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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Contents Vol.10, No.3; March 1997 FEATURES 7 Driving A Computer By Remote Control The latest-generation remote access software makes it possible to control a computer at a distant location via the telephone line. We look at two popular packages – by Ross Tester 30 Video Conferencing: The Coming Boom Video conferencing is set to revolutionise face-to-face communications. Here’s a rundown on how it works – by Sammy Isreb 76 Cathode Ray Oscilloscopes; Pt.7 DRIVING A COMPUTER BY REMOTE CONTROL – PAGE 7 Learn how the display tubes used in modern digital scopes work and how the image is built up on the screen – by Bryan Maher PROJECTS TO BUILD 18 Plastic Power PA Amplifier Rugged design includes a 100V line transformer, thermal cutout and DC offset adjustment and puts out 175W – by Ross Tester 34 Signalling & Lighting For Model Railways We describe two separate projects for your model railway: a 3-aspect signal unit and a constant brilliance lighting circuit – by Jeff Monegal 40 Build A Jumbo LED Clock Read the time at 50 paces. This digital clock has very large LED displays and is based on readily available CMOS ICs– by John Clarke PLASTIC POWER PA AMPLIFIER – PAGE 18 58 RGB-To-PAL Encoder For The TV Pattern Generator Simple add-on board replaces the discontinued TEA2000 RGB-to-PAL colour encoder IC used in the TV Pattern Generator – by John Clarke 72 Audible Continuity Tester This nifty little continuity tester varies its tone according to the resistance being measured – by Rick Walters SPECIAL COLUMNS 52 Serviceman’s Log The rich tapestry of servicing – by the TV Serviceman 62 Radio Control Preventing RF interference on the 36MHz band – by Bob Young SIGNALLING & LIGHTING FOR MODEL RAILWAYS – PAGE 34 82 Vintage Radio The importance of grid bias – by John Hill DEPARTMENTS 2 3 28 86 89 Publisher’s Letter Mailbag Circuit Notebook Product Showcase Order Form 90 92 95 96 Back Issues Ask Silicon Chip Market Centre Advertising Index BUILD A JUMBO LED CLOCK – PAGE 40 March 1997  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young Photography Glenn A. Keep SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Pay TV picture quality is poor So how many of you have signed up for Pay TV with Optus or Foxtel? Not many I hope, for your sake, because a high proportion who do quickly become disenchanted. Sure, there are lots of channels but most of them you wouldn’t be bothered watching. The “Discovery” channel on Foxtel is worth watching but most of the others you would have to consign to the video dustbin. Yes, I know that some people sign up to get sports programs but they are special cases. Even if you are perfectly happy with the program selection, eg, 24-hour cartoons, weather, endless re-runs of “I Love Lucy” or limited movies, the picture quality is distinctly poor. In fact, one of the so-called advantages of Pay TV is that you get the “free to air” channels free. So you can dispense with your ugly old TV antenna. In fact, I have seen some people argue in favour of (ugly) cable TV because it will eliminate all those ugly TV antennas! Well, you don’t have to be really discerning to see that the picture quality of the free-to-air channels as fed down the cable is far inferior to viewers’ reception from their own TV antenna. There are some exceptions, of course, and people in difficult reception areas, such as the beachside suburbs of Sydney, will get better free-to-air channel pictures than off their old TV antenna; better, but still not first class. In general, compared to the first class picture quality available from free-to-air channels in most areas of Sydney, the cable pictures are smeary and lack colour saturation. In fact, there is even ghosting present! What a big advance that is. This is what people are paying for and now digital TV has been an­nounced with its extra channels and better picture quality. If cable TV is what some people are prepared to accept, why bother with digital TV? And what if you do decide to get rid of your old TV anten­na? There is a catch. Say you want to watch the cricket on Chan­nel 9 and your wife wants to watch something on SBS or one of the pay TV channels. Sorry, no can do. You can only watch one signal at a time, regardless of how many sets you may have in your home. If you want to watch different channels on multiple sets simulta­neously, you have to pay for extra decoders. So you really can’t afford to get rid of your old antenna, can you? It seems to me that if the cable TV people cannot manage to deliver picture quality which is at least as good as you can get from your own ugly TV antenna then they are going to have even more problems when it comes to delivering the more hi-tech serv­ices they are promising such as optical fibre modems, interactive TV and all the rest of the pie in the sky stuff. Sure it will eventually come but when it does it won’t be as half as good as it is cracked up to be. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. 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. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip MAILBAG TO-220 mounting has problems Firstly, I would like to congratulate you and the staff on a very readable hobbyist magazine. It is keenly read by many I know and features some fine educational projects. I would like to comment on D. Woodbridge’s letter in the October 1996 issue. Mr Woodbridge raises some excellent points in his letter but the issues of the desirability of vertical mount­ ing of flatpak TO-220 style power devices (and indeed ICs) de­serves closer scrutiny in my opinion. It should be realised that when such components are bolted to heatsinks, soldered into a circuit board and mounted vertically when the heatsink is also bonded to the board, they are prone to two possible modes of device and/or circuit malfunction. By rigidly bonding the components in this fashion, thermal expansion of the component leads leaves them nowhere to go but either back up into the device encapsulation or further through the board. In both cases, connections of one type or another may fail and often do (ie, broken wire bonds in the device or cracked solder joints in the board). If the devices are to be mounted vertically, a heatsink clamp which affords some “give” rather than a bolt is the best option. Bonding the device leads beyond the point where the lead narrows should be fine for horizontal mounting as long as the bend is made slowly so the metal in the lead doesn’t crystallise and craze. Some device manufacturers explicitly warn against rigid vertical mounting in their power device data books. It’s also worth noting that TO-3 style devices can suffer a similar misfor­tune when rigidly fixed to a PC board, an occurrence avoided by good manufacturers either using board sockets (not the best idea for connection reliability) or using short flying leads between the device leads and the circuit board. Theory has it that TO-3 socket connections are actually kept clean and low resistance by the thermal movement of the device leads but after a moderately long servicing career, I treat connections of any sort with suspicion. M. Watts, Wellington, NZ. Dangerous computer mains wiring I would like to draw your attention to a very dangerous computer power supply I was sold recently. I do a fair number of computer upgrades and repairs for friends and am always on the constant “upgrade path”. As the prices of these 686 166MHz+ CPUs are so low at the moment, a new computer was definitely in order. All the various bits required were purchased along with a new mini tower case and integral power supply. These have those “speed displays” and I though I should set the speed to read 166 before the “guts” were inside, as otherwise it would be too fiddly to change all those jumpers with hard disks etc, in the way. After plugging in the IEC plug lead and turning it on, it read 133. Now I always have a habit of brushing the exposed metal of anything new plugged into 240VAC quickly with the back of my hand and that’s when I felt a nasty burning sensation. I thought some of these switchmode supplies were nasty but this was really nasty. Bear in mind that I was standing in the kitchen, on tiles in bare feet. I went upstairs to get the DMM and my suspicions were confirmed; the chassis (the entire case!) was at 240AC! A quick test of the IEC chassis plug revealed there was no Earth and the Active pin was attached also to the power supply case which is bolted to the computer case! Opening the power supply showed the cause. During the hand soldering of the PC board to the IEC sockets, the Earth wire, which is a little loop, had flicked off the earth terminal and sprung up, still molten and soldered itself to the Active input pin directly above, creating what is the worse possible combina­tion, a unit that will function, yet the case is live. The scary thing is that if I had grabbed the case to turn it around (I was about to) I don’t think I’d be writing this letter or a computer builder could have built the unit, sold it, and some kid on Christmas Day with bare feet in his rumpus room could have touched the case or anything attached to it (modem, mouse, or CD-ROM headphone socket) and been fried. I contacted the importer/distributor and the guy I spoke to told me they “went through 30+ cases a day” and “they don’t have time to test them”. This is when I asked about basic electrical safety testing, when they perhaps open the boxes to change the voltage switch from 110 to 240VAC – which they do not do. Basi­cally, he seemed relatively unconcerned but took my number when I asked them what they were going to do about it. Bear in mind, all I wanted was an assurance they would check all incoming cases for electrical safety. And this is from one of the biggest importers of computer parts in the country too! So there you have it, perhaps an isolated incident on the production line and nobody hurt but if it weren’t for my non-trust of anything that plugs into 240VAC until it’s proved safe, I may have been fried or at least given a bigger jolt. By the way, the earth leakage breaker did not trip – even though it does on other occasions. J. Richardson, Southport, Qld. March 1997  3 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semicustom electronics & data communications. 63 chapters, in hard cover at $120.00. Silicon Chip Bookshop Radio Frequency Transistors Newnes Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Guide to TV & Video Technology By Eugene Trundle. First pub­lish-­ ed 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $49.95. Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Digital Audio & Compact Disc Technology Electronics Engineer’s Reference Book Hard cove Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM Power Electronics Handbook Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. 6  Silicon Chip r Edited by F. F. Mazda. version now available First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $85.00. Surface Mount Technology By Rudolph Strauss. First pub­ lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $52.95.   Title  Newnes Guide to Satellite TV  Guide to TV & Video Technology  Servicing Personal Computers  The Art Of Linear Electronics  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Electronic Engineer's Reference Book  Radio Frequency Transistors  Surface Mount Technology  Audio Electronics Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95 If you have ever been in the predicament of working in one place when the files or programs you want are in another, you will understand the frustration. “If only there was some way to access that computer from where I am now . . .” It’s becoming more and more of a problem as telecommuting becomes more and more popular. Telecommuting certainly doesn’t suit everyone, nor does it suit many industries but many organisations now realise the benefits of allowing particular staff to work at home, either part of the time or all the time, and use technology to “commute” their work to the office, instead of commuting themselves to the office. It saves time in travelling (which for most people is completely wasted time) and it can save in high-rent office space. And the worker is usually a lot happier; a win-win situation if ever there was one. Most contractors and freelancers have practised a form of telecommuting for years, doing the work in one place and electronically lodging it in another. But as with employees telecommuting, they occasionally encounter a few hiccups in the sys- By ROSS TESTER tem, when things don’t quite work as intended! Let’s look at a few real-life examples (yes, these are from unfortunate experience!): I have worked hours, perhaps days, at home on a project and when I finally take it to the office or to a bureau, one of the files is missing or corrupted! I’m working in a strange office and the software they have simply won’t do the job. Or they don’t have a particular type style I want to use. If only I could get access to the software on my own computer... A client sees a proof from a fax or from a mono laser printer. Of course, they want to see the glorious living Technicolor version. And what if we moved this to there and changed this and . . . A file is bigger than 1.44MB and splitting it is not easy. But I need to get it from point A to point B. How can it be transported? My little laptop computer simply can’t handle the jobs my desktop computer can. If only I could link them . . . We could go on but we’re sure you get the picture. So how do you solve the dilemma? First you’ll need a modem What’s a modem? It’s one of those few buzz-words of computer speak which actually tells you what it does! Modem is a contraction of MOdulate/DEModulate. Its task is to take the digital information from a computer and MODulate it to analog format so that it can be fed down a telephone March 1997  7 This Dynalink 33.6Kb external modem was purchased by phone order for just $179.95 including next morning delivery. An internal version is even cheaper but should only be considered if you have plenty of vacant slots – now and for the future. line. Another moDEM will DEModulate the analog signal back to digital for the computer to process. Modems have been around for years but today’s modem is a far cry from those of even a decade ago. As everyone knows, one of the major advances in computer technology has been in the speed department. From the humble IBM XT operating at the then blinding speed of 4.77MHz, 133MHz is rapidly becoming today’s entry level computer. And 166MHz and 200MHz models are now common. At the same time, modems have also been increasing in speed. Back in the days of the XT, most modems were flat out at 300 bits per second (bps). Today, no self-respecting ‘net surfer would be seen dead with anything less than a 14,400 bps modem. Even that is considered snail pace – 28,800 and now 33,600 bps modems are virtually a necessity. Incidentally, 33,600 bps is just about as fast as modems can theoretically get using conventional phone lines and currently available technology. Just as with PCs, as modems have gone up in speed, their price has taken the opposite direction. To research this article, we bought a brand new 33,600 bps modem, over the counter, for just $179.95. By comparison, a year ago when we purchased the 28,800 bps modem we use in the Silicon Chip office, we paid more than double that! 8  Silicon Chip So modems have got much faster and much cheaper. So what? What it means is that data communication is now well and truly within the average person’s reach. Most retail computer packages now include a 14,400 or 28,800 bps modem, especially as more and more people are climbing onto the Internet band­waggon. Of course, we are not limited to using the telephone line and a couple of modems for communication between computers. These days you could connect the computers directly via their parallel or serial cables if they are close enough, or you can use an existing IPX or TCP/IP network, connection via the Internet or ISDN (Integrated Subscriber Digital Network – a somewhat expensive digital data link capable 64kb/s), or even infrared (IrDA) connections if you have them. You might be wondering why anyone would want software to communicate via a network when the network is specifically set up for that purpose. There are specific applications where the network doesn’t have the capabilities we are looking for: more of this anon. Suitable software It doesn’t take much in the way of software to get computers to talk via a modem. In fact, Windows has had quite usable communication software built in for years. If you wanted more bells and whistles then you had to buy more powerful software but even that, for the most part, has been pretty reasonably priced. Basic communication software is fine if all you want to do is send files to and from other computers, log on to bulletin boards or even access the Internet (although you’ll need other software to properly use the Net). As you might expect if you want to do much more than that you’ll need more specialised software. In this article, we’re looking at software which will do much more than allow two computers to talk to each other. It will allow one computer to control the other! We are talking about remote control or remote access software. In a nutshell, this software not only communicates with a second computer, it actually allows complete control over it. While there are many packages around which do the job in varying degrees, we looked at two main contenders: LapLink and pcANYWHERE. With minor differences, both do essentially the same job with similar performance. As its name suggests, LapLink originally started out as a program to transfer files between laptop (and later notebook) computers to desktop models using their parallel or serial ports. pcANYWHERE, on the other hand, started out as a software to remotely address one computer from another. Over the years, both packages have taken on more and more of the other’s features to the point where today there is little to choose between them. The version of LapLink we used was the 32-bit LapLink for Windows 95 (also known as LapLink V7.5). This package also includes the 16-bit software for Windows 3.11 users and is, in fact, a means of creating a bridge between machines using the different operating systems. We also used pcANYWHERE32, another 32-bit package designed for Windows 95 or Windows NT. Other versions are available for 16-bit (ie, Win 3.11, etc). But regardless of which software you use, the same program and version must be loaded on both computers. What can you do? There are three basic uses for remote software which we will examine in turn. 1: Remote Computer Control This is the most important use for remote software. With this system, you effectively “drive” the remote computer from the computer you are currently at (the local computer). It is important to note that the remote computer functions just as if it would if you were sitting at the keyboard – it provides all the power, all the “grunt” (or lack of it) – any limitations you would experience at that computer (eg lack of memory, limited disc space, etc) you will also experience remotely. However, all the software on that remote computer, its disc drives, even its network connections (if it has any) are at your disposal. Basically, the local computer simply becomes a terminal for the remote computer – all work is actually performed in the remote and “echoed” to the local computer. Windows (3.11 and 95) has software built in which sort-of does the same thing. The big disadvantage is that it tends to send a lot more information to and from each computer, information which it needs to accomplish the task because both computers are working hard in the process. Programs such as pcANYWHERE and LapLink achieve a better result by letting the remote computer do the work and simply sending screen images and keystrokes over the link, resulting in a much faster system. One application where remote control really comes into its own is in the linking of a laptop or notebook computer (which is often limited in resources) to a higher-performing computer. The laptop or notebook may not have the power to accomplish certain tasks – high-end graphics, for example. Connect it to a computer intended for the job and bingo! Another popular use: think about how remote control can make life simpler for people involved in computer support. Ask anyone in this field and they’ll tell you there is overwhelmingly one main problem: the person on the other end of the phone! Not only is that person more than likely to have caused the problem in the first place, they have a devil of a job explaining the problem to tech support. Now, if tech support had remote computer control they could solve the problem much more quickly, without having to leave the office! The potential savings in time, and therefore money, are staggering. By the way, this is not simply a possible use: many PC support companies are using exactly this approach these days. One question which arises from time to time is on the touchy subject of software licences. You know, all that “fine print” on the outside of the software which says “read me before opening” – which of course you never read – or the important message which flashes up when you load new programs: “Click here if you agree”. Yeah, yeah – everyone clicks, no-one bothers reading through all the legal waffle! What you are doing is agreeing to the terms of the manufacturer or distributor. Despite your paying good money for the software, after the event they tell you that you haven’t purchased it at all, just a licence to use it. And if you don’t comply with the licence conditions (which of course you’ve never read) they’ll come down the keyboard lead and break your $#<at>%&~ fingers! One of those conditions you’ve agreed to says that under pain of death, or worse, you will only install the software on one machine. However, if you use a remote control program you’ve beaten them at their own game! You get complete access to the software on the remote machine but it is not installed on the local machine – you are simply controlling it from there. So now there’s no need to buy a copy of the software for home as well as the one you use at the office! The two software packages we trialled: pcANYWHERE32 (above), which was capable of operating under both Windows 95 and Windows NT, and LapLink V7.5 for Windows 95 (right). There are many other programs available to do the same or similar jobs, including some excellent "shareware" versions. March 1997  9 2: File Transfer We mentioned this before: if there’s a file on one computer and you want it on another computer, remote software is one of the easiest ways to transfer it. Regardless of whether the computers are across a room or across the world, file transfer is delightfully simple. One particular advantage of using remote access software for file transfer (as distinct from generic communications software) is that if you don’t know where the file is or what it is called, you have the opportunity to search the remote machine. (Most generic programs require you to know the name and/or location of the file). Another major reason for using this type of software is that some of it (LapLink for example) has the ability to synchronise files/folders between two machines. What does that mean? Let’s say you have transferred a file from a remote machine and worked on it on your local machine. The files are now different, even though they might have the same name. Some time later you want to work on the file and . . . which one? By using remote access software to synchronise files, the files on the two machines are always updated to the latest version. More than that, you can set the parameters so that only amended files are synchronised, saving time. An example of file transfer in action: the very pages you are reading now. As you probably know, SILICON CHIP is produced in Sydney but printed in Dubbo, some 400km away. When we need to get a file to Dubbo in a hurry (presses just won’t wait!) we use file transfer via a modem and standard telephone lines. A typical page might take about twenty minutes or so to send - overall, the cost is not dramatically different to sending the file by air express and certainly a lot, lot faster! 3: Idle Chit-Chat Remote software can be used to enable a two-way conversation with someone at a remote computer. Whether that is for information, for fun or even to ask for a date(!) it’s simple. More than that, chatting can be combined with remote control or file transfer: the tech support person we talked about earlier can now not only control the remote machine, upload or download files as required (eg software upgrades or patches) but can “talk” to the remote operator at the same time. Setting up the software Whether the software you choose is on CD-ROM or floppy, loading and setting up is basically a matter of following the instructions. CD-ROMs tend to come with an autoload file which loads as soon as you put the disc in the drive. Note that Windows 95 is required for the 32-bit versions of the software; if you are still using Windows 3.11 you will need to load the 16-bit versions. Better performance can be expected from the 32-bit versions. Purely for the convenience of having two computers virtually side-by-side which we could compare, we first decided to try out the programs via their network connection instead of via the modem and phone line. According to the manual, each works in much the same way. First snag: the PCs on the SILICON CHIP network use Windows NT, the “industrial strength” version of Windows. While pcANYWHERE would operate under both Windows 95 and Windows NT, LapLink would only operate under Windows 95. To us that doesn’t make a great deal of sense, given the fact that Windows networks in industry are more and more based on NT, not 95. Of course, we wanted to stack each program against the other so Windows 95 was required. Fortunately, one of our networked PCs is a “dual boot” Windows 3.11/ Windows 95 system (see SILICON CHIP July ’96) to allow the use of some essential, but non-NT-compatbile software. And it wasn't too difficult to bring in a Windows-95 machine from home – I have three machines networked for my home-based business anyway, so connecting one of these to the SILICON CHIP network was quite simple. The sign-on screens for pcANYWHERE (left) and LapLink (right). One thing we liked about LapLink was its “Quick Steps” windows which automatically opened to guide you through the required steps. pcANYWHERE has a similar, though not quite as informative, "Quick Start" window available. 10  Silicon Chip That done, we had no trouble loading either of the programs. Setting up, though, was not quite as simple. While both programs have a step-bystep “Wizard” to guide you through the process, and we followed the step-bystep instructions to the letter, we found that neither program worked over the network when first fired up. LapLink was the first program we attacked and the cure also fixed the problem with pcANYWHERE. What we had not done was first load the specific drivers for our network. This was more a matter of ignorance on our part than anything else: had we read the packaging properly we would have found that the protocol we use on our network (NetBEUI) was not supported by the programs. Instead, they required either TCP/IP or IPX. (No, we haven’t bothered to explain what the acronyms mean – what’s the point?) To cut a long story short, once we realised this we went back into our network setup and loaded the IPX protocol (it’s a lot simpler than loading TCP/IP because you don’t have to work out machine addresses). Did it spring to life? Not on your nelly! Sod’s law No 42: if all else fails, read the manual. Under troubleshooting there was a section on enabling and disabling ports. Alas, it didn't help. The software insisted that the IPX protocol was enabled – the “enable port” checkbox was checked and the dialogue box above reported that the IPX network port was enabled. Purely on a whim, we disabled the port and re-enabled it – just two clicks of the mouse button. Presto! It worked: up came the remote computer in the dialog box above. Clicking on that brought up the message that the link with the other computer was being established and not too long after that (perhaps 15-20 seconds) the screen image of the remote computer came up on the screen. First of all, we were extremely disappointed with the screen quality – it was very difficult to read and nearly impossible to use. Then we realised that the remote computer was using a much higher screen resolution than the local computer. Once the resolution was made the same on each, the screens were almost identical. One of the remote computer’s tasks is to control a scanner. We thought a pretty reasonable task would be to remotely scan a photograph (of course, the photo had to be placed on the scanner first!). Using LapLink, we were able to scan the photograph in exactly the same way we would have done at the remote computer’s keyboard. Yes, it was markedly slower (perhaps twice as long) but the scanner didn’t miss a beat (it is sometimes temperamental) and the end result was the equal of scanning it on the spot. Think of the possibilities that brings up: if you need access to a scanner This is LapLink's setup screen to establish either a TCP/IP or IPX protocol network link. It was this window which first twigged us to the fact that we didn't have the right network protocol loaded. No wonder it didn't work first up! but don’t have one, all you need do is have someone place the photo on the scanner. You can do the rest from anywhere. You can even “chat” to them via the chat mode to tell them exactly what you want to do, all remotely! It was rather uncanny watching the remote computer screen because everything being done by the local computer was echoed – the mouse pointer moving around the screen, selections being made, even the scanning, with nobody near the thing. As mentioned, all this was tried out using LapLink because at this stage we hadn’t again tried to get pcANY­ WHERE to work. But fixing the IPX problem for LapLink also fixed it for pcANYWHERE, as one might expect. When we subsequently fired up pcANY­WHERE we were able to do exactly the same job. The times were comparable: it appears that pcANYWHERE might establish the connection slightly faster, but in use there wasn’t much in it. We mentioned before that it might seem silly to install this type of software for use on a network. But the above example highlights the versatility. You get much more than simple network connections. Control via a modem OK, so that was the network connection. What about the modem connection? The secret here, as Mrs Beaton’s In “File Transfer” mode you can see two directories: the machine on the left is the remote machine (Ross), while the machine on the right (SC100) is the local. Trans­ ferring files between the two machines is as simple as the familiar Windows “drag and drop”. March 1997  11 Cook Book might suggest, is to first catch your modem. Make sure it is set up and working perfectly before trying to use the remote software on it. You have the choice of using the installation software supplied with most modems, or letting Windows 95 install it for you. We tend to prefer the latter approach: by clicking on Control Panel and then Install New Hardware, Windows 95 will go off and look for the modem (and usually finds it). When it does, you can use the drivers supplied with Windows 95 if your modem is a common brand. If your modem is a little odd-ball, don’t despair: your instruction manual will usually tell you it can be installed as a “so and so” modem, or it may tell you to install it using the software supplied on the installation disc. Either way, it’s easy to do. You may see a lot of information about IRQ’s and addresses and so on. If these terms mean about as much to you as Quantum Mechanics and the meaning of life, don’t despair – most of the process is automated. In most cases, installation is as simple as following the on-screen instructions. And finally, refer to Sod’s law no 42 above. To test the modem, simply call another modem-equipped computer. It makes some sense to call the computer you are going to use the remote software on later because if something doesn’t work as intended at least you can eliminate the modem and connection as a cause. Alternatively, you could call one of the bulletin boards that allow free access or free limited visitor access (and there are lots of those). Don’t be tempted – yet – to sign up with an Internet Service Provider and go surfing the net, at least until you find out the cost you could be up for! It’s working! Now it’s time to call the other computer with the remote control software. Naturally, the remote computer also needs to be running the same remote control software. We have taken several “screen dumps” to show you what to expect. It’s basically a matter of entering the phone number you wish to call and clicking on dial. From there on in the process is automatic until such time as the connection is established. Once the connection is established, the remote computer screen pops up (albeit slowly) and you are ready to take full control, as outlined above. Alternatively, if you choose the appropriate options, you can very simply transfer files, chat or just examine the other system. Just as before, we were able to control the scanner, edit text in Word­ Perfect, open up a Pagemaker file and manipulate the pages . . . all as if we were sitting there instead of here! Again, operation is significantly slower than it would be if you were sitting at the other PC and performing the same keystrokes. You often have to wait for the screen to refresh after having clicked with the mouse – in fact, it is not too hard to get ahead of yourself if you are used to working quickly. But, those reservations aside, either program is an excellent way around what has been a significant problem. One of the more interesting uses, especially for business and commerce, is the ability to log into a remote network by remotely controlling one of the PCs on that network. We did this on a small scale with the SILICON CHIP network: we were able to dial in to one PC from a location several kilometres away (we could have been thousands of kilometres away) and through it, gain access to the entire network. There are countless applications where this could be a Godsend but there are also some security aspects to worry about. Both software packages we used had the ability to limit access and to use a variety of password protection devices to ensure that anyone who accessed the system – and the network – had the authority to do so. Even so, unless you have good reasons for allowing unlimited access at any time, security experts recommend gateways to networks be turned off or disconnected unless actually re­ One of the big advantages with this type of software over run-of-themill communications software is its ability to set up very detailed address books, with all the information needed to establish the contact contained in the listing. This address book listing, again in LapLink (though pcANYWHERE has a similar arrangement), is setting up a modem connection for a fictitious “Remote Computer” called “A Name” (the name must be correct) via a modem at a local telephone number 12345678. All three services available are selected but security is not. Security is vital for commercial organisations to minimise or prevent unauthorthorised access (“hacking”) especially where remote control is available. Imagine the damage that someone could do . . . 12  Silicon Chip quired.That seems like fair enough advice to us; it's something we do here at SILICON CHIP. Connecting via a cable While we have been talking about communication via modems and phone lines, or via an existing IPX or TCP/IP network, we acknowledge that there are many people who don’t have such devices. But often there is a need to transfer files between computers. If you can get the computers close enough you can connect a cable between them and, using the remote software, transfer files using their parallel or serial ports. If at all possible, you should use the parallel ports (ie, both computers’ parallel ports are connected via a special cable) because file transfer is significantly faster via the parallel port. Note that the cable must be purpose-made; ordinary parallel printer cables and most serial data cables do not work. The cable connection is selected during the setup procedure and file transfer is achieved in a very similar way to using a modem or network connection. File transfer can be bi-directional; either computer can send or receive files to or from the other. Which software? In use, we have found very little to choose from between LapLink and pcANYWHERE. There were a couple of features we liked slightly more on one than the other but these were countered in other directions. We'd be happy to use either package. The Proof of the Pudding . . . These two screen images show exactly the same Windows 95 “desktop” screen but were actually taken on two different PCs. The top screen is taken from the PC on which Windows 95 was actually running, the bottom screen was the same Windows 95 desktop, captured by pcANYWHERE, as viewed on a computer in a different part of the same building. While in this case it was being run over a network, it could have been running via a modem from the other side of the world! Both PCs were also running Windows Paint, the program used to capture these screen images. Where do you get it? LapLink For Windows 95 and pcANYWHERE32 are available at virtually any good computer store; if not in stock, they should be able to get it in for you. With recommended retail prices of $230-295, you can expect to pay anywhere from under $200 up, depending on the margin the retailer wants to make! The Dynalink 33.6Kb external modem was purchased from Software Today in Melbourne for $179.95, including next day door-to-door delivery (in fact, the modem was delivered just four working hours after ordering. That's not bad service from 1000km SC away!). March 1997  13 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au Video conferencing: the coming boom Video conferencing is set to revolutionise the way we do business, communicate and share information. Here’s a quick rundown on PictureTel’s new SwiftSite system. By SAMMY ISREB Video conferencing has traditionally been very expensive and, in the past, has been the preserve of big business and gov­ernment. For the rest of use, a face-to-face meeting with someone in another state or country has meant getting up early to catch the plane. The new video conferencing tech18  Silicon Chip nologies are set to change that. These technologies are a natural outgrowth of the multime­dia revolution and the development of high-capacity ISDN tele­phone lines. To put it simply, video conferencing supports 2-way video and audio communication, similar to those videophones you see in sci-fi movies! This means that two or more people at different locations can see and hear each other at the same time. More sophisticated video conferenc­ ing systems have the advantage of allowing data to be exchanged as well, using differ­ent protocols, along with group video conferencing. Video conferencing uses At the present time, the cost of setting up a video conferencing system is still quite high – so high, in fact, that it remains out of the reach of the average person. And although the cost is falling very rapidly, video conferenc­ing is still limited to a few key uses. In schools, for example, video conferen­ cing is ideal for providing equitable access to resources for at-risk or special-needs students. It is also ideal for isolated rural populat­ions, replacing the traditional radio schools. Also, being an interactive medium, 2-way video offers the advantages of establishing a more personal communication between people, allowing the use of body language, along with other visual teaching aids. The health industry will find video conferencing a great boon, as it allows patients in remote locations to consult with doctors and specialists that they would not normally have access to without travelling. Businesses will also benefit enormously from the new video conferenc­ ing technologies. Video conferencing will slash travel costs and allow staff in different geographical locations to communicate effectively. It will be possible to effectively demonstrate products and service procedure as well as to hold company meetings. How it works When it comes down to the nitty-gritty, most video conferencing equipment works in a similar manner. Basically, you need an audio-visual setup that consists of a monitor, camera, microphone and speaker. And, of course, you need some way of trans- Unlike many units, PictureTel’s SwiftSite is a standalone video conferencing system. All its functions, including the camera and a microphone, are integrated into a small module which weighs less than 5kg. A remote control handpiece, similar in size to a TV remote control, is included. mitting the information between the different locations. A broadband satellite-based system giving broadcast-quality video would be very nice but, as you can imagine, that is less than practical for cost reasons. More recently, advances in computer and telecommunications technologies have sparked an interest in compression based video systems. These systems can transmit information via the Internet, a telephone network, or microwave link, thus greatly reducing the cost of video confer­encing. In fact, most of today’s video confer­ encing systems operate on a single ISDN telephone line. A CODEC (short for coder-decod­er) handles the compression/decompression task Video Conferencing Terms Explained Like most other electronics-based industries, those in the video conferencing field have their own jargon. A list of these terms appears below: Group System – a video confer­ encing system that is designed for use in a conference room; hence, it is sometimes called a “room” system. This type of system usually involves large monitors, remotely controlled wide-angle cameras, a document scanner and other tools that facilitate participation in the meeting. Rollabout System – a portable group system on a wheeled cart that can be rolled into an office or meeting room and used for ad hoc conferences. Personal System – a computer-based video conferencing system that is typically used by a single person; sometimes called a “desk­top” system. These can be general-purpose computers that are enhanced with the addition of a video confer­ encing card, a small camera and so forth (just like the PCS 50). CODEC – specialised microprocessor for compressing and decom­ pressing data. A CODEC is necessary at each site that partici­pates in a video­conference. Data Rate – the speed at which a network can carry data. It is sometimes also called “channel rate.” The higher data-rate net­works are more expensive and usually convey higher-quality video signals. Group systems typically use higher data rates than personal systems. Point-to-Point Call – a videocon­ ference involving two locations, just like a regular 2-party telephone call but with the ability to see the person or people with whom you are speaking. It also includes the ability to digitally “hand” them all types of data, regardless of distance. Multipoint Call – a more complicated setup involving three or more locations simultaneously. Multipoint calls can be used to teach classes at several locations at once, or for corporations to efficiently make policy or product announcements. Video conferencing Tools – these are any of a wide variety of communication and presentation tools that can be incorporated in a video conferencing system. These tools include several types of cameras, 35mm slide projectors, overhead projectors, VCRs, com­puters, computer white­boards and so forth. March 1997  19 PictureTel’s Video Conferencing Breakthrough PictureTel, one of the world’s biggest manufacturers of video confer­encing equipment in the world, has just released two new systems that have slashed the price of video conferencing. The first of the systems, the SwiftSite, is designed to act as a stand­ alone video conferencing system. The alternative PCS 50 Desktop System is intended for installation in a PC and allows for data exchange. The SwiftSite system is a breakthrough for PictureTel, as it eliminates the need for any PC equipment. According to David Lardinais, the Managing Director of PictureTel Australia, Swift­Site will become an integral part of business communications and will support all kinds of new applications. The SwiftSite System The SwiftSite video conferencing system operates using a single ISDN basic rate interface (BRI) telephone line. All the electronics of the system, along with the camera and microphone, are integrated into a small module which weighs less than 5kg and sits on top of the monitor. The system conforms to the H.320 Plus video conferencing standard, providing up to 15 frames a second using an ISDN BRI telephone line running at 128Kb/s. Other features include an infrared remote control that is similar in size to the average TV remote control. SwiftSite also has the advantage of being simple to install, requiring only three connections: an RCA audio/ video cable bet­ween the television and the unit, a power connection and an ISDN cable connection. One of the best features of the SwiftSite system is the ability to upgrade its software remotely, using the Swift­ Site Software Server. This is claimed to be the world’s first ISDN, H.320 standard upgrade server for use with video conferencing systems. By using the SwiftSite system, any user can con­nect with the server and download the latest software upgrades. The PCS 50 System The PCS 50 System is an PC-compatible based system with some of the performance features of the SwiftSite system. The system consists of various modules, such as the CODEC desktop component. This consists basically of the CODEC card(s), as well as other modules, such as a high-end graphics accelerator card, 29-inch SVGA monitor, software and a video camera. The main advantage of this system is that it is easily upgraded, just by changing a couple of cards. It does, however, lack the versatility and portability of the SwiftSite system. Both systems are very similar in price, at around $15,000 each. Acknowledgement: thanks to Manoj Murugan of Media Solutions for his help in supplying information on behalf of PictureTel. and is usually based on a dedicated microprocessor. The CODEC samples the incom­ ing analog video signal, digitises it and then subsequently compresses it. The CODEC at the other end then has the job of reversing this process. Depending on the transmission standard used, the picture quality can be surprisingly good. The downside is that there is usually a slight delay (generally less than a second) in receiv­ ing the picture. Conclusion The SwiftSite video conferencing system is designed to sit on top of the monitor to which it is connected. Only three connections are required: an RCA audio/ video cable bet­ween the television and the unit, a power connection and an ISDN cable connection. 20  Silicon Chip The video conferencing industry is still in its infancy and it will be several years before we see solid standards set. At the same time, costs will have to continue falling in order to make video conferencing affordable for most people. Finally, medium-sized establishments that have a need for video conferencing but have concerns as to whether they can afford it should study the two new PictureTel systems (see panel), as these are a breakthrough SC in their price bracket. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Macservice Pty Ltd CIRCUIT NOTEBOOK 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. Audible headlight reminder This simple headlight reminder circuit has the virtue that no active components such as transistors or ICs are used. It is based on two relays. Relay RLY1 is actuated while ever the igni­tion is on. Relay 2 is comprised of coil L1 and the reed switch. Coil L1 is powered from Fig.1: this cheap yet effective headlight reminder circuit uses two relays and a piezo buzzer. the low beam lighting circuit. If the ignition and lights are on, no current flows via the reed switch to the buzzer. However, if the ignition is off and the headlights are on, current can flow via the normally closed contacts of RLY1 and the reed switch to sound the buzzer. R. Baker, Miranda, NSW. ($20) Low voltage drop bridge rectifier Circuit Ideas Wanted Do you have a good circuit idea languishing in the ol’ brain cells. If so, why not sketch it out, write a brief description of its operation & send it to us? Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We’ll pay up to $60 for a really good circuit but don’t make them too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. 22  Silicon Chip Automatic pump timer/controller This circuit was developed to apply insecticide on a 7-day cycle to fruit trees in an orchard. It could have uses in hydro­ ponics systems, fish breeding or other long period timing appli­cations. The pumping time is three minutes using a 12V DC 7A bilge pump. All pumping occurs at dusk, which is detected by the light de­pendent resistor, LDR1. LDR1 controls clocking of the circuit and is buffered by two Schmitt trigger inverters, IC1b & IC1b. This drives counters IC2 & IC3 which can be set for a total time of up to 99 days, using the thumbwheel switches SW1 & SW2. These counters count down from a preset value. The pump on-time can be set between 30 seconds and nine minutes, in 30-second increments, as set by switch S1 and thumb­wheel switch SW3, both of which control counter IC7 (4029). When IC2 & IC3 have counted down to zero, it is sensed by XOR gate IC4a (4070) which sets RS latch IC5b (4053), and this starts timer IC6. This turns on Q1 and the relay for the set time. Power for the circuit can be derived from a 12-14V DC plugpack or battery and this is regulated to 5V. Note, however that the bilge pump requires 12V at 7A. S. Carroll, Timmsvale, NSW. ($40)  This fullwave bridge circuit has virtually no diode drops. With the values shown it would run a low current resistive load. The prototype circuit had a forward voltage drop of 50mV at a load current of 25mA. Most transistors have a base-emitter vol­tage breakdown of about 8V. This limits the circuit to about 6VAC with common transistors and it is not suitable for capacitor loads due to the high peak currents involved. The circuit is not suitable for input voltages of less than about 2VAC. G. La Rooy, Christchurch, NZ. ($20) March 1997  23 Plastic Power PA Amplifier Open-air sporting events like this recent Australia Day surf carnival at Freshwater Beach require plenty of PA muscle. Photo by Andrew McEwen. This article adapts the Plastic Power amplifier module described in the April 1996 issue to public address use. The circuit now includes a 100V line transformer, output transistor protection, a thermal cutout and DC offset adjustment. By ROSS TESTER The “Plastic Power” high-performance amplifier module described in the April 1996 issue has already proved to be a trouble-free design. We foresaw that it would be popular for new amplifier builders and equally sought after as a high-power, high-performance replacement module for many ageing ampli­fiers out there –both commercial and home-built. 24  Silicon Chip And so it has been. But there was one use which we hadn’t really considered – public address or PA. Since the article appeared, we have had a number of enquiries: “can I use this amplifier for PA?” The immediate reaction was “why not?” After all, with power output approaching 200 watts into 4Ω loads, on first glance it would make an excel- lent PA amplifier. But on reflection, it wasn’t quite as simple as that. PA requirements For PA use, there are important requirements which don’t occur in domestic (ie, hifi) applications. Most important of these is the ability to drive a 100V line transformer. A PA amplifier that cannot work into a 100V (or even 70V) line is not considered a PA amplifier – it’s just a toy. But didn’t the specifications box in the April 1996 issue claim “unconditional stability”? Wouldn’t this mean that you could simply bung on a 100V line transformer and the amplifier would be happy? It would be if operating into complex loads was the only problem. But it is not. In fact, it is only a minor considera­tion. By far the most difficult problem to overcome when operat­ing into a transformer of any description is the DC offset at the amplifier’s output. DC offset, as the term implies, is an amount of DC voltage across the speaker output terminals. In a perfect world, or in a perfect amplifier, there would be no DC offset. But in any direct-coupled amplifier there is always some small DC offset voltage at the output and this is mostly due to the mismatch of the differential input transistors. Typically, the DC offset is around 20-50 millivolts and it can be positive or negative, with respect to the “cold” side of the speaker terminals. While this is tolerable in an amplifier intended for hifi or general audio applications where loudspeakers are being dri­ven, it causes a big problem when the load is a 100V line trans­ former. A few quick calculations will show why. For example, if the amplifier is driving a loudspeaker with a voice coil resist­ance of 6Ω (a fairly Performance Output power ........................ 175 watts into 4Ω or 100V line Frequency response ............. -3dB at 30Hz and 17kHz Input sensitivity ..................... 1.15V RMS (for full power into 4Ω) Harmonic distortion .............. <.03% from 20Hz to 20kHz, typically <.01% Signal-to-noise ratio ������������ 101dB unweighted (22Hz to 22kHz); 116dB A-weighted Stability ................................. unconditional typical value), a DC output offset of 50mV will cause 8.3 milliamps DC to flow through the speaker. This will cause a very small mechanical offset of the speaker’s voice coil from its rest position but otherwise no harm will be done. On the other hand, consider that same 50mV DC offset ap­plied to the primary winding of a 100V line transformer. In this case, the DC resistance of the winding is likely to be 100 mil­ liohms (0.1Ω) or less. Now, the DC current which will flow through the primary winding is 500 milliamps or more and this causes really serious problems. Any DC in a transformer winding is bad news. First of all, the transformer can be saturated, which causes awful distortion (hardly what you want when Mr or Mrs High and Mighty steps up to the podium to speak!). Worse, a current of 500mA is much higher than the normal quiescent current in the output stage and it will lead to extra heating, by 20 or 30 watts, depending on the ampli­fier’s supply voltages. This amplifier is capable of delivering 175 watts into 4Ω or a 100V line transformer for PA work. The heatsink shown here is adequate for general use but if the amplifier is to be operated in high ambient temperatures and expected to deliver high power continuously, a larger fancooled heatsink will be required. March 1997  25 PARTS LIST 1 PC board, code 01103971, 99 x 166mm 2 panel mount M205 fuseholders (or 4 20mm fuse clips – see text) 2 5A M205 fuses 1 coil former, 24mm OD x 13.7mm ID x 12.8mm deep, Phillips CP-P26/19-1S or 4322 021 30362 - see text 1 4Ω/100W toroidal output transformer (Altronics M1124 or equiv­alent) 2 metres 0.8mm enamelled copper wire 1 thermal circuit breaker 80°C, 10A (Altronics S5610 or equivalent) 1 large single-sided finned heatsink, at least 300mm long, 0.7°C/W 2 TO-126 heatsinks (Altronics H-0504 or equivalent) 4 TO-3P transistor insulating washers 3 TO-126 transistor insulating washers 1 200Ω 10-turn vertical trimpot (Bourns 3296W series or equival­ent) 1 100Ω 5mm horizontal mounting trimpot 13 PC board pins 4 3mm x 20mm screws 5 3mm x 15mm screws 9 3mm nuts Worse still, such a high current can easily lead to thermal runaway in the output devices, and their eventual destruction. The DC offset problem has been known for a long time, ever since direct coupled amplifiers were first produced. In fact, some years ago, National Semiconductor brought out the LMC669 as the ideal answer to this problem and SILICON CHIP featured a circuit using it in the September 1989 issue. Alas, the IC now appears to be unobtainable, so other means need to be found to cure the DC offset problem. Fig.1 shows the modified circuit of the Plastic Power amplifier. It is capable of delivering around 175 watts into a 100V line. Now let’s consider the problem of DC offset and how it is corrected. First, we include provision for adjusting the DC offset to zero (or as close as we can achieve) with a trimpot connected between the emitters of the differential pair, Q1 and Q2. This will allow any minor differences between the two “sides” of the circuit to be nulled out. The emitter resistors of Q1 and Q2 were reduced from their original value of 150Ω to 100Ω and a 100Ω trimpot placed between them. Adjustment is simple: when the amplifier is completed set the trimpot to its centre position, then adjust it so that the DC voltage across the speaker output terminals (as measured on a digital multimeter set to its lowest voltage range) is zero or as close as possible. The board pattern, incidentally, allows for either a verti­cal or horizontal mounting 5mm trimpot. A horizontal mounting pot is preferred, for ease of adjustment. Second, we have modified the PC board slightly to allow Q1 & Q2 to be thermally bonded together. Thus any tendency for one transistor to get hot, which may cause increased DC imbalance, will be reflected in the other transistor. We also did the same with Q4 and Q5, the current mirror stage. 26  Silicon Chip Semiconductors 2 MJL21194 NPN power transistors (Q12, Q13) 2 MJL21193 PNP power transistors (Q14, Q15) 2 MJE340 NPN driver transistors (Q9, Q10) 1 MJE350 PNP driver transistor (Q11) 1 BF469 NPN transistor (Q8) 1 BF470 PNP transistor (Q6) 4 BC546 NPN transistors (Q4, Q5, Q7, Q16) Reduced bandwidth Sometimes a high performance amplifier is simply “too good” for PA. If you think about it, PA is one of the worst-case audio applications: (a) Long speaker leads can act as magnificent RF antennas for any local radio or TV station or even close-by two-way 4 BC556 PNP transistors (Q1, Q2, Q3, Q17) 2 1N5404 power diodes (D5, D6) 4 1N914 diodes (D1, D2, D3, D4) 1 3.3V 0.5W zener diode (ZD1) Capacitors 4 100µF 63VW electrolytic 1 22µF 16VW electrolytic 1 0.33µF 250VAC MKP 1 0.33µF 50VW MKT 5 0.1µF 63V MKT 1 .0012µF MKT or ceramic 1 100pF 100V ceramic Resistors (0.25W, 1%) 2 18kΩ 1 180Ω 1 15kΩ 1W 2 160Ω 1 6.8kΩ 3 100Ω 1 5.6kΩ 1W 1 68Ω 1 1.5kΩ 1 47Ω 1 820Ω 3 12Ω 1W 1 470Ω 4 0.47Ω 5W 2 390Ω 2 560Ω 5W 3 220Ω radios (and many sports, coaches, etc, use two-way). (b) They’re often used in portable situations, and every location has its own share of problem electrical noises which may or may not be treatable. (c) If it is a portable setup, speaker lines may be temporary and therefore not too secure against either shorts or cuts. Speaker cabling is often exposed to the elements, with joins, plugs & sockets, etc which may be corroded, even with the best “weather­proofing”. With these problems in mind, it is wise to limit the over­all bandwidth of a PA amplifier. This can assist in reducing interference, especially electrical noise picked up by the speak­er leads. Therefore, the input RC filter and the output RLC filter have been modified. The result is that both the bass response and the high frequency response have been deliberately curtailed: -3dB at 30Hz and 17kHz, as depicted in Fig.2. This shows the frequency response of the complete amplifier, including the 100V line transformer. Protection circuitry This is something of a thorny Fig.1: the circuit is essentially the same as that published in the April 1996 issue except that it has been adapted for PA use. The main changes include the addition of a 100V line transformer, DC offset adjustment (using VR1) and current limiting. The latter is provided by transistors Q16 & Q17, which monitor the emitter currents of Q12 & Q14 respectively. Note that the frequency response has been deliberately limited to ensure reliability under PA conditions. March 1997  27 AUDIO PRECISION SCFREQRE AMPL(dBr) vs FREQ(Hz) 15.000 21 JAN 97 11:00:02 10.000 5.0000 0.0 -5.000 -10.00 -15.00 20 100 1k 10k 20k Fig.2: this graph shows the overall frequency response of the power amplifi­er, including the 100V line transformer, at a power level of 10 watts. The bass and high frequency response has been deliberately curtailed. subject, so let’s get straight into the blackberry bushes! Some designers of hifi amplifiers will have nothing to do with protection circuitry in the output stages, claiming that it causes distortion even before it becomes active and then causes severe distortion as it acts to limit current. Indeed, where foldback current limiting is used in amplifi­er output stages, it can cause squealing from tweeters, and in severe over-drive condition, can cause tweeter burnout. PA amplifiers, on the other hand, are a different kettle of fish. First, ultimate low distortion figures are of minor importance (although this amplifier is pretty good in that respect, even with protection). Second, PA amplifiers are often subjected to serious abuse. Years of experience has taught us that people can be abso­lutely ruthless when it comes to their personal enjoyment: they sit in front of a PA speaker, then complain that the PA is too loud! We have had many occasions at sporting functions where the speaker lines have been deliberately cut or shorted. Bring on the protection! Transistors Q16 & Q17, in conjunction with diodes D3 & D4, provide the protection feature. Q16 monitors the current flow through the 0.47Ω emitter resistor of output transistor Q13, via a voltage divider consisting of 390Ω and 160Ω resistors. What happens is that normally Q16 (and Q17) are off and play no part in the circuit operation. However, if the current through the 0.47Ω emitter resistor of Q13 exceeds about 4.4 amps, Q13 begins to turn on and it shunts the base current from Q10, the associated driver transistor. In turn, the drive to Q12 & Q13 is limited so that the output current does not exceed about 4.5 amps peak. The same process happens with Fig.3: suggested power supply for the amplifier. The power trans­former should be rated at 300VA or more. 28  Silicon Chip Q17 which monitors the cur­rent flow through the 0.47Ω emitter resistor of output transistor Q14. Diodes D3 & D4 are included to prevent Q16 & Q17 from shunting the signal when they are reverse-biased; this happens for every half-cycle of the signal to the driver transistors. Diodes D5 & D6 are included as part of the protection cir­cuitry although their function is ancillary. They prevent large voltage spikes from the transformer, generated when the current limiting circuitry acts to turn off the output transistors, from actually damaging the transistors. D5 does this, for example, by clamping any spike voltage to 0.6V above the positive supply rail. Similarly, D6 clamps any spike voltage to 0.6V below the negative supply rail. Normally, both diodes are reverse biased and play no part in the amplifier operation. Note that this protection circuitry provides simple current limiting, not foldback protection, where the current drops back to a low value to limit power dissipation in the output stages (and with attendant serious distortion, as outlined previously). With this simple current limiting, the transistors are protected from sudden death in the case of serious over-drive or short-circuits, although the fuses may blow before this happens. While the output transistors are protected against imme­diate destruction, their dissipation is greatly increased over what it would be if the amplifier was simply delivering full power. In fact, the output transistors can dissipate four or five times as much power as in normal operation. Hence, they get very hot very quickly and eventually, if the over-drive or short-circuit condition is not corrected, they will fail; probably sooner than later. To prevent this eventual failure, we have included a ther­mal cutout which is mounted on the heatsink. When the heatsink temperature exceeds 80°C, the thermal cutout opens and is not restored until the heatsink cools down again. Heatsink selection Note that the thermal cutout is there for a secondary reason and that is to prevent over-dissipation in the output transistors under continuously high power conditions. To elabo­rate, the maximum dissipation in a class-B amplifier occurs when it is deliver- ing about 35 to 40% of the maximum output power. Under this condition, the power dissipated in the output transistors can be expected to be about 30% more than the maximum output power. This amplifier will actually deliver about 175 watts before clipping and the maximum dissipation in the output transistors can be expected to be about 230 watts, depending on the supply regulation and the actual value of the load. 230 watts equates to almost 58 watts per transistor which means that the largest possible heatsink should be used. Ideally, if you anticipate rigorous operating conditions, the heatsink should be fan-cooled. We have specified a fairly large heatsink with a rating of 0.7°C/W but to cope fully with a total dissipation of 230 watts, the heatsink needs to be much larger, at 0.3°C/W. Hence, with the specified heatsink, the thermal cutout is a worth­while safety feature in case the amplifier’s operating conditions become a little torrid. The remainder of the circuit description is as featured in the April 1996 issue of SILICON CHIP. A suggested power supply is shown in Fig.3. The transformer should be rated at 300VA or more. AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 15 JAN 97 11:18:24 1 0.1 0.010 0.001 0.5 1 10 100 300 Fig.4: THD versus power at 1kHz into a 4Ω load. AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 15 JAN 97 11:10:15 1 Performance The amplifier’s performance is summarised in a separate panel and as you can see, it is very respectable for PA use. Fig.4 shows the harmonic distortion versus power output into a 4Ω load while Fig.5 shows the distortion versus power with the 100V line transformer connected. There is very little difference between these curves, indicating that the transformer is a high quality unit which degrades the signal very little. Construction The procedure for assembling the PC board is quite similar to that the for the original amplifier described in the April 1996 issue but there are enough differences to justify giving the complete assembly and setting-up procedure. The component overlay for the PC board is shown in Fig.6. Before starting the PC board assembly, it is wise to check the board carefully for open or shorted tracks or undrilled lead holes. Fix any defects before fitting the components. 0.1 0.010 0.001 0.5 1 10 100 300 Fig.5: THD versus power at 1kHz with a 100V line transformer. The load resistance was 57Ω (two jug elements wired in series and immersed in water)! This done, you can start the assembly by inserting the PC pins and the resistors, followed by the diodes. When installing the diodes, make sure that they are inserted with correct polarity and don’t confuse D1-D4 (1N914 or 1N4148) with the 3.3V zener diode (BZX79-C3V3 or equivalent). You should also take care to ensure that the electrolytic capacitors are all installed the right way around on the PC board. Note that the 100pF compensation capacitor from the collec­tor of Q8 to the base of Q7 should have a voltage rating of at least 100V while the 0.33µF capacitor in the output filter should have a rating of 250VAC. The 4Ω resistor in the output filter is comprised of three 12Ω 1W resistors March 1997  29 Fig.6: install the parts on the PC board as shown in this diagram. Note that while provision for on-board fuses has been made (as in the hifi version of the amplifier) external chassis-mounted fuses are more practical for PA use. in parallel. Choke L1 is wound with 19.5 turns of 0.8mm enamelled copper wire on a 13mm plastic former. Some readers who built their own version of the original amplifier (ie, not from a kit) experienced difficulty in obtaining the correct former. The one used in our prototype is a Philips CP-P26/19-1S (previously known as a 4322 021 30362). If your supplier cannot obtain this part, a possible replacement is the plastic bobbin some parts suppliers still have to suit FX-2240 pot cores. This is marginally different in size but the inductance of the coil wound (with RESISTOR COLOUR CODES                   No. 2 1 1 1 1 1 1 2 3 1 2 3 1 1 3 4 2 30  Silicon Chip Value 18kΩ 15kΩ 1W 6.8kΩ 5.6kΩ 1W 1.5kΩ 820Ω 470Ω 390Ω 220Ω 180Ω 160Ω 100Ω 68Ω 47Ω 12Ω 1W 0.47Ω 5W 560Ω 5W 4-Band Code (1%) brown grey orange brown brown green orange brown blue grey red brown green blue red brown brown green red brown grey red brown brown yellow violet brown brown orange white brown brown red red brown brown brown grey brown brown brown blue brown brown brown black brown brown blue grey black brown yellow violet black brown brown red black brown not applicable not applicable 5-Band Code (1%) brown grey black red brown brown green black red brown blue grey black brown brown green blue black brown brown brown green black brown brown grey red black black brown yellow violet black black brown orange white black black brown red red black black brown brown grey black black brown brown blue black black brown brown black black black brown blue grey black gold brown yellow violet black gold brown brown red black gold brown not applicable not applicable Fig.7: this diagram shows the heatsink mounting details for the driver and output transistors. After mounting, switch your multi­meter to a high Ohms range and check that each device has been correctly isolated from the heatsink (there should be an open circuit between the heatsink and the transistor collectors. the same number of turns) will be close enough. If installing the on-board fuse clips (see text about external fuses below), note that they each have little lugs on one end which stop the fuse from moving. If you install the clips the wrong way, you will not be able to fit the fuses. The 560Ω 5W wirewound resistors can also be installed at this stage; they are wired to PC stakes next to each fuseholder and are used when setting the quiescent current. Next, mount the smaller transistors such as BC546 & 556, BF469 & 470. Note that the transistor pairs Q1/Q2 and Q4/Q5 are thermally bonded; the pairs are mounted on the board so that their flat surfaces are touching, with heat transfer between them assisted by a smear of heatsink compound. Solder in one of the pair so that it is angled very slightly towards where its mate will go and then spread a thin film of heatsink compound over the flat surface. This done, solder in the collector and emitter of its mate and push the flat surfaces together before soldering the base, to lock the transistor in place. Repeat this process for the other pair of transistors. Both Q6 & Q8 need to be fitted with U-shaped heatsinks. The four output transistors, the driver transistors (Q10 & Q11) and the Vbe multiplier Q9 are mounted vertically on one side of the board and are secured to the heatsink with 3mm machine screws. Perhaps the best way of lining up the transistors before they are soldered to the board is to temporarily attach all of them to the heatsink; don’t bother with heatsink compound or thermal washers at this stage. This done, poke all the transistor leads through their appropriate holes in the PC board and line it up board so that its bottom edge is 10mm above the bottom edge of the heatsink. This is so that the board will be horizontal when fitted with 10mm spacers at its front corners. Note that you will have to bend out all the transistor leads by about 30°, in order to poke them through the PC board. The heatsink will need to be drilled and tapped to suit 3mm machine screws. The relevant drilling details were included in the April 1996 article (Fig.12). You can now solder all the power transistor leads to the PC board. Having done that, undo the screws attaching the transis­tors to the heatsink and then fit mica washers and apply heatsink compound to the transistor mounting surfaces and the heatsink areas covered by the mica washers. The mounting details for these transistors is shown in Fig.7. Alternatively, you can dispense with mica washers March 1997  31 Note the thermal cutout fitted to the heatsink. This interrupts the speaker line if the heatsink temperature rises above 80°C. Q6 & Q8, which are BF470 and BF469 respectively, are fitted with U-shaped flag heatsinks, as shown here. and heatsink compound and use silicone impregnated thermal washers instead, as can be seen in the photos. Whichever method you use, do not overtighten the mounting screws. With your multimeter switched to a high Ohms range, check that there are no shorts between the heatsink and any of the transistor collector leads. If you find a short, undo each transistor mounting screw until the short disappears. You can then re­mount the offending transistor, having fixed the cause of the short. The thermal cutout is mounted on the heatsink close to one of the output transistors. The leads connecting the thermal cutout switch to its appropriate PC pins should be rated at 10A. Double-check all your soldering and assembly work against the circuit of Fig.1 and the component layout diagram of Fig.6. Finally, connect the primaries of the output transformer to the output terminals, exactly as shown on the circuit diagram of Fig.1. Note that the 32  Silicon Chip primaries are connected in parallel while the secondary windings are connected in series – watch out for the colour-coding. Adjustments With no fuses in position, set trimpot VR2 fully anticlock­wise so that it is set for minimum resistance and set trimpot VR1 to its centre position. A 560Ω 5W resistor should have been soldered across each on-board fuseholder (or more correctly, the PC pins alongside). Assuming that the amplifier passes the “smoke test” when you apply power, set your multimeter to about 20-50V DC and connect it across a 560Ω resistor. Slowly adjust trimpot VR2 so that the multimeter reads 14V (equivalent to a quiescent current of 25mA or 12.5mA through each output transistor). The voltage across the other 560Ω resistor should be virtu­ally identical. Now connect the multimeter, on its lowest DC voltage range, across the output terminals on the PC board –that is, in paral­lel with the output transformer primary. Carefully adjust trimpot VR2 for minimum voltage (a digital multimeter is best for this purpose). You should be able to set VR2 so that the DC offset voltage is less than ±2mV DC. Once this has been done, leave the amplifier running for 10 minutes or so and check both voltages again. Adjust VR1 if necessary – changing this should not have any effect on the output DC offset voltage but if your DC offset has risen (in either direction) adjust VR2 once again to achieve the minimum possible. Finally, install the 5A fuses. External fuses As you may have noticed, the original module used on-board fuses for the supply rails. While not suggesting for a moment that the fuses be left out, fuses inside a public address ampli­fier are a pain in the proverbial! When the inevitable happens, it is invariably only a few minutes before the keynote speaker is due to make his/ her ad­dress, or the competitors turn Fig.8: this is the full size artwork for the PC board. Check your board care­fully for any defects before installing the parts. for their last lap in the final! Searching around for a screwdriver to open up a case can be a tad embarrassing in these circumstances. We suggest that external (ie, rear of case) fuseholders be provided and cable of the same diameter/rating as the power supply cabling used to connect these to the board. This way, the on-board fuseholders could be eliminated, with the 560Ω resistors still used to set up the module in the suggested way. Why 100V lines? In this article, we have talked about 100 volt lines as if they were “de rigueur” in PA applications. But what is a 100V line and why is it used so extensively for public address? Is a 100V line essential? Let’s answer the last question first. No, but . . . Of course “ordinary” 4Ω or 8Ω speakers could be and often are used in PA applications. In a small hall, for example, a few low impedance speakers connected appropriately will often be satisfactory. The key word here is “appropriately”. First of all, you need to worry about the overall impedance. You have to work out the various series and parallel combinations which will bring you back to 4Ω or 8Ω to suit the amplifier. Then there’s the problem of power – can the individual speakers handle the amount of power being fed to them? And are the power ratings correct for the way you want to connect them? It’s not hard to get into a mess! All of these problems are solved by the use of a 100V (or less commonly, 70V) line. Each speaker, together with its own stepdown transformer, is merely connected across the 100V line (ie, in parallel). As far as power ratings are concerned, you simply add up the wattage of the individual speakers and ensure that the total does not exceed the power rating of your amplifi­er. Even if it does, most speakers for 100V line use have multiple taps – if you want more speakers in the system (for example, to fill a sound “hole”) then select a lower wattage tap on some of your speakers to allow the extras. It really is that simple. But there is a more important reason to use 100V lines for PA use: less power loss (commonly known as I2R loss). It’s exact­ly the same reason that power authorities use high voltage for long distance transmission of elec- tricity; higher voltage means lower current and lower current means lower loss. In a typical PA installation for a sporting field or large hall there could easily be 1000 metres of speaker cable; often much, much more. Assuming that the speaker cable used was of reasonable quality, you could expect a resistance of about 2.5Ω per 100 metres. That means 1000m of cable would have an overall resistance of about 25Ω. This would be totally impractical for a 4Ω or 8Ω system but is not a serious problem for a 100V line system. Are 100V lines dangerous? Finally, let’s dispel one furphy: that 100V speaker lines are dangerous. Yes, they will give you a bit of a bite if you get across them while the announcer is waxing eloquent or the music is reaching a crescendo. But – and the but is important – the 100 volts is not constant like the 240VAC mains supply which often does kill. The full 100VAC is only present when the ampli­fier is delivering its full power. Most of the time, the voltage is only a few volts. Of course, it’s better if you don’t get yourself across a 100V speaker line, especially if a hyperventilating sports commenta­tor is getting excited at the SC other end of the signal chain! March 1997  33 Two projects for model railways By JEFF MONEGAL Project #1 3-Aspect Signalling Many railway modellers strive to achieve the ultimate in realism yet the resulting layout usually has non-operating signals or signals that constantly show a red or green lamp. The project presented here will go a long way to increasing the realism of signals. The addition of a little of animation to any model railway layout can enhance train operation immensely. That is what this simple unit has been designed to do. It operates a three-aspect (red-amber-green) signal in a most realistic manner. As a train 34  Silicon Chip approaches the signal the green light will be displayed. As soon as the locomotive has passed the signal, it changes to red. A few seconds after the last car has passed the red signal, it changes to amber. After a further few seconds delay, the signal again shows green. If the signal is used on two-way traffic lines, then a constant red is displayed while ever the train runs against the flow of the signal. It is simple in its operation but it adds a lot of realism and interest to any layout. How it works A look at the diagram of Fig.1 will show that the circuit is quite simple in its operation. As the train passes the signal, it is detected by the sensor which is placed just nearby on the track; ie, past the signal. The sensor is an LDR (light dependent resistor), the resistance of which goes high as the passing train casts a shadow over it. Fig.1: this circuit provides three-aspect (green, amber, red) signalling for a model railway. The train is detected when the locomotive passes over the light dependent resistor (LDR1) which is mounted between the rails of the track. This causes the voltage at the junction of resistor R1 and zener diode ZD1 to rise. When this voltage goes above about +4.5V, the Darlington transistor pair comprising Q1 & Q2 will turn on and pull the cathode of diode D1 to ground. This lights LED1 which indicates that a train has been detected. Capacitor C1 will discharge quickly through resistor R5 and the forward biased diode D1. This process pulls pins 1 & 2 of IC1a low which causes pin 3 to go high. This turns transistor Q3 and the red signal, LED2, on. At the same time, pin 11 of IC1b will go low which discharges capacitor C2 quickly through R8. This causes pin 10 of IC1c to go high and pin 4 of IC1d to go low. This turns off Q5 and the green signal, LED4, goes out. This condition will remain as long as the resistance of the LDR is high. As the end of the train passes the sensor, its resistance will again go low. Q1 and Q2 will turn off and C1 will start to charge through R4 and R5. When its charge reaches about half supply (+4.5V), pin 3 of IC1 will go low. The red signal now turns off. Pin 11 will now go high, turning on the amber signal. C2 now charges through R9. When it reaches half supply pin 10 will go low. D4 is now forward biased which turns off the amber signal. Pin 4 now goes high and the green signal turns back on again. Q6 and its associated components, diode D5 and resistors R11 & R13, detect when the track polarity is reversed. When the rail connected to R11 is positive with respect to the rail con­ nected to D5, Q6 will turn on. When this happens the collector of Q6 pulls the junction of R4 and R5 to ground. This triggers the signal to the red condition and this is where it will stay as long as the polarity of the track voltage remains this way. This was done so that the signal will remain red when a train is moving against the flow of the signals. If this were not done the signals would indicate a green condition when a train was coming from behind – clearly un­ proto­typical. Q7 is connected as a simple regulator. Zener diode ZD2 holds the base at +12V so the emitter will be regulated to about +11.4V. Diode D6 provides reverse polarity protection with C3 and C5 providing supply filtering. VR1 is the sensitivity adjustment for the LDR. Construction The component layout for the PC board is shown in Fig.2. There is nothing difficult about assembly so go RESISTOR COLOUR CODES – PROJECT #1        No. 1 2 1 4 1 4 Value 470kΩ 120kΩ 47kΩ 4.7kΩ 1.8kΩ 1kΩ 4-Band Code (1%) yellow violet yellow brown brown red yellow brown yellow violet orange brown yellow violet red brown brown grey red brown brown black red brown 5-Band Code (1%) yellow violet black orange brown brown red black orange brown yellow violet black red brown yellow violet black brown brown brown grey black brown brown brown black black brown brown March 1997  35 PARTS LIST – #1 1 PC board, code 3ASIGNAL, 100 x 50mm 10 PC stakes Fig.2: the component layout for the PC board of the circuit shown in Fig.1. The PC board would normally be mounted under the lay­ out, quite close to the signal unit. Note that the coloured LEDs are not mounted on the board but are part of the signal itself. ahead and load all the passive components, watching the polarity of the diodes and electrolytic capacitors. If you want to use a socket for IC1 then solder it in now. Finish with the remaining components. Then go back over your work to ensure that you have done a good job and that all components are in the right places. Testing Connect a signal or three LEDs to the appropriate termi­nals. At this stage no LDR sensor is necessary. Switch on the power. The red lamp should come on as well as the detect LED. Using a clip lead short the two sensor terminals. The detect LED should go out. A few seconds later, the amber lamp should light. A further few seconds and the amber light should go out and the green should come on. Remove the shorting lead and the detect LED should come on as well as the red lamp. If this all happened, then your signal circuit is working correctly. If not, then go back over your work, looking for the fault. More than likely you will have inserted a component wrongly or a solder joint will not be done. Installation Installing the signal is simply a matter of choosing a place for the signal then drilling a 5mm hole down between the sleepers (ties) of the track. The sensor should be placed about 100mm past the signal. Connect power and then the two wires to the track. If the red signal is constantly shown when the train is travelling in Semiconductors 1 4011 quad NAND gate (IC1) 6 BC548 NPN transistors (Q1-Q6) 1 BD139 NPN transistor (Q7) 1 3.3V zener diode (ZD1) 1 12V zener diode (ZD2) 4 1N914 signal diodes (D1-D4) 2 G1G power diodes (D5,D6) 1 3mm red LED (LED1) 1 light dependent resistor (LDR1) Capacitors 1 220µF 16VW electrolytic 2 33µF 16VW electrolytic 1 10µF 16VW electrolytic 1 0.47µF monolithic Resistors (0.25W, 5%) 1 470kΩ 4 4.7kΩ 2 120kΩ 1 1.8kΩ 1 47kΩ 4 1kΩ Miscellaneous Solder, hook-up wire, etc. the normal direction then reverse the two wires to the track. If the signal will only ever see single direction traffic then these two wires need not be connected. Simply leave them unconnected. You need one of these PC boards for each railway signal on your layout. By using 2mm LEDs you can wire HO signals for realistic operation. 36  Silicon Chip Fig.3: Q1 is a phase shift oscillator running at 25kHz. Its signal is fed to power amplifier IC1 which drives the track via its 100µF output coupling capacitor. The two inductors provide isola­tion for the DC power controller which also feeds the track to drive the model locomotives. Project #2 Constant Brilliance Lighting Circuit Add constant brilliance lighting to your model locomo­tives and carriages with this high frequency drive circuit. This will add extra realism to your layout, especially if you model night-time scenes. Model railway rolling stock these days is very realistic. The detail in the plastic mouldings is quite astonishing and you need a magnifying glass to read the fine printing of rolling stock reporting marks. Where passenger rolling stock does fall down is with in­ terior lighting. Most carriages do not have interior lighting and if they do, it is not constant in brightness. So while the train is running the carriages may be lit but when the train comes to a stop, the lighting goes out, plunging the poor (imaginary) pas­sengers into darkness; not very considerate. Furthermore, if the train goes fast, the carriage and loco lighting is bright and as it slows down, it becomes dim. This is not how it happens in the real world. A model train layout where the lights in passenger coaches and locomotives remain on at a constant level of brightness regardless of wheth­ er trains are moving or stopped has greatly enhanced realism. That is what this unit does. Frustrated by the very unrealistic appearance of my own railway models, I decided to see what could be done. The princi­ple behind this system is not new and in fact, was proposed many years ago. The basic idea is a 25kHz sinewave oscillator which is fed into a power amplifier then applied to the tracks. March 1997  37 Fig.4: this is the parts layout diagram for the Constant Brilliance Lighting Circuit. Note that the TDA1520 power amplifier IC must be attached to a heatsink. Inside each carriage and locomotive is a small ca­pacitor connected in series from track collectors on the metal wheels to each lamp. The capacitor blocks the DC track voltage while allowing the high frequency signal through to light the lamp. The locomotive motor’s inductance will block the high fre­quency so that no damage will occur to the motor while it is standing still. The high frequency is combined with the DC train control voltage then connected to the track. Any lamp and series capaci­tor connected to the track, via the track contacts, will light at a brilliance level determined by the amplitude of the high fre­quency signal and not the level of DC motor control voltage. In other words, the lamps will burn at the same level of brilliance as long as the unit is switched on and will be unaf­fected by the train control voltage. This is much more prototypi­cal. In normal use the output of the controller is connected to the input terminals of this system. The output from the unit is then connected to the track. Any train can be controlled normally using the existing controller and the lights can be adjusted in brilliance PARTS LIST – #2 1 PC board, code CBLGEN, 127 x 50mm 1 heatsink (see text) 6 PC stakes 2 prewound inductor (L1,L2) 2 3mm bolts and nuts 1 20kΩ vertical trimpot (VR1) Semiconductors 1 BC548 NPN transistor (Q1) 1 TDA1530 power amplifier (IC1) 2 1N914 signal diodes (D1,D2) 4 G1G diodes (D3-D6) 1 12V zener diode (ZD1) Capacitors 1 1000µF electrolytic 16VW 3 100µF electrolytic 16VW 3 10µF electrolytic 16VW 2 0.47 monolithic 1 0.1µF monolithic 3 .0033µF ceramic 1 680pF ceramic Resistors (0.25W, 5%) 1 150kΩ 1 1kΩ 1 47kΩ 1 820Ω 3 10kΩ 1 270Ω 3 6.8kΩ 1 10Ω 1 2.2kΩ or even switched on and off regardless of what the train is doing. The unit presented here can drive up to about 20 3V grain-of-wheat lamps with an AC supply of 15V at 1A. 15VAC has been chosen because this is a commonly available voltage found on most power packs used for model railways. If you prefer, up to about 20VAC can be used with a corre­sponding increase in the number of lamps that can be driven. Be careful though, as lamps can be easily blown if the voltage is too high. How it works Understanding how it works is not difficult. Referring to the circuit diagram of Fig.3, Q1 is configured as a standard phase shift oscillator. R4, R5 and R6 together with C3, C4 and C5 cause a phase shift of the signal that is fed back to the base of Q1. This causes the circuit to oscillate at a frequency set by the values of these resistors and capacitors. The signal is tapped off from the emitter of Q1 and then fed to the brilliance control, VR1. From here the signal is fed to power amplifier IC1. It has its gain set at 11 as controlled by RESISTOR COLOUR CODES – PROJECT #2  No.    1    1    3    3    1    1    1    1    1 38  Silicon Chip Value 150kΩ 47kΩ 10kΩ 6.8kΩ 2.2kΩ 1kΩ 820Ω 270Ω 10Ω 4-Band Code (1%) brown green yellow brown yellow violet orange brown brown black orange brown blue grey red brown red red red brown brown black red brown grey red brown brown red violet brown brown brown black black brown 5-Band Code (1%) brown green black orange brown yellow violet black red brown brown black black red brown blue grey black brown brown red red black brown brown brown black black brown brown grey red black black brown red violet black black brown brown black black gold brown feedback resistors R10 and R11. The amplified signal is then fed to the track. Inductors L1 and L2 isolate the low impedance output of the controller from the 25kHz signal and this allows the DC train control voltage to operate the train but not block the high frequency signal coming from the amplifier. The output coupling capacitor C12 also prev­ents the DC voltage from the controller from upsetting operation of the amplifier and vice versa. Power for the system comes from a bridge rectifier, D3-D6, and a 220µF filter capacitor, C14. C13 provides more supply filtering at the power input pin of the chip. The supply voltage for the oscillator is regulated to +12V by resistor R7 and zener diode, ZD1. This has been included to prevent the oscillator from overdriving the power amplifier if a higher power supply is used. This board feeds a 25kHz sinewave at a level of up to 15VAC onto the track to drive grain-of-wheat lamps in locomotives and car­riages. Each lamp needs a 0.47µF capacitor in series to block the track DC. Construction The component layout for the PC board is shown in Fig.4. There is nothing critical about assembly of the unit. Start by giving the PC board a close inspection to make sure that no tracks are touching or have breaks in them. Load the resistors, capacitors and diodes, taking care with the polarity of the electrolytic capacitors and diodes. Next insert the transistor and PC stakes. Before inserting the power amplifier IC, prepare the heat­ sink. This is made from a piece of aluminium angle 50mm long, 40mm on one side and 25mm on the other, as shown in the photos. Using IC1 as a template, mark the two holes that have to be drilled. Ensure that the heatsink is aligned with the PC board and IC1. When assembled, the heatsink should be attached squarely to the PC board, with the two screws holding both the heatsink and power amplifier securely in position. Testing When the assembly is finished, it is time to test the unit. If you have an oscilloscope, you can look at the 25kHz sinewave signal which will be present at the emitter of Q1 and the output of IC1. Failing that, it is just a matter of hooking the unit up to the power and coupling a number of “grain of wheat” lamps, each via a 0.47µF monolithic capacitor, across the output of IC1. When power is applied, it should be possible to vary the brightness of the lamps up and down by adjusting trimpot VR1. When no lamps are connected to the circuit, the DC current drain should be less than 50mA. If everything works as it should, you can install the unit somewhere under your layout and install the lamps in SC your car­riages. Where To Buy Kits & Parts Kits for the 3-Aspect Signalling and Constant Bril­liance Lighting projects are available from CTOAN Electronics. Cost of the signalling kit is $14.00 plus $3 postage within Australia. The kit includes the PC board plus all onboard compon­ents including an LDR. Cost of the Constant Brilliance Lighting kit is $26.00 plus $4.00 postage within Australia. This includes the PC board, all compon­ents and heatsink, plus 10 0.47µF monolithic capacitors. Each 3V grain-of-wheat lamp requires one 0.47µF capacitor connected in series. CTOAN Electronics will be providing a repair service for both these kits. All kits sent in for repair should be accompanied with a repair fee of $14.00 which includes return postage within Australia. Fully assembled units are also available, priced at $25 for the signalling unit and $45.00 for the Constant Brilliance Lighting project. Add $4.00 for postage within Australia. Kits can be ordered by using Bankcard, Mastercard or Visacard or by sending a cheque or money order to CTOAN Electronics, PO Box 211, Jimboomba, Qld 4280. Phone (07) 3297 5421. Oatley Electronics can supply a pack of 2mm LEDs for installation in HO scale signals. Each pack contains 10 red, 10 orange and 10 green LEDs plus 30 1kΩ resistors. The cost is $10 plus $3 for postage and packing. Oatley Electronics are located at 66 Lorraine Street, Peakhurst, NSW 2210. Phone (02) 9584 3563; fax (02) 9584 3561. 3V grain-of-wheat lamps can be purchased from most hobby shops. March 1997  39 s i h t d l i Bu Jumbo LED cloc clo This Jumbo clock has large red LED displays for high visibility in your home, in the office or in a factory. It uses readily available CMOS ICs and runs from a 12V supply. You could even use it in a boat or caravan. By JOHN CLARKE “Tempus Fugit” as they say in Latin, or “Time Flies” in English. Whichever language you prefer, it is hard to ignore this clock with its large red LED displays. In fact, they are 57mm high but the readout is so easy to read it looks larger than it really is. If you’re shortsighted, this is the clock for you. These days, clocks are available in virtually any form. You can have talking watches or clocks; digital or analog readouts with liquid crystal, LED, vacuum fluorescent or mechanical displays; oval, square, round, triangu40  Silicon Chip lar or odd shaped dials; and features such as alarm, calendar, world time, and stopwatch and timer functions. There are even “backward” clocks avail­able. What ever happened to the simple digital clock that was easy to read? Well, here it is. The SILICON CHIP Compact Jumbo Clock uses four 7-segment LED displays to provide 12-hour time; 24hour time is not an option. The only gimmicks, if you could call them that, are a colon flashing once a second and an AM/PM indicator. The display also dims in darkness so that it is not over-bright at night. The circuit is crystal-controlled and has battery backup in case of power failure. The Jumbo Clock is housed in a cutdown plastic instrument case to make it quite compact considering the large display size. A red Perspex panel forms the front of the box while at the rear are two time-setting switches and a DC input socket for a 12V DC plugpack supply. Speed-up feature Model railway enthusiasts who want a “fast clock” will be interested in the Jumbo Clock, as it can be built to run at up to 12 times normal speed. For more information on this subject , refer to the December 1996 issue. Block diagram Fig.1. shows the block diagram for the Jumbo Clock. There are two “minutes” counters to provide the requisite ock Fig.1: block diagram for the Jumbo Clock. There are two “minutes” counters to provide the requisite 0-59 count for the minutes displays, plus one counter and a flipflop for the hours displays. All three counters count in 4-bit binary code and this is fed to 7-segment decoders to drive three of the four LED displays. 0-59 count for the minutes displays and one counter plus a flipflop for the hours displays. All three counters count in 4-bit binary code and this is fed to 7-segment decoders to drive three of the LED displays. The fourth display is driven from the flipflop via a buffer stage. Timing is set by a 32.768kHz crystal oscillator, IC1, which is internally divided to produce a 2Hz output. This is further divided by two for the 1Hz colon driver and by 120 for the one minute signal for the first minutes counter, IC4. At each one-minute clock pulse, the minutes counter increments by one. Each time IC4 reaches the count of 0 (after a 9), its output clocks the second minutes counter, IC6. Thus, DISP2 shows the next digit in its count. When the count of “6” is reached, it is detected in IC11a and IC11b which clears IC6 back to “0”. Thus, DISP2 only counts from 0-5 then back to 0. When IC6 is preset to 0, the hours counter IC8 is clocked to increment DISP3. When IC8 reaches the count of 0 (after the 9), the output clocks flipflop IC10a. IC10a’s Q-bar output then drives the “1” digit of DISP4 via IC12c and IC12d. DISP4 and DISP3 now show a “10”. When IC8 reaches the count of 2 (in other words a 12 is displayed), the IC12b and IC10b circuit turns the AM/PM LED off if it was on, or on if it was off. When IC8 reaches the count of 3 (after the hours display reaches 12), the “3 detect” gates IC11c & IC11d clear flipflop IC10a. DISP4 is then switched off and the Q output drives the load input of IC8 which preloads a 1 into the counter. DISP3 Main Features • • • • • • • • • • • Large red (57mm high) 7-segment LED displays 12-hour display (4-digit readout) Compact plastic housing based on a standard case Flashing colon between hours & minutes digits AM/PM indicator Display automatically dims in darkness Crystal accuracy Hours and minutes set switches on rear panel Battery backup in case of power failure (no display) Runs from a 12V DC plugpack or battery Facility to speed up clock to x2, x3, x4, x6, x8 & x12 March 1997  41 The display board is soldered to the main PC board at right angles, as shown here. Tack solder a couple of the end connections and test fit the assembly in the case before soldering the remaining connections. now shows a 1. The count sequence there­fore changes from 12 to 1, as it should for 12-hour time. Setting the hours is achieved using switch S2 which triggers the “6 detect” output. This clears IC6 and clocks IC8. The minutes setting switch S1 resets the divide by 120 circuit which clocks IC4. The crystal oscillator divider is also reset so that the clock can be synchronised to the exact time from the beginning of the minute. Dimming of the display is controlled by an LDR (light dependent resistor) and transistor Q1. As the ambient light increases, the resistance of the LDR is reduced so it turns Q1 on harder to brighten the display. Circuit description Now let’s have look at the full circuit diagram of Fig.2. It comprises a total of 12 low-cost ICs, four large 7-segment displays, plus several resistors, capacitors, diodes and a 32.768kHz crystal. IC1 is a 4060 14-stage divider with provision for a crys­ tal oscillator at its input pins. A 10MΩ resistor is connected between pins 10 and 11 to bias the internal inverter to linear operation, while the 32.768kHz crystal 42  Silicon Chip is connected between the same pins but in series with a 330kΩ resistor. The 330kΩ resistor and trimmer VC1 prevent the crystal from operating in “overtone” mode (ie, at a multiple of the wanted frequency) by virtue of the RC time con­stant. The resistor also reduces the signal level applied to the crystal while the trimmer allows a small frequency variation for precise timekeeping. IC1 divides the 32.768kHz signal at its pin 10 by 16,384 (212) to pro­ vide a 2Hz square wave at pin 3, the Q14 output. This is fed to IC2 and IC3. These are 4526 programmable count­ers which are set to give a total division of 120. IC2 and IC3 have four preload inputs called DP1, DP2, DP3 and DP4, at pins 5, 11, 14 & 2 respectively. For our circuit, IC2 has DP4 set high to give a division factor of 8. For IC3, DP1, DP2 and DP3 are set high to give a division factor of 112. The two factors are added together to give a total division of 120. Note that, as part of the design provision for speeding up the clock for railway modellers, other division ratios can be used – see Table 1. The divided output from IC3 is applied to the clock input of IC4. IC4 counts from 0-9 and its “Carry Out” signal at pin 7 is used to clock IC6. IC5, IC7 and IC9 are 4511 latched BCD-to-7-segment decoder drivers. They take the 4-bit BCD (binary coded decimal) outputs from counters IC4, IC6 and IC8 and convert it to drive the 7-segment lines of the common cathode LED displays, via 390Ω resistors. Counting to 60 While IC4 is used as a conventional decade counter, counting from 0-9 in BCD, IC6 needs to count up to six and then flick back to zero. This is achieved by using the presettable inputs on the 4029 – J1, J2, J3 & J4 (for jam-load inputs) – at pins 4, 12, 13 & 3, respectively. With all these inputs tied low, the preset value is 0 (in BCD). When IC6 counts up to 6, its Q2 and Q3 outputs both go high and so the output of NAND gate IC11a goes low. This is inverted by IC11b which applies a high load signal to the L input, pin 1. This then presets IC6 back Fig.2 (right): the complete circuit for the Jumbo LED clock. IC1, IC2 & IC3 divide the 32.768kHz crystal by a factor of 1,966,080 (16,384 x 120) to provide one pulse per minute for the minutes counters. March 1997  43 This rear view of the Jumbo LED Clock shows the DC input socket (right) and the hours and minutes time setting switches. Power can be supplied from either a 12V battery or a 12V DC plugpack. to 0, the very instant that the 6-count is reached. This means that IC4 and IC6 actually count to 59 (for the minutes count) before being preset back to 00. The 1kΩ resistor and .001µF capacitor at the pin 9 input of IC11b provide a short time delay to ensure that the load signal is sufficiently long for the counter to function correctly. The load input also clocks counter IC8. When IC8 counts up to 9 and then to 0, its carry out (pin 7) clocks flipflop IC10a. The low data level at pin 5 (the D input) is transferred to the Q output and the Q-bar output goes high. The two segments to display the “1” digit on DISP4 are now driven via gates IC12c and IC12d. Displays DISP4 and DISP3 now show 10. When IC8 is clocked to a count of 2, its Q2 output goes high and this is ANDed with the high Q-bar output of IC10a in IC12b. The resulting high output from IC12b toggles IC10b. Hence, each time the clock shows 12:00, the Q output of IC10b toggles. This drives the AM/PM LED indicator which is the decimal point of DISP4. LEDs 3 and 4 are in series with the AM/ PM drive to allow the dimming circuit to function correctly on all display segments, but more on this later. At the count of 3, the Q1 and Q2 outputs of IC8 both go high and the pin 3 output of IC11c goes low and the output of IC11d goes high. This sets flipflop IC10a so that its Q output is high and its Q-bar output is low. Thus, the displayed “1” in DISP4 goes off and the Q output of IC10a pulls the load input (pin 1) of IC8 high, via a 0.1µF capacitor. The J1 input (pin 4) of IC8 is high and so IC8 is preloaded to a 1. Hence, when IC8 reaches a count of 3, instead of DISP4 & DISP3 displaying “13”, DISP4 is turned off and DISP3 shows “1”. The count sequence for DISP4 and DISP3 is therefore 1-9, 10, 11, 12 (AM/ PM indication) and then 1 again. Power-on reset At switch-on, counters IC4, IC6 and IC8 are preloaded so that the display reads “1.00”. For IC4, the load input (pin 1) is momentarily held high via the 1µF capacitor. This loads a 0 into the counter. The 10kΩ resistor releases the load by charging the capacitor to ground. IC6 is preset via the 1µF capacitor at pin 8 of IC11b initially being discharged. This produces a high at IC11b’s output to preload a 0. RESISTOR COLOUR CODES  No.    1    1    5    2    1  26    1 44  Silicon Chip Value 10MΩ 330kΩ 10kΩ 1kΩ 470Ω 390Ω 10Ω 4-Band Code (1%) brown black blue brown orange orange yellow brown brown black orange brown brown black red brown yellow violet brown brown orange white brown brown brown black black brown 5-Band Code (1%) brown black black green brown orange orange black orange brown brown black black red brown brown black black brown brown yellow violet black black brown orange white black black brown brown black black gold brown PARTS LIST 1 PC board, code 04302971, 224 x 94mm 1 PC board, code 04302972, 252 x 76mm 1 self-adhesive label, 89 x 49mm 1 plastic instrument case, 260 x 190 x 80mm 1 red Perspex sheet, 252 x 76 x 1.5mm 4 SC23-12EWA 57mm 7-segment common cathode LED displays (DISP1-DISP4) (Jaycar Cat. ZD-1850) 4 5mm red LEDs (LED1-LED4) 3 AA cell holders 3 AA nicad cells 1 DC panel socket 1 12VDC 500mA plugpack 2 snap action PC board mounting pushbutton switches (S1,S2) 1 LDR (LDR1) (Jaycar Cat RD3480 or equivalent) 1 32.768kHz watch crystal (X1) 1 10kΩ horizontal trimpot (VR1) 1 300mm length red hookup wire 1 300mm length green hookup wire 1 900mm length 0.8mm tinned copper wire 1 3mm screw, washer & nut 4 self-tapping screws 8 PC stakes Semiconductors 1 4060 14-stage ripple carry bina- Time setting The hours display of the clock is set by pressing button S2. This discharges the 1µF capacitor at the pin 8 input of IC11b. Thus, IC6 is preloaded to a 0 and IC8 is clocked. Upon releasing S2, the 1µF capacitor charges and IC11b's output goes low again. Thus every time S2 is pressed, the hours display is incremented. Capacitors 1 2200µF 25VW PC electrolytic 4 1µF 16VW PC electrolytic 9 0.1µF (100n or 104) MKT polyester or monolithic ceramic 1 .001µF (1n0 or 102) MKT polyester 1 8.5-50pF trimmer (VC1) 1 22pF NPO ceramic Resistors (0.25W, 1%) 1 10MΩ 1 470Ω 0.5W 1 330kΩ 28 390Ω 5 10kΩ 1 10Ω 1 1kΩ The AM/PM indicator can be set by counting to 12:00. The minutes display is set by pressing S1. This applies a reset to IC1, IC2 and IC3. A positive pulse is applied to the clock input of IC4 on each reset. Note that counter IC1 is reset to ensure that on setting the minutes, the seconds are also reset. The clock is thus reset to begin counting at the beginning of the min­ ute; ie, as soon as S1 is released. The colon between the hours and minutes displays is formed with the decimal points of DISP2 and DISP3. The 1-second pulse output of IC2 is buffered using IC12a to drive the decimal points via two series-connected LEDs (LED1 and LED2) and 390Ω resistors. Note that if the clock is set to run at a x2 or x4 speed using Electronic Projects For Cars 5 $8.9 PLUS P & $3 P Available only from Silicon Chip Price: $8.95 (plus $3 for postage). Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Use this handy form  The 1µF capacitor at pin 13 of IC11d produces a momentary high at the set input of IC10a. This sets its Q output high to produce a load signal to IC8 and thus preloads a 1. The low Q-bar of IC10a prevents the “1” digit in DISP4 from lighting. Thus on power up, the clock resets to 1:00. The AM/ PM indicator could be either on or off at power on. ry counter (IC1) 2 4526 programmable divide-by-N 4-bit binary counters (IC2,IC3) 3 4029 presettable binary counters (IC4, IC6 & IC8) 3 4511 BCD-to-7-segment decoders (IC5,IC7 & IC9) 1 4013 dual D flipflop (IC10) 1 4093 quad 2-input NAND Schmitt trigger (IC11) 1 4081 quad 2-input AND gate (IC12) 1 BD682 PNP Darlington transistor (Q1) 1 15V 1W zener diode (ZD1) 1 1N914, 1N4148 signal diode (D1) 1 1N4004 1A diode (D2) Enclosed is my cheque/money order for $________ or please debit my  Bankcard  Visa  Mastercard Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ March 1997  45 Fig.3: this diagram shows the component layout of the main PC board and wiring for the backup battery. Take care to ensure that each IC is correctly oriented. 46  Silicon Chip the pin 2 and pin 1 outputs of IC1, the colon will flash at a 2Hz or 4Hz rate. Display dimming Transistor Q1 drives the common cathodes of all four LED displays. It is connected as an emitter-follower so that the voltage at the emitter follows the base voltage. The base voltage is set by trimpot VR1 and the LDR. As the ambient light increases, the resistance of the LDR is reduced and Q1 turns on harder to brighten the display. In darkness, the resistance of the LDR increases and so Q1 is not turned on quite as hard and the display dims. VR1 allows adjustment of the dimmed display brightness. The dimming effect is dependent on the voltage drop across the LED display segments. For the main segments, there are four LEDs in series to produce an even light distribution over the lit element. Because the decimal point is smaller, only two LEDs are in series. We have compensated for this lower display voltage drop by adding two LEDs in series for the colon decimal points (LEDs 1 & 2) plus two more for the AM/PM indicator (LEDs 3 & 4). These extra LEDs are not seen in the clock display but are still illu­minated on the main PC board where they are mounted. Power The clock circuit is normally powered from a 12VDC plug­pack. These usually produce more than 15V when unloaded and so a 15V zener diode has been included to protect the ICs from overvoltage. A 220µF capacitor and nine 0.1µF capacitors dotted around the PC board provide power supply decoupling. The backup battery consists of three 1.2V nicad cells in series. These are kept charged via a 470Ω resistor from the 12V supply. If the plugpack is disconnected or the mains power is off, the battery feeds power to the circuit. Note that the voltage is too low for the displays to light, but sufficient to keep the ICs going. When power is restored, the time displayed will be correct. The battery is protected against reverse connection of the plugpack supply via D2, while ZD1 protects the clock circuit. The 10Ω resistor feeding ZD1 is likely to go open circuit if the reverse polarity connection is maintained Fig.4: the display board accommodates the four LED readouts and the LDR. Note that DISP2 and DISP4 are mounted upside down so that the decimal points are at the top of the display. The LDR should be mounted so that its surface lines up with the front of the LED displays. This device is the sensor for the automatic dimming circuitry. March 1997  47 This is the view inside the case with the top and the red Perspex front panel removed. The three 1.5V backup batteries are mounted in single-cell holders which are attached to the rear panel. but, apart from this, there will be no other damage. Construction The Jumbo Clock is built on two PC boards which are mounted at right angles to each other. The main PC board is coded 04302971 and measures 224 x 94mm, while the vertical display PC board is coded 04302972 and measures 252 x 76mm. It is housed in a plastic instrument case which has been reduced in depth so that its over­all measurements are 260 x 80 x 118mm (W x H x D). The parts layout diagram for the main PC board is shown in Fig.3 while the display board is shown in Fig.4. Begin construction by checking the PC boards for shorts between tracks, breaks in tracks or undrilled holes. Fix any board defects before proceeding. Next, insert and solder in all the links as shown on the overlay diagram. Be sure to install the links on the display board before placing the displays in position. Note that DISP4 and DISP2 are mounted upside down as indicated by the position of the decimal point. The LDR is mounted so that its face is about level with the front of the displays. Insert the resistors and PC stakes next. The PC stakes are required for mounting the time-setting switches and for the power supply connections. This done, install the capacitors, COMPACT JUMBO CLOCK SET MINUTES HOURS (SET LAST) (SET FIRST) + 48  Silicon Chip + DC INPUT 12VDC <at> 500mA + Fig.5: this full size artwork can be copied and attached to the rear panel. making sure that the electrolytics are inserted the right way around; ie, with correct polarity. Next, install the diodes, zener diode and LEDs and make sure that each is oriented correctly. The same comment applies when installing the ICs. Note that the 4511 ICs (IC5, IC7 and IC9) are oriented differently to the other ICs. Transistor Q1 is mounted horizontally with its metal face towards the PC board. We inserted a metal washer between the transistor and PC board before securing it with a screw and nut. The washer will allow the small amount of heat generated to dissipate more readily. Finally, wire in the time-setting switches, the adjustable trimmer capacitor VC1, trimpot VR1 and the crystal. Make sure that the switches are correctly oriented. Modifying the case To make a reasonably compact case, we took a standard plastic instrument case measuring 260 x 80 x 190mm and reduced its depth to 119mm. This can be easily done using a hacksaw. You will need to mark the cutting line on each case half and then cut between the integral slots. After you have finished with the hacksaw you can use a file to clean up the cuts. Note that the part that must be removed does not have the speaker slots Fig.6: here are the actual size artworks for the two PC boards. Check your boards carefully for defects before installing any of the parts. March 1997  49 The PC board assembly is secured using four self-tapping screws. These go into integral plastic pillars moulded into the base of the case. Notice how the display PC board slides into the rearmost slot at the front. in the base. The rear plastic panel will need to be chamfered slightly around the edges since the new rear slot is slightly narrower than the original. Remove all the integral mounting pillars in the base of the case, except for the four in the corners (these support the PC board). This can be done by using a large drill. The cut down case halves still join together neatly and are retained using the original two screws. Next, place the main PC board in position and locat­e it over the mounting pillars. This done, slide the display board into the rearmost front slot and mark the rear of this board where the main PC board makes contact. You can now remove both PC boards and tack solder them together at the large copper pads, making sure that they are at right angles. Finally, check the assembly in the case again to make sure that everything is correct before soldering all the matching pads. It is a good idea to apply a liberal fillet of solder to the large copper pads to improve mechanical strength. The rear panel can now be drilled to accept the DC socket and switches S1 and S2. Attach the DC socket and cell holders as shown, using contact adhesive or double-sided adhesive tape. Finally, wire up the socket and holders as shown in Fig.3. Testing Only time will tell if the circuit is working or not (Er .. sorry about that!). Rotate VR1 fully clockwise, apply power and check that the displays show 1:00. If there is no display at Table 1: Clock Speed Options IC2 IC3 Speed IC1 to IC2 Link Pin 2 Pin 5 Pin 5 Pin 11 x1 Pin 3 to pin 6 H L L L L H H H x2 Pin 2 to pin 6 H L L L L H H H x3 Pin 3 to pin 6 H L L L L H H H x4 Pin 2 to pin 6 H L L L L H H H x6 Pin 2 to pin 6 H L L L L H H H x8 Pin 1 to pin 6 H L L L L H H H x12 Pin 1 to pin 6 H L L L L H H H 50  Silicon Chip Pin 11 Pin 14 Pin 2 Pin 14 all, disconnect the power and check for reversed supply connections or incorrectly placed com­ponents. If all is well, the colon should flash at a one-second rate. You should be able to increment the hours and minutes with the time-setting switches. Check that the minutes digits count from 00 to 59 then 00 again and that the hours digits count from 1 to 12. Verify that the AM/PM indicator lights on alternative 12:00 time. Optional speed-up Table 1 shows the modifications required for faster than normal clock operation. Note that the PC board has been designed so that you only need to cut the narrowed tracks leading to the IC1 output and the IC2 and IC3 DP inputs, before applying solder bridges to make the new contacts. Most of the changes are indicated on the PC board pattern. Note that for time­keeping rates beyond x4, you have to modify the linking to IC1 and to either or both IC2 and IC3. Finally, insert the cells in their holders and adjust VR1 so that, when you place your finger on the LDR, the display dims (the final adjustment should be made in the dark). Trimmer capacitor VC1 can be adjusted if the clock needs to run slightly faster or slower in order to keep the correct time. If you have a frequency meter, it can be connected to pin 9 of IC1 and VC1 adjusted for a reading of exactly SC 32.76800Hz. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SERVICEMAN'S LOG The rich tapestry of servicing What makes a non-technical person fiddle with his VCR when something goes wrong? And why do young children like “post­ing” money into the cassette wells of VCRs? It’s all part of the rich tapestry of servicing. The tall, distinguished looking gentleman who wandered into the shop clutching his prized video to his bosom didn’t look the type to have a go – he looked more like a lawyer than a service­man. Anyway, I wasn’t presumptuous enough to enquire about his profession; instead, I politely asked him for his particulars and asked what was wrong. He explained that the tape would go in and down and wrap around the drum motor but it wouldn’t play, fast forward or rewind. He freely admitted that he had had the covers off and so I decided to carry out a few preliminary checks while he was there. I connected the machine – a Teac MV505 –to the power and pushed in a tape to confirm what he had said. His description of the problem was spot on but that wasn’t all. I also found that the tape wouldn’t eject because the cas­sette flap wouldn’t open, which meant that he had also removed the front escutcheon and not replaced it properly. This he sheep­ishly admitted was the case. After he left, I removed the covers and the front panel and re-engaged the door flap lifter so that the tape would now eject properly. Anyway, that was only a minor detail; I now had to track down the main fault. Preliminary checks The deck, surprisingly, was a Mitsubishi Fo swift mechanism and I could see that the tape was not lacing up fully. The drum motor was spinning but there was no sign of life from the capstan motor. My preliminary diagnosis was that something was wrong with the loading mechanism. But what? Was it jamming? Were the gears out of alignment? Was it the timing? Or was it a faulty mode select switch? I began by inserting a tape and when the loading motor stopped with the tape 3/4 laced up I continued to rotate it by hand, consciously feeling for any resistance. I couldn’t feel any and I so I continued to turn the motor until the arms were almost completely laced, at which point it would unload itself. Because the loading motor turned a squirrel gear, I con­cluded that this test may be misleading. Because of the gear ratio, I would not necessarily feel any resistance at my fingertips. My next step was to check if there was anything preventing the arms from completing their travel to the end stops. They seemed quite free and loose and so I concluded that either a 52  Silicon Chip gear had jumped a tooth in the loading gear chain or the mode select switch was at fault. Unfortunately, as I discovered when I removed the bottom cover, it’s not easy to check the gear alignment as there is a printed circuit board covering the master cam, along with several sliding plates. However, the mode select switch is easy to access and so I decided to check that first. This switch is soldered to the PC board via five connections and there is an alignment point which must marry up in the eject position. I replaced the switch but there was no improvement in the loading sequence. Regretfully, it looked like major surgery was required and I was extremely grateful that I had a full set of instructions for this deck, even though these were for a Mitsu­bishi VCR. It is hard to summarise the next hour of invective and bad language. The instructions make it all sound so easy and I sup­pose it is if you work on this deck all day every day. If you don’t, then it’s not quite so straightforward. Anyway, I removed the reel belt, capstan brake spring, cam plate B, three gears, the loading gear arm and five screws, before desoldering the leads to the full erase head. At this point, the deck PC board is ready to be prised off – at least in theory. However, on this model, the lower moulding that supports the deck is somewhat generous and the PC board won’t come out unless the whole deck, including the ejector, is removed. A closer inspection revealed that it would be necessary to remove about 6mm from either side of the moulding to free the PC board. As a result, I decided in the interests of time that an Australian modification was required and so I used a soldering iron to melt away the plastic so that the board could be removed (this didn’t alter the strength of the structure in any way). Finally, I had access to the main cams (1 and 2) and, after wiping away the excessive grey grease, I could check the align­ment hole. Would you believe that all was correct? The shafts and levers were all in the right places. I removed the cams and carefully examined them on both sides for broken or bent galler­ies but all were perfect. Even their teeth were straight. Worse, naturally, was to come. Any damn fool can take things to pieces – it’s getting them back together properly that sorts us out. Inevitably, I fell for all the traps, in particular the record safety lever which should be held back whilst insert­ing the board, not to mention pin “e” getting in the wrong track of the cam slide plate B. On the third attempt, it all finally came together and we were back to square one with the original fault. It was now that I had a little bit of well-deserved luck. Whilst cogitating menacingly over this vile mechanism, I noticed that it had been fitted with a new green pinch roller. Now the original pinch roller arm mechanism was made of white plastic and it is common for one of the arms that guides it down the squirrel gear cam to break. This is replaced by the green type which you can either purchase as a single part or as part of what is called “Abrasion Part Kit for Fo DECK (Rubber)”, whatever that means (the part number is 789­C007020). This kit comprises the arm, the reel belt, the circlip, a sachet of grease and a comprehensive instruction booklet. However, if a serviceman doesn’t March 1997  53 Serviceman’s Log – continued know about this kit (it isn’t mentioned in any service manual) and only fits the new pinch roller, he usually also neglects to clean and lubricate the shaft it slides up and down on. And that’s precisely what had happened in this case. In operation, the pinch roller started to slide down the shaft but it was too slow because of the friction and it was jamming the roller against the top of the capstan shaft housing in a way that wasn’t obvious to the eye. Cleaning and lubricating it with grease fixed the problem completely. Anyway, when our lawyer (?) friend arrived to pick it up, I asked him about it and he confirmed that the pinch roller had indeed been replaced just over a year previously. What a palaver over what, in hindsight, should have been a straightforward simple repair. Christmas treat After a long cup of coffee, I tackled the next job, praying it would be easy. Oh the joys of Christmas – the presents, the new VCR for Dad, the odd bit of cash for Johnny the 5-year old. And oh what a disaster this combination can make! 54  Silicon Chip Mr Grey brought in his Akai VSG220EA, with a tale of woe that his youngest son had “posted” some toy or other into it. Of course, it no longer worked and when I shook it I could clearly hear something rattling inside. The coffee had definitely improved my mood and I chose Mr Grey’s still shiny VCR – just barely out of the egg (I think) – to look at next. Removing the cover gave good access to the mid-decked VCR and I quickly found two coins – a 10-cent piece and a 5-cent piece – sitting on the PC circuit board just under the deck. I retrieved the two coins by carefully jiggling the deck upside down in the air, then carefully checked for more and for any signs of damage before powering it up. When I switched it on, the drum motor came to life briefly but no other signs of life were present – not even from the display. I pushed various buttons and nothing happened but when I pushed a prerecorded tape in and pressed play, the tape loaded normally and a picture appeared on the TV with full sound. I pushed all the buttons in turn and it paraded its full box of tricks. In fact everything was working except the display. Unfortunately, I don’t have the service manual for this particu­lar model, which meant that I would have to tackle it blind. Fortunately, the deck isn’t too difficult to remove. It’s simply a matter of removing five screws and three plugs, removing the front escutcheon/control panel, and then lifting the deck out vertically. This gives access to the PC board which is held in via two screws and half a dozen clips. Unfortunately, the clips make it rather awkward to remove the PC board assembly but eventually I was able to free it and lift it out from the rear. This done, I gave it a careful visual inspection but nothing obvious was shouting back at me so I applied power to the board and began checking voltages around the circuit. Because there was no display, I reasoned that the supply rail to it had probably gone missing. Either that or the display itself, or possibly the microprocessor that drives it, had been damaged. My initial checks revealed that a voltage was present bet­ween the two ends of the display where the filaments are connect­ed. This is typically either 5V DC or 5V AC. Having found this, I checked various other points around the display, looking for a -28V (approx.) rail, but there was none. I didn’t have a circuit diagram which was a bit of a hindrance but it all screamed of a failed -30V rail from the switchmode power supply. All I had to do was identify it. There are about 16 diodes in the secondary of the power supply, most of which are protected by low-value resistors. Unfortunately, no voltages were marked on this part circuit but it didn’t take a mental giant to figure out which diodes were in the negative rail, as their anodes connect to the negative side of an electrolytic capacitor. Anyway, I checked each of these in turn and eventually found that D209 was open circuit. I replaced it, plugged the machine into the wall socket and was immediately rewarded by a flashing “AKAI” sign in the middle of the display. Switching on the power at the machine then brought up the word “ERROR”, which is normal at this stage. Getting it all back together again was surprisingly simple, with the PC board literally falling into its supports. The deck accurately followed suit and I powered it up with a tape in place. This time, the display worked correctly and I gave it a thorough soak test before calling the customer. The house call After lunch, I was asked by a little old lady to do a house call on her aging Sony KV2764EC which had sound but no picture. This set is now about 10 years old and not getting any younger. In fact, assuming average use, this is about the “use by” date of a TV receiver. I don’t like doing service calls on these sets as access is to the main circuit board is quite poor. However, she couldn’t possibly bring the set to me, so I had to go to the set! When I got there, I found that the set was on a low table near a window and so the lighting was good. I switched the set on and the symptoms were as described – sound but no picture. This set used a PE3 chassis rather than the Rx chassis. The tube filament was alight and you could hear the familiar rustle from the EHT at switch on. As a first step, I measured the screen voltages on pins 3 and 4 (G1 & G2) of the tube. These were both around 500V which is what I would expect them to be. However, the cathodes were too high at nearly 200V. I then switched the set off and it momentar­ily flashed a white line. Ah, ah, I thought – a vertical deflec­tion failure. When I finally managed to remove the motherboard, I could see what looked like a number of dry joints and even though I worked them over, I knew that the problem just had to be IC552 (TDA3652). However, this IC is no longer available and is now replaced with a TDA3654. At the same time, you also have to replace R518 (6.8kΩ) with a 1.5kΩ resistor. As this is a well-known problem, I had the parts on boards that I carried with me and installing these quickly restored the picture. However, on departure, I advised her to start saving for a new TV. Portable players Back at the ranch, a couple of Pye ND-20 portable CD cas­ sette stereo radios had come looking very much the worse for wear. My instructions from the owner’s financier, namely the father of two teenagers, was to make one good unit out of the two. Much as I hate working on these cheap units, I reluctantly agreed to have a go. Gaining access to the circuitry of such units if often a problem but in this case, the two halves of the cabinet shell can be split after removing only eight screws. One of the sets was completely dead and I decided to work on this first, as I hoped that it would be a simple power supply prob­lem. In the event, the power was OK and I could trace the problem to the cassette deck and function switch SW2. Unfortunately, I didn’t have a circuit and so I couldn’t quite work out the se­quence of events from there on in. The function switch was fairly complex and as power was going in but not coming out, this had to be the logical suspect. To confirm this, I wiggled and twisted the switch and sprayed contact cleaner inside it until finally I managed to get some sound out of the speakers. That was enough to confirm my theory and I placed an order for a new switch right away. What about the other machine? Well, it had a smashed con­trol panel and for a while I contemplated removing its function switch for use on the other machine. However, it wasn’t worth the time that would be spent removing and refitting it, particularly without knowing its condition. Of course, the other option was to repair the smashed unit with parts from the other machine but the hole was too big and the damage too severe. Tarzan’s TV My next customer was a young man who arrived in a small 3-door hatchback. To my astonishment, he removed a 63cm stereo TV from the back seat and effortlessly carried it into the shop as though it was an empty cabinet. He plonked it down on our small counter and cheerfully informed me that there was no picture. The set was a Philips 2B-S chassis KR5987R 25CT8883/75, circa 1988. This was a fairly popular model and is one that I am quite familiar with. March 1997  55 Fig.1: the video control chip in the Philips 2B-S chassis. As the set ages, it is sometimes necessary to add a 33kΩ resistor between the +13a (12V) line (pin 6 of IC7300) and pin 26 (RGB output stage current sensor). Not bothering to even catch his breath, “Tarzan” continued to elaborate on the set’s problems. Apparent­ ly, the picture had been a little “unclear” and intermittently had taken longer and longer to come on. Initially, I was rather reluctant to take the set on, as I didn’t fancy the prospect of it taking up so much bench space for a week or two while I chased an intermittent fault. I mumbled that it could take quite some time and suggested that, in view of the set’s age, he might prefer to spend his money on a new set. His response was that he wanted the set fixed and that I could take as long as I liked. It was the wrong response but still, you couldn’t help liking him for his cheerful manner. In then end, I relented and promised to start on it straight away. All he had to do was move it to my workbench and promise to pick it up as soon as it was ready. No problem – Tarzan made the set’s removal look as though a genie had instantly answered my wish. If only he could have fixed it too! When I switched it on, there was no picture but both sound and EHT were apparent and the CRT filaments lit up. Now, this chassis will not give a picture until the beam current has 56  Silicon Chip reached a certain level. This feature is achieved using a video control chip (TDA4580/V2 – IC 7300), which also deals with brightness, contrast, saturation, beam cutoff stabilisation and beam limiting. However, a problem arises as the tube ages, in that it takes longer and longer for the picture to come on. Often, there is only a white line at the top of the screen but this can usual­ly be fixed by adding a 33kΩ resistor between the +13a (12V) line (pin 6 of IC7300) and pin 26 (RGB output stage current sensor). Unfortunately, this same symptom (ie, the white line at the top of the screen) can also be produced by a variety of other faults. And, in fact, it showed up within a minute or two from switch on. Access to the PC board in this set is not good and I find the best approach is to turn the cabinet on its side, or even upside down, to get to it. The first thing to tackle when you do get access is to remake any suspicious-looking joints, particu­larly around the transformers and ICs. In this case, it wasn’t too bad and my efforts made no difference to the problem. Next, I replaced C2571, a 100µF electrolytic capacitor in the vertical output stage. This is something that I always do as a matter of course with these sets, as past experience has shown that this capacitor can give problems. Again, it made no dif­ ference. Finally, I stopped working as an automaton, put in my re­ m aining braincell, and started measuring voltages and checking waveforms. First, I checked the 1.2V nicad battery which was OK (this battery backs up the memory for the microprocessor). This done, I checked gating pulse waveforms 43 and 44 to the chroma decoder (pin 8M10), to pin 9 of IC7550 (TDA3870/V2), to pin 10 of IC7300 (TDA4580/V2) and to pin 7 of IC7570 (TDA3654Q). I was drawing blanks everywhere, so I decided to go back to first principles and examine the CRT voltages. And as luck would have it, I found the cause almost immediately. As soon as my 100kΩ/V analog multimeter touched pin 7 of the CRT socket, the picture came on and stayed on. There was just one problem – it was out of focus. The voltage on pin 7 of the CRT is marked as 650V and is derived from the flyback transformer 7kV connection via the focus and screen control pots. And, fairly obviously, the very small current through the meter was necessary to make the focus control function. Replacing the focus control pot (33MΩ) fixed the problem. Unfortunately, the picture still wasn’t the best, even after adjusting the focus, and I suspect that the emission was down. However, it wasn’t down far enough to justify the modification mentioned earlier. When I stripped down the faulty pot, I found that the printed circuit on the ceramic base had corroded. Apparently, the extra leakage of the meter was enough for the voltage to arc across the corroded section. I might add that, on some sets, I have also had problems with the screen control (4.7MΩ), especial­ ly on the KT3 chassis, and with C2471, a 68nF capacitor which connects from the wiper of the screen control to the +200a vol­tage rail. Tarzan, true to his word, turned up not long after I made the call, tucked the set under one arm (well, not quite), and plonked it in the back of his tiny car. Fortunately, he was as happy as SC Larry. VISIT OUR WEB SITE OUR COMPLETE CATALOGUE IS ON OUR SITE. A “STOP PRESS” SECTION LISTS NEW AND LIMITED PRODUCTS AND SPECIALS. VISIT: https://www.oatleyelectronics.com/ SWITCHED MODE POWER SUPPLY:Compact (50X360X380mm), enclosed in a perforated metal case, 240V AC in, 12V DC/2A and 5VDC/5A out: $17 ...HP POWER SUPPLIES: Compact (120X70X30mm) HP switched mode, power in plastic case, 100-240V AC input, 10.6V/1.32A DC output, slightly soiled: $14 ...LASER MODULE: Very bright (650nM/5mW) focusable module, suit many industrial applications, bright enough for a disco laser light show, good results with the Automatic Laser Light Show: $75 ...AUTOMATIC LASER LIGHT SHOW KIT: 3 motors, mirrors plus PCB and comp. kit, has laser diode reg. cct, could be powered by the above 12V switched mode power supply, produces many different patterns, can be used with the laser module: $70 ...LASER POINTER: Our new metal laser pointer (With keychain) is very bright, with 650nM/5mW diode: $65 ... LEDS SUPER PRICES, INCLUDING A SUPER BRIGHT BLUE!: All the following LEDS are in a 5mm housing ...By far THE BRIGHTEST BLUE EVER OFFERED, superbright at 400mCd: $1.50Ea. or 10 for $10 ... 1C red: 10 for $4 ...300mC green: $1.10Ea. or 10 for $7 .. MAKE WHITE LIGHT BY MIXING THE OUTPUT OF THE PREVIOUS 3 LEDS? ..3Cd Red: $1.10Ea. or 10 for $7 ... 3Cd yellow (Small torch!) also available in 3mm: 10 for $9 ... Superbright flashing LEDS: $1.50 Ea. or 10 for $10 ... PHOTOTRANSISTORS: Enclosed in clear 5mm housing similar to the 5mm LEDS, 30V/3uS/<100nA dark current: $1.30 or 10 for $9 ...CONSTANT VOLTAGE DIODES: 1.52-1.66V <at> 10uA: 10 for $7 ...MASTHEAD AMPLIFIER PLUS PLUGPACK SPECIAL: Our famous MAR-6 based masthead amplifier plus a suitable plupack to power it: $20, Waterproof box: $2.50, bottom box:$2.50 ...17mm MAGNIFIERS: Made in JAPAN by Micro Design these eyepiece style metal enclosed magnifiers will see the grain of most papers, used, limited qty.: $4 Ea. ...HF BALLASTS: Single tube 36W Dimmable high frequency ballasts: $18 Ea. ...12V SLA BATTERY CHARGERS: INTELLIGENT “PLUGPACK” 240V-12V GEL BATTERY CHARGERS, 13.8V / 650mA, proper “switching” design with LED status indicator: $8.80 ...LASER POINTER KIT: A special purchase of some 660nM/5mW laser diode means that we can reduce the price of our Laser Pointer kit, includes everything except the batteries: $29 ...SPECIAL BATTERY AND CHARGER OFFER: When our 7AHr/12V SLA battery ($30) is bought with the SLA battery charger the total price for both is: $33 ...USED BRUSHLESS DC FANS: 4"/12V/0.25A: $8, 24V/6"/17W: $12 ...100,000uF ELECTROLYTIC CAPACITORS: 30V/40Vsurge, used but in exc. cond.:$10 ...12Hr. MECHANICAL TIMERS: 55X48X40mm, 5mm shaft (Knob not supplied), two hours timing per 45deg. rotation, two 25V/16A SPST switches which close at the end of the timing period: $5 ...USED IEC LEADS: Used Australian IEC leads: $2.50 ...STANDARD PIEZO TWEETERS: Square, 85X85mm, 4-40KHz, 35V RMS: $8, Wide dispersion, 67X143mm, 3-30KHz, 35V RMS: $9 ...COMPUTER POWER SUPPLY: Standard large supply as used in large computer towers, +5V/22A, +12V/8.5A, -5V/0.5A, -12V/0.5A, used but in excellent condition, guaranteed: $30 ...MAGNIFIERS: Small eyepiece: $3, 30mm Loupe: $8, 75mm Loupe: $12, 110mm Loupe: $15, a set of one of each of these magnifiers (4): $30 ... NEW NICAD BATTERY BARGAIN: 6 PACK (7.2V) OF 1.2V / 800 mAHr. AA NICAD BATT’s plus 1 X thermal switch, easy to seperate: $4 per pack or 5 packs for $16, FLAT RECTANGULAR 1.2V, 400mAh NI-CAD BATTERIES with thermal switch, easy to seperate, (Each batt: 48x17x6 mm): $4 per pack or 5 packs for $16 ...UV MONEY DETECTOR: Small complete unit with cold cathode UV tube, works from 2 X AA batteries ( Not supplied), Inverter used can dimly light a 4W white fluoro tube: $5Ea. or 5 for $19 ...MISCELLANEOUS USED LENS ASSEMBLIES: Unusual lens assemblies out of industrial equipment: 3 for $22 ...USED PIR MOVEMENT DETECTORS: Commercial quality 10-15M range, used but tested and guaranteed, have O/C transistor (BD139) output and a tamper switch, 12V operation, circuit provided: $10 Ea. or 4 for $32 ...CCD CAMERA WITH BONUS: Tiny (32X32X27mm) CCD camera, 0.1lux, IR responsive (Works in total dark with IR illumination), connects to any standard video input (Eg VCR) or via a modulator to aerial input: $125, BONUS: With each camera you can buy the following at reduced prices: COMMERCIAL UHF TRANSMITTER for $15 (Normally $25), IR ILLUMINATOR KIT with 42 X 880nM LED’s for $25 (Normally $35), REGULATED 10.4V PLUGPACK for $10 (Normally $25) ...PIR CASE FOR CCD CAMERA: Used PIR cases of normal appearance, use to hide the CCD camera, plenty of room inside: $2.50 Ea. or 4 for $8 ...CAMERA-TIME LAPSE VCR RECORDING SYSTEM: Includes PIR movement detector and interface control kit, plus a learning remote control, combination can trigger any VCR to start recording with movement and stop recording a few minutes after the last movement has stops: $90 ...GEIGER COUNTER KIT: Based on a Russian tube, has traditional “click” to indicate each count. Kit includes PCB, all on-board components, a speaker and Yes, the geiger counter tube is included: $30 ...RARE EARTH MAGNETS: Very strong! 7X3mm $2, 10X3mm $4, Torroidal 50mm outer, 35mm inner, 5mm thick: $10 ...IR TESTER: Kit includes a blemished IR converter tube as used in night vision and an EHT power supply kit, excellent for seeing IR sources, price depends on blemishes: $30 / $40 ...ARGON-ION HEADS: Used Argon-Ion heads with 30-100mW output in the blue-green spectrum, power supply circuit provided, size: 350X160X160mm, weight 6Kg, needs 1KW transformer available elsewhere for about $170, head only for: $350 ...DIGITAL RECORDING MODULES: Small digital voice recording modules as used in greeting cards, microphone and a speaker included, 6 sec. recording time: $9 ...WIRED IR REPEATER KIT: Extend the range of existing IR remote controls by up to 15M and/or control equipment in other rooms: $18 ...12V-2.5W SOLAR PANEL KIT: US amorphous glass solar panels, 305X228mm, Vo-c 18-20V, Is/c 200mA: $22 Ea. or 4 for $70 ...MIDI KEYBOARDS: Quality midi keyboard with 49 keys, 2 digit LED display, MIDI out jack, Size: 655115X35mm, computer software included, see review in Feb. 97 EA: $80, 9V DC plugpack: $10, also available is a larger model which has mor features and has touch sensitive response keys: $200 ...STEREO FM TRANSMITTER KIT: 88-108MHz, 6-12V DC supply, 8mA <at> 9V, 25X65mm PCB size, PCB plus all on-board comp’s, plus battery connector and 2 electret mic’s: $25, plastic case to suit: $4 ...WOOFER STOPPER KIT: Stop that dog bark, also works on most animals, refer SC Feb. 96, Kit includes PCB and all on board comp’s, wound transformer, electret mic., and a horn piezo tweeter: $39, extra horn piezo tweeters (drives up to 4) $6 Ea. ...ALCOHOL BREATH TESTER KIT: Based on a thick film alcohol sensor. The kit includes a PCB, all on board comp’s and a meter : $30 ...CENTRAL LOCKING KIT (NEW): A complete central locking kit for a vehicle. The kit is of good quality and actuators are well made, the kit includes 4 actuators, electronic control box, wiring harness, screws, nuts, and other mechanical parts: $60, The actuators only: $9 Ea. ...CODE HOPPING UHF CENTRAL LOCKING KIT PLUS A ONE CHANNEL UHF REMOTE CONTROL: Similar to above but this one is wireless, includes code hoping Tx’s with two buttons (Lock-unlock), an extra relay in the receiver can be used to immobilise the engine, etc., kit includes 4 actuators, control box, two Tx’s, wiring harness, screws, nuts, and other mechanical parts: $109 ...ELECTROCARDIOGRAM PCB + DISK: The software disk and a silk screened and solder masked PCB (PCB size: 105 x 53mm) for the ECG kit published in EA July 95. No further components supplied: $10 ...SECURE IR SWITCH: IR remote controlled switch, both Rx and Tx have Dip switches for coding, kit includes commercial 1 Tx, Rx PCB and parts to operate a relay (not supplied): $22 8A/4KV relay $3 ...FLUORESCENT TAPE: High quality Mitsubishi brand all weather 50mm wide Red reflective tape with self adhesive backing: 3 meters for $5 ...LOW COST IR ILLUMINATOR: Illuminates night viewers or CCD cameras using 42 of our 880nm / 30mW / 12 degrees IR LEDs. Power output is varied using a trimpot., operates from 10 to 15V, current is 5-600mA ...IR LASER DIODE KIT: Barely visible 780nM/5mW (Sharp LT026) laser diode plus constant current driver kit plus collimator lens plus housing plus a suitable detector Pin diode, for medical use, perimeter protection, data transmission, experimentation: $32 ...WIRELESS IR EXTENDER: Converts the output from any IR remote control into a UHF transmission, Tx is self contained and attaches with Velcro strap under the IR transmitter, receiver has 2 IR Led’s and is place near the appliance being controlled, kit includes two PCB’s all components, two plastic boxes, Velcro strap, 9V transmitter battery is not supplied: $35, suitable plugpack for the receiver: $10 ...NEW - LOW COST 2 CHANNEL UHF REMOTE CONTROL: Two channel encoded UHF remote control has a small keyring style assembled transmitter, kit receiver has 5A relay contact output, can be arranged for toggle or momentary operation: $35 for one Tx and one Rx, additional Tx’s $12 Ea. OATLEY ELECTRONICS PO Box 89 Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 orders by e-mail: branko<at>oatleyelectronics.com major cards with phone and fax orders, P&P typically $6. MM arch arch1997  57 1997  57 By JOHN CLARKE RGB-to-PAL encoder replacement for the TV Pattern Generator Since publication of the TV Pattern Generator in Novem­ber 1991, the TEA2000 RGB-to-PAL encoder IC used in the circuit has gone out of production. This add-on board using a diff­er­ent encoder IC can be used as a replacement. The TV Pattern Generator described in the November and December 1991 issues was a very popular project. It produced a variety of patterns, including checker board, crosshatch, dot, white screen, greyscale, red screen and colour bars. The colour bar and red screen patterns relied on 58  Silicon Chip the RGB-to-PAL encoder functioning correctly to give the colour burst and chroma wave­forms in the composite video signal. In recent months, we’ve heard from quite a few readers who want to build this project but have been unable to do so because the TEA2000 encoder IC is no longer available. This drop-in board is the answer to that problem but there is a performance penalty which we’ll discuss shortly. It can also be used to restore a circuit to working order in those few isolated instances where the TEA2000 has failed. The add-in board is based on the Motorola MC1377P RGB-to-PAL/ NTSC encoder. This device has been available for many years and after being assured by the Motorola distributors in Australia that it is still in production, we decided to use it. Although the MC1377P is equivalent in function to the TEA2000, it Fig.1: the add-on circuit is based on the Motorola MC1377 RGB-toPAL/NTSC converter (IC2). IC1 provides buffering and blanking of the RGB input signals. does not have the same pinouts and, in our circuit at least, it also requires a separate blanking facility. In addi­ tion, the TEA2000 IC operated from an 8.86MHz crystal to produce the PAL signal while the MC1377P uses a conventional 4.43MHz colour burst frequency crystal. As shown in the photos, the addon PC board is mounted on the rear panel above the main PC board using a couple of right angle brackets. This board accommodates the Motorola MC1377P encoder, its companion 4.43MHz crystal and an additional quad AND gate IC (4081) which provides the blanking facility. There are 10 external connections and these are wired directly to the original circuit. Note that the original TEA2000 and its associated compon­ ents must be removed from the main board – see construction. It’s not as good Unfortunately, the quality of the colour bar pat­tern is not as good with the MC1377P (at least not in this de- sign) as it was with the TEA2000. In particular, there are faint horizontal lines across the colour bars and much more noticeable herringbone patterns between the bars. While these effects are probably not important as far as the overall test pattern is concerned, we thought it only fair to warn readers of the poorer picture quality. The other test pat­terns are virtually unaffected. What we are saying is that this board solves a problem if you wish to build the TV Pattern Generator but don’t expect too much in the way of picture quality on the colour bar pattern. For the same reason, we don’t expect any of the retailers to supply a kit containing the add-on board, particularly as all the original kits have now been discontinued. Circuit details Refer now to Fig.1 for the circuit of the RGB-to-PAL Con­verter. IC2 is the main encoder IC and it accepts sync and RGB (red, green and blue) signals on pins 2, 3, 4 & 5 to produce a composite video output at pin 9. This composite video signal includes the horizontal and vertical sync, the colour burst and the luminance and chrominance information. The 4.43MHz crystal oscillator at pins 17 & 18 produces the timing for the colour burst and chrominance signals. VC1 allows the crystal oscillator to be precisely trimmed, while the posi­tion of the colour burst signal is set by the ramp signal gener­ated at pin 1. In this circuit, it is placed right in the middle of the back porch. Note that the chrominance output at pin 13 is fed back into the pin 10 input via a 3dB resistive divider and a .001µF capaci­tor. The divider reduces the high level at pin 13 which is in­ tended to compensate for losses if a filter were to be included. The pin 10 input connects to the main TV Pattern Generator circuit and is shunted to ground via a 0.1µF capacitor and switch S2b when either the checker, hatch or dot pattern is selected. In other words, the colour burst and chrominance information is removed from the composite video output. March 1997  59 TABLE 2: CAPACITOR CODES      Fig.2: install the parts on the PC board as shown in this wiring diagram, taking care to ensure that the ICs and the electrolytic capacitors are correctly oriented. The external connections can be run using rainbow cable. Fig.3: this is the full-size etching pattern for the PC board. Check the board carefully before installing the parts. The composite video output appears on pin 9 and is fed to a 360Ω and 470Ω resistive divider to give the correct video level. The RGB and sync inputs from the main board are fed in via IC1 which is a 4081 quad AND gate. In the case of the sync signal, IC1a simply acts as a buffer stage, the sync signal then going directly to pin 2 of IC2. The RGB signals, on the other hand, are gated with a blanking signal that’s derived from pin 1 of IC10c on the main PC board. This effectively blanks the RGB signals during the horizontal sync and colour burst periods. The gated RGB signals appear on pins 11, 13 & 14 respec­tively and are fed to voltage dividers (12kΩ & 3kΩ) to obtain 1V p-p signals. They are Value  IEC 0.1µF 100n .01µF 10n .001µF 1n0 220pF 220p then coupled via 22µF capaci­tors to the RGB inputs (pins 3, 4 & 5) of IC2. Power for the circuit is derived directly from the main PC board. Note that two separate supply rails are used. IC1 is powered from a 5V rail, while IC2 is powered from a 12V rail. Construction The RGB-to-PAL Converter is built on a PC board coded 02302971 and measuring 98 x 53mm. Start construction by checking the PC board against the published pattern for shorts or breaks in the tracks. Fig.2 shows the parts layout on the PC board. Begin the assembly by installing PC stakes at all the external wiring points, then install the two wire links and the resistors. Table 1 lists the resistor colour codes but it is also a good idea to use your multimeter to check each value just to be sure. The ICs can be installed next, taking care to ensure that they are oriented correctly. This done, complete the assembly by installing the capacitors, the trimmer (VC1) and the crystal (X1). The electrolytic capacitors must all be oriented correctly, while the crystal can be installed either way around. Installation If you are building the TV Pattern Generator PC board as well, the following components should be omitted: the TEA2000 (IC16), the 8.86MHz crystal, TABLE 1: RESISTOR COLOUR CODES          No. 1 3 1 1 3 2 1 1 60  Silicon Chip Value 56kΩ 12kΩ 10kΩ 2.2kΩ 300Ω 1kΩ 470Ω 360Ω 4-Band Code (1%) green blue orange brown brown red orange brown brown black orange brown red red red brown orange black brown brown brown black red brown yellow violet brown brown orange blue brown brown EIA 104 103 102 221 5-Band Code (1%) green blue black red brown brown red black red brown brown black black red brown red red black brown brown orange black black black brown brown black black brown brown yellow violet black black brown orange blue black black brown PARTS LIST 1 PC board, code 02302971, 98 x 53mm 11 PC stakes 1 50mm length of 0.8mm tinned copper wire 2 right angle mounting brackets 4 3mm screws and nuts 1 4.43MHz crystal (X1) Semiconductors 1 4081 quad 2-input AND gate (IC1) 1 MC1377P RGB to PAL/NTSC converter (IC2) Capacitors 3 22µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 3 0.1µF MKT polyester 1 .01µF MKT polyester 2 .001µF MKT polyester 2 220pF ceramic 1 3-30pF trimmer (VC1) The add-on colour converter board is secured to the rear panel of the TV Pattern Generator using right angle brackets and machine screws and nuts. It takes the place of the original TEA2000 RGB-to-PAL encoder (IC16). These oscilloscope waveforms show the colour bar composite video signal (top), the sync signal (centre) and the blanking interval signal (bottom). the associated trimmer capacitor (VC1), the two 5.6pF capacitors, the 1kΩ and 910Ω resistors at pin 8, the 390Ω and 470Ω resistors at pin 6, and the 330pF ca­pacitor and 36kΩ resistor at pin 15. If you have already built the board, it will be necessary to remove these components. Next, insert hookup wires (eg, rainbow cable) into seven of the vacant TEA2000 pads at pin positions 1, 3, 5, 9, 10, 11 & 16. Additional hookup Resistors (0.25W, 1%) 1 56kΩ 3 300Ω 3 12kΩ 2 1kΩ 1 10kΩ 1 470Ω 1 2.2kΩ 1 360Ω wires connect to pin 1 of IC10c, pin 16 of IC15 and to the base of Q1. The most convenient place to connect to the latter is at the junction of the 390Ω and 470Ω resistors. The add-on board is mounted on the rear panel above the BNC output socket and is secured using right angle brackets and machine screws and nuts. You will have to drill a couple of holes in the rear panel to mount the brackets. Once the board is in place, it’s simply a matter of connecting the various hookup wires to the PC stakes, as shown in Fig.2. To test the unit, first apply power and check for +5V on pin 14 of IC1 and +12V on pin 14 of IC2. It’s then simply a matter of connecting the unit to a TV set using either the video modulator or the direct video output and checking that the unit works properly. If the colour is missing, adjust VC1 on the add-on board to obtain the correct colour burst signal. Footnote: we have been informed that Rod Irving Electronics still have limited stocks of the original TEA2000 SC encoder. March 1997  61 RADIO CONTROL BY BOB YOUNG Preventing RF interference on the 36MHz band This month we discuss the new operating frequencies on the 29MHz and 36MHz bands and how a new frequency keyboard will prevent serious interference problems on 36MHz. Last month’s column has really set the cat amongst the pigeons (once again) and has resulted in a directive from the MAAA (Model Aeronautical Association of Australia) to the Fre­ quency Sub-Committee. This directs the chairman of the subcommittee to examine the issues raised in that article and ini­ tiate a course of action to overcome the problems highlighted. Before we examine the new frequencies in the 29MHz and 36MHz bands, cosmic noise levels were the greatest. Thus, it was considered to be the garbage band of the electromagnetic spectrum and therefore unsatisfactory for commercial transmission. And we did suffer during periods of sunspot activity and similar cosmic disturbances, particularly when we were using super-regenerative receivers. In spite of this, we operated quite safely and successfully for many years. Or we did, until the FCC in The bogey of 29MHz interference was the mask used to manipulate people into buying 36MHz rather than a valid technological objection. it will be helpful to look at some of the history regarding the development of the Australian frequency alloca­tions. When I began flying back in 1955, R/C modellers were considered to be part of the worldwide radio experimenters group and shared the 27MHz allocation with this group. This band, 26.962 - 27.270MHz, was given to the experimenters because it was the frequency in which naturally occurring 62  Silicon Chip America licensed it for citizens band (CB) radio, with channels every 10kHz apart. American modellers were given six spots in the middle of all of this, spaced 50kHz apart, and that set the trend for worldwide R/C development. This persisted for many years and eventually people came to believe that a 50kHz spacing was the only safe way to operate. The situation in Australia was entirely different. Modell­ ers were given the complete 27MHz block in which we could space ourselves to suit our needs. But because the only R/C equipment available at that time was American, Australia slavishly followed the American frequency spacing. Silver­tone slavishly followed as well, until 1969 when I broke the spell with the Mk.VII system. That system used AGC on the mixer plus a few other tricks and allowed operation down to 15kHz spacing, completely outperforming the imports of the day. I had a terrible battle to shift the Australian mind-set from the usual “if the Americans thought it was safe they would use closer spacings” routine. To overcome all of the objections, I had to develop the Silvertone Keyboard and the battle raged on for years. It was exactly the same sort of argument as “why 29MHz AM, when everybody is producing 36MHz FM?” Nobody ever spared a thought to the fact that the Americans never had the opportunity or need to develop narrow-band systems and that conditions in Australia were, and still are, entirely different. 30 years on, Australia has finally released the 10kHz spac­ings for general use, albeit with 2" keys, thereby utilising the Australian regulations to the full. Furthermore, the MAAA strongly recommends the use of the Silvertone Keyboard as the frequency control system! All of this is most pertinent in regard to what follows. CB radio It took some time for CB to gain momentum but sales in­creased stead- High side crystals A complicating factor was the fact that the Australian 29MHz band used high-side receiver crystals (f + 455), whereas the imported sets were designed for low-side crystals (f - 455) . This created havoc in FM sets because the detector inverted the recovered audio and the sets just did not work. AM sets do not care if the Rx crystal is on the high or low side; they work either way. So you can see there was a large amount of self-interest on the part of overseas manufacturers and their importers in the insane exodus from 29MHz. Other countries use 35MHz, therefore 36MHz operation simply required a crystal change and some retuning, a much more satisfactory situation from the overseas manufacturers’ point of view. In Australia, 35MHz is out of the question for R/C work because the frequencies are in use for base, mobile and repeater stations. Once 36MHz was released, it became almost impossible to purchase high quality sets on 29MHz and today it is no longer possible to even purchase replacement receivers for existing equipment (unless you go to Silvertone, of course). So you see that the bogey of 29MHz interference was the mask used to manipulate people into buying 36MHz rather than a valid technological objection. Thus, we now have an entire band virtually lying idle. So why not use it? This is the problem that arises when control over supply passes from Australian control to overseas sources. We must simply take what the overseas manufacturers dump on us and local conditions play no part in the development process. Actually, the way govern­ments handle manufacturing in Australia is one of my pet peeves. SILICON CHIP readers have watched the Mk.22 system evolve from a proposed simple 4-channel runof-the-mill system to a very complex state-of-the-art 24-channel AM or FM system. Along the way, I have had to deal with complex technical issues such as third order intermodulation and transmitter intermodulation 455kHz spacings. These are subjects not handled in a serious manner by any other magazine or indeed any group that I am aware of. Now the question is, how has this favourable development occurred? The answer is that SILICON CHIP gave me the reason to sit down and actually think hard about R/C systems for the first time since the IAC (Industries Assistance Commission) effectively “assisted” me out of manufacturing 20 years ago. As I got deeper into the development of the Mk.22, my in­sight into the problems and solutions facing R/C modellers here in Australia expanded and is still expanding. Which raises the question what could I have achieved during those 20 years if the government had assisted instead of effectively stopping me. If you multiply this effect by hun- Silicon Chip BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality ★ Hold up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 (includes postage in Australia). NZ & PNG orders please add $A5 each for postage. Not available elsewhere. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. Use this handy form  ily and prices of equipment dropped accordingly, until by 1974 the stage was set for a calamity to occur in the worldwide R/C movement. The situation in Australia was that it was illegal to oper­ate CB sets but it was legal to sell them. Dealers stocked up with CB sets and the explosive growth of CB began. By 1974, those R/C aircraft still surviving were ground­­ed all over Australia. Thankfully, the licensing people acted quickly and we were granted the 29MHz band for our exclusive use. The drawback was that it was to be for all R/C models, including cars and boats. Once again the explosive growth of toy cars and cheap 2-channel sets placed the aircraft modellers at risk. The problem with R/C aircraft is that the receiver is 100 metres in the air and can thus receive signals from miles away. Once again the licensing authority smiled kindly upon us and in 1980 granted us the 36MHz band, originally for the exclu­sive use of high-performance aircraft and boats and only on spots 20kHz apart. In time, some abuse of the original agreement took place and a recent ruling by the SMA (Spectrum Management Agency) has just reaffirmed the original position and R/C cars have been asked to clear the band. This time, however, we have been granted 59 spots 10kHz apart. Now the problem in all of this is that the 29MHz and 36MHz bands are exclusive to Australia and NZ, although the NZ spot frequencies are different. Overseas manufacturers hated making sets on 29MHz because of the small quantities of sets sold in Australia and the conversions were left to the local importers. Enclosed is my cheque/money order for $________ or please debit my  Bankcard  Visa  Mastercard Card No: _______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ March 1997  63 Radio Control – continued dreds of thousands in every field of human endeavour, Australia could once more be a strong industrial nation with low unemployment. So to finally answer the often-asked question “why 29MHz?”, I wanted to fill the vacuum left by the imports and stimulate interest in the 29MHz band once more. Silvertone can now supply replacement receivers for all PPM systems on AM or FM and on 27MHz, 29MHz, 36MHz or 40MHz. True, some care is required to make the 29MHz band com­pletely safe but we flew very successfully and safely for many years on this frequency and I still fly today with an AM 29MHz module. In over three years of test flying the Mk.22 system on 29MHz (even spots), we have never encountered interference nor indeed have we had any systems back due to crash damage. Some of this test flying is being done on fields that are quite close to suburban areas, which would pose the highest risk in regard to R/C car interference. This is due to the fact that the cheap R/C cars commonly available in department stores are often on the band. By using these frequencies, there is absolutely no reason why model aircraft should not use 29MHz with complete safety. An added bonus for clubs operating on 29MHz is that the keyboard is simple and cheap ($149). So there you have it. The 29MHz band is empty, it is safe on the new frequencies and cheap and simple to operate from a club viewpoint. The situation in regards to operation on the 36MHz band is difficult in that there are 59 spots, covering the block 36.0MHz to 36.6MHz. This makes the keyboard very difficult to construct mechanically as a single unit. A 1.7m long unit would soon buckle due to expan­sion in the heat of the sun. Therefore, the best arrangement is for a two-board set, laid out as per Fig 1. In addition, the new SMA allocation has required modifica­tions to be made to the original 36MHz keyboard. Keyboard explanation For those not familiar with this new 36MHz keyboard or indeed, any frequency keyboard, the following explanation should help. The keyboard The 29MHz band is empty, it is safe on the new frequencies and cheap and simple to operate from a club viewpoint. “even” 29MHz spots, in particular 12, 16, 20, 24, 28, 32 and 36. Now there are 27 x 10kHz spots in all (numbered 10 - 37 in the block 29.72 - 30.0MHz), many of which have never been officially released until just recently. The sequence 10, 14, 18, etc has been released in smaller numbers but the “odd” sequence 11, 13, 15, etc has never been released to my knowledge. 10kHz spacing Here then are safe frequencies for aircraft and other high performance models. The MAAA has cleared the 29MHz band for 10kHz spots using 20kHz keys just as for the 36MHz 64  Silicon Chip is a graphical representation of the frequency allocation, laid out on a grid wherein 1-inch represents 10kHz (this system was designed in 1969, before metric conversion). Thus, to control frequencies on a 10kHz spacing, it is necessary to have slots 1-inch apart. Each slot is identified with the frequency and band number, as in Fig.1. Hence, slot 602 is equivalent to the fre­ quency 36.02MHz, while slot 603 is equivalent to 36.03MHz – a 10kHz step. Every R/C system operating on club fields is tested by MAAA approved testing stations for bandwidth and an approval sticker is attached to the transmitter. A key is also supplied propor­ tional in width to the bandwidth of the system. Thus, a system with a 10kHz bandwidth is issued with a 1-inch key, 20kHz systems get a 2-inch key, and so on. In practice, the MAAA found no current R/C systems that could handle 10kHz spacing, so the 10kHz approval stickers were withdrawn. In use, the Tx operator walks to the keyboard and inserts his key into the appropriate slot on the board(s). If the re­quired bandwidth is available, the key easily drops into the correct slot and the operator is cleared to switch on the trans­mitter. If insufficient bandwidth is available, the key cannot be inserted correctly and the transmitter must not be switched on. However, the fuss began recently when the SMA ratified the new 36MHz allocation which included additional spots, making 59 in all (601 - 659). The new even-numbered slots are for exclusive use of aircraft and the old odd-numbered slots for shared use between aircraft and boats. R/C cars are not to use 36MHz. These additional slots added to the overlapping frequency problem. At the same time, the MAAA allowed the use of all 59 10kHz spots but using 2-inch keys only. Previously the MAAA only allowed every second spot to be used; ie, a 20kHz spacing was maintained. As subtle as this change is (we are still using 20kHz spacings), the fact that frequencies are now available on all 59 10kHz spots had a dramatic effect on the operation of the key­board. As explained above, I had broken the 36MHz board into two, which made each board more mechanically robust. (The 29MHz board, which includes the 40MHz allocation, is still OK as a single board). Now all was fine on the old system Fig.1 (right): this diagram shows the new two-part frequency keyboard for model aircraft operation in the 36MHz band. The keyboard is a graphical representation of the frequency allocation, laid out on a grid wherein 1" represents 10kHz. Each slot is identified with the frequency and band number. Hence, slot 602 is equivalent to the frequency 36.02MHz and slot 603 is equivalent to 36.03MHz, a 10kHz step. March 1997  65 Radio Control – continued as the break occurred in the middle of the 20kHz spots and I had delivered many boards before the 10kHz rule came in. However, with 10kHz spacing, it is now possible to have a situation arise wherein a 20kHz system with a 2-inch key in the end slot on board 1 (630) is in danger of interference from a 2-inch key in the first slot on board 2 (631). This necessitated the addition of an extra slot (“G”) to accom­modate a 1-inch guard key on the original boards. Thus, if a 2-inch key is to be inserted into 630, the guard key is moved across to the second board and placed in the “G” slot, thereby preventing a key from being inserted into 631. Conversely, if a 2-inch key is placed into the 631 slot, the guard key is placed into the “G” slot on board 1, preventing a key being inserted into 630. Guard keys Fig.1 shows a pair of 36MHz keyboards with a variety of operational that I finally modified the design to include the guard slot. This inter-club discussion also included an argument over a single board or two boards and more importantly from the point of view of this column, how to handle the problem of the 455kHz overlap (for more information on this, refer the February 1997 issue of SILICON CHIP). The 455kHz argument, in my mind, boils down to three choic­es: (1) partially restrict the band by closing off the top slots affected (646 - 659) and combining each overlapping pair on the lower slots, thus allowing only one of the pair to transmit. (2) Restrict the band to less than 455kHz wide; or (3) adopt a policy of dual conversion receivers only on 36MHz. Pairing the frequencies is my first choice but the keyboard is designed to cope with all three possibilities. The eventual choice is a matter for individual clubs to decide. Some of the more conservative clubs want 29MHz AM system is cheap, simple and reliable. It is free of the complications of 36MHz FM and is by far the most costeffective system for sports fliers. key arrangements. Key 653 is one of the paired fre­quencies, thus the key is in the 608/653 slot. Keys 623/625 are two normal 2-inch keys inserted correctly. Key 626 is a normal 2-inch key which cannot be inserted into the correct slot due to the system bandwidth being wider than the spacing required. Key 630 has been inserted into its correct slot after moving the 1-inch guard key across to Board No 2. Thus, Key 631 cannot be inserted, again due to excessive bandwidth. I was a little slow picking up on the need for a guard key. It wasn’t until a rash of phone calls revealed that there was much discussion taking place in the clubs on the best way to lay out the keyboard to overcome this problem 66  Silicon Chip nothing to do with 10kHz spacing and will only allow 20kHz frequencies on their field. How do I design a keyboard to accommodate all of these arguments? In the end I have designed the keyboards with all 10kHz slots milled and numbered but all slots have a 1mm safety gate across them, sealing them off until the club decides which slots to open and which to leave closed. A quick wipe with a small file soon opens the required slots. One final point – all of this complication costs money and the 36MHz pair of keyboards now sell for $399. At this point I feel that I should repeat the main conclusion of last month’s article, which is vitally important to safe operation on 36MHz: Any pair of transmitters separated by 450kHz or 460kHz will generate a strong 450-460kHz component in the mixers of all single conversion receivers, AM or FM. This will happen in every receiver operating on that flying field, regardless of the fre­quency of the receiver and regardless of the frequencies of the overlapping pair of transmitters. In other words, any pair of transmitters overlapping by 450kHz or 460kHz will simultaneously interfere with all 59 receivers operating on the 36MHz band. Therefore, never at any time should we allow any pair of overlapping transmitters to transmit simultaneously on fields using single conversion receivers. But does everyone know if their receiver is single or double conversion? For this reason, we need to be very careful about excluding double conversion receivers from this ban. For the sake of safety, the ban on overlapping frequencies should have no exclusions. The best way to use the Silvertone 36MHz keyboard on fields using single conversion receivers is to leave the top set of overlapping slots (646 - 659) closed and pair these slots on the bottom set of overlapping slots (601 614). For example 601/646, 602/647, 614/659. If a club adopts an exclusive dualconversion receiver policy, then the entire keyboard can be opened up and all frequen­cies used. For this reason the Silvertone Keyboards still include all 59 slots, with all slots closed. As you can see from the foregoing, operation on the 36MHz band is no longer a simple matter and there is now much to con­sider. If AM systems are banned from 36MHz, then the cost of operating on this band goes up accordingly. If any club does decide on a policy of dual-conversion receivers only, then this pushes the expense of operating on 36MHz even higher. The foregoing strengthens my resolve to continue to push for an expanded use of 29MHz, particularly with AM systems. It is cheap, simple and reliable. It is free of the complications and expense of 36MHz FM and is by far the most cost-effective system for sports fliers. Note: Bob Young is the principal of Silvertone Electronics. Phone (02) SC 9533 3517. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd AUDIOHM A nifty audible continuity tester Most continuity testers beep at you when the circuit being tested is good but not this one. It gives a tone which varies from a low note (a few hundred Hertz) for a low resistance to just above audibility for an open circuit. This feature prev­ents the AudiOhm from driving you mad while you are not actually measuring anything. By RICK WALTERS One of the things we frequently do in the pursuit of our hobby is to check for continuity or bridged tracks in the pro­jects we build. While some digital multimeters have a buzzer for this function, most do not. Sure, you can use a multimeter to measure continuity of circuits. Just switch it to a low Ohms range and you are in business. Trouble is, you have to keep looking at the multimeter to see if anything has registered each time you put the prods on the cir­cuit. This is where an audible indication is pretty handy. As well, the AudiOhm can test diode and transistor junc­tions and it will even give a relative indication of the ca­ pacitance and leakage of electrolytic capacitors. When using the low range, you can discriminate between a short and a resistance of 72  Silicon Chip Fig.1: the circuit is based on FET input op amp IC1 and phase locked loop IC2. The DC output from IC1 is proportional to the resistance across the probes and this signal is used to control the frequency generated by the VCO in IC2. The output from IC2 drives a loudspeaker via complementary output pair Q1 & Q2. 50Ω and on the high range a 4.7MΩ resistor will register. It can also readily differentiate between, say, a 56Ω and a 560Ω resistor – handy when you are building a project and find the colour codes hard to read. How it works As you can see from the circuit in Fig.1, only two ICs are used. IC2 is a 4046 phase locked loop but we are using only its VCO (voltage controlled oscillator) section. IC1 is a FET input op amp and its DC output, which is proportional to the resistance across the probes, is used to control IC2. Let’s look at IC2 in more detail. Its oscillator output frequency at pin 4 is controlled by the DC voltage applied to pin 9; 0V gives the lowest frequency and +9V gives the highest. The lowest frequency is set by the capacitor between pins 6 & 7 of IC2 and the resistance at pin 12. The highest frequency (with +9V applied to pin 9) is determined by both these former values and the resistance at pin 11. These frequency setting resistors have been made adjustable with trimpots VR1 & VR2 to allow you to set the tones to your particular preference, as well as to compensate for variations in ICs from different manufacturers. The maximum frequency is set by VR1 and the minimum by VR2. IC2’s oscillator output at pin 4 is connected to a pair of complementary emitter followers, Q1 & Q2. These provide sufficient current gain to drive the speaker. We have used a fairly large resistor in series with the speaker to keep the volume down to a reasonable level and also to reduce the current drawn from the battery. Our unit drew only 18mA so the battery should last for a long time. Op amp IC1 is used to monitor the voltage across the probes and amplify it a level sufficient to give the full audio range at the speaker. On the high resistance range, as selected by toggle switch S2, a high impedance voltage divider (one 4.7MΩ and two 1MΩ resistors) sets the voltage across the probes. As you can see from the voltages on the circuit of Fig.1, there is about 1.34V across the probes when no external resistance is present. Note that while we have quoted fairly precise values here, the actual values will depend on the battery voltage and resistor toleranc­es. This voltage of 1.34V is amplified by IC1 to give about 7.6V at its output (pin 6) and this is fed directly to pin 9 of IC2, to set the highest frequency. When an external resistance is present between the probes, the voltage between the input pins of IC1 will be less than 1.34V; if a short circuit is present, there will be virtually no voltage between pins 2 & 3 and so the output voltage at pin 6 will be the same as the voltage on pin 2; ie, +1.34V or close to it. This sets the minimum frequency from IC2. PARTS LIST 1 plastic case, 130 x 68 x 25 (Altronics H0342 or equival­ ent) 1 PC board, code 04103971, 57 x 55mm 1 miniature 8Ω loudspeaker (Altronics C0606 or equiv.) 1 SPST toggle switch (S1) 1 DPST toggle switch (S2) 1 9V battery 1 battery clip 1 set of test leads (Altronics P0403 or equivalent) 1 16-pin IC socket 1 8-pin IC socket 1 5kΩ PC mount trimpot (VR1) 1 500kΩ PC mount trimpot (VR2) Semiconductors 1 CA3160E op amp (IC1) 1 4046 phase locked loop (IC2) 1 BC338 or BC548 NPN transistor (Q1) 1 BC328 or BC558 PNP transistor (Q2) Capacitors 2 100µF 16VW electrolytic 2 0.1µF MKT polyester 1 .047µF MKT polyester 1 .022µF MKT polyester Resistors (0.25W, 1%) 2 4.7MΩ 2 10kΩ 3 1MΩ 1 2.7kΩ 1 150kΩ 1 56Ω 1 47kΩ Miscellaneous Hookup wire, solder. March 1997  73 When the low range is selected with switch S2, a lower impedance voltage divider is switched in parallel with the high range divider. This keeps the voltage applied to the probes the same, but allows them to sense lower values of resistance due to the increased current. Without this range switching, it is harder to resolve lower resistance values. Putting it together We designed a small PC for the Au- the IC sockets, transistors and capacitors. Make sure that they are all correctly oriented, as shown in Fig.2. If you use PC stakes, now is the time to fit them. I prefer to poke each wire through the PC board and solder it, as it makes a neater looking connection. Wire the two switches, the battery and speaker leads next. Before fitting it all into the case, you should plug the ICs in and do a preliminary test of the circuit. Connect the battery, switch the unit on and vary the MAX pot VR1. You should be able to vary the frequency from about 7kHz or 8kHz at the low end, up to the limit of audibility (16kHz+). Now short the probe pads and check that the MIN pot, VR2, changes the low frequency. If all is OK, proceed with the assembly, otherwise you will have to find and fix Fig.2: the assembly details. the problem. Take care to ensure that the The plastic case we have semiconductors and 100µF specified has provision for capacitor are correctly the battery in a separate oriented & be careful not to compartment but with a lot get Q1 & Q2 mixed up. of effort you may be able to cram everything into a different case. Stick the label onto the diOhm. It measures 57 x 55mm and is case and drill the nine holes to let coded 04103971. It is fitted into a small the sound emanate from the speaker. plastic case and the two switches are While slide switches are nice, it is fitted at one end, as can be seen from much easier to mount toggle switches the photos. (just one round hole). Drill 2 x 6.5mm The component layout for the PC holes in the top of the case for the board and the other wiring is shown switches, 16mm either side of the in Fig.2. centre line. As usual, check the PC board for Fit the two switches, then mount etching faults and shorts, especially the speaker on the front of the case the track which goes between pins 13 with a couple of dobs of contact & 14 on IC2. Fit and solder the one link cement. You probably will not be and the resistors. Next fit and solder able to position it exactly behind the RESISTOR COLOUR CODES         No. 2 3 1 1 2 1 1 74  Silicon Chip Value 4.7MΩ 1MΩ 150kΩ 47kΩ 10kΩ 2.7kΩ 56Ω 4-Band Code (1%) yellow violet green brown brown black green brown brown green yellow brown yellow violet orange brown brown black orange brown red violet red brown green blue black brown 5-Band Code (1%) yellow violet black yellow brown brown black black yellow brown brown green black orange brown yellow violet black red brown brown black black red brown red violet black brown brown green blue black gold brown This is the view inside the completed prototype. The two trimpots at the bottom, right of the PC board are used to set the frequency range of the VCO. Note the holes files in the side of the case for the probe leads. speaker holes (this will depend on the switches used). File two small half-round holes in the top and bottom left side of the case with a needle file to let the probe leads out, but don’t make them too deep. Try to file them so the probe leads are actually clamped when the case is assembled. This prevents them being pulled out and possibly damaging the PC board. As you can see from Fig.2, they are also looped through the hole adja­cent to the pad before being soldered to the PC board. The PC board can now be secured in place with the two short self-tapping screws. Setup procedure Short the probe leads together and use VR2 to set the low frequency, then open circuit the leads and adjust VR1 until the whistle sound is just inaudible. There is quite a variation in 4046 ICs from different manu­ facturers. The one we used in our unit was a Motorola device. If you use a different brand you may have to change the values of the resistors in series with the trimpots to get the required range or in an extreme case alter the value of the capacitor between pins 6 & 7 (smaller value for higher frequency and vice versa). Fig.3: this full-size artwork can be photocopied and attached to the front panel of the Continuity Tester. Using the continuity tester Using the AudiOhm to check continuity is straightforward but as we mentioned at the beginning of this article, the unit can also be used to check semiconductor junctions and capacitors. When the red (positive) probe lead is connected to the anode of a diode, the AudiOhm should indicate a low resistance but not a short circuit. When the leads are reversed, the fre­ quency should be inaudible. A shorted diode will give the lowest tone in both directions. In a similar manner, base-emitter and base-collector junctions of NPN and PNP transistors can be test­ed. Finally, when a discharged capacitor (electro­lytics on the low range, others on the high range) is connected, the tone will initially be low (indicating a short circuit) and then increase as the capacitor charges. By comparing Fig.4: check your PC board carefully against this full-size etching pattern before installing any of the parts. the charge time of a known value of capacitor with that of an unknown value, an estimate of its capacity can be made. The final frequency gives an indication of the leakage current through the capacitor; the higher the SC frequency, the better. March 1997  75 While the cathode ray tubes used in most analog oscillo­scopes use electrostatic deflection, the display tubes used in most digital scopes are virtually the same as in computer moni­tors and TV sets; they use magnetic deflection via coils on the neck of the tube. By BRYAN MAHER The magnetic deflection cathode ray tubes used in digital storage scopes are cheaper, shorter and more rugged than the electrostatically deflected tubes used in fast analog scopes. In a cathode ray tube (CRT), magnetic deflection of the electron beam is achieved by wrapping two sets of copper coils around the outside of the tube neck, as depicted in Fig.1. The horizontal deflection coils are mount­ed above and below the neck of the tube and current flowing in them generates a magnetic field which passes vertically downward through the tube. Electrons in the beam are deflected in a direction at right angles to this magnetic field; ie, across the screen. By contrast, the verti­cal deflection 76  Silicon Chip coils are mounted one on each side of the tube neck. Currents flowing in them produce a horizontal magnetic field which deflects the electron beam up or down. The two sets of deflection coils are held in one assembly called the yoke and its function is exactly the same as the yoke in a colour TV set. Fig.2 shows a more pictorial arrangement of the coils. Typically, the horizontal deflection currents are ±500mA and flow in coils having 13 millihenries inductance. The vertical deflection currents are typically ±150mA flowing in coils of 40mH inductance. Let us consider a basic digital scope having 8-bit resolu­tion. We featured a simplified description of how the digital storage scope acquires signals and stores them as digital data in part 5 of this series, in the September 1996 issue of SILICON CHIP. Now let us see how that data is displayed on the screen. To operate the deflection system, two sweep generator cir­cuits run at different frequencies, both derived from a crystal master oscillator. The horizontal (or line) system produces sawtooth waveform currents at exactly 28,800Hz in the horizontal deflection coils (shown as H,H in Fig.1). The resulting magnetic field deflects the electron beam from the left side of the screen to the right and back again in exactly 34.7222 microseconds (µs), as illustrated in Fig.1(c). The forward trace from left to right takes about 33µs and the fast retrace (flyback) takes the remaining 1.7222µs. At the same time, the vertical (or frame) system sends a sawtooth waveform current at exactly 60Hz through the vertical deflection coils. The magnetic field which results deflects the electron beam downwards comparatively slowly, taking 16ms to work its way from the top of the screen to the bottom and 0.666ms to fly back to the starting point at the top. Fig.1: the magnetic fields due to currents flowing in coils (a & b) external to the tube neck deflect the electron beam to cover the whole screen (c) with 480 raster lines. With both deflection systems operating, as we see in Fig.1(c), the electron beam starts at the top left corner of the screen. From there it traces in the phosphor a pattern of 480 fast horizontal lines, as it moves (comparatively) slowly down, to arrive at the bottom right hand corner. From there the fast retrace (flyback) returns the beam to the starting point. Auxiliary circuits always blank off both the vertical and hori­zontal retraces, so we show these as dotted lines in Fig.1(c). If the electron beam was turned on during all forward trac­es, you would see the whole screen covered in a pattern of 480 fine horizontal bright lines spaced about 0.25mm apart. In Fig.1(c) we illustrate this but for clarity we have drawn only a few lines. This is the raster and it is similar to the background line pattern you see on your computer display if you turn the brightness up at night. A standing bias, applied between the tube grid G1 and cathode K as shown in Fig.3, may hold the electron beam near cutoff, making the screen dark. A voltage drive applied to the cathode K (or grid G1) can then overcome this standing bias to illuminate the screen. Greater deflection angle Say a CRT has 16kV acceleration potential. We recall from past episodes that such a tube, when electrostatically deflected, will have deflection angles inversely proportional to the acceleration voltage. But a similar tube magnetically deflected will have deflection angles inversely proportional to the square root of the acceleration voltage. So the magnetically deflected tube can deflect its elec­tron beam through an angle four times greater. So we see why digital scopes commonly have wider screens and shorter tubes. However, because of the coil’s inductance, direct magnetic deflection is limited to frequencies below about 100kHz. Bit-mapped raster scan Most digital scopes have a frequency response that ranges up to 100MHz or a great deal more. To make that possible, an indirect method called “bit-mapped horizontal raster scan dis­play” is used. This is completely different from the direct electrostatic deflection used in analog scopes. And it is more complex. Fig.3 shows an abbreviated block diagram of a digital stor­age oscilloscope. The left hand half of this figure is the acqui­ sition section, which includes the input attenuator, analog preamplifier IC1, sampler IC2, A/D converter IC3 and the fast RAM (random access memory) IC4. In this chapter of our story we concentrate on the right hand half of Fig.3, the display section, which includes IC5, IC6, IC7 and the tube. When the digital data representing the input analog sinew­ ave is recorded and stored in the fast RAM IC4, then the display section can begin its magical work. Firstly that data is read out from RAM IC4 into the display processor IC5. This is a micropro­c essor which has running within it a scan conversion point plot­ting algorithm. This rearranges the data into a display image in scan line order, which it promptly writes into a second memory IC6, called the bit-map frame refresh buffer, which you see in Fig.3. In the basic digital scope we are describing, this buffer consists of an array of 307,200 semiconductor memory cells, electrically arranged into a two-dimensional planar matrix of 480 horizontal rows and 640 vertical columns (480 x 640 = 307,200). Fig.4(a) gives some idea of this scheme, though here for clarity we have drawn a much smaller number. Each memory cell in this buffer holds one bit: that is either a logic high potential or a logic low. And in Fig.4(a) we have drawn a 1 in some of the cells to indicate those cells which contain a logic high potential. In the remainder of the cells we have drawn a 0 to indicate those which hold a logic low. In Fig.4(a) you can clearly see a waveform in the pattern of 1s and this is called the bit map. This is an image of the original analog input waveform. March 1997  77 DEFLECTION COILS WRAPPED AROUND TUBE NECK TUBE NECK CRT FLARE Fig.2: the two sets of deflection coils are held in one assembly called the yoke and its function is exactly the same as the yoke in a colour TV set. This diagram shows a more pictorial representation of the coils. Now we aim to convert that blueprint of electrical 1s in the buffer into a corresponding display on the CRT screen. Once the processor IC5 has filled buffer IC6 with data forming the bit map, two different but intimately related actions commence simultaneously and run in synchronism, like two kids in a three-legged race. Displaying the bit map The deflection circuits cause the electron beam to commence from the top left corner of the CRT tube screen and trace out the full screen raster, line by line, as described above. During most of this time the beam electron current is reduced to nearly zero by the negative bias applied between the tube grid and cathode, which Fig.3 illustrates. So almost all of the screen is dark. At the same time, the system addresses all cells in the bit map refresh buffer IC6 and the bit value contained in each is read out. Starting at the top left corner, the system addresses the cells and reads their contents; cell by cell, from left to right and row by row. First, each cell in the whole top row is read, then those in the next row, and so on, until the bottom right corner is reached. Cells are addressed across a row of IC6 at the same speed as the electron beam is deflected across the tube screen. The final addressing of the cell in the bottom right corner of IC6 and the reading of the bit it contains coincides with the elec­ tron beam arriving at the bottom right corner of the screen. Displaying the signal In the basic digital scope we are describing, the single bit read from each buffer cell is simply a voltage, either logic high level or logic low. If a TTL system is used, logic high means about +4V and logic low about +0.5V. As each cell is read, its voltage is amplified and inverted by the following video amplifier IC7, whose output signal drives the cathode of the CRT tube in Fig.3. (Alternatively, you could drive the grid but without signal inversion.) Each time a logic 1 is read from a cell in the refresh buffer, Fig.4(a), the video amplifier IC7 inverts and amplifies this to a large negative voltage pulse, typically -30V to -60V. Applied to the CRT cathode, this is big enough to overcome the G1-K standing bias. Thus the electron beam is turned fully on momentarily. This produces a bright spot of light on the screen at a point corresponding to the address of that logic 1 cell in the refresh buffer. Each bright point is called a pixel (for picture element). In the same way, many pixels are displayed on the screen (Fig.4(b)) in a pattern which copies the disposition of cells containing logic 1 bits in the refresh buffer matrix (Fig.4(a)). But on a screen typically 135mm wide, each pixel is only 0.2mm apart, so normal spot width-blurring usually merges strings of these dots into continuous bright lines. If the sampler cannot provide enough points, firmware routines can fill in by adding more bright dots in straight line approximations or Sin(x)/x geometric curves. That trace we see on the screen in Fig.4(b) is a copy of the bit map in the buffer IC6. This is itself a copy of the original analog signal applied to the scope input socket. This is the raster scan method in action: the digital scope is indirectly displaying your input signals on a Fig.3: in a digital scope, IC1, IC2, IC3 and IC4 form the fast acquisition section. IC5, IC6 and IC7 then form the rasterising display circuits. 78  Silicon Chip Fig.4: a bit map (a) of the input waveform is drawn logically in the memory cells of the refresh buffer. Data read from this map turns on the electron beam (b) at points corresponding to the pattern of logic 1s in the bit map. magnetically deflected cathode ray tube screen. a refresh rate of 60Hz. That’s why we call IC6 the refresh buffer. Displaying a one-shot signal Video frequency Now let’s assume that the input to your digital scope was a one-shot; ie, a non-recurring signal. In the fleeting time that signal existed, it was sampled by IC2, digitised by IC3 and recorded in RAM IC4 and held there indefinitely. After the signal had gone and the sampler had stopped, the output section of your scope (the right hand side of Fig.3) then performed all the wondrous miracles we saw above. The reading of the whole buffer IC6 and the drawing of one raster on the screen displaying the waveform both take exactly 16.666ms. Digital scopes commonly use a tube with a P4 white phosphor, which has a compound 150/480µs persistence time, after which the trace fades away. To maintain a stationary picture on the screen, the scope must continually refresh the trace illumination by repeating the display process; ie, read the bit map stored in buffer IC6, amplify the signal in IC7, and drive the tube cathode to turn on the beam to re-illuminate the display. The system repeats this whole action every 16.666 millisec­onds; ie, at To perform these wonderful feats, all 307,200 cells in the buffer memory must be addressed and read every 16.666ms. So cells must be read at (16.666ms/307,200) = 54.2535 nanosecond inter­vals. This produces a serial stream of single bits passing to the amplifier IC7 at (307,200 x 60) = 18,432,000 bits/second. Because this bit stream produces a visible display on the screen, we call this an 18.432MHz video frequency. And we call IC7 the video amplifier. Notice that all this time the sampler IC2 and the A/D con­verter IC3 have stopped. This is not because they are lazy or slothful. It’s because you previously filled RAM IC4 with one record of data from a one-shot input signal, now long gone. So your scope continually refreshes the screen with the copy of that departed signal held in IC4. You are truly using the storage capabilities of your DSO to the full. Recurrent signals When you apply a continuously recurring high frequency signal to the input of your digital scope, the busy sampler very quickly takes a record of 500 (or more) samples of the signal. The A/D converts these to digital format and stores them safely in RAM. Then while the sampler has paused, that data is read from IC4, converted by IC5 to a bit map and stored in the refresh buffer IC6. Now the system reads that buffer and displays its contents on the screen raster at the much slower display speed. Once it does that, the system clock may reactivate the sampler and A/D converter, to take another record of samples and store them in RAM. These can be then read from the RAM, converted to a complete new bit map which includes any changes in the input signal and displayed on the screen, replacing the old. At fast sweep speeds, such as 2µs/ div, the sampling of one record of the input signal may take only 20µs. But in convention­al digital scopes the sampler pauses for about 20ms while the display processor and refresh buffer do their clever work and display the waveform on the screen. So typically you will see only one cycle in every thousand cycles that flow in your circuit. The elusive occasional glitch interference that you are searching for may escape detection. March 1997  79 Fig.5: block diagram of InstaVu acquisition architecture in the Tektronix TDS784 scope, which can capture 400,000 waveforms/second on one channel. Your scope would be capturing only about 50 waveforms per second and missing the rest. Alternatively, instead of deleting the old display on each refresh, the electrical variable persistence control gives you the option to accumulate old and new data points in the bit map, and hence on the screen. These can be kept over many acquisi­tions, or over some period of time between 250ms to 10 seconds, or infinitely. In this way, infrequent events can be found and displayed. Fast acquisition To increase your chances of seeing that occasional problem pulse which This is a 3MHz signal depicted on a Tektronix TDS784A digital colour scope in InstaVu mode. Here a runt signal is clearly visible, made doubly so by the colour display (although not reproduced in this B&W photo). 80  Silicon Chip is troubling your electronic system, more expensive digital scopes use proprietary methods to raise the rate of waveform capture. The Tektronix TDS400 series digital scopes can acquire 200 waveforms/ second in infinite persistence mode. In each 16ms period they capture and overlay three or more updated versions of the input waveform in the refresh buffer. This is then written to the screen at the 60 frames/second refresh rate. So you see a greater percentage of all the real cycles which flow through your circuit. But top analog scopes like the Tektronix 2467B or 7104 can display up to half a million waveforms per second, showing 90% of all cycles of your signal, because they have very short holdoff times. They show rarely occurring events dimly for emphasis and are very good at finding elusive faulty pulses! To produce digital storage scopes with equal capabilities, Tektronix introduced the very clever TDS700 series. They can capture and display more than 400,000 waveforms/ second when running at 1GHz using 500 sample points per acquisition, in one channel InstaVu Mode. How is this done? First let’s consider why you can’t just raise the rate at which the conventional digital scope rasterises and displays the signal. We saw that to display 60 updated versions of the chang­ing input signal each second produces a video signal of 18.432MHz. Could we just raise the refresh rate by a factor of 7,000? Would (7,000 x 60) frames/ second capture 420,000 wave­forms/ second? The answer is NO! To do that, a conventional architecture must read the buffer cells in IC6 at (307,200 x 7,000 x 60) = 129,024,000,000 bits/second, giving a video frequency of 129GHz. And the raster would need a vertical or frame rate of 420kHz and a line or horizontal frequency of 201.6MHz. No CRT tube cathode can respond at such a video frequency and the inductance of magnetic deflection coils prohibit such fast sweep rates! So Tektronix produced a revolutionary design. InstaVu acquisition mode For their high performance 4-channel TDS700 digital scopes, Tektronix manufactured a patented high speed dedicated processor and cache mem­ ory. It includes 360,000 transistors formed using 0.8 micron technology into a 304-pin CMOS IC called a Demux, which dissipates 2.5 watts when running at full speed. This is integrated into the acquisition system, duplicating the raster forming capability there, so keeping the required video frequency within manageable limits. Also a section of the very fast main memory is used as a refresh buffer. Here it builds up display images from thousands upon thousands of passes of the signal, including those glitches you seek. And the acquisition section can calculate its own trigger positions. This architecture, shown in block diagram form in Fig.5, is radically different from any other digital scope. The acquiring of more and more samples of the input signal almost never stops. Even while the screen display is being updated and refreshed, the sampler continues acquiring more points of the signal. In this way any elusive glitches, line reflections, jitter or bad pulses have a very high probability of being found by the sampler and shown on the screen. Making good use of available memory bandwidth, the raster­ iser operates on a 16ns clock. It can draw four complete acquisi­ tions at once into a 500 x 256 x 1 bitmap. Drawing is done in top to bottom, then left to The Tektronix TDS784 scope has 1GHz analog bandwidth and each channel samples at 1GS/s. In single channel operation all sam­plers interleave to achieve 4GS/s sampling speed. In InstaVu acquisition mode, this scope acquires 400,000 waveforms/second. The scope has a liquid crystal shutter to provide a colour display and it has an unsurpassed ability to catch and display rare glitches in signal waveforms. right fashion, so each data point in an acquisition need be fetched only once. Each read-modify-write cycle operates on 64 pixels at a time. Each cycle is 32ns long. Data is fetched in groups of eight bytes. Any column of the bit map, 256 pixels high, can be raster­ised in 32 to 128ns. When operating with one input signal in InstaVu mode, each of the four channels take turns acquiring that single input. Three channels can continue acquiring while the formed raster is unloaded in the fourth channel. This architecture raises the performance to 400,000 full screen (500 point) acquisitions and rasterisation cycles per second on one channel. This data rate represents 220,000,000 pixels/ second. The speed is limited by the trigger system rearm circuits as much as by the acquisition/graphics section. The Demux IC demultiplexes and processes the data from all four A/D converters working together on the one signal and ras­terises the acquired data. Also it performs digital signal pro­cessing for local programmability, mathematical algorithms and trigger position calculations. The firmware only intervenes every 10,000 samples to copy out the complete raster which shows the behaviour over that time. Then the acquisition section shifts out a complete bit-mapped image to the video amplifier at the modest frame rate. But as the display shows almost every cycle that ever passes through your circuit under test, the result is equivalent to a continuous running picture of the live signal. The display is so lively that signal aberrations are seen instantly. You have the confident feel of an analog scope yet also have the storage and mathematical powers of digital scopes. Colour gradations highlight sections of the traces which occur less frequently. You can show the continuously repeating part of the signal in red, with brilliant blue highlighting the occasional glitches. If the scope is left in variable persistence mode for many hours, more than 10 billion acquisitions can be amassed if neces­sary to find an elusive faulty signal. The vertical frame rate and the horizontal line rate of the raster display are approximately as described before. References: Tektronix Technical Brief SC 12/94.XBS.15M.55W-10341-0. Acknowledgements Thanks to Tektronix Australia and staff member Ian Marx for data and illustrations. March 1997  81 VINTAGE RADIO By JOHN HILL The importance of grid bias Correct grid bias is vital if valve radio receivers are to function properly. Here’s a rundown on how it works and what to look for when restoring vintage receivers. Many years ago I built a little 2-valve battery receiver called “Tom Thumb”. It was an old “Radio and Hobbies” project that incorporated a 1T4 regenerative detector, followed by a 3S4 audio amplifier which drove a pair of high impedance headphones. It was built from the circuit diagram only, without instructions, using a small output transformer and low impedance phones instead of the specified 2000Ω headphones. There was one part of the circuit that, at the time, made no sense to me at all. Why have a parallel connected 1500Ω resis­tor and 10µF electrolytic from “B” battery negative to chassis? (see Fig.1.). What could such an arrangement possibly do when “B” neg­ative usually went straight to chassis. Well, it had on my previous home built 1-valve receivers. In my “wisdom”, I chose to leave out this part of the cir­cuit and connected “B” negative directly to chassis due, in part, to the fact that neither a 1500Ω resistor or a 10µF electrolytic were on hand at the time. Besides, their inclusion seemed so unnecessary. The set was built and it worked reasonably well. Just as I thought – the extra components were put into the circuit to confuse novice receiver builders. However, while listening to my new creation it was noticed that the 3S4 output valve was decidedly warm. This caused some concern because I knew, even back then, that battery valves didn’t normally run hot. The circuit was checked and everything was in order except for the two “unnecessary” components. When a milliamp meter was placed in series with the 90V “B” battery it indicated a drain of 20mA. That is perhaps more “B” battery current than a valve portable would draw while driving a loudspeaker. Could it be that those unnecessary components had something to do with the problem? After the 1500Ω resistor and its accompanying 10µF capaci­ tor were added to the receiver, three changes were immediately apparent: (1) the B battery current dropped to less than 5mA; (2) the output valve operated at a much lower temperature; and (3) a degree of audio distortion (originally assumed to be normal for such a simple set) vanished. The mystery components were not as unnecessary as originally thought! At the time, my lack of knowledge This old Eveready “C” battery contains three size “D” cells wired in series. The close-up view (above) shows the battery connections. The terminals, from left to right, are 0V, -1.5V, -3V and -4.5V. 82  Silicon Chip regarding basic theory prevented me from knowing what the resistor/ capacitor combination actually did. Accordingly, I made a very bad error of judgement by leaving them out – but learnt a good lesson by doing so. Negative grid bias As some readers would be aware, the reason for the resistor was to create a negative bias voltage for the control grid of the output valve. This would allow the valve to work under the condi­tions for which it was designed. Without grid bias, the valve overheated, consumed large amounts of “B” battery current and, most important, created considerable distortion. Correct grid bias is important! This matter of grid bias raises two broad questions. Why do valves require a negative potential on the control grid or, more accurately, between grid and cathode. And, secondly, how are negative volts obtained when the main supply voltage – from the “B” battery – is positive? These are good questions and I will try to answer them as best I can. First, why is the grid voltage necessary? If one spends time looking through valve data books, a lot of reference is made to “characteristic curves”. In simple terms, a characteris­ tic curve is a line plotted on a graph which shows the relation­ship between changes in grid voltage and changes in plate cur­rent. Each type of valve has its own set of characteristic curves for a given range of plate voltages. A characteristic plot is not uniform: it has a curved sec­tion at the bottom (the “toe”) and another curved section at the top (the “shoulder”). Between these two sections is a substan­tially “straight” section. If a valve is correctly biased (typically at the midpoint), the voltages on the grid will be confined to the straight section of the curve and the valve will operate with minimal distortion. It will also draw the specified amount of plate cur­rent. However, if the valve has insufficient bias, the plate current will increase and there will be distortion. Conversely, if it has too much bias, there will be insuffi­cient plate current and this will also give rise to distortion. This distortion is particularly serious in the case of output valves. Note that the grid potential – in fact the potential of all valve electrodes – Fig.1: the back-bias circuit of the “Tom Thumb” radio receiver used a 1500Ω resistor in parallel with a 10µF capacitor. Fig.2: many battery valve sets used a “C” battery to apply negative bias voltage to the control grids. Fig.3: a typical back-bias circuit as used in many ACpowered receivers. is always measured in relation to the cathode. Almost all valves need some negative bias on their control grids in order to function properly. Ignoring this fact, as I did with the previously mentioned “Tom Thumb”, can lead to all sorts of problems. Of course, there are exceptions. This battery-model late 1930s Radiola uses a 4.5V tapped “C” battery for its grid bias requirements. Some special high-mu (high gain) type valves are designed to function with minimum plate current without negative bias. They are designed for class B operation in push-pull output circuits. Battery bias This brings us to the second point in this discussion; the exact circuit mechanism by which an appropriate negative voltage can be applied to the grid(s). There are a variety of arrange­ ments but one point is paramount – the basic requirement is to apply the required negative voltage to the grid with respect to the cathode. Valves have always needed to be correctly biased but, back in the dim past, in the era of battery receivers in the 1920s, the need for correct bias was not always fully understood. If it was used at all, the usual procedure was to add a separate bias battery (typically 4.5V) to the circuit. This battery was re­ferred to as the “C” battery and it was connected as shown in Fig.2. Battery bias is referred to as “fixed March 1997  83 Checking the value of bias resistors is part of any radio resto­ ration. Shown here is a restored early 1930s 6valve superhet receiver made by Eclipse Radio. bias” because the bias voltage remains constant regardless of the slowly diminish­ing “B” voltage, which is not the ideal situation. There is virtually no current drain from a “C” battery. Its sole purpose is to supply the control grid with a negative potential. It is easy to understand battery biasing – one only has to look at the circuit diagram of Fig.2 to see where the negative volts come from. If “B” negative and “C” positive are at the common point, then the negative end of the “C” battery must be at a negative Fig.4: a typical self-bias circuit. The bias voltage is applied to the grid via the grid return resistor. 84  Silicon Chip potential with respect to this point. Looking at this another way, “B” battery negative is the most negative point in the system, which means that the chassis is positive by the voltage across the resistor. This in turn means that the valve filament (cathode) must be positive with respect to the grid by the same amount. The amount of bias produced by a back-bias circuit is pro­portional to the total high tension current – not necessarily the current of the valve or valves being biased. Negative voltages produced by back-biasing are produced at the expense of “B” bat­tery voltage. In other words, if a receiver has a 90V “B” battery and the back-bias resistor supplies a 5V negative bias, then the effective “B” battery voltage is reduced to 85V. You don’t get something for nothing! Back biasing is also used in some AC-type receivers. This involves adding a resistor in the high tension centre-tap lead of the power transformer (see Fig.3). Once again, the negative bias voltage is produced at the expense of the overall high tension voltage. Any form of grid bias that does not use a battery requires a resistor to produce the bias voltage. It is common practice to place a capacitor across the bias resistor to suppress any un­wanted signals. Back bias Self-bias However, not all battery receivers used a “C” battery. Many, such as the previously mentioned Tom Thumb, have a back-bias arrangement where­by the negative voltage is produced by the voltage across a resistor (Fig.1). In this back-bias circuit, the voltage across the resistor is negative at the grid end with respect to chassis and can be used as a source of bias for one or more grids. Another form of biasing often used in AC-powered sets is cathode biasing, sometimes referred to as self-biasing (Fig.4). Cathode bias makes use of the cathode current through the valve. The cathode current is the sum of the plate and screen currents and if a resistor is placed between the cathode and chassis, then the cathode current flows through this resistor. This current flow through the Fig.6: this grid leak bias system relies on a small amount of grid current which flows through a 10MΩ resistor. Fig.5: this variable bias circuit is used as a volume control. RESURRECTION RADIO VALVE EQUIPMENT SPECIALISTS AVAILABLE VALVE RADIO & AUDIO * Spare Parts * Circuits * Valves * Books Fully restored radios for sale Wirewound potentiometers were used as variable cathode bias resistors in many old radio receivers. When used in conjunction with variable-mu valves, variable cathode bias was an effective volume control. cathode resistor produces a voltage across it and so a positive potential is developed at the cathode with respect to chassis. Because the grid is normally connected to chassis via a resistor, it follows that the grid must be negative with respect to the cathode. The term “self-bias” is used here because the bias voltage is proportional to the total current flow through the valve being biased. Another form of cathode biasing involves using a variable resistor instead of a fixed resistor. Many receivers from the 1930s used such a system as a volume control, with the pot­ent­io­m­eter in the cathode circuit of a variable-mu IF amplifier valve (see Fig.5). In its simplest form, only one terminal and the moving arm connections are used. Connecting the other potentiometer terminal to the aerial is a trick to improve the range of control but has nothing to do with the bias function. Automatic volume control If one goes probing around with a voltmeter underneath the chassis, it soon becomes apparent that there are many points in the circuit that will register negative voltages. Some of these potentials vary in magnitude depending on the strength of the signal being received. These variable bias voltages are produced by the automatic volume control (AVC) circuit. AVC voltages are negative and are directed at the grids of the front end valves; ie, the radio frequency (RF) amplifier, the mixer and the intermediate frequency (IF) amp­lifi­er. These valves have variable mu-characteristics and their amplification factor is controlled by changes in grid bias. In the case of the AVC circuit, the bias produced is proportional to the signal strength. As the signal strength becomes greater, so too does the bias voltage which automatically restricts the amplification provided by the RF valves. Basically, AGC is just another form of grid biasing and is a variable bias. Still another form of grid biasing can be found in some first audio stages and is referred to as grid leak bias. This involves connecting a high-value resistor between the grid and chassis (Fig.6). It is normal for a small amount of grid current to flow, the exact amount depending on several factors. These include the type of valve and its operating conditions. In practical terms, this bias system is suitable for use with high-mu triode valves handling low-level input signals. Running the weak grid current through the 10MΩ resistor produces the desired bias. The amount of bias is small but can be suffi­cient to set the operating point on a straight portion of the characteristic curve. Provided the input signal level is held within limits, very little distortion will be generated. Bias problems Some would argue the pros and WANTED for CASH * Valves and radios Send SSAE for Catalogue Visit our Showroom at 242 Chapel Street (PO Box 2029), PRAHRAN, VIC 3181. Phone: (03) 9510 4486; Fax (03) 9529 5639 cons of various bias methods but, as far as vintage receivers are concerned, it matters lit­tle. What is important is that the bias circuits are working as the designer intended but that is not always the case. One problem with old carbon resistors is that they often go high with age. When a bias resistor goes high so too does the bias voltage and that means that the grid can swing outside the straight part of the characteristic curve. This could cause the valve to operate near-cut off in extreme circumstances. When restoring a vintage radio receiver, it is therefore important to check the bias resistors and replace them where necessary. The bypass capacitors should be checked as well. Finally, note that when checking bias voltages, it is advisable to measure the voltage across the bias resistor itself; checking from cathode to grid can give misleading readings. Note that it’s also best to use a digital multimeter. Using a low-impedance analog meter can give a false indication, due to the current through the SC meter. March 1997  85 PRODUCT SHOWCASE Fast-charge battery controller Philips has released a single-chip fast-charge controller, the TEA1102, which is able to cope with all battery types including nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion and sealed lead-acid (SLA) batteries. The TEA1102 uses DT/dt (rate of change of battery tempera­ ture) and peak voltage detection modes to ensure that the full charge condition is reliably detected in NiCd and NiMH battery packs. To enhance the reliability of the DT/dt and peak voltage detection, both detectors are temporarily disabled for a short time at the beginning of the fast charge period and the DT/dt detector is itself temperature compensated. The detection modes can be selected individually or used together. Even if only the DT/dt detection is selected, the TEA1102 will automatically switch over to peak voltage detection if the battery pack’s temperature sensing thermistor fails, thereby ensuring maximum safety. The TEA1102 has linear and PWM outputs to control current regulator transistors and the fast-charge current can be pro­grammed to values between half and five times the battery’s nom- Light pipes for LEDs The Khatod SMT Pipe Light enables surface mounted LEDs on a PC board to illuminate front panel indicators by providing a 90 degree light path. Special shapes and symbols can be provided and the Pipe Light has electrostatic discharge protection of 15kV. They can be used with conventional LEDs of 3mm or 5mm diameter and can be ordered with or without LEDs. Pipe Light is available in red, green and yellow and can operate 86  Silicon Chip inal ampere capacity. Single cell or multiple cell battery packs can be charged. If the charger is built into equipment which must remain operational while its battery pack is removed, the TEA1102 can operate as an AC/DC adapter, delivering a regulated voltage output rather than a pulsed charging current. Charging lithium ion and SLA batteries is completely dif­ferent. When the batteries reach their maximum voltage (adjust­able), the TEA1102 automatically switches over from current regulation to voltage regulation. After a defined period, which is dependent on battery capacity and charging current, charging is terminated; trickle charging is not necessary. Other features include manually activated discharge (“re­ f resh”) of NiCd batteries before recharging to overcome “memory” effect, minimum and maximum temperature protection, short circuit and time-out protection and outputs for LEDs and a buzzer to indicate charging conditions. The TEA1102 is available in 20-pin DIP or SO packages. For further information, contact Philips Components, 34 Waterloo Rd, North Ryde, NSW 2213. Phone (02) 9805 4479; fax 9805 4466. Voice echo canceller within a temperature range of -60 to 125°C. For further information contact M. Rutty & Co, 4 Beaumont Rd, Mt Kuringai, NSW 2080. Phone (02) 9457 2222. Mitel Semiconductor is now sampling an integrated voice echo canceller designed to eliminate voice echo and distortion. The MT9122 is a dual- channel VEC that accepts 16bit linear or G.711 companded PCM formats and is compatible with the ST-Bus and SSI. Power consumption is typically 250mW. It is also claimed to eliminate distortion without the need to add separate DSPs for other functions. Applications include wireless base AUDIO TRANSFORMERS High output infrared LEDs Allthings Sales and Services has released three new LEDs which are suitable for high output video camera IR illuminators, IR remote control and IR communication (IrDA PC) links. Main parameters are: up to 52mW/steradian (continuous) radi­ant intensity, radiation angles from 24-60°, spectral radiation wavelength from 800-950nm and standard 5mm dia­meter transparent (clear) packages. All are suitable for CCD video camera infrared illuminators. A 925-950nm device has a continu- stations, video confer­encing and central office switches. Echo cancellation works by measuring the echo endpath and then using an adaptive filter to generate a duplicate echo which is then subtracted from the original echo. As the echo tail length increases, distortion begins to create the familiar hollow sound in a receiver and eventually distinct echoes emerge. For further information, contact GEC Electronics Division, Unit 1, 38 South St, Rydalmere, NSW 2116. Phone (02) 9638 1888; fax (02) 9638 1798. Handy SMD replacement kit PRB has released the CQ-1000 SMD replacement kit. This has the tools and materials to remove SMCs, clean the ous radiant intensity of 50mW/sr <at> 100mA and for remote control or IR links up to 500mW/sr when pulsed at 1A. For IR illuminators, radiation angles of 24, 50 and 60 degrees allow close matching of the video camera lens field of view with the illuminator radiation angle, regardless of whether it is mounted behind, next to or ahead of the camera. In packets of 50, they are priced between 50 and 70 cents each. Full technical specifications and data are available from Allthings Sales and Services, PO Box 25, Westminster, WA 6061. Phone (09) 9349 9413; (09) 9344 5905. Manufactured in Australia Comprehensive data available Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 BassBox® Design low frequency loudspeaker enclos­ures fast and accurately with BassBox® software. Uses both Thiele-Small and Electro-Mechanical parameters with equal ease. Includes X. Over 2.03 passive cross­over design program. $299.00 Plus $6.00 postage. Pay by cheque, Bankcard, Mastercard Visacard. EARTHQUAKE AUDIO PH: (02) 9949 8071 FAX: (02) 9949 8073 PO BOX 226 BALGOWLAH NSW 2093 This paste does not require refrigerated storage, making the CQ-1000 kit suitable for carrying in a serv­ice tool case, for the occasional field repair. For further information, contact Computronics International Pty Ltd, 31 Kensington St, East Perth, WA 6004. Phone (09) 221 2121; fax (09) 325 6686. Quad low side driver IC board and replace the component. The only other tool required is a tempera­ ture controlled soldering iron. The kit contains enough material to remove approximately 2500 SMD pins plus dental picks, vacuum pick-up tools and a new no-clean solder paste. SGS-Thomson Microelectronics has released the L9338 quad low side driver IC. It contains four driver channels, each equipped with a logic input and an open-drain DMOS output tran­ sistor with an on-resistance of 1.5Ω at 25°C and an output clamp for fast March 1997  87 recirculation with inductive loads. The switching speed is controlled to minimise electromag­netic interference and over-temperature protection is provided. A diagnostic output indicates the status of the protection function and open load conditions. The outputs default to a defined state in case of open circuit inputs. In stand-by mode, the L9338 consumes less than 2µA. It oper­ates on a supply voltage from 4.5V to 45V and is reverse bias protected to -24V. The circuit is supplied in an SO-20 surface mounting package. Typical automotive applications include relay and lamp driving. Industrial applications include driving relays in pro­grammable controllers or as a line driver. For further information phone (02) 9580 3811; (02) fax 9580 6440. TP-79 lead cutting machine Computronics Corporation Ltd has released the TP-79 lead cutting machine for radial components. The TP-79 features a gear driven cutting wheel which has a scissors action on KITS-R-US RF Products FMTX1 Kit $49 Single transistor 2.5 Watt Tx free running 12v-24V DC. FM band 88-108MHz. 500mV RMS audio sensitivity. FMTX2A Kit $49 A digital stereo coder using discrete components. XTAL locked subcarrier. Compatible with all our transmitters. FMTX2B Kit $49 3 stage XTAL locked 100MHz FM band 30mW output. Aust pre-emphasis. Quality specs. Optional 50mW upgrade $5. FMTX5 Kit $98 Both a FMTX2A & FMTX2B on 1 PCB. Pwt & audio routed. FME500 Kit $499 Broadcast specs. PLL 0.5 to 1 watt output narrowcast TX kit. Frequency set with Dip Switch. 220 Linear Amp Kit $499 2-15 watt output linear amp for FM band 50mW input. Simple design uses hybrid. SG1 Kit $399 Broadcast quality FM stereo coder. Uses op amps with selectable pre-emphasis. Other linear amps and kits available for broadcasters. 88  Silicon Chip For more information, contact Computronics Corporation Ltd, 31 Kensington Street, East Perth, WA, 6004. Phone (09) 9221 2121; fax (09) 9325 6686. 20MHz function generator the component leg, giving a clean cut, longer blade life and ease of use. It is capable of a production rate of 50,000 per hour. The lead length is adjustable from 2mm to 10mm and the blade can accommodate lead diameters from 0.3mm to 1.2mm. Adjust­ment is made by using the integrated lead length ruler marked below the moving wheels. A toothed drum ensures the leads are parallel during the cutting process, providing correct lead configuration for inser­tion of the component into the PC board. Adjustment tools, bandolier holder and a full size metal collection tray are included with the TP-79. PO Box 314 Blackwood SA 5051 Ph 0414 323099 Fax 088 270 3175 AWA FM721 FM-Tx board $19 Modify them as a 1 watt op Narrowcast Tx. Lots of good RF bits on PCB. The new Thurlby Thandar TG120 function generator has a frequency range of 0.2Hz to 20MHz over eight ranges. It can be used in sweep mode (with an external sweep source) with a sweep range of at least 20:1. Outputs include sine, triangle, square wave and DC level waveforms, as well as variable duty cycle and sawtooth pulses. The instrument has a main output of 20V peak-peak, from a 50Ω source impedance. A two-step attenuator (20dB/step) and a 26dB vernier provide levels down to 10mV peak-peak. A variable DC offset of ±10V can also be provided. For more information, contact Nilsen Technologies, 150 Oxford St, Collingwood, Vic 306. Phone 1 800 623 350; fax 1 800 067 263. 20MHz oscilloscope from Leader Instruments AWA FM721 FM-Rx board $10 The complementary receiver for the above Tx. Full circuits provided for Rx or Tx. Xtals have been disabled. MAX Kit for PCs $169 Talk to the real world from a PC. 7 relays, ADC, DAC 8 TTL inputs & stepper driver with sample basic programs. ETI 1623 kit for PCs $69 24 lines as inputs or outputs DS-PTH-PCB and all parts. Easy to build, low cost. ETI DIGI-200 Watt Amp Kit $39 200W/2 125W/4 70W/8 from ±33 volt supply. 27,000 built since 1987. Easy to build. ROLA Digital Audio Software Call for full information about our range of digital cart players & multitrack recorders. ALL POSTAGE $6.80 Per Order FREE Steam Boat For every order over $100 re­ceive FREE a PUTT-PUTT steam boat kit. Available separately for $19.95, this is one of the greatest educational toys ever sold. Leader Instruments has released a 20MHz oscilloscope for under $800 including sales tax. It features a maximum sensitivity of 500µV/div for measuring low level signals, and a maximum sweep speed of 50ns/div. A worthwhile feature is the inclusion of a buffered channel 1 output which can be used for connecting a frequency counter. Other features include variable holdoff, TV triggering and the usual operation modes of CH1, CH2, CHOP, ALT and ADD. For further information, contact Stantron Australia, Suite 1, Unit 27, 7 Anella Ave, Castle Hill, NSW 2154. Phone (02) 9894 2377; fax (02) 9894 2386. ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia March 1997  89 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. April 1991: Steam Sound Simulator For Model Railroads; Remote Controller For Garage Doors, Pt.2; Simple 12/24V Light Chaser; Synthesised AM Stereo Tuner, Pt.3; A Practical Approach To Amplifier Design, Pt.2. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car; Fitting A Fax Card To A Computer. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. July 1990: Digital Sine/Square Generator, Pt.1 (Covers 0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; Low-Cost Dual Power Supply; Inside A Coal Burning Power Station. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. July 1991: Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; The Snowy Mountains Hydro Scheme. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; StepBy-Step Vintage Radio Repairs. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C Transmitter; Index to Vol. 2. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages; A Look At Very Fast Trains. February 1990: A 16-Channel Mixing Desk; Build A High Quality November 1990: How To Connect Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Build A Simple 6-Metre Amateur Band Transmitter. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junk- ORDER FORM Please send me a back issue for:  July 1989  September 1989  January 1990  February 1990  July 1990  August 1990  December 1990  January 1991  May 1991  June 1991  October 1991  November 1991  April 1992  May 1992  September 1992  October 1992  April 1993  May 1993  September 1993  October 1993  February 1994  March 1994  July 1994  August 1994  December 1994  January 1995  May 1995  June 1995  October 1995  November 1995  March 1996  April 1996  August 1996  September 1996  January 1997  February 1997                   September 1988 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 December 1995 May 1996 October 1996                   April 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 July 1992 February 1993 July 1993 December 1993 May 1994 October 1994 March 1995 August 1995 January 1996 June 1996 November 1996                   May 1989 December 1989 June 1990 November 1990 April 1991 September 1991 March 1992 August 1992 March 1993 August 1993 January 1994 June 1994 November 1994 April 1995 September 1995 February 1996 July 1996 December 1996 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ___________________________ Card expiry date_____ /______ Name ______________________________ Phone No (___) ____________ PLEASE PRINT Street ______________________________________________________ Suburb/town _______________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ......................$A7 NZ & PNG (airmail) ..............................$A7 Overseas (airmail) ..............................$A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503.  Card No. box 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. November 1995: Mixture Display For Fuel Injected Cars; CB Transverter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. May 1992: Build A Telephone Intercom; Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC As A Reaction Timer. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Engine Management, Pt.11. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. March 1996: Programmable Electronic Ignition System; Zener Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; A Guide To Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Windows-based Logic Analyser. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80Based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags - How They Work. October 1994: Dolby Surround Sound - How It Works; Dual Rail Variable Power Supply; Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford - A Pesky Electronic Cricket; Cruise Control - How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. April 1995: Build An FM Radio Trainer, Pt.1; A Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50-Watt Per Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; An 8-Channel Decoder For Radio Remote Control. May 1995: What To Do When the Battery On Your PC’s Mother­board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Door Minder; Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1996: Making Prototype Parts By Laser; VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Build A Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. December 1996: CD Recorders ­– The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. February 1997: Computer Problems: Sorting Out What’s At Fault; Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-A-Phone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, February 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.00 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disc at $10 including packing & postage. March 1997  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Light meter wanted As an electrical contractor and amateur photographer I have always felt the need for some sort of device which would be able to measure available light. Would you consider publishing a project along such lines? The capability to obtain light readings in Lux would be most welcomed by many self-employed electricians such as myself, especially in a similar form to your recent sound level meter, which uses a DMM’s display, and if it were also capable of meas­uring the colour temperature (degrees Kelvin) of any light source, photographers, architects, designers, decorators and many others would also welcome it. As a matter of fact it would be quite a unique device. While on the subject of light, I could never comprehend the high cost of powerful flash units. Surely it would be easy for you to publish a circuit of one with a very quick recovery time, to work on 240VAC, as in a studio set up, where physical size and weight are of secondary importance. (A. F., Warilla, NSW). • We have not published such a device but we will consider the feasibility of a design. In the meantime, Poor regulation from step-down converter I have built the 6V-12V converter from the “Circuit Note­book” pages of the December 1994 issue of SILICON CHIP and after some bother with the toroidal transformer, I have a unit which works as follows: +13.65V at no load; 10.99V <at> 160mA and 8.34V <at> 340mA. After about half an hour at 160mA the toroid is warm and Q1 and its heatsink is very hot. The heatsink is a 3/8" x 1" x 4" bar with fins attached. Do you have 92  Silicon Chip you can purchase a Lux meter from Dick Smith Electronics. It is priced at $139.50 (Cat. No. Q-1400). We have considered designing a high power 240VAC flash unit in the past but have decided not to proceed. The design would be inherently dangerous, with large capacitors charged to lethal voltages. Such capacitors and the discharge tube are very expen­sive which is partly the reason commercial units are so expen­sive. Note: a suggested power supply for a photographic flash was featured in the Circuit Notebook pages for February 1997. Calculator for darkrooms Would you be able to design special purpose calculators – the sort of thing one might buy to change, say, metric to imperi­al units and the like? There are a number of darkroom functions that you can do on an ordinary scientific calculator but which require a knowledge of theory – and photographers are not, alas, noted for numeracy or the workings of the laws of physics! The areas that need “help” are “stops on and off” – espe­cially fractions thereof – and exposure changes with alterations to print height relative any suggestions as to what I have done wrong or where something has failed? (R. G., Chapel Hill, Qld). • The 6-12V converter circuit should be able to supply the 1A current you require. Perhaps the number of turns on L1 is too great. We suggest about 44 turns using 1mm diameter enamelled copper wire. The 0.5mm wire specified should also be OK. You may also be interested in the 2A SLA battery charger in the July 1996 issue. This provides 2A at 13.8V and can be modified in the same way to work from 6V. to the negative size in use; ie, image magnification stuff. What I have in mind for the former is the ability to feed in a known exposure and then to select a frac­tional on or off amount and obtain an answer. For the mag­ nifica­tion, feed in (a) neg size, present exposure and total print height, then (b) feed in new total print height. Press “compute” for new exposure. An added function might be changes in (film) development time versus temperature, with readout in minutes and seconds, not decimals. (T. W., Point Clare, NSW). • These days no-one is likely to go to the trouble of design­ing a calculator for darkroom functions. It is more likely that someone has written a spreadsheet program that would do the job. Maybe one of our readers has already done so. Oscillation in 3-terminal regulator While VHF reception at my address is excellent, that of UHF is rather noisy, although interference free. The masthead ampli­fier described by Branco Justic in the August issue of SILICON CHIP appeared to offer the solution to what has been more of a minor irritation than a real problem. Construction was very easy and I tested it at the input to the TV set to be greeted by a degraded signal on SBS and progres­ sively increasing noise patterns as the TV was tuned down the VHF band to ABC. It seemed that the masthead amplifier was oscillat­ ing and I wondered what I could have done wrong. Hooking the unit up to a CRO proved that it was indeed oscillating at just above 6.5MHz but the problem was why. I did not think I had damaged the MAR6 IC and the chance of its being faulty as delivered was remote. It then came to me that there was a capacitor across the output of the regulator and that I had a similar problem many years ago where a specified capacitor at the output of a regulator had caused it to oscillate like mad. Sure enough, it was indeed the power supply that was oscil­lating so I removed C4, the .0033µF capacitor and was rewarded with a nice stable 5V supply. The unit is now temporarily hooked up in the roof to the UHF antenna (also described in SILICON CHIP some time ago) and I have been rewarded with first class reception of SBS. When it stops raining I will install the amplifier at the antenna itself. I don’t know how often this regulator instability occurs but I bring it to your attention in case other readers strike similar trouble. (A. M., North Turramurra, NSW). • The .0033µF capacitor at the output of the regulator is much smaller than the conventional 10µF electrolytic normally stipu­lated in the National Semiconductor design literature. The ca­pacitor is specified to stop the oscillation you experienced. We would prefer to see a capacitor present and we assume that a 10µF capacitor would fix the oscillation. We also wonder if the fitted capacitor was defective or the connections open circuit. IGBTs for audio amplifiers I have just been reading the article on IGBTs in the August 1996 issue of SILICON CHIP. Could these devices be used in an amplifier module similar to the one in the June 1994 issue? This delivered 350 watts into 4Ω loads. If so, would an IGBT amplifier be more efficient and have less distortion. (Andrew, Cessnock, NSW). • It is certainly possible to design an audio amplifier with IGBTs in the output stage. Such an amplifier would have the benefit of very rugged output devices. In fact, we have seen an application note from Toshiba Electronics (UK) Ltd which featured IGBTs in the output stages (Ref No: X3504). This application note actually featured the same 40-80W amplifier using Mosfets, IGBTs and bipolar transistors in the output stage. The IGBT output stage gave about 10% more power than the bipolar output stage which was about 12% better than the Mosfet output. However, the IGBT design also gave the worst distortion. So the answer is that the IGBT design would be more effi­cient but Pintara tachometer connection I am writing to you in the hope that you can help me with a problem concerning the LED Digital Tachometer published in the August 1991 issue of SILICON CHIP. I purchased the kit from Jaycar after reading in its description that “it works with all ignitions from Kettering to Hall Effect systems” and that it had been checked on cars with electronic ignition systems. I have now built the unit and was particularly pleased with the way it went together. Its calibration using the mains-derived circuit, was virtually spot on at 1500 rpm for a 4-cylinder car. However, my car is a 1990 Nissan Pintara 2.0 litre model with electronic ignition having an inlet coil and an exhaust coil. These coils are not of the usual type, being of a rectangu­lar shape each with the high tension lead coming out of the top and four wires entering the bottom. The unit appears to be sealed in a black plastic case. would have higher distortion. The big difficulty in producing an IGBT design in Australia would be in ensuring a reliable supply of suitable devices. Incidentally, your letter did not include your surname or your full address, so we were unable to send you a personal reply. Problem with programmable ignition I have previously written to you with regard to fitting a programmable ignition/reluctor ignition unit to a Ford hot rod and you advised me to use the May 1996 “Circuit Notebook” version which I have completed but, unfortunately, it does not work. I have built two programmable ignition units which work off the points and fitted them to my sons’ Corollas and they work fine. In summary, I have tested the reluctor ignition unit/dis­ tributor (Motor­ craft unit) separately and it produces a healthy spark and works normally. I I have looked through a workshop manual on the car and am still unable to locate the negative terminal of either coil to which the input lead must be connected. I realise that the cir­cuit is some five years old but I am keeping my fingers crossed in the hope that you can answer the question: where is the nega­tive side of one or other of the coils? (G. W., South Arm, Tas). • Through the resources of our stablemate magazine “ZOOM”, we have obtained a copy of the Pin­tara’s wiring diagram. It seems likely that the switching transistor for each coil is actually inside the coil housing which is why there are four wires to each. As we understand it, both coils are fired simultaneously. Hence, it should be possible to obtain the tachometer signal from either of the white (W) wires which presumably carry the base voltage to the transistors. Since the base voltage signal will be considerably less than the coil primary voltage, the 33kΩ resistor to the coil negative, the tacho input network, should be reduced to 3.3kΩ. have programmed the programmable ignition unit and it keeps the data when accessed. The LED on the program board cycles on and off when the distributor is rotated. There is 7V at pin 7 of MC3334 which drops to 5V when the distributor is rotated. The coil output from the programmer board is 7V which drops to 6.5V when the distributor is rotated. The LED on the reluctor board does not light up unless the output wire from Q4 is disconnected. I have checked all components and circuit boards for de­fects, replaced all solid state devices and measured all passive components and wiring and swapped the programmer ICs from one of my sons’ cars. Can you give me any advice?. (F. W., Airport West, Vic). • Two points should be noted: (1) the 330Ω resistor at pin 6 of the MC3334 should be deleted; and (2) we suspect that either Q3 or Q4 is faulty or the incorrect type, because LED1 does not SC light when Q4 is connected. March 1997  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 9979 6503. _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www.mpx.com. au/~lgrant WEATHER FAX DECODERS: for HF, VHF/UHF use with JVFAX, MAXISAT and SATFAX. Details D. G. Hopkins, 4 Handsworth Street, CAPALABA 4147. (07) 3390 3328. SATELLITE DISHES: international reception of Intelsat, Panamsat, Gori­ zont,Rimsat. Warehouse Sale – 4.6m dish & pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 9482 3100 8.30-5.00 M-F. EPROM PROGRAMMERS/EMULATORS: Dataman-48 up to 48pin DIL. DatamanS4 world’s leading handheld programmer/emulator, onscreen editor, over 1500 device types including EPROMS/EEPROM/Flash up to 8Mbits. DOS/Win software, free updates. Call or email for de­tails. DIGITAL GRAPHICS P/L, PO Box 281, North Ryde 2113. (02) 9888 3105. dgriffo<at>ozemail.com.au http://www.ozemail.com.au/~dgriffo ALERT-A-PHONE Amplified Telephone Ringer Kit. Silicon Chip, February 1997. Very loud! T.T.S. P0 Box 357, Cleveland, Qld. 4163. Phone (07) 3821 1222. http:// www.globec.com.au/~tts NEW LCD 2x16 $20. Serial LCD Interface Kit with LCD $45. Largest range of PIC related products south of the equator: EASY PIC’n Beginners Book $46, CCS C Compiler $160, Basic Compilers and Interpreters. Ring or fax for Free Promo Disk. WEB search on DonTronics, PO Box 595, Tulla­marine 3043. Phone (03) 9338 6286 Fax (03) 9338 2935. MICROCRAFT PRESENTS: Dunfield (DDS) products are now available exstock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $399 + $6 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/ PALs etc from $1.50 • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent certified mail • Call Bob for more de­ tails. MICRO­ CRAFT, PO Box 514, Concord NSW 2137. Phone (02) 9744 5440 or fax (02) 9744 9280. VIDEO CAMERA MODULES from $89. Tiny 36x38x17mm. Low light & infrared sensitive. Ultra tiny 28mm x 28mm PCB modules also avail­able. A.S. & S. Ph (09) 349 9413. MINI CUBE CAMERAS ROBUST ALUM CASE with lens. From $98. 43 x 48 x 48mm. 12 VDC. A.S. & S. (09) 349 9413. Fax (09) 344 5905. COLOUR VIDEO CAMERA MODULES from $299. With lens. 12 VDC. Auto shutter. Small. Light. (09) 349 9413. VIDEO AUDIO TRANSMITTERS 7" wireless CCTV sets. TX/RX module pair only $80. (09) 349 9413. Fax (09) 344 5905. !!!!!!!! THE TINIEST !!!!!!!! VIDEO CAMERA MODULE: PCB size just 28mmx28mm, infrared & low light sensitive, with 2.8, 3.7 or 5.5mm pinhole MicroZed Computers PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 722777 – may time out to Mobile 014 036775 Fax (067) 728987    (Credit Cards OK) http://www.microzed.com.au BASIC STAMPS & PIC Tools With third party supporting products, all in stock Easy to learn, easy to use sophisticated CPU based controllers Credit cards OK   Send two 45c stamps for info MEMORY * MEMORY * MEMORY SPECIAL! (Ex Tax) 1Mbx9 – 70ns $15 30-pin Simms BUSINESS FOR SALE – GATTON, QLD TV, Video, Microwave, Audio Repairs. Little Opposition. Excellent Figs. Huge Potential. For Quick Sale: $30,000 S.A.V. Claire Stewarts Business Brokers 076 38 4377 ♦ 018 71 8669 lens. A.S. & S. (09) 349 9413. Fax (09) 344 5905. !!!!!!!!!!!!!!!!!!WARNING ! WARNING ! WARNING ! WARNING ! !!!!!!!!!!!!!!! VIDEO CAMERA MODULES Beware of low prices for a similar camera! BUY A BETTER CAMERA AT A SIMILAR PRICE! With a CHOICE OF .... 380, 460 & 600 TVL resolution. 0.05 SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $42 $36 4Mb 72 PIN-70 $50 $30 8Mb 72 PIN-70 $84 $51 16Mb 72 PIN-70 $144 $115 32Mb 72 PIN-70 $274 $230 EDO SIMMS (60ns) 4Mb/8Mb $30/50 16Mb/32Mb $102/222 LIFETIME WARRANTY!! 64Mb/256Mb $1212/2472 LASER PRINTER MEMORY 4Mb HP 4&5 $60 8Mb HP 4 & 5 $90 All other models available $Call COMPAQ 8Mb ARMADA 1100 $96 All other models available $Call TOSHIBA 8Mb Portege/ Sat EDO $119 16Mb Portege/ Sat EDO $210 16Mb Tecra 500/610 Sat $229 All other models available $Call IBM 16Mb T.Pad 755, 360 EDO $257 All other models available $Call DIMMS 4Mb - SO - 72 PIN $46 8Mb - SO - 72 PIN $82 16Mb - SO - 72 PIN $147 8Mb/16Mb - 168 PIN $58/104 32Mb/64Mb - 168 PIN $258/480 SYNCHRONOUS (SRAM) 168 PIN - 8Mb $90 168 PIN - 16Mb $171 168 PIN - 32Mb $342 Ex Tax Pricing – Delivery $8. Pricing as at 31/01/97. Phone for latest. Sales Tax 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Memory Pty Ltd Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au lux infrared & low light. TEENY WEENY 28x28mm PCBs. ELEVEN board lenses. FOUR pinhole lenses. SIX C/CS mount lenses. IR & polaris­ing filters. 800 + nm 52 mW/Sr IR LEDs. Ancillary equipment, AFTER-SALES SERVICE, HELP and SILICON CHIP FLOPPY INDEX WITH FILE VIEWER Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. Price $7.00 each + $3 p&p. Send your order to: Silicon Chip Publications, PO Box 139, Collaroy 2097; or phone (02) 979 5644 & quote your credit card number; or fax the details to (02) 979 6503. Please specify 3.5-inch or 5.25-inch disc. March 1997  95 ADVICE! Before you buy! Ask for our very detailed, illustrated price list with application notes. Also available CCTV technical, design & training manuals and interactive CD ROMs. Allthings Sales & Services 09 349 9413. Fax (09) 344 5905. DIY SECURITY ALARM SUPPLIES Professional grade equipment PIRs, autodialler alarm panels, CCTV, cable etc. Send for price list. All prices wholesale. AFFORDABLE ALARMS, 7 Firefly Crescent, Lawnton, Qld. 4501. EDUCATIONAL ELECTRONIC KITS: Best prices. Easy to build. Full details. Latest technology. LESSON PLANS FOR TEACHERS – see our web page. Send $2 stamp for catalog and price list to: DIY Electronics, 22 McGregor St, Num­ urkah, Vic. 3636. Ph/fax (058) 62 1915. Or Email laurie.c<at>cnl.com.au and let us send details. Go http://www.cnl.com. au/~laurie.c or BBS (058) 62 3303. Download details free any­time. RAIN BRAIN AND DIGI-TEMP KITS: 8-station controller and 8-chan­ n el, RS232 digital thermometer uses the incredible DS1820 sensor. Call Mantis Micro Products, 38 Garnet St, Niddrie, 3042. P/F/A (03) 9337 1917. http:/www.home.aone.net.aumantismp SIMPLE PIC84 PROGRAMMER: LED model 6 lights $65, LCD 16x2 char. $75, P+H $3. Also low-cost design, prototyping and microcontroller programming service. Eastern Electronics (02) 97893616, Fax (02) 9718-4762. Microprocessor For Digital Effects Unit Advertising Index Av-Comm.....................................31 This is the 68HC705-C8P pro­gramm­ ed micro­pro­cessor IC for the Digital Effects Unit (see Feb­. 1995). Dick Smith Electronics..... 4,5,14-17 Price: $45 + $6 p+p Earthquake Audio........................87 Payment by cheque, money order or credit card to: Silicon Chip Pub­lica­ tions. Phone (02) 9979 5644; Fax (02) 9979 6503. Harbuch Electronics....................87 Instant PCBs................................95 68HC05 & HC11 DEVELOPMENT SYSTEMS: Oztechnics, PO Box 38, Illawong NSW 2234. Phone (02) 9541 0310. Fax (02) 9541 0734. http://www.oz­technics.com.au/ EPROMS, 27C010 new, unused production run surplus, $4 each + P&P, negotiable for quantities 25+. Contact Greg at NowTech Sydney on 0414- 331968, 24 hours HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at http:// www.onekw.co.nz/onekw Jaycar ................................. IFC, 51 Kits-R-US.....................................88 Macservice..................................21 MicroZed Computers...................95 Oatley Electronics........................57 Pelham........................................95 Resurrection Radio......................85 CAR/RALLY COMPUTER KIT: including fuel sensor & speed sensor. Rod Irving Electronics .......... 67-70 PCBs MADE, ONE OR MANY. Low prices. Hobbyists welcome. Sesame Electronics (02) 9554 9760. Silicon Chip Back Issues....... 90-91 600 TVL 0.05 lux VIDEO PCB CAMERAS & MODULES from $96. Tiny 38x38x17mm. Low light & infrared sensitive. 437 664 element sensor CCD. A.S. & S. Ph 09 349 9413. Silicon Chip Bookshop...................6 Silicon Chip Binders....................63 Silicon Chip Car Projects.............45 Silicon Chip Model Railway Projects Book..........................OBC SILICON CHIP BINDERS These binders will protect your copies of SILICON CHIP. ★ Heavy board covers with 2-tone green vinyl covering ★ Each binder holds up to 14 issues Zoom Magazine.........................IBC _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. Price: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add $A5 each for p&p. To order, just fill in & mail the order form in this issue to: Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 9979 5644 & quote your credit card details or fax (02) 9979 6503. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. 96  Silicon Chip