is par-allel -loaded into the decoder latch. Oneclock cycle later, the pattern is passedthrough the data decoder, recognized aseither data or command, and captured bythe appropriate output latch. A new dataor command byte is then issued from thelatch and accompanied by a data or com-mand strobe. The byte -rate clock is alsoextracted from the incoming patternsand provided for use by the receivingsystem.

If any of the received patterns have beencorrupted into invalid 4B/5B or 5B/6B

codes, then the VIOLATION pin willidentify the coding violation.

Handshaking signals CATCH NEXT BYTEand I GOT MINE are handshaking signalswhich allow receivers to be cascaded.

High-speed datacommunication design madeeasy

The TAXIchip set directly drives coax-ial cable to achieve very fast and cost-ef-fective point-to-point communication.Or, fibre -optic cable and ODLs may beused if higher speed, longer distance. orelectrical insulation is required.Fibre -optic data communication is com-ing of age. High bandwidth and low sig-nal attenuation are attractivecharacteristics of fibre -optic cable. Op-tical data transmission also offers noiseimmunity, minimizes RFI emission.eliminates ground loops and providesdata security. Component costs are fall -

890101 - 17

The only additional hardware needed to connect the TAXIchip set to an optical fibre networkare a fibre -optic data link and a simple resistance network, which supplies bias voltage andterminates the transmission line.

ing to a point where these advantages arequickly becoming cost-effective for awide range of applications.

Cascadable for wider datapathsMultiple TAXIchip sets can be wired inparallel to share a single serial channel.This allows 16- or 32 -bit wide buses tobe replaced by a single wire, substan-tially cutting interconnection cost in sys-tems with many communications pathsor lone cable runs.

The Am7968 can be set to local or cas-cade mode by tying a single pin, CAS-CADE/LOCAL SELECT, high or low. Localmode allows a single transmitter to sendmessages over a serial channel. Addi-tional transmitters can share this chan-nel, running in parallel with the primaryAm7968, if they are put in cascademode. All cascaded transmitters simul-taneously latch a parallel word from thedata or command inputs upon seeing acommon strobe pulse. Each byte of thisword is individually encoded and thenshifted one bit at a time, through thechain of transmitters and on to themedia. Since the entire word passesthrough the primary transmitter, themaximum transmission rate of this con-figuration is still 125 MHz, with a maxi-mum data throughput of 100 Mbps.The Am7969 has two pins. CATCH NEXTBYTE and 1 GOT MINE, which can be con-figured to allow TAXIchip receivers tooperate singly or in parallel. These hand-shake signals tell each Am7969 when tocapture its respective byte from themedia, so that multiple -byte words canbe reconstructed correctly on the receiv-ing end of a communications channel.These wiring options allow TAXI -based


r

Am7968

PLCC DIP.

CO,

0.0

LOC,

art

CO,

Am7969

PLCC

communication channels to be struc-tured in a number of ways. For example,one transmitter can broadcast a messageto several receivers, multiple TAXIchippairs can be cascaded to share a serialchannel. or, for the fastest data through-put, multiple Am7968 and Am7969TAXIchip pairs can operate in parallel,each pair using a separate serial link.

Simple parallel interfaceTAX1's bus interface lines operate muchlike those of an ordinary register. Asimple strobe/acknowledge handshakeis used to latch parallel information intothe Am7968 TAXI transmitter. Data isthen automatically - transparently -

encoded, serialized, de -serialized.decoded, and issued from the Am7969TAXIchip receiver with an accompa-nying strobe pulse. In a system. thesetwo chips act much like a single latch orregister.

Integrated 125 MHz phaselocked loopAm7969 TAXIchip receivers areclaimed to have the fastest commerciallyavailable integrated circuit. Using so-called Current Mode Logic technology.the PLL operates over a frequency rangeof 40 to 125 MHz, and will track datawith jitter of up to 40c'e of a bit time. ThePLL requires only a single capacitor

Am7968/7969 TAXI Chip SetTransparent Asynchronous Transmitter/Receiver Interfa

FiberOptic orLink

DataLink

Receiver

Parallel Data

Am7968Transmitter

Am7969Receiver

Parallel Data

with ±10% tolerance to be made oper-ational.

Group encoding andidentification of code violation4B/5B and 5B/6B encoding schemes areused to combine clock and data into asingle bit -stream and ensure that dataintegrity is maintained. These encodingmethods essentially expand each byte bytwo bits. The resulting patterns are rela-tively free of DC bias and can passthrough a standard AC -coupling circuitwith minimal distortion.

Since these coding methods are so effi-cient, bandwidth requirements for theserial link are held to a minimum. The4B/5B code uses a 125 MHz signal totransfer data at a rate of 100 Mbps. Thepopular Manchester encoding/decodingscheme would require a 200 MHz signalto achieve the same 100 Mbps datathroughput.

The Am7969 detects most noise -inducedtransmission errors. Invalid 4B/5B cod-ing patterns are recognized and identi-fied on a special VIOLATION output pin.

TAXIchipm, is a trademark of AdvancedMicro Devices, Inc.

Further information on theAm7968/Am7969 may be obtained fromAdvanced Micro Devices P.O. Box3453 Sunnyvale CA 95088 USA.

AMD UK can be contacted at (0925)828008 (Manchester area) or (04862)22121 (London area).

ELEKIOR ELECTRONICS MAY 1989

54

CODE CONVERTOR FORCENTRONICS-COMPATIBLE

PRINTERS

This simple EPROM -basedconverter solves awkward

interfacing problemsraised by incompatibilityof the character codes

used by certain computerprograms and thoseactually available in

parallel printers.

Very few problems can be expected toarise when a computer sends nothing butstraight ASCII to a Centronics -com-patible printer. Not so with many specialsigns, diacriticals and Greek characters.however, which many printers haveavailable but never seem to get rightuntil lots of DIP switches have beenreset. and the printer is found to run in amode entirely different from thatdesired.Fortunately. today's wordprocessorsprovide configurable printer drivers thatobviate the use of copied ASCII codetables and overviews of DIP switch con-figurations. Such a printer driver is,however. not available with many otherprograms, such as assemblers, interpre-ters. compilers (BASIC. PASCAL).CAD/CAM programs ( netlisting!) and anumber of databases. Users of these pro-grams are often faced with real difficul-ties when characters beyond thealphabet. numbers 0 to 9. and the basicset of arithmetic operators are to be usedon an otherwise perfectly functioningprinter. Not surprisingly, the first hard -copy produced on the fly looks far worsethan that of the wordprocessor.

The above deficiency is. in general. sim-pler to overcome with hardware thanwith software, which, in view of the re-quired speed, must needs rely on ma-chine code and code conversion tables.In many cases. code -converting hard-ware is available from printer manufac-turers in the form of a ROM claimed tomake the printer compatible with a par-ticular type of computer. The main dis-advantages of such a chip are first andforemost that it is often relatively ex-pensive. and secondly that it is difficultto remove and replace when, occasion-ally. another computer is used.A fair compromise between printerdriver software and the printer -resident

by N. \Villmann

R1I R21R3IR41

05V

9 0 9

K1

MOn

2

10p63V

DO

02

3 D1O4 D2

O 5 D3

6 D4

7 05o -8 D6O9 D7

0

S1B 7 6 5

0 011 2 3 4

11

12O13O14O15O16O17

18019

20021

22O23

24

25026

O27O28

29

32

33

sib

0

9

7

6

5

3

25

24

21

23

28

AOVpp

Al

A2

A3 D2

A4 ICI D3

A5 2716 D42732

A62764

A7 D6

AS D7

A9

A10

AllAl2 GND CS

26 27PGM

OE

DO

D1

K2

2

11 DO 2

12 D1 3

13 D2 4

15 D3 5

16 D4 6

17 D5 7

18 136 8

19 D7 9

ack

2 14 20

10

busy 11

O

paper end 12

select 13

auto feed 14O

15

gnd 16

5V 17

18

error

19-o

20

21

22

23

24

25

26-o

27

280

29

32gnd 33

890058 - 11

Fig. 1. Circuit diagram of the code convertor for Centronics -compatible printers.

ELEKTOR ELECTRONICS MM 1989

Table 1.

address data

x00...x0F 00 01 02 03 04 05 06 07 08 09 OA OB OC OD OE OFx10...x1F 10 11 12 13 14 15 16 17 18 19 1A 1B 10 1D 1E 1Fx20...x2F 20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2Fx30...x3F 30 31 32 33 34 35 36 37 38 39 3A 3B 3C 3D 3E 3Fx40...x4F 40 41 42 43 44 45 46 47 48 49 4A 4B 4C 4D 4E 4Fx50...x5F 50 51 52 53 54 55 56 57 58 59 5A 5B 5C 5D 5E 5Fx60...x6F 60 61 62 63 64 65 66 67 68 69 6A 6B 6C 6D 6E 6Fx70...x7F 70 71 72 73 74 75 76 77 78 79 7A 7B 7C 7D 7E 7Fx80...x8F 80 81 82 83 84 85 86 87 88 89 8A 8B 8C 80 8E 8Fx90...x9F 90 91 92 93 94 95 96 97 98 99 9A 9B 9C 9D 9E 9FxAO...xAF AO Al A2 A3 A4 A5 A6 A7 A8 A9 AA AB AC AD AE AFxBO...xBF BO B1 B2 B3 B4 B5 136 B7 B8 B9 BA BB BC BD BE BFxCO...xCF CO Cl C2 C3 C4 C5 C6 C7 C8 C9 CA CB CC CD CE CFxDO...xDF DO D1 D2 D3 D4 D5 D6 D7 D8 D9 DA DB DC DD DE DFxEO...xEF E0 E1 E2 E3 E4 E5 E6 E7 E8 E9 EA EB EC ED EE EFxFO...xFF FO Fl F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF

ROM is offered by the circuit of Fig. 1.This code converter is EPROM -basedand allows any printer code to be re-placed by another. Due care should betaken, however, to avoid the conversionof codes related to printer control com-mands (escape sequences).

Circuit descriptionThe circuit works on a simple basis. The

databyte received from the computer'sCentronics port is used to address anEPROM programmed to hold the desiredprinter codes. The EPROM thus containsa list with 256 (0-255) entries that sup-ply a particular printer code for eachcomputer code applied. The EPROMmay contain several such lists, which areselected by switch Si. The maximumnumber of lists is determined by theEPROM used: a 2 Kbyte Type 2716 may

Fig. 2. The contact fingers at the PCB edges can be inserted between the two rows of pinson the Centronics connectors.

hold up to 8 lists, while the larger Types2732 (8 KByte) and 2764 (16 KByte)have capacity for 16 lists (the 2764 thenhas further free memory, which is notused here). The choice of the EPROMfor the present project is mainly gov-erned by availability and price (the 2764is probably the cheapest these days).

The larger part of the circuit is formedby direct connections that carry theprinter control and handshaking signalsbetween the input connector. Ki. and theoutput connector. K2. Only the 8 da-talines are 'broken' and applied to the 8least -significant address lines. Aothrough A7, of EPROM ICI. The STB(strobe) line is tapped to drive the OE(output enable) pin on the EPROM. Thisis done to ensure that the data on the8 output lines is stable when it is loadedby the printer.The interface is powered from the +5 Voutput available at pin 18 of the printer.It should be noted that not all printershave such an output, which may, there-fore, have to be provided by the user.Alternatively, the code convertor may bepowered from a small, regulated, 5 V

Parts list

Resistors (%):

Capacitors:Ci=100nC2=1011; 63 V

Semiconductor:IC1=2764 (see text)

Miscellaneous:Si= 4 -way DIP switch block.Ki= female 36 -way Centronics connectorwith straight pins.K2= male 36 -way Centronics connector withstraight pins.PCB Type 890058 (not available throughthe Readers Services).


56

source. The 5 V supply rail of the circuitis made available on Ki so that it maypower further equipment, such as aprinter buffer.

Conversion listThe data given in Table 1 may appearuseless at first sight because it leavesapplied data unchanged. The table ispurposely compiled as it is. however, fortwo reasons.First, it is the list used in the lowestaddress range of the EPROM (list num-ber 1, EPROM address range 0000H-OOFFH or OD -225D). Because the tabledoes not alter the computer codes, itguarantees correct operation of theprinter when this is used in graphicsmode.Secondly, the given data forms the start-ing point for the building of other lists inthe EPROM. Copies of the default listare then ready for editing. i.e.. enteringone's own codes, on paper. To do this.simply look up databyte at the addressthat corresponds to each code you wantto change, eradicate the given databyte,and replace it with the required code.Now load or type the new list into yourEPROM programmer, starting atEPROM address 0100n or 256o (listnumber 2). The other tables, when re-quired, are built and loaded in a similarmanner. Do not forget to document thesettings of S for the available conver-

sion tables.

ConstructionThe printed -circuit board shown inFig. 2 is designed such that pins 1

through 18 of Centronics -style connec-tors Ki and K2 can be soldered direct onto the contact fingers at the edges. The

other row of pins, 19 through 36, iswired in accordance with the overlay onthe board. DIP switch block Si may bemounted at the copper or componentside of the board, whichever location ismost convenient for easy accessing oncethe completed board has been installedin an enclosure.

NEWS

Award for young radioamateur of the yearThe Department of Trade and Industry(DTI) recently announced its sponsor-ship of the Young Amateur of the YearAward for 1989's outstanding achieve-ment by a young amateur radio en-thusiast.Anyone who is under 18 and: is keen on do-it-yourself radio con-

struction; or is interested in using radio and gain-

ing operating skills; or is using radio for a community ser-

vice, such as helping the disabled orin emergency communication net-works; or

is good at encouraging interest inamateur radio; or

is involved in amateur radio in anyway, such as in a school scientificproject

is eligible for the 1989 Award and its£250 prize.The prize for the most outstandingachievement between 1 April 1988 and31 July 1989 will be awarded by the DTIand presented at the Radio Society ofGreat Britain's HF Convention in Oc-tober 1989.

On top of the £250 prize, DTI will pro-vide every genuine entrant with a copy ofits coloured chart of radio frequencyallocations in the UK. The winner willalso get to see DTI's radio experts atwork at its Radio Monitoring Station atBaldock in Hertfordshire.Last year's Award went to 15 -year -oldAndrew Keeble, from Norwich, for hisenthusiasm in encouraging others' in-terest in radio, his radio constructionskills, and voluntary activities. He waspresented with his prize by HRH PrincePhilip who is patron of the RSGB. An-drew also saw the work of the BaldockStation, and in addition got some sur-prise awards which were: a one -weektraining course at the College of MarineElectronics, sponsored by the MobileRadio Users' Association; an engravedRC14 receiver given by the RSGB; and aweek in Vienna as guest of the OVSV, theAustrian national radio society.

How to enter the competionClosing date for applications is 31 July1989. Entrants do not need to be a radiolicence holder to enter, and the competi-tion is open to anyone in the UK, theChannel Islands, or the Isle of Man,who is under 18 on 31 July.Young people may either enter directly,or an adult may nominate a candidate

for the Award on the strength of theadult's knowledge of the entrant. In thecase of the candidate making his ownentry, it should be supported by a shortletter from a licenced radio amateur orother adult who knows him or her welland vouching for these achievements.Entries should be reasonably full andgive a clear picture of the can-didate's achievements. Enough detailshould be given to allow an assessmentto be made of their quality.Candidates should submit somebackground information on themselveswith their entry, e.g., their other hob-bies, especially if amateur radio is in-volved, their school achievements and, ifknown, their career intentions.

Applications or nominations for theAward must be sent to:

The Secretary Radio Society of GreatBritain Lambda House CranborneRoad Potters Bar HertfordshireEN6 3JE. Telephone: (0707) 59015.


SUPER-VHS-TO-RGB-CONERTERdesign: ELV GmbH

Almost any radio and TV salesman will confidently tell you thatthe excellent picture quality from a S -(super) VHS video cassetterecorder can only come into its own on a new, compatible, TV

set with separate luminance and chrominance inputs.Unfortunately, these TV sets are still relatively rare and also quite

expensive. The SV7000 converter presented here is acost-effective alternative to a new TV set. This is because it

provides a function not available on most S -VHS VCRs:conversion of the luminance and chrominance signals into RGB

signals that can be applied to a SCART-compatible TV set.

There can be no argument that super -VHS (S -VHS) video tape recorders pro-vide higher resolution and better picturequality than any of the currently avail-able high -quality (HQ-) models. Al-though the price of S -VHS VCRs iscoming down, and many video enthusi-asts are beginning to see the real benefitsof the new system, the cost of a matchingTV set is nearly always a prohibitivefactor. For some reason, S -VHS com-patible TV sets are in rather short sup-ply, so that many owners of a newrecorder are forced, for the moment, tomake do with the reduced picture qualityoffered by their existing TV set, whichmay be upgraded in some cases with anS -VHS interface. Alternatively, anaudio/video (AV) connection, or, worstof all, a UHF modulator, may be used toget the new S -VHS VCR to work with acurrent TV set. Clearly, these solutionsgive poor results considering the outlayfor the new VCR.

The SV7000 S-VHS-to-RGB converterdescribed here accepts the luminanceand chrominance signals from the S -VHS VCR, and converts these into RGBsignals for driving the corresponding in-

puts on the SCART input of the TV set.This solution is very cost-effective com-pared with buying an S -VHS compatibleTV set, and guarantees the best possiblepicture quality from the combination ofan S -VHS recorder and a SCART-com-patible TV set.

Simple to connectMost currently available S -VHS VCRshave a so-called mini -DIN 4 -way socketthat carries the two components of thepicture signal, luminance (Y, brightnessinformation) and chrominance (C. orcolour information). These two signalsare fed to the corresponding inputs on anS -VHS TV set via a flexible, 2 -way, in-dividually screened, cable terminated in4 -way mini -DIN plugs.The SV7000 is inserted between the Y -Coutput of the S -VHS recorder and theSCART input of the TV set. The audiosignal(s) from the recorder is also ap-plied to the SV7000, in this case via apair of phono plugs and mating sockets.The SCART output of the SV7000 car-ries all the necessary signals for drivingthe corresponding input on the TV set:colour signals R (red), G (green) and B(blue), composite synchronization and

the audio signal (mono VCR) or signals(left/right: stereo VCR). Hence, theSV7000 is connected to the TV set via astandard SCART cable.

It should be noted that the presence of aSCART socket on an S -VHS recorderneed not mean that ROB signals are ac-tually available: on some models, thepins reserved for the R, G and B signals(15, 11 and 7) are not connected. In thecase of TV sets with a SCART socket,the RGB inputs are, fortunately, nearlyalways connected. None the less, thisshould be checked by consulting the usermanual or the supplier.The external RGB inputs of the TV setare automatically enabled when theSV7000 is connected to the SCARTinput.The SV7000 is powered from a 12 VDCmains adaptor capable of supplying300 mA. Provision has been made toprotect the circuits in the SV7000 frombeing damaged when the external supplyvoltage is accidentally reversed.

Front panel controlsSo far, the video industry has not beenable to define a common standard for


58

a

151 5$

b '0

a

IOS

1-3+1=='-"-; $+

a

o

__1=1+

Q.1_

2

;.4

11122

amosvim_-1§iamo.a Eiw. sg-

AM,

Z+(;1

as

C

fi

uommaes isanuo0 ssatayBini

1 51

nl

Fig. 1. Circuit diagram of the Super-VHS-to-RGB converter. A synchronization separator and a PAL decoder convert the Y -C signals fromthe VCR into analogue RGB and composite sync for driving a SCART input.

ELEKTOR ELECTRONICS MAY1989

59

12

SMOICAS,

Arametass4.0.1

1 AK LtvELCOL.01,42.

COMIKAS2

c` tTcpt

TOA356IA

a. \J LOG

COnviAtt.

CLAVittrO LYNX,

CC I P.330ATCA

>Leas,1/-T1

12111CCULAT041 WA12211a

DATAMS2R212.

CLA:2,5t t

aV1tl: EA LAP TER

LA, LOG

CCAVE RT 2

GATED

AW4'1EP

00172101.0_1:1

Cr1Atlit/04..CEammo

OE 21 C204

GATID12Cogt.-11COV220.1.

IC "r1

WATitti

lb

II,

00111001A.A204 11-

luttST

OCTICT011

sou

052.1s.s.20,21

I - I021020u1.4212i

'At911701

2

904 V FT

%RATA.

4:.04,

MOJA.,tSIEP nen

cus.ichvr,/AMU. rIA

GiEFk

cuTsvr

'C

CLIONiAG

DATAINSL PT*,

CLAWY

"3..1aut2a

147

CfT14.11

12

ttlert.irt

I- rya.

13

1r1-

899506-11

Fig. 2. Block schematic of the TDA3561A PAL decoder (courtesy Philips Components).

signal amplitudes. To ensure that theSV7000 gives optimum picture qualitywith any S -VHS recorder, it is, there-fore, provided with three front panelcontrols to compensate level differen-ces.The 'Contrast' control at the left of thefront panel allows the SV7000 to handlea wide range of luminance signal levels.The centre control, 'Saturation', doesthe same for the chrominance signal.The function of the third control,'Brightness', speaks for itself. Together,the three controls make the SV7000 aremarkably flexible converter because itcan be used with virtually any input sig-nal level, while giving the user the op-portunity of setting the picture controlsto his personal taste.

Circuit descriptionThe circuit diagram of the SV7000 isshown in Fig 1. The luminance and chro-minance signals supplied by the S -VHSVCR are fed to the SV7000 via pins 4and 3 respectively of mini -DIN socketBU2. Both signals are terminated in 82 S2resistors, R46 and R26, to ensure correctmatching to the cable and the drivers inthe VCR. The chrominance and lumin-ance signals are coupled capacitively tothe corresponding inputs of single -chipPAL decoder IC3 by C24 and C25 respec-tively. The PAL encoder is a TypeTDA3561A from Philips Components.The block schematic of this interestingchip is given in Fig. 2. The application

circuit used here is different from that inmany modern TV sets to obtain a greaterluminance bandwidth. In a laboratorytest with a high -resolution colour moni-tor, the converter was found capable ofcorrectly processing luminance signalsof up to 6 MHz.The clock oscillator on board theTDA3561A is set to work at 8.86 MHz(2 times the PAL chrominance subcar-rier frequency) under the control of aquartz crystal, Qs, which is trimmed byC27. All operations internal to the chipare timed by signals derived from the8.86 MHz clock.PAL delay line VZ, (a Type DL701)introduces a delay of 1 picture line(64 gs) and enables colour differencesignals B-Y and R-Y to be extracted

from the chrominance signal. Phase cor-rection is provided by inductor L2; am-plitude correction by Li and preset R29.Potentiometers R22, Rue and R14 allowcolour saturation, contrast and bright-ness to be set to individual taste.The decoded RGB signals available atpins 12, 14 and 16 of the TDA3561A arefed to drivers Ti, T2 and T3 via seriesresistors R35, R34 and R33 respectively.The 68 fl emitter resistors ensure correctmatching to the respective RGB inputson the colour TV set.Pin 16 of the SCART connector is madehigh via R42 to force the TV set to con-nect the inputs of its RGB amplifiers tothe corresponding inputs on the SCARTsocket.

- 11V burst gating &black level clamping

a 4.5V horizontal blanking= 25V vertical blanking

899506. 13

Fig. 3. The sandcastle 15 aveform has timing and level -definition functions.


60

The synchronization pulses are ex-tracted from the S -VHS luminance sig-nal with the aid of integratedsynchronization separator TypeTDA2579 (ICI), an IC typically used inconjunction with the TDA3561. Drivenby buffer T4, the TDA2579 generatesseparate horizontal and vertical syn-chronization pulses and a so-calledsandcastle waveform (Fig. 3) which theTDA3561A needs for its internal timing,level definition and keying out of thecolour burst. The sandcastle waveformavailable at pin 17 of the TDA2579 isfed direct to pin 8 of the TDA3561A.Exclusive -OR (XOR) gate IC43 com-bines the vertical synchronization pulsesfrom pin 1 of the TDA2579 with thehorizontal sync pulses from one -shotsIC2.-IC2b. The resulting composite -syncsignal is fed to pin 19 of the SCARTconnector via series resistor R43.

The 11 V regulated power supply for theS-VHS-to-RGB converter is a low -dropdesign around discrete components -see Fig. 4. Diode Di protects the conver-ter circuit and the supply itself by caus-ing fuse S I i to blow when theunregulated input voltage from the 12-15 VDC mains adaptor is accidentallyreversed.

ConstructionPopulating the high -quality printed -cir-cuit board (Fig. 5) and the further con-struction of the S-VHS-to-RGBconverter is a straightforward job that

will take three hours or so. Wiring iskept to a minimum by PCB -mount soc-kets and potentiometers.The construction of the PCB is beststarted with fitting the 15 wire links.Then follow the low -profile parts, thevertically mounted parts, and the PCB -mount connectors. Before mounting thepotentiometers, their spindles are cut toa length of 10 mm.

Carefully check the completed PCB be-fore securing it to the rear panel of theenclosure with two M3x10 screws.These are inserted through the holes inthe rear panel and those in the flanges ofthe SCART socket, and then locked withnuts at the inside of the enclosure.Remove the locking nut from the PCB -mount 3.5 mm jack receptacle for thesupply voltage before inserting this inthe relevant hole provided in the rearpanel. Then turn the nut on the threadedshaft and secure the receptacle firmly.The front panel is fixed to the PCB in asimilar fashion. Remove the nuts fromthe potentiometers, insert the spindles inthe holes provided, and then use the nutsto secure the front panel. Lastly, fit thethree knobs on to the spindles.

Now first align the circuit as detailedbelow.

After alignment, the converter is housedin the attractively styled. lightweightABS enclosure supplied with the kit.Place the PCB with front and rear panelattached into the grooves provided in the

BU3

80240

R5

C391=+ C40 =1+

=N WM MI2200u 1COu

12- 16V 16V

15V

R5

R53

T5

C41 + 02

ZPO. 5V616V

BC548

6 c ER55j_ R57

R55I

CV

T6

R50

8

86548

R58

+11V

0R59

GND0

Parts list

Resistors:Ra9;R4o;R4.1=68RR io;R26;R4s=82RR27;R28;1142-220RR54;Rss;fiss=270RRat=39ORI:132=470RR2=560RRi 1 ;R43=820RRir,Ras;R37;R3aR44;R45;R47;R48;Rsa;R52;

Rs3=1KORao=1K2R33;R34;Ra5=2K71:14;R6K8F17;1313;Rts=10KR3=12KRt2;R215KR6;Rs7=22KRi9;Rsa=27K1316; R2o;R24=47KR21;R25=68KRso=82KRI:No=100KR17=120KR49=150KR29=1K0 preset HR5=10K preset HRs9=100K preset HR14;Ria;R22-10K potentiometer

Capacitors:Cs=120pC2s;C2270pCr2=470pCri=ln0C4=3n3C20;C24;C30;C31=10nCr 7=22nC2;C3;C6;C10;C21;C22;C23;C33;C34;C36;Cas=100n

C25=220nCi9=330nCas=470nCr=1µ0; 16 VC13;C15;C26=2µ2; 16 VCia;C32--4g7; 16 VC9;C41=10µ; 16 VCI;Ce=2211; 16 VCia-,--47g; 16 VCis;C4100u.; 16 VC39=2200µ; 16 VC27=40p trimmerC37= not fitted

Semiconductors:D =1N4001D2=5V6; 400 mW zener diode

incl.=BC548T7=BD240ICI=TDA2579IC2=4528IC3=TDA3561AIC4=4030

Miscellaneous:Ch= quartz crystal 8.86 MHz.VZ1= DL701 PAL delay line.VZ2= 330ns delay line.Li;L2= 10pH adjustable inductor.Mt= female SCART connector.BU2= mini -DIN S -VHS socket.BUJ= 3.5 mm jack socket.B114;BUs= phono socket.Sh= fuse; 0.63 A slow; with PCB -mountholder.

Fig. 4. Circuit diagram of the on -board low -drop power supply. The unregulated inputvoltage is obtained from a mains adaptor with 12 to 15 VDC output at about 300 mA.


1117

1; 0

0 All'

iF

9E3

(S

t?0_

00A

IWW

aS3

od 1

-4) 2.

LI I

cuon

nD

I

0.O

W -

L-

1711

1'90

Ann

nrin

nin

l3I

-L9 0

-00

0.1-

---

-00-

00

outo

uvot

)0T

O0

:111

0' *

I

918

A,7

WM

.W

M

EEa

Rite

.1

1//q

11.

9E8

ZZ

8I 0

0 0

10.

0.0

EL

)SI

)

0

ri-

93'0

Off

_0

0---

-00 0---

-0FO

L

0E

DI

6Z 2

2.9Z

]11

3 0-

1 1-

0

113

En

CH

F°

Ll

d0S8

11

00-C

LS

El

0Z

hel

ops,

7073 L

a./

0110

-6E

.0

0

O00

70

00

LZ

A0

0

0 0

0 0

0 0

0 0

0 0

0lne

0 0

0 0

0 0

0 0

0 0

-0 0

In

+hE

9l)

1E8

134

eLa

I 0

00,

991J

NA

tir70

X)

)0 70'

o-to S ;4

11

: lot ".

,Z

E3 00

4115

111

01.

0

0

X1

1.11

60

ZO

0 O O L1

fn

00

zne

Ene

62

75'4W...,

Yellow Cyan Green

COLOURMagenta Red Bile Basch

B B

- BARB B

6 6R

6 6R R

B StaircaseI

W

0% 25% ( 50 % 1 75%, 100%

100%W SERVICE - IDENT 100%W

100% I Ms 21412 I 3t3111124.tz1311Itz

16 -VI 90°

100% W 100%W

!V (5*v/tooth) Colourless areas

U (Savrtooth) V et/

899506-1B

Fig. 6. Functional analysis of the test signals available in the Type FuBK electronic testchart.

bottom section of the enclosure. Thenmount the top section, and secure it tothe lower section with the aid of twolong screws inserted from the underside.

Setting upThe S-VHS-to-RGB converter is rela-tively simple to align with the aid of anS -VHS recorder, a recording of an elec-tronic test chart, and a TV set or monitorwith SCART input.Start with a separate test of the powersupply and adjust preset R59 for an out-put voltage of 11 V.Make a recording of half an hour or soof an electronic test chart. The FuBK(Fig. 6) and PM5534 (Fig. 7) test chartsare given here for reference.Connect the SV7000 to the recorder, theTV set and the mains adaptor. Set thetrimmer, the two presets and the threepicture controls to the centre of theirtravel. Start the tape. If necessary, syn-chronize the picture by adjusting Rs. Thecolour may fail at this stage, but can berestored by carefully adjusting trimmerC27.

The PAL decoder is aligned by carefully

tttlp--41111,

aw tIc

3U:0001

SdillHdt LLTIA

411.P17096

I

01141.11., 4-1-0,

CI a-4;

Top view of the completed printed -circuit board. Note the use of PCB -mount potentiometers and sockets.


63

looking at the picture areas reserved forthe sawtooth ±V and ±C(FuBK/PM5534: ±U) test signals and thecolourless areas ±V and ±C(FuBK/PM5534: ±U). Any colouredhorizontal lines or other patterning ef-fects noticed in these areas point to am-plitude errors that may be corrected byadjusting R29 and Li. Similarly, whenhorizontal bars are noted in the G-Yarea, the causative phase errors may becorrected by adjusting L2. The picturequality is then optimized by small, alter-nate, corrective alignments of the ampli-tude (R29 -Li) and phase (L2). Theinductors must be aligned with an insu-lated trimming tool. Never use a metalscrewdriver because this changes the in-ductance of the coil while the core isbeing adjusted.This concludes the setting up of theSV7000 S-VHS-to-RGB decoder.

Final notesThe RGB-status is forced in a fairlycrude way by resistor R42, and causes theTV set to switch to RGB input irrespec-tive of whether a programme is playedback on the VCR or not. This may beremedied by installing the simple exten-sion circuit of Fig. 9. which does not pullpin 16 of the SCART connector highuntil synchronization pulses are de-tected.The PLL circuit internal to the syn-chronization separator may not be fastenough to follow tape speed variationsthat occur in certain types of camcord-ers. Fortunately, this problem is solvedsimply by the fitting of a 180 kil resistorin parallel with Cio.The vertical synchronization signal doesnot contain the so-called back -porchequalization pulses. On a few types ofTV set or monitor, the absence of thesepulses may cause slight instability ordeforming effects near the top of thepicture.

Note: we regret that photocopies and/orfilms of PCB Type ELV60497 can notbe supplied through the Readers' Ser-vices.

A complete kit of parts for the SVR7000S-VHS-to-RGB converter, which is de-signed in West -Germany, is availablefrom the designers' exclusive worldwidedistributors (regrettably not in the USAand Canada):

ELV FranceB.P. 40F-57480 Sierck-les-BainsFRANCETelephone: +33 82827213Fax: +33 82838180

Fes 1151",.

vocr2 yhn TO OniCk CTg

SISaz_PSF. 17,7,1

.471 er...cv_s so otc....-,EstSVrninC,

115771X-1

Fig. 8. Functional analysis or the test signals available in the Type PM5534 electronic testchart.

9+11v

SCART-SOCKET

C. Pin 8 AV - control voltage

Pin 16 RGB status

899506-16

Fig. 9. Modified RGB status driNer that switches the TV set to RGB (=S -VHS VCR) inputwhen synchronization pulses are detected.

ViAnrYbf]Alf]itiC.141:JcIP44440

SCART connectorsVirtually all modemvideo equipment isfitted with a SCARTconnector. The pinassigment is uniformamong manufacturers.but in some cases notall pins are used.

pin signal1 audio out R or

Ch. 22 audio in R or Ch. 23 audio out L or

Ch. 1 (or mono)4 ground (audio)5 ground (blue)6 audio in L or Ch. 1

(or mono)7 blue8 control voltage9 ground (green)10 not used11 green

12 not used13 ground (red)14 not used15 red16 blanking (active

high)17 ground (video)18 ground (blanking)19 CVBS out20 CVBS in21 conector shield

and/or ground


Fig. 10. For reference: pinning of the SCART socket.

64 Please mention ELEKTOR ELECTRONICS when contacting advertisers

BUYERS GUIDE

GARLAND BROS. LTD

ELECTRONICCOMPONENTS

Electronic Components Spec ariscs

Chesham House. Deptford Broadway. LondonSE8 40NTelephone: 01 - 692 4412

L.F. HANNEY77 Lower Bristol Road, Bath. Avon.

Tel. 0225-24811Your electronic component specialist for Avon,Wilts. & Somerset.Closed Thursdays

CRI f L TD op40 CRICKLEWOOD BROADWAY

LONDON NW2 3ET01-452 016101-450 0995 TIx:914977

THELECTRONICSKITS & COMPONENTS

13 BOSTON RDLONDON W7 3SJ

Tel. Orders: 01-S616110Enquiries: 01519 9134

Shop Houn: Mon -Fri. Sam-SpmSat. lOarn4pm.

PROGRESSIVE RADIOTHE ELECTRONICS SPECIALISTSAerials/Components/Ham & CB Radiosive range_93 Dale Street. Liverpool L2 2JD.Tel- 051 236 0982Also at 47 Whitechapel. LiverpoolTel 051 236 5489

-- a fully comprehen

OMNI ELECTRONICSstock a wide range of electronic components at

174 Dalkeith RoadEdinburgh EH16 5DX

tel: 031 667 2611situated midway between Commonwealth Pool and Cameron Toll

BDL PRIME SPEC COMPONENTS BDLLCD module; LED; RFI filters; BNC C S\IB connectors:Semiconductors. Call or write to BD Limited for an illustrated. FREEcomprehensive list. Baes of bargains.Contact BD Limited (Ref P0) 88 Bewick Road Gateshead Tyne & Wear NES IRS Tel. 091490 1975 Fax 091490 1918

D. P. HOBBS (NORWICH) LTD.13 ST. BENEDICTS STREET 3HEO)

NORWICH. NORFOLK NR2 4PETel. 0603 615786

Electronic component specialistsAmateur radio equipment

P/exchanges welcome - Access B/CardOpen 9 a.m. - 5.30 p.m. Mon - Sat.

rhursda.s 9 -

Deansgate ElectronicsWe stock a large range of electronic components,test equipment, telephone accessories, computer

accessories. microphones. mixers. meters. stylus. socall in and have a look around.263 Deansgate, Manchester

Telephone: 061-834 1185

TEMPERATURE MODULERange: -20`C 12 7 -- LCD Display

Optional: 0°F Sar: rate: 1 sec

Accuracy: ± 1 rr a or %-.

Hi I Lo setting ;7: 12 :lock4 Khz Alarm out;:.::Supp :1,5V@1551A

Battery Life: > 1 year

68 35 A 23 mm deepAn extremely versatile digital thermometer combined with a 12 hour clock display. Thebattery is housed behind the module which has an on board temperature sensor andprovision for an external probe It comes complete with plastic bezel and full instruc-tions. The external probe is available separately at f_ 2.75.

PRICE £ 7.95 inclusive VAT and postageDon't be without a copy of our 74 -page illustrated cataloc.a Pr:ce Et. crammed withthousands of Electronic and Mechanical bargains, Tools, Materials and fastening devices.Mail enter or,!y.

J.A. CREW & Co.SPINNEY LANE ASPLEY GUISE MILTON KEYNES MK17 9JT

(0908) 583252

A Fair Deal ForOur AdvertisersNo guesses, no wishful

thinking - the circulation ofthis magazine is audited to thestrict professional standardsadministered by the Audit

Bureau of Circulations

ABCThe Hallmark of Audited Circulation

LLEKTOR ELECTRONICS M. 1989


MAIL ORDER AND RETAIL SHOP.Stocklist of: -Large range of Semiconductors;- Transistors, DiodesZeners, Thyristors, Triacs, regulators, opto isolators LED,Integrated circuits: TTL, Cmos, CPU, support device,Roms-proms, controllers and generators etc.Resistors; Pots, presets, Capacitors, including computergrade, trimmers, tuners stc.Chokes, transformers, Relays, Buzzers, Speakers Etc.Switches; standard, miniature, slide, rockers, pushbuttonsetc.Connectors large range including ready made leads, IDC,URO, Din, plugs and sockets etc.Dil sockets: low profile and wire wrap etc.Panel meters, soldering irons, solder suckers, solder etc.Aerosol switch cleaners, lubricants, protectors andfreezers etc.Motors, modulators, trimmers, oscillator modules,rechargeable batteries, solar panels etc.Power supplies Linear and switch mode by Astec, Farnell,Siemens, Advance, Gould, Gresham etc.Disc Drive Units: 5.25, 3.5 inches, hard disc, and cablestec.Test Instruments: Analogue, Digital, Oscilloscopes,Generators etc. Large range of instrument cases.

WE BUY COMPONENTS AND INSTRUMENTS

Callers Welcome. Shop Hours; Mon -Fri 9am to 5.30pm,Sat. 9 am to 2 p.m.

Fuselodge Ltd 475.4

267 ACTON LANE, CHISWICK, LONDON W4 5DDTelephone: 01-994 6275

LOW COST S.B.C. RANGEELTRAK Electronics have introduced an extended rof low cost single board controllers to meetrequirements of the OEM user.

Based on the INTEL's MCS-the EIM06x range

* Up to

,Af;d ug to 36

CMOS Options.

amity of miy olustriat ctstea aid

es of rqkukrii,,AQisiqh res 01:44itym

BYtes4V4°'"AZCOL-°r311'tuweepu,,,LA suw6-7,,ame Clock.

I/O lines.

....... ...

............

t

rs

with full range of expansion cards eg:-

(a) I.E.E.E. Interface,(b) Digital Interface,(c) Analog Interface.(d) Barcode facilities.

...... .... AA:

r-rrj tee..er.A3113

10 units

* Card size is 80 x 100mm.

Educational package introducing use ofmicrocontrollers now available

MONIFIETH BUSINESS CENTRESOUTH STREET. MONIFIETH.DUNDEE DD5 4PJTEL: 0382 534944 VISA

1

ILA FAX: 0382 535093

I h II IIn electronics ltd Asses

INL

KITS AND COMPONENTS FOR ELEKTOR ELECTRONICS PROJECTSAT YOUR SERVICE: SPECIAL COMPONENTS ...AND A WIDE RANGE OF KITS

J. ' 1'!245_035950

i --e; sr r Us 93

loca

;Anted Streit r: :: i 7= ...1.ltel 7 ...... .- - : - --

r.c.:-.1 par*Es. CaltErti .- .tS Str 7... ' = -- ' : .rA;.,es. Parte List._ A ., _; more, . -.._ _ , _ .,. ....,

f.,:ics.re 4,2 ,::. -: :-_- : _- -+r V.' _ _ =

Iteesfarners ei -. - -. tos . r A _

s:-.f.cral eft:erre. : - := : :extte---.: - -

3-s St 1 (RC_

1111..1 1....e 0, Al

At=-:" FA 44_25.152.2 .. 17z0

FS= -27 . . 750

18 CO

_ . 825254' :ii 17.65

1,4; . 23.73L2-4- 3125LV3.24. _ _ _ 1830

i'LLI15421(6 --42504931 41.170AT=ES4C5 i.25

sFal IV( . . . 525

2164" 7'15

1.1.11251::= 4,5ifec:31:--:-. sm to11CIFS-4 13.50

5.0051%67:: ., 31.25XS41371. 525S47AA ... . 925ra-4714 . 18.25Stest ..... 6 75

EISMISSIES

:7i_.:111:: 4.5.7a

074-01412A .. -4875,o,c- 222

__ .10,0

orwA91..2511 . .. 1535

4_;1arerolve-. . -J:6' :---: 47-621

1,--,:-.4 ',..=30.....i in=7;,., i... -4-,,..7.45,' =-- _

4s7 Was

P.:. 11=5".., _ _ Wit 5E5...A ign i-= .se army . 1-4353_ -_ F3J .. . __ sae SU3 ,_.s. SA ....a __ 61 50

V.17 1982:74:Psce test- 98 50

'. = coNs-ar 51.50L..; TA FX 129.50

425119E3Sard ;seer..., . _ _ 77 501--, _nA 81504.±...e "..,:.7.-A., 413 SO

VtitiV

-14t16

43IeTi

232-4.2i _ 62525C7 Si i 17_65

25211ZI:41425 _ . 14

15-75S45.1 CAS

,,,,13 50

1.15SCIV _ 11_50MEM=VAT 1,0-17A 0.65

291At . 4173. . ec.is..2 2525

ma Am,. 0.75ChIPUCTORS

TEST EQUIPMENT:...,..'Itt:_. Er! 41-04e.C.

- ,.s. ts - ... -

A F:33,_ Et ',el: re.s-t-.er Ye-s=A re SS"---=4:..34 54003

410:CTIONG9ISATOR '21A. Cif,Ae.t rtill.,..-.,_

Fier: ere."-'' K-5' - ':4,W V.-= v5 Ver.e.. _ _ 26550

cAttAaTAlla 1.181111 t2 21J,.5,0455 p-4,-....,5,4-5 rer:=-.7.5. II firs :Are,. mar.,..col re Vests. 20 00

VASIA91.1 DUAL FOnSit4.54LY ts55. ,......t.e. re::-...e.. tin atet if Pes. Fr_,..3.,!,..11011r-re=re, 14

44503

1,8111.11-UNCTM FS-00ENCY WM it 2E7=241: CerrCiett r==ertat, a P Sere ;a-4 , .1.3G-izxt.--.. reVe-,tc- t-4.5.% ....,..5facer r...ccein

36510

1800C041710.1131-1397V-E.iPOSES .52744...7 S i 7 i SS

'::-' '..- -. :s..,

: "' '''''::5 ..

. . .

r-..-.... erd vvia ., .-

' .5-'e E°

Setlietectree nor FS 00-.re. PL. a -d emer rs

lis, 1Si IDU, , 717;s0A -A :7_, --- rear 21675

C'.. ' ' ' : : : : ' '-'--.. .-31255Alai EDe t..-.: ',-3 12950Vu, , : - - - , 49971711 :-,. e-rerse 9750Ika-se 1E33Marx -case. 119.50Pr-tcite,Ot .714 21475.34. Vote Ttee2 set ASI-4,cm set ex APi &::

1155Fab:nary 1989-0g. Vale Seel . . 35.75t.le man, ilr.-21r...Cr.',

5360Cir ste.: r4.2... 72_25

Amery 195304 VD: r.-±=tr 25-s SO

Fell --Ass __ . acoDemebor 194910 .....,-,-..--f-e, _ _ . 32500CD szesO co-rs . 6350TA 44, ...A..- 1E3 50CV -4317,- se -tut- . 31.25Nonater 1923114.157 -7.en:bo:i 453.03

So.=.51 156-00

R'''''''' 2 " '''' 57'5'LCD as kaexce . _ . 215 CO1-9-100:01 14.35151S

65 00Sere. * re 11.4 7930CesAbte 1988

ts j-, ,-.. r-t"..r 133751,---ovi.c,-...t...6.' 37.07C4,4 riCer a93Sweeter 1983Vi"[ 514 P.14 P-031AC5 ca -3s. W-2511290 81170011 sr-neer 4-17-6-ro-et.r..-4,,e. _ _ . 99_03

5.1102-; ., 3.152975 . 6251E51:0474 -- 15-00.175 415,Dc-tv..5 . . 11752,7.4731 17-90i ..." .J. 11.15

-:- _232]

- 15259.75

17_50

.. -.- 8_75,:. 57A- 27.757:5S.-734- P 34_75

5 A.V54 12_50

5 re -51 1225

81494. .. 0-55

ron5°01D4.-.- ,9251225

is21511 . 76_25assi 4 a5

ha72.14 la 75h5AA,27i 575ht..w2 92550523 . - . -825FA -510 . _ . 11.501.3554a 975U5655' .1472VAISSO.. 1750orra3 . 29533753 2_40

N752.. . 34071.7M4C 1000

Tease:5:s 5525

,:,._1'S r,,56257572

ta71750.7133

39 508507

C117217: 27154347221A 49_50L52220 . 55 00

4372 37 4250' - - -

3200AV731-0 ___ . 40.004.1.1791 " K -C°29302 11.53SSW 1950

.575..S 91509,1070".. "6 - 530s=49510 15 75105a7-5.0 ea 91

st,-. ..

V° 12)-472n= 013VAT SKAI-Sr.e 0.95VAT IsOIA5 _ . 1.05ta7 Ai7 4.51VAT (CS 9.50Sitieel 53 - atreLes ts A,7 075Tiderrosty: 1n0 toile7,-,.. oasLiaius se57e t,A1rife, . 0.7597 rri ..... L75

ae cr F.40). =V!'

:.1.''' 1-'.- 2"Gi.. a ':71 .TW-2 _ 3.7AT53.6 175T -v.7-12 175'.i.c.fc 71 E 4.03'.7:: : "F i 4901

..,i,::,.7. - =. ACO

.,,,,,,, -.- 4.25

Wee ' ' . ' 4/5Tolz:SisliV 4551757-41 4-55' : : : '' cm

latent 1933Se TV saimr 7250S,-.7. sects, 1E550A *m.o. y .. 11900

Feinan (0053s fr7.144-7- - 119.501.2 Ce5 Aress.se _ . . TEST

MIDI:DD/E51088.25

incl.datasheet

SOT

ltruz7 1983611'41-' VICO6,..-K Li-ise 5130

0.4=4. IS,LC:, w ,t'..0 - 143-00F,S.7,3,-, re2r 1ST KITRC ear 57.r 7O4 . -

11300

Koraeter 1787aksc 5.,.....55 209.133

20 3.,-,^ ma ...5: 19930Drre 64 3054.4,..t. 1557549341 eet.ser _ _ tatoVOI 4,15 aVAt 9.1Teta.% CA% SI3514 eSS.

li)aGO -}

se-___...

7A 1 S7-

3893A±

586HM=

11.95

4505551.45

-" I As7?.. 1_45

79.... 1,5323777-3: 5.25

SO iDr 4_00

TC1.755 . __ 3.25

11557 - 54 755E51 _ 3 75

vs?. ! 3 75STe-7 3.75ADC10:5 , _ . 4175DAC TX'S 33.25

150 .024 6.25

vel JAG=V4:1441154 . 175019:145026 ---.635VC.145027 . . El 75

WI MS ULM14C175157 _--26.75lACI00GS.74 _ 1135HDEIS:13 F3175

t. .,te4orte5r., r7 -41C:3,,,, 51w,

=mum16_5y_si _ 2 -...,i

225:555n25.;_ _ _ 24::,,, 4.95

4554 95

. 335.25

125

- -- -....335:..-:f-.1 ca-ccre frxei- Lte dmrir 16_95

MC. C.SO0.. 759

ZWACTC .925ZFIA.Pfit 9_25

542.._ IS9P1492 , 3_754:"A55 _ , 3_10

SAA1027 11.25sutois 3103AV123S 19255V12362 . 17.25su4six . 30 70m51420_55 34 75

144151.0 , 27 SO

COMAS'S CVOS 711,LSTTs s 'Cr1.4.`"43-.1-33- EX'570CA4-,: svi=.'moxam.

to110N 5.00

rt"iV4., 5-4X,

114......,107 , 99.00

LAAAsw117 - - - - 51-03ETDC121 CM _3725

VAC7.184912552455

IMMEUE='1231,J1-42-5101 625 OV3H tinoA NO ONIONV.LSA4119 1195

3155 or,s35170 1..

-C1-4701. ___ NMSUA23.7. -- 7750

LV1612 . - 36 501310517 13.25DAIWA 1730LUISA . 11502072702 4751502003 . 575

100474 11.50

1.013 VE3 - - 11.501573 Wiz 1.10&cat wiz :.14243 0.4

Ibt,

IMENEMEMCamSete D IX.BYE

0 m,.k.

rrsiabt.

V2310245411115.50

f12 -S3

.. , . -F.-.-:.-: aso

r. fret ss ire a IA a: r esene ra% Or lv-ce 4 wlb= ecr. tee ce re cr:.re /IV ao-st re 3..r.cercra,-,,5-C-1 Boorceika P.O. Bas 22399 6930 AB WO TeoKaheeents I-r_oss olt ,W.: ten el stemoreer_4. vds we e.. -a-, 9_..^t Giitst fer-.. o- * G:. stec mcerce. as -an ;ea ease. re £2.1..s,61 e -.: 5.2 .kMY I. 0= VAT is 15.59.: se el_are 2.91... Fee5,0ff? Seco Er=iio..e! ?V cor034---_, 17.00-. ess.ceaseerofri.EsS !eagl shway . !ilet advert /4 ES' 7.543.Eani ac, ti21041872 Gm. =. secmm F55 ectute se0-1,1-12 & 0)0705 a -.1-7:4 s-cosi-o; 1610

314.47315 0-75 TEAMS 5.505403

= MUMCOCO krItiS.250 1 60 OV20i9._ ._. i2.506.533 Vett A. ..t.,As 1241X52X5:41.4

S2MASC 1.75S2644 _ . . (09540255-4,11 2730112679 525I -La?, . 225nr.-27: -...3.25

07.12C50 17_25CA12060.. . .. 2515u20658 7,75

011.7370 3933x522,...,5, 05 11 75

aeasEcA 543

84°C) 11.4.: D

&iI6 wvz 4.50

9_216 Vet4 65010703 890 ....4.10119-592 Wiz- 6.50

5'12 5ie 0.15 :- : ' 42.15

516 iSi .. .... 0.55 ..' : ' , 72505450.17 225 14.41.:445 15-95

5117/101293 _ _ 3_15 U740.53R 15,.%

7010 0.I 3 _ _ _ _ 215 Se 5.9. _ _ 28-95


Superb Triple -Trace 20MHz OscilloscopePrecision laboratory oscilloscope.3 Channels -3 Trace.Sensitive vertical amplifier lmVidiv allowsvery low level signals to be easily observed150mm rectangular CRT has internalgraticule to eliminate parallax error.X -Y mode allows Lissajous patterns to beproduced and phase shift measured.TV sync separator allows measurement ofvideo signals.2Ons/- div sweep rate makes fast signals

Algebraic operation allows sum or differenceof Channel I and 2 to be displayed.Stable triggering of both channels even withdifferent frequencies is easy to achieve.50mV/div output from Ch I available to driveexternal instrument e.g. frequency counter_A hold -off function permits triggering ofcomplex signals and aperiodic pulsewaveforms

I 40MHz Trip e-"Yace Oscilloscope

!:

Order Coupon Send to P.O. Box 3, Rayleigh..%68LR

Qv Descnpnon ace Fri

A carnage

Name Tmat

E&

Address

Post C.,..dp

authorise yc=i debit my Credd- Card BCCO,-MI for the cflo of ocodsmespambed

.-,ard No

Access. Amex Atm rh.lwe as legturedUordenng by Credo. Cud manEsptry date of Creds Card

1

E

As above, but with 40MHz bandwidth andsuper bnght 12kV tube even at the highestfrequencies. This instrument p,Iv has adelayed sweep time base to providemagnified waveforms and accurate timeinterval measurement. Truly superbprecision instrument.

incitideS

84VATCarriageldell.

_=1-, ELECTRONICS

P.O. Box 3, RAYLEIGH, ESSEX SS6 8LR.

PHONE BEFORE5PM FOR SAMEDAY DESPATCH /02 554161

ALL PRICES INCLUDE VAT.

All items subject to availability. Subject to availability both items will be on sale inour shops in Birnunaham, Bristol, Leeds, London, Manchester, Nottingham,Southampton and Southend-on-Sea.

uk £1.60 ir £2.35 (incl. vat) - worldradiohistory.com...wordstar handbook e11.95 dbase-ii for the...

Documents