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UHF or VHF television: which is best? S3.50 MAY 1988 NZ $4.95 ~~i- -= SERVICING -- HIFI --=----. 1 ,- -NEW~ ltiC1t\Otl\C!.:i 2'i;l;M•lt• :JM!liMi -11 Variable rate flashing light Building tbe Railpawer model train controller Easy-to-lit car burglar alarm aeromodellers Digital Electronics Inside memory circuits Fluke. First Family of DMMs. When accuracy, performance and value are important, professionals the world over look to Fluke - the first family of DMMs. Reliable Fluke-quality 3½- or 4½-digit DMMs fit every need - from design engineering to industrial troubleshooting. There's the low-cost 70 Series - the most DMM you can get for the money. The tough 20 Series - totally sealed and built to survive the dirtiest, grimiest, roughest jobs. The reliable 8020B Series - made to withstand the rigors of the field service environment. The precise 8060A Series the most powerful and complete test and measurement system available in Phandheld package. And, of course, the versatile Bench/Portables that carry on the Fluke tradition for precision and durability in lab-quality bench instruments. Fluke comes in first again with the world's largest selection of quality accessories to help extend the capabilities of your DMM even further. There's no need to look anywhere else. Uncompromising Fluke design and leading edge technology are the reasons why attempts at imitation will never fool the millions of professionals that accept nothing less than a Fluke. FROM THE WORLD LEADER IN DIGITAL MULTIMETERS. IFLUKEI ® ELMEASCO Instruments Pt,,. Ltd. Dealer enquiries welcome faik to your local Elmeasco distributor about Fluke • A.k.L._ John Pope Electrical (062) 80 6576 • J Blackwood & Sons (062) 80 5235 • George Brown (062) 80 4355 • ~ Ames Agency 699 4524 • J Blackwood & Sons• George Brown 519 5855 Newcastle 69 6399 • Auto-Catt Industries 526 2222 • D.G.E. Systems (049) 69 1625 • W.F.Dixon (049) 69 5177 • Ebson 707 2111 • Macelec (042) 29 1455 • Novacastrian Electronic Supply (049) 62 1358 • Obiat Ply Ltd 698 4776 • Petro-Ject 569 9655 • David Reid 267 1385 • Selectroparts 708 3244 • Geoff Wood 427 1676 • N.TERRITORY J Blackwood & Son (089) 84 4255, 52 1788 • Thew & McCann (089) 84 4999 • O~EN¥£ Auslec (07) 8541661 • G.Brown Group (07) 252 3876 • Petro-Ject (075) 91 4199 • St Lucia Electronics 52 7466 • Cliff t::le rorncs 55 • Nortek (Townsville) (077)79 8600 • L.E.Boughen 369 1277 • Fred Hoe & Sons 277 4311 • The Electronics Shop (075) 32 3632 • Thompson IQstruments (Cairns) (070)51 2404 • S AUSTRALIA Protronics 212 3111 • Trio Electrix 212 6235 • Industrial Pyrometers 352 3688 • J Blackwood & Sons 46 0391 • Petro-Ject 363 1353 • TASMAWA George Harvey (003) 31 6533 (002) 34 2233 • VICTORIA Radio Parts 329 7888 • George Brown Electronics Group 878 8111 • G.B. Telespares 328 4301 • A.W.M. Electrical Wholesalers • Petro-Jee! 419 9377 • J Blackwood & Sons 542 4321 • Factory Controls (052) 78 8222 • Meklronics Co 690 4593 • Truscott Electronics 723 3094 • WAUSTRALIA Atkins Carlyle 481 1233 • Debbie Instruments 276 8888 • Protronics 362 1044 MAY 1988 FEATURES 6 Restoring Vintage Radio Receivers by John Hill It's time to start collecting 42 Motorola's MC3334P High Energy Ignition IC CHECK OUT ENGINE RPM on your model airplane with this easy-to-build optical tachometer. You can also use it to measure the speed of fans and rotating shafts. See page 18. by Leo Simpson New device optimises spark energy 76 The Evolution of Electric Railways by Bryan Maher Pt.7 - The first electric mainline system 84 Digital Fundamentals, Pt. 7 by Louis Frenzel Memory circuits PROJECTS TO BUILD 18 Optical Tachometer for Aeromodellers by John Clarke Checks engine speeds up to 25,000 RPM 32 Fit High-Energy Ignition to Your Car by Leo Simpson Improves power, eliminates tune-up hassles 44 Walkaround Throttle for Model Railroads Pt.2 INTERESTED IN RESTORING vintage radio receivers? If so, it's time to start collecting. Turn to page 6 for the first article in this great new series. by Leo Simpson Building the circuit into a console case 62 Ultrasonic Car Burglar Alarm by Branco Justic A high-performance design that's easy to install 72 Build the Party Light by Stephen David Uses a commercial 12V strobe light SPECIAL COLUMNS 12 The Way I See It by Neville Williams Is UHF TV really as good as it's cracked up to be? 56 Serviceman's Log by the original TV serviceman Double or quits - FIT THIS HIGH-ENERGY ignition system to your car and forget tune-up hassles. We explain the benefits and show you how to build it starting page 32. toss ya! 70 Amateur Radio by Garry Cratt Designing and building attenuators DEPARTMENTS 2 Publisher's Letter 3 Mailbag 4 News & Views 9 Subscription page 50 Circuit Notebook 83 Back Issues 92 Product Showcase 94 Ask Silicon Chip 96 Market Centre ULTRASONIC ALARMS have one big advantage - they're easy to install. This unit can be used in car or house installations and has special circuitry to stop false triggering. Details page 62. M A Y 1988 1 SILICON CHIP Publisher & Editor-In-Chief Leo Simpson, B.Bus. Editor Gr~g Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Regular Contributors Neville Williams, FIREE, VK2XV Bryan Maher, M.E. B.Sc. Jim Yalden, VK2YGY Garry Cratt, VK2YBX Jim Lawler. MTETIA David Whitby Photography Bob Donaldson Editorial Advisory Panel Philip Watson, MIREE, VK2ZPW Norman Marks Steve Payor, B.Sc., B.E. SILICON CHIP is published 1 2 times a year by Silicon Chip Publications Pty Ltd . All material copyright (c) . No part of the contents of this publication may be reproduced without prior written consent of the publisher. Kitset suppliers may not photostat articles without written permission of the publisher. Typesetting/makeup: Magazine Printers Pty Ltd, Waterloo, NSW 2017 . Printing: Macquarie Publications Pty Ltd, Dubbo, NSW 2830. Distribution: Network Distribution Company. Subscription rates are currently $42 per year (12 issues). Outside Australia the cost is $62 per year surface mail or $1 20 per year air mail. Liability: Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Address all mail to: Silicon Chip Publications Pty Ltd, PO Box 139, Collaroy Beach , NSW 2097 . Phone (02) 982 3935 . ISSN 1 030-2662 * Recommended and maximum Australian price only. 2 SILICON CHIP PUBLISHER'S LE'J-JER Lo, the dreaded • m1croprocessor Thanks to all those readers who have responded to the call for feedback in our March issue. Many have written in with requests for all sorts of interesting projects, some of which we already had on the "list of songs" but many others which we would not have considered. Largely as a result of specific reader requests, a number of projects are now under development and will be published in the next few months. Others will appear in the longer term. If you are one of those who had considered writing but did not get around to it, please write to us anyhow. We do value your ideas. What has been interesting in a number of letters is that people have congratulated us on the format, made a number of project suggestions and then warned us to "stay away from computers". We can understand this feeling. So much of what is written about computers and microprocessors is boring or impenetrable unless you have already picked up a grounding in the subject. But I have a dreadful truth to reveal. Sooner or later, articles on microprocessors, computers or computer-related projects will appear in SILICON CHIP. There, I've gone and said it - the truth is out. But before you throw the magazine across the room in a rage, let me tell you a bit more. Some of my acquaintances who have been anticomputer in the past are now deeply immersed in the subject. This is probably as great a surprise to them as it is to me. If you are an anti-computer person, you no doubt find that your electronics interest is in the fascinating world of analog components and the complexities of their multifarious parameters. You may not have thought about it that way but it's true isn't it? By comparison, microprocessors may seem mundane and uninteresting; all those digital inputs and outputs and a whole lot of timing diagrams to consider. But if you are immersed in computers, it is the "instruction set" of the micro that provides the real fascination; what you can do with it, when you know the rules. And so it is that there are tens of thousands of people who are hyped on the Z80 and 8080, or its later derivatives, 8086, 80286 and so on. And there are other tens of thousands who are hyped on the 6502 (from their experience with Apple, Tandy Co-Co or Commodore machines), many of whom are now graduating to the 68000 micro (used in the Macintosh). All these people can't be wrong. Micros and computers can be equally as fascinating as analog electronics and when you ultimately read about them in SILICON CHIP there is even a chance that you, too, might be hooked. Don't worry, we won't ram them down your throat. And if our articles on micros leave questions unanswered, write into us. That way you'll find out the answers and we'll see how our articles can be improved. Leo Simpson MAILBAG Vintage radio circuits Congratulations on your successful start with SILICON CHIP. You certainly have my support. For those people interested in restoring old radios, I have copies of the Australian Service Manuals covering Australian-made radio receivers from 1937 to 1946. I would be happy to supply copies of receiver circuits in return for two 37 cent stamps to cover copying and postage. In addition to the make and model, it would be helpful to know the year of manufacture, number and types of valves, and the wavebands available. J. Emery 19A Fyfe Circle, Bull Creek, WA Comments on magazine In the March issue of SILICON CHIP, you ask for comments and likes and dislikes. I have seen the magazine in the newspaper shops and this month decided to have a look at it. You do seem to have got away from the usual run of things for which I commend you. I liked the articles on antique radio (I am a member of the Historical Radio Society of Australia) and also the articles on electric railways. I do hope your SILICON CHIP does not fall into the rut followed by most other magazines. That is, the description of common gadgets for around a year, then the following year the same equipment updated and so on ad infinitum. A section for beginners, where we can really get down to the fundamentals as against the trend towards complexity, is required. The article in the March issue concerning the repair of portable cassette-radios is excellent as far as it went. Surprisingly, no mention is made of the most common fault in cassette players - the failure of the motor drive belt. At least, this fault is common in Queensland and is no doubt due to our hot climate. What happens is that the belt becomes stretched and distorted, resulting in wow and flutter. In its final stage, the fast forward and rewind operations fail to work. The result is that the serviceman, in most cases, has to almost dismantle the cassette player to reach the faulty belt. Even in the easiest cases, it is one hell of a job and many service organisations refuse to tackle such repairs. Do you know of anyone who has an answer to this problem? My main hobby is in researching old circuits and bringing them up to date. This can involve taking a circuit that was designed around germanium transistors and modifying it to accept modern silicon types. Some of the results have been startling. The germanium transistors were like early valves with poor gain and poor radio frequency performance. Because of the poor performance of these transistors, the circuits around them had to be the best available. It follows, therefore, that if these circuits are re-worked around modern high-efficiency silicon transistors, the results are bound to be excellent. John Ratcliffe Southport, Qld Good mix of articles Just a few lines to say how much I have enjoyed the initial issues of SILICON CHIP, and to wish your venture every success. The mix of articles seems very good with a nice balance of product news, constructional articles, developments in industry, and items of general interest such as Bryan Maher's series on electric railways. I'm also enjoying the Digital Fundamentals series in which Louis Frenzel has explained clearly to me a subject which I previously found difficult to grasp. The technical level of the magazine is just about right for enthusiasts like myself I have no formal background in electronics nor am I employed in the industry - and I know that the editorial staff can be relied upon to publish projects which are useful and which work in the manner intended. This is a difficult time to launch a new magazine but I am sure that if you can maintain the standard of the SILICON CHIP, PO Box 139, Collaroy Beach 2097. initial four issues, then you will achieve the success you deserve. Clive S. Wallis, VK2DQE Miranda, NSW Super crystal set In the Serviceman's Log, March 1988 issue, a 1000µF 16V electrolytic was suspect, but tested OK and was replaced. With a retail price of about 33 cents, surely replacement would have ensured better service for the customer. The old service adage has always been "if in doubt toss it out". Conversely, a kit price of $89 .50 plus $5 packing and post for a crystal set (same issue) would deter most youngsters from enjoying the thrill of building a crystal set. For very little they could build a tapped coil tuned crystal set, with nuts and bolts for terminals, a baseboard, a couple of capacitors, alligator clips and a razor blade for a detector if they did not have a crystal. Sure, performance would be down, but the thrill of building the crystal set at minimal cost would more than compensate. Keith Goldsmith Shorncliffe, Qld A fresh approach It has been a long time since we have seen a series of magazines with such quality of presentation and content as you have been able to produce. Your magazine certainly represents a fresh and uncomplicated approach and has a good balance between informative articles and excellent projects. Without doubt, the quality of your print, drawings, layouts and photographs is far superior to that of your competitors. As a team of individuals, you have shown courage and determination in departing your previously held secure positions and entering a highly competitive field. Considering the size of your team and your resources, your achievem ents a re to be commended. Branco & Lydia Justic Oatley Electroni cs Oatley, NSW MAY 1988 3 NEWS&VIEWS to "the preservation, restoration and collecting of early radio sets". The proposed organisation, to be called The Early Wireless & Sound Society of NSW, will have it first meeting on Friday June 24th June. Anyone interested should contact John Murt, PO Box 623, Lane Cove, NSW 2066. Phone (02) 488 8184. Agreement on high-band option for Video-8 format Vintage radio devotee John Murt made a proposal for a new society to the Phonograph Society of NSW. First meetings will be held in June. Membership drive for Phonograph Society With the increasing interest in restoration of vintage radios, it is not surprising to find that there is a society for those interested in old phonographs. The NSW Society has been going since 1973 and has a regular journal. They are presently having a drive for new members. Those interested in knowing more about the society should contact the President, David Mccallum on (02} 692 9633 or the Secretary, John Hanna, on (02) 636 8648. A proposal has also been made by vintage wireless devotee John Murt to form a new society devoted The developer of the 8mm video format, Sony, has announced that an agreement has been reached on specifications for a "high band" version of the Video 8 format. This is intended to provide higher resolution pictures, in much the same way as PCM (pulse code modulation) is presently offered as a high quality sound option on Video 8 recorders. Taking part in the agreement were companies such as Aiwa, Canon, Hitachi, Matsushita, Sanyo and TDK. Tape cassettes for this new format will be equipped with a detection hole to enable automatic identification by the VCR. Warning from Telecom on non-approved devices With the publication of the Line Grabber circuit in the March issue, it seems that Telecom has become officially aware of the existence of SILICON CHIP. A representative from the NSW Regulatory Branch of Telecom has pointed out that devices such as the Line Grabber are non-approved and constitute a breach of regulations if they are connected to Telecom lines. If Telecom technicians discover such equipment they are empowered to disconnect it and as set out in the front pages of your Telecom directory, "will charge if called to faults which are due to such equipment". Furthermore, if the user persists in using such equipment, Telecom is empowered to disconnect the user's line at the exchange. So 4 SILICON CHIP much for the official line. It seems that Telecom is not interested in whether the equipment conforms to technical requirements or not but merely whether it is authorised. In the normal course of events, Telecom would not have any means of detecting the presence of devices such as the Line Grabber, Off-Hook Indicator (published in the November 1987 issue of SILICON CHIP), o.r the Personal Phone Ringer (published in the January 1988 issue), short of a physical inspection of the customer's installation. Telecom's blanket attitude to non-approved gear extends to modems built from kits and once again, they are empowered to disconnect. The message seems to be "don't make a call for service unless you are absolutely sure that all equipment connected to Telecom lines is approved". If you do have a fault in your installation and you leave nonapproved equipment connected while the technician calls, you may end up in trouble. We are in two minds about Telecom's policy. On the one hand, non-approved devices such as wireless phones on illegal frequencies can cause havoc with communications. And badly designed equipment with poor mains isolation can also constitute a safety hazard for Telecom personnel. On the other hand, devices such as the Line Grabber are powered from the phone lines, cause no loading, are not hazardous and are undetectable. So why worry? South East Radio Group Convention The South East Radio Group at Mt. Gambier will be holding its annual convention during the Queen's Birthday weekend in June. As well as the usual convention activities, there will be a display of vintage radio equipment, both commercial and amateur, and enthusiasts are invited to bring along their favourite pieces of gear for display There will be also be a working "Ham Shack" demonstrating some of the various modes available to amateurs and it will be using the Bicentenary call sign Vl88SA, providing a once-only opportunity for amateurs who like to collect station QSL cards. · For further information on the convention program and registration forms, contact the South East Radio Group, PO Box 1103, Mt. Gambier, 5290. ACS: a meal ticket for the community FM stations Now that Ancillary Communications Services are becoming established as a recognised adjunct to FM stations, a number of community FM broadcasters are clamouring to get in on the act. They recognise it as a meal ticket and a way to generate a secure income. There is another side to the coin though. While there may well be more opportunities for broad~ casting of data and background music, business users are going to want absolute reliability of service. To guarantee this, FM stations are going to have to make sure their entire installations have built-in redundancy, right up to the transmitter. That's an expense that many stations could not afford. If they don't have it though, they are leaving themselves open to litigation if their ACS transmissions are interrupted. Just imagine the potential loss to a business client if stock exchange data was interrupted at a critical stage in the market. Winding back speedos won't be possible The practice of winding back speedos before cars are sold will not be possible in the future if the trend to replace mechanical odometers with electronic chips continues. The indications are that it will with the recent release of a new MOS chip by Siemens. Designated the SLE4501, the new chip is a PROM (programmable read-only memory) which can store more than four million events, the eguivalent of more than 400,000km when counting in units of 100 metres. An additional chip , the SLE4502 CMOS prescaler, permits the electronic odometer to be programmed to suit any type of car, taking into account its wheel and tyre sizes, gearbox and differential ratios. To do this, the divider ratio is programmable from 1 to 65,000. It also has two 16-bit registers that perform the functions of speedo and resettable trip meter. The storage capacity of the SLE4501 chip is more than 400,000km which is certainly more than any normal car or even a taxi would be expected to cover in normal service. By contrast, most large trucks and buses would routinely exceed this figure. One outstanding quality of the electronic odometer PROM is that it is non-volatile (ie, the memory contents are not lost when the power is removed very necessary for automobile use}. It also includes a comprehensive data protection system which prevents tampering. Hence, winding back the speedo may become a thing of the past. Even so, we can think of two devious ways around such electronic odometers. What about forcing the PROM to count past zero or why not just replace the device with a new one having a lower reading programmed in? Maybe the designers have thought of the first approach but how would they counter the second? Cellular radio gives cheaper petrol to outlaw this price chaos? We hope they don't. With the intense competition between petrol stations in the cities, particularly in Sydney and Newcastle, petrol prices can change several times a day. The petrol companies have found that once a station drops its price it gets more than 80% of the business in its immediate area. That means that competing stations can lose thousands of dollars an hour while ever they are at a price disadvantage and waiting to get authorisation to drop their prices too. The petrol companies have found that they can substantially reduce these losses by equipping their representatives' cars with cellular phones. This allows the reps to be contacted quickly to authorise a price change. What will happen though when and if the State governments decide French to develop car navigation system The French are getting under way with the development of an integrated car navigation, communications and diagnostics system. The system will be included in cars of the future, probably in the late 1990s. It will allow road users to find the best route as well as improving the car's performance. Taking part in the project are Philips, Renault, RTIC (a French Philips affiliate), Sagem and TDF (Telediffusion Francaise). The first two phases of the project will take four years to complete and the total budget, contributed by the companies involved and the Dutch and French governments, will be close to 50 million European Currency Units. MAY198 8 5 VINTAGE RADIO By JOHN HILL It's time to start collecting If you 're going to start collecting vintage radios, there is no better time to start than now. Unrestored treasures lie waiting in houses, antique shops and garages, and can generally be picked up for a few dollars. Collecting is a well recognised hobby which has many adherents. Collecting not only gives the collector a purposeful interest but also consumes his spare time in a most pleasant manner. Unfortunately, some forms of collecting can cost heaps of money, megabucks in fact. If your interest happens to be veteran cars, antique clocks or rare postage stamps, then you will need a very thick wallet if you are going to build up a worthwhile display. / As I write this I am surrounded by my collection of radios and looking around, I see that I paid $40 for one (got ripped off there), a number of others which cost $20 or less and ten that were given to me. There are also a few horn speakers that average out at about $59 each. I mention this to give readers some indication of how relatively inexpensive collecting old radios can be. Admittedly it does cost money but in my case, I can comfortably finance my hobby with my pocket money and have done so since I started collecting about three years ago. Some people spend more on cigarettes than I spend on radios. Collecting old radios If you are thinking about collec- Sets that can't be restored should. be stripped for spares. If you're a serious collector, those parts are going to come in handy. 6 SILICON CHIP ting old radios there are a couple of things you will soon find out. First, if you look in the right places there are heaps of old valve radios around just waiting to find a new owner. Second, you need not outlay large sums of money because $25 will buy a good many of them. Now if you are serious about getting a vintage radio collection together and have done nothing about it, then you had better get going. Even during the short time that I have been collecting, I have noticed that the more collectable items are becoming scarcer. Actually there are quite a number of valve radios that are still in everyday use. The oldest set that I know of that is still going strong for its 78-year old owner is a 1939 "Airzone", a very stylish console model. Although most operational sets are not that old, many have been going for years and may go many more before they finally stop working. When that fateful day comes it will be the point of no return, for suddenly the radio will become useless and almost worthless. The reason for this is that under most circumstances, the set cannot be repaired. Almost no radio/TV repair shop can service valve radios anymore. They have neither the desire or the necessary parts to repair them. In some cases, they may even lack the know-how. This is the type of radio that the vintage radio collector is likely to pick up. It will either be given to him or be bought very cheaply. It is this type of radio that is seen at flea markets, garage sales and in junk shop windows. They usually don't work and a very fine line separates them from the rubbish tip. This neat little Radiola was produced in both bakelite and plastic and is a fairly common radio from the early post-war years. Three of the these four plastic cabinet radios are in the process of cracking up. While they were reasonable radios in their day, they have little appeal to most serious collectors. These pre-loved radios will most likely be relatively late-model valve sets and may only be about 25 years old. (Valve radios were still being sold in 1966). To a collector, such a radio is rarely considered a good collectable item, mainly because the last generation of valve radios lack the enduring qualities of the earlier sets. They just haven't got the same appeal. Different categories In order to explain further, now would perhaps be a good time to. place these old radios into categories. One way of classifying them is to place them into groups according to their age. I see these groups as follows. Any radios that are pre-1930, and have separate speakers and reaction circuits, would have to be genuine antiques. As stated elsewhere, these are very collectable items. The next category is pre-war (1930 to 1940). This is also an interesting era for radio because receivers improved so much during that decade. They came from being relatively primitive to quite sophisticated. Next was the post-war period to about 1955, a period where valve radios were perhaps at their best - good receivers with excellent speakers. Many of the radios in this age group are what I consider to be very collectable; old enough to be interesting, yet modern enough to sound really good. Finally, there was the plastic era when plastic began to replace Bakelite and timber. While these radios are interesting in some respects, they are not satisfying from a collector's point of view. Unfortunately the plastics used in these radios are inclined to selfdestruct after 20 years or so and they simply weren't built to last as were their predecessors. Valve radios can also be classified into various types of receivers such as 240-volt operated; battery operated; battery vibrator; battery portables; mantle radios;, table models; consoles; radiograms and even car radios. Collectors have plenty to choose from but most seem to concentrate on one or two particular categories. In my case, I collect radios from the 1020s to the 1950s. I do not collect radiograms for the simple reason that they occupy so much space; I cannot accommodate them. I also have a few battery sets and operate them on a combination of rechargeable batteries and a "B" eliminator. Generally speaking , batteryoperated valve radios are only mediocre in their performance and usually fail to compare favourably with their 240-volt brethren. Some of the early "permag" speakers were only fair and this could be one of several reasons why battery sets are a bit lacking in sound quality. The 1920s era In my opinion, the really collectable radios are those from the 1920s era. These are the most expensive to buy and the most difficult to locate. They sound terrible but from a display point of view they are quite unique and therefore very desirable. I have only one genuine late 1920s receiver and it in extremely good condition. As this set only cost $20, I consider my.s elf most fortunate to have bought it at such a MAY1988 7 A 1941 model Radiola; timber cabinets have much more appeal than plastic or Bakelite. reasonable price. I would like to own others and am prepared to pay whatever they are worth. However, most people who have these ancient receivers want to keep them. Where to look Anyone making a start at collecting should consider everything as collectable. They should not miss a single opportunity to pick up any valve radio. Collecting need not be restricted to valve radios for some collectors wish to include transistor radios in their collections. Sometimes junk is the only word to describe some of the "treasures" one collects and it is incredible that these neglected old sets have not been dumped long ago. However, any wrecked radio, no matter how derelict, usually has a few usable parts that are worth salvaging. The logical places to look for old radios are in junk shops, opportunity shops, used furniture stores, auction rooms, school fetes, white elephant sales, garage sales and antique shops. Regarding the latter: the better class of antique dealer doesn't sell old radios. It's the antique-cum-junk shop that is more likely to carry a vintage radio treasure. Bakelite radio cabinets are more durable than plastic. This Kreisler of about 1948 vintage has survived 40 years quite well. 8 SILICON CHIP While old radios can often be picked up at reasonable prices at any of the above-mentioned places, some secondhand dealers put ridiculous prices on their wares. These seemingly high prices are usually negotiable as the following story indicates. I was in an antique shop looking at a large table model radio that was in very good external condition. It was a 6-valve Philips, with dual wave coverage, a timber cabinet and a tip up dial. The price tag was $32. After finding out that the set didn't work, I commented that it seemed like a lot to pay for a bung radio. I was immediately offered the set for $10 which was a far more reasonable amount. Actually, I would have paid up to $20 but I didn't argue over the price. If the truth was known, that set had probably sat there for a considerable time without a single enquiry and it must have seemed like the ideal time to sell when I showed an interest in it. On the other hand, a radio in good going order must command a better price. What's more, if it's going, there is a lot less risk involved. It could well suit come collectors to buy this type of radio. It may cost more but at least it's a goer and you know what you're getting. One must always keep in mind that buying from shops is probably the dearest way of obtaining old radios. Shopkeepers have overheads and that puts up the price of the items they sell. However, there Old radio service equipment is also worth collecting. Shown is a "University" radio frequency generator._ THE ELECTRONICS MAGAZINE FOR THE ENTHUSIAST WE INVITE BECOME You To A SUPPORTER We believe that electronics is a fascinating pursuit, and the most useful hobby that anyone can have, particularly for a young person in school. Anyone with a good grounding in electronics is better prepared to meet the challenge of today's and tomorrow's technology. Because we believed that many more people should come to know about and enjoy electronics, we decided to start a new magazine expressly for electronics enthusiasts, whether they be nervous beginners or seasoned veterans. We called it SILICON CHIP, a name which focuses on the very basis of today's electronics technology. We started SILICON CHIP as an independent magazine completely free from the influence of any existing publishing company, because we wanted to establish the highest possible standards for accuracy and attention to detail. Our team is very small: founders Leo Simpson and Greg Swain, plus full time staff members John Clarke and Bob Flynn. SILICON CHIP has now been on sale for seven months and has been very well received. Even at this early stage, you, the readers, have clearly indicated that SILICON CHIP is the most entertaining and best produced electronics magazine in Australia. Considering the hard work in getting started, it has been a very gratifying response. But we want to make SILICON CHIP even better. To do this, we need the resources to employ more people; we need the services of technical illustrators, writers, designers and other creative people. This is the only way that we can be sure of attaining the highest possible editorial standard. We know this is what you want. Your letters tell us. But we can only do this with your enthusiastic support. Already, many hundreds of readers have taken out subscriptions to give SILICON CHIP a solid start but we we would like to have thousands more. If you haven't already done so, please give us your vote by becoming a subscriber. By doing so, you will be ensuring the future of an entertaining, informative and independent SILICON CHIP magazine. Regular Features * * * * * Constructional Projects For The Enthusiast HiFi Review Digital Electronics Course Circuit Notebook Vintage Radio Junk Mail * * * * The Serviceman's Log Amateur Radio, by Garry Cratt, VK2YBX The Way I See It, by Neville Willams Book Reviews Most magazines sell their subscriber list to mail order companies, to earn extra income. We will not do this. We will lose some money by adopting this policy but we believe that your privacy is paramount. BECOME A SUPPORTER BY FILLING OUT THE POST AGE FREE SUBSCRIPTION COUPON OVERLEAF ► MAY 1988 9 FREEPOST SUBSCRIPTION COUPON To: Freepost 25, Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097, Australia. 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Subscription to commence in ............................................................. •.... •· ·· GIFT 1 to: NAME (Mr/Mrs/Ms).................................................................................... Issue Highlights STREET ...................................................................................................... . December 1987: 1 00W Power SUBURB/TOWN.......................................................... POSTCODE ............ . Subscription cost: 1 year (12 issues) 2 years (24 issues) Within Australia D $42 D $84 Overseas surface mail D $62 D $124 Overseas air mail D $12 0 D $240 Enclosed is my cheque or money order for$ ........... or please debit my D Bankcard D Visa Card No ...................................................................................................... . Signature .................... .. ................ ............ Card expiry date ...... ./ ...... ./ ...... . 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March 1988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator; Endless-Loop Tape Player. April 1988: Walkaround Throttle for Model Railroads ; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF and UHF Bands. Price: $5 .00 each (incl. p&p). Fill out the coupon on page 83 (or a photostat copy or letter) and send it to : Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097 . Card No ........................................ ..... ... ..................................... ................. . Signature ......................... .. .............. .. ... .... Card expiry date ....... /....... /...... . Subscription to commence in ........................................................ ... ......... .. Note: photocopy this coupon if you don't wish to cut the magazine, or include the relevant details in a letter. 10 SILICON CHIP LIMITED NUMBERS OF BACK ISSUES ARE AVAILABLE SO DON'T DELAY Typical unrestored treasure; incomplete, doesn't go, but soon will. are other ways of getting into vintage radio sets. Old radios can be found in peoples' homes, sheds and garages; . in farmers' barns and cow sheds: as well as a few other less likely places such as factories and offices. In many instances their owners are quite happy to give them to anyone who can put them to good use. The fact that the radio will be restored and placed in a collection is very pleasing to many owners, particularly those who have some sentimental attachment to the set. Therefore, the first priority when collecting is to tell others of your interest, being careful not to bore them with too many details. I have made a point of telling just about everyone I know or come into contact with that 1 collect old radios and most of these people keep me in mind. often get a phone call about a radio that is collecting dust in somebody's shed and, in many instances, it is only a matter of picking it up and it's mine. A couple of months ago I had a phone call from an old acquaintance who I have only seen once in r A Radiola console model from 1940; these larger radios usually have a very mellow tone. the last 20 years. During that meeting I found out that he had become interested in amateur radio and he learned that I was dabbling around in vintage radio. The phone call was to tell me that he had found a heap of old radios if I was interested in collecting them. To cut a long story and a 300-kilometre trip short, I ended up with a whole car full of radios, including an oscilloscope and a radio frequency generator for a mere $180. So there is just one example of how it pays to advertise amongst those whom you know. Most radio collectors, unless they are particularly rich, will have to be content with collecting whatever they can find. It is all very nice to want a roomful of 1920s style radios in perfect condition, but they simply aren't available to collect. These sets were comparatively rare in the 1920s and very few have survived the ravages of time. I find it more realistic to collect more recently made receivers and I'm particularly fond of those pleasant sounding console and large table models. The majority of these radios have timber cabinets which makes such sets a triple bonus. They have good sound, good looks and are a pleasure to own. Summing up, if you haven't started collecting and wish to do so, then now is the time start - before it's too late. Spare parts My approach to collecting valve radios is to buy just about anything I can lay my hands on. I restore what is restorable and wreck for spare parts what is not. My score at the moment is two dozen restored sets with about the same number in the garage waiting their turn. I also have a good supply of bits and pieces including a quantity of valves. Collecting old radios, or anything else for that matter, is really good fun. There is nothing quite like the feeling of getting onto a nice "new" treasure. However, collecting radios is only half the fun. The other half is the repairing and restoring process. Next month we get stuck into the finer points of restoring these-ancient and often defunct radio receivers. ~ MAY 1988 11 THE WAY I SEE IT By NEVILLE WILLIAMS Is UHF TV really as good as it's cracked up to be? Having in mind the heat that was generated when plans were first announced to re-deploy Australian TV services into the UHF band, the actual implementation appears to be progressing almost routinely. Are the problems less serious than some anticipated or is it that we have yet to come to grips with reality? Like many other Sydney viewers, I went through the exercise, some time ago, of reorganising my reception of SBS from VHF channel O to UHF channel 28. Perhaps because of a latent streak of "she'll be right, mate", the procedure proved to be a rather messy example of: "do as I say, not as I do"! But more about that later. I'm prompted to discuss the subject here by reason of a short letter from one of our readers, which reads as follows: Dear Neville, I have been told that UHF reception is potentially better than VHF reception although, on virtually every occasion I have seen SBS on channel 28, it has been nowhere near as good as the best reception I have come to expect on VHF. Could you throw more light on this whole question? Is UHF supposed to be as good as VHF and if not, why not? R.D. (Box Hill, Vic.) When publisher Leo Simpson rang to tell me that a copy of the letter was on the way to me, what began as a brief conversation developed into a full-scale review of the events that led to the present 12 SILICON CHIP situation and the implications for SILICON CHIP readers over the next couple of years. So R.D's request to "throw more light" on the subject is timely. I'll therefore set about describing how, when, where and why! In the mid '50s, the guidelines adopted for Australian TV broadcasting seemed enterprising enough for our particular situation. Australia would use the new 625-line CCIR System-B video standard - the first country to do so and would set aside ten clear channels in the VHF spectrum (30-300MHz). They would hopefully accommodate three stations in the capital cities and two stations in strategic provincial centres across the nation. VHF technology was proven and predictable, and the equipment clearly within the capacity of local industry to adapt, make, install and service. What was not forseen was the enormous penetration rate, unique by world standards, which peaked at 430,000 new TV receivers in 1959/60. In its wake came public and commercial pressure for additional TV services resulting, in 1961, in a decision based on the industry-inspired Huxley Committee Report, to increase the number of VHF channels from 10 to 13. The proposal involved shuffling those not already occupied by major stations (see list) and re-locating TV channels 3, 4 and 5 within the commonly recognised international FM band (88-108MHz). Who needed FM broadcasting? The move had widespread support at the time, because loss of the FM band - then sparsely used in Australia - seemed a modest price to pay to perpetuate the technical convenience of an all-VHF TV system. Moreover, AM radio was itself in total eclipse and AM station operators were not about to mourn the setting aside of a potentially competitive system! By way of concession, it was agreed that if and when an FM radio service was required, it could be technically up-graded (to advantage) and accommodated in the sparsely populated UHF spectrum (300-3000MHz). Besides (sotto voce) it would be rather nice, in that event, if Australian receiver manufacturers had the Australian FM market to themselves by reason of unique frequency and system standards! But like the modern-day "greenies", a small pro-FM lobby was vocal and tenacious in canvassing the merits of stereo FM broadcasting, and in getting across the point that Australian broadcasters and listeners alike would be severely disadvantaged if we sought to establish an FM service out of step with the rest of the world. My views at the time were summarised in the April 1962 issue of "Radio TV & Hobbies", in a trenchant criticism of the ABCB (Australian Broadcasting Control Board) and the "smokescreen" being created by the TV industry to cloud the issue. And cloud it they did. with all but a few supreme optimists reluctantly resigned to Huxley's fait accompli. But in 1974, following the recommendations of an inquiry chaired by Sir Francis McLean, the Federal Government reversed the 1961 decision, authorising restoration of the FM band and progressive redeployment of the TV service into the UHF spectrum. So in September 1974, a surprised and delighted Music Broadcasting Society was invited to apply for licences and within a few months, was on the air with 2MBS in Sydney and 3MBS in Melbourne. A new era had begun. There is room for speculation as to why the Whitlam Government appeared so partial to VHF FM but technical evidence and revisionist policy apart, it certainly complemented the earlier decision (1972) to reduce artificial protection of the local electronics industry. Tariffs had gone and now so had the notion of uniquely Australian FM receivers. As it turned out, the market was soon flooded with imported AM/FM tuners and receivers and largely as a result, FM broadcasting has since emerged as a major competitor for AM. A dual VHF /UHF TV system A provision in the 197 4 decision was that receivers for colour television, which was scheduled to begin in the following year, should include facilities for UHF reception. This requirement later became applicable to VCRs too. At the time, it looked almost like a "sticking plaster" clause but so far normal re-equipment with colour receivers and VCRs seems largely to have kept pace with the installation of UHF transmitters and translators. Theoretically, most viewers are now in a position lo take advantage of UHF TV transmissions if and AUSTRALIAN TELEVISION CHANNELS ORIGINAL PLAN 13-CHANNEL PLAN (1961) Channel Number Frequency (MHz) Channel Number 1 5 49-56 63-70 85-92 132-139 139-146 6 7 8 9 10 174-181 181-188 188-195 195-202 209-216 1 2 3 4 5 5A 6 7 8 9 10 11 2 3 4 o Frequency (MHz) 45-52 (a) 56-63 63-70 85-92 (b) 94-101 (b) 101-108 (b) 137-144 (c) 17 4-181 181-188 188-195 195-202 208-215 215-222 NOTES: (a) Mainly used for translators and RF input to TV receivers from VCRs, &c. Long-term use for major transmitters under review but doubtful. (b) To be ultimately cleared nationwide to make room for VHF FM sound broadcasting. (c) Used mainly for translators. Continued use for major transmitters still under consideration. when they have to but, as we shall see later, there is more to it than simply pushing a different button. In case you aren't familiar with the basic figures, Australian TV transmissions each occupy a nominal bandwidth of 7MHz, as compared with about 200kHz for an FM-stereo sound transmission. For this reason, TV channels can only be accommodated in the very-high and ultra-high frequency bands (VHF and UHF) or at still higher frequencies, as for satellite technology. Having in mind the number of services that have to be accommodated nowadays, the amount of spectrum space which can be conveniently allocated for TV channels is severely restricted in the VHF sector and by no means unlimited even at UHF. Hence the hassle. Well then, what are the advantages and limitations of the VHF and UHF bands and how do they affect ordinary viewers? Pros and cons of VHF TV VHF TV signals are best received with actual or near line-of-sight conditions involving a tall. wellsited lrnnsmitting tower and (ideal- ly) an elevated outdoor rece1vmg antenna with a clear path towards the transmitter. In practice though, VHF TV signals are subject to a fair amount of refraction and reflection, which often allows them to be received at a "watchable" level over a considerable distance (100km or more), or in the lee of rolling hills, or in other ostensibly "shadowed" situations. While this is a bonus for viewers in problem areas, reception can still be compromised by the fact that the low-end channels in particular (0, 1 & 2) are vulnerable to interference from car ignition systems and electrical appliances, and from arcing across dusty highvoltage insulators. Thunderstorms also cause considerable interference. The weaker the signal, the more noticeable the effect on the picture. Again. the same low-end VHF transmissions are sensitive to transitory atmospheric disturbances (eg, sporadic-E ionisation and meteor showers) which can produce "anomalous" propagation, with the signal being received hunMA Y 1988 13 A good antenna is essential for noise-free UHF reception. Shown above are the TC-10 and TC-18 UHF antennas from Hills Industries. dreds of kilometres away, perhaps in areas where another station is operating on the same channel. The resulting risk of mutual interference limits the number of geographically isolated stations which can share the low-end channels, in particular. At the receiving end Within the normal service area, a VHF receiving antenna can usually be a fairly simple configuration with 7 or 8 elements, connected to the set via 70-ohm coax or 300-ohm ribbon. Not highly directional, such antennas do not need to be lined up on the station with pinpoint accuracy. But, equally, they provide only limited discrimination against "ghosting", caused by reflections from prominences or large buildings on either side of the transmission path or from beyond the receiving site. By reason of the long elements (up to three metres or so) bird and wind damage can be a problem, as evidenced the the recent fate of a neighbour's VHF antenna. Prominently placed to "see over" my own home, it is hardly a thing of beauty but it must have proved attractive to a passing flight of galahs, which chose to settle one by one, on the reflector element. Under their combined weight, I watched the rod sag and finally break, spilling birds in all directions! The interesting thing is that this very antenna is still in use, along 14 SILICON CHIP with any number of other aged and bedraggled antennas in the area, all presumably still pulling in pictures. Indeed, many viewers in the capital cities may well be wondering what the fuss is all about. They have a reasonable choice of programs and with a little effort, galahs notwithstanding, most of them receive reasonable pictures. Even the lazy ones seem to manage in most suburbs, so why do we need a new system? (You could argue about what constitutes a reasonable picture but that is a story for another day). The reality is that there are simply not enough VHF channel options to cater adequately for problem urban areas, such as the coastal fringe of Sydney, let alone provincial centres and smaller pockets of population. Whether 10 channels or 13, substantial re-deployment into UHF is a necessity, not an option. (See the Publisher's Letter, January issue). How does UHF compare? In Australia, in the UHF band, there is space for many more channels (currently 39) than on VHF (probably about 10). As well, UHF signals are not prone to random or anomalous propagation, so that frequencies can be used over and over again across the continent. with little risk of co-channel interference. The fact that the frequencies are higher and the wavelengths smaller makes it easier to design transmitting antennas with well-defined directional characteristics and a higher effective gain or ERP (effective radiated power) towards the service area. It all adds up to the possibility ot many more TV transmitters than would be possible on the VHF channels, including a multiplicity of lowpower community stations and very low power translators. The higher ERP is also a potential bonus, with SBS channel 28 in Sydney, for example, radiating an effective 300kW, compared with lO0kW from ABN-2 on the same tower. This means stronger signals in the service area although signals elsewhere may be weaker, because there is less tendency for UHF to be refracted around or over hills or other obstructions There is a plus factor in that UHF signals are substantially immune to interference from power lines, mains appliances and automotive ignition. In very strong signal areas, viewers sometimes report use able UHF signals from existing VHF antennas - more commonly from Yagi than log-periodic types. There is probably an element of luck in such cases and it is almost certain that they would get much better signals from one of the combined VHF/UHF antennas that are now on the market. Viewers who enjoy consistently satisfying UHF reception via an indoor antenna should count themselves even more fortunate, in that UHF signals are very vulnerable to absorption or deflection by metal beams, wiring, metal furniture, blinds and even people moving around the room. Luck aside, the logical starting point for good UHF TV reception is an adequate UHF antenna, designed for the relevant band(s) or channel(s), mounted as high as practicable on an outdoor fixture or mast and orientated as accurately as possible towards the distant transmitter(s). The present UHF band/channel frequencies. by the way, are as shown below. Band 4: Channels 28-35; 526582MHz. Band 5: Channels 39-69, 603-820MHz. If combined VHF/UHF reception is required, as in Sydney, the options are a new VHF/UHF array or a separate UHF antenna. Because of the high frequency and small wavelengths, UHF antennas use quite short elements and are much less unsightly, cumbersome or damage-prone than their VHF counterparts. At the same time, they are highly directional and this provides greater discrimination against "ghost" images. (It also requires the antenna to be pointed accurately towards the transmitter). Typical UHF antennas currently available are the 10-element (TC-10) and 18-element (TC-18) Yagi types from Hills Industries. Separate versions are available for Band 4 and Band 5 reception, with the gain, front-back ratio and directivity of the TC-18 being superior in each case. For further comment and details of an alternative homebuilt high-performance "bow-tie" Band 4/5 antenna, see SILICON CHIP for January 1988. Coaxial cable, diplexers, &c If . the antenna needs to be carefully installed, so must be the · signal feed to the TV set. An unduly long downlead is a no-no; 300-ohm ribbon is out; nondescript coaxial cable is out. unless you are sure that it is of 70-75 ohms impedance and equal to the task; so also are nondescript baluns, splitters and diplexers left over from the VHF era. By way of interest, a spec. sheet for once-popular general purpose coaxial cables indicates imped;mce figures from 45 to 75 ohms. Of the 70-ohm types rated for operation at 600MHz, the attenuation figures, converted to metric, range from 17dB/100m. to just over 40dB/100m. If correctly identified and in good condition electrically, the first should still be OK for UHF TV: the second, hopeless! The attenuation of modern general-pupose VHF/UHF cable ranges from about 19-25dB/100m at 600MHz. equivalent to 2-3dB for a domes tic down-lead of around 10m. For longer runs. or where losses are critical. the more expensive semi air-spaced cables can reduce attenuation by 2:1 or more. In typical installations, the need may arise for the occasional balun, combiner, splitter, diplexer or outlet and again, it is essential to ensure that the unit chosen is suitable for UHF signals. Possible receiver problems It would be nice to be able to say that, with the antenna system spic and span, the remainder would be automatic. Not quite! Some older receivers rely on manual tuning for UHF coverage. You click the normal VHF turret tuner around to a "U" or "UHF" position, then carefully rotate an ordinary tuning knob until the wanted signal appears - hopefully somewhere near the appropriate number on the dial scale. Turn too far one way and the picture dissolves into streaks; too far the other way and the colour disappears first , followed by the picture and finally by the sound. With a light touch and a little practice you should be able to get it right, making sure not to overlook the AFC (automatic frequency control]. Don't forget the old adage: when all else fails, read the instruction book! If only one UHF station is involved, it should normally be possible to leave the UHF tuning preset and simply switch to "U", as necessary. If there is more than one, you'll probably start saving up for a receiver with a pushbutton tuner - or you'll begin using your VCR as the tuner. (See our article entitled "UHF Shenanigans With a VCR" in the December 1987 issue). Whether in the VCR or TV set, pushbutton tuners avoid most of the hassles. In general, the setting-up procedure is exactly as for a VHF station, except that the little bandset slider has to be set to "U' ·. Again, don't forget the instruction book! Whether the tuner is manual. preset or automatic. the ultimate quality of the picture in terms of noise content is going to depend on the intrinsic signal/noise ratio of its front-end circuitry . The SIN ra tio may be much the same as for VHF. in which case your efforts with the UHF antenna could reward you with an even better picture . But don ·t be surprised if the UHF tuner Problems? ... and you don't have our 112 page catalogue ... you've got real problems! ARISTA ... your one-stop problem solver. Audio leads ... Batteries ... Chargers ... Battery holders ... Cables ... Car accessories ... CD accessories ... Converters ... "Cutec" ... Earphones .. . Fuses ... Headphones .. . Intercoms ... Knobs .. . Microphones and accessories ... Mixers .. . Multimeters ... Plugs/Sockets, etc ... Plug adaptors ... Power packs and leads ... PA ... Disc and Tape care ... Security equipment ... Signal modifiers ... Solderless terminals ... Storage boxes ... Switches ... 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The CPF.provides protection from dangerous electrical spikes that can cause anything from obvious damage (like immediate equipment failure) to less obvious harm that can drastically shorten a system·s life . C PFs superior circuitry design and semi conductor technology responds ~:~~-~t~t:!~~~~~~a~~f~a:!t~g free operation. Additionally. CPFs1iltering capabttity helps eliminate troublesome and annoying interlerence, general hash cre_ated by small motors, fluorescent lamps, and lhe like that threaten the performance and shorten equipment life of unprotected electronic components. SPECIFICATIONS , Elect rical rating : 220-260 volts (AC) SOHz 10 Amp Spike/RF! Protection : 4 ,500 amps for 20m/second pulses. Maximum clamping voltage : 27SV differential mode. Cat.X10088 $69.95 • • • • " NO BRAND" DISKS !! Now you can buy absolute top quality disks that are also the cheapest ir: Australia ! They even come with a 5 year gua rantee! So why pay 2-3 times the price !o r the same quality? 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Ac:c:essories: RCA to RCA aucio lead RCA to BNC video lead Size: 70(W) x 85(0) x 28(H)mm W eight: 170 gram s SPECIAL, ONLY $129 P 10964 3 PIN LINE FEMALE HIGH INTENSITY RED LED BAR GRAPH ~~e~:;~:~?t\~~~~~7;;,v capacitance meter and transistor tester. use $4.50 ········· ······ ······· $3.90 C METEX M-3650 MULTIMETER WELLER WTCPN SOLDERING STATION $7.95 NORTHCOTE . 42S High St Phone (03) 489 8866 $8·00°' $26 CAR ANTENNA BOOSTER • In-line mstalat1on • 12V boosts 1000,o Cal A 12073 CLAYTON : 56 Renver Rd Phone (03) 543 7877 SOUTH AUSTRALIA · Electromc Discounters P l . 305 Morphett St. ADELAIDE (A LL PRICES PER 10 DISKS) $27 '-- Rod Irving Electronics DOUBLE SIOED/OOUBLE DENSITY 10· 01SKS 100'- DISKS 1.000 ... DISKS $8·50°' ~ MELBOURNE : 48 A ·eeckett St Phone (03) 663 6151 5¼" " NO BRAND" DISKS $9·00.. UTILITY BOXES Plastic boxes with aluminium tops. and available in four sizes Very popular for projects and very ecconomical! H t 0 101 150x90x50mm $ 3.25 Ht01021 95x 113x60mm $ 4.50 H1 01 03 130x68x41mm $ 2.75 H 10105 83x54x28mm $ 1.95 H 10110 120x65x38mm $ 2.95 H10 112 120x65x38mm $ 2.95 fMetal tool __,.. GOLD INSERT LOW PROFI L E IC SOCKETS $8.95 CPF CONTI NUOUS POWER FILTER SPIKE ARRESTOR ENCLOSED PRINTER STAND SPE CI FI CATIONS: each $10.95 $5.95 Y16009 • Austrahan plug to U S socket 10A STEP DOWN CONVERTER DC-DC Input Voltage: 24V DC Outp ut Voltage: 13•8V DC X 15668 : 0 6 9 Plug to 0825 Socket X15669 : 0 6 9 Socket to 0 8 25 Plug U.S. TO AU STRALIAN TELEPHONE ADAPTOR $99 .95 black. NEW ' The ideal sOluuon ! Features gold plated pins . $29.95 ra ted (S·SA m ax ) Size : 125(W) x SO(H ) x 90(0 Jmm Weig ht : 450 grams ~tJc3t~o f5~s"S~Y ~~n7~~;~~ matt 9 PIN TO 25 PIN CONNECTOR ADAPTORS • For recording or amplification • 3·5mm plug with 1 melre cord • Peel-off slick-on adhesive back SPECIFICATI ONS , Input Voltage : 24V DC O utput Voltage : 13-SV DC Primary Current : 4 2A (24V input 4 A output) Output Cu rrent : 4 Amp cont1m.,ous A16 155 5r> ~~ ~ NE"" 1 ~ This spectacular, rugged and compact OMM has a bright yellow : irr~~~~g~ ' =~~~t~\gJ~~~)~es diode and transistor test. continuity (with buzzer), capacitance meter, up to 20 amp current measurement and comprehensive AC/OC voltage. current and resistance ranges. CHEC K THESE FEATURES .... • Push-bunon ON/OFF switch . • Audible continuity test • Single function , 30 posi1ion easy to use rotary switch for FUNCTIO N and RANG E selection. • Transistor test • Diode test • Quality probes • 11.2" High contrast LCD • Full overload protection • 20Amp • Built in tilling bail • Capacitance meter • Instruction manual 091550 .. . . Normally $165 Special, only $,149 MAIL O RDER H OTLINE 0 08 335757 fTOLL FREE J /STRICTLY ORDI RS ONL YJ LOCAL O RDERS &IN Q U IRIES f03J 54 3 7877 POSTAG E RATES : S1 S9.99 S24.99 $49.99 S2.00 S3 .00 S4 .00 S5.00 S10 S25 S50 S99.99 S100 $199 S7.50 $200 S499 S500 plus S10.00 S12.50 T he above postage rates are for basic postage only. Road Fre1ghl. bulky and fragile items wlll be charged at different rates . All sales tax exempt orders and wholesale inqumes to : RITRONICS WHOL ESALE. 56 Renver Rd. Clayton . Ph . (03) 543 2166 (3 lines) Errors and om1ss1ons e)(cepl ed PrrcPS ;m<f <:,pec1llcat1ons SUbjC!Cl !O ·t>ange :~:~~~!;., ~ '. ;r·~.;~_1;•~~:;:~7,~;;~:\ f.1.1 hlr,•· ·[).,p, •;;~, ' Aopit·,·,irf'<)''i'•>rf>ntr. ► h•m.ir ► rNJ•-,t,•r •· 1 'r.tdrn,1r~·- t lht·, rf'',j3P<. ' •vt' l N fh'r" ■ESZ THE WAY I SEE IT - CTD is down a bit, in which case, you will need all the signal you can get to preserve the status qua! Do as I say - not as I do! Now comes the moment for confession! Some years ago, in an effort to improve reception of SBS channel 0, I installed a Hills log periodic antenna designed to cover VHF TV channels 0-11, as well as the FM band. Since it provided ample signal from the TV stations, it seemed like a good idea to insert a home-made resistive splitter in the cable - within easy reach of the man-hole - to feed the FM tuner as well. Rather than cut the original cable, I hauled it back and left the surplus lying loosely in the ceiling space, running an extra odd length of coax from the splitter to the TV set and a few metres of 300-ohm ribbon to the FM tuner. Don't laugh, it worked fine , apart from occasional (and fully expected) interference to channel O from the nearby high voltage mains. Some time later, facing the need to convert to channel 28, I mounted a TC-10 UHF Yagi on the existing VHF antenna support, pointing in the general direction of channel 28. Signals from the two antennas were brought down by short lengths of coax to a VHF/UHF combiner. tucked up under the eaves, and thence on to the receivers via the original length of ea ble in the ceiling . VHF and FM reception appeared to be totally unaffected hy the change - good, clear, virtually noise-free pictures from all channels. As for channel 28, John Logie Baird would have been enraptured with it back in 1930 but by present standards, it was appalling: a wobbly, tinted image seen through an overlay of dancing dots! So I climbed into the ceiling and re-arranged the 300-ohm ribbon into a separate folded dipole to suit the FM band and suspended in the rafters, broadside on to the general direction of the incoming FM signals. The splitter was removed and the cables to the TV receiver connected end-to-end and taped over. The UHF signal was certainly much better now but by no means noise-free. So, on the next cool day, I climbed back up into the ceiling and by dint of much wriggling and grunting, removed the extra piece of odd cable and re-routed the original single length so that it ran directly across the ceiling, down the wall behind some curtains to the VCR and TV set - with a couple of metres to spare. This time around, the UHF signal had edged up into the virtually noise-free category - provided it was fed first to the VCR. acting either as a preamplifier or tuner. Clearly, its signal/noise ratio was better on UHF than that of the TV set. With hindsight, even though my location is average/good for UHF, I would probably have been wiser to spend the extra few dollars on a TC-18 Yagi and benefit by the extra 3dB of forward gain. Of course, I guess I could get really industrious and build Bob Flynn's four-bay bow-tie effort in the January issue! Or I could over-compensate by following the lead of one viewer I heard about, who lives below the If your TV set doesn't have a UHF tuner and you don't have a VCR, this UHF-to-VHF converter can be used instead. This unit is available from Tandy Electronics. escarpment separating SBS channel 28 from one of Sydney's beachside suburbs. He's installed a high-gain UHF antenna followed up by a masthead preamplifier. Despite that escarpment, his dilemma now is that his VHF reception looks crummy against channel 28 ! Ahead: facing up to reality As indicated earlier, the DTC is currently proceeding with the introduction of UHF TV. In some cases, as in Sydney, there is little immediate alternative to using it to supplement the existing VHF service which occupies "non-problem" channels. In other areas, involving the FM band or otherwise inconvenient channels, it may make more sense to opt for an all-UHF service, providing for extra channels and strategically placed, shared UHF transmitting antennas. In the short term it may be more traumatic but it should obviate the need for multiple receiving antennas. This latter course represents the hard core "reality", referred to earlier, with which the industry and viewers will have to cope. At the top of the list for full-scale VHF/UHF conversion is the 11lawarra area - the coastal strip south of Sydney, generously dotted with picturesque hills, mountains and escarpments. The Newcastle area, north of Sydney, will follow in 1990. If all goes to plan, VHF TV transmissions in the Illawarra region will cease on January 1, 1989 and apart from those who are able to snag signals from the Sydney VHF channels, south coast viewers will be entirely dependent on UHF TV. How reception will compare across the total community remain~ to be seen. I'd be surprised if there weren't plenty of complaints over the first few months. But will things go to plan? Will all the UHF transmitters be up and working in time, providing the planned coverage? Will the majority of viewers be ready for them? Will the VHF transmitters actually be switched off on January 1? Nobody's quite sure or, if they are, they aren't saying. But don't count on it. ~ MAY 1988 17 eck out engine RPM on yo~r . odel airplane wiJh .tltis-easy7 .. uiJd:opticaJ tachometer. . ti can also use it to measure··.· -spQed of fans and'. rotating·-· 0 . 4 ' fts> · By JOHN CLARKE & GREG SWAIN -; PARTS LIST 1 PCB, code SC4-1-688, 85 x 56mm 1 plastic utility case, 130 x 68 x 41mm 1 Scotchcal front panel, 126 x 63mm 1 meter scale, 52 x 43mm 1 MU45 50µA meter 3 SPOT toggle switches 1 LED bezel 1 9V battery clip Semiconductors 1 4093 quad Schmitt NANO gate 1 4013 dual-D flipflop 1 555 timer 1 7805 3-terminal regulator 1 2N5485 N-channel FET 2 BC549 NPN transistors 1 BC327 PNP transistor 3 1N4148, 1N914 diodes 1 LD271, CQY89A IR diode 1 BPW50, BP104 IR photodiode 1 5mm red LED Capacitors 2 1 OOµF 16VW PC electrolytic 1 4 7 µ,F 16VW PC electrolytic 1 22µF 16VW PC electrolytic 1 1Oµ,F 16VW PC electrolytic 18 SILICON CHIP ·. ! 2 0 .1µ,F metallised polyester 1 0 .022µ,F metallised polyester 1 0.001 µ,F metallised polyester 1 680pF ceramic Resistors 2 x 470kn, 1 x 100kn, 2 x 68kn, 1 x 4 ?kn, 1 x 22k0, 1 x 1 Okn, 1 x 6.8kn, 1 x 3 .3k0, 1 x 1kO, 1 X 3300, 2 X 1000, 1 X 330, 1 x 200kn miniature vertical trimpot, 1 x 20kn miniature vertical trimpot Miscellaneous Rainbow cable, twin shielded cable, standoffs for meter terminals (only if required , see text). It's easy to measure the speed of rotating objects with this project. There are no wires to connect, since the circuit counts pulses of reflected infrared light. You just point the tacho at the propeller or whatever and check the reading in RPM directly on the meter scale. Actually, the idea for this project started when a colleague became interested in flying model aircraft and sought our help after several in-flight engine failures. Model aircraft engines require careful adjustment, particularly when new, if they are to run reliably. An optical 100k +5.6V 10 + 16VWI 100 + 16VWJ ""er~\o, ~ 3 BP104 CK IC3b 68DpF +0.51V .,- .,. 470k .,. .,. .,. .,. 1k +1 DETECT LE02 DIVIDE S2 '/>. +5.6V +2 A .,. POWER ~-------+5.6V 22 16VWI -: D1 1N4148 10k 47 + 68 16VW+ k 03 1N4148 0-20000RPM 0·2000RPM VR1 200k RANGE S3 3.3k 0.1 ,,, 100 16VW~ .001.:r .,. OPTICAL TACHOMETER SC4-1-688 ~ IN OUT GNO SENSITIVE ARE~ .qK Al I ll: K A BPW50 BP~04 + G<at>D B EOc VIEWED FROM BELOW Fig.1: the circuit uses 555 timer IC1 and Ql to provide a pulsed (20kHz) infrared signal. This signal is reflected by the rotating object, picked up by photodiode ID1, and processed to drive the meter movement. tachometer was required to monitor engine speed as carburettor and idling speed adjustments were made. Engine speed measurements are even more important for multiengined models. Here, the engines must be carefully adjusted so that they have the same speed regardless of throttle setting. Differences in engine speed of more than 100 RPM or so will make the model uncontrollable. Of course, our optical tachometer can do more than just measure the speed of model aircraft engines. You can use it to measure the speed of virtually any rotating machine, including multibladed fans and rotating shafts. Pulsed infrared When the instrument is turned on, an infrared LED (light emitting diode) at one end of the case emits a continuous stream of infrared pulses at 20kHz. The blades of the rotating propeller then reflect pulses of this infrared light back to a detector mounted adjacent to the LED. The pulses are then processed by the circuit and used to drive the meter movement. Why have we chosen to pulse the infrared beam at a 20kHz rate rather than simply use a continuous source? There are two reasons. First, it allows the circuit to function reliably under various lighting conditions, such as sunlight and fluorescent light. Second, the pulsing technique allows the infrared LED to be driven much harder to increase the light output. This, in turn, increases the useful operating range between the tachometer sensor and the rotating machine. The RPM readout is displayed on a meter with two ranges: 0-2500 RPM and 0-25,000 RPM. These ranges are selected using a toggle switch. A second toggle switch provides selectable divide-by-1 or divide-by-2 readings. The divide-by-2 switch setting is used when there are two light reflections per revolution; eg, when measuring a two-bladed propeller. If there are more than two reflections per rev, you simply divide the reading by the appropriate figure: eg, divide by 5 for a five-bladed fan. How it works Fig.1 shows the circuit details of our new optical tachometer. We'll start with the transmitter section which is based on ICl. Ql and LED 1 provide the 20kHz pulsed infrared signal. ICl is a 555 timer wired in astable or free running mode. Its output at pin 3 is high while the O.OOlµF capacitor on pins 6 and 2 is charging via the 68k0 and 3.3kn resistors, and low when the O.OOlµF capacitor is discharging via the 3.3k0 resistor. These timing components set the frequency of operation to about 20kHz, with the output (pin 3) being low for 2.3µs and high for 49.4µs. The output of ICl drives PNP transistor Ql via a 1000 base resistor. Each time the output of ICl switches low, transistor Ql switches on and drives the LED. Since the LED is driven for only about 4.6% of the time, it can be safely pulsed with currents of more than lOOmA. The infrared pulses reflected from the rotating object being MAY1988 19 K :~ 10 METER 11<at> 7~ ~LE02 A Fig.2: here's how to mount the parts on the printed circuit board. Twin core shielded cable must be used for the connections to the photodiode (ID1) but all other wiring connections can be run using rainbow cable. measured are picked up by photodiode IDl. This produces a 20kHz pulse train which has been interrupted by the rotating object. The voltage pulses produced across the 68k0 resistor are buffered by the FET source-follower QZ and then fed to the base of Q3 via a 680pF capacitor. Q3 and Q4 are a DC feedback + pair with 100% DC feedback from the emitter of Q4 to the base of Q3. Q3 is biased from the emitter of Q4 and the values of the resistors in the circuit are selected to give approximately 1/2Vcc [ie, half supply) at Q4's collector. AC current feedback is also applied from the emitter of Q4 to the base of Q3 and the gain is set by the ~ ,.f o::f" I~ ml ~'1 2'- Fig.3: this is the actual-size etching pattern for the PCB. 20 SILICON CHIP ratio of the 470k0 resistor to the output impedance of the source follower [QZ). So Q3 and Q4 together provide a gain of several hundred times. The amplified '20kHz pulse train on Q4's collector is now squared up by Schmitt trigger IC2a. Thus, whenever 2.3µs pulses are received by IDl, the output of IC2a goes low and discharges the 0.022µF capacitor at the input of IC2b via diode DZ. This, in turn, causes the output of Schmitt trigger IC2b to switch high and clock D-type flipflop IC3a. At the same time, the output of IC2b is inverted by IC2c to light the Detect LED. When no pulses are being received by IDl, the output of IC2a remains high and the 0.022µF capacitor charges to the positive rail via a 22k0 resistor. Because the RC time constant is about 0.5ms, the 20kHz signal is filtered out by this network. IC3a is part of a 4013 dual-D flipflop and divides the signal on its CK (pin 11) input by two. Its job is to provide a square wave with a duty cycle of exactly 50%, which is necessary for the following stage. The output frequency appears at the Q output [pin 13) and depends on the number of times the rotating object reflects the infrared light. The other half of the 4013, IC3b, is clocked by the Q-bar output of IC3a. It also divides by two and provides an output on pin 1 which is half the frequency on pin 13 of IC3a. Switch S2 selects between the output of IC3a and IC3b to give the divide-by-1 and divide-by-2 functions. From there, the signal is fed to a O. lµF capacitor which differentiates the square wave signal to give a series of negative-going voltage spikes. Diode D3 prevents the input to IC2d from going more than 0.6V above the positive supply rail. VRl , the 10kD resistor, and range switch S3 set the differentiator time constant. When the 0-2500 RPM range is selected, VRl sets the time constant so that broad negative-going pulses are produced at the input of IC2d. When the 0-25,000 RPM range is selected, the c. ..l... MU-45 CLASS-2.5 • • Fig.4: this artwork is used to replace the existing meter scale. As shown in this view, the bodies of the 0.1µ,F and 0.022µ,F capacitors lie flat against the PCB. Make sure that all polarised components are installed correctly. This view shows how the PCB mounts on the back of the meter. The pen points to the 0.1µ,F capacitor which is soldered to the back of the PCB for calibration of the high range (see text). 10k0 resistor is switched into circuit to give much narrower pulses. IC2d inverts these pulses which are then averaged by VR2 and a 100µ,F capacitor to drive the meter movement. Calibration adjustments are made by means of VRl and VR2. VRl provides calibration for the low (0-2500 RPM) range, while VR2 provides adjustment on the high (0-25,000 RPM) range. A 9V battery powers the circuit. This feeds a 7805 3-terminal regulator which has its GND ter- minal connected to earth via series diode D1. This "jacks up" the output of the regulator to give a nominal + 5.6V regulated supply for the circuit. Building it Most of the parts are accommodated on a small printed circuit board (PCB) coded SC4-1-688 and measuring 85 x 56mm. The board is mounted on the back of the meter and the whole assembly is housed in a plastic box measuring 130 x 68 x 41mm. We have produced a front panel artwork to suit the case, along with a suitable meter scale. Fig.2 shows the parts layout for the PCB. No particular procedure need be followed when installing the parts but take care with the orientation of polarised components. These include the electrolytic capacitors, diodes, regulator, transistors and ICs. The 0.1µ,F and 0.022µ,F capacitors must be mounted flat against the PCB as shown in the diagram, to provide sufficient clearance for the meter. Once assembly of the PCB has been completed, holes can be drilled in the front of the box for the infrared LED and photodiode. The hole for the photodiode should be filed to shape so that it is a tight fit. Secure the parts using an epoxy adhesive but be careful not to get any adhesive on the face (active area) of the photodiode, otherwise its sensitivity will be degraded. The front panel artwork can now be attached to the lid of the case and the holes drilled to accept the meter, switches and Detect LED. Mount the various items in position, then complete the wiring as shown in Fig.2. Rainbow cable can be used for the switch and LED wiring, but you must use twin-core shielded ea ble between the photodiode and the PCB. Once the wiring has been completed, the PCB can be mounted on the meter terminals (see photo) and secured with the meter screws. Be sure to install the two spring washers supplied with the meter between the screw heads and the PCB. These will bite into the copper pads to provide a good connection to the meter terminals. MAY 1988 21 We made up our strobe disc using a paper cutout attached to the back of a conventional turntable strobe. is because the cheap meters available these days will have a different zero setting depending on whether they're in vertical or horizontal orientation. The 0-25,000 RPM range is very easily calibrated using the light from an ordinary fluorescent lamp fitting. We simply take advantage of two facts: (1) a fluorescent lamp is extinguished at 100 times a second, and (2) it contains some infrared energy and therefore can be used with the infrared detector diode. To calibrate the unit, we first need to modify the circuit slightly to make the unit sensitive to the frequency of fluorescent lights. This involves shunting the 680pF capacitor at the source of Q2 with a 0. lJLF capacitor (ie, connect the two in parallel). You can do this by The low-range is calibrated by using a turntable set to 45 RPM and a strobe disc (see Fig.6). Adjust VR1 for a reading of 900 RPM (see text). If you want to be doubly sure, the washers can be soldered to the PCB pads. Depending on the meter supplied, it may also be necessary to add a couple of 6mm standoffs to the meter terminals to provide sufficient clearance for the PCB. We used a couple of LED bezels for this job and substituted longer meter screws. regulator (7805) is at about 5.6V. The voltages around Q3 and Q4 should also be checked to confirm that they correspond with those marked on the circuit diagram. Now check that the range switch is set to the 0-2500 RPM range. You should now be able to get a reading on the meter by moving your hand rapidly back and forth in front of the infrared LED. Testing High range calibration Now for the smoke test. Connect .up a 9V battery, switch on, and check that the output of the Before calibration, you must decide whether you want to use the unit vertically or horizontally. This lo 0 0 w ~ w ,- + 0 :aE 0 () 0 <t N + I- J: 0 ~ (.) z w w 0 <t () 0 0 ~ a. 0 0 IC ...J L.: :i cc 0 0 ,X 0 0 0 0 ,X ..:J Fig.5: here is an actual size reproduction of the front panel artwork. 22 SILICON CHIP The prototype meter was calibrated 0-20,000 RPM but was later modified for readings to 25,000 RPM. soldering the 0. lµF capacitor to the pads for the 680pF capacitor on the copper side of the board (see photo). Next, set switch S2 to the 7 1 position, S3 to xl000, and VRl to mid-position. VR2 can now be adjusted so that the meter reads exactly 6000 RPM in the presence of fluorescent light. (Remember to zero the meter first, in say the horizontal position, and then calibrate it in the horizontal position). You will find that this method of calibration works extremely well. You don't even have to be up close to the fluorescent light; as long as the photodiode is pointing towards the light, it can be a couple of metres away. Low range calibration The low range is calibrated using an ordinary phono turntable and a strobe disc (see Fig.3). First, remove the 0. lµF capacitor on the back of the PCB, set S3 to xlO0, and set the turntable speed to 45 RPM. The infrared LED and photodiode can now be positioned a few millimetres above the strobe disc, near the edge, and VRl adjusted for a meter reading of 900 RPM. Why 900 RPM? Because the turntable speed is 45 RPM and there Fig.6: this strobe pattern makes low-range calibration a cinch. Cut the pattern out carefully, place it on a turntable set to 45 RPM, and adjust trimpot VRl for a meter reading of 900 RPM. are 20 lines across the strobe disc (ie, 20 X 45 = 900). Note that the meter circuitry will have to be positioned outside the case during this adjustment procedure, so that the meter is oriented either vertically or horizontally. Do not lry lo calibrate the unit with the meter upside down as this greatly upsets the meter zero setting. Because the two calibration trimpots interact, you should now go back and repeat the calibration procedure for the high range. Having done that, check the low range again and repeat the calibration procedure once more if necessary. Using the optical tacho To check model aircraft engines, hold the unit close to the propeller blades and observe the Detect LED to confirm correct operation. If the LED is fully lit (and there is no reading on the meter), the sensor is continually receiving reflected light and so cannot respond to the rotating blades. When this happens, it's simply a matter of moving the unit away from the blades until the LED dims (indicating that the LED is flashing) and a steady reading is obtained. The range switch should be set to the correct RPM range and the 7 2 position selected for two-bladed propellers. For rotating shafts, the situation is a bit different since there are no blades to reflect the light. This problem is easily solved by attaching a reflective (or non-reflective) strip to the shaft so that there is some difference in reflectivity. This means that a non-reflective strip should be attached to a shiny shaft, while a reflective strip (eg, white paint) should be attached to a dull shaft. As before, the detect LED can be used to determine the correct position for the optical tacho. Just adjust the distance so that the LED switches on and off as the shaft rotates, depending on the position of the strip. ~ MAY1988 23 Jaycar No.1 f or Silicon Chip Kits 50 and 100w Amp Modules with Polyswitch Speaker Protection Modem End-of File Indicator Ref: SIiicon Chip February 1988 This simple proJect can be easily fitted lnmostmodems and sounds a buzzer at the end of file transmission. cat. KC-5024 Ref: SIiicon Chip December 1987 50WATT Cat. KC-5018 $32.95 Ref: SIiicon Chip NOV. jl7 Build one Into each phone so that a LED will then flash on every extension to Indicate wheneverthe line Is In use. cat. KC-5011 $12.95 $9.95 RDE115 thermistor to suit cat. RN-3415 $8.95 each $99.SOfor 100WATT cat. KC-5019 Off Hook Indicator for Telephones stereo1oow modules RDE245A termlstorto $38.95 ~~~~RN-3418$10.95ea sub carrier Adaptor for FM Tuners wlthfull speaker protection Ref: SIiicon Chip Jan 88 This simple adaptor circuit fits In your FM tuner and lets you tap Into hidden FM transmissions. cat. KC-5014 1CHz Digital Frequency Meter Ref: SIiicon Chip November /December 1987 This superb 1GHz Digital Frequency Meter will outperform any other Instrument In Its price range. Kit Is complete with laser cut silk screen front panel, anodised punched rear panel and all parts. cat. KC-5013 $22.95 $299 Dual Tracking Power supply Ref: SIiicon Chip January 1988 This one gives from ±1.2Vto ±18.Svolts <at>1.7ampsbetween ±3Vand ± 10V. Above 10Vthe available current reduces to 200 milliamos at ±18V. cat.KC-5022 Telephone Ringer $99.95 Ref: SIiicon Chip Jan jl8 Are you tired of the sound of your telephone bells? You can change to a modern sounding chime by building this simple module. cat. Kc-so1 s Protector car Alarm Ref: SIiicon Chip February 1988 This refined car burglar alarm has Just about every feature you could want and is easy to build. Cat. KC-5021 $19.95 car stereo in your Home Ref: SIiicon Chip November 1987 Adapt a surplus car radio/cassette player for use In your hOme. Cat. KC-5012 $28.95 $79.50 universal Speed controller Ref: SIiicon Chip December 1987 KIT 1 This multipurpose circuit can be used as a speed control for elect ric drills or fans, as a power controller for electrlc blankets or soldering irons, or as a table lamp dimmer. complete kit includes pre-assembled PC board, box and front panel, mains cable, plug and socket. Cat. KC-5016 ALL FOR $18.95 KIT 2 UNIVERSAL SPEED / LICHT / .___ _ _ _ _ _ _ _ _ __. HEAT CONTROLLER· SHORT FORM As used in the above kit. It is available separately If you wish to mount in a piece of equipment. cat.KJ-5522 $9.95 ~ ' .· . ,{-• .'.~ff" ~ ou Telephone Line crabber Ref: Silicon Chip March 1988 When you pick up the phone this simple circuit cuts the extension dead. stopping them from listening In or dialling out. Cat. KC-502 5 • $21 99 UHF Remote switch for your car Burglar Alarm Cat.KC-5026 $33.95 Ref: Silicon Chip Build this circuit and you can turn your car,:; burglar alarm on and off by pressing the button on a small keyring transmitter. Low Ohms Capacitance Adaptor for you.rDMM Tester for DMM Ref: Silicon Chip Feb '88 This low ohms tester plugs straight into the terminals of your digltal multimeter. and can accurately measure resistance values from 1k ohms down to 0.01 ohms. Cat. KC-5023 Ref: Silicon Chip November 1987 Plugs directly into your digltal multimeter. Plug the unknown capacitor into the test terminals and read the value in picofarads (pF) or microfarads (uF). Cat. KC-5010 $29.95 24V to 12V Converter for Trucks Ref: Silicon Chip December 1987 This 24Vto 12V converter can deliver upto 5 amps. Cat. KC-5017 Door Minder Ref: Silicon Chip February 1988 This project will sense a door opening in a large or small room and will sound a two-tone chime. Cat. KC-5020 $37.50 $59.00 - --- $27.95 TURN YOUR SURPLUS STOCK INTO CASH!! Slider pot pack Cat. RP-3903 NORMALLY $10.00 THIS MONTH $6.00 SAVE 40% Mixed pot (trimmer, rotary, slider} Pack Cat. RP-3902 NORMALLY $10.00 THIS MONTH $7.50 SAVE 25% Mixed Electrolytic Pack Cat. RE-6280 NORMALLY $10.00 THIS MONTH $8.00 SAVE 20% Jaycar will purchase your surplus stocks of components and equipment. We are continually on the lookout for sources of prime quallty merchandise. Perteet for use where long throw is needed. PA's and musical instrument use. Freq. Response 3.828kHz ±3dB, max input 25V rms (100 wan amp power}, no crossover required. See catalogue for size. Cat. CT-1910 CALL GARY JOHNSTON OR BRUCE ROUTLEY NOW ON (02) 747 2022 MOTOROLA KSN 1005A $19.95 Temperature Probe Adaptor for Digital Multimeters Universal Pre-Punched Experimenters Boards The low cost way to build prototypes or one-off projects/ We now stock 3 sizes of Phenolic board that has a matrix of punched holes on a 0.1 • (2.5mm) pitch with a 'donut ' of tin plated copper around each hole. Each donut is separated from Its neighbours by about a 0.5mm gap. This effectively isolates each pad but also makes It easy to brifge solder across to make interconnections. Each board also has lingers' on opposite ends. These can be used to connect to and from the board or to a card edge connector. Finally the non-solder side of the board has an alpha-numeric grid printed on it to assist in component identification board layout. 3 SIZES : SMALL 95 x 72mm, 25 x 30 holes (750) 3.6mm edge pitch This device simply plugs into the banana sockets of your digital multimeter. It will give an output of 1mV (millivolt} for every degree increase in temperature. This means that on, say, your 200mV DC range you can read the temperature on the multimeter directly. You can switch from °C to °F . A very high quality probe with semiconductor sensor in the tip. A generous curl cord connects the probe and adaptor housing. Requires 9V cell. SPECIFICATIONS: Linear Voltage Output : Meaurement Range: Accuracy: Sensor: Power: Current Consumption: Response Time: Battery Check: Dimension: Weight: Cat. QM-1590 1mVi"C or 1mV/°F -50°C to+ 150°C or -58°F to 302°F ±0.5°C or ±1°F Semiconductor type 006P 9V battery 2mA typical From 23°C to 99.9°C 30 sec in stirring water 'l.OBAT"LED lights automatically when battery is exhausted Probe: F5mm x L 160mm Adaptor: 38(W} x 70(L) x 39(H)mm Wire: 3.5 metres retractable cord 120 grams Multimeter not included Cat. HP-9550 $2.45 MEDIUM 140 x 95mm, 29 x 50 holes (1450) 2.5mm edge pitch Cat. HP-9552 $3.95 LARGE 210 x 78mm, 24 x 67 holes (1608) 3.6mm edge pitch Cat. HP-9554 $59.95 Twinax $4.50 $9.95 ea Twin Coax Chassis Socket ~t_\-if!Itit.I (as used on IBM and other computers) Twin Coax Male Plug (as used in IBM and other computers) cat. PP-0610 ~ :':. \ -~~~ $11s~95 eq _at4/6 10+$10.95ea ~ 10+$8.95 ea ~---------------' 3" DIRECT RADIATING TWEETER - ~ .,-· ·· 1988 CATALOGUF Looks like a normal 3" cone tweeter except it doesn't need a crossover. Ideal for Hi Fi systems in the home or car sound. See catalogue for dimensions. Cat. CT-1906 ..;;,- If you missed out on obtaining a copy of our NEW 132 page Engineering Catalogue :• Call into any of our stores - only $1.00 • Send $2 to PO Box 185 Concord 2137 and we will $9 .95 · -- KSN 1089A OU SAVE $22.55 OVER BUYING INDIVIDUAL PARTS! Jaycar Don't ever t>e short of that resistor again. Jaycar now has available 7 different packs of 1/4W 5% resistors available. Introduces the Each pack contai ns 10 of each value, and packs cover the complete range from 1 ohm to 10M ohms. Values (1 Oof each) 1, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7. 5.6,. 6.8, 8.2 ohms Total 120 Cat. RR-1690 $3.95 (10 of each) 10, 12, 15, t8, 22, 27, 33 , 39, 47, 56, 68, 82 ohms Total 120 Cat. RR-1691 $3.95 Easy Way t O Values Values (to of each) 100, t20, 150. 180,220,270, 330,390,470,560,680, 820 ohms Total 120 Cat. RR:1692 $3.95 Buy 1/4 watt Values (10 of each) 1k, 1.2, 1.5, 1.8, 2.'l, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2k Total 120 Cat. RR-1693 $3.95 Values (10of each) 10k, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68, 82k Total 120 Cat. RR-t694 $3.95 Resistors Values (10 of each) 100k, 120, t 50, 180,220,270,330,390,470, 560,680, 820k Total 120 Cat. RR-1695 $3.95 A GREAT WAY TO NEVER BE OUT OF THAT ODD RESISTOR AND SAVE A PACKET AT THE SAME TIME!! Values (tO of each) 1M, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2, 10M Total 130 Cat. RR-1696 $3.95 1 pack of each of the above. 7 packs in all giving a total ol 850 resistors 1Oo/ each value Cat RR-1697 VALUE AT $19.95 SAVE $7.70 over bu~ng individual packs 12" Guitar Speaker Finally available, our updated guitar speaker with extended frequency response. Especially suited for not only Bass guitar but Rythm and Lead as well. Resonant Freq. 60Hz (was 80Hz) Impedance 8 ohm Freq. Response 60 - 5,000Hz (was 80-4kHz) Power Handling 100 watts RMS Magnet Weight 40oz Net Weight 361 og (was 3520g) Sensitivity 102dB But the best news is the price - NO INCREASE Cat. CG-2380 $89.50 Mic Insert 1988 CATALOGUE -10 Great replacement electret mic inserts for tape recorders, etc. Handy for hobby projects. Includes data sheet and applications circuit. Operates from a single 1.5V battery. 10mm diameter. 50Hz 15kHz. Cat. AM,4010 ... . $ 1.95 ·' . If you missed out on obtaining a copy of our NEW 132 page Engineering Catalogue:• Call into any of our stores - only $1.00 • Send $2 to PO Box 185 Concord 2137 and we will post one to you fr ··•·· or more $1.65 each Low Cost Test Gear for1988 0000000000000 0000000000000 Audio Generator Jaycar is proud to announce a range of high quality direct import test equipment. This equipment was finally chosen because of its excellent value for money. This unit matches the QT-2312 RF generator in appearance. It too has a sturdy metal cabinet with carrying handle and large readout scale. The QT-2310 has the following faetures: • High frequency stability: within ±2Hz • Output voltage floating: within ±1dB • Sine wave signal output: more than BV rms • Equipped with synchronised input terminal of signals enabling high power output signals to be accurately controlled by small signals, SPECIFICATIONS SQUARE WAVE OUTPUT Frequency Range: Accuracy: Output Impedance: Output Control: 10Hz - 1MHz 5 decade bands ±3%+2Hz 600 ohms, unbalanced High, Low (-40dB) and fine adjuster SINE WAVE OUTPUT Range Output Voltage Output Distortion GORE HILL OPEN UNTIL4pm ON SATURDAYS AC Millivoltmeter av - SYNCHRONISATION 1 $239 I Dimensions: Weight: Accessories: Cat. QT-2310 . fu:vm ~ - ·.:••..I 150Mhz Universal Digital Frequency Counter Up to 8 digit resolution between 10Hz and 150MHz. It has many features amongst which is a memory hold switch which enables the counter t retain a measured frequency permanently on display until not needed. This is not a kit it is a fully built unit with a 3 month warranty. Can be upgraded to 500MHz by adding a $ l 99 • SO prescaler. Cat. QT-2330 Colour Bar Pattern Generator The QT-2325 is designed for repair or adjustment of Australian/New Zealand standard PAL system TV. The RF output covers Australia channel 3 and 4. This clever design uses a crystal controlled progressive scanning circuit and is portable. Power Requirerrents Dimensions Weight Cat. QT-2325 PAL-B.D.G.H.H.I.K. System, VHF 55Hz - 63MHz. continuously adjustable; with 55.25MHz preset 1OmVrms into 300 ohm load 300 ohm balanced X'tal, vertical 50.036Hz, horizontal 15.611 kHz 4.43361875MHz ±50Hz 1. Colour divided into upper and lower portions. Upper hall: Red, Bluish Green, Blue, GreenishYellow, White Lower hall; four Grey, Black 2. Dots 19(V) x 15(H) White 3. Crosshatch 19 x 15 square. White 4. Vertical lines.19 White 5. Horizontal lines 15 White 6. Rasters fixed 100% brightness White 240V AC 50Hz 55(H) x 150(W) x 200(D)mm 1.2kg $249 i ,, , Signal Generator This lully solid state product is capable of generating stable FR from 1OOkHz to 150MHz. It is designed as both a bench and portable instrument. It also features an internal 1kHz oscillator to modulate the RF carrier. External modulation to the RF output is provided as well. The QT-2132 is supplied in a sturdy metal cabinet, with carrying handle and large easy to read scaled readout panel. It is ideal for checking and aligning the front ends of AM, FM and TV sets. SPECIFICATIONS Frequency Range SPECIFICATIONS RF Output Level Impedance Synchronising Signals Sub-Carrier Frequency Patterns: . "~w- - "t,c-+ Jl • f RF Ranges ±3% of oscillator frequency per Vrms Approx 1OM ohm 10Vrms AC 1151230V, ±10%, 50/60Hz, 3VA 1SO(H) x 250(W) x 130(D)mm Approx 2.5kg Test lead 1, ground lead 1 Input Impedance: Maxmum Input: Power Requirement: The model QT-2320 is a sideband Millivolt Meter for measuring AC voltages from 0.3mV to 1OOV in 12 ranges with bandwidth of 5Hz to 1MHz. Each range shares 1O dB. The effective sensitivity at 0.3mV range Is 30uV. This voltmeter is equipped with three colour scales for easy visual distinction, namley Volt, dB and dBm. The millivoltmeter also has a FET input with 1OM ohm input impedance so circuit loading is negligible. Finally once again supplied in a sturdy metal case with carrying handle. Cat. QT-2320 1$225 20Hz - 20kHz 15V p-p max 0.5uS Range 10Hz - 1MHz rms, max Less than 0.05% 400Hz - 20kHz Less than 0.3% 20Hz - 200kHz Less than 0.05% 500Hz - 50kHz Less than 0.5% 50Hz - 500kHz ±1dB (1kHz) Output Flatness Range Output Voltage Rise Time A 1OOkHz - 300kHz B 300kHz - 1OOOkHz C 1MHz - 3.2MHz D 3.0MHz - 10MHz E 10MHz - 35MHz F 32MHz - 150MHz Up to 450MHz on 3rd harmonics Frequency Accuracy ±3% RF Output 1OOmV rms, approx (up to 35MHz) Output Control High-Low switch and fine adjuster Modulation INT. 1kHz (AM) 30% approx. EXT. SOHz - 20kHz, at less than 1V rms input Audio Output 1kHz, MIN.1V rms (fixed) Crystal Oscillator For 1 - 15M Hz crystal in type HC-6u holder (not included) Power Requirements AC 115/230V, 50/60Hz, approx 3VA Dimensions 150(H) x 250(W) x 130(0)mm Weight Approx. 2.5kg Cat. QT-2312 $l 9 9 NiCad CHARGER FM MINDER BUG Ref: AEM April 1988 Will fully charge then trickle charge - or trickle charge only. Will charge up to 10 cells at once. Incorporates own plug pack box. Cat. KM-3067 Ref: AEM March 1988 Low power FM transmitter that picks up sounds and transmits on FM. Cheap version of baby minder or pool minder, etc. Cat. KM-3068 $ $24.95 BABYMINDER TRAIN CONTROLLER Ref: ETI April 1988 Monitor your baby's room for crying. Will trigger a light or buzzer in another room. Kit includes box, PCB, and all components except 12V AC plugpack and dynamic mic. Mic is currently on special for $4.95 (Cat. AM-4095) Cat. KE-4732 Ref: Silicon Chip April 1988 Includes all the features of The Railmaster plus walkaround throttle. All components supplied less box and relay. Cat. KC-5028 $ 200WATT 3WAV $34.95 CROSSOVER • Crossover frequency 500, 3500Hz • 12dB attenuation • 200 watts RMS • 8 ohms Cat. CX-2621 $69.50 _ 89 00 Key Fob Transmitter and Acces~ories 12 volt key lob •ansmitter for use with LR8810 receivEl. Cat. LR-8814 $27.95 Remote Control Receiver Can be used to cootol solenoid door locks as well as no enty delay rurglar alarms. Cat. LR-8810 $54.95 12 Volt Door Lock Actuator {Master) A solenoid device desgned for altEl-market installations. Cat. LR-8816 $29.55 BENCH AMP/ SIGNAL TRACER Ref: EAApril 1988 Amplifier offers power output of 5 watts, signal tracer has high input impedance and a wide range of input sensitivities. Complete kit including box, speaker, PCB and all components . Plug pack not supplied. Cat. KA-1699 $39.95 ,, Similar to above but without microswitch Cat. LR-8817 $24.95 CD HEADPHONE AMPLIFIER Ref: Silicon Chip April 1988 Kit includes PCB, box, all components and hardware. Requires 12V AC plug pack Cat. MP-3020 $13 .95 Cat. KC-5029 As used in 1he Silicon Chip pH meter. This polypropylene bodied probe is a price breakthrough. The membrane protector is an integral part of the barrel. The OP-2230 has a 'speaf shaped membrane which allows easy and effective cleaning wnh a cotton bud. SPECIFICATIONS: pH range O - 14 Response 98% 20 sees Temp Cable $79.95 ~~~' • - ■rz:zs:...~ VISA P.,~,~:;i:.:,~ --, <>•¥ 0 mi:,.... -.. j '( <W SENSffdJ!fi 0 \'01.UM!: <at> Kit includes PCB, plastic case, meter and scale, front panel and all components. Probe is extra. Cat. KC-5027 $49.95 pH probe and solutions to suit Cat. QP-2230 $79.95 IDEAL FOR THE YOUNG SCIENTIST, RESEARCHERS ETC. HEAD OFFICE MAIL ORDERS 115 Parramatta Road Concord 2137 P.O. Box 185 Concord 2137 Telephone (02) 747 2022 Telex 72293 HOTLINE (02) 7471888 POST & PACKING 9 ~9 ~o FOR ORDERS ONLY $25 ~h g~ $49.99 s 4.50 $99.99 $ 6.50 10 00 ~F_A_cs_1_M_IL_E~(0_2~)_7_44_0_7_6_7_ _ _ _T_O_L_L_F_R_E_E_(~00_8_)0_2_2_88_8_ _0_vE_R_s1_00_ _ _ s _ . _ _ _~ $50 ___________________________________ ;~I ~ , .._MAIL ORDER VIA YOUR s lNPm , - - -- o - so• Coaxial 0.8 metre long unterminated Buffer solutions included. Cat. OP-2230 $24.95 • Plastic Bodied Low Cost pH Meter Probe . :. e.\.lB:(ffl)ij!{\$.,$),/:$'1'$1AJ!t< j BENCH AMP 12 Volt Door Lock Actuator (Slave) _ 11 95 ROAD FREIGHT ANYWHERE IN AUSTRALIA $13.50 SYDNEY· CITY 117YorkSt. (02)267 1614Mon-Fri 8.30 - 5.30 Thurs 8.30 pm• Sat 9 • 12 GORE HILL 188 Pacific Hivy cnr Bellevue Ave (02) 439 4799 Mon-Fri 9 • 5.30 Sat 9 - 4pm CARLINGFORD Cnr. Carlingford & Pennant Hills Rd (02) 872 4444 Mon,Fri 9 - 5.30 Thurs 8.30 pm - Sat 9 - 2pm BURANDA OLD 144 Lo9an Rd (07) 393 0777 • Mon-Fn 9 • 5.30 Thurs 8.30 • Sat 9 - 12 115 Parramatta Rd (02) 745 3077 Mon-Fri 8.30 - 5.30 • Sat 8.30 -12 MEL BOU RN E-CITY Shop 2. 45 A"Beckett St City (03) 663 2030 Mon-Fri 9- 5.30 Fri 8.30 • Sat 9 -12 121 Forest Rd (02) 570 7000 • Mon-Fri 9 - 5.30 Thurs 8.30 pm - Sat 9 -12 SPRINGY ALE VIC 887-889 Springvale Road Mulgrave (03) 5471022 Nr Cnr. Dandenong Road Mon-Fri 9 - 5.30 Fri 8.30 • Sat 9 - 12 ICONCORD ~ HURSTVILLE _. JAYCAR N0.1 FOR BARGAINS UHF TV TUNER 1 Sanyo Model T1087RA $29.95 1 Yet another fabulous scoop purchase. A compact high quality tuner that operates from 526-814MHz (corresponding to channels 28 thru 63). This tuner is designed for Australian standard reception (AS1053 1973), and is offered at a very low price. You can grab one now for the silly price of $29.951 This price includes circuit diagrams and connection drawing. You can have a photocopy of the complete manual for $4 but a lot of the info is in Japanesel This is a very cheap way to convert a VHF only TV to UHFI (Some skill may be required). Spees: Power +12V DC nominal <at>14mA. Case neg. Bandwidth 526-814MHz (28-63 eh). AFT +6.SV. Dimensions 150 x 65 x 28mm. Tuning multirotation of 1/4 " shaft. Knob not supplied. Cat. DM-1000 MIDRANGE AND TWEETER LEVEL CONTROL BARGAIN This unit is designed for midrange and tweeter controls on multiway speaker systems. It is sultable for systems up to 80 watts power handling capacity. It presents a constant 8 ohm impedance to the load, and so does not disturb the crossover points. Unit is fully sealed, mounting plates and is labelled high and mid with rotary controls. Both high and mid are in the one unit, and we can offer these far below the normal price. Cat. AC-1683 ONLY $9.95 TELEPHONE DOUBLE ADAPTOR SENSATION Another Jaycar exclusive purchase. Allows you to connect two phones to the one socket. These normally sell for $7.50. MAY SPECIAL SAVE47% Cat. XT-6020 $3.95 ea TURN YOUR SURPLUS STOCK INTO CASHII Jaycar will purchase your surplus stocks of components and equipment. We are continually on the lookout for sources of prime quallty merchandise. CALL GARY JOHNSTON OR BRUCE ROUTLEY NOW ON (02) 747 2022 6 .3VOLTMES GLOBES SPEAKER CLOTH Don I miss this bargain. OEM's contact Bruce Routley (02 747 2022). NORMALLY 50 cents ea THIS MONTH , 4 for $1 ,,. 10 for $2 / . .. . Up until now, nyou wanted speaker cloth you had the choice of black or blackl We now have available brown speaker cloth, and its in 2 sizes. Top qual.lty, acoustically transparent. Cat. No. Colour Size Price CF-2751 Black 1m x 1m $9.95 CF-2752 Black tmx 1.7m $13.50 CF-2754 Brown 1m x 1m $9.95 CF-2755 Brown 1m x 1.7m $13.50 Solar Powered Exhaust Ventilator The Sunvent is a high capacity solar cell and DC motor powered fan in a well designed cowling. The cowling has been cleverly designed to keep watter out and back draughts out. Simply cut a 120mm hole in a bulkhead or deck - or whatever - and the Sunvent will remove stale damp air and cut down mildew growth . It will extract dangerous LP gas or petrol fumes safely as the motor is sealed. The Sunvent is at its best in bright sunlight but will work quite well even on bright cloudy days. It will move about 35 cubic metres of air every ha~ hour in good conditions. Supplied with cover to turn off cells and stop all alrllow. • Boats r--------, • Caravans LESS THAN HALF • Port-a-Loos THE PRICE OF • Greenhouses NEAREST • Sheds EUROPEAN MADE • Holiday homes EQUIVALENTI • Backyard dunnies • Kitchens • Weekenders etc Cat. YX-2500 $49.95 GOREIDLL OPEN UNTIL 4pm SATURDAY START YOUR OWN BUSINESS? MAKE A FORTUNE! One of the great Australian Dreams is to own your own business. Most people dream of it but NOW is your chance to do something about it. · HOW? We all know that shoplifting and vanalism cost a small fortune very year. It has been demonstrated that television surveillance cameras in the right environment can discourage this activity. This is where you come in. We have made a great purchase of realistic-looking Dummy TV Cameras. They are Australian made, are supplied with adjustable swivel mounting bracket , fixing screws, flashing LED circuit board and 2 flashing LEDs. One red LED is mounted in a bezel on the front of the camera to add reality and the other - would you believe - is mounted BEHIND the dummy cameras lens I It looks really corny when It flashes and you COULD disconnect that LED but if a thief was ignorant of the cameras operation it may make the camera look more realistic to him. Also supplied is the 2 x D cell nylon battery holder to power the flasher circuit. A fake cable wallplate is also supplied as well as a very conspicuous 210(W) x 160(H) self adhesive sign which says "THESE PREMISES ARE PROTECTED BY TIME-LAPSE ANTI-THEFT CAMERAS" The text of the sign is in orange-red fluorescent ink against a black background. You can start your own business by installing these devices in your area. Liquor shops, service stations, car parks, other shops in fact anywhere where the proprietor of a business has a security problem. Dummy TV Cameras generally sell for about $90 each PLUS installation. By using your skill as an electronic enthusiast you could MAKE A FORTUNE by SELLING AND INSTALLING this camera for less than the cost of a normal camera. You could easily double your money every time you sold and Installed a cameral BUT HURRYI We have around 300 of the cameras at this below normal manufacturers price. We do not ever expect to be offered similiar stock again. Just imaginel You could earn a WEEKS WAGES on a Saturday! We have special bulk prices for installers at the one-off price you can make heaps I Cat. LC-5310 1 - 4 pieces _ _ 5 - 9 pieces 10 - 19 pieces 20+ pieces $49.95 $42.95 $39.9 5 $ 37.9 5 each Jata ~ THE BARGAIN OF THE YEAR OUMMYCAMERABARGruN ANOTHER WIRE WRAP WIRE Now available in 2 sizes in 5 metre lengths. High quality US made wire wrap wire in 24 and 28 guage. Both green In colour. Cat. WW-4350 24 guage $2.95 5 metres length Cat. WW-4365 28 guage $2.95 5 metres length WELLER TIP SALE We have a small quanmy of tips to suit the Weller W60D and W1 ODD 240 volt temperature controlled soldering irons. Weller No. Cat. No. Oty Avail CT5BB8 2.4mm 427° TS-1390 11 CT5CC8 3.2mm 427° TS-1391 54 CT5DDB 5mm 427° TS-1392 103 CT5EEB 6.4mm 427° TS-1393 41 These would normally cost about $11 each . Because ofthe small quantities, you tl better be quick. ONLY $4.95 each ~ EL CHEAPO DESOLDERING BRAID Our usual desolderwick Is sold in a plastic spool and contains 5 feet for $2.50. That's approximately $1.50 per metre. El cheapo braid is 2mm wide and will take solder off a PCB reasonably well although the braid gets a bit hot because there is no plastic spool to hold. You could easily put some in your old spool. Supplied in a 5 metre length for $2.50. That's 50- metre - or 1/ 3rd the price of normal desolderwick. Cat. NS-3025 5 metre pack Please note: braid is not loaded with flux and will not work quite as well as normal desolder braid. $2.50 SCOOP PURCHASE Hi Quality Speakers at Silly Prices 5"WIDERANGE 7 watt Bohm This is your chance to grab some high quality speakers at prices well below normal. They are made in New Zealand. 5"WIDERANGE 5 watts ohm Cat. AS-3021 $4.25 ea 10+ $3.95 ea 100+ $3.50 ea $3.95 ea 5" WIDERANGE 10 watt Bohm 10+ $3.65 ea 100+ $3.25 ea $5.95 ea NORMALLY $8.95 each 10+$5.50 ea Cat. AS-3020 Cat. AS-3022 5"WIDERANGE S"TWINCONE 10 watt 4 ohm 15 ohms Cat. AS-3011 Cat. CE-2322 $3.95 ea $8.95 ea 10+ $3.65 ea 10+ $8.00 ea NORMALLY $13.95 ea 6"x 4" Bohm Cat. AS-3014 S"TWINCONE 20 watt4ohm $4.95 ea Cat. CE-2323 10+ $4.50 ea NORMALLY $10.95 ea $13.95 ea 10+ $12.95 ea 5.25"DISC SENSATION Another unbelievable scoop purchase by Jaycar. We have available a quantity of US brand '1Jiscimate"5.25"SSDD discs. They are supplied in a handy plastic box of 10 which opens to allow easy access to discs. The box has one of the best opening actions we've seen. We can offer a 5 year warranty. These discs are so cheap we can only sell them in boxes of 1o. Cat. XC-4751 ONLY $13.95 box of 10 :•~ .'..... •.--, .. $12.95 10 or more boxes each. MAGNAVOX 6 WATT WOOFER/MIDRANGE Another new addition to our range of Australian made Magnavox woofers. Sultable as a woofer or a midrange. Power Handling 40 watts RMS Freq. Response 50 - 6500Hz Resonant Freq. 55Hz Voice Coil Dia. 25mm Sensitivity 93dB Will give excellent results as a midrange in the frequency range 500Hz - 5kHz. Needs to be mounted in a sealed enclosure of 2-4 litres. Will handle 60 watts RMS as a midrange. SPECIAL INTRODUCTORY PRICE Cat.CW-2107 -· ,,) ' ~ .:'/ Sa 6"x 2" SPEAKER!!!! Yes, a e· x 2"speaker, that's 157 x 57mm. The size may be strange, but the quality certainly isn I. They are Japanese made, with a large magnet. It even has a foam roll surround . These were used in colour TV's, so the quality is excellent. Sanyo brand B ohm 5 watt. Limited quantity. These would probably cost $30 as a spare partll Cat. AS-3020 $4.95 ea 10+ $4.50 ea 2-Wire AC Mains 7.5 Amp Flex This cord has a moulded 2-pin (i.e. no earth) approved plug with a very generous 3 metres of flex stripped and tinned at the end. Ideal as a replacement lamp cord or any long cord that need not have an earth . Worth $3.95 $19.95 ea ., THIS MONTH $2.00 Cat. PS-4112 UHF Antenna - BUY NOW Massive scoop purchase of quality Japanese-made (DX Antenna Co.) high gain UHF antennal (ch28-63) . ,::;. This 14 element unit has incredible front to back gain and would be suitable for '1ringe" UHF areas. (Gain 7.5 11.5 dB depending on actual frequency). The boom measures 1.2 metres long is even fitted with a diagonal support strut for extra ruggedness. Not only that, this antenna is fitted with a 300/75 ohm weather proof balun as standard I (You can use either 300 ohm ribbon or 75 ohm coax). This antenna is priced about 50% below Its true retail value. We have less than 200 so be quick! At $39.95 they wont lastl Cat. LT-3176 ONLY $9.95 Spare filters Cat. YF-5523 Only $1.00 ONLY $39.95 BARGAIN Walkie Talkies • Good range • Includes AM radio • Includes Morse key transmitter • Morse code symbols on the front panel of each unit • Solidly constructed • 7 transistor, 2 diode design • Low current drain (25mA standby) • Nifty belt clip included Cat. DW-3040 $29.95 A PAIR _ ;_AN ____ ~tli~t_::~o---=-N=E-w-P-=-a---=o-=o-u-----,c:,---T---,:s,--------1 INTELLIGENT MODEM PRICE SLASHED!! A very well known Australian manufacturer of modems came to us with a problem. They had a smallish number of their No.1 selling Intelligent modems left from their final production run. (The product was being discontinued because their upgraded 1988 model intelligent modem is fitted in a smaller more attractive case. They were anxious to clear the old stock to make way for the new. To be frank, however, there is a snag even though it is in reallty a very small snag. What is It? HAYES COMPATIBILITY. 1-layes"command protocol is used by the intelligent modems to communicate with each other. The problem is that this Intelligent modem only uses a subset of the Hayes command protocol. (This can be likened to IBM Clone'type computers. Most are not 100% IBM compatible. They work well anyway). Mind you, the above is only a problem tt you were say, a bank or large corporation trying to use this modem to receive information at high speed from their intelligent modems I BUT if you use It as an ORIGINATE modem, i.e. as a house use/hobbyist etc., it is perfect WE GUARANTEE THAT. This is a wonderful opponunlty to buy a high speed (1200 baud FULL DUPLEX) modem with auto diaVauto answer FOR THE PRICE OF A LOW SPEED DUMB MODEM I RSM EMBER the only drawback is that It will not ALWAYS work with 'Smart 'software but will always work In the terminalNiatel mode. We have purchased this product FAR BELOW manufacturers factory cost. Massive savings are being passed on. This price is 1/2 the price shown In our 1987 catalogue. A condition of purchase was that we did not reveal the manufacturers name, but you can always make an AVerage guess I SPECIFICATIONS:• Speeds 300 baud full duplex, 12oons limlted full duplex 1200 baud full duplex (option) , • Data standards CCITT V21, CCITT V23, Bell 103, CCITT V22 (option) Bell 212 (option) • Interface CCITT. V24 (RS232) • Data format Asynchronous• Diagnostic Analogue and digital loopback • Filtering dlgltal, no adjustment crystal locked• Power 240V AC• Modulation Frequency shift keying phase shift keying (with V22 option)• V21N22/V23 (1200/1200 option fitted) Cat. XC-4834 SAVE OVER 50% WAS $699 NOW ONLY $349 Low Cost Temperature Probe for Multi meters Ref: EA January 1988 This is an easy to build temeprature probe which adapts a multimeter or electronic voltmeter into a general purpose thermometer. Prototype was tested from -20" to 120°c at 1% accuracy. Aluminium tube not supplied. Cat. KA-1696 30 + 30 Watt Stereo Amp 200WATT 3WAY INCLUDING PREAMPLIFIER CROSSOVER Fully built and tested with separate bass, treble, balance and volume controls. This superb amp has less than 0.1 % distortion. There are inputs for microphone, phone and auxiliary (line) and all power supply components are on board. Just connect a transformer, speakers and a signal - and away you gal Requires 36-38VAC x 2. Size: 186 x 145 x 40(H)rnm Cat. AA-0300 • Crossover frequency 500, 3500Hz • 12d8 attenuation • 200 watts RMS • 8ohms Cat. CX-2621 Transformer to suit $69.50 Cat. MM-2010 $22.50 $19.95 $69.95 TEXAS Tl-56 CALCULATOR RUNOUT This is a true programmable scientific calculator at the price of a cheapiel NORMALLY $49.95 THIS MONTH .!:~. · . · ~ ~ \,'\ ,x.:: ~-- ,av■RIK Instant power pre-built amp module made in Australia and GUARANTEED TO WORK. Complete with quality diecast heatsinks. Just add DC power, a signal and a speaker and you are away! SPECS: 100 WATTSRMS into 8 ohms Cat. AA-0382 50 WATTSRMS into 8 ohms Cat. AA-0380 50 WATTSRMS- NORMALLY $99 SAVE 25% THIS MONTH ONLY $75 100 WATTSRMS- NORMALLY $125 I SAVE 20% THIS MONTH ONLY $99 "JAYCAR GIVES POWER TO THE PEOPLE" ~~~✓-------:,,,_./4~= ======1....'c= === ===== = = = = ========= -===== ==== ==; Motorola KSN 1038 Digital Multimeter + \ ... - 10 Amp Transistor Tester + Capacitance Meter JUST WOK AT THESE FEATURES • 0.5" high digits • High quallty probes supplied • LED and buzzer continuity test • Precision.thin film resistors for long term stability • CMOS logic Y 1,000 - 2,000 hours battery life • Meter protection fused • Complete with battery and spare fuse • Floating decimal point • Auto polarity • Vinyl carry case Cat. QM-1540 , .- ·"··.,_, ...•. .. :. Over 100 watts rms, frequency 4 30kHz. No crossover required. Especially suited for Hi Fi. For size see 1988 Catalogue. Cat. CT-1914 ·:-. NORMALLY $ l 29 THIS MONTH LESS $ 20 ONLY$1O9 $18.95 _J Breadboards Jaycar breadboards are a convenient and economic way to build circuits and test parts without soldering. Components can be then reused many times. Made from ABS Polymer. Internal contact terminals are made of alloy of silver and nickel and then plated. Resistance is under 1 milliohm at 1kHz. LIFETIME GUARANTEE Breadboard Specifications MOTOROLA KSN 1135 This unit which is very slmilarto our CT-1910 handles 75 watts rms and has an SPL of 96dB. Replace those Asian copies with the original for less costl No crossover required. For size see our 1988 Catalogue. Cal. CT-1908 Cat No Length Width PB-8810 PB-8812 PB-8814 PB-8816 PB-8818 PB-8820 172 172 172 224 240 264 13 39 65 150 195 240 Weight Tie Points 10 10 10 20 2 21 100 640 840 1680 2420 3260 5 Con' Term 128 128 256 384 512 25 Binding Con' Post Bus 4 8 16 20 28 3 4 4 Price IC Cap" 14'" $3.75 $10.75 9 $17.50 9 $39.95 18 $57.50 27 $69.95 36 • Connected " Capacity"' Pins ONLY $14.95 MOTOROLA KSN 1016 50 x 125mm exponential horn has a full so• horizontal dispersion angle. With harmonic disortion of less than 1%, this unit is ideal for HI Fi use. Frequency range 3 - 30kHz ±3dB. Maximum input 25V rms and no crossover is required. For size see our 1988 Catalogue. Cal. CT-2026 ONLY $22.95 MOTOROLA KSN 1025A A 50 x 150mm rectangular hom with the widest frequency range of the plezo horns. No crossover required. Cal. CT-1912 ONLY $29.95 ,. NEW KITS FOR MAY· FROM THE KIT LEADERS OPTICAL TACHOMETER RF DETECTOR PROBE Ref: Silicon Chip May 1988 Check the rotational speed of objects remotely with this project. Ideal for cars, model planes, fans, rotating shafts etc. The Jaycar kit comes with all specified parts case, etc. Cat. KC-5031 Ref: EA May 1988 This simple but very effective RF probe enables you to troubleshoot RF circuits by ..-nabling you to 'heaf the RF signall You can 'trace' RF just like audiol Kit includes all specttied parts except the felt tip pen case. The project must be used in conjunction with the KA-1699 Bench Amp ($39.95) described in April 1988 EA. ONLY $49.95 Cat. KA-1701 SIMPLE TESTER FOR POWER TRANSISTORS Ref: EA May 1988 Previous magazine projects can't really check power transistors properly. This project kit can and is extremely simple. It will measure current gain and Vbe of all popular power transistors - even Darlingtonsl All project specttied parts In the kit. Cat. KA-1700 ONLY $22.95 ~~~' 1 1 - ;~I VISA -,,:--~ I , 1 ' lVEW-•88 EM 5507 MAINS SAFETY CHECKER ONLY $13.50 LOW COST 50MHz 4 DIGIT DIGITAL FREQUENCY METER Ref: EA May 1988 For those who don't need Gigahertz pertormance, a low cost but high sensitivity, high input impedance unit measuring to well over 50MHz. All parts mount on one PCB. The Jaycar kit includes case, front panel and all specified parts. Cat. KA-1702 ONLY $99 Ref: AEM May 1988 This project revolves around the Jaycar HB-5950 3 pin mains plug case. All the electronics are inside the case. The project will check the following via LEDs: • Mains socket operational (power available) • Ground open circuit or O.K. • Active/Neutral swapped ort O.K. • Neutral-Earth leakage or overload A must for the safety conscious enthusiast or the electrician. Cat. KM-3069 ONLY $29.95 JAYCAR NUMBER ONE FOR KITS HEAD OFFICE MAIL ORDERS POST & PACKING 115ParramattaRoadConcord2137 P0.Box185 Concord2137 0 9 ~~.~~ Telephone (02) 747 2022 HOTLINE (02) 7471888 $25 $49.99 $ 4.50 Telex 72293 FOR ORDERS ONL y $50 $99.99 $ 6.50 ~FA_C _S_I_M_IL_E_(0_2_) _74_4_0_7_6_7_ _ _ _T_O_L_L_F_R_E_E_(_00_8_)0_2_2_88_8_ _0_vE_R_$1_00_ _ _ s1_0.0_0_ _ __ , ~, r, IL ~U~ _M _A _1_L_o_R_o_E_R_v_1A_ Yo _ uR _ _ _R_o _A_o _F=R=El~G=H~T'-=A_NY_w _ H_E_RE-"'-1_N A=U~S~T= RA =L =•~A~$~1~ ~ -so = =-=..1 SYDNEY· CITY 117YorkSt (02)2671614Mon-Fri 8.30 - 5 30 Thurs 8.30 pm - Sat 9 - 12 GORE HILL 188 Pacific Hwy cnr Bellevue Ave (02) 439 4799 Mon-Fri 9 - 5.30 Sat 9 - 4pm CARLINGFORD Cnr. Carlingford & Pennant Hills Rd (02) 872 4444 Mon-Fri 9 - 5.30 Thurs 8.30 pm - Sat 9 - 2pm BURANDA OLD 144 Lo~an Rd (07) 393 0777 Mon-Fn 9 - 5.30 Thurs 8.30 - Sat 9 -12 115 Parramatta Rd (02) 745 3077 Mon-Fri 8.30 - 5.30 - Sat 8.30 - 12 MELBOURNE-CITY Shop 2, 45 A'Beckett St City (03) 663 2030 Mon-Fri 9 - 5.30 Fri 8.30 - Sat 9 -12 121 Forest Rd (02) 570 7000 Mon-Fri 9 - 5.30 Thurs 8.30 pm - Sat 9 - 12 SPRINGVALE VIC 887-889 Springvale Road Mulgrave (03) 547 1022 Nr Cnr. Dandenong Road Mon-Fri 9 - 5.30 Fri 8.30 - Sat 9 -12 , CONCORD rd. HURSTVILLE -~··~ · Fit high-energy ignition to your car Is your car still limping along with outdated Kettering ignition? What? You are still cleaning points, adjusting the dwell, checking timing and all that automotive drudgery? Now you can fit this High Energy Ignition System and forget those tuneup hassles. By LEO SIMPSON & JOHN CLARKE These days the vast majority of new cars are fitted with breakerless ignition as standard equipment and they perform much better for it. In fact it is safe to say that with the lean fuel/air mixtures now used in modern vehicles, they probably wouldn't run at all if they did not have a high energy ignition with long spark duration. But what about all those tens of 32 SILICON CHIP thousands of older vehicles which still rely on the old Kettering ignitions? They can benefit greatly by being fitted with electronic ignition, whether the points are retained or the system is converted to breakerless operation. What are the benefits? If you have an older vehicle without electronic ignition, you can obtain several benefits by making the changeover. You can get a little more power, slightly better fuel economy and smoother engine performance, particularly at idle and with four cylinder engines. But the main benefit is the greatly increased times between tune-ups. Once tuned up, the car will stay that way much longer than when Kettering ignition is fitted. With the Kettering system (ie, conventional ignition with the points switching the current through the coil), the ignition "tune" starts to deteriorate almost from day one. When you consider the much longer period between tune-ups and the fact that the engine stays "on song" for much longer, the overall benefit of better performance and ~ Ideally, the high energy ignition module should be installed in the coolest available spot underneath the bonnet. This location in a Mazda 323 is suitable. Use 12mm x No.10 selftapping screws to secure the module to the fender. better fuel economy is very considerable. Add in the benefit of better starting on cold days or when the ignition system has been drenched and you're way ahead. If your car has been modified to increase its engine power, you should have a "high energy electronic ignition" system, as presented here. It will give equal or better performance than a so-called "sports" coil and will also solve the problem of points which burn out in no time at all. The high energy electronic ignition system we present here can be used with the existing points in your car's distributor or you can go the whole hog and replace the points with an electronic breaker system. Why "high energy"? Modern cars need a high energy ignition system. Because they use relatively lean fuel/air mixtures to meet pollution standards, they need a longer spark duration to make sure the leaner fuel/air mixture actually burns completely. The way to ensure long spark duration is to make sure that the ignition coil stores a lot of energy; ie, to make sure that the current through the coil is high. That way, when a spark is initiated across a spark plug, it takes some considerable time to discharge the energy stored in the coil. Actually, the story is a good deal more complicated than that, as will be apparent as you read on. Another reason why modern cars need higher energy from their ignition systems is that, in general, modern engines deliver their maxim um torque and power at significantly higher revolutions than older engines. So while the Kettering ignition system may have been reasonably adequate for older engines the higher spark rate needed for modern engines means that considerably less energy is available, just when it is needed. Even for older engines, electronic PARTS LIST 1 PCB, code SC5-1-588, 1 02 x 59mm 1 diecast box, 11 0 x 30 x 63mm 4 6mm standoffs 3 solder lugs 1 grommet 1 T0-3 mica washer and insulating bushes 1 T0-3 transistor cover 1 eyelet/lug assembly (see text) Semiconductors 1 MJ10012 NPN power Darlington (Motorola) 1 BC337 NPN transistor 4 1N4761 75V 1W zener diodes ignition can deliver significant benefits because considerably more spark energy is available, at virtually all engine speeds above idle. For those readers who would like to know a little more about the workings of standard Kettering ignition, we suggest that you read the accompanying panel which explains what you need to know for the purpose of this article. Over the past twenty years or so, the staff at SILICON CHIP have had considerable experience with the design of electronic ignition systems for cars. In setting out to design a new circuit we knew we 1 1 N4002 1 A diode 1 MC3334P ignition IC (Motorola) Capacitors 2 0.1 µF 1 OOV metallised polyester 2 O. O1 µF metallised polyester Resistors (0 .25W, 5%) 1 x 4 70kQ, 1 x 56kQ , 1 x 22k!J, 1 X 1 OkQ, 1 X 2.2k!J, 1 x 3300, 1 x100Q5W, 1 x47!J5W Miscellaneous Automotive wire, screws, nuts, shake proof washers, solder, heatsink compound , etc . had to come up with something which offered significant advantages over previous designs. Ultimately, a microprocessorcontrolled engine management system is the real answer. It is specially programmed to control the timing of the ignition and the fuel injection and to do it in such a way that engine performance is greatly enhanced under all conditions. Short of going out and buying a new car though, you can't have it. As far as we know, there is no after-market "add-on" engine management system available for any car, anywhere in the world. In any event, we weren't going This is what the ignition module looks like when all the components have been installed on the printed board and then fitted into the diecast case. The diecast case serves as a heatsink for the switching transistor. MA Y 1988 33 1 ------- I I I r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + 1 2 V VIA IGNITION SWITCH I I I I I I f I I I 41n I 5W 100!1 5W 2.2k 470k I I c, I I I ---HTTO DISTRIBUTOR I I ___lL I 330\l I 1N4002 05 I .01 22k 5 1--'......_.'IH,----, IN 02 BC337 IC1 ----=-H.... 7 OUTt-- MC3334PREF 3 4x1N4761 (75V 1W) POINTS POINTS CAPACITOR 0.1 56k - - - - : - -- - - - - - - - - - - ,- - . . - - - - - - - - + - - - - + - - - - - - + - - - - - - . . . _ _ _ . C H A S S I S 1 I.__ _ _ INPUT _CIRCUITRY _ _ _ _ JI .,. CASE HIGH ENERGY IGNITION SYSTEM SC5-1-588 0 ;-c 0 B VIEWED FROM BELOW Fig.1: the key components are the Motorola MC3334P high energy ignition integrated circuit and the MJ10012 high-power Darlington transistor. The Darlington transistor switches the heavy currents through the coil. The string of four zener diodes protects the Darlington against excessive coil volts if a spark plug lead becomes detached. for the ultimate. What we were after was a circuit that gave improvements over existing designs, whether it was in the performance delivered, reduced circuit complexity and cost, improved reliability or better compatibility with the various types of distributor now available. We believe we have achieved all of the aims just mentioned. The new circuit is less complicated, is easier to build and dissipates a lot less power so it should also be a lot more reliable than existing designs. Key parts from Motorola The new circuit is based on two key components specifically designed for automotive ignition by Motorola. They are the MC3334P high energy ignition integrated circuit and the MJ10012 power Darlington transistor. Elsewhere in this issue we give a run-down on the specs and application of the MC3334P but let us just touch on the main points now. First, the MC3334P is designed specifically to drive the MJ10012 power transistor (such long type numbers these beasties have). The MJ10012 takes the place of the ignition points and switches the heavy coil current. 34 SILICON CHIP Second, the ignition IC is designed to run at extreme temperatures, from - 40° right up to 125° Celsius (that's hot!). By contrast, most ICs for consumer applications are only rated for operation at up to 85° Celsius. Third, the IC is designed to operate over a wide range of voltages and incorporates transient protection on its inputs and outputs. That is very desirable for any electronic device working in the onerous environment of a car, especially under the bonnet. Fourth, the IC provides dwell extension so that a long spark duration is assured. We'll talk about dwell and dwell extension later. Well with all that magic built in, what did we at SILICON CHIP do in producing this design? Merely reproduce the Motorola circuit? Now how could you think that! Anyhow, it wasn't that simple. There is always a catch and in this case there were several. The first catch is that the MC3334P is specifically designed for distributors which have reluctor type pickups, as used in many standard electronic ignition systems fitted to new cars. So we had to adapt the circuit for use in distributors which have conven- tional points. That proved to be a tricky piece of design but we also went one step further and made sure that the circuit could be used with distributors having Hall Effect pickups. For this month though, we are only presenting the circuit for conventional points operation. Circuit description Now have a look at the circuit diagram for the ignition system. Besides the MC3334P and MJ10012 devices just mentioned, the circuit includes one small transistor, one diode, a string of zener diodes, four capacitors and eight resistors. Ql is the MJ10012 power Darlington transistor. It is the workhorse of the circuit, switching the heavy currents through the coil. Since it is a Darlington transistor (essentially two transistors connected in cascade) it has high current gain and so requires only a small base current to switch the heavy current in the ignition coil. Ql also has a high voltage rating sufficient to allow it to withstand the high voltages developed across the primary winding of the ignition coil. To be specific, the MJ10012 has a collector current rating of 15 amps How Kettering Ignition Works +12V FROM IGNITION SWITCH The conventional ignition system fitted to all cars is based on a system developed by Charles Kettering in about 1910. It is only in the last decade or so that significant refinements have been made to Kettering's circuit to improve its reliability and performance. The standard Kettering circuit is shown in Fig.2. This shows a battery connected to the primary winding of the ignition coil and with the current interrupted by the distributor points. The distributor points are opened and closed by a cam on the shaft of the distributor. The distributor cam is arranged so that the points are opened at the start of the firing stroke for each cylinder. When the distributor points close, current builds up in the primary of the ignition coil and produces a magnetic field in the iron core. This magnetic flux is the energy stored in the coil. When the points open, the coil current is suddenly stopped and the magnetic field collapses. This produces a sharp voltage spike across the coil primary winding. Now, let's imagine that the points capacitor has not been included in the circuit. As with any inductance, the voltage produced across the coil primary is such that it attempts to maintain the current through the points. If you consider that one side of the coil is tied to the + 1 2V terminal of the battery, the other side of the coil swings negative by hundreds of volts. The natural consequence of this large voltage at the points terminal of the coil is that an arc develops across the points as they open . The arc tends to maintain the coil current at its previous value until the points have opened too wide for the arc to continue . Having an arc across the points each time they open is bad news because it means that the point contacts get seriously burnt and pitted. The cure for this is the capacitor connected across the points. At the instant the points open, the capacitor appears as a short circuit (because there is no voltage across it) and so the voltage across it now begins to rise at a rate determined by the inductance and resistance of the coil. And, the lack of any voltage across the points as they open means that no arc occurs. Meanwhile, the ignition coil is also a transformer, so the large voltage spike which appears across the coil primary is stepped to appear across the secondary. The secondary coil voltage is then fed via the rotating contact in the distributor and via the high tension leads to the appropriate spark plug. It is the voltage required to fire the spark plug which ultimately determines how much voltage appears across the coil. This can range from under 5000 volts to over 15,000 volts, depending on the conditions within the cylinder. In the lc1te 1 950s a change was made to the Kettering ignition system with the addition of the ballast resistor. This resistor was placed in series with the coil primary so that, effectively, the peak and a collector voltage rating Vceo (the rating with the base open circuit) of 400 volts. Its current gain at a collector current of 6 amps is typically 350 but can range as high as 2000. In fact though, the current gain of the transistor is not really all that important in this circuit since we drive the transistor's base pretty hard to make sure it is well and truly saturated (ie, turned hard on). IGNITION COIL PRIMARY 10 I 10 ~ TO CENTRE POST OF DISTRIBUTOR SECONDARY ...J FIG.2 voltage applied to the coil was never more than about seven volts. When the engine was cranked over, and battery voltage would normally be low, the ballast was switched out to apply the full battery voltage to the coil. This gave a hotter spark for starting but meant the points were more liable to be severely burnt because of the heavier coil current. Pros and cons of Kettering ignition The advantages of the Kettering system are that it is simple, gives plenty of spark energy at low engine speeds, and is easily adjusted and maintained by the average motorist or mechanic. The disadvantages are that spark energy is greatly reduced as engine revs rise and that the points quickly burn out and need frequent cleaning, adjustment and replacement. This means that the engine is rarely in peak tune. The above explanation of the Kettering system should be regarded as a brief summary of its operation because the more you look into its operation, the more complex it becomes. For example, the ignition coil is connected as an autotransformer and the two windings are connected so that the spark plug voltage is negative with respect to the chassis. If the connections to the coil are reversed, the spark plug voltage is reversed in polarity and this makes the spark plug much harder to fire. The required voltage to fire the plug can be 20% to 40% higher than for the correct connection. The reason for this is that the centre electrode of the spark plug is hot and is therefore an electron emitter. This makes it much easier to fire with a negative potential applied. When Ql is turned on (to feed current through the primary of the ignition coil), its base current is supplied via a 1000 5 watt wirewound resistor. Ql is turned off when ICl pulls its output pin 7 to MAY 1988 35 COIL CURRENT (a) I~ ►/]~► M /1_______...,____/1--t--------TIME n M(ms) 5 10 15 20 25 30 COIL CURRENT (ms) (b) TIME 0 10 15 20 25 30 Fig.3: this diagram shows the primary coil current with and without dwell extension. In (b), the spark duration is fixed at one millisecond and so coil energy is not wasted in useless primary resonance. This allows the the coil current to start from a high value for each cycle rather than from zero. ground, which effectively shunts the base current for Ql to the zero volt rail. Ql has an adequate collector voltage rating to cope with the high voltages developed across the primary winding of the ignition for all normal spark plug conditions. But if a spark plug lead becomes detached, the coil primary voltages can go to extreme levels and thus cause "punch through" of the Darlington transistor. Protection against that circumstance is provided by the string of four 75V 1W zener diodes. These limit the maximum voltage at the collector of Q4 to 300 volts. Wetting current Shown on the lefthand side of the circuit are the points in the distributor, together with the points capacitor which is left in place. When the points close, current passes through them via the 470 5W resistor. Depending on the battery voltage [between 12 and 14.4 volts under normal conditions), the points current is around 250 to 300 milliamps. This relatively high current is necessary to keep the points clean and stop them becoming fouled in the fume-laden atmosphere inside the distributor cap. When the points open, Q2 is turned on by base current supplied via The high-power Darlington transistor is installed on the outside of the diecast case and fitted with a plastic cover to prevent shorts or "tingles" from inadvertent contact. 36 SILICON CHIP the 470 resistor and diode D2. Capacitor C2 is there to filter out hash and to provide a degree of "de-bouncing" for the points. When Q2 turns on, its collector is pulled low and the resulting negative-going signal is fed to a differentiating network consisting of capacitor Cl and the 470k0 resistor. The O.lµF capacitor at pin 3 of ICl· filters the internal reference supply for the comparator input at pin 5. Pin 5 is normally held high via the 22k0 resistor and 470k0 resistor to pin 6. The 22k0 resistor provides current protection for the zener clamped input. The pin 5 input is used to provide the timing signal for switching Ql. As soon as Q2 switches on (taking its collector low) pin 5 of ICl is pulled low via capacitor Cl. ICl then pulls its output at pin 7 low and this turns off transistor Q2. The interruption of the coil current then causes a high voltage to be developed to fire the relevant spark plug. Capacitor Cl now begins to charge via the 470k0 resistor and after about one millisecond, the voltage at pin 5 reaches the threshold of a comparator inside ICl. This causes the output at pin 7 to go high so that Ql turns on again. Thus the spark duration is limited to one millisecond. When the points finally close again, Q2 switches off and a positive signal is applied to pin 5 due to the charged Cl. This has no affect on the operation of ICl and the voltage is clamped with a zener diode at pin 5. Cl discharges via the 2.2k0 and 470k0 resistors. Because the spark duration is limited by ICl, the total energy stored in the coil is not fully dissipated each time a spark plug fires. Paradoxically, this means that the spark energy is actually higher. This apparent contradiction is explained by Fig.3. Fig.3(a) shows a plot of ignition coil current when the time between sparks is 10 milliseconds. This corresponds to a spark rate of 100 sparks/second or 3000 RPM in a 4-cylinder motor. Note that no current flows for about 50% of the time, because this is the time the points are open. plugs themsevles. So there is more likelihood of a high tension failure. Second, if the system fails (unlikely but possible) you will need to change all the plugs back to their normal settings in order for the car to start and run easily. Third, if you open up the spark plug gaps, the resulting spark may have a longer path, but because it requires a lot more energy to maintain that spark, it will extinguish earlier. So you will not get the full advantage of the dwell extension. Construction Fig.4: the wiring diagram. All wiring from the board should be run in 4mm auto cable which has a generous current rating. This means that for about 50% of the time the ignition coil is doing nothing at all, even though the actual spark lasts for less than a millisecoqd. And after this millisecond, any coil energy which was not dissipated in the spark is then wasted in a useless ringing of the primary coil winding (it resonates with the points capacitor). Now have a look at the waveform of Fig.3(b). This is with dwell extension, where the Darlington transistor Q1, handling the coil current, is switched on one millisecond after having been switched off. Now, instead of the coil current starting from zero amps after each spark, it starts at a level of several amps and gets close to the saturation current before the next spark is required. So each time the Darlington transistor is turned off, the coil is able to deliver much higher energy to the spark discharge. Effectively, the dwell extension circuit means that the current through the coil is much higher at all times. More current means a lot more spark energy. And more spark energy means a longer spark duration. That results in better fuel combustion. There is one drawback to putting more current through the coil the coil gets somewhat hotter. But in practice this has not been found to be a problem. Spark plug gaps In the past it has been common practice by car enthusiasts, when they have fitted electronic ignition, to increase the spark plug gaps. This was done to take advantage of the higher spark voltage and thereby obtain a longer spark "path". We don't recommend this practice, for a number of reasons. First, it places much greater voltage stress on the car's high tension components; the coil, distributor, spark plug leads and the spark 0 0 CASE ~-INSULATING BUSH ~-soLOER LUG <at>-WASHER ®----SPRING WASHER <at>----NUT Fig,5: the Darlington power transistor is mounted using insulating bushes and a mica washer. Don't forget to use heatsink compound. The circuitry for our high energy ignition system is housed in a small diecast box. It may not look "high energy" but it is. The box measures 110 x 30 x 63mm and provides what little heatsinking the main Darlington transistor needs. Under normal operation, the transistor and the case become warm but not hot; or no hotter than the surrounding metalwork underneath the bonnet. All the circuit components, with the exception of the MJ10012 transistor, are mounted on a printed circuit board measuring 102 x 59mm (code SC5-1-588). Note that the diecast box is the only type that we recommend. This is because it is splashproof, rugged and provides the heatsinking for transistor Q1. We don't recommend folded metal cases because they are not splashproof. Begin construction by mounting components onto the PCB by following the overlay diagram. Note that because the PCB is designed to be compatible with Hall Effect distributors, some component holes are shown vacant. These holes should be ignored. Mount the two 5W resistors so that they are raised about 1mm from the PCB surface to allow cooling. The five diodes should be mounted with a loop in one of the leads to provide stress relief. For the remaining components it is important to insert them into the PCB without stressing their leads. The component leads should move freely in the PCB holes before they are soldered. Once assembly of the PCB is complete, work can begin on the diecast box. Drill holes for the corner mounting positions of the PCB, a MAY 1988 37 Background to Electronic Ignition Conventional ignition systems suffer from two basic drawbacks. First, the points deteriorate quickly and have to be frequently cleaned, re-gapped and the timing adjusted in order to keep the engine in reasonable "tune" . And once they have been freshly set they immediately start to deteriorate again. So much so that most car manufacturers recommend cleaning and adjustment of the points at least every 15,000km or so. Ideally though, points need to be adjusted much more frequently, at intervals of 8000km or less. Second, the spark energy available from conventional ignition systems falls off with increasing engine speed; ie, the more sparks required, the less energy per spark. This is because it takes an appreciable time for the coil primary current to build up to its full value. As engine revs go up, there is less time available for the current to build. With a typical ignition the time taken for the coil current to reach its maximum value (and thus give maximum spark energy) is around 15 milliseconds or so. And with a typical engine, the points give a duty cycle of about 50%. This means that if the sparks are required less than 30 milliseconds apart, spark energy will be reduced from the maximum level. Just to put that in perspective, if the sparks are only 30 milliseconds apart, that corresponds to a spark rate of only 33 cord entry in the side of the box large enough for the grommet, and finally holes for the earth terminal, transistor mountings and the base and emitter leads. The transistor is mounted on one side of the case with the emitter lead located near the relevant connection on the PCB. The transistor is mounted using a mica washer and insulating bushes to electrically isolate it from the diecast case. The method of assembly is shown in Fig.5. You can mark the holes for mounting the transistor using the T0-3 mica washer as a template. After 38 SILICON CHIP sparks/second which is equivalent to only 990 RPM for a 4-cylinder engine, or not much more than typical idle speed. Incidentally, if you talk about "duty cycle" of points to automotive electricians they are likely to look at you as though you come from another planet. Car manufacturers specify duty cycle in terms of "dwell angle". For example, for a 4•cylinder motor, the distributor cam has four lobes and therefore, for a duty cycle of 50% (ie, points closed for 50% of the time), the dwell is 45 ° or a little more. Typically, for a 6-cylinder motor, the dwell angle is 30 to 35°. Early transistor ignition To overcome the problem of the long times required for coil current to build up to maximum, early transistor ignition systems used special low resistance coils which pulled a much higher current, sometimes up to ten amps or more . This wasted a lot of electrical power and put a big load on the car's electrical system. (In essence, this idea is back in vogue with the "high energy" ignition systems used in cars such as the Holden Commodore.) In the seventies, enthusiasts fitted capacitor discharge systems which gave very high spark energies but were plagued with two problems: unreliability of the electronics and "cross-fire". Cross-fire was due to the high 7 5mm DIA. _J I LtJ 19mm LtJ I ~32mm~ Fig.6: this eyelet lug assembly fits over the points terminal on the coil (see text for connections). energy and very fast risetime of the voltage applied to the spark plug. Not only was the wanted spark plug fired but there was enough energy left over to give weak sparks in other cylinders. This gave symptoms similar to 'pinging' and, in severe cases, could lead to breakdown of piston crowns. These days, the_use of capacitor discharge systems is confined to motorbikes, outboard motors and motor mowers. With the introduction of the Chrysler "lean burn" engine in the late seventies, another variation on transistor ignition was introduced: dwell extension . This makes use of the fact that in a transistor system, there is no reason why the switching transistor should not turn on again once the spark has been extinquished . In a conventional system, once the spark is extinquished, the remainder of the enrgy stored in the coil is dissipated in useless "ringing" in the primary winding. By turning on the switching transistor before the spark actually extinquished, primary coil resonance never occurred and so the average energy stored in the coil was much higher. Thus the energy per spark was maintained to much higher engine revs. This may seem like a paradox but is demonstrated in the waveforms shown in Fig .3. The ignition system featured in this article relies on dwell extension to give high spark energy. drilling, remove any burrs using a larger diameter drill. With the heatsink area (ie, where the transistor mounts onto the case) free of any metal swarf or grit, smear a thin layer of heatsink compound onto the transistor mounting base and the mating area on the case, before placing the mica washer in position. When the transistor is screwed down, check that it is completely isolated from the case by using a multimeter (switched to a high "Ohms" range) or a continuity checker. The PCB is mounted on 6mm stan- ble at the + 12V side of the coil ballast resistor. However, some vehicles have the ballast resistor as part of the wiring lead to the coil and this means that the + 12V connection must be made at the fuse box. Fig.7: the full size artwork for the printed circuit board. BALLAST RESISTOR HT +12VTO IGNITION CIRCUIT TO COLLECTOR OF 01 Fig.8: if making a direct connection to the ignition switch is too difficult (in cars with the ballast resistance in the harness), you can use this relay hook-up to make a more convenient connection to + 12V. doffs within the case. We recommend using shakeproof washers on all screws to ensure that they don't become loose. The wires to the power transistor and to the various external connections should be via 4mm auto cable. This won't fit into normal PCB holes so we suggest you use PC stakes. Use one-metre or longer lengths of wire to provide the chassis, points, coil and battery connections to the circuit. Installation Choose a convenient and well ventilated spot in the engine bay, away from the heat of the exhaust manifold and clear of any possible splashing from water. If you can, choose a position reasonably close to the coil so that long wires can be avoided. For our prototype, we were able to mount it simply with two large self-tapping screws in one side of the case and into a bulkhead near the wheel well. It was just a matter of having suitable holes drilled in the case and bulkhead. Then insert the two screws and then screw on the lid of the case. A plastic case fitted over the power transistor is a good idea because it prevents any possibility of shorts from stray tools. It can also avoid the possibility of a "tingle" to any unsuspecting mechanic working on the car while the engine is running - and that could include you! After mounting, the electrical connections can be made. We recommend an eyelet/solder lug assembly for the points connection, as shown in Fig.6. This connects to the standard points side of the coil and the collector of Ql connects to this at the solder lug point. The second (isolated) eyelet connection goes to the points and the solder lug to the points input to the transistor ignition. This method allows a quick conversion back to standard ignition should the transistor ignition fail. The final connection for the transistor ignition is to the + 12V supply which comes via the ignition switch. In some cars this is accessi- Once the ignition system is installed, the vehicle can be tested. The ignition timing can be checked using a timing light in the normal way. Note that if you use a dwell meter, it will give misleading results due to the extended dwell feature of the ignition. The points gap should be set exactly according to the manufacturer's spec. If you haven't replaced the points for a fair while, it is a good idea to install a new set. And while you won't have to replace them for a long time, if ever, it is a good idea to check and adjust the points gap (and re-do the timing) every 20,000km or so, to compensate for wear in the rubbing block. 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Cat 0-1777 ONLY sgg ------------------ • NSW • Albury 27 8399 • Bankstown Square 707 4888 • Blacklown 671 7722 • Bondi Junction 3871444 • Brookvale (Warringah Mall) 93 0441 • Campbelllown (046)27 2199 • Chatswood Chase 411 1955 • Chullora 642 8922 • Gore Hill 4395311 • Goslord 25 0235 • Homsby 477 6633 • Liverpool 600 9888 • Maitland 33 7866• Miranda525 2722 • Newcastle 611896 • North Ryde 88 3855 • Parramat!a 689 2188• Penrith (047)32 3400 • Railway Square277 3777 • Sydney City 267 9111 • Tamworth 66 1711 • Wollongong 28 3800 •ACT• Fyshwick 80 4944 •VIC• Ballarat 37 5433 • Bendigo 43 0388 • Box Hill 890 0699 • Coburg 383 4455 • Dandenong 794 9377 • East Brighton 592 2366 • Essendon 379 7444 • Footscray 689 2055 • Frankston 783 9144 • Geelong 43 8804 • Melbourne City 670 9834 • Richmond 428 1614 • Ringwood 879 5338 • Springvale 547 0522 •OLD• Brisbane City 229 9377 • Buranda 391 6233 • Cairns 311 515 • Chermside 359 6255 • Redbank 288 5599 • Rockhampton 27 9644 • Southport 32 9863 • Toowoomba 38 4300 • Townsville 725722• Underwood 341 0844 •SA• Adelaide City 232 1200 • Beverley 3471900• Darlington 298 8977 • Elizabeth 255 6099 • Enfield 260 6088 •WA• Cannington 451 8666 • Fremantle 335 9733 • North Perth 328 6944 • Perth City 481 3261 • TAS • Hobart 31 0800 •NT• Stuart Part< 81 1977 Manufacturer's data on the Motorola MC3334P high energy ignition IC Motorola's MC3334P is designed specifically to suit five terminal ignition systems made by Delco (USA) for the aftermarket (ie, for fitting to older cars). The MC3334P, driving a high voltage Darlington transistor, provides an ignition system which optimises spark energy at minimum power dissipation. By LEO SIMPSON a transient voltage of up to 90 volts for up to 300 milliseconds. Output sink current (into pin 7) is quoted as 300 milliamps (maximum, steady state) but it can take up to one amp for as long as 300 milliseconds. Operating temperature range is from - 40° to + 125°. Fig.1 shows Motorola's suggested application circuit for the MC3334P. This shows input pins 4 and 5 connected to a reluctor pickup with an inductance of 1.35 Henries. Reluctor or variable reluctance pickups are used in many modern vehicles and consist of a toothed wheel (one tooth for each Motorola quote the following features for the MC3334P: • Very low peripheral component count • No critical system resistors • Wide supply voltage operating range (4-24V) • Overvoltage shutdown (30V) • Dwell automatically adjusts to produce optimum stored energy without waste • Externally adjustable peak current • Transient protected outputs Maximum supply voltage is quoted as 24V DC (steady state) although the device will withstand cylinder) which rotates near a permanent magnet which has a coil of wire wound around it. The signal generated by the reluctor is shown on Fig.1 as a spiky waveform which is processed by the IC to give correct turn-off time for the Darlington transistor (MJ10012). The capacitor at pin 3 controls the dwell time which means that the Darlington is turned on after about one millisecond. A sensing resistor, Rs, is connected in series with the Darlington transistor to monitor the coil curVBATT 4-24 Vdc RBATT 300 CFILTER :I 0.1 -::- 6 Vee r-, Reluctor : Pickup 1.35 H : ,,;•.o--......------.--------..N\,--+--.---1 : C1 • Power Output and OVP RL : "<:<>--<1----47_0_ _,_o_k....,_"VV\,-C--l---l----,----~ L-' Ignition Coil Primary 8.0 mH RoRIVE 100 OUT c2• =!;:0.01 *Optional Parts for Extended Transient Protection .. A 350 V zener clamp is requ ired when using the standard MJ10012 . This clamp is not required if a selected version with V(BR)CEO(sus) "" 550 V is used. Dwell Reference Buffer Current Liniit Sense 8 MC3334 Sense 2 1 Power Ground Ground~- - - - - - - ' -::- Fig.1: Motorola's suggested circuit for the MC3334P ignition IC. It uses a reluctor pickup which is typical of electronic ignition fitted as original equipment on many new cars. 42 SILICON CHIP VBATT = 13 2 Vdc 6 .0 5.5A 5.0 }40 ~ .2 30 . 2.0 1.0 bj3 260 I I I I I 133 100 70 50 I I I I I I I 10 0 I I I I I I 15 I I I I 33 Freq (Hz) I I 20 I I I I 25 I I I I I I I I 30 ms Fig.2: the primary coil current diagram for spark rates up to 333Hz. The "flat-topped" waveform shows the effect of the inbuilt current limiting associated with pin 8. rent. Pin 8 of the IC is used as a current sense input to limit the coil current to a suggested value of 5.5 amps. The idea behind this is to limit the coil dissipation at low engine revs. (Our circuit does not have the current limit feature because it will be used mostly with cars that have ballast resistors in series with their coils. The second reason for not using the current limit feature is that it will automatically increase the power dissipation on the Darlington transistor at low engine revs. Finally, the third reason for not including current limit is that we did not want any trimpots or user adjustments in the circuit.) Fig.2 is a rather strange diagram depicting the ignition coil current and transistor conduction times for spark rates from 33Hz to 333Hz (lefthand side). It also shows the coil current being limited to 5.5 amps at low engine revs. 333Hz is equivalent to 5000 RPM for an 8-cylinder motor, 6700 RPM r - - - - - - - - - - - - -, for a 6-cylinder motor, and 10,000 RPM for a 4-cylinder motor. While it may not be immediately obvious from Fig.2, the MC3334P does provide a variable dwell angle feature. It does this by measuring the slope of the reluctor waveform, with the dwell reference buffer, and stores the value on the dwell capacitor at pin 3. Our circuit for points-equipped distributors does not use this feature and the spark duration is fixed at close to one millisecond. ~ .s Vee -- - - - ---7, - ----------7 I I I I I I I I : I I 14V I I I I 5.2 V 2.0 '1> I I I I I 5 .2 V I I ~---~ 5 I X S2 I I I I I I I Input I Comparator I l with 1 Hysteresis I I I Simplified Internal I I Power Supply I I I I 1I I 1 I 1 I I I I I I L _ _ _ _ _ _-=-_ ___ ;::,7 _ I I L ___ __ _ __ _ _ _J 4 , - - -- 7,------ --- -- 7 Sl I I Output Stage with OVP and -=- : : I _J I L_ 2 Current Lim iting _ - - _ _ _ _ _ _ _ _j Sense Ground 1 r Powe r Ground I I Charge Up Fig.3: internal schematic of the MC3334P. Not~ that the output at pin 7 is open-collector so it will "sink" current but cannot "source" any current without an external pull-up resistor. I I I 3 C Charge Oown I I I I I 1 I I 1 X I I -::L _____ I I I I I I _ _ _j L __ - ___ - Dwell Referen ce Buffer _ _ _ _ _ _J MAY1988 43 -ARO Last month we presented the first article on the Railpower walk-around throttle for model railroads. This month we give the constructional details and show how to customise it for your particular application. By LEO SIMPSON PART 2: MODEL RAILROADERS (or are they railway modellers?) cannot be dictated to. They each want to build their train controllers their own special way, leaving out or adding in the features that they particularly want. So be it. In reading the construction information for the Railpower walkaround throttle remember that you can vary things around, as long as you don't take liberties with the basic circuit design. By that we mean that you can incorporate or leave out control features as you wish but don't play around with the componentry on the printed circuit board unless you really know what you are doing. With that in mind, let's discuss the assembly of the printed circuit board. To do this you will have to refer to the printed board overlay diagram, Fig.6, which was also publisheo on page 39 of last 44 SILICON CHIP & JOHN CLARKE month's issue. In fact, the overlay was printed a little too dark last month, making it hard to follow. To correct that, we are running it again in this article. Fig.6 shows all the components mounted on the board itself. The components not on the board are connected via the multiway connector strips. The 6-way connector is for the handheld throttle and the sixteen way connector (actually two eight-way units) is for the rest of the connections. Heatsinks required Assembly of the board can start with the wire links, small diodes and the 0.25W resistors. When these have been installed, you can concentrate on mounting the four output transistors, the 3-terminal regulator and their associated heatsinks. Three heatsinks are required. Ql and Q3 are mounted on one heatsink while Q2 and Q4 are mounted on another. We made ours from 0.8mm aluminium (equivalent to 22 gauge) although the thickness is not important. For each two-transistor heatsink W\:l used a piece of aluminium 30mm wide and 55mm long, with a rightangle bend 9mm from one end, which becomes the foot. Four 3mm holes need be drilled in each heatsink, to take the two mounting screws for the foot and the mounting screw for each transistor For the 3-terminal regulator heatsink we used a piece of aluminium 20mm wide by 45mm long, with a rightangle bend 9mm from one end. Three 3mm holes need to be drilled in it, two for mounting screws and one to secure the regulator. The three heatsinks 'should be secured to the printed board before the transistors and regulators are soldered into place. Note that the two transistor heatsinks must not touch otherwise they will short out the DC supply. Attach the regulator and the power transistors to their respective heatsinks and then you can solder their leads to the printed board. Note that mica washers are not necessary for the transistors or the regulator. Once the transistors and regulator are in place, the rest of O'I*I'LE FOR MODEL ROADS l°FOR :i TO HANO HELD UNIT - "l · .. RUN ov +12V LED3 -BUZZER + TRACK LED1 BI-COLOUR LED2 0 0 REV STOP ~11~fr{1J.'~ rf,'//' RAIL POWER ~I~ //0~ L: .:.J SPEED Fig.8: front panel artwork for the handheld controller. Fig.6: parts placement diagram for the PCB. Be sure to use the correct part at each location and note that IC2 is oriented differently to the other ICs. VR1 and VR2 set the maximum and minimum track voltages (see text). the components can be mounted on the printed board. We suggest that you solder in the small transistors, then the two trimpots, the wirewound resistor, the four integrated circuits, the four rectifier diodes and the capacitors. Leave the connector strips till last, otherwise they tend to get in the way when you are soldering other components. Note that ICl and IC2, the two LM324s, are oriented differently on the board (ie, they point in different directions). Power transformer Fig.7: this is the wiring diagram for the handheld controller. The numbers on the leads correspond to the numbers on the terminal block at the top of Fig.6. VR4 and VR5 set the running and braking inertia. FROM MAIN BOARD There are several options for the power transformer. Some modelling enthusiasts may already have a suitable transformer in the form of an old controller (containing just transformer and rectifier) or perhaps a battery charger with an output capacity of several amps. Virtually any transformer with a MAY 1988 45 ,-----------7 CONSOLE UNIT CONTROLS I I I I I I I I I SPEE VR3 I I I I I I I I 14 I I I I I REVERSE I I I S2 TO AILPOWER CIRCUIT I FORWARD L -- - - - - ---- - - - _J .,. LOCAL rEt~TE 16 i-- - - - - 2 I , 5 FORWARD - j --- - 3 6-PIN DIN PLUG _ _ 7USOCKET j S2 m~~ I I j j 4 SPEED VR3 INERTIA VR 4 I I RUN j I I I ~m VHS I L__ - j 220k -~NOHEL~~-AROUNO'U~ _ _ _ _ _ I I j Fig.9: this diagram shows the circuit additions required for switching between the handheld controller and the console controls. secondary voltage of around 12 to 15 volts and a current capacity of two or more amps could be used, although the more current capacity, the better. Be wary of old transformers that may have lain around for years and years. Such trannys may be a doubtful safety proposition as they will have absorbed a lot of moisture over the years and may be prone to breakdown. Modern transformers with split bobbin construction are much safer. Remember that you have virtually direct access to the output of the transformer when ever you touch the rails of the layout. If you have to buy a transformer, a 60V A multi winding unit, available from Jaycar (Cat. No. MM-2005) or Altronics (Cat. No. 46 SILICON CHIP M-2165) is good value. Two windings are connected in parallel to provide 12VAC at up to 5 amps. For many users, this would be enough to power two separate controllers. We give a little more detail on this later. Bare board plus walkaround throttle Many enthusiasts will want to build this controller as a bare board unit, to be buried somewhere underneath the layout and then have a handheld walkaround throttle, as described last month. There is nothing wrong with that idea but we suggest that the transformer and printed board be mounted together on a small metal chassis which is connected to the mains earth. We also suggest that all mains wiring and connections be well shrouded, allowing no possibility of accidental contact, whether by you or your children. If you are going to use a walkaround throttle, you'll probably want to plug it in at more than one point on your layout. This will require one or more 6-pin DIN sockets and some sheathed 6-way cable such as that sold by Jaycar as 6-way computer cable (Cat. No. WB-15 75). You could use telephone cable for wiring up the sockets (3-pair, single strand) but it is more prone to breakage. The sockets can be wired in parallel, in "daisy chain" fashion. Wiring up the handheld control is a simple matter. Just follow Fig.7 and the photos on page 40 of last month's issue. Powering up Having completed the wmng, check all your work carefully and then apply power. A number of voltage checks should now be made. To make these easier, turn the main board around so that it is oriented in the same way as the diagram of Fig.6 and have last month's issue open at the circuit diagram on page 37. That way, it will be easier to find your way around the board. Switch your meter to a 20V DC range and check that + 17V is present at the IN terminal of the 3-terminal regulator (you can pick it up at the end of the adjacent 2.2k0 resistor) and at the emitters of Ql and Q2. Depending on the incoming mains voltage, the measurement is likely to be anywhere between + 17V and + 21V or even a little more, depending on your transformer. Now check for + 12V at the output of the 3-terminal regulator and on each of the supply pins of the ICs: pin 4 of IC1 and IC2, pin 1 of IC4, and pin 14 of IC3. Again, the actual voltage will vary between + 11.4V and + 12.6V, depending on the actual 7812 (or LM340T-12) used. The voltages around IC1 and IC2, as shown in Table 1, should now be checked with the handheld throttle disconnected. These voltages are "ballpark" figures only but should This is the view inside the completed console unit. Note that the PCB and transformer are mounted on an aluminium baseplate which is then connected to mains earth. Table 1 IC1 : pins 1,2,3 ... ... ... .... ... ... .... ... ... ...... ... ....... .... .. .. about +1.2 volts IC1: pins 5, 6, 7 .. ... ....... ........ ... .. . about +4.8 volts (triangle waveform at pin 9, square wave at pin 7) IC1: pins 8, 9, 10 ......... ....... .. ..... .. ...... ... .. .. .. ... . same as wiper of VR1 IC1: pins 12, 13, 14 .... ..... ... ..... ... ..... ... .. ......... same as wiper of VR2 IC2: pin 1 ..... .... ... ....... ....... .... ... .... ... .... ............... ... about+ 11 volts IC2 : pin 2 ...... .. ... .... .......... ... .. ...... ... .. ............... ....... .. .......... 0 volts IC2: pin 3 ... .... .... ...... ... .... ... ... ... ..... ..... ... .... .... .... ... ....... .. +0.6 volts IC2 : pin 5 .... .... .... ........... ..... ....... .... .. ............ .. ... .. ...... . + 10.1 volts IC2 : pin 6 ... ....... .......... .... ....... .... ... ... ...... ............. ...... ... . +9 .8 volts IC2: pin 7 ....... ... ..... .. .... .. ...... .. ....... .... ... .. ...... ... .. .. .. about + 1 2 volts IC2: pins 8, 9 , 10 ..... ... ...... .. ...... ..... ......... .. .... ....... close to zero volts IC2: pin 12 .... ,... .. .. ... ....... .. .. ... .... ..... .. .... ..... .. ....... . about+ 1.8 volts IC2 : pin 13 ...... ........ .. .... .......... ......... .... .. .... .. ... ... same as pin 6 , IC1 IC2: pin 14 ... ..... .... ...... ... .. ..... ........ ........ .... .. ...... ........ ... .. zero volts be a good guide to see that things are working. Now you can plug in the handheld control and check that the voltages at pins 3 and 4 swap from high to low or vice versa when the forward/reverse switch is operated. Check the voltages at pins 6, 7, 9, 10, 11, 12, 14, and 15 also change state when the forward/ reverse switch is operated. Now connect your multimeter across the output terminals of the controller and wind the throttle control up to maximum. Adjust VRl so that the voltage is 12 volts (or whatever is the maximum recommended operating voltage for your The handheld controller plugs into a 6-pin DIN socket on the side of the case while the pulsed DC output to the rails goes via banana sockets. locos). Rotate the throttle to the minimum and adjust VR2 for an output of 1.5 volts or thereabouts (you will want to "fine tune" this minimum setting once your start operating trains). Now note that the polarity of the output voltage changes when you operate the forward/reverse switch and that the colour of the track LED changes (from red to orange or vice versa). Now wind the throttle to about the half-way mark and briefly short MAY 1988 47 6' 5' I'i;/4 ✓ 3' TRACK LED1 ~~3A _K PO ANS M2 LOCAL/ REMOTE S4 EARTH LUG <at> 19 22 7 8 9 10 11 12 13 14 OVE B 15 METAL BASEPLATE 16 ~ ~. 17 18 19 20 1 2 FORWARD/ REVERSE S2 <at> r. Fig.to (above): how the console case is wired up. Be sure to shroud all mains connections with heatshrink tubing and note the earthing lug under the power switch S3. Fig.11 (left) shows the PC artwork. the output terminals. The overload LED should light and the buzzer should sound. You can also listen to the operation of the controller by connecting a loudspeaker to the output terminals via a 1000 resistor. (Don't connect it directly otherwise you'll probably blow the loudspeaker). At low throttle settings the loudspeaker will have a thin, reedy sound. At higher settings, the sound will be louder but more mellow. Building a console c:o c:o ~ T'9 I 0) u en ~ 48 SILICON CHIP Some model railway enthusiasts will not be happy with just a tiny handheld walkaround throttle. They will want a console unit instead, or with the handheld throttle as well. To cater for those people we have built such a unit and prepared the necessary diagrams and photos. The console case we recommend is a plastic sloping-front unit with an aluminium lid. It is supplied by Jaycar, Cat. No. HB-6240. It measures 170mm wide, 214mm deep and 82mm high at the rear. We have designed a front panel for it too, featuring the NSW class 44 diesel electric loco. Fig.9 shows the circuit additions needed for switching between the console controls and the handheld walkaround controller. Essentially, the only addition, apart from the doubling up of controls, is the 3-pole switch S4. This is called the local/remote switch on the front panel of the console. The console controls are shown at the top of Fig.9 while the handheld control is shown at the bottom. Note that VR4 in the console is now a control in its own right rather than just a trimpot, as in the handheld unit. The idea behind this is that you can vary the inertia to suit the train. If you are doing shunting operations, you can turn off the inertia altogether. If you are just running a loco and short train, you'll want a medium setting for the inertia; if you have long train you'll want maximum inertia. Fig.10 shows how the console case is wired up, with a number coding system used for clarity The numbers down the righthand side of Fig.9 refer to the 6-way connector on the printed board, as shown in Fig.6 and on Fig.10. Pins 3, 5 and 6 of this connector go to the centre poles of switch S4. One side of the switch then goes to pins 3, 5 and 6 (labelled 3-dash, 5-dash and 6-dash on Fig.10) of the 6-pin socket for the remote handheld controller. You can use light duty hook-up wiring for all the ea bling in the console, except for the mains wiring and the figure-8 cable to the output terminals. The terminals of the mains switch should be sleeved with heat-shrinkable tubing, to prevent accidental contact. We recommend the use of a metal chassis plate within the console box for mounting the transformer and printed circuit board. The chassis plate can be made of steel or aluminium sheet (say 18 or 20 gauge} or, as with our prototype, you can use copper-clad laminate as used for printed boards. Note that the overload buzzer is The console unit features a large knob to vary the speed and a smaller knob to vary the inertia. The local/remote switch (top-right) provides selection between the console controls and the hand-held controller (when plugged in). wired directly to the printed board terminals (pins 13 and 14} and can be fixed to the inside of the case using a small piece of double-sided adhesive tape. The three LEDs are held in the front panel using clip-in bezels. VR5, the braking trimpot, is soldered direct to one of the pins of brake switch S1. When the wiring of the console is complete, you should go through the powering up procedure listed above. To do this, switch the local/remote switch to remote and do not connect the handheld controller. Other options Other options are sure to have suggested themselves as you have read through this article. For example, a pair of terminals could be provided on the rear of the console box to provide a regulated 12V output for accessories. These terminals would be connected to pins 17 and 18 on the printed board connector strip. You could also provide a pair of terminals for 12VAC output (connected to pins 20 and 21 on the aforementioned connector strip). Ideally, this output should have a fuse (say 2A rating} to protect it from short-circuits. This 12VAC output could be used to power an additional Railpower controller. Just connect the 12VAC lines to pins 20 and 21 on the connector of the second controller board. The rest we'll leave to your imagination. Have fun! le MAY 1988 49 Interesting circuit ideas which we have checked but not built and tested. Contributions from readers are welcome and will be paid for at standard rates. Voltage and current metering for power supplies Here is a way to measure current or voltage from a power supply using a single meter. Apart from the meter, you will need a 3-pole 2-position switch, two trimpots, two resistors and two diodes. The meter should be the common moving coil variety with a full-scale deflection current of lmA or 50µA. Generally, the lmA movement is more robust than the 50µA type. Which ever type you use, you will need to know its internal resistance. This can be measured using the circuit of Fig.1 which is simply a 1.5V cell and a trimpot, VRl. VRl should be adjusted until the meter's pointer is fully deflected. '"CY3 + ~ Fig. 1 The value of VRl will depend on the sensitivity of the selected meter use 50k0 for a 50µA meter and 2k0 for a lmA meter. VR2 can be about half the value of VRl. Next, connect VR2 across the meter and adjust it until the pointer is at half scale. Disconnect VR2 and measure its value at that setting. This will be equal to the meter's internal resistance. The circuit to measure both voltage and current is shown in Fig.2. This will allow a lmA meter (with internal resistance of 1000) to measure up to 20V or 200mA FSD (full scale deflection). To change the current or voltage sensitivity of the circuit, Rl and R2 will need to be substituted. To calculate the value of Rl: Rl = (VRl/2 + Rm)/(Ir - Im) where Rm is the internal resistance of the meter; Ir is the maximum current to be measured; and Im is the FSD current sensistivity of the meter. To calculate the value of R2: R2 = Vrlim - VR2/2 where Vr is the maximum voltage to be measured; Im is the FSD current AO Sla OUTPUT INPUT Fig. 2 of the meter; and VR2 is about 20% of R2. Where the meter's internal resistance is significant, the value of R2 should be decreased by this amount. To avoid damage to the meter, two silicon power diodes are reverse-connected across the meter terminals. $20 to: N. Jackson, Kilsyth, Vic. Handy Hints Hint #1: In some pieces of test equipment it is necessary to insulate the BNC input sockets from the chassis. This can present problems as they are often only available in chassis-mount versions without the insulating kit. If this is your problem, your local hardware store can solve it. Purchase two fibre washers with an inside diameter of 3/8-inch and an 0-ring ring as fitted to a standard 1/2-inch water tap. The chassis mounting hole for the socket should be drilled to 1/2-inch or 12mm. Mounting the socket is then a matter of fitting 50 SILICON CHIP one Jibre washer on each side of the metal panel, with the 0-ring sandwiched between the two to prevent the socket body from contacting the chassis. Hint #2: Heatshrink tubing makes a neat cover for joins in wire, switch lugs and so on. If you have no heatshrink tubing handy, you can try substituting ordinary plastic sleeving that has been soaked for an hour in acetone solvent (such as lacquer thinners). Soaking the sleeving makes it swell up after which it gradually returns to its original shape. Take care with the solvent though; keep it away from flame and sparks and do not spill it on plastic cabinets. $5 to: N. Jackson, Kilsyth, Vic. Hint #3: Ordinary toothpaste makes a good cutting polish to remove scratches in plastic cabinets and on Perspex. If the scratches are deep, you may need to first use some "wet and dry" emery paper. You can then finish off with Brasso or car polish. $3 to: N. Jackson, Kilsyth, Vic. Improvements to end-of-file indicator Since the End-of-File Indicator was published in the February 1988 issue a number of enhancements have suggested themselves, one to a reader and a couple to us. We'll look at our reader's version first: I decided to use the End-of-File Indicator for receiving files also. I have downloaded some software that took up to 20 minutes and wanted to be able to leave the computer while this was taking place. But since the bulletin board concerned disconnects you unless you press a key every minute or so, you must be able to tell when a download is finished. All that is needed to add the facility for receiving files is a DPDT centre-off toggle switch (Jaycar Cat. No. ST-0560 or similar) to replace the SPST switch originally specified. Fig.1 shows how the modification should be done. One section of the switch is connected to select either pin 10 or pin 26 of the 7910. The other section of the switch is wired in series with the buzzer. $10 to: Michael Dobbins, Charlestown, NSW. In the SILICON CHIP office we have have found that another refinement is worthwhile and would apply particularly to those modems which do not incorporate "hand-shaking" (ie, those which will send a file even though the phone line may have been disconnected). It is also possible to have the carrier drop out even though the phone line is still connected and so you can be blithlely sending material which is not being received. The cure for this is to add a 74LS00 quad 2-input NANO gate which is wired as an OR-gate connected to pin 10 and pin 25 (the carrier detect output) of the 7910 (see Fig.2). In this way, if either the CD (carrier detect) or TD (transmit data) pins on the 7910 go low for more than a second or so, the buzzer will sound. The circuit works as follows. Both the CD and TD pins on the 7910 are active low and so if data flow stops or the carrier drops out, +5v------------------ TRANSMIT 470k 47k 2.2 16VW IC1 555 .,. PIN 1O _. TRANSMIT O 2.2 + 16VWI TO 7910 WMC PIN 26 RECBVEO _ 1 S a .,. PIN 10 7910----1---t, TO 1ASE OF 0 1 - - + :, P~~ TO +5V > TO BUZZER 23---...-L_I1 Fig.1: this circuit modification shows how to add a DPDT centre-off switch to give end-of-file indication for transmit or receive. +5v---.-----.-----..---------+--~ ON 470k 47k 2.2 IC1 555 16VW - 3 14 74LSDD TO CARRIER DETECT PIN 25 OF AM7910 TO PIN 10 OF AM7910 .,. 2.2 + 16VWr T Fig.2: carrier dropout detection can be added to the end-of-file indicator by wiring in a 74LS00 NANO gate package. the respective output will go high. These signals will be inverted at pins 3 and 6 of the 74LS00, respectively. So if either or both signals go high for more than a second or so, the signal at pin 8 of IC2 will go high, Ql will be off and the buzzer will sound. High-Q notch filter uses small capacitors This high-Q notch filter circuit takes advantage of the very low bias current and high input impedance of the OP-41 operational amplifier IC (made by Precision Monolithics, Inc, USA). This enables high value resistors and low value capacitors to be used, even at low notch frequencies. The values shown give a notch at 60Hz. The 5-picoamp bias current for the OP-41 causes an input off- Another mod which we have found desirable is to add a 2.2µF capacitor across the buzzer. This increases its output level. There is no reason why all these circuit mods cannot be combined. We have shown them separately for clarity. R1 10M -v C1 27DpF C2 27DpF fo:1/2 7fR1C1 R1:R2=2R3 C1=C2:C3/2 set voltage of only 100 microvolts (developed across Rl and R2). Note: this circuit taken from PMI applications literature. PMI op amps are distributed by VSI Electronics (Australia) Pty Ltd. Phone (02) 439 8622. MAY 1988 51 Great Kit Projects To Build Many Just Released For 1988 I Calling All Audio Purists This Great New Amp From Silicon Chip Is For You Power House 600W Inverter (See EA Dec'87) Go Anywhere 240V Maine Power rrom your car or truck battery with theae fanta1tlc DC to .AC Inverter, A must for farming, camping, mining, boating, remote settlements and wherever else 240W power isn't available. Featurea: Strong custom steel chassis• Industrial grade power coat finish• Can be configured to operate off either 12Vand 24V DC• Very little internal wiring• Manual or Auto start facilities • Low battery cut out • Compact Toroid transformer. Fully Built & Te ■ted K 6770 . 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Remember with our Overnight Jet1■ rvlc■ we deliver next day. il\jfi/ 174 Roe St. Perth W.A. 6000 PHONE TOLL FREE 008 999 007 Perth Metro & After Hours (09) 328 1599 ALL MAIL ORDERS P.O. Box 8350 Perth Mail Exchange W.A.6000 ALTRONtCS RESEl,LERS Chances are there is an Altronics Reseller right near you - check this list or phone us for details of the nearest dealer. Plea1e Note: Resellers have to pay the cost of freight and insurance and therefore the prices charged by ind ividual Dealers may vary slightly from this Catalogue - in many cases, however, Dealer prices will still represent a significant cost saving from prices charged by Altronics Competitors. Don't forget our Expreu Mall and Phone Order Service • for the co1t of • local c■ II, Bankcard, Vlea or Ma1tercard holders can phone order for Hme day de1patch. If you have a Retail Shop, you could increase your income significantly by becoming an Altronics Dealer, Phone Fred Bloffwitch (09) 328 2199 for Details. WA COU NTRY ALBANY BP Electronics ■ 412681 ESPERANCE Esperance Communications 713344 GERALDTON K .B .Electronics & M a rine 212176 KALGOORLIE Todays Electronics ■ ·212777 KARRATHA Daves Osc l tronics 854836 MANDURAH Lance Rock Ret ravision 351246 NEWMAN Watronics 751734 WYALKATCHEM D & J Pease 811132 ALICE SPRINGS Ascom Electron ics 521713 Farmer Electron ics 522967 ACT CANBERRA Bennett Commercial Electronics 805359 Scientronics 548334 CITY Active Wholesale ■ 6023499 All Electr o nic Components 6623506 SUBURBAN ASPENDALE Gilt ron ics 5809839 CHELTENHAM Talking Electronics 5502386 CROYDEN Truscott El ectronics ■ 7233860 PRESTON Preston Electronics 4840191 COUNTRY BENDIGO KC Johnson ■ 411411 MORWELL Morweli Electronics 346133 SWAN HILL Cornish Radio Services 321427 S CITY Deisound P/ L 8396155 SUBURBAN FORTITUDE VALLEY Economic Electronics 2523762 SALISBURY Fred Hoe & Sons Electronics 2774311 WOODRIDGE David Hall Electronics 8082777 COUNTRY CAIRNS Electronic World ■ 518555 BUNDABERG Bob El k ins Electronics 721785 GLADSTONE Supertronics 724321 MACKAY Philtronics ■ 578855 NAMBOUR Nambour Electronics 411604 PALM BEACH The Electronic Centre 34 1248 ROCKHAMPTONAccess Electronics (East St. ) 221058 Electron World 278988 Purely Electronics (Shopping Fair) 280100 Xanthos Electronics 278952 TOOWOOMBA Hunts Electronics ■ 329677 TOWNSVILLE Solex ■ 722015 SA CITY Electronic Comp & Equip. 2125999 Force Electronic ■ 2125505 SUBURBAN BRIGHTON Force Electronics ■ 2963531 CHRISTIE$ BEACH Force Electronics ■ 3823366 ENFIELD Force Electronics ■ 3496340 FINDON Force Electronics ■ 3471188 PROSPECT Jensen Electronics ■ 2694744 COUNTRY MT.GAMBIER South East Electronics 250034 WHYALL A Eyre Electronics ■ 454764 TASMANIA HOBART George Harvey ■ 342233 LAUNCESTON Advanced Electronics 315688 George Harvey ■ 316533 Nichols Radio TV 316171 NSW CITY David Reid Electronics ■ 2671385 SUBURBAN BLACKTOWN Wavefront Electronics 8311908 CARINGHAH Hicom Unitro ni cs 5247878 LEWISHAM PrePak Electronics 5699770 SMITHFIELD Chantronics 6097218 COUNTRY ALBURY Webb ' s Electronics ■ 2540 66 COFFS HARBOUR C oifs Habour Electronics 525684 GOSFORD Tomorrows Electronics ■ 247246 NELSON BAY Nelson Ba y El ec tr o nics 813685 NEWCASTLE Novocastrian Elect.Supplies ■ 621358 NOWRA Ewing E l ectronics ■ 218412 RAYMOND TERRACE Alback Electronics 873419 TENTERFIELD Nathan Ross Electronics 362204 WINDSOR M & E Electronics ■ Communications 775935 WOLLONGONG Newtek Electronics • 271620 Vim com Electroni cs 284400 Blue Ribbon Dealers are highl ighted with a ■. These Dealers generally carry a comprehensive range of Altronic products and kits or will order any required item for you. Double or quits Yes, this situation could easily toss you. How many things can go wrong with what should be a relatively straightforward service job? If you think you've been there, and know the answer, this story might well make you think again. This is not my story, but is from one of my regular correspondents, J.L., of Tasmania. More precisely, it is really two stories about the same set and, to further confuse the issue, also contains a story from my own bench covering a virtually identical problem. This is how J.L. tells it. J.L.'s first story A customer recently brought in two identical AW A sets; a rather rare occurence, but it was too much to hope that they would both have the same fault. They didn't. They were models C608; 48cm sets fitted with the Mitsubishi "G" chassis. The fault in the first set was so . simple that I can't remember what it was. The second 24,0V, 56 A one was a different story. The set was shut down and the 103V rail was up to 120V plus. There was no voltage on the collector of the horizontal output transistor, nor were there any subsidiary rails operating. Quite obviously, the horizontal stage was not working. As I tried to trace the course of the main rail towards the horizontal output transistor, I wondered why these sets didn't fail more often. They are a maze of plug and socket connections, any one of which can cause trouble. From the regulator board the main HT (103V} rail passes through an unreliable edge connector into the main board. It then goes into and out of a link in the deflection "'"'1,,'J; ~OOt> CA~AC\T'OP-, ?V,- ACROSS SHOUL-'t> S-rAV a>OL At-l.- t>A.V••• SILICON CHIP toss ya! yoke plug (DY}, back into the main board, via plug MF to the horizontal output transformer (Pin 3}, from pin 2 to PCB-FR via plug EA, through fuse F591 (1.6A}, then back to the main board via plug MA. Finally, it goes via plug MB (pin 1} to the collector of the horizontal output transistor. (See accompanying circuit, with path picked out in colour}. I was able to trace the HT voltage up to the fuse F591, but no further. The fuse was open circuit, but did not appear to be blown, just broken. I hoped it might be a spontaneous breakdown - but I should have known better. I fitted a new fuse and switched on. There was a rush of sound and I thought I heard a burst of EHT. But only for a second. The new fuse failed with only the tiniest flicker. There was obviously an overload, but only a small one - and that meant it was going to be hard to find. I started at the horizontal output transistor. This item unplugs easily for testing, but in this case it was a waste of time; the transistor was perfect. But I changed it anyway. Rather than blow another fuse, I connected a 1.5A thermal cutout in its place and tried again. I had sound and a trace of EHT for a couple of seconds before the cutout tripped. Which confirmed that the horizontal output transistor was intact and trying to function. The next items on the "output" side of the fuse are four flyback tuning capacitors, C531 to 534 inclusive. Two are rated at 2kV each and the other two at 630V. It's hard to measure leakage on high voltage caps with an ordinary multimeter so my trick is to put them across 240V AC and see if they get warm. A good capacitor should stay cool all day and these four passed the test. The last item on this board is --------------· ----------· J405 ZSC9l6 81< 12sc 1 5tA V.OUT 'tI I s,oE·' I ,...!181 :g-L .l ~ ~i~ l ---Pr-<. . •-•;~;;, 1':f'"'"""" ,w ~ -:. ' r-'V'\/\r 0~9l "4VT • lOS 115U 200 .,. UNIT-HV-RECT Fig. 1: horizontal output stage for the Mitsubishi C608 "G" chassis. The orange overprint shows the tortuous path of the main HT rail from the regulator hoard to the horizontal output transistor. boost diode D531. I checked it for leakage using 30V from the bench power supply and could detect no sign of leakage. It's not a perfect test, considering the voltage they have to withstand, but at least it's a guide. Tracking back from this board, via plug MB, I came to diode D571, a high voltage type that supplies 800V to the picture tube screens. This rail is bypassed by three 1µF, 450V electros in series. Considering that low voltage electros are unreliable beasts, I was prepared to find one, or all, leaky. I also suspected the diode. These capacitors and diode were as far out of reach as any windscreen wiper motor you have ever seen. They were tucked away on the main board, underneath the "tower" that supports the entire horizontal output stage, board, transformer, tripler, etc. The diode and two capacitors were on top of the board and one capacitor underneath. To make matters worse the underside of the board had been covered with some kind of goo which resembled anti-vibration compound used in cars. Before I could unsolder any joints I had to peel, scrape, and brush this goo away using Shellite and a stiff bristle brush. I eventually unsoldered the underside capacitor and freed the other two and the diode, but I could not get these latter out from under the "tower". This is held to the chassis with only three screws but also involves plugs EA, ED, MA, MB, and MF, plus the focus and EHT leads to the picture tube. Of course, after all that, all four items checked out perfectly. And those were the last items on the HT rail. So what was loading this section of rail? The only answer seemed to be the horizontal output transformer shorted turns? - or a faulty tripler. I disconnected the tripler from the transformer, then switched on while watching the fuse. It didn't blow, and there was a very healthy corona around the bare lead on the transformer overwind. So it was a dodgy tripler. This presented several problems. First, it was going to be an expensive repair. Second, I had been told that these units were no longer available. And, third, the UNIT-HVRECT , as Mitsubishi calls this assembly, incorporates the focus resistor chain and a very large Z00MQ bleed resistor. This makes any idea of a tripler substitution a very dicey one. I asked around among my colleagues whether anyone had ever fitted a substitute tripler to a "G" chassis. No one had, but they couldn't think of any reason why it wouldn't work. So I resolved to give it a try. I separated the rectifier unit from the focus and bleeder resistor unit, and found that there was room to mount a common tripler on the plastic casing of the focus unit. Everything went together nicely, but I deliberately left the bleeder resistor disconnected at this stage. Time enough when I knew it was going to work. Fortunately, I didn't fit the ultor MAY 1988 57 SERVICEMAN'S LOG srr ..... ,,.. L.-OC>Ks t\S -m()C.)(p'"' 9™tc: w,u_ g e:G,.O N\& ~"10"n\E,1\. '"ru"'1"-\ £. ..... cap to the tube. I brought it outside the cabinet and poked the high voltage probe into it. Then I switched on. To say that it worked would be the understatement of the year. The meter needle slammed hard against the 30kV stop and a loud zzzzz came from the ultor cap. I switched off hurridly. At this point it looked as though the bleed resistor was an essential part of the system. I carefully exposed the wire in the EHT lead, attached the resistor to it, then wiped a generous layer of silastic over the joint and left it to cure. I added another layer the next day and by the third day I was ready for another test. This was just as dramatic as the first. A bit slower, perhaps, but just as violent. Then I did what I should have done in the first place - looked more carefully at the schematic diagram of the "tripler". Had I done so I would have seen that the HV-RECT contains only three diodes. And three diodes don't make a tripler. I had replaced a voltage doubler with a tripler. No wonder I had excess voltage. So, with no HV-RECT units available, it looks as though the set 58 SILICON CHIP will become another junkie, useful only for whatcan be salvaged from it. I have yet to tell the customer the bad news. My story Well, that's the first part of J.L.'s story, and this would seem to be an appropriate time to take a break and consider what Yours Truly was doing during this time. In fact, my story would have started rather earlier than J.L.'s because I encountered several long waiting periods but, unfortunately, neither of us knew what the other was doing. My story is also about a "G" chassis, but in my case it was a model C609, 33cm set. And the symptoms were almost identical with those observed by J.L. But I was lucky. According to Murphy's Law, whichever end of a chain one elects to start from, it will always be the one furthest from the fault. Murhpy knows this and I know this. But on this occasion Murphy reasoned that I would reason, that Murphy would reason ... well you know what I mean; I beat Murphy at his own game. I took a punt on the transformer/tripler end of the string and picked it in one. It was the tripler - or what I believed to be a tripler at the time. I was lucky in another way too; nobody had told me anything about any shortage of triplers and, since the Mitsubishi Electric AW A spare parts division was only a 20c untimed phone call away, I simply dialled the appropriate number. When I told the bloke at the other end I was interested in a tripler for a "G" chassis, he didn't hesitate. "Yes we can supply a replacement high voltage unit for a "G" chassis exstock. It'll cost you about $70 plus tax. I can give you the exact figure in a moment.' ' I thanked him and said that would be near enough for now. I still had to get the customer's OK. The $70, plus Mr Keating's cut, would put the price over the $100 mark which, with my service fee, would make it a fairly expensive repair . Naturally, I didn't expect the customer to be too happy about the cost, but I didn't expect he would knock it back. But he did. He reckoned it wasn't worth it and that he'd rather put the money towards a new set. I didn't argue, of course - it was his decision. I simply told him that he could pick the set up any time, no charge. I put the set in the store room and more or less forgot about it for several weeks. Then, meeting the customer in the street, I reminded him that I still had his set. "Yeah, I must collect it sometime.' ' He didn't sound very convincing and, in fact , this episode, with variations, was repeated several times over the next couple of months until, eventually, it became obvious that he had no intention of collecting the set. Well, that suited me fine ; I had my own plans for it. More specifically, I needed another workshop monitor for VCR servicing and, if I could salvage this set for $100, it would be ideal. It's not a tripler So I placed an order and the new unit arrived in a couple of days. And it was only then that I realised that it was a substitute device, needing a moderate amount of mechanical modification to the chassis to accommodate it. And ~ \UF\S A 1\\00SHT ~ also that it was a doubler rather than a tripler. Thus prompted I looked at the circuit again and it became obvious that it could not possibly be a tripler. Anyway, the new unit was duly fitted without any serious problems, the set switched on, and up came a first class picture. It was as simple as that. So it was with some surprise that I read J.L.'s story, set out above, which came to hand shortly after. In particular I was surprised to learn that there was a supposed shortage of doublers for the "G" chassis, since I had just bought one. I realised that it could be a different type, being for a different size picture tube and, at the first opportunity, I checked with the Mitsubishi spare parts division. In fact, it is different, but I was assured that there were ample stocks of this model. I was on the point of writing to J.L. - in fact I had drafted a letter - when a sequel to his first story came to hand. This is how he tells it. J.L.'s second story When told the bad news about his set [that it was unlikely that I 1WSH 0,: SOONt) ANO "! \EA~O P. ~ OF ~ ' - • • could obtain the necessary part), the owner's response was quite unexpected. He had a special reason for wanting the set repaired and was prepared to spend up to half the cost of a new set to this end. I was to make any reasonable effort to get a new part, or a second hand one as a last resort. The first thing I did was borrow the doubler from the customer's other set and try it in the dud set. It came good immediately, the picture tube was in excellent condition, and a new doubler would make the set as good as new. I put in a call to Mitsubishi AW A spare parts in Sydney and, to my surprise, was told that, "Yes, 'G' cha ssis high voltage units are available" . There would be no change out of $100, but it was available, contrary to what I had been told earlier. I checked with the customer, then placed the order. When it arrived I was shocked to find that it was the wrong type; it was for the later "K" chassis, not the "G" chassis. I was about to throw a tantrum when I picked up what I had thought was an invoice and found that it was an instruction sheet on how to fit this doubler to a "G" chassis. There were 11 separate instructions on the sheet, mainly involving drilling various mounting holes and re-arranging the focus and earth wiring. It is a rather awkward arrangement with the focus control tucked away inside the set, but it does fit. Volts but no picture At switch-on the new doubler worked like a charm. There was EHT and sound and I waited for a picture to appear. But after two minutes there was no more than a few coloured specks , and occasional picture highlights. From these prelimina ry, clues I deduced that the problem might be around the video output stages. The meter showed 140V on the picture tube cathodes, some 30V higher than the figure on the circuit diagram. This same voltage appeared on the output transistors ' collectors and was very close to the B3 rail voltage which supplies them, suggesting that they were not turned on. The voltages at the base and emitter of these three sta ges were also higher than normal but, significantly, were the same for base and emitter. The absence of M AY 1988 59 the normal 0.6V difference between of electrolytics and resistors which these elements supported the idea were marginally off, but achieved that the transistors were not turned nothing. In desparation I rang a colon. league who I knew had a good "G" The base voltages for these three chassis and arranged to borrow the stages are derived from the colour video board from it. difference stages - Q619, 620 & I was shocked to find that this 621 - on the chroma board. These board was only a little better. There are driven, in turn, via coupling was now a picture outline and betcapacitors C621, 622 & 623 from ter highlights, but it was still far pins 1, 2 & 4 of the chroma IC from right. (IC106). The three coupling capacitors were in good condition, so the wrong voltage was arising 411: after the IC. This left Q619, 620 & 621, plus the DC clamper as possible suspects. The emitter voltages for the three \ stages are applied via a direct coupled network that goes back ' almost to the video detector. Included in this network is the second ' video amplifier (Q202), the ~ . \ luminance delay line (D1202), the video buffer (Q206), and the third video amplifier (Q203). The signal then passes via switch S20~ to the ~•--'---"'emitters of the output transistors. ~ .. Also associated with this net- '----__,.._..._. ► work is an automatic beam limiter t W~ Pl\Q\M' ,O '™tM ~ stage, QZ04, which funtions by if:\tJThUM Wli\£1\J RXJt\lt) .... varying the bias on Q203, in response to a voltage derived from 'M& INVO\CE WAS ~N pin 6 of the horizontal output , NS°TRvC1'"cO~ SMEJ:..'"\ ••••· transformer (T591). This varies the amplification of Q204, the bias on the picture tube cathodes, and the Comparing both boards revealed diode and a larger capacitor. I beam current. only one significant difference: the altered my board accordingly and Strangely, it was only the emitter network R208 and C203, between was rewarded with a similar order voltages on the three video output of improvement. the video buff er and the third video transistors which were significantMore importantly, the modificaly wrong. The colour difference out- amp, had been changed in my colleague's board to include an extra tion had somehow changed the puts were correct, as were the voltage levels around the the beam voltages on the bases of the three limiter, Q204. This suggested that it output transistors. Again, in the was a beam limiter fault but, also, TETIA CORNER video chain, all voltages were close that it might not be on the video to correct and the oscilloscope Philips K9 chassis board. This would account for both showed that all seemed to be proSymptom: One colour missing boards seeming to be faulty when cessing video normally. completely. Output stage voltages they had worked previously. It was only when I checked the are normal, as are the grid and Control voltage for the beam waveforms more carefully that I cathode voltages on the picture limiter is generated across R272 realised there was something · tube base board . The G2 voltage and R274 in parallel, these being wrong. The level at the delay line for the missing colour will be low, connected to pin 6 of the horizontal input was about normal at 3V p-p, although there is no measureable output transformer and diode D595 but at the output of the third video leakage on the rail. and C594 between pin 6 and amplifier it was les.s than half the Cure: the beam switch on the conchassis. Diode D272 is suitably ..6.5V p-p shown in the diagrams. vergence board has developed a biased to prevent this voltage leakage path at high voltage. The reaching the limiter transistor until easiest repair is to remove the Lost gain a certain critical level is exceeded. switch and bridge the appropriate I went right over this network, but Clearly, the video amplifier had pads. The switch is not essential to found nothing wrong. lost a lot of gain. Yet I could find the operation of the set. In desperation I tried to brute nothing wrong. I changed a number ,·~ __ _ _L.J_\~-- ,·.. \ ' . ' - ni~T 60 SILICON CHIP r force a change in voltage levels from the limiter transistor onwards. To turn the third video amplifier on harder I patched a 22kf! resistor from base to chassis - and was rewarded with an immediate increase in screen brightness. But the picture was still so washed out as to be virtually useless. This agreed with the very low amplitude video signal that I had noted on the CRO earlier, and convinced me that it was the beam limiter system that was falsely biasing the video stage. There aren't many components in the beam limiter circuit. I checked them all and found nothing wrong. Finally, I came to a conclusion that I should have reached hours before. Near the beginning of this story I mentioned that the set had worked perfectly with a borrowed doubler. Nothing had changed since then, so it should still work perfectly with an original "G" chassis doubler. Therefore the problem must due to the new "K" chassis doubler. Perhaps this unit is not a direct substitute for the original. Perhaps there is something different about it which has to be allowed for. Granted, the modification notes are purely mechanical, with no mention of electrical changes. But this would not be the first time that essential information has been omitted from such notes. The service manual decription of the beam limiter action suggests that the key voltage is that at the junction of R272/274 and diode D272. The limiter bias on Q204 varies with this voltage, so I decided to change it and see what happened. The easiest way to do this was to remove one of the two resistors. This would increase the resistance and indicate in which direction the change should go. With R272 out of circuit the picture became much darker, so this was the wrong way. R272 is 180kf! so I replaced it with lO0kf! and achieved an immediate improvement. I continued reducing R272, each time getting a brighter picture until finally, at 33kf!, I had a perfect picture with a small reserve in the brightness control range. It is not my usual practice to re- design a set while I am repairing it. I normally acknowledge that the original designer knew better than I what value should be assigned to each component. Yet there are times, like this, when what looks like a communications breakdown leaves me wondering just who is responsible for advising of changes in circuit values. In this case it appears that the replacement doubler has significantly different characteristics, requiring a change in external circuit values to achieve correct operation. The trouble is, the hours it took me to solve this problem are not chargeable to anyone. I have to bear the cost and hope that a similar job comes to light in the future to help me recover some of the losses. Conclusion Well, that's what happened to J.L., and it's not a pretty story. Not to put too fine a point on it, somebody goofed and, in my book, it wasn't J.L. Remember that J.L. had been able to test the chassis with a known good doubler and establish- ed that there was nothing else at fault. So what went wrong? J.L. suggests that Mitsubishi neglected to include all the information covering the substitution; ie, the information was available, but not enclosed. My bet is that the information was not enclosed because it didn't exist. Could it be that someone had established that the "K" type doubler could be used with the "G" chassis, but only on the basis of a trial in one, or perhaps two, "G" chassis types? While all " G" chassis are basically the same there are minor differences according to the size and type of picture tube used. As well as whole range of picture tube sizes, some sets use the delta gun tubes, others the in-line gun version, and EHT and other element voltages are provided to suit. So was the model C608 the odd one out, unable to accommodate a slightly different EHT voltage and/or loading created by the substitute doubler? I don't know, but I'd like to find someone who does. ·~ MAY 1988 61 High perforinance design has special SOMCCAR This ultrasonic movement detector can be added to your house or car alarm system, or can be used as a selfcontained ultrasonic car burglar alarm. By BRANCO JUSTIC The unit to be described here is a proven performer. It's easy to build, does not require any alignment, and has been field tested in several cars. It's also extremely sensitive and will instantly respond to the opening of doors, glass breakage or movement anywhere in the vehicle. Unlike other ultrasonic alarms published in the past, this unit includes special circuitry to guard against false triggering. We'll talk about that feature a little later on. There is also full provision for back- up battery operation, a flashing dashboard light and two separate instant trigger inputs which can be wired to bonnet and boot switches. A single control line is used to enable and disable the circuit. This line can be controlled by a simple mechanical switch, by relay contacts, or by digital logic circuitry. If you wish, you can easily add the UHF Remote Switch described in the March issue of SILICON CHIP. This will let you switch your ultrasonic alarm on and off simply by pressing the button on a small keyring transmitter. Another possibility is to use the ultrasonic movement detector as a sensor for the Protector Car Burglar Alarm. In that case, you would simply feed the output of the ultrasonic movement detector to one of the inputs on the Protector, instead of to an external siren circuit. By combining the two units in this way, you will end up with a comprehensive car burglar alarm with features to rival any commercial unit. Crystal control All ultrasonic movement detectors include an oscillator circuit which drives an ultrasonic transducer element, generally at 40kHz. Many designs use freerunning RC oscillators but these can lead to all sorts of problems, in- This version includes the optional lamp flasher/battery back-up circuit and can be used as a self-contained car burglar alarm. The two transducers are fitted with rubber spark plug covers and spring steel clips which attach to the windscreen pillar trim. 62 SILICON CHIP circuitry to stop false triggering BURGLAR ALARM eluding loss of sensitivity as the oscillator drifts and false triggering due to amplitude and phase changes. The design described here solves those problems by employing a crystal locked oscillator. This allows extremely high sensitivity settings without false triggering problems. As a bonus, it eliminates the need for critical frequency adjustments during construction. We'll talk more about the crystal oscillator later on in the circuit description. How it works Fig.1 shows the circuit details. In brief, it works like this: oscillator IC2a-IC2d provides a 40kHz drive signal to the transmitter transducer (Tx) which generates the ultrasonic output signal. This signal is picked up by the receiver transducer (Rx) and undergoes two stages of amplification (ICla and IClb) before being detected by Dl. In a still environment, a steady DC signal appears at the output of the detector. When movement occurs, the detector output varies accordingly and these amplitude variations are coupled to low frequency amplifier stage IClc which then triggers a monostable consisting of ICZe and ICZf. The monostable then drives switching transistor Ql which can be used to activate an external alarm circuit or to trigger an external relay. Let's now look at the circuit in more detail. The transmitter section employs four inverters (IC2aIC2d) in a 4049 hex inverter package. ICZd is biased in the linear mode by the 270k0 resistor and its output also biases ICZc in the linear mode. Thus, ICZd and ICZc form a linear amplifier with an overall phase shift of 360°. The 40kHz crystal forms part of the If you wish, you can build the circuit and transducers into a plastic case for installation on the dashboard or the rear parcel shelf. This version can be used as a movement detector for an existing car or house alarm. The two transducers can be soldered directly to PC stakes on the PCB or connected via shielded cables. The LED turns on when movement is detected. feedback path between input and output and so the circuit oscillates at the crystal's resonant frequency - ie, 40kHz. Note the lOOkO a nd 27k0 resistors on pin 13 of ICZc. These form an attenuator circuit which prevents excessive drive voltage from being applied to the crystal. Inverters ICZb and ICZa buffer the oscillator output and produce complementary 40kHz output signals (ie, signals that are 180° out of phase with each other). These complementary signals are then used to drive the 40kHz transducer. MAY 1988 63 .,. + 1M +9V +12V .,. 100+- 0.11 LINK D3 1N4148 +12V 08 1N4004 t + 10M 1+ 27k D6 1N4148 100k OUTPUT TO RELAY/ALARM -:- -:- D4 1N4148 220!l + TO DISABLE -:- B t SEE TEXT 1NOouT EOc GNO VIEWED FROM BELOW ULTRASONIC MOVEMENT DETECTOR/ALARM Fig.1: 40kHz signals from the transmitter (IC2a-lC2d) are picked up by the receiver, amplified by ICla and IClb and detected by D1. When movement occurs, the output of IClc swings high and triggers an output monostable (IC2e and IC2f). Because the drive signals are out of phase, the peak-to-peak transducer drive voltage is approximately twice the rail voltage; ie, 18V p-p. Receiver The 40kHz signal from the transmitter is picked up by the receiver transducer and applied to a low pass filter (lkQ and 680pF). From there, the signal is fed to sensitivity control VRl before being AC-coupled to the inverting input of op amp stage ICla. ICla and ICl b form two identical amplifier stages with each stage having a gain of 37, or 31dB. Thus, 64 SILICON CHIP the overall gain of these two stages is 62dB. The 2.2pF capacitors across the lMQ feedback resistors roll off the gain of each op amp stage above 70kHz. The amplified output from ICl b appears at pin 4 and is fed to diode detector Dl. Dl 's output, in turn, is fed to a low pass filter stage consisting of the lOkQ and lO0kQ resistors and a 0.1µ,F capacitor. This detector/filter circuit produces a varying output voltage when movement is detected and this signal is AC-coupled to lowfrequency amplifier stage IClc. IClc also has a gain of approx- imately 30dB and a bandwidth of approximately 230Hz. Its output, which is normally biased low, is fed to a "charge accumulator circuit" consisting of a lOkQ resistor, diode DZ, a 1µ,F capacitor and a lMQ resistor. This circuit allows rapid charging of the 1µ,F capacitor (via the 10kQ resistor) when IClc's output swings high (ie, when movement is detected), with the lMQ resistor then discharging the capacitor over a much longer period of time. Because it takes a relatively long time for the capacitor to discharge, the inclusion of this circuitry prevents the alarm from false trig- + 0-/41+-'W,h-il_ _ _ _....,._....,....._...---.--......--......--O.ULt moTN~C FROM ALARM VEHICLE 100 + SUPPLY 16VW _ D2 22 {1 1N4004 -.i 1W BACK UP BATTERY + +12V VIA IGNITION SWITCH GNi ., B ELJc VIEWED FROM BELOW Fig.2: this is the optional lamp flasher/battery back-up circuit. When the ignition is off, 555 timer ICl drives Q2 and the lamp at a lHz rate. When the ignition is turned on, Q2 turns on and disables the 555 timer. gering on noise or other brief disturbances. At the same time, it has no affect on the unit's sensitivity in a practical situation. Inverters IC2e and IC2f and their associated components form the output monostable circuit. This circuit monitors the voltage across the lµF capacitor via diode D3. Here's what happens: Normally, pin 7 of IC2e is low and pin 6 is high and so both sides of the 22µF capacitor are at + 9V. This means that the output of the monostable (pin 4 of IC2f) is low and thus Ql is off. If movement is detected, the output of IClc swings high and charges the lµF capacitor via DZ and the 1okn resistor. When the voltage across the lµF capacitor reaches approximately + 5V, pin 6 of IC2e goes low and this pulls pin 5 of IC2f low via the 22µF capacitor. Pin ·4 thus switches high and turns on Ql and indicator LED 1. At the same time, the monostable latches up via diode D4 which connects the output (pin 4) back to the input, pin 7. The monostable timing period now commences, with the 22µF capacitor charging towards the + 9V rail via the 10Mn timing resistor. After about two minutes, the voltage on the capacitor reaches + 4.5V and pin 4 of IC2f switches low again, thus turning off Ql and the indicator LED. Alternatively, if the link is installed, the monostable timing period is PARTS LIST 1 PCB, code OE102, 129 x 62mm 1 pair of 40kHz ultrasonic transducers 1 40kHz crystal 1 6-way PC-mounting terminal block 4 PC stakes 1 plastic case to suit Semiconauctors 1 CA3401 quad Norton op amp 1 4049 hex inverter IC 1 BC337 NPN transistor 1 78L05 3-terminal regulator 1 1N4004 silicon diode 7 1N41 48 silicon diodes 1 5mm red LED Capacitors 2 100µF 16VW PC electrolytics 2 22µF 16VW LL electrolytics 4 1µF 1 6VW LL electrolytics 2 0. 1µF ceramic 7 680pF ceramic 2 2.2pF ceramic cut to one second, as set by the 10okn resistor. The link should be installed during testing, or if the ultrasonic movement detector is to be used as a sensor for another alarm circuit. There are a couple of other details in this part of the circuit that remain to be discussed. First, when Ql turns on, it quickly discharges the lµF capacitor via Resistors (0.25W, 5%) 4 x 1 oMn , 5 x 1 Mn, 1 x 21okn , 5 x 1 00kn, 5 x 27 kn, 7 x 1 0kn, 1 x 1kn, 2 x 220n, 1 x 150n , 1 x 4. ?kn horizontal trimpot Lamp Flasher/Backup Battery Circuit 1 1 . 2Ah gel battery 1 '8-way PC-mounting terminal block 1 1 2V bezel lamp Semiconductors 1 555 timer IC 1 BC327 PNP transistor 1 BC548 NPN transistor 1 15V 1W zener diode 2 1N4004 silicon diodes Capacitors 1 100µF 16VW electrolytic 1 22µ,F 16VW electrolytic 1 .01 µ,F ceramic Resistors (0 .25W, 5 %) 2 x 22kn, 2 x 1 0kn, 2 x 1kn, 1 x 22n (1W), 1 x 4.7n (1W) D5 and its series lOkn resistor. This effectively resets the trigger circuit. Second, if a voltage of 6V or more is applied via diode D7, the output of IC2f remains low and the alarm is unable to respond to received signals. This is the DISABLE input. In practice, the anode of D7 can be switched to the + 12V rail to disable the alarm. This is made MAY 1988 65 ... w ,z ~ 3: "' et 12V o ~ s ~ CUT PCB HERE IF REQUIRED I= - + + s z t LINK FOR DETECTOR (1 s). OMIT FOR ALARM (2m). i 40kHz TRANSMITTER Fig.3: the PCB layout includes both the alarm circuit and the lamp flasher/battery back-up circuit. The transmitter is wired using twin-core shielded cable while the receiver is connected with single-core shielded cable. possible by the inclusion of D6 which clamps the input of IC2f to the + 9V rail. Protection for the bonnet and boot is provided by the two instant trip inputs. These inputs are each coupled via a lµF capacitor and a common low pass filter network to the inverting input of IClc. Shorting either input to ground briefly pulls pin 11 of IClc low and instantly triggers the alarm. Power for the circuit is derived from the vehicle's battery via a 78L05 3-terminal regulator (which is the low power version of the familiar 7805). The combination of the two resistors associated with the 78L05 jacks its output up to + 9V. The associated lOOµF and 0.lµF capacitors provide supply line decoupling. Lamp flasher circuit Fig.2 shows the optional lamp flasher and battery back-up circuit. In this case, power from the vehicle's battery is derived via isolation diode D1 and a 4.7n resistor. Diode D2 isolates the optional back-up Where to buy the parts Parts for this project are available from Oatley Electronics, 5 Lansdowne Pde (PO Box 89), Oatley, NSW 2223 . Telephone (02) 579 4 985 . Prices are as follows: · PCB plus on-board parts fpr ultrasonic movement detector section only (excludes ultrasonic se nsors) ...... .... ........ .. .. .. ..... $2 5 .90 On-board parts plus bezel lamp (no PCB) for the lamp flasher/battery backup circuit ...... .. .. .... .. ...... .. .. .. .. .. .. .. .... .. .... .. . $ 7. 50 40kHz ultrasonic transducers (pair) .... .. .... .. ...... .. .. ...... .... .. .... . $ 1 3 .50 Pair of transducer covers plus spring steel wire .. .......... ..... ... ... .. $2. 50 12V 1.2Ah gel battery ........ ... .. .. .......... .. .. .. ..... .. .... .. .. .......... $24 .90 Relay kit (includes PCB, relay and standoffs ) .. .. .. .. ...... .... ...... .. .. $3 .80 Note: copyright for the PCB artwork associated with this project is retained by Oatley Electronics. 66 SILICON CHIP battery, while zener diode ZDl protects the lamp flasher circuitry from spikes on the supply rail. Normally, D2 is reverse biased and the back-up battery is charged via the 220 resistor across D2. However, if the vehicle's supply is disconnected, D2 is forward biased and power is supplied to the alarm circuit from the back-up battery. ICl, Ql and Q2 form the lamp flasher circuit. It operates quite independently of the ultrasonic movement detector circuitry. When the ignition is off, the lamp flashes; when the ignition is on, the flasher circuit is disabled. ICl is a 555 timer wired in astable mode and oscillates at a frequency of approximately lHz (ignition off). Its pin 3 output drives PNP transistor Q2 which switches the lamp on and off. Alternatively, a high-intensity LED and a current limiting resistor could be used instead of the lamp. When the ignition is turned on, Ql saturates and pulls pins 2 and 6 of the 555 timer low. This immediately disables the 555, with pin 3 remaining high and Q2 and the lamp off. WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS ... WOOD FOR CHIPS .. . WOOD FOR CHIPS .. . WOOD FOR C LED DISPLAY SPECIALS SYDNEY'S MOST COMPREHENSIVE RANGE OF DIN41612 CONNECTORS? ~ ~ (t 0 "Cl 0 ~ ~ c It 0 "Cl 0 ~ ~ :t (.) It 0 "- Cl 0 ~ Geoff is now stocking most of the DI N41612 :E::::Et?S:5=2:i:iES:i::i:i:$~:iE:ii:: range of plugs and sockets . The coding for '!'"_ -_..,....._........,........,_ _ _ _ __ _........,__..l!i the uninitiated is as follows •· "" · There are three rows of pin locations A,B and C. £ indicates even pins only . The body size and number of pins is quoted SOCKETS each time thus 96/32 is a 96 hole body fitted BODY/PINS CONNECTION PRICE with 32 pins S64/32 A STR PCB $8.00 STR = straight connection RIA = Right S64/64 A+B STR PCB $13.65 angled S96/96 ALL STR PCB $16.35 PCB = circuit board mounting WW = Wire S96/32 A STR PCB $8 .00 Wrap S96/64 A+C STR PCB $12.55 PLUGS S96/32 A+CE STR PCB $8.00 BODY/PINS CONNECTION PRICE P64/32 A STR PCB $8.00 S64/32 A RIA PCB $8.00 P64/64 A+B STR PCB $12.55 S96/96 ALL RIA PCB $18.40 P96/32 A STR PCB $8.65 S96/64 A+C RIA PCB $13 .55 P96/32 A+CE STR PCB $8.65 S96/32 A+CE RIA PCB $8 .65 P96/64 A+C STR PCB $13 .55 S96/32 A RIA PCB $8.65 P96/96 ALL STR PCB $11 .45 S64/32 A STR PCB $8.00 A P64/32 RIA PCB $5.90 S96/32 A STR PCB $8 .65 P64/64 RIA $8.40 A+B PCB S96/32 A+CE STR PCB $8.00 P96/96 ALL RIA PCB $12.55 S64/64 ALL $13.55 STR PCB P96/32 A RIA $5.85 PCB S96/64 A+C STR PCB $11.45 P96/64 RIA $8.40 A+C PCB P96/32 A RIA PCB $6.40 S32/32 A STR WW $8.65 P96/32 A+CE RIA PCB $6.40 S64/32 A STR WW $8.65 P96/64 A +G RIA PCB $8.40 S96/32 A STR WW $8.65 S96/32 A+CE STR WW $8.65 P64/32 A $8.65 STR WW S96/64 A+C STR WW $11 .45 P64/64 STR WW $13.65 A+B S96/96 ALL STR WW $18.35 P96/32 A STR WW $10.65 S96/96 ALL STR WW $18.35 P96/32 A+CE STR WW $10.65 S96/32 A STR WW $8.65 P96/64 A+C STR WW $11.45 S96/64 A+C STR WW $13.65 P96/96 ALL STR WW $13.55 S96/32 A+CE STR WW $8 .65 Don't just ask Geoff for DIN41612... You'll find one of the widest ranges of HEADER PLUGS leading brands of connectors - ex stock - at 0.1" PITCH IDC CARD EDGE CONNECTORS 40way $11.55 50way $13 .95 $8.50 $9.40 IDC "D" CONNECTORS ~ It 0 "Cl 0 10way RIA 14way RIA STR 16way RIA STR 20way RIA 26way RIA 34way RIA STR 40way RIA STR SOway RIA 60way RIA Geoff Wood's . So call in and discuss your requirements! 26 way 34 way ~ Plug $6.40 Socket $6.40 1Spin Plug $7.60 Socket $7.60 25pin Plug $8.40 Socket $8.90 37 pin Plug $20.40 ~ 0.8" GREEN DISPLAYS 7 segment common cathode with R&L hand decimal points. Peak wavelength is 565µm If is lOmA (25mA max) Only a few available LTS3403 $4 .50 1.02" GREEN DISPLAYS 7 segment common cathode with R hand decimal point. Peak wavelength is 565µm If is 10mA (25mA max) Only a few available LTS1723 $5.50 $6.90 $7.65 $5.90 $4.20 $4.20 $7.65 $4.90 $6.20 $5.40 $8.55 $9.80 $10.60 $11.70 10way $3.55 14way $4.75 16way $4.70 26way $5.20 34way $5.70 40way $7.80 50 way $7.40 64way $14 .85 ~ 0 0 ..,, 0 J:) () :i: ~ 1.02" RED DOT-MATRIX DISPLAYS Anode column by cathode row dot matrix display with 35 leds . Peak wavelength is 655µrn If is 10mA (25mA max) Only a few ava ilable LTP1057 $7.50 10 POINT BAR GRAPH DISPLAYS Red, light red, green and yellow Extremely limited quantity only LTA1000 $4.50 ~~, 11 TRANSITION SOCKETS 9pin ~ ~ FND500 REPLACEMENT So many projects have used the popu lar FNDS00 led display . Alas the FNDS00 is no longer available. But Geoff has found a direct replacement - the LTS543 from Liton . And they're only B0cents each if you buy ten of 'em . But hurry I LTS543 $8.00/ten $1 .20 each. ~ j 11~ . f□OO~~O~ ',' 5mm SQUARE LEDS Parallel sides for easy stackability . Ch oice of three colours - red , light red and gree n - all at the same low price of 30c each ($2 .70 for ten all the same colour) And if you 're after 3mm Yellow leds they're just 20c each 1 PHOTO INTERRUPTER A real handy gadget for anyone into robotics . Consi sts of a LED(Max If 60mA ) and 30V phototransistor faci ng each other acro ss a 3mm x7mm gap. Any object in the gap stops the light and switch es the transistor off. Very fa st (5µs ). Easy to mount. Use in counting , position sens ing , tacho , opto ignition etc. \ You could pay more \ than twice Geoff's price of $4.00 each. ~ 0 0 ..,, 0 J:) () :i: 'i; (/) :"i: a 0 0 GEOFF WOOD ELECTRONICS PTY LTD ..,, 229 Burns Bay Road , (Corner Beatrice St.) INC IN Nsw Lane Cove West, N .S.W . P.O . Box 671 , Lane Cove N .S .W. 2066 0 0 Telephone: (02) 427 1676, Fax: (02) 428 5198. () Cl 8.30am to 5.00pm Monday to Friday , 8.30am to 12 noon Saturday. Mail Orders add $5.00 to cover postal charges . Next day d elivery in Sydney add $5.00. It "0 ~ All prices INCLUDE sales tax. Tax exemption certificates accepted if line value e xceeds $10.00. J:) :i: r"'=""°' ="= --,~,, --'S=-T -,1 TO I~ BANKCARD. MAS TE RCA RD. VISA. CHEQUES OR CASH CHEERFULLY ACCEPTED ~ BONNET 12V RELAY BOOT :.:5 +12 GROUND....,...._.-. +12V FROM BACK.UP BATTERY....;f--_;;;3A~l<N•L:::IN::JE~FU::SE_..;,+~----• cur• LINK• +12V VIA IGIITIOH SWITCH . FLASHER LAMP +12V TO ALARM CIRCUIT~ GROUND eg BA - ··· ·· · 0---+12V IGNITION SWITCH ~DASHBOARD • CHASSIS 1 ,e/ FLff~~R Fig.4: here's how to wire the unit as a self-contained car burglar alarm. In practice it would be best to delete the disable switch and use the UHF Remote Switch described in the March issue instead. The optional lamp flasher/back-up battery circuit has been deleted from this movement detector version. Angle the transducers away from each other as shown if they are soldered to the PCB. Construction All the parts are mounted on a printed circuit board (PCB) coded OE102 and measuring 129 x 62mm. The optional lamp flasher circuit is accommodated at one end of the PCB and this section may be separated from the main part of the board if not required. Two versions of the circmt can be built up: (1). An ultrasonic movement detector only, without the lamp flasher circuit. This version could serve as 68 SILICON CHIP a sensor for a house or car alarm (eg, the Protector Car Burglar Alarm described in the February 1988 issue of SILICON CHIP). The ultrasonic sensors could either be soldered directly to the PCB (eg, for use in a house) or connected to the PCB via shielded cables [for use in a car). (2). An ultrasonic detector/alarm for use as a self-contained car burglar alarm. In this version, the lamp flasher circuit would typically be retained and the alarm output used to trigger a relay to sound a siren horn. Both the above versions are shown in the accompanying photographs. Follow the parts layout diagram shown in Fig.3 when wiring up the unit. No special procedure need be followed here but make sure that all diodes, transistors, ICs and electrolytic capacitors are correctly oriented. Also, be sure to use the correct part at each location. Regardless of which version you build, the link in series with the lOOkO resistor should initially be installed. This will set the monostable period to about one second and make the unit much easier to test later on. If you are going to use the unit as a free-standing alarm, the link can be cut later on to extend the alarm time to around two minutes. Leave the link in circuit if you intend using the ultrasonic movement detector to trigger another alarm circuit. PC stakes are used to terminate the connections from the transducers, while PC-mounting terminal blocks terminate the remainder of the external wiring connections. Don't confuse the two transducers. The transmitter will be marked with and an "S" or a '·'-T" while the receiver will be marked • PROTECTOR CAR BURGLAR ALARM •• • +12V ;• ••• •• • • • • •9 INSTANT •10 DELAYED __-1 CHASSIS~ ' r - T O DISABLE OUTPUT OF UHF REMOTE SWITCH •• ~~Cl>Wf- ~::1~~~ ~~=+~= ULTRASONIC MOVEMENT omcTOR t INSTALL 6 LINK Fig.5: the ultrasonic movement detector can be used as a sensor for the Protector Car Alarm. Just follow the wiring diagram shown here. with an "R" or an "M". Damage may result if the transducers are interchanged. Note that the transmitter should be connected using twincore shielded cable. Rubber spark plug covers are used to cover the transducers as shown in one of the photographs. These are pushed over the transducers which are fitted inside coiled pieces of spring steel wire. The other ends of wires are shaped to clip onto the windscreen pillar trim. Testing This step is straightforward since no adjustment of the transmitter frequency is required. To test the unit, set the sensitivity control midway and connect up a 12V DC power supply. The unit should now be operational; ie, the LED should light for about one second whenever movement occurs. You can now check the alarm output by connecting your DMM between the OUTPUT terminal and The lamp flasher/battery back-up circuit can be used separately if required. ground ( - ve ). Set the DMM to the 20V range and check that the OUTPUT terminal switches from + 12V (nominal) to less than 1V whenever movement occurs . Installation Once assembly has been completed, the PCB can be installed in a suitable plastic case. We mounted the detector version in a plastic jiffy case, with cutouts to clear the LED and the two transducers. Alternatively, you can wrap the PCB in foam rubber and then "poke" the assembly into a suitable spot behind the dashboard. Use plastic cable ties to secure the assembly behind the dashboard. In many cars, you can gain access behind the dash panel by temporarily removing a loudspeaker grille and the loudspeaker. Fig.4 shows how to wire the unit as a self-contained car burglar alarm. Note that the disable switch will have to be mounted externally since the unit has no exit and entry delays. · A far better scheme would be to get rid of the disable switch altogether and substitute the UHF Remote Switch described in March 1988. It's really quite easy - just connect the disable output of the remote switch to the disable input of the ultrasonic alarm (see Fig.5). Fig.5 shows how to use the ultrasonic movement detector as a sensor for the Protector Car Burglar Alarm. In this case, the optional lamp flasher circuit is deleted from the movement detector and the + 12V supply is derived from terminal 7 or 8 on the Protector PCB. Connections to the remaining terminals on the Protector PCB are as shown in Fig.5, p.25 of the February issue. Fig.12, p33 of the March issue shows how to use the UHF Remote Switch to control the Protector alarm, instead of the original on/off switches. Finally, make sure that you install the alarm in a professional manner. Hide the back-up battery in the boot or some other inaccessible location, and use a crimp connector kit to correctly terminate the wiring leads. ~ MAY 1988 69 AMATEUR RADIO By GARRY CHATT, VK2YBX Designing and building attenuators Many people are haffled by the theory behind attenuator design hut once understood, attenuators can he easily made for most applications at minimal cost. This article outlines the theory behind attenuator design and provides practical guidelines for home construction. Basically, an attenuator is a network of resistors intended to produce a specific loss between a known source impedance and a kriown load impedance. Attenuation is normally expressed as a ratio in decibels, and is the same regardless of the direction of operation. Two basic forms of symmetrical resistive networks are available that can be used as attenuators. Although there are many other configurations that could be discussed here, this article restricts itself to easily constructed, symmetrical networks. These two configurations are called the "T"-section and the "1r" -section. Fig. l(a) shows the circuit for the T-section attenuator, while Fig. l(b) shows the 1r-attenuator. The value of both types Gan be calculated as shown. For the T-section attenuator with 50 ohms impedance: Attenuation in dB = 20 log (Rl + 5'0)/(Rl - 50) when R2 = (50 + R1)/2R1 T SECTION 7r SECTION (a) (b) Fig.1: circuit configurations for T·section (a) and 1r-section (b) attenuators. For the 1r-section attenuator with 50 ohms impedance: Attenuation in dB = 20 log (Rl + 50)/(Rl + 50) when R2 = 2 x 50R1/(R1 + 50) For those not mathematically minded, Fig.2 shows calculated resistance values for values of attenuation between 0dB and 40dB, for an impedance of 50 ohms. Multiply these figures by 1.5 to obtain 75-ohm attenuators and by 12 for 600-ohm attenuators. For fixed attenuators, intended for the lower frequencies (ie, from audio to 50MHz or so), the physical layout is of no real consequence. These " pads", as they are called, can be used between transmitter stages to stop interaction, to match levels, and to calibrate S-meters. Switched attenuators A more useful instrument is the switched or stepped attenuator, which can be used to insert preset amounts of attenuation while maintaining the correct impedance. Such a device is useful for evaluating the gain of antennas, preamplifiers and power amplifiers, for preventing receiver overload and for determining power amplifier compression. Once the required amount of attenuation is determined, a fixed value pad can be built into the equipment. At VHF and UHF, the techniques used in the construction of such attenuators become important. This is because the higher frequencies are prone to attenuation errors, due to stray coupling between stages. For this reason, it is better to cascade several stages having a lower value of attenuation, rather than use a single stage of high attenuation, as the coupling error will be a much smaller percentage of each stage. In practice, 20dB is the largest single step of attenuation achievable. At these higher frequencies , the OUTPUT INPUT SBG;fl 68Q ! 68i ? f Fig.3: practical design for a 50-ohm 8-step attenuator with an attenuation range from 1dB-80dB and an upper frequency limit of 450MHz. It should be built into a diecast metal case with shielding between stages to prevent RF leakage. 70 SILICON CHIP resistors must be non-inductive types such as carbon composition, or better still, cracked carbon. Fig.3 shows the design of a 50-ohm, 8-step attenuator having an attenuation range from ldB to 81dB and a useable upper frequency limit of 450MHz. Such a device can be used with a directional antenna to locate or track a hidden transmitter. The closer you get to the source, the more attenuation required to maintain the same signal level. ATTENUATION NETWORKS R1 I Attenuation dB 0 Construction The physical construction of a stepped attenuator for VHF and UHF use is important, and the following guidelines should be noted: (1). House the attenuator in either a diecast metal box, or fabricate the housing from double sided printed circuit board. Shields between the stages can be made from sections of double sided PCB, and can be soldered into place, or slid into the internal ribbing of the diecast box. (2). Use good quality connectors. Normally the most convenient type is BNC but ensure that it is the correct impedance and rated for RF operation. Avoid cheap video BNC connectors. (3). Use non inductive resistors. Remember that if you use quarterwatt types, the power handling ability of the attenuator without causing damage is one quarter of a watt! Parallel combinations of halfwatt resistors will give a higher power rating, but in all cases keep lead lengths to an absolute minimum. (4). It is preferable to use full size DPDT slide switches as they give greater isolation than smaller types. Subminiature toggle or slide types are not acceptable. (5). Ensure that your design is practical. It is extremely difficult to accurately provide more than 80 to 90dB of attenuation, as leakage around the outside of the unit will affect any measurements that are made. Design for the maximum practical attenuation you are likely to need. Use several smaller stages of attenuation rather than one large stage, and never attempt to exceed 20dB in one step. 11 11 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 11 .0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0 34.0 36.0 38.0 40 .0 R1 R1 IT 7r SECTION T SECTION 50 Ohms R1 0 0.298 0.568 0.86 1.15 1.43 1.74 2.02 2.29 2.58 2.87 4.32 5.73 7.16 8.56 9.93 11 .32 12.68 14.00 15.33 16.61 17.88 19.14 20.35 21.53 22.69 23.82 24.91 26.0 28.0 29.92 31.71 33.37 34.9 36.32 37.62 38.82 39.92 40.87 42.64 44 .07 45.22 46.17 46.92 47.55 48.04 48.42 48.76 49.01 50 Ohms R1 R2 00 4184 2190 1455 1089 872 720 619 545 482 434 287.7 215.2 171.1 i41.9 120.7 104.1 92.42 82.3 73.9 66.99 60.9 57.1 51 .3 47.3 43.75 40.6 37 .75 35 .13 30.62 26.81 23.57 20.78 18.37 16.26 14.41 12.71 11.37 10.1 7.99 6.3 5.02 3.98 3.17 2.51 1.99 1.58 1.26 1.00 0 0.6 1.14 1.71 2.29 2.87 3.47 4.04 4.59 5.19 5.72 8.69 11.62 14.62 17.71 21 .5 23.96 27.05 30.37 33.82 37.29 41.05 44.75 48.72 52.85 57.12 61 .57 66.2 71.17 81.65 93.25 106.1 120.2 136 153.9 173.6 195.3 222.5 247.5 312.7 394.7 498.75 629.2 791.7 994.2 1250 1580 1985 2500 R2 00 8375 4782 2908 2175 1743 1436 1240 1092 966.7 870 579.2 436 349.6 292.1 251.7 220.9 197.1 178.4 163 150.6 139.9 130.7 122.9 116.1 110.2 105 100.3 96.17 89.25 83.5 78.84 74.92 71.63 68.83 66.44 64.4 62.64 61 .11 58.63 56.73 55.28 54.14 53.27 52.57 52.03 51 .61 51.27 51.01 Fig.2: calculated resistance values for 50-ohm attenuators (0-40dB attenuation). The values are simply scaled for 75-ohm and 600-ohm attenuators. Component Suppliers (1). Cracked carbon resistors: Allen Bradley Pty Ltd, 22 Parramatta Rd, Lidcombe, NSW 2141. Telephone: (02) 648 2652. (2). DPDT slide switches: use 3PDT types from Dick Smith Electronics, Cat. No. S-1017, $2.99. it MAY1988 71 B 'Illf. PARTY LI Would you like some coloured flashing lights at your next party but con 't afford a full light show? Here's how you con modify a 12V-powered coloured strobe light to get a similar effect. By STEPHEN DAVID Modern rock groups certainly do make effective use of flashing light to create a good atmosphere for their performances. You can go part of the way to achieving the same effect by having flashing lights at your next party. There's no need to spend a lot of money on strobe lights though. You PARTS LIST 1 coloured strobe light (Arista WL3 or equivalent) 1 1 2V DC plugpack (battery eliminator) 1 1 MO pot, 16mm diameter 1 180k0 0.25W resistor 1 0.33µF 1 OOVW metallised polyester capacitor can modify a standard strobe very easily. The specific model we are talking about is an Arista product (Arista Cat. No. WL3) and sells for about $35. It is widely available from Arista outlets and has a fixed flash rate of about 120 flashes per minute. It runs from 12VDC, battery or mains plugpack, and draws about 150 milliamps. As it stands it can be used as a warning beacon on cars or boats, for shop displays, or as an exterior indicator for a burglar alarm. It has a screw-on lens cap which is available in red, orange or blue. And since it is intended for outdoor use, it is weatherproof. When we had a look at one of these units recently we thought it could be an attractive unit to ac- Modifying this commercial strobe unit to give a variable flash rate is simply a matter of adding a pot and two other components. company the music at a party. But the fixed flash rate would be a drawback; it would have to be variable. As it happens, that is easy. We'll show you how to install a variable flash control on the strobe. Then you can set it up next to your stereo system at a party, set the flash rate to match the music beat and dance away. How it works Before we tell you how to do the mods, let's have a look at the unit in its original condition. Pulling it apart is easy. Just unscrew the coloured lens cap and you'll see two small screws which retain the flat reflector underneath the Xenon discharge tube. Undo these two +o------------. 220 16VW 12V + 47 on w 01 2SC10 1N4002 D1 0.33 10 16VW o--11-ff-t-------+--l_ll+_....__ _ _ _ _ _ _ _ _...__~T._RI-GG_.ER_ _ ___._ TRANSFORMER PARTY FLASH __,:Jt MODIFICATION FOR ADJUSTABLE FLASH RATE Fig.1: the circuit of the Party Flash uses a ringing choke inverter to drive a Xenon flash tube. The parts to be added are on the righthand side of the diagram. 72 SILICON CHIP screws, lift of the reflector and a layer of insulation and you'll find the printed circuit board. The pattern side is uppermost, the components underneath. The full circuit is drawn out in Fig.1. It is a masterpiece of minimalist circuit design with only six active components, including the Xenon tube. Diode Dt is there to prevent the supply being connected up with the wrong polarity. So if you connect the supply the wrong way around nothing happens and nothing is damaged. The 220µF capacitor is there as a filter and reservoir to supply the DC to DC inverter. This uses transistor Qt and transformer Tl. Qt and TI comprise a "ringing choke" inverter which works in the following way. When power is first applied, base current flows via winding W2 and the 4700 resistor. This causes Qt to conduct heavily via Wt, so that the base end of W2 is swung up to + 24V. Then, when the current flow through Wt reaches its maximum value, the transformer action stops and the voltage across Wt suddenly collapses, turning off the base current to Ql. This turns off Qt and so the voltage across the windings is suddenly reversed. The process then repeats itself as conduction occurs via W2 and the 4700 resistor, Qt turns on, and so on. This all happens extremely rapidly, at several thousand cycles per second, which you can hear as a high pitched whistle. The voltage swing across winding Wt is stepped up in winding W3 and then rectified by diodes D2 and D3 to give about 400 volts DC across the 2µF 630V capacitor. This is the high voltage supply which powers the Xenon discharge tube. Then we have another oscillator which is based on the neon tube. This is a "relaxation" oscillator which works because the neon is an open circuit for low voltages but when the voltage across it rises to a threshold value of about 90 volts or so, it suddenly breaks down to become a low resistance. The oscillator works as follows. The .033µF 200V capacitor is charged from the 400V supply via The 1MO pot is mounted in the base of the strobe unit near one of the mounting pillars (see text). Be careful of the 2J.LF capacitor - it could give you a very nasty shock if you touch its leads. TRACK SIDE DF PCB STROBE CASE \ 0 FLASH TUBE Fig.2: this diagram shows how to modify the circuit board. You need to remove two 8.2MO resistors and a .033J.LF capacitor. Substitute a 180k0 resistor and a 0.33J.LF capacitor as shown. the two series 8.2MO resistors. When the voltage across the neon reaches the neon's threshold value, the neon breaks down and discharges the .033µF capacitor via the primary of the trigger transformer. The secondary of the trigger transformer then applies a high voltage pulse to the electrode wrapped around the Xenon tube, causing it to fire and discharge the 2µF capacitor. At the same time, the tOµF capacitor delivers a positive pulse to the emitter of Qt so that the DCDC inverter is stopped. If it wasn't stopped, it would continue to deliver current via W3, Dt and D2 and the Xenon tube would never stop conduction. When the Xenon tube stops conduction, the Tt inverter recharges the 2µF capacitor and the two 8.2MO resistors then begin the recharge the .033µF capacitor until the neon breaks down again. This gives the overall flash rate of about two per second. Modifications To make the flash rate variable, we alter the resistor charging path to the capacitor across the neon. continued on page 93 MAY1988 73 • Real Time Clock • Games Port • Both CGA/MGA Standard • Fully Expanded Memory in Dual and Hard Drive System All prices include Mono Monitor (X-2400) - y'" "'"' $50! I ThenewACER500+ byMult1tech: setting new standards for power, performance ... and value! For business or home use you won't find better than the IBM compatible ACER 500+ by Multitech. New models feature even more than before· you reap the benefit! • Real II• clock - now standard! • C6A and MGA graphir:s- now standard! • 611111 Port - DOW staadardl • Fully expanded memory OR dual drive & hard drive systems - now standard! • MS-DOS V3.2 - now standard! • Mono Video Monitor- ROW staadard! 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Transmitter/receiver can handle up to 8 functions plus mute and Up/Down! What's more, it allows you to cus~om build the kit to suit yourself - construct with all functions or just a few! Cat K-3434 · S Receiver Measures 200 X 160 X 70mm. 11995 Hand Held IR Transmitter Pre-punched and screened front panel. Cat K-3433 s49ss TV Colour Bar & Pattern Generator There's only one kit supplier you can trust for quality, range and professional back-up. With our "Sorry Dick, it doesn't work!" service and our specialist R&D department to rely on - there's only one No.1 In Kits: Dick Smith Electronics! Wireless Stereo Headphone Link Ever had someone trip over you r headphone cable? Having your ears ripped off is no fun at all! With the DSE lnfrared Headphone Transmitter/Receiver you can enjoy high quality sound reproduction without messy cables. Relatively easy to built, both the transmitter and receiver have volume controls and a range more than adequate for a larger than average size room. 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Type AAA 180mAh AA 500mAh C 1800mAh D 1200mAh Cat No. Was S-3350 $4.95 S-3351 $4.75 S-3352 $12.95 S-3353 $11 .95 Now $4.50 $4.50 $9.95 $10.95 DICKt3SMITH ELECIRONICS PTY LTD THE EVOLUTION OF ELECTRIC RAILWAYS In the history of railways, those countries which had the courage to pioneer often reaped the benefits in selling their experience to other nations. So it is with the Swiss who built the world's first mainline electric railway system in 1906. In 1902 there was not one fullsize, long distance, fully electric standard gauge mountain railway in the world. In one tremendous act of engineering innovation a small Swiss company, the BLS of Bern, rewrote the book and added immeasurably to the world's store of electrical railway knowledge and experience. Just after the turn of the century, the citizens of Bern petitioned their government to build a railway. Their plea was rejected, as governments worldwide are wont to do. Often it seems the principal function of democratic governments everywhere is to refuse the sensible requests of their people. And just what so stirred the good folk of Bern? Well, the year was 1906 and the brand new Simplon tunnel was carrying railway traffic under the Alps from Switzerland directly into Italy for the first time. Holiday goers and business people were all enjoying the new short-cut to their neighbour's country. But for revellers and entrepreneurs alike, to live in the national capital, Bern, was to be penalised. Their city was on a dead- PT.7 THE FIRST ELECTRIC MAINLINE SYSTEM 76 SILICON CHIP LEFT: THE BERN-LOTSCHBERGSIMPLON railway was the world's first electric mainline and also the first to use AC. The line is shown here between Lalden and Brig on the south slope down from the Lotschberg Tunnel. Photo courtesy BLS. end in the national railway scheme. Residents of the larger city Zurich and the smaller cantons Basel, Geneve, Lauzanne, Luzern, even Sargans and Brig, found that the European world came to their doorstep, and vice-versa. Switzerland was fast becoming the railway crossroads of Europe, and those other lucky Swiss cities were on the National Trunk Railway System which more or less circled around their mountainous country. Connections to other cities of the continent radiated out like spokes of a wheel and now the Simplon tunnel through the Alps gave an even shorter path into Italy. This meant good business for the Swiss. But not for Bern, placed as it was off the main railway. Thus the petition whereby the people of Bern requested the government to build a short railway, a mere 120 kilometres long, from Bern to meet the northern end of the new Simplon railway tunnel at Brig. Not surprisingly, the government refused. For standing in the way of the proposed railway was a huge branch of the mighty Alps, running half of the length of the country from south-west to north-east as an enormous barrier between Bern and the Rhone river. Including the 4170 metre high Jungfrau and the 4180 metre high Aletschhorn peaks, nature had strewn any proposed route with high cliffs, glaciers, mountain lakes, deep chasms, snow and ice, all prone to landslides and avalanches. "Let our Government-owned rail system continue to go around them, as our faithful steam locomotives and high-class trains do at present, via Lausanne or Zurich on the government lines'', was the government's response. The BLS company But the Swiss are determined, ingenious types. The citizens of Bern THIS VIEW SHOWS A BLS high-speed electric train on the line near Eggerberg, descending from Lotschberg Tunnel. The train has a maximum speed of 140km/hr. (BLS photo). formed a public company, the BLS (Bern-Lotschberg-Simplon). Shares were sold, capital collected. The conception of the trans-alpine railway dated from as far back as 1866, now they would build it. Yes, they would build their own railway direct from Bern to Brig where it would join the new existing Simplon tunnel entry into Italy. Construction began in 1906 at Spiez and proceeded up the Kander Valley towards Kandersteg. From Frutigen to the high valley town of Kandersteg the line was constructed to rise continuously for 20 kilometres at a ruling gradient of 1 in 37. That might not sound much but the track also negotiates the 46 metre high Kander river viaduct, a 265-metre long beautiful example of the stone-mason's art, and two complete corkscrew circles in a zigzag pattern (one circle mostly within a tunnel), to bring trains up the cliff face to meet the main trunk of the mountain range. At the same time, drilling of the 14,612-metre long Lotschberg tunnel through the range began. As the tunnellers toiled deep within the mountain they pierced an unsuspected vertical fault in the rock strata whereupon, in a few horrific seconds, 25 men perished in the fall, along with all the equipment. The only thing to do was tunnel around the fault, a course which involved the introduction of three extra curves and the abandonment of more than one and a half kilometres of tunnel already drilled. Construction of the 26km long southern ramp from the southern end of the tunnel at the Lotschental river crossing down to Brig on the Rhone river was simultaneously undertaken. This southern approach to the tunnel, though different from its northern counterpart, is no less spectacular. The southern track has to cross many rivers, deep ravines and three icy valleys, including the tail ends of the Jolital, Bietschtal and Mankin Glaciers. MAY 1988 77 SPECTACULAR SCENERY: A BLS TRAIN CROSSES the new reinforced concrete viaduct over the Kander River. Behind the new viaduct is the original stone masonary Kander Viaduct which is some 46-metres high. The new concrete structure is part of a 10-year project to double-track the entire line. (BLS photo). Added to the breathtaking beauty of nature in this region is the ingenuity of man. Still geologically active, the Alps include many deep clefts whose sides are sheer rock faces hundreds of metres high, making the construction of a railway difficult in the extreme. Tunnels were bored from both sides towards the cleft, then a bridge had to be constructed joining the opposite tunnel openings in the cliff walls, high above the ice or river below. One such is the famous Bietschtal arch featured on many European postcards. On the Bern or northern side of the Lotschberg tunnel the approaches rise 680 metres to a height of 1240 metres above sea level in the centre of the tunnel. Then the southern ramp falls over 500 metres to its crossing of the Rhone river at Brig, joining the Swiss Federal Railways. From here 78 SILICON CHIP the government line enters the Simplon tunnel on its way to Italy. Major constructions Including the Lotschberg tunnel, the line from Bern to Brig required the drilling of thirty four tunnels a total of 27 kilometres long. Also necessary was the construction of 25 difficult bridges and viaducts as well as ten avalanche galleries, safety walls and terraces many kilometres long to protect against landslides and snowslides. To decrease the risk of avalanches burying the line, the company planted ten million trees on 386 hectares of mountain slopes. The Lotschberg tunnel, begun in 1906, was drilled wide enough for double track from the start and completed on March 31, 1911. It is one of the world's longest and, at 1240 metres above sea level, is the highest standard gauge tunnel in Europe. (An interesting aside is that Australia's own standard gauge railways reach a higher point, 1377 metres above sea level at Ben Lomond in New South Wales. Of course other Swiss private narrow gauge lines rise much higher, to almost 3600 metres.) Without sufficient funds for a totally double track line, the northern and southern approaches were constructed single track with crossing loops. However, some bridges, such as the Bietschtal main arch, were built to double track width. Most tunnels had the complete roof arch cut in anticipation of eventual double tracking. The complete line was opened for traffic on June 15, 1913 allowing through trains from Italy to all of Europe to run via Bern. Today you may even extend your train journey all the way to London. r------- ----------- I I r- - 7 J I I I j J CAB I I iE\~N~~i PRIMARY 15kV I I I ~---....J SECONOARY 200-500-1000 V 15 5 - Hz I II I j I I j I ORIVE ROO I L __ _j .J k-L - - - 0 v-----~ ,------C~-_:~~~~~----..'r---"--~ 1 I coNrnoLLERs TRANSFORMER - - 7 I _t J I L__ _J I _.,.__..___~~'----!---__,c;_-~-----""---~-,c:__- kV RETURN '<c-----.---r----=-~+--'--"c......+--r--~---rr---=~--r---= - - - - LEADING BOGIE 10 DRIVING WHEELS J 0 L J- ~ TRAILING BOGIE FIG.1: OUTLINE SKETCH OF AN early BLS 2-10-2 electric locomotive. External drive rods were used to couple the 10 driving wheels in the same manner as on steam locomotives. THE BLS ELECTRIC LOCOMOTIVES USE A DIAMOND style pantograph to pick up current from an overhead contact wire carrying 15kV 16.6Hz AC. (BLS photo). The total cost of the line's construction was 138 million Swiss Francs of which over 52 million Swiss Francs were expended on the drilling of the Lotschberg tunnel. With clever design and construction effort the average grade was held down to 1 in 48 and the ruling grade (maximum incline) to 1 in 37, allowing heavy trains and high running speeds, provided high powered locomotives were used. By comparison, some other lines in Switzerland rise much more steeply, as steep as one in four. First electric mainline Constructed from the start as a fully electric line, we must marvel when we recall that this electrical engineering design work was being done when there was no previous high-power long-distance electric traction experience to ref er to. The BLS engineers had to personally invent the electrical concepts and gain the experience, and thereby established themselves as the world's leading high voltage AC railway traction consultants during the next twenty years. First AC locomotives Taking a cue from standard mountain steam locomotive practice of the day, by 1910 the electrical engineers had built an electric locomotive having the same wheel arrangement as for a 2-10-2 steam engine (ie, one pair of leading small bogie wheels, a mainframe carried on ten large driving wheels on five axles, followed by two small bogie wheels). External drive rods coupled all five driving wheels on each side in the same manner as on steam locos. Within the locomotive body, carried on the mainframes, one large commutator AC motor was either gear coupled or rod coupled to one driving axle, from which the external drive rods transmitted driving forces to all ten coupled wheels, as in our outline sketch (Fig.1). This basic design, known simply as a 'Rod Drive Electric Locomotive', became the standard for high-powered medium speed electric locomotives for many years, a design adopted by those few other railroads that dared venture into high-power mainline electric locomotive design in the period from 1906 to 1950. The Virginia Railroad of the USA and the Swedish State Railways were two such railroads Eventually the BLS superseded the rod drive principle in favour of modern bogie electric loco design, to obtain higher running speeds. It is interesting to note that the unbeaten world record for locomotive tractive effort was established by a rod-drive electric locomotive of the Virginia Railroad. Examples of rod drive electric locomotives were still highly valued MAY 1988 79 ELECTRIC RAILWAYS - CTD and running until recent times, on such famous railroads as the Pennsylvania Central, the Virginia RR and the Lapland Railway. Some of these locos run even now. DC or AC? Because of the fairly long length of the Bern-Lotschberg-Simplon line, the engineers had to break away from the standard DC practice of the day. In Germany and in London at that time, short distances were covered by electric trains running on 750 volt DC third rail systems, taking their power from steam-driven generators. But the proposed high power electric locomotives of the BLS would take extremely large currents at such a "low" voltage as 750, leading to excessive line voltage drop and regulation problems. Therefore, a much higher voltage system, 15,000 volts, was adopted. We should note that the BLS had no quarrel with the principle of direct current per se, for the driving of traction motors. Far from it, for even today the DC series motor has the greatest shaft-torque/ armature current ratio. In this type motor alone, the shaft torque (and hence the loco tractive effort) is proportional to the square of the armature current. Hii h starting currents hence give enormous starting tractive effort, even more than can be transmitted by the driving wheels to the rail. Hence the continued use of this system around the world, including Australia. Hydroelectric plants Also we must remember that most of the electric power in Switzerland comes from hydroelectric plants where falling water turns turbine-driven alternators. Such plants naturally must be sited at the river, dam or waterfall, perhaps a long distance from the rail track, exacerbating voltage drop problems. In the very early 1900s, AC or Alternating Current was only just 80 SILICON CHIP being developed as an alternative to DC for street lighting and industrial uses. No one had even considered its use in high powered long distance rail traction. In 1906, the year construction of the line began, one could search the world to even find a power line 120 kilometres long, much less a system of railway overhead contact wires, catenaries and feeder lines of that length. AC chosen The Swiss engineers decided to adopt 15kV AC as their overhead contact wire system, and to step that voltage down using a large transformer carried in each locomotive. The transformer secondary would supply the loco's traction motors at a convenient voltage between 500 and 1000 volts. Their traction motors were series motors with commutators and brushes, identical to the motors used by other railways on DC except that, to minimise eddy currents in iron, the whole magnetic yoke and all pole pieces were of laminated steel (rather than the cast iron used in DC motors). Interpoles were used to improve the commutation (that is, to reduce arcing between brushes and commutator). Interpoles are small series wound poles placed between all main field magnet poles, as in Fig.2. Their function is to cancel the distortion of the main magnetic field caused by the magnetic field of the armature currents. Such field distortion would cause arcing under the brushes. The engineers found that their traction motors would not run well on AC supply at the standard 50Hz frequency and arcing occurred under the brushes, burning both brushes and commutator. This was because the inductive reactance of the field windings, armature coils and interpole windings caused phase delays, preventing the interpoles from properly cancelling the aforesaid distortion of the main fields. Solving the brush burning problem clearly meant reducing the in- THE FAMOUS 46-METRE high Kander Viaduct. This beautiful example of the stonemason's art is 256 metres long. (BLS photo). ductive reactance of all motor windings. This reactance is proportional both to frequency and winding inductance. As reduction of inductance was not the way to go, they took the innovative step of reducing the frequency to one third of the previous 50Hz, to 16.6Hz. This was a brave decision, as it TELEPHONE EXTENSION LEADS The very best available. Six conductor telephone lead, fully Telecom permitted (C85n/44) with standard plug and socket. Suits all telephones. Choose ten or fifteen ---:::::~§~~ metre lengths. Standard ivory colour with full three year guarantee. (10 metre T5016, 15 metre T5017) CORDLESS TELEPHONE MP-25O Telecom permitted (C86/35/34). Features call facility battery level indicator, mute and redial. Excellent reception and transmission range of up to 250 metres. (T4000). REMOTE ANSWERING MACHINE The very latest design using microprocessors to ensure reliability and trouble free operation. Featuring beeperless remote control - access your machine and messages anywhere in the world simply by using pre-programmed voice patterns. 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They would need a completely separate system of power lines, feeders, alternators, switchgear, protection and all the paraphernalia of a full electricity system. Undaunted, they proceeded. To obtain their low frequency 16.6Hz power supply they had (and still have) two alternatives: • Method (1) was to build separate power stations (or sections of power stations) specifically to generate the low frequency supply. At that time, their trains would probably use more electricity than most other users, so it would be sensible for the railway to build its own power stations. Compared to a 50Hz alternator, the 16.6Hz alternators would either run at one third the speed, or have one third as many poles. • Method (2) was to build normal 50Hz power stations, which could be interconnected to the growing electricity system of the rest of the country and run 50Hz 3-phase transmission lines to various trackside substations. Within these substations the 50Hz supply could be converted to 16.6Hz supply. In 1906 the only method available for such a frequency conversion was to use a 50Hz 3-phase high voltage synchronous motor direct-coupled to an alternator which generates the low frequency 16.6Hz supply. Frequency changing As new ways for frequency changing were invented, such as the later German invention of frequency division by "cycloconverters" whfch used banks of controlled mercury arc rectifiers, the natural tendency was to gradually shift from method (1) to method (2). Not only the BLS, but the great majority of other electric railways of the world which followed them at some time chose method (1) initially, only to slowly shift to method (2) over many years as new and better technology evolved. Some countries, for example Australia's own SRA, finally changed to method (2) only in the 1960s and 1970s when very large solid state controlled 82 SILICON CHIP THE LATEST HIGH-SPEED COACH bogies for electric trains feature disc brakes, side-sway shock-absorbers and roller bearings. In addition, the axle box can move sidways to allow both axles to self-align to the radius of curves, thus permitting higher running speeds (ie, the axles can point to the centre of the track curve for minimum friction). rectifiers (thyristors) became available. We observe that method (1) is the cheaper way (less large equipment) but method (2) is the more convenient. Some readers will want to know why method (2) is more convenient. First, there is the nicety of being able to interconnect to other 50Hz power generating systems, a handy aspect in the event of power station breakdown. Second a new railway must build stations, and these will want lights; on platforms and in buildings, and in the railway workers' homes, trackside workshops, goodsheds and ancillary buildings. But filament lamps operated on low frequencies like 16.6Hz give severe flicker problems. If the low frequency railway supply is all that is available at a location, the only cure is to use quite INTERPOLE - low voltage high current lamps, hoping that the heavier filament wire used will not cool down so much from one cycle to the next, so that the lamp brightness will not flutter so much. Other countries eventually faced the same problem. In Australia, at the Bullock Island railway yards, the original yard lighting system used 60 volt 20 amp lamps, in the hope that the heavy filament would reduce the flutter in brightness when operated on a low-frequency 25Hz system. Train control The original method of starting and controlling train speed was by switching resistances in series with the traction motors. All resistance is placed in the circuit to control motor current when starting, the driver gradually switching out sections of resistance as the speed in- ~ ~t~~ a,.::::=---a:::::,.,1 - ArJ:~nRE ~:~ . . . "-<> M INTERPOLE - ~ ~ MOTOR FRAME "'~" FIG.2: SERIES TRACTION MOTOR with four main field poles and four interpoles. The interpoles reduce arcing between the brushes and the commutator. creases. At full speed all resistance is switched out of circuit, to place the motors directly on the line. With high voltage AC operation the locomotive carries its own stepdown transformer on board. This gives the second option of switching to lower voltage tappings on the transformer secondary for starting. This wastes less power and uses less current from the line for starting, but the transformer is somewhat more expensive. The BLS engineers found by hard experience some control system facts not previously known to the world. We keep in mind that the BLS is a mountain railway, and that there will be some trains going uphill and others going downhill in other sections. A train using full power on a level section may come to a downhill grade and find its downhill speed held in check by another train ascending the hill in another section. The downhill train is actually generating electricity, driven by gravity and its own mass. Such generation is today called "regenerative braking" as it causes Did you a useful braking effect on the downhill train. This generated current feeds the other ascending train (rather than the current coming from the power station) if the power station is far distant. Troubles occur when the ascending train suddenly stops at a station or crossing loop. The decending train suddenly loses its electric braking and must resort to its air brakes for control. The moment the ascending train shut off its motors some of the current still generated by the descending train would flow back to the power station and momentarily drive the power station alternators. The power station water-turbine speed controller would then have to fight for control of the overspeeding turbine. In the early design and trial years, the BLS electrical engineers gained very valuable experience in the design and control of large high voltage dynamic loads. Such knowledge and expertise placed them in the forefront of the electrical world for decades to come. In company with the Swiss • IIllSS private manufacturing companies Brown, Boveri & Cie; Schweizerische Lokomotivund Maschinenfa brik; and Verkehrshaus der Schweiz; the BLS advanced the world's store of knowledge in the design and operation of motors, locomotives, power stations, and dynamic control systems for large heavy-haul long-distance ACelectric railways. Enter bogie locomotives For many decades, right up to the 1950s, the rod -drive style locomotive was predominant. Modern Swiss locomotives now are bogie types, in line with the rest of the world. These modern locos come in powers up to 10 megawatts (13,400 horsepower) and feature a variety of drive systems from thyristor controlled DC motors to 3-phase gearless axle mounted induction motors. How all these operate in various parts of Europe from a single phase AC of either 50Hz or 16.6Hz or DC overhead contact wire is another fascinating story. We'll have a look at that next month. ~ these issues? Issue Highlights February 1988: 200 Watt Stereo Power Amplifier ; Deluxe Car Burglar Alarm ; End of File Indicator for Modems; Simple Door Minder; Low Ohms Adapter for Multimeters. Please send me a back issue for □ November 1987 □ December 1987 □ dftl'ltlflFY 1 QaS (Sold Out) □ □ February 1 988 □ March 1988 April 1988 Enclosed is my cheque or money order for $ ...... .. or please debit my □ Bankcard □ Visa Name ... .. ..... ... .... ........ ... .. .... ...... ........ . ....... .... ... ..... .. ....... .. ...... .... .. . Address ....... .... ....... .... .... ..... .. .......... ... .... ...... ........ .... ........ ... .. .. .. .. . Suburb/town ... .. .. ... ......... ... ... ... .... ... .. .... ..... ... ... Postcode ... ............ . Card No ... .... ..... .. ........ ...... .... ... .... ........ .......... ...... .... ... .. ... ......... ... . March 1 988: Remote Switch for Car Alarms; Telephone Line Grabber; Low Cost Function Generator; Endless-Loop Tape Player. April 1 988: Walkaround Throttle for Model Railroads; pH Meter for Swimming Pools; Slave Flash Trigger; Mobile Antennas for the VHF & UHF Bands Price: $5.00 each (incl. p&p). Fill out the coupon at left (or a photostat copy) and send it to : SILICON CHIP, PO Box 139, Collaroy Beach 2097. Signature ........ ...... ...... .... ..... .... .. .. .. ..Card expiry date ... .. . ./ ...... ./ .... .. . ~------------------------~---------------~ M A Y 1988 83 .. ~ --·r , T ~==..D. !'---~,.,.........._........... ~., . ,-I G . . -1.·.·.T· · . A. .I.J T [-'· 1 1 ~ ·t :Jl '1: [>~--.-:_,,...... _, T:1 ·M ·: ·N. rr_• -~"}L .. . . J. ;I1. _ _ 0; '. · A· ·-s - -".-,_._ E --- - 1 ~T··· ----h --·= ~h-. By Louis E. Frenzel The basic circuit for storing binary data in digital circuits is the flipflop. In a previous lesson, you saw how flipflops could be combined to form storage registers capable of remembering a binary word of any length. You also saw how flipflops could be combined to form counters and shift registers where binary numbers could be manipulated in a variety of ways. All digital equipment contains one or more counters or registers to store and manipulate binary data. But as you probably know, there are some kinds of digital equipment that require the ability to store large amounts of binary data. The most obvious example, of course, is the digital computer which has memory capable of storing many thousands of instruction and data words. Other kinds of digital equipment also have the need to store large amounts of data. To meet that requirement, special electronic memory circuits have been developed. Like counters and registers, some of those memory circuits are made up of flipflops. In other memory circuits, different kinds of storage elements are used. In this lesson, you'll learn about integrated circuits designed specifically for storing large amounts of digital data, and how they are used in computers and other digital equipment. Memory Organisation and Operation An electronic memory is a place where hundreds or thousands of binary words may be stored. The memory is divided up into discrete locations where a fixed-size binary number may be stored. Those individual word-storage locations are , in turn, made up of bit memory elements such as flipflops and other cir84 SILICON CHIP cuits [which we'll discuss later). The organisation of such a memory is illustrated in Fig.1. Its two key characteristics are the number of bits per word and the total number of word-storage locations. Most electronic memories are capable of storing standard binary word sizes such as 4, 8, 16 and 32-bits long. Of course, other sizes can be created. The total word-storage capacity of a memory also varies widely. Typical sizes are 256, 1024, 4096, 16,384 and 65,536 words. You've probably recognised that all those memory sizes are some power of two. But the word length and memory size are dependent upon the application in which they are used. To describe memories, we use a shorthand notation that gives both memory and word sizes. For example, the designation 1024 x 4 refers to a memory containing 1024 4-bit words; the designation lK x 4 is used to define the same memory. In other areas of electronics, k usually means 1000, but in memory jargon, K = 1024 - which is an even power of two. STORED DATA 1 0 1 0 1 0 1 1 1 1 0 0 0 0 0 0 1 1 0 0 1 1 1 0 1 0 1 0 1 0 0 1 MEMORY LOCATION 4093 .....----------------. 4094 1 1 1 0 0 0 1 1 4095 1 1 1 1 1 1 1 1 Fig.1: this illustration of the organisation of a memory chip - which is capable of storing 4K or 4096 bytes of data - shows that the chip is made up of lots of storage locations, each having a distinct address (0-4095). NUMBER OF BITS IN ADDRESS WORD NUMBER OF MEMORY LOCATIONS 8 256 10 1,024(1K) 12 4,096(4K) 16 65,536(64K) 20 1,048,576(1M) 24 16,777,216(16M) 32 = = 4,294,976,296(46) = = K KILO WORDS 1,024 M MEGA WORDS 1,048,576 G = GIGA WORDS = 1,073,741,824 Fig.2: unlike other areas of electronics where lk represents 1000, 1K in memory jargon means 1024. Using that method, any memory size can be designated. For example, a memory capable of storing 65,536 bytes would be designated as 64K x 8; a 256K memory for 32-bit words would be designated 256K x 32. Address To locate a specific word in memory, each word is given a unique number called an address. In Fig, 1, for example, the 4K x 8 memory has 4096 storage locations, numbered from Oto 4095, for byte-length words. The numbers are the addresses, and are used for each specific storage location. To use an electronic memory, you first apply an address to it. The address is a multi-bit binary word. A specific number of address bits are required to address the memory locations. For example, with a 12-bit address, 4096 individual states can be defined (2 to the 12th power = 4096), which means that a 12-bit word would be used for the address of the 4K memory in Fig, 1. A 16-bit address would permit up to 64K (65,536) memory locations to be addressed. The table in Fig.2 shows the number of locations different word sizes can address. Random-Access Memories The memories that we've just discussed are generally referred to as random-access memories (RAMs ). As this name implies, any specific memory location may be accessed at random. Early computer designs used a serial data-storage format , which required that data stored in memory be accessed sequentially. A given word could not be directly selected; instead it was necessary to wait for that word to come around. Today's electronic memories are parallel devices and any given memory location may be accessed directly without reference to any other memory location. Random-access memories break down into two basic types: read/write and read-only memories . The read/write device permits both storage and retrieval operations to take place. New data may be stored in any memory location and any location may be accessed and recalled. Such memories are generally ref erred to as random-access memories or RAM for short. The other type of random-access memory is the read-only memory or ROM. Data is permanently stored in such memories. The desired data is stored in memory at the time that the circuits are manufactured but in some ROMs, the data may be stored later by the user. Once that data is written into the memory, it cannot be destroyed or changed; because of that, only read operations are possible thereafter. There are many applications where it is desirable to permanently store data or programs. Read-only memories are said to be non-volatile because their contents are retained even when power Store and Recall Operations Once the address has been applied and a specific storage location enabled, a read or write operation is performed. A read operation simply means that the binary number stored in the addressed location is recalled - ie, read out or transferred for use elsewhere. The read operation is non-destructive, in that the contents of the addressed memory location are retained. A write operation is the process of storing new data in the addressed memory location; the operation is equivalent to loading a storage register. Access Time The most important specification of any memory device is its access time - the time it takes for a word stored in a memory to be addressed and read out. It is that interval between the application of the address and the appearance of the data at the output. Most MOS memories have access times in the 100-500 nanosecond (ns) range. Bipolar TTL memories have access times in the 20 to 90ns range. ROW SELECT COLUMN SELECT 7 07 WAITE AMPLIFIER 1 3,STATE CONTROL WAITE AMPLIFIER 2 Fig.3: this diagram of a single storage element in a static memory chip illustrates the operation of each cell in the memory. In the static-memory cell, the storage element is a flipflop. MAY 1988 85 is removed from the circuit. In read/write memories all data stored in the memory is lost when power i~ turned off; such memories are said to be volatile. Despite the fact that both read/write and read-only memories are of random-access organisation, read/write memories are usually referred to as RAM and read-only memories are simply called ROM. Both types will be discussed in detail in the following sections. RAM Storage Cells ADDRESSED COLUMN t COLUMNS ROW s I I ACTIVATED MEMORY CELL Fig.4: most semiconductor memories are organised as a matrix of storage cells. To access a particular cell, one row and one column must be activated. SILICON CHIP WRITE AMPLIAER STORAGE CAPACITOR There are two basic types of storage cells or elements used in read/write memories - static and dynamic cells - both of which store one bit. Each type has its advantages and disadvantages. In most cases, the memory cells are made up of metal-oxide semiconductor field-effect transistors (MOSFETs ). Each storage element is capable of storing one bit. Many thousands of storage cells can be fabricated on a single silicon chip. By combining a number of the chips, you can form a memory of any desired size. Let's take a look at how the static and dynamic cells work. Fig.3 shows a diagram of a typical static memory storage cell. The basic storage circuit is a latch or flipflop made up of enhancement-mode MOSFETs Ql-Q4. Ql and Q2 are the active transistors, while Q3 and Q4 have been biased into conduction and act strictly as load resistors. The circuit in Fig.3 has two stable states. One state is where Ql is conducting and Q2 is cut off. With Q2 cut off, the supply voltage through Q4 on the gate of Ql keeps Ql conducting. With Ql conducting, its drain is near O volts and below the conduction threshold of Q2. Therefore, Q2 remains off. The other stable state is where Q2 is conducting and Ql is cut off. With those two states, either a binary 0 or binary 1 can be represented. The gate to source capacitances of Ql and Q2 are charged through either Q3 or Q4 to keep the conducting transistor on. All the additional circuitry in Fig.3 is used for storing data in the cell or reading it out. Transistors Q5 and Q6, as well as Q7 and Q8, are switches used for addressing purposes. 86 DATA OUT I DATA IN Fig.5: the architecture of a dynamic storage cell differs somewhat from that of a static unit. Here, miniature capacitors, which must be refreshed periodically, are used as the storage elements. In most memories, each storage cell is part of a matrix of storage cells arranged in a row and column format. To address a particular cell, address signals activate the desired row and column in which the cell appears (see Fig.4). In Fig.3, when a binary 1 is applied to the row-select line, transistors Q5 and Q6 conduct, allowing the signals at the drains of the flipflops, X and X-bar, to be passed through to Q7 and Q8. When the column-select line is binary 1, Q7 and Q8 are also turned on. At this point, the latch output signals pass through Q5 and Q7 as well as Q6 and Q8 and appear at the inputs to the sense amplifier. The binary state stored in the flipflop appears at the sense amplifier output. Usually, the sense amplifier is a 3-state device whose output can be turned off or effectively disconnected from the output so that the memory cell can be used in bus configurations. To write data into the circuit, both the row and column-select lines are made binary 1 so that transistors Q5-Q8 conduct. The data to be stored in the circuit is then applied to the data-input line. For example, to store a binary 0, a binary O is applied to the datainput line. The signal is then applied to write amplifier 1, and to write amplifier 2 through an inverter. That results in write amplifier 1 delivering a zero, while amplifier 2 delivers a 1. The zero output of write amplifier 1 pulls the drain of Ql low. Since Q5 and Q7 are conducting, they appear to be a near short circuit and therefore regardless of the state of the latch, the drain of Qi goes to binary 0. That turns Q2 off if it should happen to be on, which in turn, causes Ql to conduct. The circuit then holds that state, storing a binary 0. If a binary 1 were applied to the data input, the output of write amplifier 2 would be binary 0 , causing the drain of Q2 to be pulled low through Q6 and QB. The drain of Ql (X) would go high and so the circuit would store a binary 1. The basic storage element in a dynamic memory cell is a capacitor. When the capacitor is discharged, it stores a binary 0. When the capacitor is charged, it stores a binary 1. Dynamic memory ICs pack thousands of tiny capacitors on the chip with related control circuits to read and write information. RAS TIMING AND CONTROL CIRCUITS ----------- ..... I I I ADDRESS STORAGE REGISTERS INPUT ADDRESS A0-A7 ROW CIRCUITS I I ROW DECODERS 256x256 STORAGE MATRIX SENSE, WRITE/ REFRESH AMPLIFIERS BUFFER FF DATA OUT COLUMN DECODERS COLUMN DATA IN (D) FF Fig.6: functional block diagram of a 4164 64K x 1 dynamic RAM IC. Such a circuit is said to be volatile because without refreshing (ie, period recharging of the storage capacitors), all data stored in memory would be lost. Note that the IC contains on-chip refresh circuitry. A simplified drawing of a typical dynamic storage cell is shown in Fig.5. Transistors Ql and Q2 are switches that permit access to the storage capacitor. As in most memory architectures, dynamic cells are arranged in the form of a matrix with rows and columns. To access a given memory cell, the specific row and column in which it appears is activated by row and column-address signals. In Fig.5, the row-address signal is applied to Q2 and the column-address signal is applied to Ql. When the transistors are turned on by the address signals, data may be stored in or read out of the capacitor. If data is to be stored, it is applied to the data-input line and passed through the write amplifier, which causes the capacitor to charge or discharge through Ql and Q2. To read data out, the charge stored on the capacitor is simply connected to the read-amplifier input through Ql and Q2. The capacitance of the tiny capacitor in each storage cell is only a fraction of a picofarad. But while it is very small, it's still capable of holding a charge that can determine the binary state of the cell. However, leakage in the circuit causes the capacitor to discharge over time, despite the fact that MOSFET circuits are typically very high impedance in nature. The effect of such leakage is that the state of the cell changes over time. Of course, such a memory is not reliable. To overcome the problem, dynamic memory cells are periodically refreshed. That is, special circuitry in the dynamic memory periodically looks at the state of the cell and refreshes it - either charging or discharging the capacitor as required. In most memory ICs, the refresh operation takes place approximately every two to four milliseconds. The refresh circuitry reads the state of the cell and reapplies it to ensure data integrity. The entire refresh operation is transparant to the user who never knows that it's going on. Typical RAM ICs Now let's take a look at some typical static and dynamic memory ICs. Many manufacturers supply a wide variety of memory-chip configurations. However. over the years some configurations have become more or less standard. For example, most dynamic RAMs come in one of four configurations: 4K x 1, 16K x 1, 64K x 1 and 256K x 1. The 64K x 1 chip contains 65,536 storage locations for 1-bit binary words. Naturally, to form large memories, many chips must be placed in parallel. To form a 64K x 8 memory would require eight such chips. Static-memory circuits are available in a wider range of configurations. But because static-memory cells contain many more components, they take up much more space on a chip. As a result, static memories typically are capable of storing less data than dynamic RAMs. Today, a practical commercial dynamic RAM is capable of storing up to 256K bits. Typical static RAMs have a maximum storage capacity of 64K bits. As for memory organisations, static RAMs are available in some of the following configurations: 4K x 1, lK x 4, 4K x 4, 4K x 16 and 8K x 8. An example of a dynamic memory is Texas Instruments' popular 64K x 1 dynamic RAM, the 4164. That chip, made by many manufacturers under different model numbers, is widely used for personal computer memories. Housed in a standard 16-pin dual-in-line package (DIP), it operates from a single + 5V supply, and has a typical access time of 150ns. A simplified block diagram of the 4164 is shown in Fig.6. The dynamic memory cells themselves are organised into a matrix of 256 rows and 256 columns capable of storing 65,536 bits. Note that the 4164 has 8 lines labelled AO to A7. With eight a ddress bits, 256 separate locations can be addressed. The question is: how do we address the full 64K? To address 64K bits requires a 16-bit address. The 16-bit address is fed to the chip as two 8-bit segments. The eight least significant bits of the address are first applied to the address line and are strobed into the row address register with a control signal called RAS (row address strobe). The higher order eight bits of the address are then placed on the eight address lines, loaded into memory by the control signal, CAS-bar (column address strobe), and stored in the column-address register. Both the row and column-address registers feed row and column decoders that convert the eight address bits into 256 lines. One column-decode and one rowM A Y 1988 87 WE A3 A4 AS A6 ROW DECODER 64x6~fitll~AGE (4096 CELLS) uo CIRCUITS DATA INPUT/OUTPUTS A7 AS COLUMN DECODER AO A1 A2 A9 Fig.7: block diagram of the 2114 4K-bit RAM, which uses a 10-bit address code; six address lines (A3 to A8) for the row decoder and four address lines (AO, Al, A2 and A9) for the column decoder. decode output is required to activate each memory cell. Once a particular memory cell has been addressed, a read or write operation is then performed. The W-bar input line selects the mode. If W-bar is high, a read operation is performed; if it's low, a write operation is performed. Assuming that a read operation has been selected, the addressed storage cell will be enabled. A sense amplifier reads the charge stored on the cell capacitors and passes it through to a data-output flipflop. For a write operation, W-bar is made binary 0. The bit to be stored in the selected cell is placed on the D-input line and stored in a flipflop. When control signal CAS-bar goes low, the data is stored in the selected cell. Finally, keep in mind that, because this is a dynamic memory circuit, a refresh operation must be performed. In the 4164, a refresh operation is performed approximately every four milliseconds. The row address is incremented by an external counter and after each count, the RAS line is strobed, which causes the 256 bits in each row to be refreshed. Static RAM The 2114, a popular 4K-bit static RAM, is organised in a lK x 4 configuration; ie, it can store 1024 4-bit words. Since the 2114 can address 1024 words, it uses a 10-bit address word. Housed in an 18-pin DIP, it operates from a + 5V supply, and has a nominal 250ns access time. Fig. 7 shows a simplified block diagram of the 2114. The memory cells are arranged in a 64 x 64 matrix. producing 4096 individual storage cells. Six of the address bits A3-A8 are applied to a row-select decoder that's used to enable the 64 rows of storage cells. The other four address bits (AO, Al, A2 and A9) are applied to a column decoder. The 16-column decode outputs are used to enable 16 4-bit words, as illustrated in Fig.8. For a given address, one of the 64 rows will be enabled. The column decoder enables four columns simultaneously, thereby defining a 4-bit word in the selected row. In this memory, four pins are used for both input and output (I/0). The write-enable (WE) input signal 88 SILICON CHIP determines whether a read or write operation is to be performed. If the WE signal is low, a write operation is performed. The data on the four I/O pins are accepted as inputs and stored in the memory locations selected by the address. When the WE line is high, a read operation is designated. The 4-bit word stored in the location designated by the address is read out and placed on four I/O pins. A chip-select (CS) signal is used to enable the chip. When CS is high, the chip is disabled and no read or write operations take place. However, when CS is low, the chip is selected or enabled and a read or write operation may occur. Read-Only Memories A read-only memory (ROM) is a semiconductor circuit in which a number of binary words has been permanently stored. An input address selects the desired word to be read out. Read-only memories are used in those applications where it is desirable to permanently store binary information. In a computer, for example, it is usually desirable to incorporate a ROM that contains instructions that make up frequently used programs. In that way it is not necessary to load those programs into the computer's RAM from some external peripheral device. ROMs are also used in various logic applications. By assuming that the address lines are inputs and the data lines are outputs, the ROM can be considered as a form of combinational logic circuit. By storing specific bits in the ROM, it can perform a wide variety of special functions, such as code conversion and table-look-up functions, which are less conveniently implemented with more conventional combinational logic circuits. Diode Matrix ROM To better illustrate the concept of a ROM, refer to the circuit in Fig.9, a simple 8 x 4 ROM. It stores eight 4-bit words. A 1-of-8 decoder circuit is used to translate a 3-bit address word into eight output lines. In this particular circuit, for a given address, only one output line will be active. The decoder has active-low outputs, which means that the enabled output line will be binary O while all other output lines are binary 1. The data is stored in ROM by the presence or absence of a diode. Whenever a binary O is desired in one of the words, a diode is connected between the decoder output and the ROM output line where the O is desired. Assume that the input address is 001. That COLUMNS ADDRESSED 4-BIT WORD LOCATION "'-1T } ROWS~ 64x64- MATRIX Fig.8: the 2114, with its 1K x 4 configuration, can store 1024 4-bit words. The memory is arranged in a 64 x 64 matrix, providing 4096 individual storage cells. 1 OF 8 DECODER \ ACTIVE LOW OUTPUT D(MS8) C B A(LSB) Fig.9: in this illustration of a ROM, the presence or absence of a diode determines whether a 1 or a O will be sensed when a particular memory location is accessed. means that the 1 output line will go low, causing diodes Dl, DZ and D3 to conduct. Therefore, they effectively bring the output lines to which they are connected low. Since all of the other decoder-output lines are high, the remaining diodes in the network are cut off. Therefore, the other output lines are high at this time. The output word DCBA is thus 0100. While small simple ROMs can be constructed using the diode-matrix technique, prepackaged ROMs are used in most applications because they're capable of storing many more bits of data and are far more useful. There are two basic types of ROMs: maskprogrammable and electrically-programmable. Maskprogrammable devices are programmed during the manufacturing process. A special mask, conforming to the bit pattern stored in memory, is custom-designed to interconnect the circuits on the ROM chip. In other words, the data to be stored is permanently manufactured into the device and cannot be changed. Electrically programmable ROMs. called PROMs (programmable read-only memory) can be programmed by the user. When the ROM comes from the manufacturer, it contains all binary 0's or all binary 1 's depending upon the circuitry involved. The user places the ROM in a special programming instrument called a PROM programmer and enters the data to be stored. In some cases, data storage is permanent. At other times. data storage is semi-permanent: that is. the data remains in memory even when power is removed from the circuit, but can be erased or reprogrammed. In high-volume production applications, where the information to be stored is reliable, masked ROMs are to be preferred because of their very low cost. On the other hand, where the data to be stored may have to be changed for some reason, PROMs are preferred. During the design process of any equipment using a ROM, the program or data may change several times as the "bugs" are worked out or as performance is improved. Even in production units, it may be desirable to update the ROM if an important change occurs. In such applications, PROMs are preferred. However, PROMs are far more expensive than masked ROMs for most applications. During the development process though, nothing can beat a PROM for flexibility and ease of up-dating. Both masked and programmable ROMs are made with both MOS and bipolar technology. Most ROMs are of the MOS variety because of their low cost and high storage density - currently up to 256K bits per chip. On the other hand, bipolar ROMs are much smaller. Because· the circuitry is more complex and dissipates more power, it takes up more space on the chip; thus, fewer bits can be stored. Most bipolar ROMs are small and are limited in practice to only several thousand bits. The big advantage of the bipolar ROM over the MOS ROM is speed. Access time for a typical MOS ROM is in the 200 to 500 nanosecond range, while bipolar ROMs have access times of typically less than 100 nanoseconds. In fact, bipolar ROMs with access times in the 20 to 50 nanosecond range are available for high speed applications. In most applications, you will encounter the MOS ROM, which is available in a wide variety of sizes. The main difference between ROM and RAM organisation is that while typical dynamic RAMs are designed to ADDRESS{ INPUT ROW DECODER BIT LINE 02 DATA OUT COLUMN DECODER ~ ADDRESS INPUT Fig.10: in this simplified diagram of one type of ROM structure, the presence or absence of a MOSFET transistor (Qt in this example) at each possible junction determines whether 1 or O is stored. If a MOSFET exists (ie, is connected) at the junction, a binary 1 is stored; if not, a binary O is stored. MAY 1988 89 store multiple 1-bit words, ROMs are usually organised to store bytes (eight bits). Typical ROM storage configurations are 1K x 8, 2K x 8, 4K x 8, BK x 8, 16K x 8 and 32K x 8. COLUMN Masked MOS ROM Most MOS ROMs use the row and column matrix structure discussed earlier. Two sets of decoders, one for rows and another for columns, are used to address a matrix of storage elements. The state of the storage elements determines whether a binary 1 or binary O is stored. Fig.10 shows a simplified diagram of one type of ROM structure. In this circuit, the presence or absence of a MOSFET (Ql) at each possible matrix junction determines whether a binary 1 or a binary 0 is stored. If the MOSFET exists, a binary 1 is stored. If the MOSFET does not exist, a binary O is stored. MOSFETs exist at every junction but the mask determines which ones are connected and which are not connected. In connection with the MOSFET transistor storage elements, another transistor (QZ) is associated with each column. The column decoders turn the MOSFETs on or off as required. To select a particular bit in ROM, an address is given to the row and column decoders and each, in turn, activates one line. If the output of the activated row decoder is binary 1, Ql (if it exists) is turned on, causing a binary 1 to appear on the bit line. The column decoder output turns on QZ. Therefore, the sense-amplifier output will see ground or binary O through Ql and QZ. The output, therefore, will be a binary 1. If the transistor, Ql, does not appear in the matrix, effectively an open circuit exists. The bit line being open causes an open condition to appear at the output amplifier if QZ is turned on, placing a binary O at the output. Bipolar PROMs Bipolar ROMs are made programmable by placing a fuse element in the circuit as illustrated in Fig.11. Note that the output of a decoder is used to enable a bipolar transistor at each matrix junction. The emitter of the transistor is connected to the column output line RCA Radio Pty Ltd is the only company which manufactures and sells every PCB & front panel published in SILICON CHIP, ETl & EA. 651 Forest Road, Bexley, NSW 2207 Phone (02) 587 3491 for instant prices 4-HOUR TURNAROUND SERVICE 90 SILICON CHIP ADDRESS INPUT l----+----3~-+----+-___;.,_ROW OUTPUT AMPLIFIERS v DATA OUTPUT Fig.11: bipolar ROMs are made programmable by the inclusion of a tiny nichrome or silicon fuse which is placed between the transistor emitter and the column output line. If the fuse is good and the output of the decoder is high, the transistor turns on and a binary 1 is applied to the output amplifier. through a tiny nichrome (an alloy of nickel and chrome) or silicon fuse. If the output of the decoder is high, the transistor turns on. If the fuse is good, a binary 1 is applied to the output amplifier; that results in a binary O output. To cause a binary 1 to appear at the output, the fuse can be blown. A high current is passed through the fuse which causes it to open. Now when the decoder output is high, the transistor does not conduct because its emitter circuit is open. The resistor at the input to the output amplifiers holds the input low, resulting in a binary 1 at the output. Once the fuses are blown in such a PROM, data is permanently stored there and cannot be changed. The advantage of such a ROM is that it can be programmed in the lab by the design engineer or in the field by a service technician rather than at the factory. The disadvantage is that such permanence is often undesirable. During the engineering design process it may be desirable or necessary to change the data stored in the ROM. That means that an entirely new ROM must be programmed. However, this problem has been overcome by an improved kind of ROM known as the erasable PROM. Erasable PROMs Erasable programmable read-only memories (EPROMs) are a special type of MOS ROM whose data can be obliterated when necessary. The most common erasing technique is ultraviolet light. The chip is usually contained within a standard dual-in-line package. However, there's a transparent quartz window directly over the chip that physically seals and protects the chip, while allowing light to pass through. If ultraviolet light is applied to the chip for a short period of time, all the data will be erased. Typically, all the bits in the storage matrix are set to binary 1 by this process. By being able to erase the chip, it can be reprogrammed and reused. The stucture of an EPROM is similar to other MOS ROMs in that it consists of rows and columns of MOS transistors. In the EPROM, a special floating-gate MOSFET is used at each matrix junction. The floating gate means that the gate element of the MOSFET is not physically connected to anything. It is the charge on the gate that determines whether or not the MOSFET conducts or is cut off. The state of the MOSFET programs a binary 0 or binary 1 into the matrix. To program the chip, a high source-to-drain voltage is applied to each MOSFET for a given period of time, which causes an avalanche breakdown in the PN junction between the gate and the source. Current flows and some of the electrons pass through to the gate, thus giving it a negative charge. With the gate sufficiently charged, the programming voltage is removed. Now, when power is applied to the PROM, the MOSFET (P-channel) conducts. Because the gate is isolated and insulated from the rest of the structure, it retains its charge for a considerable period of time. Where the MOSFETs are conducting, binary 1 's are stored. To program binary 0's, the MOSFETs at the desired location are not subjected to the high programming voltage. To erase the stored data, the MOSFET is exposed to ultraviolet light, which removes charge on the gate. It takes approximately twenty minutes of intense ultraviolet light to completely erase the chip. Since ultraviolet light is contained within normal ambient lighting, it too can be used to erase the chip. But because the ultraviolet content of most normal lighting is low, erasure would take a considerable amount of time. Nevertheless, it does happen. Therefore, once an EPROM is programmed, the quartz window must be covered to prevent accidental erasure. A variation of the floating-gate MOS ROM is an electrically erasable version known as an EEPROM, which is programmed in the same way as the light EPROMs. The floating gate MOSFETs are charged or discharged as desired to store the desired bit pattern. To erase the EEPROM, however, an electrical pulse can be applied. The pulse, usually about 20 volts, removes the charges stored on the MOS gates. The entire chip or only individually adressed words may be erased. EEPROMs have become extremely popular because they have the advantages of permanent data storage combined with the ability to erase and reprogram by an electronic process. §;l Reproduced from Hands-On Electronics by arrangement. (c) Gernsback Publications, USA. SHORT QUIZ ON DIGITAL FUNDAMENTALS - LESSON 7 1 . An 8K x 4 memory contains how many bits? a. 8192 b. 32,000 c . 32,768 d. 65 ,536 1 0. The two basic types of RO Ms are _ _ _ __ and _ _ _ _ _ _ _ _ _ _ _ __ _ __ __ 2. The common name for a read/write memory is 11 . What binary numbers are stored in adresses 2, 3 , 5 and 7 in Fig.9? 2 _ _ _ _ _ _ __ __ _ __ _ _ _ _ __ 3 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 5 _ _ _ _ _ _ _ _ _ _ __ _ __ _ _ __ 3 . The interval between address application and data output is called the _ _ _ _ _ _ _ __ _ ? _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ 4 . Most memory cells are organised as a _ _ __ of _ _ _ __ _ _ _ and _ _ _ __ __ _ 6. The basic storage element in a dynamic cell is a _ ______________ __ __ 1 2. Which of the following are volatile or nonvolatile? RAM _ _ _ _ _ _ _ _ _ _ _ _ _ __ ROM _ _ _ _ _ __ __ _ __ _ __ _ 7. The numerical location of a word in memory is called the _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ 13. Data is stored in a PROM using a device called a _ _ _ _ _ _ __ _ _ _ _ _ _ __ 5. A static memory storage cell is a _ __ __ 8. In order to prevent data loss in a dynamic memory, a ____ operation must be periodically performed. 9 . How many words may be addressed with 8 bits? a. 256 b. 512 c. 1024 d. 2048 ANSWERS ~O ~ 14. EPROMs can be erased with _ _ _ _ __ oran _ _ _ __ _ _____ _ _ _ _ _ __ 15 . A store operation is called a __ , and a recall operation is called a _ __ __ _ _ _ _ __ _ ~ - L ~~. ~~-9 pBaJ '8l!JM ·g ~ as1nd 1-eoppa1a '!45!1 ia10JA-BJlln ·v ~ 1aww-e1601d INOHd ·s ~ 81!lBIOA-UOU -'-- !NOH am-e,oA - IN'v8 . Z: ~ 0000 - 8 ~ ~O ~ Z: . ~ ~ a1qBWWBJ60Jd PUB pa)!SBW ·o ~ Z:~9 ·q "6 4saJJ8J "8 (89L'Z:8 = vX \;$8JPPB JOl!OBdBO (l!OlBI) dO!Jd!IJ suwn100 'SMOJ 'X!JlBW aw1i ssaoo-e IN'vH 2:6 ~8 = >!8) 89L ' Z:8 ·o M AY 1988 .L ·g ·g ·v "8 ·z: .~ 91 the exact centre of the stud. It works like magic. We checked it on a portion of unfinished Gyprock wall (so we could see exactly where the studs were) and it works precisely as claimed. It also works on metal framed walls and can be used to find pipes and conduits in walls so that you don't drill into them by mistake. How does it work? The instructions on the package claim that it "detects changes in the wall density to find exact stud location". Inside the little instruction leaflet it has a couple of paragraphs entitled "For the technically curious". The Studfinder operates by measuring variations in dielectric constant. It certainly is an intriguing and effective gadget. It is available from all Tandy stores at $54.95. Electronic studfinder for builders and handymen How many times have you had to drill a hole in a Gyprock or plaster wall and have missed the stud? It is immensely irritating. In the past the solution has been to use a nailfinder - find a few nails in a stud and then you can determine the centreline and then drill. Oh yeah? It is not always that easy. Cladding nails are not necessarily driven into studs; they are sometimes driven into noggins. Now there is an electronic stud finder which really does find the centre line of a stud and you don't have to look for the nailing points. Just press the stud finder against the wall or ceiling and hold down the on/off switch. Wait until the calibration LED goes out and then slide the device over the surface of the wall until the LEDs flash to indicate a stud. Then move it back and forth and the LEDs will identify Intelligent modem Solar powered exhaust fan This must be one of the most obvious applications of solar power ever thought up - a solar powered extractor fan. It is specially designed for ventilating boats but can be used for caravans, greenhouses, garden sheds or any small place that tends to get stuffy. If you've ever gone on board a small boat which has been closed up for several weeks or entered a caravan wpich hasn't been opened in months, you'll know how much this product is needed. It would also be ideal for ventilating a Portaloo! (Ever been in one of those on a hot day?) Cunningly ensconced in a splashproof circular housing is a 10cm fan which is powered by a large solar cell, also 10cm in diameter. The fan runs even in overcast conditions and while it does not create a powerful 92 SILICON CHIP draught, it certainly does move the air. For really stormy conditions there is a yellow plastic lid which fits over the solar cell to stop water being blown through the fan. Funnily enough, in really bright sunny conditions, the solar cell will still run the fan even with this lid on. Called the Sunvent, this answer to a boatie's prayer is available from Jaycar Electronics, priced at $49.95. Datasat Information Systems Pty Ltd have released their new Vtex intelligent modems in IBM half-card and free-standing desk format. This Hayes-compatible unit operates at 300 or 1200 bauds and includes the usual "intelligent" features such as auto-dialling, auto-answer and au to-disconnect. Also included (in Vtex software) is a feature called auto reverse. This allows communication with a remote unattended computer whereby either modem can automatically send or receive alternatively at 1200 bits/second. This means that high data transfer is obtained, even on poor quality lines, so Telecom charges are minimised. For further information, contact Datasat Information Systems Pty Ltd, Suites 3 & 4, 67 Scott Street, Liverpool, NSW 2170. Phone (02) 82 1 1622. Engraving tool from Tandy Need to label your hand tools to identify them? Perhaps you want to label your VCR and audio equipment in line with the recommendations of your local Neighbourhood Watch scheme. This little ba ttery powered engraving tool is just the ticket for these jobs. It takes two AA cells (preferably alkaline for longer cell life) and has a hardened serrated steel tip which is rotated at high speed to do the work. Pressing a button on the side of the housing turns on the motor. You just hold it like a pen. It works well although for best results you need a light touch; pressing too heavily will just stall the tool. With a little practice you can print or write. It costs just $5 .29 (not including the cells) and is available from all Tandy stores. TDK "limited edition" audio cassette New logic analyser uses 100-LED arrays Logic analysers are usually dedicated oscilloscopes which may have six, eight or more traces for displaying logic pulse waveforms. As such they are fine for design work in the laboratory but are often too cumbersome for production or service work in the field or workshop. To meet the need for a compact logic analyser with visible displays, the LogicBridge was developed. This is a dedicated instrument with four 100-LED arrays which give the ability to display two logic waveforms. The effective real time pulse bandwidth of the LogicBridge is 10MHz although its inbuilt glitch Cheapie motors for toys and models Jaycar have two economy motors available which are good value if you're involved in robotics, model cars or model trains. One type runs from 6V at 2400 RPM (35mm long with 38mm diameter) while the other runs from 3V (nominal) at 5100 RPM. Jaycar must have bucketloads of these because they're flogging them off at a dollar each. At this price it's worth snaffling half a dozen just in case. You never know when they might come in handy. Flashing party light TDK has released a new version of its popular SA formulation tape which is housed in a more rigid cassette. It also comes in a new stylised case with rounded corners to make it easy to carry in your pocket. The new cassette is only available in a 90 minute version. Called the TDK SA-LTD, the new tape has a very low bias noise of - 63dB. Recommended retail price is $8.60. catcher captures pulses down to -50 nanoseconds. The unit also has sufficient memory to allow it store up to 100 traces of 100 bits each, for later display and analysis. For further information on the LogicBridge, contact Emona Instruments, 86 Parramatta Road, Camperdown, NSW 2050. Phone (02) 519 3933. continued from page 73 and we alter the value of that capacitor. We used a 0.33µF capacitor and a 180k0 resistor in series with a lMO pot. The pot allows the flash rate to be varied from about two per second up to about 13 per second. We u::ied a 16mm diameter pot which fits easily into the lower part of the strobe casing. The two 8.2MO resistors and the 0.033µF capacitor need to be removed from the board. Install the 180k0 resistor and the 0 .33µF capacitor in their place, as shown in the wiring diagram of Fig.2. The lMO pot is wired to the PCB with two short lengths of hookup wire (you could use a twostrand length of rainbow cable instead). We also suggest you wire a 12V DC plugpack permanently to the strobe light which will make the whole unit self contained. The plugpack should have rating of 300mA or more, to cope with the higher cur rent dr ain when the flash rate is increased. ~ MAY 1988 93 ASK SIUCON CHIP Got a technical problem'? Can't understand a piece of jargon or some electronic principle'? Drop us a line and we'll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Wants parts for frequency meter After reading the articles on the 1GHz Digital Frequency Meter, I thought that I would be able to construct an invaluable piece of electronic test equipment for myself. I discovered that I had all the necessary components except for the main semiconductors, namely the SAB6456, 7216A and the Motorola devices, 10116, 10100 and the 10131. I thought that it would be a waste buying the kit because I would be buying components I already have. After going to local electronics stores in Melbourne to buy these parts, I was told that the 10100 was obsolete and no longer available. What's the use in starting an expensive project only to be told that one part is unavailable? What happens if a kit builder needs spares? Would it be at all possible if you could tell me where these parts are available from and their respective prices? (M.B., Lower Templestowe, Vic). • Unfortunately, the response you have had to requests for hard-to-get parts is all too common. When a store does not have a part in stock it is very easy to claim that it is obsolete or no longer available. If we really had produced a design with obsolete parts, we'd look "right 'nanas", wouldn't we? (let's hope it never happens). In our time we've been told that all sorts of components are no longer available but which are still widely on sale, years after they were supposedly obsolete. The real problem is that two of the ECL (emitter coupled logic) devices used in the DFM have not been stock items. Nor have the SAB 6456 prescalers for that matter and they were virtually unobtainable for the first few months. At least no- Door minder query I've recently constructed the Door Minder project described in the February issue. I did not build it from a kit but from a homemade PG board with parts from my junkbox and some bought. I deleted the two-tone chime IC and connected a small buzzer in its place, as I'm just experimenting with the circuit which I hope to use as a sensor for a burglar alarm. Upon completion I just couldn't get it to work properly. All the voltages were correct with those indicated in the article. The only response I could get was if I blew on the microphone; opening or closing the door had no effect. As a last resort, I tried changing the electret microphone and it worked perfectly. It was so sensitive that I could put it in a room at one end of the house and close the door to that room, yet it 94 SILICON CHIP would still sense a door opening at the other end of the house. Thank you for a very simple yet ingenious little project. Does this mean that some electret microphones are not suitable, as I remember reading that some are more sensistive than others? Or would you say that the electret microphone was faulty? (T.W., Albany, WA). • We really don't know how consistent these cheap electret microphone inserts are. They are made by the squillion in Asia and imported into this country by the bucket load so it's anyones guess how good they are. On the positive side though, we have not come across a faulty one in many years and they do seem to very sensitive. Either way, we'd have to conclude that you were unlucky to strike a faulty one. one has had the hide to suggest that they were obsolete; they are widely used in Europe as prescalers for UHF tuners in TVs. Incidentally, the ECL devices are made by Philips as well as Motorola. At the moment, the only store that we know that will sell you these parts, without you having to purchase a DFM kit, is Geoff Wood Electronics in Sydney. Phone (02) 427 1676. Also wants DFM parts I am currently building the 1GHz Frequency Meter published in the November and following issues but am having trouble finding a few of the components for it. I have searched all over Sydney in the major electronics shops (and some of the smaller ones too) but have have no luck in finding these components: 10116 line driver, 10100 3-input quad NOR gate, 10131 dual D flipflop and SAB6456 prescaler. (M.G., Leura NSW). • As you can see, the answer is immediately above. Incidentally, the 10116 has been a stock item for years at stores such as Dick Smith Electronics, Jaycar and Altronics. It is still listed in current catalogs. Endless loop tape player I am writing about the endless loop tape player published in the March issue of SILICON CHIP. To me, this seems rather cumbersome as there is no way you can be sure that it will start and stop in the same place every time. Unless a sensor is incorporated to stop the circuit when the tape reaches the end, or a timer to do the same thing is included, the position that your tape starts and stops is at the mercy of whoever presses the button. Answering machines use a continuous tape with a metal sensing foil , and a sensor to tell the next Wants more design info I am very interested in designing electronic circuits and have quite a few operational circuits to my credit. However, my knowledge in this field is limited and the more information I can get on the subject, the more I enjoy the hobby. How about a small article tagged on the end of each or even some of your projects to explain a few things? Things like why did you choose a particular transistor or diode in a circuit; what made you choose certain frequencies or time delays in your circuits; and why use one component when perhaps another will do. An example of this is your UHF remote switch described in the March issue. In both the receiver and transmitter you have used transistors which mount underneath the board. Why didn't you use a BF199 which I am fairly sure would do the job, which mounts in the usual way, and which is commonly available? I feel I am not the only one who would like more information on electronics design and the inclusion of this in your project text, even in a small way, would not go astray. I have another question on the UHF remote switch. I wish to use the transmitter and receiver up stage that the tape has reached the 'end'. This continuous tape is available separately at business machine shops and some electronics stores. Tandy sells a to-second continuous tape for $5.95. This can be used by modifying a conventional cassette player. A metal strip is bent so that it pokes into the cassette housing through a hole between the rec/play head and the pinch roller. By testing the resistance between this metal strip and the rec/play head, you can stop the tape in the correct position. I mounted the metal strip on the righthand mounting nut of the rec/play head. Note that it must be to the output of the MC145028 IC in an alarm system. Can I redesign the circuit to a different shape and leave off the parts I don't require? In other words, is the layout of the RF section critical in any way? (J.M., Georges Hall, NSW). • The problem with giving a lot of background information in presenting a project is "where do you draw the line"? We think that there is an unlimited fascination in the design of electronic circuitry and we find a great deal to argue about when we are working out the details of new circuits to be published. But if we gave all the pros and cons which are discussed when even quite simple circuits are being designed, we would end up with a magazine which was three or four times as big as it is now. (What a wonderful target to aim for!) We are very conscious of the demands of our readers and we are trying to give as much info as we can within the limits of our space. For example, in this month's article on electronic ignition we have devoted a number of panels on background info. Even so, we are sure that in the minds of many readers, a lot of questions will remain unanswered. The Ask Silicon Chip pages can partly fill the gap and we are mounted using insulated washers. To control the cassette player power supply I use a flipflop that is set or reset when one of the inputs is grounded; ie, by applying 0V to the set or reset input. You have started an excellent magazine and I hope the standard stays high, as I have no doubt it will. But it won't if you allow the end of articles to become lost. What happened to the end of the article on continuous loop players? (B.S., Aranda, ACT). • We agree that the endless loop tape player is a little cumbersome but it was published mainly as a novelty item. We are sure that many of our readers will enjoy glad to answer any questions that readers may have. As far as the UHF remote switch is concerned, the BFR91A was specified for the transmitter and receiver because it has a very high gain-bandwidth product of 6 Gigahertz. (The gainbandwidth product is also known as the transition frequency, Ft, where the gain of the transistor is unity). More to the point, the BFR91A is specifically intended for use in UHF and microwave amplifiers. It is ideal for the UHF remote switch even though it is a teensy-weensy device that is a bit of a pain to mount. Still, them's the breaks if you want something that really works at UHF. By contrast, the BF199, although it may be presently more readily available, is more your steam-age device. It has an Ft of only 550MHz and is intended for video applications; ie, frequencies less than 50MHz. We doubt whether it would work satisfactorily at more than 300MHz. There is no reason why you cannot redesign the layout of the UHF remote receiver as long as you keep the RF paths reasonably short. In fact, you could just chop the existing layout in half, as the the basis for your design. experimenting with it. Similarly, many readers are likely to be interested in your ideas for using continuous tape cassettes although some may think that they, too, are a little tricky. For our part, we think that one man's cumbersome method may . turn out to be another's ingenious solution to a problem. It was a little ironic that the story on the Endless Tape Loop should appear not to have ended. In reality, the ending of the article was "turned over" to page 89 but unfortunately the turnover line at the end of the text on page 42 was omitted. The proof reader has been kicked. ~ MAY1988 95 CEN'l Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE NEARLY 1500 PRINTER buffer kits now sold . Prices start at $39 for a 256K short form kit. All items advertised are in stock. Dealer enquiries welcome. Bulk discounts. Schools, Govt. Depts. orders accepted. Oh yes!! IBM compatible. Australian designed and manufactured. Ideal project for user groups and students. For a free catalog send a 37c stamp to: Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. OATLEY ELECTRONICS - take note of our low prices and some May 1988 specials on kits and ready made items. FM Stereo Transmitter: yes, this unit transmits the complex FM multiplexed stereo signal to any conventional FM stereo receiver! And it's not a kit - it's ready made, housed in a small enclosure (72 x 38 x 21 mm) and powered by just one 1.5V AAA battery with a life of 100 hours. Unit transmits on 90 .35MHz and is tunable from 89 -91 MHz; automatically switches on when an audio signal is applied to its input and automatically switches off about two minutes after the input signal ceases . Input impedance is 32 ohms, range is about 15 metres (less than 15mV/metre at 100 metres), and the unit has a mono-stereo switch. Input signal is obtained via a standard 3 .5mm stereo plug which can plug directly into the headphone outputs of your hifi equipment, stereo TV, " Walkman" cassette player, compact disc player etc. For example , you could use it to transmit a stereo signal from your house hifi or TV to your Walkman or car stereo. Great for people with hearing problems and people who like loud music without disturbing their neighbours. During May, we will supply the Stereo FM Transmitter for an unbeatable price of only $59.95 plus $2 p&p - and we'll include two 1.5V AAA alkaline batteries in the price. Remote Controlled Ultrasonic Car Burglar Alarm: this is not a kit - it's a complete commercial alarm. Unit is remote controlled by a small keychain transmitter, has a self-contained untrasonic movement detector which mounts on your dashboard, and a siren/alarm unit which would normally be mounted in the engine compartment. Installation is made simple by employing a pre-wired loom which includes connectors! Even the pin switches (eg , for bon- 96 SILICO N CHIP net/boot protection) and the alarm stickers are provided . Features include ultrasonic movement detection , digitally encoded UHF remote control (8-metres range) , 60-second exit delay, no entry delay. Armed with ignition key, auto reset after a 1-minute alarm, LED status indicator and panic button on ultrasonic movement detector. Suits 1 2V negativeearth vehicles. Compare this unit with other commercial alarms and realise that this unit is a true bargain at only $129.95 plus $5 p&p. Car Battery Isolator: you can easily add back-up battery operation to the above alarm or to any other alarm with our car battery isolator. Isolates the car's battery and charges the back-up battery. All you need to add is a 1 2V rechargable battery (read on). The back-up battery isolator is priced at only $5.50 plus $1.00 p&p. Satellite Siren (Sept.87 EA): perhaps this unit is better referred to as a Back-Up Siren. Add the protection of this complete second alarm system into your existing alarm system. Automatically gain the benefit of back-up battery operation and a complete and remotely placed second alarm system . This unit is simple to install; it only requires two connections to your existing alarm system. It comes into action when the main alarm is vandalised, the main alarm power is interrupted or the vehicle battery is disconnected. For the month of May we are offering a complete kit for the Satellite Siren at a very special price. What's in this kit? - PCB and components, battery holder, barrel key switch (with two keys), a su itable plastic box, four rechargable nicad batteries (penlite), and a 12V mini piezo siren (that's everything you 'll need). Add up some of the normal prices for the items listed and realise that this project is a May bargain at only $44.95 plus $2.50 p&p. Ignition Killer: let's the burglar get away with your car for a few seconds only. The car then stops and is able to be restarted after a few seconds , then it stops again and so on. This kit also includes the required external hidden switch . The design is almost identical to the very popular one published in EA except that it uses an economy heavy duty relay. The complete PCB and components kit for this project is available during the month of May for a giveaway price of only $9.95 plus $1.50 p&p. Dashboard Flasher (flashing light): this ever popular "Claytons" car alarm simply Advertisers Index Our advertisers are vital to the success of SILICON CHIP. Please give them your support. Altronics ....... .. ..... .... ...... 52-55 Arista Electronics .... .. ... ....... . 1 5 Autotron Australia .. ...... .... .. .. 39 Avtek ........... .. ........ .... ..... .. IBC Dick Smith Electronics .... 40,41, 74,75 Elmeasco ... ... ...... .... ... ....... IFC Geoff Wood Electronics ....... . 67 Jaycar Electronics .... ... ... 24-31 Kenwood Australia ....... .. ... OBC RCS Radio .. ... ... ...... ... ......... 90 Rod Irving Electronics ..... ...... 16 Scan Audio ..... .. ... .. ..... .. ... .. . 61 Zap Electronics ........ .. ... ...... 81 PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd , Bexley, NSW 2207 . Phone (02) 587 3491 . • Jemal Products, 5 Forge St, Kewdale , WA 6105. Phone (09) 451 8726. flashes a lamp on the dashboard of your vehicle when the ignition is turned off. The kit includes the PCB, all components and an incandescent lamp assembly. The price for this kit for the month of May is an incredible $6.99 plus $1.00 p&p. How about our prices on some of our individual items: popular 11 0dB Mini Piezo Screamers $16.00; larger 120dB Piezo Screamers $23.00; large Metal Sirens - $25.00; 12V 1.2Ah Rechargable Gel Batteries $23; Soldering Iron Stand/Cleaner clearance at 50 cents (ask for a free one with any other purchase) ; quality commercial FM Microphones in attractive metal enclosures at only $15.00! Mail address: Oatley Electronics, PO Box 89, Oatley, NSW 2223. Shop adresss: 5 Lansdowne Pde, Oatley West, Sydney, NSW 2223. Phone (02) 579 4985. Bankcard, Mastercard and Visa Card accepted with phone orders. Shop hours: Mon; Wed; Thur; and Fri. between 10am and 5pm. Other times possible with prior arrangement. MODEMS Don>t buy imported unsupported The Avtek advantage • Australian designed Australian manufactured Australian supported MEGAMODEMS 12/123 The Avtek Megamodems provide Australia's best value communications products, with a range of fully automatic, autodialling modems. Megamodems are suitable for data transfer from personal computers, terminals, mainframes and mini host computers and for all videotex services such as Viatel. The use of the latest technology has enabled us to make the Megamodem more compact and reliable than any other modem. Price is very competitive and reflects efficiencies incorporated in the design. The Megamodems are locally designed and built. Service, support and specialist R&D for the Megamodem range is all based in Australia. Available either as a standalone RS232 model or as a plug in 1/2 card for IBM PCs and compatibles. The Megamodem range of modems are Telecom authorised. Specifications Data Standards Data Rates MAIL ORDER WELCOME VISA Automatic Dial, Answer, and Disconnect: The Megamodems will automatically answer an incoming call and connect the computer to the line.When originating a call it will then dial out the required number and auto-connect to the computer at the other end. It will then "hang-up" at the end of a communications session. Both pulse and tone dialling are supported. The modem Is compatible with new Telecom exchanges and modern PABXs and can handle high speed tone dialling. Fully Hayes AT Smartmodem Compatible: The Megamodems are industry standard ''HAYESSMARTMODEM "compatible which means they can take advantage of all the communications facilities of packages such as Crosstalk, Open Access, Symphony and Multicom. All communications parameters such as baud rate, parity and number of stop bits are set up automatically by the software and the Megamodem. Using appropriate software data can be sent and received while the Megamodem is unattended. CCITTV27, Bell 103, CCITT V22 Bell 212. (123 model only CCITT V23) 300/300, 1200/1200 (123 model only 1200/75, 75/ 1200) MasterCard BUY DIRECT FROM THE MANUFACTURER Model 12 & PC12 $375 nctax Model 123 & PC123 $449nctax (~ . . =~ vi-rr L(;·~·-=- ~, I ~J CJ PO Box 651 Lane Cove 2066 Telephone (02) 888 5533 Facsimile (02) 887 2839