113

September1984

ctronicstachometer SCART adapter flash meter

electronic cross -over filter anodizing (aluminium

lamp econfoniiler news views

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'ATTENTION'ALL PRICES ARE

SUBJECT TO CHANGEWITHOUT NOTICE

TEC:11\011.M: LTD

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MAIL ORDERS TO: 17 BURNLEY ROAD, LONDON NWIO IEDSHOPS AT: 17 BURNLEY ROAD, LONDON NWIO

(Tel: 01-452 1500, 01-450 6597. Telex: 922800)305 EDGWARE ROAD, LONDON W2

JUNIOR COMPUTER KIT MI6 plus Et p&pAll Junior Computer Extension Boards availableJUNIOR COMPUTER BOOK: 1E4 2.3 & 4 E4.50 ea p & Wok 701,1TV Games Extension beards availableELEKTERNIINAL KIT £50 (plus El p & p1TELETEXT DECODER KIT £85 (plus £1 p 8,0)Decoding Board and Keyboard Elektor Nov 81)Reprint of Teletext arlieles £1.25 (plus large SAE)

PROGRAMMED EPROMSJunior Computer 2 x 2716Intelekt Chess ea 682708 Basic £8 2716TV Games E8

2716 Tape Management £8 71301 Elekterminal £7

2716 Prog. Management £8 2716 Disco Lights £882S23 Interface Es 82523 Freq. Counter (IC 3C4: ea E5

2716 Housekeeper £8 2716 Tatk,ng Dee EdPCBs for most Elektor Projects available

SEE OUR FULL PAGE ADVERT IN THIS ISSUE FOR DETAILS O'7.BBC COMPUTER PRINTERS etc.

PLEASE AIM 51)1) p&p &151,1:Vr (Export: no VAT. p&p al Cost)

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Detailed NICE' List on request.Stock items arc normally by return of post LA*

elektor september 1984

news - views - people 9-18

selektor -9-22Scene of science: a look at the Science Museum in London.

data communication by telephoneLinking your computer to the telephone network is the 'in' thing for 1984:what happens between two communicating computers is described in thisarticle.

active cross -over filterA versatile active network which provides far better audio frequencytransfer than most passive filters.

digital cassette recorder with the ZX81As promised in May, here is the solution to the problems which haveprevented our digital cassette recorder from being used satisfactorily withthe ZX 81.

flash meterEssentially a light meter, this unit is intended as an aid to achieving theright flash under all conditions: a 'must' for the serious amateurphotographer.

missing link 9-41

PC board pages 9-42

digital tachometer 9-45To many drivers a tachometer is more important than the speedometer:yet, most car manufacturers fail to provide one. Here's your chance tomake good that regrettable omission.

DIRPUT 9-50We offer a couple of new instructions for the Junior Computer with theOhio Scientific disk operating system.

SCART adapter 9-52A new plug -and -socket connection between a television receiver andassociated equipment such as a video recorder or teletext decoder isbecoming a European standard.

anodizing aluminium 9-56

9-24

9-28 row.j

9-35

.

:1 . .

The front cover illustrates adirect -coupled data circuit

9-36 terminating equipment (DCE),popularly called a modem(contraction of modulator/demodulator) and a tele-phone: the two essentialunits for /inking a computerto the telephone network. Inthis issue we describe whathappens between transmittingand receiving computers thatare linked by a telephone line.Next month we offer you theopportunity of building yourown modem.

An alternative means to paint -spraying for the protection of aluminiumcases and panels.

lamp saver 9-58A unit which is easily added to existing installations to increase the life ofincandescent light bulbs.

double -sided printed circuit boards 9-62Ways and means of making your own through -plated printed circuitboards.

applicator 9-64A new memory IC from Mostek that is compatible with both the CMOSRAM 6116 and the 2716 EPROM.

market

switchboard

appointments

readers' services

index of advertisers

9-66

9-71

9-75

9-80

9-82

A selection from nextmonth's issue: direct -coupled modem

design video reverser ZX 81 pulse cleaner simple wind direction

meter RS 232 centronics adapter fuel consumption meter programming the 6845

CRTC

9-03

Elektor Publishers Ltd., Elektor House,10 Longport, Canterbury CT1 1P E, Kent, U.K.Tel.: Canterbury (0227) 54430. Telex: 965504.Office hours: 830 - 1230 and 13.30 - 16.30.

Editor: P.V. HolmesAssistant editor: E.J.A. KrempelsauerUK editorial staff: R.E. Day, G.P. McLoughlin, L. SeymourOverseas editorial staff: P.H.M. Baggen, A. Dahmen, I. Gombos,

P.E.L. Kersemakers, R.P. Krings,P. v.d. Linden, D.R.S. Meyer,G.C.P. Raeciersdorf, J.F. van Rooij,G.O.H. Scheil, Wijffels

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40-16-11, a/c 11014587Giro a/c no. 315-4254

Elektor Electronics is published on the third Friday of themonth preceding cover date with a special 'Summer Circuits'issue for July/August.

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The circuits are for domestic use only. The submission of designsor articles to Elektor implies permission to the publishers to alterand translate the text and design, and to use the contents in otherElektor publications and activities. The publishers cannot guaran-tee to return any material submitted to them. All drawings,photographs, printed circuit boards and articles published inElektor Electronics are copyright and may not be reproduced ortransmitted in any form or by any means, including photo-copying and recording, in whole or in part without prior writtenpermission of the publishers. Such written permission must alsobe obtained before any part of these publications is stored in aretrieval system of any nature.

Patent protection may exist in respect of circuits, devices, com-ponents etc. described in this magazine. The publishers do notaccept responsibility for failing to identify such patent or otherprotection.

Elektor Electronics is also published in Dutch, French, German,Greek, Italian, Spanish, and Turkish.

Dutch edition:

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Elektuur 8.V.,6190 AB Beek IL), the Netherlands.Elektor Sari, Le Seau, 59270 Bailleul, France.Elektor Verlag GmbH,5133 Gangelt, W -Germany.Elektor, Karaiskaki 14, Voula, Athens.Elektor Electronics PVT Ltd., 3 Chunam Lane,Bombay 400 007.Elektor, 20092 Cinisello B., Italy.Elektor, Av. Alfonso XIII, 141, Madrid 16.Elektor A.S., Refik Saydam cad. 89, AsianHan kat 4, Sishane Istanbul.

Distribution in U.K.:Seymour Press Ltd., 334 Brixton Road, London SW9 7AG.

Copyright ©1984 Elektor Publishers Ltd., Canterbury.

Volume 10 - Number 9

Semiconductor typesA large number of equivalentsemiconductors and ICs existswith different type numbers.For this reason, 'universal'type numbers are used inElektor wherever possible:for instance, '741' stands forpA741, LM 741, MC741,MIC 741, RM 741, SN 72741,and so on.

Type numbers 'BC 107B',`BC 237B', 'BC 5478' allrefer to the same 'family'of almost identical good -quality silicon transistors.In general, all membersof the same family can beinterchanged.

BC 107 (-8, -9) families (NPN):BC 107 (-8, -9),BC 147 (-8, -9),BC 207 (-8, -9),BC 237 (-8, -9),BC 317 (-8, -9),BC 347 (-8, -9),BC 547 (-8, -9),BC 171 (-2, -3),BC 182 (-3, -4),8C 382 (3, -4),BC 437 (-8, -91,8C 414

BC 177 (-8, -9) families (PNP):BC 177 (-8, -9),BC 157 (-8, -9),BC 204 (-5, -6),BC 307 -91,BC 320 (-1, -2),8C 350 (-1, -2),BC 557 (-8, -91,8C 251 (-2. -3),BC 212 (-3, -4),8C 512 (-3, -4),BC 261 (-2, -3),8C 416.

Resistance and capacitancevaluesDecimal points and largenumbers of zeros are avoidedin values of resistors andcapacitors wherever possible.Instead, the following prefixesare used:p (pico-) = 10-'2n (nano-) = 10'9µ (micro-) = 10-6m (milli-) = 10;3k (kilo-) = 10'M (mega-) = 106G (giga-) = 109

A few examples of resistancevalues:2k7 = 2700 C2; 3M33,300,000 12; 820 = 820 CZResistors used are Y. watt,5% carbon types, unlessotherwise stated.

A few examples of capaci-tance values:4p7 = 4.7 pF=0.000 000 000 004 7 F;10 n = 0.01 j.LF = 10-' F=10,000 pF

elektor september 1384

ISSN 0308-308X

The DC working voltage ofcapacitors (other than elec-trolytic or tantalum types)is normally assumed to be atleast 60 V. As a rule of thumb,a safe value is usually ap-proximately twice the DCsupply voltage.

Test voltagesDC test voltages shown aremeasured with a 20 k1 -?/V in-strument, unless otherwisespecified.

U, not VNormally, the internationalletter symbol 'U' instead ofthe ambiguous 'V' is usedfor voltage. 'V' is reservedas an abbreviation for 'volts'.For instance, Ub = 10 V,not Vb = 10 V

Mains voltageMains (power line) voltages arenot given on Elektor circuitsas it is assumed that ourreaders know what voltageis standard in their part ofthe world!Readers living in areas whichuse should notethat Elektor circuits aredesigned for operation from50 Hz supplies. This will nor-mally not be a problem, butin cases where the mains fre-quency is used for synchron-isation, some modification tothe circuit may be required.

Missing linksAny important modificationsto, additions to, improve-ments to, or corrections in,Elektor circuits are generallypublished under 'MissingLink' at the earliest oppor-tunity.

Services to readers.Subscription serviceTechnical queries serviceSoftware serviceFront panel serviceBack number serviceCopy servicePrinted circuit serviceBook service

Details of all these can befound on pages 80 and 81.

Printed in the Netherlands.

9-04

ABC

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9-17

elektor september 1984

Great expectations in theUK . .

The new ICC Business Ratio Report'The Telecommunications Industry'describes the outstanding prosperityof the sector in terms of rapid salesand profits growth along with in-creasing returns and margins. Itpoints to how the Telecommunica-tions Industry has replaced the oilcompanies as the most desirable sec-tor in which to invest. The telecom-munications sector is unusual inbeing one of the few industries toenjoy more or less continuousgrowth during the current recession.During the period 1982/83 sales andprofits increased by seventeen percent, while the average return oncapital employed increased to 24.6per cent. The report ascribes muchof the sustained confidence in thetelecommunications sector to the1981 British Telecommunications Actwhich removed the state monopolyheld by British Telecom. This led tothe liberalization of the UK industryalong the lines of the new Americansystem. The report concludes thatthe telecommunications industry hasa bright future and that its fullpotential for growth has not beenfully realized. The more optimisticpredictions for the future, includingthat of staff working from home andusing a computer link to their of-fices, can only be achieved throughgreater use of telecommunications.

. . . and in the USAAccording to 'The Power Semicon-ductor Market in the USA', a newstudy recently published by Frost andSullivan, the US market for powersemiconductors will treble over the1983-1989 period, with MOSFET andpower ICs leading the charge. Thesetwo products accounted for twelveper cent of 1983's $763 million sales,but will take 58 per cent of the$2.2 billion market forecast for 1989.These figures are based on the 1984value of the dollar. The currentlydominant bipolar power transistorwill drop sharply from a 45 per centmarket share to eighteen per cent in1989, although it will eke out two percent average annual real growth.Power rectifiers, silicon -controlledrectifiers, and zener diodes will eachexperience 9 . . . 10 per cent averageannual sales increases over theperiod, but will still see theircumulative share slide from43 per cent to 25 per cent in thisburgeoning market.

Tat for tatThe managing director of BritishTelecom International, Mr AnthonyBooth, recently signed an agreementfor British Telecom in Paris to providefor the construction of a £210 million

rif it

optical fibre submarine cable systemthat will span the Atlantic in 1988.The cable, code -named TAT -8, willconnect the UK and France with theUSA. It will be capable of carryingmore than 7500 simultaneous phonecalls - almost double the capacityof the present cable, TAT -7, whichwas brought into service inSeptember 1983. The project will befunded by 29 co -owners to constructand maintain the 3600 nautical mile(6657 km) system. The cable is uni-que in including an ocean floor junc-tion box - located just off the Euro-pean continental shelf - which willallow it to branch into two sections.

The Italian connection . . .

Plessey Semiconductors (U.K.) havejoined Neohm Elettronica, the Italianfirm renowned for its involvement inthick -film hybrid circuit technology, indeveloping a design centre for gatearray and cell -based semi -customICs. The new design centre is basedat Leini (Turin); a design team trainedat the Plessey design centre in Swin-don has been established to providetechnical and application support forcustomers implementing semi -customdesign.

. . . and the ScottishconnectionWinchester Electronics, a division ofLitton, the US high technology con-cern, has officially started its newplant at Glenrothes, Fife, Scotland.The factory will produce a broadrange of connectors and sophisti-cated interconnection systems for thegrowing needs of the British corn-

puter and telecommunications in-dustries. Winchester Electronics (UK)Ltd. is a newly -formed subsidiary ofWinchester's Biberach, West Ger-many, facility within the Litton elec-tronic components group. The Ger-man facility, 13 years old, startedfrom about the same small scale asthe Scottish plant. Since then it hasgrown rapidly to about 200employees after a number of expan-sions.

OmnibusWith official approval nearing for theP1000 STE (acronym for STandardbus on Eurocard) backplane bus,a number of companies have formeda manufacturers and users groupto promote its market acceptanceand use. The new chairman, BobSquirrell of Dage Systems, com-ments that the bus brings sorely -needed standardization into thesingle Eurocard area. 'There are atleast fifty single-Eurocard buses onthe market. Many are proprietary andthe majority are simply dedicated toa single processor family. STE bringsnot only standardization to this area,but also a quantum leap in perform-ance: The 8 -bit STE bus draws onthe experience of dozens of theworld's best designers. It isprocessor -independent, and may beused 'stand alone, or in a multiple -bus system.

Down in BritainThe British govemment have finallygiven the green light to a£400 million joint venture betweenthe BBC and the commercial televi-sion companies to develop directbroadcasting by satellite (DBS). Un-fortunately, at this moment prospectsfor satellite and cable television alikelook pretty gloomy. Already thenumber of homes wired to cable net-works has fallen by over fifteen percent since 1980 and all the signs arethat this trend will continue, at leastfor the foreseeable future.

Up in France?Meanwhile, France, too, is planningcable television: it hopes to havesome 300 000 homes wired up by theend of 1985 and to increase thatnumber twentyfold in ten years' time.The system is being installed by thestate post and telecommunicationsauthority but will be run by regionalmixed economy groups.

Break even in U.S.All the signs are that the UnitedStates after running close on£4000 million surplus on computers,consumer electronics, telecom-munications equipment, andsemiconductor components threeyears ago will just about break eventhis year.

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elektor september 1984

Good for working modellersMicroelectronics has a natural attrac-tion for the working modeller, butuntil recently the big problem waswhere to get the necessary bits andpieces. Mail order and friends havebeen the usual, but by no meansalways satisfactory answer. But nowMicromate Limited of Bedford havestarted to make a packaged range ofmicroelectronic components availableexclusively through the High Streetmodel and hobby shops. The brain-child of Michael Kish, managingdirector of Circuit Board ComponentsLimited, a distributor of componentsto the electronics industry, and amodel railways buff, Micromate hasalready drawn an encouragingresponse from the trade, and MikeKish expects before long to have astockist in every major town. Thoughspecialist retailers' staff tend to beknowledgeable enthusiasts for theproducts they sell, not everyone is anelectronics expert, so Micromatepacks contain a comprehensive datasheet on the component concernedand kindred items. Where the range,which is extensive but basic, doesnot include some specifically neededcomponent, the shopkeeper canorder it direct from Micromate'sstocklist of 2000 components, allbought direct from the manufac-turers for ex -stock delivery.

Not so good for investorsInvesting in personal computer com-pany's shares appears to be one ofthe better ways of losing money -at least in the USA. Already decid-

\EVIE

PECPLE

01110811

edly wobbly, these shares were givena firm push downwards by IBMs de-cision in early June to cut the priceof its personal computers by around20 per cent. Hardest hit seem to bethe makers of machines that arecompatible with IBM's. Notable losershere are Activision, Applied CircuitTechnology, Televideo Systems, andKaypro, all of whom have seen theirshare prices tumble by over fifty percent this year. But even companieswithout any links with IBM or itsequipment, such as Tandy andApple, are faced with a drop in theirshare prices of up to forty per cent.A recently published book, 'Com-puter Industry Shakeout: Winners,Losers, and Survivors'; by Mr.S. McClellan of Salomon Brothers,the business analysts, predicts thatpersonal computer makers will seetheir share prices drop even furtherover the next 6...12 months.

Mercurial business...The Space Er Microwave Division ofMarconi Communication Systems Ltdis currently putting the finishingtouches to the provision and com-missioning of two containerizedsatellite earth stations forMercury Communications on theLondon Isle of Dogs site. This is thesecond major satellite earth stationdevelopment which Marconi has pro-vided in the Docklands during thepast few months. The two systemson the Mercury site are both workingin the 11...14 GHz band, one to anIntelsat over the Atlantic. This willshortly be providing digital com-munications to the USA and will alsobe capable of providing internationalTV transmit and receive services. Theother system, which is slightlysmaller, uses an 8 m aerial in thesame frequency band and is intendedto work to an Eutelsat satellite toprovide a dedicated TV transmit ser-vice for European cable TV users.

...and Olympian researchPlessey Public Networks Limited hasbeen awarded a contract to carry outan enigineering study of integratedfront-end transportable earth stationsfor use with the Olympus I (L -Sat)and planned communication satel-lites. The contract was awarded bythe European Space Research andTechnology Centre (ESTEC), adepartment of the European SpaceAgency (ESA). The study is to definethe optimum front-end design whichwill lead to well-balanced re-quirements for 20...30 GHzmicrowave equipment. The Olym-pus I Satellite is scheduled to be putinto orbit by Arianne, the ESAlaunch vehicle, in early 1987. Thesatellite whill then be used for videoconferencing and educational tele-vision services.

Mixed fortunesFigures published recently show thatsales of personal computers in theUK increased by more than 70 percent in the first quarter of 1984 com-pared with the same period in 1983.In the USA, however, during thesame period sales dropped to 750 000a month. Magazines, too, are feelingthe pinch: so far this year aboutthirty computer magazines in theUSA have bitten the dust and allothers report sharp reductions in cir-culation and advertising revenue(more than 30 per cent forComputers and Electronics -formerly Popular Electronics, the'largest electronics magazine in theworld'). The situation in the UK isnot nearly so alarming, but manyeditors must be keeping an anxiouseye on the developments in theUSA! There is a widespread feelingin the industry that there are toomany magazines in the computerfield; David Bunnell, publisher of PCWorld and MacWorld reckons that inthe USA as many as fifty moremagazines will cease publicationbefore the year is out.

One up for down underPrestel, British Telecom's world-beating viewdata system based onGEC computers, has recordedanother major international successby winning the prestige Australianpublic service contract. The all -British system has been chosen byTelecom Australia for its new Viatelservice which will start in early 1985.The contract for GEC computers andPrestel software, which is worthinitially £2 million with more to followas Viatel develops and expands, waswon against stiff international com-petition. The Australian decisionmeans that ten countries have nowpurchased national videotex systemsfrom GEC-Prestel - more than all in-ternational competitors combined.The Prestel viewdata system wasdeveloped by British Telecom'sResearch Department. It waslaunched commercially in 1979 as aworld -first. The UK network now has44 000 terminal attachments, almost40 per cent in homes. Users have in-stant access to 320 000 frames(pages) of information through ordi-nary telephone links.

Compatibility assuredFollowing what is believed to be thefirst 'all -digital' transmission of stereotelevision sound, using the CrystalPalace transmitter after close -downon 24 May, 1984, the BBC is nowconfident that a digital system willbest fulfil the requirement for stereowith television from terrestrial trans-mitters. The transmission was the la-test in a series of tests which beganat Wenvoe (South Wales) in October,

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elektor september 1984

1983. The first tests confirmed theruggedness of digital stereo TVsound in areas of difficult reception.Compatibility trials from CrystalPalace in March this year then con-firmed that no significant interferencewould be caused to sound or visionreception on existing receivers. Inconsultation with the Home Office,discussions with the IBA and indus-try are now well under way with aview to the early establishment of anagreed UK specification. In the meantime, now that compatibility is as-sured, it is hoped that further testscan be arranged from time to timeduring normal programme hours.

Wee chipsThe Scottish Development Agency'sannual report, published on June 26,1984, reveals that employment andinvestment in the electronics sectorin Scotland has been such in theyear ending March 31, 1984, that theScots are now producing about halfof the U.K:s computers, peripherals,and related products, and as muchas eighty per cent of the country'stotal output of ICs.

A lasting marriage...The recent renewal of an exclusiveUK distribution agreement betweenToko Inc, who are the world's largestmanufacturers of wound com-ponents, and Cirkit Holdings PLCmarks the beginning of the two com-panies' second decade of associ-ation. The original agreement, signedin 1974 with Ambit International, oneof the principal founding members ofthe Cirkit Holdings group, madeAmbit the first franchised Tokodistributor in the UK, and since thattime the number of products stockedhas grown steadily. In addition to be-ing the sole UK stockist of Tokocoils, Cirkit holds a comprehensiveinventory of their other components,including filters of all types, fixed in-ductors, bi-polar ICs, varactors, andpush-button switches. The mostrecent addition to the Cirkit range ofToko products is a range of helicalfilters.

...and an engagementTexas Instruments, the world's largestsupplier of semiconductor com-ponents (sales first quarter of 1984:$1340 million), and NationalSemiconductor, a leading supplier ofsemiconductor components andsystem products (sales first quarterof 1984: $383 million), have formallyagreed on a long-term cooperativetechnical effort in the area of ad-vanced 32 -bit microprocessors andperipherals. They will exchangespecific technologies in the 32 -bitfield, including development, sup-port, and software. In addition, Texas

Instruments acquires the right tomanufacture National's Series 32000family of microprocessor products.

New jobs in MiltonKeynes...Monsanto, the world's largest sup-plier of polished silicon wafers, isplanning to invest more than£35 million in a research andmanufacturing facility in MiltonKeynes, Buckinghamshire, England. Itis expected to create more than 400jobs during the next five years. Thisproject will provide the UK with adomestic source of Czochralskisilicon polished wafers currently im-ported by the IC manufacturers whilethe research facility will play a criticalrole in Monsanto's worldwide elec-tronics research programme.

...in Ilfracombe...Power supply manufacturer CoutantElectronics have been granted plan-ning permission for a new 19 000square feet factory next door to theirexisting 30 000 square feet site inIlfracombe, North Devon. In line withthis, Coutant, already the largestprivate employer in the area, will berecruiting more than 100 extra staffover the next three years.

...and in ShropshireTatung, the Taiwanese electrical andelectronics company, is planning amicrocomputer plant in Shropshire,England.

Screen Typers forGermany...Office and Electronic Machines PLC(OEM), the UK's leading officesystems company, have recentlysigned a contract to supply theirScreen Typer to Dreusicke GmbH, aBerlin -based company that operatesin office systems related marketsthroughout Germany. Screen Typerwas the first office word-processingsystem that integrated the typewriterwith screen data processing. Thesystem is based on a Z80Amicroprocessor with 64 K of memoryand operates under OEM's owndeveloped operating system. Thecontract, which is open ended, isscheduled to run over the next fiveyears and is valued at £3.3 million.

...and Nimrod decoders forSwitzerlandA substantial order for 2500 Nimrod450CS decoders for use in Swiss PayTelevision has been awarded toRacal -Oak Limited by Autophon ofZurich, Switzerland's largest providerof Cable TV equipment. Autophonalready provides cable TV services to

350000 homes in 500 Swiss com-munities, and is planning to supply25 satellite receiving stations andprovide cable TV equipment topotentially 800 000 subscribers.Nimrod is a family of addressable,high security scramble and descram-ble video and audio equipmentdeveloped by Racal -Oak, a joint ven-ture company established by RacalElectronics PLC and Oak IndustriesInc in early 1983.

Exhibitions: past...Exhibiting companies at Software 84,held at Earls Court, London, fromJune 5 to 7, reported a busy threedays. Almost 100 companies par-ticipated in the show covering awhole spectrum of software for alltypes of micro, mini and mainframecomputers. Packages available wereas diverse as programs for schoolrecords to multi -currency banking.The price variance was just as broadranging from just a few pounds tomore than £50 000. The exhibitionwas sponsored by SoftwareMagazine, Computer Weekly, and theNational Computing Centre.

...present...The Semiconductor 84 Exhibition isbeing held at the National ExhibitionCentre, Birmingham, from 25 to27 September.

...and futureAlongside Software 85, to be held atEarls Court from 4 to 6 June, 1985,will be a new computer exhibitionproviding visitors with an opportunityto see a comprehensive range ofhardware and peripherals.

V\EIE UPECPLE

011#109-20

elektor september 1984

They come...Mr Anthony Thatcher, managingdirector of Dowty Electronics Divi-sion, and a director of the DowtyGroup PLC, has been appointedchairman of Gresham Lion PLC. Theappointment follows the acceptanceof Dowty Group's offer to acquirethe whole of the equity share capitalof Gresham Lion. The latter companyspecializes in the field of submarinetorpedo electronic fire controlsystems, computer graphics, displayterminals, and advanced power sup-plies.

Mr Denys Johnson has been ap-pointed chairman of ERA TechnologyLimited, the Leatherhead-basedelectro-technical research anddevelopment company. DenysJohnson has had a distinguishedcareer in the electrical engineering in-dustry, having been the chiefexecutive and/or chairman of anumber of electrical companies, in-cluding Simplex Electric, Allen West,Creda, Russell Hobbs, WallacetownEngineering, and Power Centre. He isa past president of BEAMA andserved on the president's committeeof the European Trade AssociationORGALIME. He is currently chairmanof the National Economic Develop-ment Council's Electrical EngineeringCommittee.

...and they goMr J. Duncan MacEwan, controllerOperations and Engineering, Radio,retired from the BBC on 25 June1984 after a career spent almostequally in radio and television. Hisperiod as Chief Engineer, Radio, sawsignificant advances in BBC radio.The 13 -channel PCM (pulse codemodulation) radio distribution systemwas established to distribute highquality stereo signals to the BBC'snationwide network of VHF transmit-ters. The period also heralded the ex-pansion of Local Radio to cover mostof the main areas of population inEngland and development of theradio services in the NationalRegions.

Aerial viewFollowing the BBC's decision tochange over to circular polarizationfor all their VHF radio broadcasts,CErS ANTENNAS LTD of Strood,Rochester, Kent, is supplying thecorporation with a special aerialsystem. This system includestransmitting and receiving aerials, atransmitter combiner, and associatedfeeders. Circular polarization is nowfavoured by the BBC because itgives equal quality of reception toboth vertical (portable and car) andhorizontal (domestic) aerials.

License to operateThe Licence under which BritishTelecom PLC will operate waspublished in late June. The chairmanof British Telecom, Sir GeorgeJefferson, said this was another im-portant step on the road to flotationand added that he did not thinkanyone would be surprised by thecontent of the Licence, whichfollows the broad lines of the draftpublished last autumn, modified inthe light of concerns expressed inParliament and elsewhere.

\EVIE

PEO LE

A Q(uantum) Lleap)forward?Almost since its introduction lastJanuary Sinclair's QL computer andits makers have attracted virtuallynothing but criticism. And perhapsunderstandably so. When the firstwave of anger about the seriousdelays in delivery was still gatheringmomentum, fresh vehemence wasadded when it was announced thatthe computer had been released forproduction too soon and that conse-quently all the promised features didnot quite fit in the case. Amidst allthe confusion Sinclair arrangeddemonstations to prove the viabilityof the machine to the press, butthese were counter -productive whenthe programs did not work correctlyor not at all. However, most pro-blems now appear to have beenironed out, although the firmware isheld in three 16 K EPROMs insteadof two ROM ICs. In an announcementto the computer trade in mid July,Sinclair and Quest Automation jointlystated that Quest will market theCP/M (Control Program for Micros)

operating system for the QL at only£50. This will enable the QL to haveaccess to a large range of existingsoftware and to be linked to conven-tional disk memories, such as floppydisks, for instance. Furthermore, itwas stated that production (that is,20 000 per month) will be as plannedby this month (September), and that

production plans for next year in-dicate 750 000 models. In addition,there will be a Winchester diskavailable; the micro drive will be im-proved from a scanty 100 Kbyte to1 Mbyte; and over twenty programswill have become available towardsthe end of this year while softwarecompanies have been contracted toproduce many more. If all theseplans and intentions come to fru-ition, they should help Sinclair in hisplans to go public later this year.Bad news for Sinclair is, however,the recently announced decision bythe BBC to extend its agreementwith Acorn Computers for the pro-duction and marketing of the BBCcomputer for a further term of fouryears as from this month. Sinclairhad hoped to take over this lucrativecontract.

A great British successstoryLynwood, the leading British ownedmanufacturer of intelligent terminals,has come a long way from itshumble beginnings above an antiqueshop in the Hampshire village ofHartley Wintney. Founded in 1969,the company had a turnover of £2.5million in 1980/81, £8 million in1983/84, and is now forecasting salesof £11 million for 1984/85. Apartfrom the seven locations in Alton,Hampshire, for manufacture, engin-eering, training, and administration,Lynwood has offices in London, Bir-mingham, and Harrogate, and thereare plans to expand in Scotland aswell as in Europe, where there aresubsidiaries in Switzerland and theNetherlands. Moreover, in July thecompany set up a wholly ownedsubsidiary in the USA. Known asLynwood International Inc., the newcompany will market the full LynwoodAlpha and Beta range of intelligentcomputer terminals and the DialogAPL software from its Dyadic sub-sidiary. Right from the early days thefounders decided that the company'sgrowth would be based on technicalexpertise and the philosophy has car-ried through to today with excellenttechnical development groups in bothhardware and software. Lynwoodnow has two main ranges of intelli-gent terminal: the Alpha, a highly in-telligent 16 -bit Z8001 based terminalin both monochrome and colourform that offers 32 K ROM and192 K RAM; and the Beta, less in-telligent and based on the 8 -bit Z80Awith 16 K ROM and 8 K RAM.

9-21

elektor september 1984

I

Scene of science

London's Science Museum is dif-ferent from most museums. It is,as stated in one of its brochuresfor visitors, a crowded andfriendly place. "It is not a placewhere people stand in silencebefore objects they feel theyshould, and possibly do, admire,and move quietly, as in a church.It is somewhere where peoplefeel free, and often excited;where they talk loudly(sometimes too loudly) and evenlaugh." What is not widelyknown is just how much highly -skilled work goes on behind thescenes to maintain a constantly -changing panorama of sciencepast, present-and future.

London's Science Museum leads allothers as a tourist attraction. Visitorsin 1981 were some four million, twiceas many as visited the Tower ofLondon or St Paul's Cathedral. Itsonly world rival is the DeutschesMuseum in Munich, and it can besaid that the Science Museum hasthe biggest collection of science andtechnology in the world. There arecertainly other well-known museumsbut not one that specializes entirelyin science.Its method of management has beenchanged recently. Up to now it hasbeen financed by the UK Depart-ment of Education and Science, withadministration wholly the responsi-bility of the Director, DameMargaret Weston, and her staff. Thisis to change, to bring the museuminto line with others, and theadministration will be in the hands oftrustees appointed by the PrimeMinister. Whether this will produceany significant change in policyremains to be seen.Another aspect of the ScienceMuseum's activities underlines howwidespread its reputation now is inBritain. This is the appearance ofoutstations in several parts of thecountry. The latest of these - theNational Museum of Photography,Film and Television - was opened inBradford, an industrial town in north-ern England earlier this year. It hasone of the largest cinema screens inBritain and the very latest in filmprojection systems, called IMAX. Thefirst film to be shown was an award -winning history of flying. The theatrealso has a multiscreen slide showcontrolled by computers.Such use of the most advanced

techniques shows how much wemust revise our notions about whatwe call a museum. It need not beonly a collection of 'old' material; the.Science Museum is right up-to-dateand looks into the future, too.There is also an exhibition at theFleet Air Arm Museum in Somerset,where one can see the first British -made Concorde. Yet a third outstat-ion is the National Railway Museumat York, the famous cathedral city inthe North-East. All of this suggeststhat the Science Museum is morethan its name implies; it is a nationalinstitution.It is situated in what might well bedubbed museumtown, a large part ofWest London that includes theVictoria and Albert Museum, theGeological Museum and the famousNatural History Museum. The areacovers about 120 000 square metres.We can ignore all the involvedhistory - it has been enthusiasticallyrecorded by Sir David Follett' - andsay that the Science Museum as weknow it really began with theappointment of Colonel Henry Lyonsas Director in 1920. By 1933 when heretired he had, as Follett wrote,

"developed the Museum into one ofthe foremost technical museums inthe world." By 1928 the first newbuilding was ready for opening byKing George V, and has been grow-ing ever since.But why have a science museum?Indeed, what purpose does amuseum of any sort serve? Therewere none until a very few centuriesago, and even those were more col-lections of curiosities culled by worldtravellers and victorious generals thana museum as we now understand it.(The Ashmolean Museum at Oxford,which celebrated its tercentenary lastyear, started in a similar way.)

New CultureThe people of earlier times were van-dals: famous buildings almost disap-peared to serve ambitious thieves, orcrumbled from philistine neglect. Itwas not until the Renaissance waswell under way that people becameinterested in the story of nationalculture, first of all in artistic andcultural artefacts. Then, in the late18th century, Britain opened the firstcampaigns of the Industrial Revol-ution, which grew rapidly in the 19th

Hooke's Compound Microscope (Photograph from Hooke's Micrographia (1665)1

9-22

elektor september 1984

century. Science and technologybecame challenging new aspects ofculture, and with them came a grow-ing interest in earlier science.These developments made peoplereflect on the aims and functions ofa museum. First, there was preser-vation. Machines and apparatuswould disappear like old toys unlessthey were carefully preserved. Some-times machines endure and are in avery dilapidated condition; then it isthe task of the Museum's specialstaff of metal workers and cabinetmakers, with the help of whateverold drawings may still be available, toreconstruct and present them in theiroriginal state. The originals of manydevices no longer exist or are notaccessible, in which case the crafts-men build models to scale, oftentravelling far afield to look at surviv-ing pieces. New materials andadhesives are studied to keep thetechnical side up-to-date.Another task is education, whichinvolves presentation. Objects inmuseums devoted to artistic pursuitsspeak for themselves and need littlemore than a name, but in a sciencemuseum this is not so. The purposeof a piece of apparatus and how itworks must be explained in somedetail.Finally, there is the job of entertain-ing. It would be of very little use tobunch exhibits together in anunorganized way. Furthermore,things with moving parts may haveswitches or other means of makingthem work at the wish of a visitor.This is done at the Science Museumto a great degree; there is even aChildren's Gallery where youngpeople may do their best to testdevices to destruction without eversucceeding.Every scheme imaginable is used atthe Science Museum to makepresentation entertaining. There arepictorial techniques, for example thediorama of mediaeval agriculturepainted by a well-known artist. Thereare working models, such as a com-puter with print-out and visualdisplay unit against which a visitormay try his skill. There are life-sizemodels of settings with sculpturedmen or women, as shown with the18th century wooden printing pressand a surgery of 1900, with a doctormeasuring a patient's blood pressure.One can see a steel -maker at workon the open-hearth furnace; carefuluse of colour and light gives a veryconvincing picture of red-hot steel.This technique is even moreimpressive when displaying a redhotingot of iron: one feels afraid totouch it.

Continuous tapes looped intorecorders give a running commentaryon processes nearby. There are life-size models of space -exploringsatellites and in the Children's Gallerythere is, among many other things ofcourse, a periscope of the kind usedin a submarine, which can beoperated by any visitor.There is a life-size model of a phar-macy of 1905 with two customersand one pharmacist, representing atime when many a chemist made hisown pills. There is a reconstructedship's bridge. One could go on for along time selecting fascinating itemsthat show the display skills of the50 -strong team of craftsmen, manyof them artists, working in the well-equipped workshops of the Museum.Educationally the Museum is uneq-ualled. There can surely be no bettermethod of teaching, say, physicsthan by taking pupils to the ScienceMuseum. They can learn a great dealabout microscopes, for example, bylooking at exhibits that range fromLeeuwenhoek's device and Hooke'sto the most modern instruments foroptical or electronic magnification.More can be learned in an hour thanby many hours in a classroom. Andit is not all old material. TheApollo 10 spacecraft is there, with afull-size copy of the Apollo 11 lunar'lender' module and a one -sixth scalemodel of Surveyor; there is also afull-size model of the Sputnik. Toencourage pupils in an educationalway, many leaflets on various sub-jects are available with questionnaireswhich the pupil can answer on thespot and at home.The Museum acquires its exhibits inseveral ways. Some are given. Someare bought privately or by bidding atauction. Others are on permanentloan. One famous addition is theWellcome Museum of the History ofMedicine, which covers such mattersas the story of antiseptics,anaesthetics, scientific aids for doc-tors, and the eradication of smallpoxin every part of the world.For good presentation the exhibitsmust be organized into families orgroups such as motive power, ironand steel, agriculture, sailing ships,magnetism and electricity, spaceexploration and rocketry, structure ofmatter, meteorology, locks andfastening, photography, atomicphysics and nuclear power, com-puting and so on.

Special ExhibitionsAmong the crowded galleries on fivefloors, space is provided for specialexhibitions. Some of them are openfor only a few weeks or months,

after which they may be taken roundBritain. Last year there was an enor-mous special exhibition, Telecom-munications, marking the centenaryof Standard Telephones and Cables(STC). It showed everything fromline telegraphy to radio and satellites,and optical fibres (the world's firsttelephone link by this means wasopened by the UK Post Office, nowBritish Telecom, in 1977). Very littlewas left out in this fascinating story,from Oersted's work on electriccurrent through to the first primitivetelegraphy, followed by the earliesttransatlantic cable, the coming ofradio, the thermionic valve, then thetransistor, electronic telephoneexchanges, subscriber trunk dialling(STD), the use of lasers with opticalfibres, and so on.Among the wealth of material thereare many 'firsts' or near -firsts. Thereis, for example, the world's earliestsurviving steam locomotive,Puffing Billy of 1813. There is thefirst locomotive to pull a passengertrain, Stephenson's Rocket of 1829.The visitor can see the world'searliest photographic negative (byFox Talbot, the founder ofphotography as we know it).In basic physics there isJ.J. Thomson's apparatus with whichhe 'discovered' the electron in 1897.There is also C.T.R. Wilson's cloudchamber, with which for the firsttime the tracks of atomic particlescould be seen, work that speeded upthe study of the structure of matterprobably by a decade at least. Thereare very early motor -cars, including aRolls-Royce Silver Ghost of 1909.(Incidentally, though the primaryinterest is science, many earlyexhibits are aesthetically interestingand many, indeed, beautiful: seeearly telephone receivers or sewingmachines, for example, elegant inbrass scrollwork.) But this is oldhistory and in a way contributes tothe notion that museums are stuffy.Science and technology, however,are developing disciplines. What isnew today will be old tomorrow. Inthis respect the Science Museum isup-to-date and even projects into thefuture: nuclear fusion, as a source ofpower, is not yet proven, and thereare huge machines still experimental;nevertheless there is a display cover-ing the technology.

*The Rise of the Science Museumunder Henry Lyons, by David Follett,1978.

C.L. Boltz Spectrum 185

9-23

data transmission bytelephoneelektor september 1984

In the last few years the telephone network, which was originallyintended for voice communication, is being used more and more fortransmitting (digital) data. The growth in the popularity of homecomputers has been startling but it is not really surprising that theirusers should seek to use the telephone lines as a medium forexchanging programs and data. What happens between transmittingcomputer and receiving computer is, hpwever, still a mystery to manypeople so we felt that is was time to clarify this. Also included inthis article is a description of the AM 7910, which is a commonlyused dedicated modem IC.

data transmission bytelephonehow dotwo computers`converse overthe telephonelines?

Figure 1. In the normal(two -wire) telephonesystem the signals inboth directions travel onthe same line.

When Alexander Graham Bell first had thebrainwave that led to the development oftelephone he would have found it difficultto envisage the idea of two computersusing his system to communicate witheach other. Cassette tape, which, again,was designed for storing audio 'infor-mation', has long been used for storingcomputer data, and in the same way thetelephone line can perform a duty otherthan allowing far -away friends to converse.There are certain limitations, of course,but using the telephone lines two com-puters can exchange messages, programsand data in digital form. It is of littleinterest for the purposes of this article todeal with the actual telephone network aswhat we are really concerned with is howdata can be transmitted over telephonelines, what speeds are possible and whata modem does. As a start, however, wewill talk about the telephone.

The telephone lineThe normal telephone line, that runs intoevery subscriber's home, is what is knownas a switched line. There are a number ofswitching points (mostly in the form oftelephone exchanges) between any twosubscribers. The frequency range of this

sort of line is from about 300 to 3400 Hz,which is quite sufficient for speech. Thisrange limits the speed at which data canbe transmitted to less than 2400 baud,however, as transmission rate is frequency -dependent. Another type of telephoneline is the hire line, which has a higherquality. The maximum transmission rate ona normal hire line is 2400 baud, going upto 4800 baud for a local hire line and even9600 baud on a high -quality hire line. Hirelines are not generally used by amateurs.Each end of the line is almost invariablyconnected to a telephone receiver. Thebasic principle of the telephone system(except for the dialling section) is outlinedin figure 1. The actual connection is madevia two wires, a and b. There is also anearth line present which our drawing doesnot show. The signal provided by the car-bon microphone is superimposed on thed.c. voltage supplied from the exchange.At the other end the signal is extractedfrom the d.c. and causes the bell in thesecond telephone to ring. When the hand -piece is lifted from the hook the 'a' line isconnected not to the bell but via atransformer to the earpiece, where thesignal is reconverted to the original audioinformation (generally speech). We are notinterested in any other circuitry in the ex-change or the interconnecting line. We

1

9-24

now know, in any case, that the signal issuperimposed on a d.c. voltage and thatthe same lines carry information in bothdirections. This latter fact is particularlyimportant as special measures are neededif both sides want to transmit data at thesame time.

A modem at each endThe connection between computer (or ter-minal) and telephone line is made via aso-called modem (MOdulator/DEModu-lator). Two basic types of modems exist:acoustically -coupled and direct -coupled.In the case of the first of these the infor-mation must be exchanged with thetelephone handset via a microphone anda loudspeaker. The second type, as itsname suggests, is connected directly tothe telephone line. The direct -coupledmodem is much less sensitive to noiseand interference so there are less faultsduring data transmission but it must bedesigned very carefully so as not to pro-duce interference itself. Both types ofmodem must have type approval.The actual function of a modem is to con-vert serial digital information into ananalogue signal that can be transmitted viathe telephone line, and to receive andreconvert information from the line. Toenable different modems to be connectedto the same network a standard is re-quired. The CCITT (Consultative Com-mittee for International Telegraph andTelephone) makes various recommen-dations for the different transmission ratesand types of line. The V24 standard ap-plies for the link between computer andmodem. The modem itself should keep tothe V21 and V23 standards. These stan-dards specify whether the modem usessynchronous or asynchronous trans-mission, what the data transmission rate is,what the procedure is for automatic calland answering, what tests should be car-ried out and whether there is a control(back) channel present. In short: theyspecify everything needed to enable twomodems to communicate with each otheron the same level.The CCITT's V21 recommends a trans-mission rate of 300 baud in full -duplexmode over a two -wire connection (allow-ing simultaneous transmission and recep-tion of data). V21 is used for all normaldata transfer.The V23 standard, on the other hand,recommends a dual -speed half -duplextransmission at a speed of 1200 and75 baud. The 75 baud channel is thenused for control purposes.

Bits in the telephoneBefore the data can be transmitted via theanalogue telephone line it must be coded.The modem does this by means of modu-lation. There are several different ways ofdoing this:AM, in which the amplitude of the carriersignal changes with the logic level (see

2

0

0

110 0 011 1 0 1 110

o 1 o 0 oIl 1 o 1 1 0

11 .11111 MA

1 0 0 1 1 0 1 1 0

84090-2

3

V21

300 baud

17.

//1300 980 1180 1650 1850 3400

1750f (Hz)

V231200 baud

0 300 390'450 1300 2100 3100420 1700

f (Hz)tc

84090-3

figure 2a). The simplest form of AM is'on/off keying' in which case the carrier ispresent for a '0' and not for a T.FM, in which the simplest form, FSK (Fre-quency Shift Keying), is generally used.The two logic levels are represented bythe carrier having two different possiblefrequencies. Data transfer over switchedlines almost always uses FSK.There are two more advanced techniquesworth mentioning, namely DPSK (Differen-tial Phase Shift Keying) and QAM(Quadrature Amplitude Modulation). Thefirst of these uses phase shifting(figure 2c) and the second uses amplitudeand phase shifting. Both of these tech-niques permit the data transfer rate to be

data transmission bytelephoneelektor september 1984

Figure 2. Various differentmethods of modulationare used when data isbeing sent over ananalogue line. Indicatedhere are: AM -amplitude modulation -(a). FSK - frequencyshift keying - (b) andDPSK - differentialphase shift keying - (c).

Figure 3. The carrierwaves used in V21 mode(a) and V23 mode (b)must remain within thefrequency range used bythe telephone system.

9-25

data transmission bytelephoneelektor september 1984

Figure 4. In the AM 7910IC, whose block diagramis shown here, a com-plete modem is fitted on-to a single chip. Thesignals are processedcompletely digitally.

Figure 5. The transmittersection of the modem inslightly greater detail.

Figure 6. Here we see thevarious different sub-spctions that make up thereceiver section.

increased (relative to the othersmentioned).All of these techniques use one or anumber of carrier waves so the fre-quencies used must be carefully decided.The frequencies recommended by V21and V23 are indicated in figure 3, whichalso shows their position within the fre-quency range used in telephones. Full -duplex operation at 300 baud uses twobands around 1080 and 1750 Hz, with200 Hz separating '0' and '1' in both cases.One channel carries data in one directionwhile the other carries data in the reversedirection. The main channel in the V23norm is centred at 1700 Hz, and the backchannel is at 420 Hz.

That is all that needs to be said about theactual transmission via the telephone line.A modem is, however, required at eachend of the line so we will now have a lookat a modern modem contained in a singleIC.

The AM7910, a single -chipmodemVirtually everything in this IC that couldbe digitalised has been digitalised. Eventhe filtering and generating the carrier (asine wave) is done digitally. A blockdiagram of the complete IC is shown infigure 4. As could be expected, it contains

4

TRANSMITTEDDATA 2a

BACK

CAP, ps

CA -P2 0 7

RECEIVED 0 5CARRIER

TRANSMITTERa

17MCA

MC, o18

19MC2 0

20MC:, 0

MCI21

DATA TERMINAL 0 15READY

XTAL1/CLK 0

XTAL2 0

RECEIVER

-0 TRANSMIT TEDCARRIER

MAIN 29

RECEIVED5

DATA

BACK

INTERFACE CONTROL

24

1

23TIMING

CONTROL

120 REQUEST TO SEND

13

25

11-0

CLEAR TO SEND ,11 MAIN

-0 CARRIER

o/

REQUEST TO SEND

270 CLEAR TO SEND

0 CARRIER DETECT

:0 RING0 RESET

O 2 0 -5V Vcc

o i 0 -5V V8890 10 AGND

220 0 DURO

BACK

84090-4

5

TO

MCD-81C4

Y

>--- SINESYNTHESIZER

DIGITALANDPASSFILTERS

DACANALOG

POSTFILTER

TC VAr

84090-5

6

(VW RCANALOG

PREFILTERADC

DIGITALBANDPASS

FILTERS

DIGITALDEMODULATION

CARRIERDETECT

RD

CD

84090- 6

9-26

7 data transmission bytelephoneelektor september 1984

1 - I

/ / / / / 1 -'-=.1z4 1

a transmitter and a receiver, both of whichare controlled by interface control andtiming control sections.Details of the transmitter are seen infigure 5. The serial data that are to betransmitted are fed in one side and leavefrom the other side as an FSK signal thatcan be sent over the telephone line. TheFSK signals must be perfect sine waves inorder not to clutter up the telephonelines. Sinewaves, at two different fre-quencies, are generated digitally andswitching from one frequency to the otheris only done when the signal is at its zero -

crossing point. The digital FSK signalpasses through a digital band-pass filterand is then fed via a digital to analogueconverter to an analogue filter. All thisfiltering is needed to limit the amount ofpower fed onto the telephone line. Thispower must conform strictly to the regu-lations in order to reduce crosstalk andinterference.The modem's receiver section, shown infigure 6, reconverts the FSK signals todigital ones. The signal arriving over thetelephone line is first fed to an analoguefilter before passing to an analogue todigital converter with an exceptionallyhigh-speed of 496 kHz (it needs to be fastbecause of the FSK frequencies). In thisway the effects of the higher harmonics inthe FSK signal are reduced. The final twostages are a digital band-pass filter and adigital demodulator after which only thedata remains. A carrier detector indicateswhen there is data present.

All the 'traffic' between computer (or ter-minal) and modem is controlled by the in-terface control. This section has several in-puts, MCO ... MC4, to enable the modemto be set to the various different standards(such as V2I and V23).The exact frequencies for the FSK trafficare generated by the timing control,which takes its reference from a crystal.The block diagram clearly indicates thelines for main and back channels. This isonly needed for V23 (1200/75 baud) as V21only makes use of the main channel.An important feature of the IC is its auto -answer facility. This enables the modem torespond automatically to a telephone call.The communication protocol betweencomputer and modem is very importantand quite involved, as the tinting diagramof figure 7 indicates. The example hereshows the various signals and relation-ships for the AM 7910 when it is operatingin V21 mode.At first sight it may not be entirely obviouswhy a modem needs to be so complex. Itsoon becomes apparent, however, that allthis complexity is, in fact, needed toensure that data is tranferred without anyerrors even when there is interference onthe telephone line. It is also vital to pre-vent the modem from generating noisethat could affect other telephone users. 14

84090-7

Figure 7. The timingfor the modem

(shown here in V21 mode)shows all the signalsused and how they relateto each other.

9-27

active crossover filterelektor september 1984

active crossover filter

for activeloudspeakersystems

One of the first questions that has to be answered when consideringa new loudspeaker system is what sort of filters are to be used.Should it be a 'normal' passive design or is an electronic active filterwhat is needed? When the pros and cons are weighed up it will beobvious that, from a musical point of view, an active filter ispreferable. When finances are taken into account, however, thepassive system's lower price may prove to be the deciding factor.For the purposes of this article we will assume that finances take aback seat to faithful sound reproduction and simply concentrate onthe design of this very versatile active crossover filter. We will,however, look at the differences between the two systems. Theprinted circuit board allows a choice between a two or three-wayfilter with a roll -off of 12, 18 or 24 dB per octave. It is also possible touse various different types of filter.

In electronics we call a circuit 'active' if,along with the usual (passive) componentslike resistors, capacitors and inductors, itcontains an amplifying element. It is ob-vious, therefore, what an active filter is,but the term 'active loudspeaker may notseem so obvious. A loudspeaker, whichreally only consists of the cabinet anddrive units (the actual loudspeakers), can,strictly speaking, only be passive, unless ithas some mechanical feedback. Ingeneral, however, a loudspeaker equippedwith an active crossover filter is called anactive loudspeaker. This is partly due tothe fact that power amplifiers are thenoften built into the loudspeaker cabinets.The differences between active andpassive loudspeaker systems can be seenwith the aid of the diagrams in figure laand figure lb. In the passive system(figure la) the output signal from thepreamplifier is passed through the poweramplifier to the loudspeakers. A passivecrossover filter, made up of coils and

capacitors, ensures that each of the driveunits - woofer, mid -range and tweeter -is fed the appropriate part of the audiofrequency range.The active system, shown in figure ib,operates slightly differently. An obviousdifference is that the filtering is doneearlier, directly after the preamplifier, infact. The result of this is that the threefilter outputs must each be followed by apower amplifier so that three of these areneeded per channel instead of one. Thismakes the active system more expensivethan a passive one.

Active or passive?There is no definitive answer to the ques-tion 'Which is better, an active or passiveloudspeaker system?'. The active systemhas more pros than cons but that does notnecessarily mean that it is the right choicefor everybody. Basically the active systemis more complicated, bulkier, and moreexpensive than a passive version but

9-28

la passive loudspeaker systemactive crossover filterelektor september 1984

preamplifier*

rtbd-rtnes

[Nagle,

.:1

84071-1a

lbactive crossover filter

L 3[371.1p

these are the only drawbacks. That is notto say that the active system always soundsbetter. There are some passiveloudspeakers whose sound cannot befaulted, just as there are some activesystems that are very mediocre. Ingeneral, though, the active system ispreferable. Its main advantages are: It is very easy to match different

loudspeakers by amplifying the signalat one filter output or amplifier input. (Thisis also very accurate). With passivesystems matching involves adding resistorsfor extra attenuation, which is fine fortweeter and mid -range but it will not workwith a woofer (because it affects thedamping factor). An alternative is to use asuitable transformer (which will beexpensive) but this will mean that awoofer with a higher output than the mid-range and tweeter used can never besatisfactorily incorporated into a goodthree-way passive system. The loudspeakers are connected di-

rectly to the amplifier outputs (and notthrough big coils as in a passive set-up) sothe damping of the loudspeakers is better.This results in more accurate repro-duction, which is particularly marked inthe bass range. This is probably thegreatest plus point in an activeloudspeaker system. The impedance curve of the loud-

speaker in an active system does notaffect the behaviour of the crossover filterso this always operates as it should. Con-sequently there is no need for any sort of

impedance -matching network. Without the numerous coils and

capacitors used in a passive system theload seen by the power amplifier is lesscomplex, which means that the soundreproduction is improved. The power amplifiers are located much -

closer to the actual loudspeakers (oftenwithin the loudspeaker cabinet) so thelength of the loudspeaker cable is greatlyreduced. This removes the need forspecial, expensive loudspeaker cable.

Basic circuitsElectronic crossover filters are actuallyquite easy to make nowadays, especiallywith the very good low -noise opamps thatare available. It is a matter of choosing thecorrect characteristics and a practicallayout. The actual filters can be chosenfrom a number of standard types. Thebasic circuits making up our crossoverfilter are shown in figure 2. Any sort ofcrossover filter can be made simply bycombining a number of these circuits.The upper two circuits (a and b) are low-pass filters; below them, c and d are high-pass filters. Circuits a and c each containtwo RC sections and are therefore knownas second -order filters. Their characteristiccurve has a roll -off of 12 dB per octave(6 dB per RC section). Circuits b and d arefirst -order filters with a single RC sectionand a roll -off of 6 dB per octave. If a and b(or c and d) are placed one after the otherthe result is a third -order filter with a roll -

Figure la. In a passiveloudspeaker system thecrossover filter, made upof coils and capacitors, islocated between thepower amplifier andloudspeakers.

Figure lb. The filter in anactive system is placeddirectly after thepreamplifier. Each driveunit then needs its ownpower amplifier.

9-29

active crossover filterelektor september 1984

Figure 2. These are thebasic circuits that will beused in our activecrossover filter. The uppertwo (a and b) are low-pass filters while theother pair (c and dl arehigh-pass filters. The roll -off of the filter can bechanged by combiningthese basic circuits.

Figure 3. The three curveshere show the frequencycharacteristics of the'same' filter for three dif-ferent values of roll -offslope.

84071-2

off of 18 dB per octave. A pair of type a (orc) circuits in series form a 24 dB/octavefourth -order filter. When connecting filtersections in series the component values inthe various sections must be carefullyselected, as we will see later.In figure 3 we see a comparison betweenthree filter curves, of 12, 18 and 24 dB peroctave. The filters in question have a low-pass characteristic with a cut-off fre-quency of 1 kHz.The number of dBs of attenuation per oc-tave that a filter provides is not the onlyimportant factor. For acoustic applicationsthere are several other important criteria,such as the precise shape of the filtercharacteristic, the behaviour within thepass -band and the phase shift. Within cer-tain limits these qualities can be changedby carefully choosing the filter com-ponents. This is very important as it meansthat the circuit does not have to bechanged in order to have a different typeof filter.Three of the most common filters are theChebychev, Butterworth and Bessel types.None of these conforms to the 'ideal' filtercharacteristics of constant gain and linearphase shift (within the pass -band) verysteep roll -off outside of the pass -band andnegligible undesirable oscillation. Allthese characteristics cannot be combinedin one filter so the right filter for any ap-plication is chosen by first deciding whatis the most important feature.

3

This is ably illustrated by figures 4 and 5.The three diagrams in figure 4 show thecharacteristics for Chebychev, Butterworthand Bessel filters. In each case the fourth -order low-pass filters have a cut-off fre-quency of 1 kHz; the continuous line is theamplitude curve (frequency characteristic)and the dotted line is the phase shift.When steep roll -off is most important theChebychev filter (4a) is clearly thefavourite. The gain within the pass -band isnot very constant, however, and the phaseshift curve is not noticeably linear. Theselast two are greatly improved in the Butter-worth type, whereas in the Bessel filter (c)a 'flatter' phase curve is achieved at theexpense of a slightly less steep roll -off.The most commonly used filters incrossover networks are Butterworth andBessel types. Very often the Butterworth ischosen for its more favourable frequencycharacteristic. For music reproduction avery important characteristic is theresponse to an input pulse, as figure 5shows. From this diagram we see that theBessel filter's characteristic is the better ofthe two and it also has less secondaryoscillation. The Chebychev filter'scharacteristic is not shown here as it is farworse than the other two.We have designed our crossover filter insuch a way as to enable it to be con-figured as either a Bessel or Butterworthtype. It is then up to each user to choosewhich is more suitable for the particularapplication.

The complete crossover filterHaving dealt with the basic theory wehave now come to the practical part ofthis article, namely describing the filter inits final form. The mono version is shownin figure 6. The same circuit is simplyduplicated for stereo operation.The power supply, seen at the lower left-hand side, has the usual format. In ad-dition to this we see input buffer Al andthree output buffers, A2, A3 and A4. Theoutput levels can be trimmed by means ofPI (low range), P2 (mid range) and P3(high range). The input to Al comesstraight from the preamplifier, and the out-puts from A2 ... A4 are fed directly tothree power amplifiers.The actual filter is based on A5 ... Al2and is set up as a fourth -order three-waysystem. The crossover frequencies are at500 Hz and 5,000 Hz with the componentvalues indicated. The three sections of thefilter are fairly obvious: A5 and A6 definethe cut-off point for the woofer (500 Hzhere), All and Al2 block all low andmedium frequencies (less than 5,000 Hz inthis example) to the tweeter, and the mid-range frequencies are passed to the ap-propriate output by the combination ofhigh-pass filter A7/A8 and low-pass filterA9/A10.The three-way 'character' of the filter is byno means fixed. A two-way system can bemade simply by leaving out band-pass

9-30

4a b active crossover filterelektor september 1984

UIda)

C

44.711.4

PHI('I

5

1

Butterworth

I I,

44015

filter A7 ... A10 and buffer A3. The samething applies for the steepness of the roll -off. All the sections are, in principle, setup as 24 dB/octave filters but this could

easily be changed to 18 dB/octave or12 dB/octave. This is done by leaving outsome components or replacing them withwire bridges.

6

15V

Al ,A2 = IC1 = NE5532NA3 .A4 = IC2 = NE5532NA5 , AS -IC3= NE5532NA7 ,A8 = IC4 = NE5532NA9 . A10 = ICS = N E5532UAll. Alt = IC6 = NE5532N

1... C14. CI, CM 123

Figure 4. The frequencyand phase curves for thethree most commonlyused filter types areshown here - a =Chebychev, b = Butter-worth, c = Bessel. Allthree are fourth -orderfilters with a cut-off fre-quency of 1 kHz.

Figure 5. As regards reac-tion to a pulse input it isclear that the Bessel filteris far better than its But-terworth counterpart. Ithas a much shorter delaytime and shows hardlyany secondary oscillation.

Figure 6. The completecircuit for the filter. If itis used as shown it has acharacteristic of 24 dB/octave but this can easilybe changed to 18 dB/octave or 12 dB/octave.

id., C" I IC3 IC4 ICS M. IC

0 0 0 0 0co 04 cw

15V

9-31

active crossover filterelektor september 1984

Table 1. The values of thefrequency determiningcomponents in the circuitare calculated from theseformulae. The filters maybe either Bessel or But-terworth types.

Setting the component valuesApplying the circuit of figure 6 to anysituation is quite easy. Start by looking attable I, which gives the formulae for allthe frequency -defining components. Ifyou've suddenly discovered that yourcalculator batteries are flat don't panic -we have taken the trouble to include afew tables giving the component values touse with the most commonly used fre-quencies.The first thing to be decided is the slopeof the filters' characteristics. If 24 dB/octave is chosen the rest is very easy asthe circuit remains just as it is. In the low-pass filter C21, C22, C23 and C24 corre-spond to CA, CB, CC and CD respect -

Table 1

Bessel Butterworth

...s

= 0.9076CA -

1.414CA -

2 7 f - R

0.6809

2.cf-R

0.7071C *.:1

low-pass: 12 dB/octave

C B2 z i - R

B2 7 f - R .s

0

0.%482 N.

CA - 5c.

.7=

--

Nt. 2 rt f - R

0.4998CB -

2 sr f - R

0.5CB -

0.ca"6

2s 1 - R

0.757-

21. f - R

1

CD -

.

Etg

low-pass: 18 dB/octave 2-Rf- 2 z f - R ..0.7290

CA -1.0524

CAI

2. 1 - R 2 f - R;...ae0' .*

0.6699Cg -

ct

0.9239CB

L,:,

- ="4=ii"r.c.=

2 s 1 - R

1.0046cc -

2 7 f - R

2.6130cc --....

2 171 - R

0 3872co

2 . f - R

co - 0.3827low-pass: 24 dB/octave =

2a t - R 2s f - R

..0 RA =1.1017 0.7071

-1I-*-11-'

..0

----2 .7 1 - C

1.4688RB

2 . 1 - C

1.414RB

high-pass: 12 dB/octave

27 1 - C 2 st C u.a0

1.0474 0.5,--si

.c c-11-'-i

1,RA -

2 7 f C

2.0008Rg

RA2 7 f - C

2Rg -

i"a

U

-2 7 1 - C

1.3228RD -

2.1C

1

80 -

:-

F,

high-pass: 18 dB/octave 2 7 f C 2 7 t - C .=1.3701

RA0.9239

RAI

2 f - C 2 f - C

" 0 0s

1.4929

z

1.0824Rg -

Z.)

c ,-11-'-I

F....

2 7 f C

0.9952RC -

2 Is f C

0.3827RC...

24 dB/octave

2 7 1 - C

2.5830

-2 7 1 - C

RD - 26130high-pass: RD - 2,1-C 2.1 C

84071

ively in table 1; for the low-pass filter inthe mid -range section these are C29, C30,C31 en C32. Taking 18 dB/octave,capacitors C23 and C31 in the low-passfilters are removed and resistors R10 andR18 are replaced by wire bridges. Simi-larly R14 and R22 in the high-pass filtersare left out and C27 and C35 are replacedby wire bridges. If the roll -off required is12 dB/octave the whole second section ofeach filter is removed and the opamps justwork as buffers. In this case C23, C24,C31 and C32 (in the low-pass filters) aswell as R14, R15, R22 and R23 (high-passfilters) are removed, and resistors RIO, RII,R18 and R19, together with capacitors C27,C28, C35 and C36, are replaced by wirebridges.When the roll -off, cut-off frequency andtype of filter have been chosen the valuesof the frequency -determining components,CA ... CD and RA ... RD, can beselected from the formulae in table 1. Thevalues needed for a large number of dif-ferent cut-off frequencies have alreadybeen calculated and are indicated intable 2 (low-pass filters) and table 3 (high-pass filters). In these tables the com-ponents in question have the samedesignations as in table 1:C21... C24 and C29 ... C32 areCA ... CD; and R12 RI5 andR20 ... R23 are RA ... RD.We have purposely not rounded off thevalues of resistors and capacitors to thenearest standard values to enable accuratevalues to be obtained by means of paralleland series combinations of components.Using E12 values makes the filters lessthan ideal so, if possible. use E24 -seriesvalues.

ConstructionConstructing this filter is simply a matterof fitting the correct components, selectedaccording to the desired characteristics,into the printed circuit board shown infigure 7. For the 18 dB/octave or 12 dB/octave versions a number of componentsare left out or replaced by wire bridges.Apart from the supply transformereverything fits onto the same printed cir-cuit board. For stereo operation, of course,two boards are needed, one per channel.The way in which the project is finished isa matter of personal taste. It could, for in-stance, be housed in its own case butthen there will be three cables comingfrom the case and going to the poweramplifiers, which is not such a good idea.A more logical idea is to include filterboard plus three power amplifiers in theactual loudspeaker cabinet. Each channel(left and right, in the case of stereo) isthen fed from a single screened cablecoming from the preamplifier. While onthe subject of screened cable it is ad-visable to use this for interconnecting thefilter outputs and the power amplifierinputs.If the filters and power amplifiers are built

9-32

Table 2 active crossover filterelektor september 1984

low-pass12 dB/octave

Bfrsspl Butterworth

low-pass18 dB/octave

Besse! Butterworth

low-pass24 dB/octave

Bessel Butterworthf1Hz)

R = 5k6CA

(2x)CB

R = 5k6CA

(2x)CB

R = 5k6 (3CA 1 CB

x )

' CD=

CA5k6 (3CB

x )CD CA

R = 5k6CB

(4 x )

CC CD CAR = 5k6(4x)

CB CC CD1nF) (nF) (nF) (nF) (nF) (nF) nF) InFl (nF) (nFl InFl (nFl (nF) 1nF) (nF) 1nF) InF) (nF)

100 257.9 193.5 401.9 200.9 271.4 142_0 14.9 568.4 142.1 284.2 207.4 190.1 . 285.5 110.0 307.6 262.6 742.6 108.8200 128.9 96.8 200.9 100.5 135.7 71.0 107.4 284.2 71.0 142.1 103.7 95.2 142.8 55.0 153.8 131.3 371.3 54.4300 85.9 64.5 133.9 66.9 90.4 47.3 71.6 189.5 47.4 94.7 69.1 63.5 95.2 36.7 102.5 87.5 247.5 36.3400 64.5 48.4 100.5 50.2 67.8 35.5 53.7 142.1 35.5 71.1 51.9 47.6 71.4 27.5 76.9 65.6 185.7 27.2500 51.6 38.7 80.4 40.2 54.3 28.4 42.9 113.7 28.4 56.8 41.5 38.1 57.1 22.0 61.5 52.5 148.5 21.8600 42.9 32.3 66.9 33.5 45.2 23.7 35.9 94.7 23.7 47.4 34.6 31.7 47.6 18.3 51.3 43.8 123.8 18.1700 36.8 27.6 57.4 28.7 38.8 20.3 30.7 81.2 20.3 40.6 29.6 27.2 40.8 15.7 43.9 37.5 106.1 15.5800 32.2 24.2 50.2 25.1 33.9 17.8 26.9 71.0 17.8 35.5 25.9 218 35.7 13.8 38.5 32.8 92.8 13.6

1,000 25.8 19.4 40.2 20.1 27.1 14.2 21.5 56.8 14.2 28.4 20.7 19.0 28.6 11.0 30.8 26.3 74.3 10.91,500 17.2 12.9 26.8 13.4 18.1 9.47 14.3 37.9 9.47 18.9 13.8 12.7 19.0 7.34 20.5 17.5 49.5 7.252,000 12.9 9.68 20.1 10.0 13.6 7.10 10.7 28.4 7.11 14.2 10.4 9.51 14.3 5.51 15.4 13.1 37.1 5.442,500 10.3 7.74 16.1 8.04 10.9 5.68 8.59 22.7 5.68 11.4 8.30 7.61 11.4 4.40 12.3 10.5 29.7 4.353,000 8.59 6.45 13.4 6.70 9.04 4.73 7.16 18.9 4.74 9.47 6.91 6.35 9.52 3.67 10.3 8.75 24.8 3.623.500 7.37 5.53 11.5 5.74 7.75 4.06 6.14 16.2 4.06 8.12 5.93 5.44 8.16 3.14 8.79 7.50 21.2 3.114,000 6.45 4.83 10.0 5.02 6.78 3.55 5.37 14.2 3.55 7.11 5.19 4.76 7.14 2.75 7.69 6.56 18.6 2.725,000 5.16 3.87 8.03 4.01 5.43 2.84 4.30 11.4 2.84 5.68 4.15 3.81 5.71 2.20 6.15 5.25 14.9 2.18

10,000 2.58 1.94 4.01 2.0 2.71 1.42 2.15 5.68 1.42 2.84 2.07 1.90 2.86 1.10 3.08 2.63 7.43 1.09

Table 3

high-pass12 dB/octave

Bescel Butterworth

high-pass18 dB/octave

Bessel Butterworth

high-pass24 dB/octave

Bessel Butterworthf C =4n7 (2 x) C - 4n7 (2 x) C = 4n7 13 x ) C = 4n7 13 x I C = 4n7 (4 x 1 C = 4n7 (4 ., I

(Hz) RA RB RA RB RA RB RD RA RB RD RA RB RC RD RA RB RC RD(kQ) (kg) (kg) (kQ) (kQ) Ikg) (kQ) Ikg) (kg) (kg) Ikg) (kg) (kQ) (kg) (kg) (kg) (kQ)

100 373.1 497.4 239.4 478.8 354.7 677.5 447.9 169.3 677.3 338.6 463.9 505.5 337.0 874.7 312.9 366.5 129.6 884.8200 186.5 248.7 119.7 239.4 177.3 338.8 223.9 84.7 338.6 169.3 231.9 252.8 168.5 4373 156.4 183.3 64.8 442.4300 124.4 165.8 79.8 159.6 118.2 225.8 149.3 56.4 2258 112.9 154.7 168.5 112.3 291.6 104.3 122.2 43.2 294.9400 913 124.3 593 119.7 88.7 169.4 111.9 42.3 169.3 84.7 115.9 126.4 84.3 218.7 78.2 91.6 32.4 221.2500 74.6 99.5 47.9 95.8 70.9 135.5 89.6 33.9 135.5 67.7 92.8 101.1 67.4 174.9 62.6 73.3 25.6 176.9600 62.2 82.9 39.9 79.8 59.1 112.9 74.7 28.2 112.9 56.4 77.3 84.3 56.2 145.8 52.1 61.1 21.6 147.5700 513 71.1 34.2 68.4 50.7 96.8 63.9 24.2 968 48.4 66.3 72.2 48.1 124.9 44.7 52.4 18.5 126.4800 46.6 62.2 29.9 593 44.3 843 55.9 21.2 84.7 42.3 57.9 63.2 42.1 109.3 39.1 45.8 16.2 110.6

1,000 37.3 49.7 23.9 47.9 35.5 67.8 44.8 16.9 67.7 33.4 46.4 50.6 33.7 87.5 31.3 36.7 12.9 88.51,500 24.9 33.2 15.9 31.9 23.6 45.2 29.9 11.3 45.2 22.6 30.9 317 22.5 58.3 20.9 24.4 8.64 58.92,000 18.7 24.9 11.9 23.9 17.7 33.9 22.4 8.47 33.9 16.9 23.2 25.3 16.9 43.7 15.6 18.3 6A8 44.22,500 14.9 19.9 9.57 19.2 14.2 27.1 17.9 6.77 27.1 13.5 18.6 20.2 13.5 34.9 12.5 14.7 5.18 35.43,000 12.4 16.6 7.98 15.9 11.8 22.6 14.9 5.64 22.6 11.3 15.5 16.9 11.2 29.2 10.4 12.2 4.32 29.53,500 10.7 14.2 684 13.7 10.1 19.4 12.8 4.84 19.4 9.68 13.3 14.4 963 24.9 8.94 10.5 3.70 25.34,000 9.33 12.4 5.98 11.9 8.87 16.9 11.2 423 16.9 8.47 11.6 12.6 8.43 21.9 7.82 9.16 3.24 22.15,000 7.46 9. 4.79 9.58 7.09 13.6 8.96 3.39 13.5 6.77 9.28 10.1 6.74 17.5 6.26 7.33 2.59 17.7

10,000 173 4. 2.39 4.79 3.55 6.78 4.48 1.69 6.77 3.39 4.64 5.06 3.37 8.7 3.13 3.67 1.30 8.85

into the loudspeaker cabinet a specialsection should be screened off to housethem. This will provide an acoustic barrierto prevent the electronics from playinghavoc with the bass and it will also makeit easier to cool the amplifiers.

Final tipsIn an article such as this we cannot dealwith all the details about how to set up acomplete three-way active system butthere are a few practical points to note.When talking about high -quality soundreproduction (which we cart take as read)you should not allow yourself to betempted by attractively priced loud-speakers of unknown origin. This willprove to be a false economy. Good names,such as Kef, Audax, etc., are the ones tolook for, especially as these manufacturersgenerally supply quite a lot of informationwith their loudspeakers. This informationabout output, frequency characteristic,recommended cabinet dimensions and soon is of vital importance.Experimentation is very easy with thefilter board shown here so our advice is totry various different types of filter arrange-ment. Your own taste will then decide ifyou prefer the 'sound' of a Bessel filter

Table 2. The componentvalues for a number ofcommonly used crossoverfrequencies can simply beread off this table. Onlythe low-pass filter valuesare given here.

Table 3. Commonly usedcrossover points for high-pass filters are given inthe first column here. Theother columns list the ap-propriate componentvalues that should beused.

9-33

7active crossover filterelektor september 1984

Parts list

Resistors:

R1,R2,R4,R6 = 47 kR3,R5,R7 = 100R8 ... R11,R16 ... R19 = 5k6

R12,R20 = RA - see tablesR13,R21 = RB - see tablesR14,R22 = RC - see tablesR15,R23 = RD - see tablesP1 ... P3 = 22 k preset

Capacitors:

C1 = 2.2 pi (MKT)C2,C3 = 820 nC4 = 1 pi (MKT)C5 = 470 nC6,C7,C9 . C14,C19,C20 = 100 n

CS = 15 nC15,C16 = 1000 11/25 VC17,C18 = 10 µ/25 VC21,C29 = CA - see

tablesC22,C30 = CB - see tablesC23,C31 = CC - see tablesC24,C32 = CD - see tablesC25 . . C28,C33 ... C36 = 4n7

Semiconductors:DI . D4 = 1N4001IC1 ... IC6 = NE CC17NIC7 = 7815IC8 = 7915

Miscellaneous:

FI = fuse, 200 mAslow blow

S1 = double -pole mainsswitch

Trl = mains transformer,2 x 15 V, 100 mA

Heatsink for IC7 and IC,8(optional)

Figure 7. All the varioustypes and combinationsof filter, as described inthe text, can be made byusing this printed circuitboard.

over that of a Butterworth type. Really it isessential to try different things as it is nosimple matter to set up a'good three-waysystem.A good pair of ears is very importantwhen setting up a loudspeaker system butwe do not advise you to rely totally on

them. Art appropriate instrument for anyaspiring loudspeaker builder is the 'real-time analyser' described in the March,April and May issues this year. This is thetest instrument to use for optimising an ac-tive loudspeaker's frequency character-istic. 14

9-34

In the May 1984 issue of Elektor we mentioned that connecting thedigital cassette recorder described in January of this year to theoutput of a ZX 81 can cause problems. Since then we have workedday and night (in spirit at least) to find a solution to help owners ofthis computer. This article deals with what we came up with.

digital cassette recorderwith the ZX81elelctor september 1984

digital cassette recorderwith the ZX81A few changes are needed both to thecassette recorder board and the ZX 81board and we will begin with the latter.Part of the circuit of the ZX 81 is shown infigure 1. The computer's output signalmust be amplified by making a newcassette output. This is done by connec-ting a 10 k resistor to the TV/TAPE output(pin 16) of ICI. All this means is solderingthe resistor to R29 on the printed circuitboard, as indicated by figure lb. The out-put signal then has an amplitude of150 mVPP- The digital cassette recorderoperates by driving the tape into satu-ration but the ZX cannot do this very eas-ily as the impedance of its EAR input istoo high. All that is required to lower theimpedance is to cut the connection of R34to EAR.Moving on to the cassette recorder board,the hysteresis of Al must be reduced byincreasing the value of resistor R6 to 82 k.The amplification of the playback sectionis reduced by increasing the value of R20to 10 k. The pause -level is improved bygiving C8 a value of 10 n. The pair ofrelays, Rel and Re2, can better beoperated by hand. In normal use thevideo signal is present at the cassette out-put of the Sinclair with the result that thecircuit will always select recording. Theeasiest way to solve this problem is to cutthe copper track close to pin 6 of Re2 andlink pin 6 to +12 V via a switch. For thosewho want the ultimate, a band-pass filter(with a centre frequency of about 5 kHz)can be added in the playback section. Inthis case C6 = 10 n, C8 = 2n2, C9 = 100 nand R20 remains 1 k. All that remains thenis to connect a 560 p capacitor parallel toR21.To enable the circuit to be calibrated ashort program with a large loop must bewritten into the computer and the SAVEcommand is then given. The preset at theinput, PI, must now be trimmed so thatLED Dll lights properly. The analogue out-put, AN, is used when playing a recordedprogram back to the ZX81. For playbackpreset P3 must be set so that the programis read into the computer correctly. Thiscan be seen by looking at the width ofthe black bars on the screen. Thereshould be slightly more black than whitevisible.When reading in a program it is importantthat preset PI should be turned com-pletely to ground or that the plug beremoved from the input of the recorder

laI

UK1

USA 72 USA 3 ;X 2

IE

- - -I II

12 6r sten-sv

57R3

r3s%1E1Fr,3cuu.m

oscov

SF

ONLY 0mrusA

I 0Vfir_ -Frost

Ri2/

11K

975

TC1EAG R33

(1

R34%30

USADUY

5 ryFrAn

73 F5.0231 (KO7; r.07227 FED375 (5/0A

DI 323:,

:2 2973 23DA

:5 23D3 r

7 /5

K22 /Eli 39 1.7773

4

cv

circuit. Under no circumstances may LEDDll light during playback. This is essentialto prevent cross -talk between the recor-ding and playback sections. Probably thebest solution is to short-circuit the inputby using a 3.5 mm socket with a built-inswitch. As soon as the plug is removedfrom the socket the input is thengrounded.When the modifications given here arecarried out there will be joy in the heartsof Sinclair ZX81 users as this computercan finally be used with the Elektor digitalcassette recorder.

84076 -la

makes thestoring ofprograms morereliable forSinclair'ssmallest

9-35

flash meterelektor september 1984 The flash units used by most photographers today are carefully

designed to provide the correct amount of light. This is only true,however, in standard circumstances: with the flash mounted on thecamera and the aperture set to the value recommended for the flashunit. This is not usually very creative and it does not take intoaccount the practice of using a number of flash units and/or ordinarylights. In these cases either a lot of arithmetic or this flash meter isrequired. The most obvious advantage of this meter over similarready-made units is its lower cost but its versatility is what reallymakes this design stand out from the rest.

flash metermeasureslight ......in a flash

Modern cameras, and flash units for thatmatter, now contain quite a lot of elec-tronics to ensure that the photographs arecorrectly lit. It might seem somewhat un-necessary, therefore to have a separate(flash) light meter, but this is, in fact, notso. It is not only for special effects that aphotographer (whether amateur or pro-fessional) might want to do more thansimply fix the flash unit onto the cameraand press the button. Photographs takenin this way often have a very `hard' qualityabout them. The flash can be pointed at areflective surface, of course, but only ifthere is a suitable surface available. A bet-ter idea is to use a number of (inexpens-ive) flash units to give the light a muchmore natural appearance. The cameramust of course be set correctly for this.A computer -controlled flash can becomeconfused in this sort of situation as it isnot the only light source and it must alsobe set up for the camera's position.A camera with Tu., flash measurement(which measures the flash through thelens while the actual photograph is beingtaken) is better in this case but is onlyusable with (expensive) flash units that arematched to the camera. The best idea ofall is to use a flash meter. First make a testflash to find out what aperture should beselected and then take the actual photo-graph.When we decided to design a flash meterit is only natural that it would have to bemuch less expensive than ready-madeunits but we decided that it must also bemore versatile. Most available meters havea fixed measuring time and operate on theprinciple that if the flash occurs within thistime most of the light will be measured. Ifthe camera's flash synchronization time islonger than the meter's the effect of theextra (ambient) light will be neglected.The design proposed here has a measur-ing time that can be set to the same valueas the camera. Normal light measurementscan also be taken, with the result given inthe aperture value (f1.4 ... 22 in half stops)that must be selected on the camera. Thisinstrument is also fitted with an automatic

switch -off facility and provides thepossibility of summing a number ofmeasurements (for multiple exposures, forexample).

The circuitThe power supply for the circuit, which isillustrated in figure 1, is provided by a 9 Vbattery. The automatic power switch -offcircuit ensures that the battery lasts aslong as possible. Pressing S4 causes C12to be charged via D5 and at the same timedarlington T5 is driven open thus connec-ting the negative pole of the battery to thecircuit. After about 40 seconds capacitorC12 is discharged enough so that T5 isswitched off.Pressing S4 also fulfils another function,namely that T4 is caused to conductmomentarily via D4 and R14. This dis-charges C7 and any of the other fourcapacitors (C8 ... C11) that are in parallelwith it. These capacitors play an essentialrole in this circuit. In the first place theyconvert the photo -current of D3 to ananalog voltage, which, like the photo -current, is directly proportional to theamount of light present. The capacitorsmust also store the measured value withas little leakage as possible. We willreturn to this point later in the article.The light is measured by a BPW 21photodiode (D3) which has the right sen-sitivity for our purposes. Its photo -currentis conducted to ground by T3 when D3 isin its quiescent state. During themeasuring time transistor T3 will beswitched off so C7 and, depending on thestates of switches S5 ... S8, some of theother four capacitors will be charged. Inthis circuit MOSFET T2 is used as a diodeto provide a threshold for the photo -current when no measurement is beingtaken. Its very low reverse current alsotends to prevent the capacitors fromleaking.The measuring sequence can be startedin three ways. The first makes use ofswitch S1 and is the simplest way. The

9-36

flash unit(s) can be connected to theSYNC input. Pressing the switch causesflip-flop N3/N4 to toggle. This switches offtransistor T3 so the photo -current flowsinto the capacitor network. At the sametime the flash is triggered via the SYNCconnection and counter IC2 is started byreleasing its reset input. A clock signal isprovided by oscillator N2/R6/C2 to enablethe counter to run for a certain time, asdecided by the position of switch S2. Aftera certain length of time the appropriate Qoutput of the 4040 will go high. The flip-flop then resets, the photo -current is againconducted to ground by T3 and thecounter stops. The meter can now bereset by pressing S4 but if this is not donea second measurement can be taken andthe total result is the sum of the twomeasurements.The second method of triggering the

meter is by pressing the button on theflash unit to make a test flash. This isdetected by Dl and the flip-flop is set viaNi. The circuit consisting of RI, R2, Cland Ti ensures that only sudden changesin the light intensity will affect the flip-flop. As a result this method is suitableonly for flash measurements, not for nor-mal light measurements.The third way of triggering the circuit isby pressing the shutter release button onthe camera. Either the flash itself (as inmethod two) or the shutter release switchin the camera (if this is connected toSYNC) will start the meter. The film in thecamera will, of course, be exposed at thesame time and it may then be cold com-fort to know that the picture will be underor over -exposed due to the camera beingincorrectly set.Whichever of these methods is used the

1

D1

BPW 34

91

CVIM

SYNC

9v

R3

02#

IAAUU AL

BM 21

9V

C2

A L920

9V

AS

517 mi. p

Cainn

9V

1N4148

NEM S. 011047n

9VNI ... N4 = ICI = 4093

1C3 ICSIC4 IC6

95

1C24040

Rw ts-

o 0 0 0 0 0 0

1009

03

BC 5508

mim

9V

BF 256A

27 24 21 19 19

400 200 100 64 50

SSI 56I 971 Sal

tonCa ca C10 C77

7.72.77.1.

4

MODE

DINISO/ASA

13: LEDD6 013

.3

C3LM 3915

i§1 2sF,

IC52 3130

D4

IN4148

9V

flash meterelektor september 1984

Figure 1. The circuit ofthe flash meter, as thediagram here shows, isstraightforward. All thecomponents should befreely available, except,perhaps, the photodiodes.Other types of high-speedphoto detector (for D3)and infra -red photo detec-tor (for D11 will probablywork in the circuit butsome of the other com-ponent values may haveto be changed.

10 FLED014 D23

-1 18 17 16

REF403

-+IC6

2 3130

C12

Tanti=226/ 16V

16 l 14 131 12 11 101

LM 3915

WV -RESET

BC 517

uctsa

HATT.CHECK

94061

9-37

flash meterelektor september 1984 2

Figure 2. Depending onthe type of case used forthe circuit, it may benecessary to cut off thefour corners of theprinted circuit board toprovide clearance forparts of the case.

Parts list

Resistors:

R1 = 10 MR2 = 2M2R3,R17,R18 = 1 MR4,R5,R15 = 100 kR6 = 560 kR7 = 22 kR8,R14,R20 = 10 kR9,R10 = 5k6R11 = 2k7R12 = 1k82, 1%R13 = 56k2, 190R16,R19 = 1 kP1 = 100 k presetP2 = 5 k preset

Capacitors:

Cl = 56 nC2 = 82 pC3 = 47 nC4 = 3n3C5,C6 = 100 pC7,C8 = 10 n (MKT)C9 = 22 n (MKT)C10 = 27 n (MKT)C11 = 18 n (MKT)C12 = 22 u 16 V TaC13,C14 = 560 pC15 = 10 0,16 V TaC16 = 1 µ/I6 V Ta

Semiconductors:DI = BPW 34D2,D4,D5 1N4148D3 = BPIN2ID6 ... D23 = LED,

rectangularD24 = 5V6 400 mW zenerT1,T5 = BC 517T2 = BF 256AT3,T4 = BC 5506ICI = 4093IC2 = 4040IC3,1C4 = LM 3915IC5,1C6 = 3130

Switches:

S1,S4 = push buttonS2 = single -pole 12 -waywafer switch

S3 = single -pole spring -loaded changeover

S5...S8 = 4 -pole DILswitch

12+ 5 16 19 Qt1-0 01100CIV0041°0,1+0

(>08Q>8" th

15+ 77 istrOl06 .**() N--023

13/ 52

6h

photo -current is now stored as a certainvoltage by the network of capacitors.Some way must be found of displayingthis, ideally on a logarithmic scale such asthat used for the aperture scale on acamera.The capacitor voltage is buffered bymeans of a voltage follower (IC6). This isessential because in order to store themeasured value the charge on the capaci-tors must be as constant as possible. Theactual read-out is given with the aid of apair of LM 3915 ICs. These are LED driverswith a difference as they have a logarith-mic scale that rises in steps of 3 dB andcan be used for either a bar -graph or dotdisplay. In this case we will use the dot -display mode as we only want to indicatea single aperture value at a time. A side -effect of having only one LED at a time litis that the current consumption is keptlow.The buffered capacitor voltage is takenfrom pin 6 of IC6 and fed to the signalinput of IC4 (pin 5). This IC compares theinput to a reference set with P2 to deter-mine which LED should light. A total often LEDs are connected to the outputs ofIC4 so the range spans 30 dB. This is notsufficient for our purposes so it is ex-tended by amplifying the IC4 signalvoltage (with ICS) and feeding it into thesignal input of IC3. The ratio of output to

input voltage that gives a range of 30 dB is31.6 so this is the factor by which thesignal must be amplified before being fedto IC3. In this way IC3 will drive its LEDsto indicate a value in the lower part of thetotal measuring range while IC4 takes overfor the upper 30 dB of the range. The gainof IC5 is fixed by means of two 1%resistors. R12 and R13.Two of the outputs of IC3 are not con-nected to any LEDs. The total number ofLEDs used is 18, giving a range of 54 dB.Each 3 dB step corresponds to a half stopso the meter can be calibrated in aper-tures from f1.4 (D6) to 122 (D22). If themeter senses too much light LED D23 willbe lit - this acts as a sort of overflowindicator. When the light intensitymeasured is too low no LED will light.Changing the reference voltage enablesthe scale to be set to whatever range theuser selects, so it could run from f2 tof32 or f2.8 to f45, for example. The valuesof C7 ... Cll, which are used to set themeter to the right sensitivity for the filmused (the film speed), can also bechanged to suit personal needs orpreferences.A battery checking facility is provided byS3. When the battery is good an initialcheck should be made to see which LEDlights. This will be dependent on thereference voltage set with P2. When the

9-38

meter is in service a battery check willlight successively lower LEDs as the bat-tery power decreases.

3 flash meterelektor september 1984

ConstructionAs we have already hinted the leakagelosses of capacitors C7...C11 must bereduced as much as possible. Thisexplains the use of MKT (Siemenspolyester layer type) capacitors here. Thedesign of the printed circuit board alsoincorporates some precautions in thisrespect. The junctions of C8 ... C11 withS5 ... S8 are surrounded by tracks thatcarry a similar potential (connected to theoutput of the voltage follower). There isnone the less still a danger with home-made boards that the material itself couldpermit some leakage. The same problemcould arise with the lacquer sprayed ontothe board. It is, however, advisable to usea suitable (highly-insulative) lacquer as aprotection against dampness. The printedcircuit boards supplied by Elektor throughthe EPS meet all the above demands.There are two points to note when con-structing this circuit. The rotary waferswitch, S2, must be fixed to the board bymeans of the lock -nut on its spindle. Pointsa...h are wired to points 1...8 respect-ively on the switch. If you use a single -pole 12 -way switch the four remainingcontacts are simply left open. The com-mon pole of the switch is wired to thepoint marked M near T2 (refer to the sec-tion on calibration).The setting for film speed is carried outwith DIL switches 55...58. These werechosen to reduce the amount of wiringaround capacitors C7...C11. Theseswitches must protrude significantly abovethe printed circuit board in order to comeup to the level of the exterior of the caseused. This is done by using an eight -pinwire wrap socket or a suitable number ofordinary eight -pin IC sockets.A suitable case must be found for the cir-cuit and everything must then be fittedinto it. For our prototype we used aVerobox with dimensions of 120 x 65 x40 mm but if you have another suitablebox then by all means use it. The boardmust be mounted on spacers to leaveroom underneath for the battery and partof S2. The push buttons, Si, S3 and S4, alsofit below the board, but are mounted onan aluminium bracket at the side of thecase. This bracket can be fixed to the boxby means of a pop rivet. If the SYNCsocket is to be fitted it can be placedclose to, and in parallel with, SI.The photodiodes fit in one of the smallsides of the case; Dl simply fits behind asuitable hole but D3 must be providedwith a tube or pipe about 15 mm long and8 mm in diameter. This tube, which can beseen in the photo of figure 3, shouldideally be black and we will come backto its purpose in the next section.The cover of the box must now beprepared by cutting three holes in it. Thephoto in figure 5 shows the end productand here we see that a bit of care and

attention is needed when cutting theholes for rotary switch S2, DIL switchesS5... S8, and LEDs D6... D23 in order toproduce a good result.

CalibrationTo operate correctly the meter must becalibrated, beginning with compensatingthe offset of IC5. Pressing S4 switches onthe unit for 40 seconds after which it willautomatically switch off. This push buttonwill therefore have to be pressedrepeatedly. Temporarily short the non -inverting input of IC6 (pin 3) to groundand measure the voltage at pin 6 of ICS.Rotate PI until a value of a few dozenmillivolts is measured and then trim it untilthe value is reduced to zero volts but nofurther. Reconnect pin 3 of IC6.The oscillator must now be set so that themeasuring time is the same as the shuttertime in the camera. Although the oscillator

Figure 3. The printed cir-cuit board must bemounted on spacers toprovide room for the bat-tery, push buttons andthe body of S2underneath it.

Figure 4. This view of thetop of the printed circuitboard shows how the DILswitches should bemounted in a wire wrapsocket so that they finishflush with the top of thecase. An alternative is touse a number of ordinaryeight -pin IC sockets.

9-39

flash meterelektor september 1984

Figure 5. The finishedunit is very easy to usebecause of the wayeverything is laid out.Rectangular LEDs shouldbe used instead of roundones if possible as theyimprove the appearanceof the unit.

Figure 6. The oscillator isset up with the aid ofthis circuit. When con-nected correctly to theflash meter this 4040causes the multimeter todeflect eight secondsafter the flash meter isstarted (if the oscillatorfrequency is right).

Table 1

DIN ASA ISO switchesclosed

18 50 50° S5... S819 64 64° S5... S721 100 100° S5, S624 200 200° S527 400 400° none

Table 1. These are the dif-ferent film speeds thatcan be selected by meansof the four DIL switches.

6

012IC2

9V

is built of fixed components the differ-ences in switching thresholds for theschmitt trigger given by various manufac-turers can mean that the frequency is notcorrect. An oscilloscope is very handy inthis case as the frequency measured atpin 10 of IC2 should be 32 kHz (giving aperiod of 31 us). Playing around with theresistance of R6 will enable this value tobe achieved.There is another method of checking thisfrequency, for those intrepid souls who donot have access to an oscilloscope. Thelongest measuring time is 1/8 of a second,which is a bit too fast to check with awristwatch. The alternative is to use thecircuit shown in figure 6, with the 4040'sclock input connected to pin 1 (QI2) ofIC2. A multimeter can then be connectedto pin 4 of the test IC. Depending on theJC manufacturer this output may be calledQ6 (if the numbering runs from Q0...011)or Q7 (when the outputs are numberedQ1...012). The common pole of S2 mustbe temporarily disconnected so that IC2will keep counting rather than being reset.Counter IC2 is started by pressing Si andafter 8 seconds the multimeter shoulddeflect. If this takes longer the value of R6must be reduced. If the time is too shortthe resistance must be increased. Afterthe frequency is correct remember toreconnect the common pole of S2.The last calibration involves the sensitivityof the meter. Before this can be properlyset it is essential that the light is measured

from the right angle. A 'naked' BPW 21measures light incidence within a range ofabout 180° so the measured value wouldbe higher than the actual amount of lightthat affects the exposure of a photograph.This problem is solved by mounting thisphotodiode away from the side of the caseat the end of a short length of (preferablymatt black) tubing.The light meter in the camera is used toprovide a reference value. Point both thecamera and the flash meter at the sameobject from the same position then pressSI and trim P2 until the reading given bythe meter is the same as that given by thecamera. If P2 does not have a sufficientrange for this to be done the values ofC7 ... C11 must be changed. To increasethe read-out (making the instrument moresensitive) these capacitor values must bereduced. Whatever values they have besure that the various ratios of the capacitorvalues always remain the same.The setting for film speed must, of course,be the same on both flash meter andcamera. This adjustment is made with DILswitches S5 . S8, where the sensitivity isreduced by closing more switches. At 27DIN all four switches are open, for 24 DINS5 is closed, 21 DIN requires S5 and S6 tobe closed, at 19 DIN S5, S6 and S7 areclosed and finally for 18 DIN all fourswitches are closed. The correspondingASA and ISO values are given in table 1.During calibration it may occur that,especially at the highest sensitivity, themeter read-out may drift. This is due toleakage in C7 ... C11 so some sort of solu-tion must be found. Make sure the relativesection of the board is clean and dry. Ifthe board is home-made spray someplastic lacquer on it and let it dry beforetrying again. It may be necessary toexperiment with various different things toreduce the leakage as much as possiblebut this is well worth the effort.Finally, as regards using the meter: alwaystake measurements from the camera'sposition. This is the only way to be sure ofknowing how much light will fall on thefilm - and that's what it is all about. 14

9-40

elektor september 1984

capacitancemeter(February 1984, page 2-52)

Some unfortunate errorscrept into the above article.The first two paragraphsunder 'construction' shouldread:

First of all, mount and solderall components except C10and R12, where pins shouldbe fitted. Next, fit all com-ponents (but wire linksinstead of resistors R1 andR7) to the display boardshown in figure 7. The displayand LEDs must be located onthe track side; the LEDsshould be soldered as close tothe board as possible toensure that they are flushwith the display. Lastly, fitwire bridge B.

Additionally: Note that neither wire

bridge A nor input Zshown in figure 5 is used. It is advisable to fit C15

and IC8 on the track sideof the metering board toensure that the switch shaftof the range selector projectsfrom the front panel on finalassembly. It is recommended that a

type 1N4148 diode be con-nected in series with each ofthe LEDs 134.. _D7 to preventpossible malfunctioning ofES1...ES3 through leakagecurrents of the LEDs. It happens from time to

time that when a capacitoris measured with Si set totoo high a range the displayindicates odd values. Thismay be prevented by solder-ing a 100 ohm resistor be-tween pin 6 of IC2 and the+ Cx terminal. R1, R7, Di, and D3 are

not used and shouldtherefore be deleted from therelevant circuit diagram andparts list.

daisywheeltypewriter printerinterface -

(June 1984, page 6-34)There is an error in Table 2 ofthis article. The 'Y2(OAHex)'should read 'Y5(0AHex).-

universal activefilter(January 1984. page 1-42)In the circuit diagram offigure 1 we have somehowmanaged to confuse a

number of pins in IC5. Pins 4,5 and 6 should be connectedto the + 10 V line whereaspins 8, 9 and 12 should beconnected to ground.

frequency meter(July/August 1984,page 7-44)The circuit diagram on page7-44 indicates IC4 as 4515.This should, in fact, be 4518,as the parts list correctlystates.

maximum andminimummemory(June 1984, page 6-39)Offset tolerances in the op -amps used can result in thememory range of 0 to 1 voltnot operating correctly. Thisis noticed when the input is0 V as the output voltage inthe minimum position dropsfrom 1 V (after a reset, forexample) to almost 0 V andthen jumps to 1 V only to falltowards 0 V again, and so itgoes on. Just the oppositehappens for the 'maximum'voltage.The cure for this condition isto provide an offsetcorrection for A5 byconnecting a 25 k presetbetween pins 1 and 5 withthe wiper to +5 V.

9-41

elektor september 1984

The following pages contain themirror images of the track layout ofthe pc boards relating to projectsfeatured in this issue to enable youto etch your own boards. To do this,you require an aerosol of 'ISOdraft'transparentizer (distributors for theUK: Cannon & Wrin, 68 High St.,Chislehurst, Kent, 01 467 0935, whowill supply the name and address ofyour local stockist on request, amercury vapour lamp, sodiumhydroxide (caustic soda), ferricchloride, positive photosensitiveboard material (which can be eitherbought or home made by applyinga film pf photo -copying lacquer tonormal board material). Wet the photo -sensitive (track)

side of the board thoroughly withthe transparant spray. Lay the layout cut from the rel-

evant page of this magazine with

active cross -over filter

PC board pagesDANGER! Ultra -violet light is harmful to your eyes, sowhen working with a mercury vapour lamp, wearsome form of effective eye protection.

its printed side onto the wet board.Remove any air bubbles by carefully'ironing' the cut-out with sometissue paper. The whole can now be exposed

to ultra -violet light. Use a glassplate for holding the layout in placeonly for long exposure times, asnormally the spray ensures that thepaper sticks to the board. Bear inmind that normal plate glass (but notcrystal glass or perspex) absorbssome of the ultra -violet light so thatthe exposure time has to be in-creased slightly. The exposure time is dependent

upon the ultra -violet lamp used,the distance of the lamp from theboard, and the photo -sensitiveboard. If you use a 300 watt UVlamp at a distance of about 40 cmfrom the board and a sheet ofperspex, an exposure time of 4 ... 8

minutes should normally besufficient. After exposure, remove the layout

sheet (which can be used again),and rinse the board thoroughlyunder running water. After the photo -sensitive film has

been developed in a sodiumhydroxide solution (about 9 gram-mes of caustic soda to one litre ofwater) for no more than 21/2 ... 3mins at 20°C, the board can beetched in ferric chloride (500 gram-mes of FeCl3 to one litre of water).Then rinse the board (and yourhands!) thoroughly under runningwater. It is advisable to wear rubberor plastic gloves when working withcaustic soda or ferric chloridesolutions. Remove the photo -sensitive film

from the copper tracks with wirewool and drill the holes.

lamp saver

0--\--1

lamp saver

EVOINEI

9-42

e!=ktor september 1934

SCART adapter PC board pages

flash meter

8118908e6 OBIIIIIIII

digital tachometer

digital tachometer

9-43

elektor september 1984

PC board pages

9-44

Opinions as to what is the most important part of a car are manyand varied. For some people it is the seat they sit in for hours at atime, for others it is the engine under the bonnet, and for othersagain it is the built-in safety feature designed to save a life. There aredifferences of opinion, too, on smaller details, such as what is theinstrument in the dashboard that could least be missed. Thespeedometer is generally the largest instrument making it easy toread at a glance. The most important instrument, however, is thetachometer rather than the speedometer, although most car makersconsider it as an 'extra' or leave it out altogether.

digital tachometerelektor september 1984

digital tachometerThe importance of a rev counter in a caris greatly underestimated, largely becauseit is considered as 'something for sportscars' and run-of-the-mill car manufacturersare reluctant to fit anything that is neithera legal requirement nor guaranteed to in-crease sales. Of late a number of carshave become available with an indicator toadvise the driver to change gear whenthe engine revs rise above the mosteconomical level. This is one use of atachometer; namely the pursuit of fueleconomy. Another purpose of a revcounter is to enable a driver to make thebest use of his engine's power - bywhich we do not mean the irresponsiblecarry -on of many 'boy racers. The trueprofessionals (rally drivers, race drivers)use the tachometer both to keep theengine within it's power -band and to avoiddamage due to over -exuberant use of theloud pedal. Finally, there is one other ap-plication where a tachometer is absolutelyessential: when tuning a car.

Converting engine revolutionsinto digital pulsesThe principle of our design for a digitaltachometer can be gleaned from theblock diagram of figure 1. Ignition pulses(at half the engine speed - for a four -cylinder four-stroke engine) are takenfrom the car's contact -breaker points (c.b.)and are formed into a more suitable signalby a pulse shaper. This section is carefullydesigned to ensure correct operation atall times. The pulses are used to trigger amonoflop which, in turn, provides theclock signal for three BCD counters. Thedata lines from the counters provide theinformation for the LCD drivers to tellthem which segments must be enabled.An RC oscillator produces a signal which,when divided by 16, is used to providethe a.c. needed for the LCD display anddrivers. Two more dividers are includedto reduce the signal frequency even moreand to provide two different values thatcan be selected by means of a switch.

The signal chosen in this way passes to apair of monostable multivibrators (MMV)which provide latch pulses for the displayand reset pulses for the BCD counters.The effect of this selection is to enablethe measuring time (the time duringwhich c.b. pulses are counted) to beeither long (3 s). which gives an accuracyto 10 r.p.m., or short (0.3 s), in which casethe display is accurate to within 100 r.p.m.To summarise, then, what actually hap-pens is this. The pulses from the c.b.points are counted by three BCD counters.Every 3 or 0.3 seconds the count istransferred to the display and the countersare then reset.The circuit diagram of figure 2 and timingchart shown in figure 3 provide moredetailed information about the operationof the circuit. The timing diagram is div-ided into two sections, the first of whichshows the progression of the ignitionpulses through the pulse shaper andmonoflop to become clock pulses for theBCD counters. The second part deals with

reads up to9990 with anaccuracy of 10r.p.m. on anLCD display

9-45

digital tachometerelektor september 1984

Figure 1. All the variousparts of the circuit can berecognised in this blockdiagram but as allembellishments are doneaway with the principleof operation can beclearly seen.

the signal generated by RC oscillatorR4/R5/P1/C4 and passed through thedividers in IC2 and one half of IC3 until iteventually triggers the latch pulse that ap-pears at pin 3 of N2 and the reset pulse atpin 11 of N3.

Points to noteThere is little reason to deal with the cir-cuit in great detail but there are somepoints about it that are important. The RCoscillator, as we have said, is made up ofresistors R4 and R5, preset PI andcapacitor C4. In order to ensure satisfac-tory stability it is essential to use apolystyrene capacitor for C4.The update -frequency of the display ischanged by switching the position of Si.Doing this affects three parts of the cir-cuit. First, Sla selects the actual frequency(either 0.33 Hz or 3.33 Hz) which deter-mines the measuring time. In the 'fast'position Sib feeds the BCD counter forthe second digit (pin 2 of IC4) directlyfrom monoflop N4. In the 'slow' positionthis signal is taken from the Q4 output ofthe lowest BCD counter. The final functionof the switch, Slc, is to connect the clearline of the lowest counter (pin 15 of IC3)either to +5 V or to the output of N3. Bydoing this the least significant digit of thedisplay is always zero when the 'fast' pos-ition is selected. Otherwise it is simply

reset, along with the other two counters,by the pulse from N3.The significance of this switching is clear:one position gives optimum resolution andthe other gives good readability. In the lat-ter position one of the major disadvan-tages of many digital tachometers, namelythat the display tends to flicker a lot, isavoided. The actual measuring time in thisposition is a compromise between resol-ution and readability and was determinedby means of trial -and -error experiments.A liquid crystal display is used instead ofthe more common LED or fluorescentdisplays as it provides much more contrastin high -brightness environments, has lowerpower consumption and is more reliable.Only the lower three digits of the LCDdisplay are used. The data about which ofthe segments should be visible is pro-vided by the BCD counters in IC3 and IC4via display drivers IC5 ... IC7. The displayfrequency inputs (pin 6) of the threedrivers and the back plane of the display(BP, pins 1 and 40) are fed a 53.33 Hzsignal from the Q4 output of IC2. All un-used segments are also tied to this line.The appropriate decimal point (DP2) iskept on permanently by connecting it tothe inverse of this latter signal. As shownin the diagram here the low frequency isselected and thereby the tachometer is atits more accurate setting.

1

1102)

3.33 Hz

853.33 Hz

OSC.

16

÷ 16

displayfrolosocy

Iii IC31

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1N1)

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static 7 -segment decoders1

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11-4 11C414 fri tc31

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8

9-46

2 digital tachometerelektor september 1984

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BC 5478

NOM -2

ConstructionAs circuits go this is not particularly largebut we chose to put it on two printed cir-cuit boards in order to keep the size fairlysmall. Both boards are clearly visible fromthe photograph at the end of the article.The board on the right is single sided andits layout is shown in figure 4a. A numberof the components, mainly resistors, aremounted vertically; the component layoutindicates which are the ones in question.The four connection points to the 'outsideworld' are located on this board and eachof these should be fitted with the usualautomotive type connectors.A total of ten connections must be madebetween the two printed circuit boards.This can easily be done with a shortlength of ribbon cable as all the points,

numbered 0 ... 9 in the circuit diagram,have been kept together at one side ofeach board. The second board is double -sided and as supplied by Elektor hasthrough -plated holes. If you make yourown (non through -plated) board bear inmind that the two sides will have to belinked by soldering both sides of the com-ponent leads as appropriate. Socketsshould be used for the ICs and also forthe display. The 31/2 -digit LCD display re-quires special attention as it is mountedabove the ICs, and the necessaryclearance is made by using two 40 -pin DILsockets with the cross -pieces cut out.The leads for the three -pole toggle switch(Si) should be kept as short as is feasible.The bulb to illuminate the display must bemounted level with the LCD and con -

Using the tachometer forengines other than4 -cylinder 4 -stroke

The frequency of the RCoscillator, R4/R5/P1/C4,must then be recalibrated. Inmost cases this requires nocomponent changes. Thefrequency is calculated from:

2560xkxcf - whereS

2560 is the division factor-16 x 16 x 10 -(1C2/1C3a)k is a constant = 0.333c = number of cylinderss = number of strokesThe corresponding fre-quencies are given in thetable below, for the mostcommon configurations.

c s f (Hz)

6 4 12805 4 10664 4 853.333 4 640

With the values shown theoscillator frequency range(given by f = 2.2 x R5 xP1 x C4) is 838 to 1454 Hzso only when a 3 -cylinderengine is involved need anycomponent be changed. Inthis latter case R5 becomes470 k.

Figure 2. The values ofthe frequencies stated inthe circuit diagramshown here apply for afour -cylinder four-strokeengine. These will becompletely different foranother type of engine.As illustrated the switch,S1, is in the 'longmeasuring time' ('slow')position.Current consumption isabout 5 mA.

9-47

digital tachometerelektor september 1984

Figure 3. This timingdiagram, as alreadystated in the text, isdivided into two parts.These must be seen asessentially separate astheir time -bases are com-pletely different.

Figure 4. The printed cir-cuit boards for thetachometer, as indicatedhere along with the com-ponent overlays, havebeen made circular inorder to retain the mostcommon shape for thissort of instrument.

Parts list

Resistors:

111,132,R3,R7,R9,R10,R13100 k

R4 = 4M7R5 = 680 k+R6 = 100 QR8 = 47k

1111.R12 = 22 kP1 = 500 k linear preset

Capacitors:C1,C2 = 22 pC3 = 1 14;16 VC4 = 560 p polystyrene

4a

3signal fromc.b. points

(Al

5collector

T1o v

04 N4

014 IC2

03 N2

0'11 N3

latch 94.1111

1 usrmt pu4a

POWEROh

02.13N2/N3

840753

nected to the board with two off -cuts fromthick component leads, for example. Werecommend that a 24 V bulb be used as a12 V one may be too bright. The 'finishingtouch' for our prototype was provided byfitting it into a short length of plastic pipeand adding a perspex 'front glass'.

Calibration and installationThe only part of the circuit that requirescalibration is the RC oscillator. Theauxiliary 'calibration' circuit shown infigure 5 is used to generate a 50 Hz signal

C5 = 100 µ/25 V= C6,C7,C10,C11 = 100 n

C8 = 10 nC9 = 33 n

Semiconductors:D1,D3,D4 = 1144148D2 = 12 V/400 mW zenerT1 = 13C 54781C1 = 4093IC2 = 4060IC3,1C4 = 4518105 ... IC7 = 40561C8 = 78L05

Miscellaneous:

La1 = 12 V 124 V1150 mAbulb

S1 = switch, three -poletoggle

LCD = 31'2 digit LCDdisplay. 12.7 mm characterheight, 40 pin

two 40 -pin sockets formounting the LCD display

six 16 -pin IC socketsone 14 -pin IC socket

= see text

that is then fed into input A of thetachometer. As this signal corresponds to1500 r.p.m. for a four -cylinder four-strokeengine the display should read 1.50. If thisis not the case calibration is carried outby trimming preset P1.Installing the tachometer is simply a mat-ter of finding a suitable position for it inthe car dashboard. It must then, of course,be connected to the appropriate points inthe cars electrical circuit: A to the coilside of the c.b. points, B to an unusedcontact on the lights or dash -lights switch,0 to the car's earth, and + to a fused+12 V line.

Using the tachometerThe various uses of a tachometer havebeen outlined at the beginning of thisarticle so we will not repeat them here.One point must be made, however, con-cerning the switch, Si. The short measur-ing time should be selected when the caris accelerating as the least significant digitthen reads zero and is thus less distract-ing. The 'slow' position, on the other handis more suitable for motorway driving andparticularly for tuning the car. In this lattercontext, indeed, it is quite feasible to use

9-48

4b digital tachometerelektor september 1984

this tachometer purely as an aid to tuninga car as there is then plenty of time toread the display and take advantage of itsaccuracy.The majority of cars today have four -cylinder four-stroke engines so this circuitwas designed mainly for this type ofengine. The tachometer can. however. beused with most other engine configur-ations. Full details of this facility are givenby the notes in the margin beside figure 2.

14

!!'

Figure 5. This circuit canbe used for calibratingthe tachometer. Its pur-pose is to simulate thec.b. pulses at 50 Hz) nor-mally fed into the circuitat point A by an engineturning at 1500 r.p.rn.

Photo 1. Here we see thetwo boards that make upthe tachometer. Toachieve the compact formshown in the photo at thebeginning of this articlethe two are mounted oneabove the other in theform of a 'sandwich'.

9-49

DIRPUTelektor september 1984

F. Schmidt

two newcommands forthe JuniorComputerwith DOS

Table 1. Two new func-tions, DIR and PUT, canbe incorporated into theJunior Computer's diskoperating system byloading this program inthe appropriate place.

The Ohio Scientific disk operating system, as applied to the JuniorComputer, has shown its worth and its versatility. Any user familiarwith the DOS software can quite easily change it to add certainoptions such as those dealt with here. One of these is an extensionof the DIR instruction (which lists the files in the directory withoutusing BEXEC) and the second is an extension of PUT (stores fileswithout the need to first add their names to the catalogue). To makeit all the more interesting we also introduce a 'turbo byte'.

DIRPUTIt is surely a sign of progress (?) when inorder to make our lives easier, using com-puters, we have to complicate them evenfurther, with these same computers. Theend result decides whether it has beenworth the trouble and certainly in the caseof the few changes described here thebenefits are clear.

Two extra commandsThe new 'DIRECTORY' instruction of theDOS (its shortened form is when it isnot followed by a track number, providesa listing of the contents of a diskette fromthe DOS command interpreter withouthaving to call some BASIC program. It isstill possible to use the original form

DI TT, where TT is the number of a track.The result in that case gives the numberof sectors in the track. It is important toremember that only the first half of thedirectory (32 of the 64 possible file names)can be accessed with the new instruction.This is not usually such a drawback as itis very rare that a diskette contains morethan about thirty different files.The existing PUT filename instruction onlyallows a file to be stored if the name'filename' already exists in the directory,and that is not very user-friendly. Fromnow on, however, it will be possible tocrive the PUT command with the name ofa file that does not yet exist in the direc-tory. When the DOS does not find thisfilename it tests to see if there are enough

Table 1.8 1 2 3 4 5 6 7 8 9 A B C D E F

E488: AC E5 2C B1 El C9 28 30 BA C9 23 F8 86 28 2E 2D

E418: 4C F3 29 28 73 2D BA 20 28 28 44 49 52 45 43 54

£426: 4F 52 59 eD OA 8A 88 28 IF E5 A9 79 85 18 A9 2E

£438: 85 11 28 34 E5 F8 2D A0 88 Bl 18 28 43 23 C8 C8

E440: 86 DB F6 28 73 2D 28 28 88 Ae 06 131 19 28 92 2D

E458: 28 73 20 28 2D 28 88 Ae 87 B1 18 28 92 2D 2? 73

E468: 2D 80 8A 88 28 41 E5 D8 C9 68 28 54 27 28 SA 26

E478: 28 66 26 4C 61 27 68 AA 68 AB 48 SA 48 C9 DF DB

E4m: 29 C8 28 D8 25 A5 E0 80 ES 2C28 IF E5 28 78 E5

E448: AD 70 3A 85 18 A8 A2 FF E8 E828 Fe 7E 88 38 8E

E448: 130 AE £5

E5 18 FA

Fe

A9

F3 44 IA 4C

88 18 F8 69 8198

E4 A9

CA De

8C DO 6A 38 8A

FB D8 48 28 58

E4Ce: E5 DB 52 68 A8 136 91 18 C8 18 F8 6D 7D 311 E9 e8

E4De: 08 91 18 38 A5 18 ED E5 2C 85 18 B8 82 C411AC

E4E0: ES 2C 92 86 B1 El C9 23 F8 84 C9 19 113 86 C8 91

E4F8: El A9 2e 91 18 CS CA Cie EA A9 81 BD 5E 26 80

E88: 5F 26 A9 79 85 FE A9 2E 85 FF 29 54 27 28 El 27

E518: 68 68 4C DO 22 68 A9 8F 4C 4B 2A A9 8E De F9 A9

E528: 79 85 FE A9 2E 85 F A9 12 28 BC 26 A9 81 80 5E

E538: 26 4C IA 28 A8 85 81 18 C9 23 De B4 18 F7 C8

E549: 68 18 A5 18 69 88 85 18 115 II 69 88 85 11 C9 2F

E55e: De 88 A5 18 C9 79 De 82 A9 88 68 A979 85 18 A9

E5:68: 2E 85 11 28 34 E5 F8 87 28 41 E5 De F6 A9 F 68

E57e: A2 27 A9 88 90 AE E5 CA 1 FA BE AE E5 A9 79 85

E588: 18 A9 2E 85 11 28 34 E5 F9 1E A@ 87 01 18 88 48

E5913: A.2 FF 38 F8 E9 81 E8 138 FB 68 38 F1 18 08 A8 A9

EY48: FF 90 AE E5 CA 88 18 F9 28 41 E5 D8 08 68

9-50

free tracks to store the file. Assumingthere is enough space the new filename isincluded in the directory and the PUT in-struction is executed normally. As with thenew DIR command, this new PUT instruc-tion only considers the first half of thedirectory. If the available tracks containnon -documented data (with no file name)they will be destroyed by the new file.None the less the new PUT command canonly be used with appropriately formatteddiskettes. If the DOS does not find enoughfree tracks for the file it gives themessage 'ERR#E' and if there is no spacein the first half of the directory for thenew file name the message 'ERR#F'appears.

How it is doneAs we are making some fairly significantchanges we may as well take the oppor-tunity to make a small alteration to the 1-10and SE instructions which load the readhead but do not unload it. Replace theD4HEX at 26A5HEx by D2HEX and thencarry out several read and write oper-ations on a number of successive tracks. Ifthis works properly your floppy disk unithas accepted the increase in operatingspeed. If, on the other hand the systemdoes not respond you will have to revertto the original data and forget about the'turbo' byte for the moment ...In order to carry out the modifications toyour system simply follow the instructionsgiven below. In the interests of simplicitythe new program is located in RAM atE400HEx. There are other, shorter butmore complex, possibilities but we preferto avoid them here. Start by making acopy of the Ohio Scientific tutorial disk 5in the version used for the Junior Com-puter. Then make the following changesto this copy: Start the extended monitor (EM) and

load the hexdump from table 1 at theaddress indicated.

Save this program with the instruction!SA 12,5=E400/2(it just so happens that sector 5 oftrack 12 is free)

Load tracks 1 and then 0 as follows:!CA 4A00=01,1:!EX 41FD =00

The extended monitor allows thechanges given in table 2 to be madequite easily after giving the command::D4280,42A0A number of addresses must then bechanged:4E42 : FF 4E43 : E34663: 4C 4664 : 6A 4665: E44E0D: 76 4EOE : E4and finally46A5 : D2to speed up the head movement.

Reload the contents of track 1 on thedisk with the instruction!SA 01,1=4A0W8

Load the track 0 control routine asfollows:!CA0200= 06,4and then start it with the command

Table 2. 1 DIRPUTelektor september 1984

8 I 2 3 4 5 6 7 8 9ABCDEF4288: 8C 08 23 A2 81 8E C6 2A A9 88 85 FE A9 E4 85 FF

4249: A9 12 28 BC 26 A9 85 80 5E 26 28 67 29 4C B3 22

Table 3.

PRINT: PRINT: PRINT: PRINT

98 PRINT 'CHOOSE ONE OF THE FOLLOWING OPTIONS:'

188 PRINT

118 PRINT ' - ENABLE DOS -EXTENSIONS (1)'

128 PRINT - DISABLE DOS -EXTENSIONS (2)'

138 PRINT

148 PRINT SPC(7):: INPUT 'YOUR CHOICE ':CHOICE

158 IF CHOICE.' OR CHOICE=2 GOTO 208

168 END

288 DIM ADDR(6).BYTE(6)

218 REM ADDRESSES

228 DATA 11842.11843: REM POINTER TO DI -1

238 DATA 9827.9828.9829: REM JMP TO HOME

248 DATA 11789.11798: REM POINTER TO PUT

258 REM DATA

268 DATA 255.227.76,186.228.118.228

278 DATA 48.43,32.138.38,75,42

288 REM LOAD MACHINE LANGUAGE ROUTINE FRCN TR 12. SEC 5

298 IF CHOICE.] THEN DISIO'CA E488=12.5'

388 REM CHANGE ADDRESSES IN DOS

318 FOR 1=8 TO 6: READ ADDR(I): NEXT

328 IF CHOICE=1 GOTO 348

338 FOR 1=8 TO 6: READ DUMMY: NEXT

348 FOR I=8 TO 6: READ BYTE(I): NEXT

358 FOR 1=0 TO 6: POKE ADDR(I).BYTE(I): NEXT

368 ON CHOICE GOTO 488.588

488 PRINT: PRINT ' --- DOS -EXTENSIONS ENABLED ---1

418 PRINT '!!' MEMORY FROM $E488 GI IN USE !'!'

420 NEW

508 PRINT: PRINT ' DOS -EXTENSIONS DISABLED ---'

518 NEW

!GO 0200

Save the contents of track 0 by meansofW420W220R8and the modifications are finished.

The versatile solutionRather than making any permanentchanges to the existing DOS it may bebetter to be a bit cautious, which is poss-ible with the BASIC program shown intable 3. This is, in effect, a DOS extensionsenable/disable switch. The RAM betweenE400HEx and E5ADHEX remains usable ifyou decide to include the new PUT andDIR instructions, but there is no longerany need to manually change the contentsof tracks 0 and 1 as the BASIC programtakes care of this. If you decide to placethe machine code program somewhereother than sector 5 of track 12 do notforget to change the load instruction inthe program of table 3(DISK!"CA E400=12,5"). N

Table 2. These are thechanges that must bemade to track 0 of disk 5.The modifications totrack 1, and the pro-cedure for saving tracks 0and 1, can be found inthe main text.

Table 3. If you are reluc-tant to permanentlymodify the contents oftracks 0 and 1 of yourmain diskette or if you donot want to monopolisepart of the RAM thisBASIC program can beused according to the in-structions given in thelast paragraph of thisarticle.

9-51

SCART adapterelektor september 1984

SCART is the name given to the new plug -and -socket connectionbetween a television receiver and associated equipment such as avideo recorder or stereo amplifier. The name is an acronym ofSyndicat des Constructeurs d'Appareils Radiorecepteurs etTeleviseurs, the French association of radio and television receivermanufacturers. This association decided some time ago to terminatevarious inputs to, and outputs from, TV receivers into a 21 -waysocket, which is becoming a European standard.

SCART adapterEuropeanstandard forvideo and audioconnections

Figure 1. The 'old'arrangement willundoubtedly pertain forquite a few years to comein many households. Ifyou want to get morefrom your television set.however, you need aSCART connector. Onlythat will, for instance,allow you to make fulluse of all the possibilitiesoffered by the connectionbetween your personalcomputer and colourtelevision set.

The reasons for the adoption of a multi -way connector are not hard to find. Not solong ago, all that needed to be connectedto the TV receiver were the mains supplyand the aerial. Nowadays there is thevideo recorder, video disk player, gamescomputer, Prestel, and the facility to feedthe audio to your hi-fi installation. Thecables required for all these connectionswould make the back of your televisionset look like a hi-fi rack. Another aspectof this is that even if sockets for all theseconnections were provided on the TV set,they would more often than not be of adifferent type than the plugs provided

with the recorder or games computer.And special cables or adapters are notexactly cheap!Connections old and new are shownschematically in figure 1. It is clear thatthose between a video recorder and theTV set are quite simple: a disadvantage is,however, that the r.f. signal is taken to theTV receiver via an r.f. modulator in thevideo recorder. This round -about way ofsignal transfer leads to reduced picturequality, and normally it also means thatonly one ancillary unit, in this case thevideo recorder, can be connected to thetelevision receiver at any one time.

1

VIDEO RECORDER

PRESTEL DECODER

9-52

OLD NEW 84072.1

Table 1 SCART adapterelektor september 1984

ATV socket-12 V

to DIN 45 482

(wen Irons wising side

ttastirsop 1w -itch ifrom the camera

video -recorder

0

-12V- -4 -- 0 --q--0

I 947

SCART socket screen

4- -CE + 4- 4- 1 -

+ + + + + + + + + +I 5 s 9 5 13 5 11 c

SCART ping Men3 S.7

II I I I 7 I 7

I I I2 I 1I

Ewen from wising Wde)84072-3

A/V connectorThe quality of the transferred signal is im-proved by applying the audio and videosignals direct to the relevant amplifier inthe TV receiver or video recorder. Thismay be done via BNC (video) and phono(audio) connectors as shown in figure 1:four conductors are then required forrecording and playback. Many modern TVsets are therefore fitted with a six -way A/V(audio/video) socket. Signals applied tothe A/V socket should really be amplifiedby 6 dB (2 x) and it is therefore advisableto use the A/V socket for playback only:recording can be accomplished directfrom the aerial. To do this, pins 1 and 5 ofthe A/V socket must be interconnected.Signals are transferred between the TVreceiver and the video recorder via a six -way cable, but even so, and in spite of theimproved transfer quality, only one an-cillary unit can be connected to the TVset at any one time.

SCART connectorThe use of a number of ancillary unitsbecomes possible only when SCART con-nectors are provided. An example of thisis shown in figure 1 from which you cansee that a colour TV receiver fitted with aSCART socket can be connected to thePrestel service and to a video recorder atthe same time.The pin connections of the A/V andSCART connectors are given in table 1,from which it becomes clear why the

A/V connector (DIN 45 842)

Pin Recording Playback1 Input switching voltage

0V2 Video output

Output impedance: 75 gNominal output voltage:1 Vpp into 75 gColour sync signallevel: 0.3 V

3 Earth

4 Audio output (left-hand)Output impedance:

1 kg (above 20 Hz)Output signal level:0.1 . .. 2.0 V into 10 kg

5 Supply voltage input:+12 V

6 Audio output (right-hand)Output impedance:<1 kg (above 20 Hz)Output signal level:0.1 ... 2.0 V into 10 kg

Input switching voltage-12VVideo inputInput impedance: 75 QNominal input voltage:1 VppColour sync signallevel: 0.3 VEarth

Audio input (left-hand)Input impedance:>10 kg (above 20 Hz)Input signal level:0.1 . . 2.0 VSupply voltage input:+12 VAudio input (right-handlInput impedance:>10 kg (above 20 Hz)Input signal level:0.1 . .. 2.0 V

SCART connector

Pin Function Level1 Audio output (right-hand)

or channel 22 Audio input (right-hand)

or channel 23 Audio output (left-hand)

or channel 1 or mono4 Audio earth5 Blue earth6 Audio input (left-hand)

or channel 1 or mono7 Blue component

8 Switching voltage:0 = TV reception1 = operation of

associated units

9 Green earth10 Not used11 Green component12 Not used13 Red earth14 Not used15 Red component16 Blanking signal

1 = blanking

17 Video earth18 Blanking signal earth19 Video output

20 Video input21 Housing screen and/or

earth

0.5 V for outputimpedances 1 kg0.5 V for inputimpedances> 10 kg0.5 V for outputimpedances 1 kg

0.5 V for inputimpedances> 10 kQDifference betweenpeak value and blankingsignal level = 0.7 V;load impedance = 75 Q:superimposed directvoltage = 0 . . 2 V0 = 0 . . 2 V1 = 9.5 . .. 12 Vat input resistanceof710 kg and inputcapacitance of <2 nF

Identical to 7

Identical to 70 = 0 .. 0.4 V1 = 1 . _ 3 VLoad resistance =75 Q

Difference betweenpeak white level andsync signal = 1 V;Output resistance =75 g;Superimposed directvoltage = 0 . 2 VSynchronization signalonly = 0.3 VppIdentical to 19Connected to chassis

Table 1. Pin connectionsof the A/V and SCARTconnectors.

9-53

SCART adapterelektor september 1984

Figure 2. The circuit ofthe SCART adapterconsists of the bufferstages for the video andblanking signals, and thematching stages for thered, green, and bluesignals. The output levelsare in accordance withthose given in table 1.

SCART connectors have twenty-one pins.In contrast to the A/V facility, the record-ing and playback signals are not switchedbut are available simultaneously. Apartfrom the audio and video inputs and out-puts, there are connections for the red,green, and blue signals, and the blankingsignal. Together with the individual earthconnections for all these lines, this ac-counts for the use of a total of sixteenpins.Of the five remaining pins, one is used forswitching from TV reception to operationof one of the ancillary units. With A/Vconnectors (and in some cases even withthe SCART arrangement) this switching iscarried out manually. Pin 21 is connected

to the housing of the SCART plug orsocket and therefore also to the chassis(earth) of the TV receiver. Standard con-nections to pins 10, 12, and 14 have as yetnot been agreed, although it appears thatin due course 10 and 12 will be normal-ized as data connections.

SCART adapterProper normalization is, of course, not onlya matter of co-ordinating the pin connec-tions, but also one of matching the inputand output levels of the TV receiver andthe various associated units. For thatreason we have included these levels inTable 1. The question remains, however:

2

NI ... N4= ICI = 4093 02

DI ... D6 = 1N4148 cs.Z3

1

* \-7*sM text

RIGI8

0 105 V

N2

lAR5 d NI

03

C189.

5V

cirim

N4

R7

N3

270 p

0= SCART pins

044 ft OS Vppr/5

R11

EMI 2:1

0RI°

11

5V

vitt. input

CBLKu.- 2 ..2.3 Vp0/75

16

84072.2

9-54

384072

SCART15

13

11

9

75

2017

16

18

how can you be sure that the output levelof your personal computer matches thesensitivity of the RGB inputs of the TVset? Well, we have designed a means ofanswering that!The sensitivity of the SCART inputs is toohigh for signals at TTL or CMOS levels,such as, for instance, the outputs of homecomputers. Moreover, the input im-pedance of 75 Q is too low. We havedesigned matching circuits to counterthese differences and accommodatedthem all on one printed circuit.With reference to figure 2, only simplebuffer stages (T3 and T4) are needed tokeep the level of the video and blankingsignals within acceptable limits. Thesestages should preferably be fed fromopen -collector outputs (collectorresistance about 330 Q).The red, green, and blue sianals shouldbe treated rather more carefully. Leadingas well as trailing edges of the rectangularsignals must be transferred without anydelay to prevent colour distortion occur-ring. The stage for processing thesesignals (T1 and T2) is therefore more ex-tensive than the buffers. The outputvoltage is maintained at a level just underthe nominal sensitivity of the TV set(0.7 Vpp) so that the receiver cannot beoverloaded.

Red, green, and blue signals at a fre-quency lower than the line frequency -

must be switched off periodically to allowthe input capacitor in the TV receiver todischarge. This switching is arranged byICI which is connected to the colour pro-cessing stage via diodes D2 (one for eachcolour). If the colour signals are obtainedvia the 'analytical video display' (seeElektor, May 1984, page 5-31), IC1 isdefinitely necessary. If, however, there areno coupling capacitors in the TV set, ICImay be omitted.All stages can be accommodated withoutany problems on the printed -circuit boardshown in figure 3. All signals are fed tothe printed circuit by screened cables.The earth connections are soldered to theterminals adjacent to those for the input oroutput signals: each signal line has itsown individual earth connection!It is recommended to fit the printed cir-cuit in an earthed box and to use BNCconnectors for the inputs and outputs. Thesupply voltage of 5 V may be applied viaan appropriate low -voltage plug -and -socket arrangement.It may well be that by using the circuitand relevant control signals you willdiscover numerous new aspects in yourtelevision receiver. Good luck with theexperiments!

SCART adapterelektor september 1984

Parts list

Resistors:

R1,R2 = 2k2'R3 = 100 Q'R4= 47 Q.'R5 = 39 2R6, R8, R12 = 10 kR7 = 47 kR9 = 4k7R10, R13 = 470 QR11, R14 = 68 0

Capacitors:

CI = 270 pC2 = 33 pC3 . . C6 = 100nC7 = 10;4'10 V

Semiconductors:DI, D2 = 1N4148'T1 = BF 451'T2 = 2N2219'D3 ... D5 = 1N4148T3, T4 = BC 5476(Cl = 4093

Miscellaneous:

10 BNC socketsScreened casePrinted circuit 84072

' one of eachrequired for red, green,and blue respectively

Figure 3. Copper trackand component layout ofthe printed circuit for theSCART adapter. Each!screened) signal line hasa separate earthconnection for whichcorresponding terminalshave been provided.

9-55

anodizing aluminiumelektor september 1984

Ready-made equipment cases are often quite expensive andsometimes impossible to get in the dimensions required. In suchinstances many electronics hobbyists design and produce their owncases. As they often have neither the skill nor the tools to work withperspex or sheet iron, they invariably turn to aluminium, which islight, easy to work, and looks good. The only troubles withaluminium are that it does not look so good when it oxidizes andthat it is easily scratched. The remedy for these troubles need notalways be paint -spraying: anodizing is a worthwhile and attractivealternative.

anodizingaluminiumin your homeworkshop

J. Laakmann

Anodizing is a process whereby a hard,non -corroding oxide film is depositedonto the aluminium. This film is harderand far more scratch -resistant than thealuminium itself; it also protects againstfingerprints which can be a real nuisance.

Ingredients and equipmentrequired:caustic soda lye (1:10)nitric acidsulphuric acid solution (1: 7)distilled watera piece of leada suitable tanka variable mains power supply or heavy-duty batteryBecause of the sulphuric acid, the tankmust be of glass or plastic, and it must, ofcourse, be large enough for your pur-poses. A photographic developing tray

1

1 ..ppty ca&e 1.12= -work p...

may, for instance, be suitable; alternativesare a large plastic bottle or container withthe top cut off, domestic glass basins,plastic washing-up bowls, and so on.An electric direct current of 1.5 ... 2.5 Afor every 100 square centimetres (16 in2) ofaluminium should be available. This ismost easily obtained from a variablepower supply, but a suitable heavy-dutybattery and appropriate variable resistor tokeep the current within the limits statedmay also be used.For the electrolysis the aluminium is madethe anode, while the cathode is formed bythe piece of lead. The surface areas of thealuminium and lead should be roughlyequal.Obtaining the chemicals should presentno problems, although you will not beable to buy them in the concentrations re-quired. The caustic soda lye is preparedby stirring 10 grammes of sodium hydrox-ide in 100 ml of distilled water: this sol-ution cannot be stored in glass vessels,only in plastic ones. The concentration ofthe nitric acid is not critical: add one partto about nine parts of distilled water.Preparation of the sulphuric acid solutionis a little more complicated although thefollowing formula should be a great help.ml = m2 (x% - y%)/y%, whereml = distilled water by weightm2 = sulphuric acid by weightx% = concentration of sulphuric acidy% .= concentration of required sulphuricacid solutionIf, for instance, a 1: 7 (say, 15%) sulphuricacid solution is required, and250 grammes of sulphuric acid in a 50%concentration is available, the relevantamount of distilled water by weight is583 grammes.Warning! Always add acids to water,never water to acids.Always be careful when working withthese chemicals. Ensure good ventilationof the working space, do not smoke(because of the production of highly com-bustible oxy-hydrogen gas), do not wear

9-56

your best clothes, and do use rubber orplastic gloves and some form of effectiveeye protection.

ProcessingFirst smooth the aluminium with grade 400wet -and -dry emery paper: take care not tooverheat the aluminium as this may causeblemishes during the anodizing. Next, im-merse the aluminium for about tenminutes in the caustic soda lye (at roomtemperature) to remove all grease.Decolouration often occurs, but this dis-appears when the aluminium is etched ina 1: 10 nitric acid solution.Only now can the actual electrolysis takeplace. Suspend the sheet of lead, con-nected to the negative terminal of thepower supply or battery, in the sulphuricacid solution. The aluminium should beconnected to the positive terminal via astrip or piece of aluminium: othermaterials may dissolve during the pro-cessing. A suitable means would be analuminium C -clamp as used in modelbuilding in which a screwthread is cut asshown in figure 1. The supply cable is ter-minated into a soldering tag which isfastened to the clamp by a screw driveninto the freshly cut thread. The aluminiumwork piece or sheet must be slightlylarger than required because no ano-dizing can take place under the clampscrew.At a solution temperature of 16 ... 20°C(inspect frequently), the processing willtake about one hour. The solution mayhave to be cooled now and then, while anoccasional stir is also advisable. When the

current drops, the electrolysis may be ter-minated. The aluminium work pieceshould be thoroughly rinsed in distilledwater after each of the operationsdescribed.Finally, the aluminium must be conden-sated in boiling water for about fifteenminutes. In this, the pores of the oxidefilm close to some extent and the wholework piece hardens.

Protection of the environmentWhen the chemicals are no longer re-quired, they should be neutralized beforethey are flushed away. Nitric and sulphuricacids may be neutralized with the causticsoda lye. You may not have enough left ofthis and it is then necessary to make upsome more. The pH value may bechecked with a pH meter or litmus paper(which turns red in acids and blue inalkalis). It is also possible to use indicatorssuch as phenolphtalein (C20H1404) whichis colourless in acids but turns red inalkalis, or methyl orange(C14HI4N3Na03S) which is red in acidsand gradually changes through orange toa full yellow colour in alkalis. 14

9-57

lamp saverelektor september 1984

Most incandescent bulbs have an estimated lifespan of about athousand hours of brightness. The actual time when the bulb blowsis determined by the weakest link - the thinnest part of thefilament. The most obvious way of increasing the filaments lifespanis to concentrate on the weak part, and in particular by limiting thepeak current at switch -on as this is what causes the filament to burnout. Two versions of this zero -crossing switch have been designedand both are easily built into existing installations.

lamp saver

increases thelongevity ofincandescentbulbs byswitching themon at the zero -crossing pointof the mains

About this time of the year home ownersare forced to start thinking about makingcertain preparations for the winter, suchas ordering fuel for the central heating. Atthe same time most people are likely toconsider how to economise, and not onlyon the central heating bill. Lower wattagelight bulbs are then used and insulatingproducts are bought. More significantsavings can be made by changing yourhabits, by drawing curtains sooner, turningthe central heating down one or twodegrees, by not leaving doors open un-necessarily and so on. These economymeasures do not even involve any ad-ditional expenditure.Under the heading of 'energy conscioushabits' is the idea of switching off lights inthe room you are just about to leave. Thiscertainly saves some electricity but it isnot without fault. Continuously switchingan incandescent lamp on and off willshorten its lifespan quite considerably.

The filament in an incandescent bulb hasa lower cold resistance than when it iswarm, so it acts as a resistor with apositive temperature coefficient (PTC).The peak current at switch -on willtherefore be much higher than the maxi-mum continuous current, especially if thelight is switched on when the voltage isnear its maximum value (see figure 1). Inorder to understand what this high currentdoes to the lamp we must realise that thefilament is not smooth and even but ratherit is very rough. The switch -on peak willtherefore cause hot spots to appear at thepoints where the filament is thinnest.These points suffer from wear and tearwhich eventually leads to one of them

immediatelyupon switch -on.The lifespan of the incandescent lamp isdetermined by the weakest point in thefilament. We can protect this weak spot byswitching on the lamp at the mostfavourable moment, namely at the zero -crossing point of the mains. During thefirst quarter cycle of the mains the currentthrough the filament will heat it enough sothat when the voltage is first at its maxi-mum the resistance will be high enoughto keep the current, and therefore thetemperature of the hot spot, fairly low (seefigure 2). In this way the lifespan of thelamp is improved.

The requirementsWhat we want is a circuit that will detectthe zero -crossing of the mains and switchon the appropriate lamp(s) at this time. Itshould also be easy to fit into existing in-stallations without having to run extrawires or knock holes in the masonry.Finally the cost should be low to enablethe investment to be earned back quickly.The circuit described here meets thesedemands and is a particularly attractiveproposition if you use expensive bulbs.Another interesting application of thelamp saver is in cases where the lamp isdifficult to reach for replacement.Lest there be any misunderstanding, let usstate clearly that this circuit is only usefulfor incandescent lamps. It cannot extendthe lifespan of fluorescent lights at all.

9-58

The two versionsBuilding this lamp saver circuit intoexisting installations is simplified by thefact that we have developed two differentversions. Version 1 is a circuit that must befitted to an existing lamp but no changesto the wiring are required. The wires thatwere connected to the lamp fitting arenow connected to the circuit instead andthe fitting is linked to the appropriatepoints on the printed circuit board.Version 2 is somewhat smaller as it isprimarily intended for mounting behindthe light switch in the wall. If there is notenough space for this the original switchcan be replaced by a miniature 240 V oneas the current passing through it is verysmall. Version 2 is not suitable for use withtwo-way switches; version 1 must be usedin this case.

The circuitsMoving on to the circuits we will nowbegin with version 1. Technically speakingthis is the more interesting of the pair.Various sections can be seen in the circuitdiagram of figure 3: a d.c. supply for thegate pulses (RI, Cl, C2, Dl, D2), a zero -crossing detector (R2, R3, T1, T2) and, ofcourse, a triac with R7 and C3 to suppressexcessive voltage peaks. When the switchis closed the mains voltage is appliedacross the voltage divider consisting of R2and R3. As long as the voltage at the junc-tion of R2 and R3 does not exceed 0.7 Vtransistors Ti and T2 are switched off. Inpractice this means that neither Ti nor T2will conduct when the voltage is withinthe range of about -8 V to +8 V. A 'win-dow' is thus formed around the zero -crossing point of the mains. If the instan-taneous mains voltage is greater than+8 V T2 will conduct, whereas when themains value is more negative than -8 VT1 will conduct.As soon as the mains voltage is applied tothe circuit capacitor C2 is slowly chargedvia Cl, RI and D2 up to a maximum of10 V (defined by Dl). After a few periodsC2 will be charged enough to provide atrigger current for the triac. This is sup-plied via transistor T3, but only around thezero -crossing point. At all other times T3is kept off through the action of Tl or T2(depending on the phase).Summing this up: Ti ... T3 ensure that thetriac can only conduct at around the zero -crossing point. The gate pulses aredelayed a few periods after switch -on (byC2 and everything to the right of it) toallow transistors Ti and T2 to get into theirrhythm.Version 2 of the circuit is slightly simplerthan version 1, at the price of a few con-cessions. The switching window is set upin the same way (with R3, R4, Tl and T2)

but the supply for the gate of the triac ischanged. In this case the gate current issupplied via C2 and R2. When on/offswitch Si is closed the triac will never betriggered so the lamp remains off. WhenS1 is open, on the other hand the triac can

1

2

be triggered but only within the windowdefined by R3, R4, Ti and T2. In order forthis circuit to work it is essential that themains is always present and that the lamp,Lal, is connected in series with it. If thecircuit were connected straight across themains and this just happened to be at itsmaximum value the triac would im-mediately be triggered via C2 and R2even before Ti or T2 starts conducting. Inthat way the lamp would switch on whenthe mains voltage is at its maximum value,which is exactly what we wanted toprevent.

3

TIC 20613 ctTIC225D

Al,A2

100n400V

D21N

4001

R2

1 %V

La 1

T T3 = BC 549C; BC 550CT i1 = TIC 206D (4 A)

TIC 225D (8 A)

R7

0

lamp saverelektor september 1984

Figure 1. When an in-candescent lamp isswitched on at the peakvoltage level the peakcurrent is about ten timesas high as the maximumconstant value in normaluse. The lamp in questionhere is an expensivespotlight with built-inreflector.

Figure 2. In contrast tothe situation in figure 1,the lamp switched on viathe lamp saver at aboutthe mains zero -crossingpoint only has to handlea current five times ashigh as the maximumnominal value. Thishalving of the peakcurrent corresponds to areduction of the maxi-mum power by a factorof four.

Figure 3. Version 1 of thelamp saver should bebuilt into the light fitting.The light switch, S1, thenswitches the whole cir-cuit on and off.

\ 51

C3

47n

630Yti84073-3

9-59

lamp saverelektor september 1984

Figure 4. Version 2 of thecircuit is slightly simplerthan version 1. Correctoperation is ensured byconnecting the circuitcontinuously to themains. If space is at apremium a small (lowcurrent) 240 V switch maybe used.

Figure 5. The usual careis required when fittingthe components to theprinted circuit board (ver-sion 1 is shown here) butno special precautionsare needed.

Parts list

- Version 1

Resistors:

RI, R3 = 4k7R2 = 47 kR4, R6 = 10 kR5' = 470 QR7 = 220 Q

Capacitors:

Cl = 100 n/400 VC2 = 22 1.4/16 VC3 = 47 n/630 V

Semiconductors:DI = 10 V/1 W zenerD2 = 1N4001TI . T3 = BC 549C.

BC 550CTril = triac. such asTIC 206D (4 A) orTIC 225D 18 Al

A subtle difference between this versionand the first one is that in this case T2 is aPNP transistor. This is necessary becausethe gate of the triac is fed an az. ratherthan d.c. signal. The gate current thereforealternates between negative and positiveso a PNP transistor is needed to conductthe negative gate current.The disadvantage of this version of the cir-cuit is that is must always have a mainssupply connected to it. Naturally thismeans that there will always be a certainamount of current consumed but in termsof the normal values of current we talkabout for mains -powered equipment thisis negligible.

Construction and installationBuilding either version of the lamp saveris child's play using one of the printed cir-cuit boards shown here. Which version isused depends on your own individual re-quirements. If the light in question is con-trolled by more than one switch then ver-sion 1 must be used. As we have already

said, this board is mounted into the actuallight fitting. All the necessary construc-tional details can be gleaned from figure 5and figure 6.Space is saved by not mounting the triacson a heatsink but this means that themaximum power that can be handled is abit limited. This is dependent upon theway in which the board is mounted, par-ticiilarly as regards the amount of coolingair that flows around the triac. The circuitcan handle 300 W in any case, and this isquite sufficient for the vast majority ofdomestic applications. If, however, this isfound to be insufficient the triac can becooled by mounting it on an aluminiumbracket This will have to be madeespecially to suit the space available.Another possibility is to use a morepowerful triac, 8 A instead of 4 A, in whichcase it may be necessary to reduce thevalue of resistor R5 to 330 Q (in version 1).The triac is then always triggered by apositive gate current, irrespective of thephase. The TIC 225D's greater gate current

4

TIC 206D

R3

Al G

A2

R4

*4,4144.

T1 = BC 549C; BC 550CT2 =BC559CTril = TIC 206D

ti2.4073-.-

5

Qvi94073

= see text

9-60

lamp saverelektor september 1984

requirement has the result that it is onlytriggered during positive half -cycles sothe lamp will be seen to flicker.It is difficult to give any specific adviceabout installing the lamp saver as thisdepends on the individual application. Analternative to mounting version 1 in thelight fitting is to fit it into a small case. Inthis way the circuit can also be used withlamps that are plugged into a mains wallsocket. For the circuit to operate correctlyin this application it is essential that theswitch is connected between the wallsocket and the lamp saver.

Version 2 of the circuit is small enough tofit behind the wall switch in most cases. Ifthis is not so a smaller switch may beused as it only has to be able to handlethe (small) gate current. Whatever switchis used must, however. be rated at 240 V.One last piece of advice: when installingthis circuit be sure to remove the mainsfuse beforehand and put it in your pocket.If you don't do this some `helipful' personis bound to notice the fuse and helpfullyput it back where it belongs. This sameperson is likely to be quite shocked atyour comments! 14

Parts list

- Version 2

Resistors:

R1 = 100 Q/1 WR2 = 1kR3 = 47 kR4 = 4k7

Capacitors:CI = 47 n,'630 VC2 = 100 n,400 V

Semiconductors:Tl, T2 = BC 559C.

BC 560CTril = triac. such asTIC2060 (4 Al orTIC 225D 18 Al

Miscellaneous:

St' = switch

= see text

Figure 6. As in version 1of the lamp saver, thetriac in version 2 is notmounted on a heatsink. Ifthe power handlingcapabilities are found tobe too limited Tril may bemounted on analuminium bracket.

9-61

double -sidedprinted circuit boardselektor september 1984

how to makethem yourself

Figure 1. The easiest wayof connecting the twosides of the printed cir-cuit board is by solderingthe component leads atboth sides.

Few electronic hobbyists today have any qualms about makingprinted circuit boards. Building a project on a printed circuitboard is much easier than using Veroboard or something similar,wiring is kept to a minimum and fault finding is greatly simplified.The project also takes on a far more professional appearance. Theseplus points make it worth while to etch printed circuit boards. Ingeneral this is quite straightforward and, as the process is wellknown, we will not go into it here. Double -sided boards, on the otherhand, are quite a different matter.

double -sided printedcircuit boardsDouble -sided printed circuit boards arequite commonly used in electronics, par-ticularly in HF, where one side acts as anearth plane, or in circuits where a largenumber of connections between variouscomponents have to be made in a rela-tively small area (such as computers).Making these boards is somethinghobbyists are happy to leave to pro-fessionals and, indeed, without the rightfacilities it can be very tricky.One of the difficulties with makingdouble -sided printed circuit boards is thatthe copper tracks on both sides must becorrectly aligned. This is dependent onthe process used but in general termswhat it involves is preparing one side ofthe board first, by developing it if photo -etching is used, or applying transfers oretch resist. Then a few holes are drilled,the most common being the corner ones.The second side of the board can then beprepared in the same way as the first andusing the holes to facilitate alignment.Another possibility is to etch two printedcircuit boards corresponding to the twosides of a double -sided design. These are

then drilled and strong glue is applied tothe reverse side of each board. Theboards are then carefully aligned witheach other, by inserting pins in some ofthe holes, for instance, and stuck together.When the glue sets the board is ready foruse.So far this is nothing any hobbyist couldnot handle but after the board is etchedMurphy strikes with a vengeance. Pro-fessional double -sided boards (like thosesupplied by Elektor through'through -plated' holes so that they connectthe copper on both sides of the board.The equipment used to plate the holes isgenerally only found in businesses orschools so unless you have the right con-nections an alternative will have to befound.The most simple alternative is shown infigure 1. This simply involves soldering thecomponent leads on both sides of theboard if there is a copper pad on bothsides. Great care is required when doingthis if the components are very heat -sensitive as the soldering iron is closerthan normal to the components and for

1

9-62

twice as long as usual. Use a heat shunt ifpossible.Sometimes it may not be feasible to soldercomponents on both sides or there maynot be a component where the two sidesof the board are to be linked. This bringsus to figure 2a and 2b. Pins for insertioninto printed circuit boards are available intwo sizes, as figure 2a shows. These canbe inserted into the board and (ifnecessary) soldered at both sides to pro-vide a more professional appearance thancomponent leads (or off -cuts of same). Analtogether better solution is indicated infigure 2b, in the form of through -PCB pins.As the drawing shows, these are simply in-serted into the hole and soldered at bothsides to provide a good connection.It is quite feasible to make double -sidedprinted circuit boards using the methodsoutlined, or, as is more likely, a combi-nation of them, but in the case of com-plicated circuits they would almost cer-tainly demand a redesign of the printedcircuit board. There is, however, analternative to all these methods that doesnot require any redesign. This is shown infigure 3. A hollow through -PCB pin is in-serted into the hole drilled for it and issoldered at both sides. In order to preventthe hole in the insert from filling withsolder it is necessary to thread a length ofenamelled copper wire (about 0.8 mm indiameter - SWG 20) through it duringsoldering. When this is removed the resulthas the same effect as a through -platedhole. The insert is prevented from con-tinually falling out of the hole duringsoldering by first widening its narrow endabove the diameter of the hole with a nailor something similar. Unfortunately this'wonder insert' has one disadvantage - itis not yet freely available in the U.K., as itis on the Continent, but we hope thissituation will soon improve.

2a

2b

84080-3

double -sidedprinted circuit boardselektor september 1984

Figure 2a. Pins areavailable in two sizes forinserting into PCBs. Aspecial insertion tool isneeded to do this.

Figure 2b. Another way ofconnecting the two sidesof a board is to insert thissort of through -PCB pinand solder it at bothsides.

Figure 3. The next bestthing to through -platingthe holes is this insert.Using this it is possibleto make very gooddoublesided printed cir-cuit boards withoutneeding any specialequipment.

9-63

2716 + 6116 = 48Z02Memory IC type MK48Z02 fromMostek is compatible both as regardspinout and functions with the byte -wide CMOS RAM 6116 as well as thetype 2716 EPROM. This may appearto be a contradiction, but a look atthe photograph (where you can seetwo lithium batteries) will make mat-ters a little clearer: the 48Z02 is, inprinciple, nothing but a battery -buffered RAM. In contrast to earlierattempts at such a device, as for in-stance the (PROM, the batteries aswell as the voltage control are nowcontained in the same housing asthe chip. Except for its height, whichis slightly greater than normalbecause of the batteries, the housingis of the standard 24 -way dual -in -linetype. The 48Z02 can therefore beused as a direct replacement of a2716 or a 6116 to offer the followingadvantages:II high storage reliability due to the

integrated, secure voltageswitching;II data retention in the absence of

power;MI data security provided by

automatic write protection duringpower failure;

long data retention period1>10 years) due to HCMOS

technology.At the moment, because of its priceof around f35. the 48Z02 is too ex-pensive to be used as a simple pro-grammable EPROM substitute, butthere are applications where the priceis justified. These will be discussedlater in this article.

Technical characteristicsThe pinout of the 48702 is shown infigure 1: except for pins 18, 20, and21, it is in accordance with that ofthe 2716 or 6116. Pin 18 of the 2716 isdesignated CE (Chip Enable); that ofthe 6116 is CS (Chip Select), and inthe 48Z02 it is E (Enable). In prac-

1 A, 1 111 24 Vcc

A, 2 23 AAs 3 22 AsA, 4 IN 21 cc

A, 5 20A, 6 19 A,A, 7 18A, s l II 17 DO,

1311 9 MI 15 00,DO, 10 15 DO,

oa, 11 no,GND 12 13 Da,

84074-1

Figure 1. Pinout of the MK48Z02.

2

01.ALGIL_.max,CX*11.44.131;,..___

GOV*.e*.0

I

C11a

elektor september 1984

cocuvn oicron

*44- 4.A.

Figure 2. The functions of the RAM/EPROM can be easily recognized here.

tice, these differences are mean-ingless. In the same way, 'forget' thedesignation G at pin 20 of the48Z02: this pin is the OE (Out-put Enable) terminal exactly as in the2716 and 6116. Pin 21 of the 2716carries the programming voltage:after programming this terminalshould be made logic 1. In the 6116and 48Z02, this pin is theWrite Enable terminal (abbreviated toWE or W I: it should be logic 0before any data can be written intothe store.In the block diagram of figure 2, thetypical structure of the actualmemory with its memory matrix, rowand column decoders, and so on, iseasily recognized at the right. At theleft are the voltage switching circuitsand the lithium batteries. The com-parator compares the voltage atpin 24 (Vcc) with the internallygenerated reference voltage.The normal supply voltage may liebetween 4.75 V and 5.5 V (max-imum). Below 4.75 V there are twofurther important levels: 4.5 V and3.0 V. If the supply voltage dropsbelow 4.5 V, the data bus will gointo the high -ohmic state (threestate) independent of the levels onterminals E (pin 18) or W (pin 21).This prevents the data in memorybeing affected by the on and offswitching of the supply voltage.When Vcc drops below 3.0 V, it is

switched off and the lithium batteriesprovide the required power.When the external supply voltage liesbetween 4.5 V and 4.75 V, thelithium batteries are tested. If thevoltage of one of them is below2.0 V, a flag is set. This flag inhibitsthe first write cycle after the supplyvoltage has been switched on. It istherefore easy to ascertain by meansof a software loop whether thelithium batteries are in good workingorder:III read the contents 'N' of an ar-

bitrary memory location 'X' andwrite these in a different position inthe system;

load a value different from 'N'into location 'X';

check that the new value is storedcorrectly;reload 'N' into 'X'.

This routine must, of course, be car-ried out as a first write operationwhen the 48Z02 is used after apower -on reset.The timing diagrams of figures 3 and4, as well as table 1, contain thedetailed operating conditions of the48Z02. The write -cycle time, tWC, inthe 48Z02 is equal to the access time(read -cycle time), tRc. The device isavailable with a read/write cycle timeof 150 ns, or 200 ns, or 250 ns,which is shown in a suffix to thetype number: 15, 20, or 25. For in-stance, an MK48Z02-20 is the version

9-64

elektor september 1984

3

DQ -Da,

4

a

w

00,.

WRITE

ra-

jr\r- t".-7 \

,vaITE READ

VAUD vAlr0

READ READ WRITE

;cc

84074-3

IC:1:1=1/41111111# 1=1.

84074-4

Figure 3, 4. These timing diagrams show the detailed operation of the MK48Z02.

Table 1. Electrical characteristics of the three versions of the MK48Z02.

(0 TA<79°C) (Vcc = 5.0 V 10% -5%)

MK48Z02-15 MK48202-20 N1K48202.25

Sym Parameter Min Max Min Max Min Max Units

SRC Read Cycle Time 150 200 250 ns

IAA Address Access Time 150 200 250 ns

ICEA Chip Enable Access Time 150 200 250 ns

10EZ Chip Enable Data Off Time 35 40 50 ns

tOEA Output Enable Access Tirne 55 65 75 ns

10E2 Output Enable Data Off Time 35 40 50 ns

10H Output Hold from AddressChange 15 15 15 ns

WC Write Cycle Time 150 200 250 ns

tAS Address Setup Time 0 0 0 ns

ICEW Chip Enable to End of Write 90 120 160 ns

tAsN Address Valid to End of Write 120 140 180 ns

sliVD Write Pulse Width 90 120 160 ns

11NR Write Recovery Time 10 10 10 ns

tWEZ Write Enable Data Off Time 50 60 80 ns

tDSVV Data Setup Time 40 60 100 ns

t()HW Data Hold Time 0 0 0 ns

with a 200 ns access time.Power consumption amounts toabout 250 mW when the chip is be-ing accessed (E = 0), and around5.5 mW on standby IE = 1). Thestandby power consumption is notthe same as the drain on thebatteries!

A I in al , the 48Z02 is a useful, prac-tical building block: it may bedescribed as a RAM and used as anEPROM or ROM. It may be insertedinto the available EPROM socket, aspin 21 of this is always logic 1. Andin contrast to EAROMs, the 48Z02may be loaded as often as you wish

and at the normal speed of thesystem.

Some applications-As we said before, the 48Z02 is tooexpensive to be used as an EPROMreplacement. It makes goodeconomic sense, however, to use itin applications where the contents ofa ROM are required to be amendedfrequently and/or rapidly, and moreparticularly so where such amend-ments result in circuit changes.Typical applications are as the digitalstore of large numbers of tuner fre-quencies, and as memory for a con-trol computer the working programof which is changed regularly by acentral processing system (if the pro-gram is not too long, the 48Z02 mayat the same time take over the dutiesof the RAM).The 48Z02 should also be of interestto computer fanatics, for instance, toalter a monitor program. You thencopy the EPROM content into the48Z02, amend and test the programas often as required, and once youare satisfied with the modified pro-gram, copy the content of the 48Z02in one go into an EPROM. If youhave ever loaded and erased anEPROM a dozen times or so during aparticular design stage, you will soonlearn to appreciate the possibilities ofthe 48Z02.Another possibility is the modifica-tion via the software of the contentof a code reyersal memory orcharacter generator during operationof the system (the hardware must, ofcourse, be suitable for this). It isthen, for instance, possible totransfer graphic character recordsfrom a diskette to a charactergenerator, or, if required, to provide akeyboard inverter with severaldesignations for individual keys (forinstance, BASIC shorthand com-mands, followed by Pascal or Forthshorthand instructions, or graphicscall -in, and so on).

Literature2K x8 ZeropowermfRAM MK48Z02(81-15/20/25United Kingdom:

Mostek UK LtdMasons House1-3 Valley DriveKingsbury RoadLONDON NW9Phone: 01 204 9322

International:United Technologies Mostek1215 W. Crosby RoadCarrolltonTexas 75006U.S.A.Phone: 214/465-6000

9-65

New portable mains filterLF 134New from Roxburgh Suppressors Limited is amulti -outlet portable mains filter Type LF 134.Rated at 13 A, the unit provides four 13 Asockets and is constructed in a steel case fittedwith a neon mains indicator. The LF 134 hastwo metres of mains lead and is complete witha 13 A plug for immediate use. The device pro-vides a high degree of protection from mainstransients and interference for analogue anddigital instruments, and microcomputersystems and their peripherals. Maximum pro-

tection is obtained by the incorporation of ahigh performance mains filter with a varistortransient clipper. Dimensions are425 x 78 x 45 mm, and the unit weights1.5 kg. Unit price is £54.34 excluding VAT, car-riage and packing.

Roxburgh Suppressors Ltd.Haywood WayNyhouse LaneHastingsEast Sussex TN35 4PL(04241 442160 (3008 MI

DC solid-state relayInternational Rectifier has introduced a newrange of solid-state relays, the Crydom Series1 -DC, which use a HEXFET (the trademark forInternational Rectifier power MOSFETs) out-put stage to offer d.c. switching at up to 40 A.The input of these relays can be driven frommost logic circuits and requires less than1.6 mA at 5 V d.c.International RectifierHurst GreenOxtedSurrey RH8 9BB1088 33) 3215/4231

(2986 Ml

Programmable, single -chipvideo generatorPlessey Semiconductors has released for pro-duction a single chip video generator,MR9735, with an on -board character setwhich the company claims can be pro-grammed in virtually any language. TheMR9735 can replace up to three ICs in cur-rently available Prestel/Teletext chip sets. TheMR9735 is designed to meet the new CEPTspecifications for Prestel and Teletext.Plessey Semiconductors LimitedCheney ManorSwindon SN2 2QW(0793) 36251

(2987 MI

True r.m.s. voltmetermeasures complexwaveformsThe Type 22610 portable voltmeter from Mar-coni Instruments, which provides true r.m.s.voltage measurements on waveforms of anycomplexity, can now be hired from MicroleasePLC. The instrument offers a bandwidth from5 Hz to 25 MHz and measures voltages from2 mV to 700 V on seven ranges and handlessignals with crest factors as high as 7:1, allow-ing waveforms of virtually any complexity tobe applied to its high impedance input. Coup-ling between the input and thermal conversionmeasurement circuit may be a.c. or d.c., allow-ing measurement of asymmetric signals,signals with a d.c. component, or pure d.c.fundamental measurement period is around40 ms, providing a reading rate of 225/s, butlower rates down to 0.2/s may be specified.The instrument may be used in autoranging or

manual mode. Decibel measurements are alsoprovided. Readings are presented on an LCDdisplay, along with an analogue meter for con-venience when making peak measurements.The voltmeter can be hired from Microlease forperiods of a week upwards; the weekly 'hirerate is from M.8.50.Micro/ease PLCForbes HouseWhitefriars EstateTudor RoadHarrowMiddlesex HA3 5SS101 4271 8822 (3009 Ml

Dot Matrix EvaluationSystemA Dot Matrix Evaluation System now availablefrom Lascar Electronics is claimed to save hun-dreds of man-hours and thousands of poundsin development costs. It allows use of DotMatrix Displays by users without specialisedmicroprocessor knowledge.The system is available at a special offer priceof £49.95 (± p&p and VAT/ and comprises a

1l CAR DI. MODULE

elektor september 1984

16 -character line display complete with bezeland panel mounting kit, a microprocessorbased controller module, inter -connectingcable and a full instruction manual, A 5 V d.c.supply is all that is required to have an LCDDOT Matrix Display system up and running inminutes.The controller module contains a pre-programmed EPROM which contains theinitialisation programme plus 15 standard'messages. On -board hexadecimal and pro-gramme switches allow custom messages andprogrammes to be developed. These can thenbe saved, either by implementing a 'powerdown' mode or by reprogramming theEPROM.Expansion of the system is easily attained asall controls, data lines etc. are brought out toa 32 way double -sided edge connector.The programme messages can also beswitched to the display by contact closure oropen collector transistor output.The EVAL-1 Evaluation System will allow manypotential new users of Dot Matrix Displays tofit them to their instruments in the minimumtime and cost.Lascar Electronics LimitedModule HouseWhiteparishSalisburyWiltshire SP5 25J107 9481 567 (3006M)

Holders for direct PCBmounting of zinc -airbatteriesGould Micro Power Systems has introduced anew range of plastic battery holders whichallow the company's range of zinc -air buttoncells to be mounted direct onto printed -circuitboards. The new holders, which cover all thestandard sizes and ratings of zinc -air cells, willenable the exploitation of the energy -densitybenefits of zinc -air cells in memory -back-up or

portable equipment applications. Typically, theType 630 EL zinc -air cell offers 950 mAh witha maximum drain rate of 42 yA. The newholders are produced in a heat -stable materialwith a low -profile design and spacer feetallowing air flow.Gould Micro Power Products Division11 Ash RoadWrexham Industrial EstateWrexhamClwyd LL13 9UF109781 61984 (3007 Ml

9-66

elektor september 1984

New single -board computeris STD bus compatibleBurr -Brown International Limited of Watford.Hertfordshire, have announced a new single -board computer which offers many functionsnot usually found on similar boards. Known asMP6102, the Z80A-based board is designed tooperate either in single -processor mode ormaster/slave mode for multi -processor en-vironments. It may eliminate the requirementfor additional serial or parallel I/O cards,counter/timer card, or a separate interruptcontroller since these functions are all in-cluded on the board. The MP6102 can be usedin conjunction with separate RAM cards, alsoavailable from Burr -Brown, while 2 K bytes ofRAM are provided on the card.Burr -Brown International LimitedCassiobury House11-19 Station RoadWatfordHens WD1 lEA(0923) 33837

(2984 Ml

True reverse style 0.1 inch(2.54 mm) connectorPlessey Connectors has introduced a truereverse style 0.1" pitch printed circuit connec-tor, the Series 20. to meet the growing de-mand for reliable, cost effective indirect inter-connections between printed circuit board andbetween PCBs and racking frames. TheSeries 20 connectors, available in 2 -row64 -way or 3 -row 96 -way mouldings, will besupplied with a choice of contact styles for ap-plications in telecommunications, computers.and industrial electronics, including hostile en-vironments. The Series 20 connectors are cur-rently undergoing approval testing to BS9525F0017 and British Telecom 02580 specifica-tions.

Plessey Connectors LimitedP 0 Box 30KingsthorpeNorthampton NN2 6NA(0604) 712000

12985 MI

Polisher/grinderA versatile, lightweight, suspended or bench -mounted polisher/grinder is available fromToolrange Limited. It has been designed foruse in small engineering works, or a homeworkshop, in clock making, jewellery settingand small electronics workshops. The flexibledrive is light, very flexible, and bends withoutstrain. The hand piece is of aluminium and hastwo ballraces to give optimum precision athigh speed: it comes complete with a -

chuck and four steel collets - 0, 1.5 mm,2.5 mm, and 3.0 mm. The speed is 10 000rev/min; the supply voltage is 240 VAC andpower consumption is 90 W (0.45 A). The unitis supplied with a variable speed foot pedaland a cast base for bench mounting. Thepolisher/grinder, together with over 3000other tools and production aids, can be foundin the Toolrange 1983/84 catalogue.Toolrange LimitedUpton RoadReadingBerkshire RG3 4JA10734)29945 (2996 Ml

Remotely controlled rotatorfor aerials or camerasA substantially built rotatable mounting withremote direction control gets the best out oftelevision, CB. or FM radio aerials, or can beused to mount security cameras. Known asthe type 200XL, it is available from Semicon-

ductor Supplies, Sutton, Surrey, by mail orderfor only £49.45 inclusive. Aerials and cameraequipment weighing up to 45 kg (100 Ib) canbe mounted and rotated by mains power over365 degrees. Speed of movement is onerevolution per 65 seconds. The weatherproofcase is made of metal castings.Semiconductor Supplies International LimitedDawson House128/130 Carshalton RoadSuttonSurrey SM1 4RS(01 643) 1126

(2983 MI

Single -chip teletext decodercontrols up to eight pagesThe new TPU2700 from ITT Semiconductorsprovides a single -chip solution to teletext, andoffers improved performance with thecapability of acquiring and storing eight pagessimultaneously. It decodes the standardLevel 1 teletekst transmissions widely used inthe UK and other European countries, andinterfaces direct to the digital -signal -processing Digit -2000 IC family. Up to eight

stored pages are controlled by the processor,giving a much reduced access time overcurrent multi -chip decoder designs. A menu ofthe stored pages is also available to the user.The only external components necessary tobuild a decoder is some RAM in the form of a64K x 1 device, or a number of 16K parts. Itcan serve in receivers for eight differentlanguage teletext transmissions, either on PALor NTSC standards. The TPU2700 comes in a40 -pin plastic DIL case, and requires a single5 V supply; consumption is typically 1.25 W.

ITT Semiconductors145-147 Ewell RoadSurbitanSurrey KT6 6AWEngland101 390) 6578/79

ITT Semiconductors500 Broadw-ayLawrenceM"-tachusetts 01841USA617 688 1881

12995 MI

'Slopefront' LCD multimeterA new low-cost LCD multimeter, type DP2020has been announced by Lascar Electronics. Aunique feature is the angled display whichmakes the instrument very easy to use eitherhand-held or laid on a bench. The case ismoulded in ABS, making the DP2020 suitablefor use in the laboratory or field use. Six func-

dons are available: DC volts, AC volts, DCamps, AC amps, resistance, and diode check- a total of 21 measurement ranges. Protec-tion against accidental overload is built in. Theinstrument can work up to 2000 hours from astandard PP3 battery. It is available from stockat 24.95 + VAT.Lascar Electronics LimitedModule HouseWhiteparishSalisburyWiltshire SP5 2SJ(07 948) 567 (2997 Ml

9-67

Tenth edition ofIC MasterThe new International edition of IC MASTERhas been released by Hearst Business Com-munications. The new edition lists key speci-fications for more than 313,000 integrated cir-cuits, microcomputer boards, microprocessordevelopment systems. PROM programmers,and custom/semicustom integrated circuitsmade by 220 manufacturers. Only productscurrently available worldwide are described inthe product data tables. Both new and discon-tinued devices, however, are shown in analternate -source directory. which provides in-formation on replacements, and lists approxi-mately 60,000 IC substitutions.The two -volume set contains more than 3,300pages divided into 20 sections (such asmicroprocessors, memories, linear integratedcircuits. customisemicustom ICs, etc.) Eachproduct group is organized by key specifi-cations so, for example, all 64K dynamicmemories are grouped together by organiz-ation, and then arranged in order of speed. Asan example of the use of IC MASTER, supposean engineer needs a CMOS single -pole, single -throw analog switch with a driver. All of thesedevices are grouped together, first arranged byincreasing 'on resistance, and then by increas-ing signal range and supply voltage. Althoughthe IC with the exact specifications may notexist, he will be directed to the one that isclosest to his needs.More than 70 IC manufacturers, includingAdvanced Micro Devices. American Micro-systems Inc., Fairchild, Harris, Intel, Motorola,National Semiconductor, Plessey, RCA,Signetics, Texas Instruments, and Zilog havesupplemented the editorial material and tableswith extensive data -sheet sections.The eleven technical data sections, organized

by function a.riti Y.c, parameters, arc military.digital, interface, linear, memory, micro-processor, microprocessor developmentsystems, microcomputer boards, microcom-puter support boards, customisemicustomICs, and PROM programmers. The eight sup-porting sections are the advertiser's productindex, part number index, part number guidelin this section, each company's part number-ing system is explained), guide to logos, ap-plication note directory, alternate source direc-tory, manufacturer's and distributors' direc-

tory, and function index (in this section. allfunctions found in IC MASTER are arranged inalphabetical order).

U.K. distributors are:PatelsoniSteadman and Partner Ltd.,The Hub,Emson ClosgSaffron Walden,Essex CB 10 1HL.Telephone: 07 99 27067.And:J. B. Tratsart Ltd.,Dogmetsfield Nr.,Baskingstroke,Hampshire RG27 8SU.Telephone: 02514 3334.

Add-on function generatorfor Scopex oscilloscopesA function generator which is available as anadd-on unit for any existing Scopex oscillo-scope and operates over the frequency range0.2 Hz...200 kHz is now in full productionwith Scopex Electronics Limited. Sine, rec-

tangular, and triangular pulse trains can begenerated and a 10 : 1 variability in the dutyfactor allows the instrument to be used togenerate single pulses, ramps, and skewedsine waves. Voltage -controlled frequencyinput facilities allow an external voltage to beused to sweep the generator over its fre-quency range either continuously or as asingle sweep.Scopex Electronics Limited63-65 High StreetSkipton,Vorth Yorkshire BD23 1EFx0576169511 (2998 M)

High speed opampDesigners working on video instrumentation.graphic CRT displays, videband amplifier, orhigh-speed track and hold applications, cannow take advantage of the technology em-bodied in the latest monolithic high-speedopamp available from MCP Electronics.Designed and manufactured by TeledynePhilbrick Microcircuits, the TP1342 features aslew rate of 600 V/jis, and settles to + 0.1 percent in 350 ns. The device is housed in a14 -pin ceramic DIL case, has a 600 MHzgain/bandwidth product, and in its standardversions operates over 0°C to +75°C.MCP Electronics Limited38 Rosemont RoadAlpertonWembleyMiddlesex HAO 4PE(01 9021 5941

(2979 MI

elektor september 1984

Third handFew DIY lobs are more frustrating than theone that needs "three hands": two to hold thework and a third to apply solder or adhesive.Gripmate, produced by an innovative Sussexcompany, is basically a tiny clamp that pro-vides not just one extra "hand" but four toenable it to grip small electronic componentsand similar items in an infinite number of posi-tions. Any of the semi -rigid wires may bereplaced with one holding either a magnifyingglass or a magnet where this is more ap-

propriate than the clip shown. Gripmate is notonly clever: it is also inexpensive. The four-handed model costs £4.85 la basic type withtwo arms sells for £1.00 less), and themagnifier and magnet are £2.50 and £1.50respectively extra. These prices are inclusiveof VAT and postage.Kempfant LimitedDurfold WoodPlaistow,BillingshurstWest Sussex RH14 OPN(048 6491 344

(2982 Ml

Coutant's GPE range oflinear power supplies winsBritisch Telecom approvalThe Coutant range of linear power supplieshas been approved by British Telecom for'user connected' equipment and conforms toPost Office Technical Guide 26 and BritishStandard 3861 (IEC380) for electrical safety ofoffice machines and, therefore, meets the re-quirement of the Health and Safety at WorkAct. The range includes single and twin out-put units covering one to fifteen amps at 5, 12,15, 24, 28, and 48 volts. The universal inputstage works from mains supplies from 110 to240 V at 48 to 65 Hz.Coutant Electronics LimitedKingsley AvenueIlfracombeDevon(0271163781

12980 MI

9-68

ELEKTCOR BOOKSRESI & TRANSIA series of strip cartoons in book form inwhich two enterprising characters explorethe field of electronics in their own inimi-table way. Their adventures are full oftension, because they often go against thecurrent - whereby they encounter muchresistance - before they reach their goal.These books familiarize the reader withelectronics in an unusual way: exciting,playful. yet thorough. Part I comes com-plete with a printed -circuit board and resi-Meter.Pen I: Banish the Mysteries

of Electronics £6.10Pan II: Hands off my Bike! £4.80

TV GAMES COMPUTERThis book, provides a different - and. inMany ways, easier - approach to micro-processors. The TV games computer isdedicated to one specific task, as thename suggests. This provides an almostarihaue opportunity to have fun whilelearning!Price £7.10

DIGIBOOK

Presides a simple step-by-step inuoduc.bon to the basic theory and applicationof dais* electronics and gives clearertathations of the fundamentals ofdgita circuitry. backed up by exper-iments designed to reinforce this newtyacquired knowledge. Supplsed with anexperimenter's PCB.PrCe £6.30

300 CIRCUITSFor the home constructor - 300 projectsrangng from the basic to the wry saphistkatedPrice £5.80

DATA SHEET BOOKHere at last is tine book that designers havebeen waiting for- the Elektor Data SheetBook. In 240 Pages it gives you a CMOS,a Lana*. spec.* Function and Audio DataBook: extensive .nformation on 269 ofthe most annostant IC's. A very usefuland economical reference book!Price £8.40

JUNIOR COMPUTER BOOK 1For anyone wishing to become familiarwith Imicrokornputen, this book givesthe opportunity td build and program apersonal computer at a very reasonablecost.Price £6.90

JUNIOR COMPUTER BOOK 2Fellows in a logical continuation ofBook 1, and contains a detailed appraisalof the software_ Three major programmingtools, the monitor, an assembler and aneditor. are discussed together with practi-cal proposals for input and penpherals.Price £8.90

JUNIOR COMPUTER BOOK 3The next, transforming the basic, single -board Junior Computer into a completepersonal computer system.Price £6.90

JUNIOR COMPUTER BOOK 4Book 4, the last in the series, describes allthe software required to operate the com-plete system. A number of peripheraldevices, such as a printer and a videoterminal. may be 'hooked up' to thecomputer_ During the final stage in its'growth', the machine is able to extendits linguistic skills. toe a special version ofBASIC is now available on cassettePrice 0.90301 CIRCUITSThe book is a continuation of our popularand very successful 300 circuits publi-cation_ It is composed of 301 assortedcircuits ranging from simple to morecomplex designs, described and explainedin straightforward language_Price E5-1110

MICROPROCESSOR HARDWAREThis book describes a range of peripheralequipment that can be connected andused with an assortment of personalcomputers which use the 6502.6809, 280or the 8080 CPU.Price £7.90

JUNIOR COMPUTER VIA 6522This book deals with the well-knownVersatile Interface Adapter (VIA) type

6522. Although it is an indispensable ad-dition to the four books already devotedto the Junior Computer, it is not aimedsorely at Junior users, but at anybody whohas a system with one or more 65Th. Itaffords a complete familianntion withthis flexible and effective component.Price £3.50

SC/MPUTER (1)Describes how to build and operate yourown microprocessor system - the firstbook of a series - further books sillshow how the system may be extended tomeetr,various requirements.Price £5.80SC/MPUTER (2)The second book in series. An updatedversion of the monitor program (Elbug 111is introduced together with a number ofexpansion possibilities. By adding theElekterrninal to the system described inBook 1 the microcomputer becomes evenmore versatile.Pr ice £5.80FOR MANTComplete constructional details of theElektor Formant Synthesiser - comeswith a FREE cassette of sounds thatthe Formant is capable of producingtogether with advice on how to achievethem.Price £6 30

33 ELECTRONIC GAMESA setect:on of circuits which give as muchenjoyment in building them as actuallyplaying the games. The circuits are fasci-nating although the electronics invohedare not complex and therefore anyonewith a good soldering iron will find thisbook satisfying. These are electronic gamesthat do not need a TV screen, and as arersuict can be played jun about anywhere.Price £4.80

JUNIOR PAPERWARE 1Modifications of the PM/PME EPROM:Source listings, Hex dump of the Softwaretrundler and puncher (Elektor 85, May1982)Price £2.10JUNIOR PAPERWARE 2Source listing of the bootstrap loader

for Ohio Scientific Floppys: Hex dumpof the EPROM (ESS 5151Price £2.10

PAPERWARE 3 & 4The hardware for a Universal Terminal hasalready been described in Elektor. Itconsists basically of a VDU and and aCPU card, but, of course, to make theterminal work some software is alsoneeded. Two new books are now availableto meet this need. Pape'ware 3 not onlyincludes all the necessary software, butalso deals with all the 'ins and 'outsof the terminal. Papenware 4 pros -desall the software and other informationfor using the Universal Terminal with theJunior Computer-, either in expanded formor with DOS.Price: Paperware 3 £2.70

Paperware 4 £2.80

EXTENDED PRESET UNITFOR THE POLYPHONICSYNTHESIZERThis book is the culpination of a projectwhich was started ifs the October 1981issue of Elektor and to which since thenno fewer than nine articles have beendedicated. It is no exaggeration to saythat the polyphonic synthesizer can beused to its full potential only with theextended preset unit. The booklet isdivided into five distinct sections: theconstruction and fitting of the variouscards, a functional description, calibrationand testing, fault-finding, and trackingof the voltage -controlled filter and low -frequency oscillator. It is possible tobuild and test all the circuits and thenfit them all at once into the synthesizeror build arid add them piecemeal. Asthe booklet is intended more as a referencework than a full instruction manual, thechapters can be read in any order. Thebooklet assumes reasonable familiaritywith computer technology.Price £1.60

To order please use the postage paid ordercant In this issue_ADD 55p P & P U.K. (OVERSEAS £1.101

DaDmmilmv11:1 wwIluummENELascar Electronics Limited,Module House, Whiteparish, Salisbury, Wiltshire SP5 2SJTel: Whiteparish (07948) 567 Telex: 477876

DOT MATRIX DISPLAYS

The Full Service

LPSCAR ELECTK:4ICS P-airsPCOULES, E-E.:F.L.F. c.c:11-t',_ _Ea' ratiLES

Display modules all supplied with mounting bracketsand display bezels.

Controller modules save hardware and softwaredevelopment time.

An evaluation system allows use of Dot Matrix Systemwithout specialised microprocessor knowledge. Only a+5V DC supply is needed to have a system up andrunning in minutes. Evaluation system Evat-1 contains a16 character 1 line display, a controller module, inter-connecting cable and a full instruction manual.

DATA CASSETTES &FLOPPY DISKSPack of 5 good qualityCl 2 cassettes.ONLY £1.95 (BK9SD)

Pack of 10 top quality 5' 4infloppy disks single -sided,single or dual density.ONLY £17.95 (Y.100A)

SOLDERRecommended for general purpose,fine work and pcb's, a top quality flux -cored 60% tin, 40% lead solder. 22swg.ONLY 82p for 10 metres (FR21X)

RELAYSSub-minoture 12V relays will switch up to 10A at 240V AC.

Coal Contact ratingsvoltage resistance DC current AC Current (refslive)

Size(mm)

S:ngle-polechangeover 8.4 to 15.6V 400ft up to 10A at 30V up to 10A at 240V 21 x 16x14Dcuble-polechangeover 8.4 to 13.2V 2708 up to 5A at 30V up to 5A at 240V 29x20x 13Relays ore fully enclosed and direct pcb mounting.INCREDIBLY LOW PRICE £1.65 each(SINGLE -POLE YX97F)

(DOUBLE -POLE YX98G)

VIDEO COPYING KITCopy video tapes to and from virtuallyany VHS or Beta machine. Kit makes sixdifferent video and six different audio leads.ONLY £9.95 (RK71N)

RESISTORSFor superior to carbon film, thesesuperb quality, very high stability,exceptionally low noise resistorshave a =1% tolerance and arerated 0.4W at 70=C yet are only6.5mm long and 2.5mm diameternominal. E24 range 101) to 1 M.EXCEPTIONALLY LOWPRICE 2p each (M -VALUE)

C o MPARE OUR PRICESthen choose MAPL1,W

for Quality and Service as well!Well over £1 1/2 million worth of top quality electronic components always in stock

D -CONNECTORGold over nickel plated contactsand solder terminations. Thermo-plastic cover allows side or topentry and includes cable clamp.

SUPERB QUALITY .

AND AMAZINGLYLOW PRICES

Plug9 -way 68p (RK600)15 -way 45p (BK58N)25 -way 0.39 (YQ48C)

Socket95p (RK61R)

£1.43 (BK59P)E2.19 (YQ.I9D)

Cover£1.14 (RK62S)99p (BK60Q)£1.14 1YQ50E)

COMPARING OUR PRICESWhen you compare our prices, remember that many of ourcompetitors quote VAT exclusive prices. This hidden extramakes a big difference to their seemingly low prices.On an order as little as £6.67, the VAT is o whole £1 extra

r

SHOPS ONLYPRESENT THIS COUPON IN ONEOF OUR SHOPS AND WE'LL KNOCK5% OFF ANY ONE COMPLETE ORDERVALID UNTIL 1st SEPTEMBER 1984

E9-1

TELEPHONE CONNECTORSThree examples from our range of telephone fittings.All are BT approved and sockets are shuttered.

Flush fitting jack socket for maintelephone. ONLY £3.99 (F/27E)Flush fitting jack socket forextension telephones.ONLY £2.65 (F134N)Line cord, 3m long, spadeterminals to phone plug.ONLY £1.95 (FG29G)

N.B. All our prices INCLUDE VAT and Carriage. A 50p hancLng charge must beadded if your Iola! order is less than £5 on mail-order.

MAPLIN ELECTRONIC SUPPLIES LTD.Masi Order: P.O. Box 3, Ray4&gh, Essex SS6 SLR. Tel: Southend (0702) 552911.SHOPS BIRMINGHAM Lynton Square, Perry Barr, Te!: 021-356-7292. LONDON 159-161 King Street, Hommersm:th, W6. Tel: 01-748-0926. MANCHESTER 8 Oxford Road, Te!: 061-236-0281. SOUTHAMPTON 46-48 Bevois Volley Road, Tel: 0703 25831. SOUTHEND 282-284 London Road, Westdiff-on-seo, Essex. Tel: 0702 554000.Shops closed a'i day Monday.