April 1992 - Silicon Chip Online

Outer Front Cover
Contents
Publisher's Letter: The dangers of computer viruses
Feature: Understanding Computer Memory by Paul Lynch
Review: Yokogawa's 100MHz Digital CRO by Leo Simpson
Project: Studio Twin Fifty Amplifier, Pt.2 by Leo Simpson & Bob Flynn
Project: Build The Executive Thingie by Darren Yates
Serviceman's Log: Found dead in a motel room by The TV Serviceman
Feature: Amateur Radio by Garry Cratt, VK2YBX
Feature: Remote Control by Bob Young
Feature: The Electronics Workbench by Darren Yates
Project: Infrared Remote Control For Model Railroads, Pt.1 by Leo Simpson & John Clarke
Project: Differential Input Buffer For Oscilloscopes by John Clarke
Vintage Radio: The basics of receiver alignment by John Hill
Back Issues
Order Form
Market Centre
Advertising Index
Outer Back Cover

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HEWLETT ~~ PACKARD _, _/ ~ _/ ~ ~ ... _/ ~ _/ "'f_f_J _J -'fl-j~ -·-'A ~ _/ ~ ~ _/ _/ -,_J_ "J /..&_ _/ '-iL=-l _/ ~ ~ _J _/ J / u _J _J 1/_J ---..,J '..,I - -- :~_c , !I J _/ ...a.../ r, _J _J _J _/ :::!, _jl ..i _J' J _/ _/ _J' -l' _/ _/ }I "'""' srwolWlll~ ....,,_~- ~ ;;,.~~ -t · O', ~: . :; :~ }~. ·-,'c_~ OUR NEW STEREO AMPLIFIER delivers 50 watts per channel into 8-ohm loads. This month, we give you the full construction details. Turn to p.18. _/ _/ Vol.5, No.4. April 1992 FEATURES 6 Understanding Computer Memory by Paul Lynch Learn how computer memory is organised 14 Yokogawa's 100MHz Digital CRO by Leo Simpson Features an in-built thermal printer ADD INFRARED REMOTE control to your model railroad. Our project on p.64 has pulse power, inertia, braking & full overload protection 56 The Electronic Workbench by Darren Yates A low-cost circuit simulation package PROJECTS TO BUILD 18 Studio Twin Fifty Amplifier, Pt.2 by Leo Simpson & Bob Flynn Second article has the construction details 30 Build The Executive Thingie by Darren Yates Produces four tones to calm those frazzled nerves 64 lnfrared Remote Control For Model Railroads by John Clarke Uses the original Railpower pulse controller board 76 Differential Input Buffer For Oscilloscopes by John Clarke Lets you observe mains waveforms in calibrated mode SPECIAL COLUMNS 36 Serviceman's Log by the TV Serviceman Found dead in a motel room 42 Amateur Radio by Garry Cratt A SAMSUNG TV set "carked" it in a motel room this month but was brought back to life by the Serviceman. The story starts on page 36. Receiving weather satellite signals - the hardware required 53 Remote Control by Bob Young Switching frequencies in speed controllers 84 Vintage Radio by John Hill The basics of receiver alignment DEPARTMENTS 2 4 12 56 88 Publisher's Letter Mailbag Circuit Notebook Product Showcase Back Issues 90 Ask Silicon Chip 93 Order Form 94 Market Centre 96 Advertising Index THIS DIFFERENTIAL INPUT buffer will allow you to monitor calibrated mains waveforms on your oscilloscope & to observe signals which cannot be referenced to earth. Details p. 76. APRIL 1992 1 Publisher & Editor-in-Chief Leo Simpson, B.Bus. Editor Greg Swain, B.Sc.(Hons.) PUBLISHER'S LETTER Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Darren Yates Reader Services Ann Jenkinson Sharon Macdonald Sales & Marketing Mgr. Sharon Lightner Phone (02) 979 5644 Mobile phone (018) 28 5532 Regular Contributors Brendan Akhurst Jennifer Bonnitcha, B.A. Garry Cratt, VK2YBX Marque Crozman John Hill Jim Lawler, MTETIA Bryan Maher, M.E., B.Sc. Jim Yalden, VK2YGY Bob Young Photography Stuart Bryce Editorial Advisory Panel Philip Watson, MIREE, VK2ZPW Norman Marks Steve Payor, B.Sc., B.E. SILICON CHIP is published 12 time$ 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: Magazine Printers Pty Ltd, Alexandria, NSW; Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $42 per year in Australia. For overseas rates, see the subscription page in this issue. Liability: Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Editorial & advertising offices: Unit 1a/77-79 Bassett Street, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 979 5644. Fax (02) 979 6503. ISSN 1030-2662 2 SILICON CHIP The dangers of computer viruses Several years ago , when reports of computer viruses first began to appear in the media, I did not take them too seriously. Of course, I could see that the philosophy was inherently correct - any large population of complex organisms such as animals or plants, in close contact with each other, is always ripe for exploitation by an opportunist organism such as a predator, parasite, bacteria, virus or whatever. That is why the human population is so vulnerable to viruses - there are huge numbers of us and because of international travel, any new virus can go around the world in a matter of months. For computers, the situation is very similar. There are now tens of millions of computers around the world and because they are in close contact with one another, via modems, bulletin boards and software swapping, computer viruses can go around the world and infect very large numbers of computers in a matter of weeks or even days. No computer can be regarded as safe. In our offices, we have already had several occasions when we have detected viruses, once in new software which had been sent to us in a review package. Most recently though, one of our machines "caught" the Michelangelo virus and the reason was that it happened a few days before we had obtained the latest virus scanning software. As I write this, on February 25th, it is possible that millions of computers have been infected by this latest piece of devilry. What I want to know is this: what do the authors of these nasty little programs think they are doing? Their germ-like creations can lead to untold data being lost in computers and millions of man-hours in retrieving it. They could also lead to very large losses in some companies with the result that they may go out of business and throw all their employees out of work. When you think about it, computer viruses are little more than economic sabotage. If an insurance company or bank is ultimately infected, it could have disastrous affects on the economy of any country. Think about the billions of dollars locked up in superannuation funds and you will see what I mean. In my opinion, anyone who creates or knowingly passes on a computer virus is a criminal. The ramifications of computer viruses are extremely serious and there seems little doubt that sooner or later, a computer virus will cause a disaster. In the meantime, be on your guard as much as you can. Make backups regularly, keep up to date with anti-virus software and be wary of bulletin boards and pirate copies of software. 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No restriction to the number of extensions o r other devices connected to It. Compact Design, being a llttle larger and he a vier than a packet of cigarettes . Proven Rellablllty backed up with a 2 YEAR Exchange Warranty. Also works with Commander, Keyphono or PABX (technical Installation requ'd) The EASY-CONNECT Is compatible with the changing needs. Provides Lightning prote c tion for the Fax and other devices connected to It. Made In the U.S.A. Telecom Australia Permit Number; A90 / 14B/ 0342. Size : 85mm x 90mm x 33mm . Wgt: 225g. Our ..llor•• new product for '92 FLUKE 10 ■ 4000 count display. ■ Continuity beeper. ■ Diode Test. ■ Sleep Mode. ■ AC voltage. ■ DC voltage. ■ Ohms range. ■2 year warranty. ii••l3•0 ■ ■ ■ 4000 count display. Continuity beeper. Diode Test. ■ Sleep Mode. ■ AC/DC voltage. ■ Ohms range. ■ V Chek. ■ Capacitance. ■ 2 year warranty. 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FREEi MAILBAG Mistral GyroAire fans were crook I hate to pull you up on your comments in the January editorial but the Mistral GyroAire GA12 & GA16 fan units were only box-type cooling fans and not fan-heaters. If they had been fan-heaters there would have been 10 times the number of fires and deaths. These Mistral box fans were in general a shocking product-the National Panasonic box fan was so far superior it wasn't funny. The Mistrals rattled badly at lower speeds and had no provision for lubrication which they needed regularly if they were to be a little bit quiet. In short, they were a typical crook product. It is a pity the makers lasted long enough to put the flammable plastic models on the market. Harry Swan, Bulimba, Qld. Smaller inverter wanted I wish to congratulate you on your 40W Inverter published in the February issue of SILICON CHIP. I'm going to build this project as it is inexpensive and it looks easy to construct. I was wondering if you could design an even smaller inverter that only requires a transformer and a few components mounted on a small PC board. Michael Harris, Maiden Gully, Vic. Comment: as noted in the February article, we now have a smaller version of this project. It will probably be featured in the coming June issue. Support for bulletin board I am writing in reply to Greig Sheridan's suggestion (February 1992) about SILICON CHIP starting a bulletin board service for its readers. I am in favour of such a bulletin board service. You could set up the BBS so readers can give feedback through their computer instead of mail (like I have done). You may also like to include where readers can buy components for certain projects you publish in your magazine. I'm sure if SILICON CHIP did set-up 4 SILICON CHIP a BBS, many readers and organisations would use it. I certainly would! Glen Taylor, Werribee, Vic. More support for bulletin board I would like to throw my support behind Greig Sheridan's suggestion for a Bulletin Board System. I am an assistant sysop of a BBS here in Sydney as well as being a computer engineer with a major computer firm and a radio amateur. I think such a link would be ideal, especially in today's environment. I think that many would tend to communicate directly with you via such a medium rather than by mail as it is simpler and easier than having to remember to post a letter. I am also a user of Packet Radio BBS's and use them to send all publicity material to the WIA here in Sydney for inclusion in their regular Sunday morning broadcasts. Another spinoff of such a system would be a saving in time to type up everything as items would already be in electronic format ready to edit and use. I do hope this idea does go ahead and look forward to its implementation. E. van de Weyer (VK2KUR), Vaucluse, NSW. Drawing standards OK So Standards Australia don't like your zig-zag resistors? I love 'em. Anyway, what standards and for how long? Years ago, the bloke on the wireless would tell the central pressure of any approaching cyclone in pounds (one syllable) implying per square inch and the oldies would either go fishing or head for the hills. Then some Grand Pooh-Bah decreed inches (two syllables) of mercury. It took a couple of dozen cyclones to sort that one out, in time for the next G.P-B to decree millibars (three syllables), once again knocking the oldies for six. Now we just stare at the box feeling so sorry for the poor girl who has to stumble over heck-tor-pass-kalls (four syllables) We don't even notice the SILICON CHIP, PO Box 139, Collaroy Beach 2097. meaningless number and some boffin tells us that "people are becoming complacent about cyclones". Not so, mate, we're thoroughly confused by experts. Getting back to the zig-zags, I'd appreciate 1k8 as an assurance that Louie the fly has not autographed the page, otherwise no complaints. If the standards people, years ago, had persuaded transistor manufacturers to always put the base in the middle and, oh rapture, distinguish PNP from NPN with a different colour case, say black vs grey, the millions of man-hours and tons of paper squandered on dog-eared equivalent books may have tipped the whole economy of the nation into prosperity - who knows? Fred Hawkins, Townsville, Qld. Standards should stay as they are I feel compelled to offer my one cents worth with regard to your drawing symbols as per Mailbag in the Febrt1-ary 1992 issue. Basically, stay as you are, with maybe an article giving and comparing the various symbols in use. A lot ofreaders both young and old must understand the drawings symbols in use, in the various English language electronics magazines, or they would soon go broke, so why change? Keep up the good work. Greg Freeman, Nairne, SA. Zig-zag resistors are correct I wish to add some comments related to the letter by R. Lions on circuit standards, in particular the use of a zig-zag line to represent resistors. First, there is no such thing as "correct circuit symbols" in the absolute sense, though there is some case for adopting some standard conventions, at least in some applications. The zig-zag symbol probably goes back to the very earliest drawing of circuit diagrams, possibly inspired in the first instance by wire-wound resistors which were originally the only types used and were, perhaps, hand made, to suit early application prototypes. On historical grounds, then, the zig-zag has a strong claim to correctness. I am used to dealing with both representations and can live with either. However, the zig-zag is unique in general appearance and does suggest the offering of resistance to the flow of current. Probably because of this, I find I prefer the zig-zag when assessing the design of electronic circuits perhaps there is a temporary mental block while mentally translating the significance of a white rectangle to the meaning of its function . Also I find when sketching out circuit designs by hand that the zig-zag is marginally quicker to draw. Since the purpose of a magazine such as yours is to instruct and to describe the principles of circuit design, it seems to me that the zig-zag is to be preferred. As you note, most English language magazines use symbols very similar to the ones you use. There may once have been a justification for the use of the rectangle for manual drafting techniques but there certainly is no argument in these days of electronic drafting. Bearing in mind the need for people to be "ambidextrous" in view of the need to employ international standards in international transactions, the best solution would be simply for your magazine to publish a list of your symbols and the international standard equivalents with explanations perhaps two or four times a year. H. W. Holdaway, Moonee Ponds, Vic. Rectangles do not help Your drawing standards (symbols) are similar to those used by the semiconductor manufacturers and are quite readable. They are what I have used for years. With my experience in industry, I have found that chief draftsmen select the symbols, not the users of the circuits. They try to simplify everything to make their job easy but rectangles do not help the user in understanding the circuit. Component values should also be on the circuit and not on numerous loose sheets of paper as appears to be the current trend. Perhaps only draft- ers sit on the standards committees for drawing standards and so the symbols are simple but the content is poor. One chief draftsman of a company in which I worked disposed of all the sc,hematics in the drawing office as he said that they were not used in production. This attitude made his life easy but the users suffered. These whims are very common. With changes of in-house standards yearly, I find that I am now resistant to change, especially when a significant time is spent re-drawing schematics. I agree with the symbols for large digital devices as shown by the recent changes in International Standards but not the changes for small gates or the use of unmarked rectangles for inductors. These do not help understanding. I believe that the maximum information should be conveyed by the circuit. Some government departments have demanded some very strange variants of logic gates and it can be difficult to change their minds. In one case, it took many hours of arguing but they finally agreed to use the (previous) Australian Standards. Drawing standards do have a use. With the emerging widespread use of CAD packages in electronics, I have also found that it takes considerable time to fix the symbols, especially the aspect ratios. I have not seen any version of CAD software that has a good set of symbols as standard. Leigh Brown, Burwood, Vic. Belated response to PCB article I have only recently read the article from the October 1990 issue of SILICON CHIP entitled "What You Need To Know About PCBs". Having done so I would like to add some comments, not only about these products but other chemical materials used for similar purposes. For many years, I worked as a research scientist in various industries. In the 1950s, we were greatly attracted by the quoted low volatility, inertness and flame retardance of both the chlorinated hydrocarbons and the phosphate ester plasticisers. These were all widely used in plastics, surface coatings and adhesives of many types during the 1950s and 1960s. There were some reservations about some of the phosphate plasticisers and in fact the 1962 edition of the "bible" of the surface coatings industry, "The Science of Surface Coatings" by H. W. Chatsfield, devoted several sentences to warnings about these materials. But the chlorinated hydrocarbons, of which the PCBs were only one small group, were still extolled for their general inertness and were used as inert plasticisers for protective coatings used both on plant and machinery and containers used in the chemical and food industries, as well as for mining machinery, water and sewerage equipment, swimming pools and so on. The chlorinated hydrocarbons (ie, PCBs and chlorinated waxes) were in use well into the 1970s at least and I can never remember any handling warnings associated with any of these products, in their literature or on their containers. As late as 1971, when I was doing work on RF plasmas for polymerising surface coatings, we used PCB transformer oil to cool the plasma generator. There were no handling warnings on the containers even then! In a career time associated with the chemical industry going back 50 years, my experience has been that even the best of chemical companies have been loath to publicise any doubts about their products. The worst have gone to quite extreme lengths in cover-ups. For example, there is a particular group of aromatic amino compounds which has disastrous long-term (up to 50 years) carcinogenic properties. These compounds were sold into various industries and in various countries over a period of 100 years between the 1850s and the 1950s. Each new introduction of the compounds was done without any warning of the ill-effects already known. The 1(1.st usage was in the 1950s when they were sold as epoxy curing agents and were used, among other things, in potting compounds for electrical devices. A definitive condemnation of the compounds was finally published in the early 1960s. R. Roberts, Lindfield, NSW. APRIL 1992 5 Understanding emor By Paul Lynch Confused about computer memory? Learn how the memory in your PC is organised & what the various terms mean. SK ME THE years my parents were born and I will consult my memory and tell you. If I have the same information in my computer, I won 't consult its memory I'll look on the hard disc. The stuff there is called "storage ". It's not memory. "Memory" is one of the most misleading words in the computer field. Understanding the difference between memory and storage will make things much clearer for computer users. Failing to understand it causes simple errors which are hard to correct. Here's a simple example: a colleague some years ago bought a type-font A program which allowed for varying sizes of cache. The faster the cache, the faster the font operation. Reasoning that he had a 40Mb hard disc, he allotted an 8Mb (eight megabyte) cache. His system, of course, fell over. According to his computer, all he really had was 2Mb - in RAM (random access memory). He now has a modest 192Kb cache and things work well. The original PC Would that all memory difficulties be sq simple to explain and understand. Of course, it isn't so, for two main reasons. One is that, in 1992, we're still trying to push back the This EEMS RAM card accepts the DIP-style RAM chips. A total of 2Mb can be installed on this full length card. (Electronic Solutions, PC Marketplace). 6 SILICON CHIP envelope created for the original IBM PC more than 10 years ago - a machine without hard discs, a machine with an 8-bit bus, a machine designed with the idea that it might help do things like balance the family cheque book. The other reason is that software developers .h ave run amok designing applications, operation systems and the like, with no common, comprehensive standard for memory usage. So instead of an orderly traffic-like flow of instructions and data through such memory as your computer may hold, you've got something closer to the 9am rush on the first day of the post-Christmas department store sales. Several different applications in your computer can demand the same particular item - and demand it simultaneously. Sometimes there's a winner. Often, everybody loses - the systeip. hangs, or even crashes. This may cost you important data. It certainly isn't what you want. Almost certainly within the next two years, you'll be able to buy PCs which don 't have this problem - or at least, don't have it nearly as often. While they will look like today's PCs, they will -have memory organised differently in what a number of US and Most high density memory expansion boards use at least one VLSI (very large scale integration) chip to take care of memory refreshes and memory formatting. This 8Mb board uses SIMMs memory cards and is designed for the 286 bus. It features an EEPROM (electrically erasable programmable read only memory) to store the memory configuration and will operate as conventional, extended or expanded memory. (Pelham Pty Ltd). European manufacturers have agreed to call the Advanced Computing Environment (ACE). ACE machines will be fast and highly-optioned. Sadly, even before the first ones hit the market, it's obvious that the companies which have set up the standard have ever-soslightly different views of exactly how it should work. So the millennium is not quite as close as advertisers might be suggesting later this year. Let's have a look at the memory in today's PC and examine why it's as it is. today the lineal descendants of that first DOS are still used on all PC clones today: today's machines are much faster and more complex than the original PC and DOS has had to become far more complex with them. DOS originally addressed only 1Mb -- 2Mb EXTENOED MEMORY The DOS environment All PCs are designed to operate in an environment known as DOS. There are many proprietary DOS packages, Microsoft's MS-DOS being the bestknown. IBM's is called PC-DOS and another leading brand is Digit al Research's DR DOS. All arise from a few weeks' work by a young Bill Gates back in the 1970s. Gates was asked by IBM to figure out an environment for a machine that IBM never expected to be such a big seller and so he designed an operating system for the size and capacity of the first machine IBM had in mind. It's a tribute to human ingenuity that ,- 1Mb HIGH MEMORY USUALLY HAS BIDS AT TOP, VIOEO DISPLAY AT BOTTOM 640Kb VIDEO DISPLAY ,_ AVAILABLE RAM :=~ PERATING SYSTEM Fig.1: how memory is configured on most PCs with 2 megabytes of RAM. All or part of the extended memory shown could be configured as expanded memory. of memory, which was the amount in the original PC chip, the 8088. It seemed generous, fabulously generous, at the time and in terms of the simple software available at that time, it was. The 8088 chip stored its own BIOS (basic input output system) at the "top" of that 1Mb. IBM decided that the video memory - the stuff that lets you see on your monitor what's going on in the CPU and your applications - would start at hex A000, an "address" located 640Kb from the start of the chip's memory. The space below the 640Kb was allocated to CPU random access memory (which is what most people mean when they talk about "memory"). DOS itself needs chip space, and grabs the lowest part of that 640Kb of memory for itself. The memory above the 640Kb limit was called the Upper Memory (UM) by IBM. No matter how much memory you have in your PC today, the space between 640Kb and 1Mb is still called upper memory. It totals 384Kb. This was sensational 10 years ago and many thought it offered more than mere humanity could ever desire. Software complexity They did not reckon on the increasing complexity of software. Here's an example of that: one of the first DOS packages was the word processor WordStar which sold on one 360Kb floppy disc. The last version I bought, some five years ago, occupied 19. It did a great deal more than the first APRIL 1992 7 This 6Mb RAM card comes with drivers that support both EMS & LIM 4.0 operation. Also included is software to support a printer spooler & RAM disc. The RAM disc can be configured to any size and will speed up any application where frequently used files can be stored in RAM. (Rod Irving Electronics). This 30-pin SIMMs (single-in-line memory module) card has a capacity of9 x 1Mb Fujitsu MB81C1000 surface-mount chips. Eight of these cards can be fitted to the BOCA 8Mb card shown on the previous page. (Pacific Microelectronics). version and it made major demands on my hardware to do it. But even this 1: 19 ratio doesn't give you the full picture of how software is pushing the hardware envelope. For presentation-quality word processing, I now use a Windows-based package and its demands are such that no original PC can run it. I need a higher-level CPU chip - 80286 or better - and I need more memory than that original 1Mb. The new minimum is 2Mb of RAM. And remember, word processing is one of the simplest data processing applications. Now the 80286 chip is much faster than the original 8086s and 8088s. The 80386s and i80486s are faster again. But all these younger chips are backward compatible with the original PC chips. So they all have the original 1Mb limit of chip memory and the original 640Kb limit on RAM. Expanded memory So a new form of memory had to be 8 SILICON CHIP designed for those programs that need more RAM than 640Kb. Leading software (yes, software) companies got together with the chip-maker Intel and agreed on EMS - the Expanded Memory Specification. Its first version allowed software to run above the 640Kb barrier, in upper memory spaces unused by video, BIOS and accessory cards. Version 4, released in 1987, allows you to run up to 32Mb of expanded memory. This was quite an advance on the original 1Mb but it's only a small portion of the amount of memory you can address on the modern PC if you have a lot of money and the burning desire to spend it. You can address up to four gigabytes of memory from an 80386 chip. I can't imagine that anybody would, but then, the IBM engineers couldn't imagine that anybody would want more than 640Kb of RAM not so long ago. Most PC users know of one more type of memory - extended. This is not a particular memory type. It's simply any and all memory in the computer above the original 1Mb that the CPU can address. Expanded memory is usually fitted to the computer in expansion boards. It can be converted by software from extended memory. Microsoft Windows allows this on 80386 and i80486 machines and other applications allow it as well. Software juggling of this type speeds up the operation of most applications and makes others possible. If you are working in graphic-intensive applications, you want expanded memory and software juggling can be the cheapest way of getting it. It can also create clashes with other applications or your normal mode of operation. The memory you've software-configured as expanded cannot be used at all on an 80286 or 80386 machine running Windows in protected mode. You can see that a certain amount of confusion about memory arises from the language designed to describe machines now almost obsolete. If you lash out to buy an i80486 with 16Mb of RAM, the "upper memory" finishes 15Mb below the "top" of the actual memory present. And by software juggling, you can have either no expanded memory in the machine, or megabytes of expanded memory, whenever you wish it. You may find this linguistic eccentricity irritating and confusing, but it arises from honourable motives. The backward compatibility of the 86 series means that no favourite old software has to be discarded as you move up the speed slope within the family. Shadow RAM There are other features of memory that the original IBM team probably never considered. Take shadow RAM, for example. Much of upper memory holds Read Only Memory files. You can read them but you can't change them. ROM is slow and if you're using software that calls on your BIOS a lot, this can slow things down. So with some of the newer chips, you can "shadow" (or imitate) your ROM with part of your much faster RAM. This gives you faster operation, at a price: the part of upper memory you're using for shadow RAM is no longer available for applications to use for RAM. So it may be to your benefit to use shadow RAM or it may be to your disadvantage. Only you can tell by trial and error. Another piece of software juggling is the RAM disc. You've just read how RAM can pretend to be ROM ..It can also pretend to be a hard disc. If you set up a "RAM disc", you have fooled DOS into believing it's your hard disc. You have mock tracks and sectors and DOS can call on it just as it does on your hard disc. But much, much faster. When calling out information from the RAM disc, DOS has no need to move read/write heads, no need to wait while the right hard disc sector rotates under the heads, and so on. RAM discs are usually not large. They measure in the kilobytes or less. If you lose power while your RAM disc is open, you lose everything in it. And there's a certain amount of housekeeping. The most recent versions of DOS offer RAM discs as part of the package. Disc caches More versatile for most purposes is the software attribute called a "disc cache". There's a DOS disc cache and a Windows disc cache and you can go to the computer shop and buy a specialised utility that's nothing but a cache. The better ones work out what you want your computer to do and change around to help you do it. Key in a print instruction, for example, and part of the disc cache switches to enlarge your print spooler. Most hard disc users certainly have provisions for a disc cache in their software, whether they use it or not. Using it reduces wear and tear on your disc and speeds up many of your operations. It can cause trouble in a number of ways - especially if you plan to compress or unfragment your hard disc using Norton Utilities, PCTools or some similar package. All such packages advise you to disable your disc cache before disc compression. If you don't do this, you run the risk of trashing many of the files on your disc. The easiest way to disable it is to put a REM notation at the start of the line establishing the RAM disc in your CONFIG.SYS file. I've not addressed the issue of memory clashes in this piece. It merits a fresh start with a clear mind. What they are, how you recognise them, and how you resolve them, will be the subject of a future article. SC *** SAVE ON OUR APRIL SP COMPUTER CONNECTOR & CABLE SPECIALS Quality connectors, leads and adaptors at great prices including DB9/25 and IDC connectors, ZIF SQCkets and many popular memory ICs. COMPUTER CABLE SPECIAL D25 Male to Centronics 2m/5m .... $9.95/12.95 025 Male to Male 2m/5m ............. $9.95/12.95 IBM Keyboard Extensions ........................ $7 .50 D9 Male/D25 Female Adaptors ................ $6.50 EPROM , MEMORY & RAM IC 's 4116's .... .. .......................................... ...... $2.00 4164's ...................................................... $3.45 2732/27C32's .......................................... $6.90 DB PLUGS , SOCKETS & B/SHELLS 9-pin solder type (each) ........................... $1.30 15-pin solder type (each) ......................... $1.50 25-pin solder type (each) ......................... $1. 70 TEST EQUIPMENT & MULTIMETERS Labtech 20MHz Dual Trace O'scope ......... $594 Freq. Counter 1GHz (new model) ............. $399 Lodestar Audio Frequency Generator ....... $265 Lodestar RF Signal Generator ................... $246 Bell BC120 Multimeter ............................... $ 29 Economy Multimeters from ....................... $16 Testmate 295 Digital Autorange ............. .... $79 Economy Digital 17 Range .......................... $45 HG Autoranging Digital ............................. $114 KT65 LCR & Multimeter once-only price. $129 Panel Meters (MU45 variety) ...................... $15 CAR RADIO & CB AM/FM A/stop Cassette/Radio .................... $39 Tenvox TXBBO Cassette/Radio *A/rev/fader/clock/Dolby/loudness/ *Hi-power/separate bass & treble ........ $199 Fox 4-inch Dual Cone Spkrs (pr) ................ $15 Tenvox TX 2000 200 Watt Car Amplifier ... $149 4-inch Co-Axial 35-Watt Poly Spkrs (pr) .... $49 6-inch 200 Watt Tenvox Spkrs (pr) .. .......... $89 Car Radio Antennas from .............................. $4 40-Channel AM CBs from ........................... $69 □Iron CB Base Antenna (inc mount kit) ...... $65 Tenvox CB1 Extension Speaker .................. $12 5-lnch Helical Whips from .......................... $12 UHF CBs from ........................................... $289 Marine CBs from ......................................... $99 □Iron 24/12 Volt 3 Amp Converters ........... $39 CORDLESS PHONES & ANS MACHINES Uniden, GE, Call mate, James Hardie, Phoneworld and Panasonic - inc. the mighty KXT3000 'flip· phone'. From single-tape home units through to state-of-the art digital/handsfree machines. CODE·A·PHONE 1620 Single tape answering machine ................... $99 PANASONIC KXT 3000 The smallest & best cordless phone ........ $359 JAMES HARDIE/PHONEWORLD 660AUS Proven budget cordless ........................ ... $149 CODE-A-PHONE 3420 Digital answering service ......................... $169 KITS! KITS! KITS! Inverters, test equipment, power supplies, alarms, amplifiers and FM transmitters -we'll have something for you. Kits available ex stock from Altronics, Talking Electronics, Oatley Electronics & Drew Diamond. We also stock the Dick Smith 'Funway' Kit series. Laboratory Power Supply 3·50V/5A ......... $187 EA 12/87 600 Watt Inverter ...................... $384 4-Digit Capacitance Meter ........................ $109 1GHz Frequency Counter .......................... $249 50MHz Frequency Counter .......................... $94 Colour TV Pattern Generator .................... $109 Screecher Car Alarm ................................... $47 High Energy Car Ignition ............................. $55 Low Voltage Cut-out For Cars & Boats ........ $22 12V Gell Cell Charger .................................. $22 2 Sector Home Alarm .................................. $84 TV Transmitter for VCRs ............................. $65 200 Watt Mosfet Amplifier Modules ............ $74 12V/2-Watt Laser & Supply ..................... $210 240VAC 2-Watt Laser .......................... ..... $229 1 & 3-Watt Intro. Laser Kits ..................... $149 5-Watt lnfrared Diode & Supply .................. $59 APRIL SPECIALS inc. soldering irons & aids, many diecast & utility boxes and many discount transformers. Country readers should ring for a special price on their UHF TV Antennae - we'll get you receiving at very competitive prices. An extensive range of semiconductors, FETs & special Mosfets, power & zener diodes, SCRs, Triacs, Linear ICs, 74LS/HC & 4000 series ICs, high-intensity LEDs and displays are available ex stock. Other electronic accessories inc. pots, trim· pots, RF chokes, voltage regulators, relays, fuses, globes, heatsinks, as well as a comprehensive range of many popular switches, knobs, plugs & sockets (inc. quality Acme, Cannon and Link connectors). There's a huge range of resistors, capacitors and popular TV parts at competitive prices. We now offer a speedy, courier delivered , mail order service. Don't forget our disposals store at South Croydon. There's plenty of hard-tofind parts and help you won't get elsewhere! Phone 723 2699 (ask for Mai). APRIL 1992 9 ------, r---------------, ER ARM : LG>G>K I I I I I I ltlon your monitor I ctty where you want axlmiae deak apace I olid ateel atructure • pan 33cm ray 30cm (tilting +I• 15) j Give your 1 computer that I profesaional 1 I Deak clamp range 3cm -7.5cm I Maximum load SO kg : 21079 ............. ........ $199 I ---------------~ FAX ROLLS • MONITOR MOVER CAN ROTATE 360° • LIFTS MONITOR WEIGHTS UP TO 22KG 'PLATFORM TRAY 13 :114" X 12 1/4" 'PLATFORM CAN SWIVEL 360' & TILT 25" • BOMM DESK CLAMP OPENING • SCREW CLAMP CAN BE MOVER 90' ' UNIQUE CONSTRUCTION. LOCKS IN PLACE WITH MONITOR ON TRAY. C21082 ...........................$199 1-9 10+ C20092 $9.95 $9.50 Size: 2101111 .5 x 30m C20094 $9.95 $9.50 Size: 210 x 25.4 x 50m C20096 $19.95 $17.95 Size: 210 x 25.4 x 100m C20098 $9.95 $9.50 Size: 216 x 25.4 x 30m C20100 $11 .95 $11 .50 Size: 216 x 24.4 x50m C20102 $9.95 $9.50 rr u The Fort ran C PF Filtered Electronic Spike Protector provides a protective electronic barrier for microcomputers. prin ters. telephone systems and modems electronic typewriters. audio and s1ereo systems and other sens,11ve elec1ron1c equipment RIBBONS "SI ""' . PRINTER RIBBONS TO SUIT: 1-9 10+ ·C:22036 ......... $19.95 $17. 95 • MX80.FX80. RX80, FX800, MX70, MXao. LX800. ·c22~1 .........s1&.95 $15.25 • MX1 oo. FX100, RX100, LO1000 C22002 .......... $19.95 $17.95 • LX80 C22003 ..........$12.95 $11 .95 • CITOH 8510-1550 C22051.. ........$13.95 $12.50 NATIONAL PANASONIC KXM110 PRINTER RIBBON C22034 ............. ............$19 .95 The CPF provides pro1 ec11on from dangerous alectncal spikes that can cause anything from obvious damage fhke 1mmed1ate equrpmen l !a1lure ) to less obvious harm that can drasllcally shorten a systems hie CPF s superior cIrcuItry design and sem, conductor technology responds instantly 10 any potentially da maging over-voltage. ensurmg sale trouble free operation DELUX PRINTER STAND C21058 .................. ...... $89.00 WIRE PRINTER STAND 021054 •• 80 col•mn ....... $29.95 C21056 •• 132 Col•mn .... $34.95 SPECIFICATIONS : Electrical rating: 220-260 veils (AC) SOH2 10 Amp Splke/RFI Protection : 4.500 amps for 20m,second pulses Maximum clamping voltage : 275V d1tterent1al mode Cat.X 10088 $69.95 RITRON EXECUTIIVE CASE X11089. Includes power supply..... $119 NEW STYLE MINI TOWER CASE WITH POWER SUPPLY X11103 .................... $149 IBM COMPATIBLE EXTENDED KEYBOARD (101 KEYS) g x12022 ........................... $6 J;;;; 101 KEY TRACKBALL KEYBOARD Keyboard & mouH In on, X12030.~ .. $199.95 ~ KEYBOARD STORAGE DRAWER 021083 .. ~ 84.95 51/4" x 100 DISK CAPACITY ONLY•• $6.95 31/2"x 40 DISK CAPACITY ~ , ONLY...$6.95 MINI VACUUM CLEANER C21087 .. ~ ... ~14.95 KEYBOARD COVERS 021089 64 KEY............ $4.50 C21088 101 KEY.........$5.95 DISK BOXES RS232 BREAK OUT BOX A simple way of monitoring RS232 interlace lead activity Interlace powered , pocket size for circuit UV EPROM ERASER lndlcatora: Tricolour LED·s for TO AD. RTS. CTS. DSR. CO. TC. RC . DTR. (E)1 C It will 1r111 up to 9 x 24 pin devlcH In complete Hfety. In about 40 mlnUIH (1111 time for leaa chlpa) • Chip drawer haa conducllve foam pad • Maln1 powered • High UV lnttntlly It chip 1urlace 1n1ur11 EPAOMa are lhoroughly .,..,d Power : lnter1 ar.e power Encloaure: Black h1gh ImpacI plasttc Without timer X1"950 ...... ....... ........$99 \e;~~~af:!~~1; 9 (Eg~a~~~,ng 2 spares . 24 switches enables you to break out circuits or reconfigure and patch any or au the 24 active positions SPECIFICATIONS: Connectors : D825 plug on 80mm ribbon cable and 0825 socket Jumper Wlrea: 20 tinned end pieces Dlm1n1lona: 85 , 95 , 30mm X15700 .. ,n.85 """"'-------------NEW • The MotrsE"· MINI TOWER CASE 200 X 415 x 330mm with 200W power supply x11100 ........ .................. $199 Add1t1onat1y . CPF s hltenng capabdIty he lps eliminate troublesome and annoying rnterterence . genera l hash cre.ated by small motors. lluorescenI lamps. and the hk e that threate n the performance and shorten equIpmenI life of unprotected etectronrc components PRINTER STANDS ~ i TOP OF THE RANGE BUDGET famous MOUSE ' · Microsoft QUICK conipatlble MOUS reamllne design t S an amazing Image $29.95. onl o· KEYBOARDS CPF CONTINUOUS POWER FILTER SPIKE ARRESTOR 1 look. X11105 ... .. ....................... $199 Power supply to suit (220W) X11102 ............. ..$199 ROD IRVING ELECTRONICS HAVE THERE NEW 116 PAGE 1992 MAIL ORDER CATALOGUE OUT NOW!! PICK UP YOUR FREE COPY AT ANY OF OUR STORES. 100 x 5 1/4" ECLIPSE 018042 ........................ $11.95 40 x 3 1/2.. ECLIPSE C18040 ........................$8.99 120 x 3 1/2" LOCKABLE 016039 ........................$21.95 100 x 51 /4" LOCKABLE 016020 .................... ..... $13.95 50 x 5 1/4.. LOCKABLE 016025 .. ................:.. .. .. $11.95 120 x 5 1/4" LOCKABLE 018028 ........... .. ............ ,19.95 with Tlmer........$169 ....,Jl'f:tl'!l!!,,~~-----.aii . BUDGET IBM JOY STICK compatible with IBM, Pc. XT, AT Elegant apptarance & durable mechanism Auto return cantering An lncredlbla •••••••••••..• $24.95 Z•NIX BUS MOUSE ANO WINOOW?J 1 !:ckag• \.. ·.;;">(/ Change ""the way you URI your computer $189 Microsoft Compatible FREE mouae · houae & mouae mat Plus FREE pop up menu ooftware X19955 ...................... $69.95 SUPER BUS MOUSE 2 DESIGNED TO FIT THE PALM ·,. / ·. OF YOUR H A N O I ~ GREAT FOR , SAVING A SERIAL PORTI ~ , 2 FREE TELEPAINT DISKSI X19951 ... .. .... .................. $119 MICROSOFT MOUSE The top of the range! Support& hunderda of application a. FREc MICROSOFT PAINTBRUSH SOFTWARE BRINGS YOUR COMPUTER TO LIFE. X19958 ........................ ,179 IBM' CARDS - . . ,121 XT HD CONTROLLER....... AT HD CONTROLLER....... ,149 RS232/SERIAL CLOCK......49 MONO COLOUR CARD.......71 MULTI 1/OCARD................. fH PRINTER CARD ...................29 EGA CARD..........................179 DIAGNOSTIC CARD............791 TTL PRINTER...................... '89 IM AT EX/EXP......................321 FAXCARD........................... HH 4 POAT SERIAL CARD ...... •111 2 WAY FDD CONT (3110) ......39 RS/232 SERIAL CARD .........39 GAMES CARD ..................... '21 AT 8/P/G 2 S/P/Q ................ "49 4 WAY FDD CONTROLLER (380•1.44M).......................... 121 2 WAY FDD CONTROLLER (380-1.44M)......................... '89 CLOCK CARD.....................31 SMART DRIVE ADAFITOR IDE/FDC............................... "41 SMART DRIVE ADAPTOR IDEI/OFDC......................... 189 512K/578K RAM CARD .......... VGA CARD 18 BIT 250K.... 181 VGA CARD 18 BIT 5121<. ... $121 VOA CARD 18 BIT (1 MEO).$181 ' LEDS ~I== ~I== i : BNC MALE PLUG ,: 1-8 10-89 100+ ,: ,: :, ,: ' """ ~ "·~ ,: BNC PANEL SOCKET ., •• 1-8 10+ 100+ :; : Pt0516 $2.50 $2.25 $1 .50 . •. -LU BNC CRIMP PLUG 1-8 111-98 100+ ·• Pt0530 $3.95 $3.75 $3.00 i I Q[® BNC SOLDERLESS TWIST ON PLUG :- } { ( :·:: / ) QUALITY 5mm LEDS / ( Z10150(R). S0.15 S0.12 S0.10 Z10151(C). S0.25 S0.20 S0.18 ( Z10152(Y).. S0.25 S0.20 S0.18 } / ( ( ( FLASHING LEDS / RED 5mm 1-9 10+ :::: 210159 s 1.10 s1.oo QUALITY 3mm LEDS 1-8 111-98 100+ Z10140(R) S0.1.~ S0.12 S0.10 Z10141(C).. S0.20 S0.18 S0.15 Z10143(Y).. S0.20 S0.18 S0.15 Z10145(0) .. S0.20 S0.18 S0.15 ------== r-- 7 I PICK UP YOUR NEW 1992 MAIL ORDER -. CATALOGUE AT ANY Of OUR ROD IRVIIIG I I ELECTRONICS STORES or PHONE 008 33 5757 : FOR YOUR FREE COPY or WRITE TO PO aOX 620, I I CLAYTON, MELB. VICTORIA. 3161 I .. I Designed to transmit at 40kHz (L 19990) & recieve at 40kHz (L 19991) withup to 20V 1/P on the transmitter. These units can't be heard so are ideal for TV remote controls, water level dectectors. burglar alarms, motion dectectors & information carriers as they can be either pulsed or used in a continuous wave mode. Transmitter 1-9 10+ L19990 ....... $2.95 $1.95 L---------------------------.J \ KEYBOARD ~ RECTANGULAR LEDS •• RED PANEL METERS '' ORANGE 1-9 C: CANNON TYPE 3 PIN LINE FEMALE 1•9 111-98 ,100+ Pt0964 $3.95 $3.50 $2.90 a CANNON TYPE 3 PIN CHASSIS FEMALE 1-1 111-98 100+ P10966 $4.95 $4.50 $3.50 LOW PROFILE IC SOCKETS Savo a small fortunt on ]: thast "Dlroct Import" low •::::: profllt IC sockets! PCB mounting 1oldor 1111. All tin plattd phosphor bronza or btrrylllum and dual wipe for r•ll~~~tt~~ 100+ P1osso a pin 15e 12e 1oe P1058014pln 20e 18e 15e P1osss 16pln 2oe 1se 1se P1056718pln 30e 25e 22e P1osss 20p1n 35e 30e 25e P10589 22pln 35e 30t 26e ::: P1os10 24pln ase 30e 2se P1os12 28pln 45e 35e 30e P1os1s 40pln 45e 40e 35e 1 n,; ~-- • II• oonduotor ohlelded .,,.,,ui.. lnlMI•• Olble. Wt 2e10 • c1ce 1•1M 10Mt e con. 100Mt ,1.30M ,1.1OM ,1 .00M W1H72 • CICI I con. 1-1 M 10Mt 100Mt ,1,IIOM ,1,IIOM ,1.20M W1H74 • CIC12 12 con. 1•1M 10M ♦ 100M ♦ '2,IIOM '2.20M ,1.IOM W1H7e • CIC11 ,. con. 1•1M ICM ♦ 100M♦ '3,5OM f3,2OM '2.50M W12978 • CIC25 25 con. 1·1M 10Mt 100M+ S3,IOM S3,40M S3,00M 100+ :",: ) ::::/ ::;:: 0B25 CONNECTOR SPECIALS 1·9 10+ P10880 DE9P $1 .00 $0.80 P10885 DE9S $1 .00 $0.70 P10891 DA15S $1.00 $0.70 P10892 DA15C $1.00 $0.90 P10895 OA15S $1 .00 $0.80 P10902 DB25C $1 .00 $0.80 P10904 0825P $1 .00 $0.80 P10905 DB25S $1 .00 $0.80 D TYPE IDC SOCKETS 1.9 10+ 100+ • DESS 8 pin IOCkel P121&1 $1.50 s1.20 s1 .oo • DA15S 15pln 1ockel P121&8 $1.50 $1.20 s1.oo 28 ~~: ;:,~ $l.50 sr~~ i, -1-9 10+ • Plug P12200 so::~~ p~::, 5 q~~;~l~v! l~ lrt .,,: ' wrap IOCkttl ... tin pl1t1d if pho ■phor bronzt, ,:::::,:, .. COMPUTER CABLES 10+ • DE9P Spin plug P12166 $1 .50 $1.20 $1.00 • DA15P 15pln plug P12168 $1.50 $1.20 $1.00 , DB25P 25 p1,1 plug P12110 $4.50 $3.95 $3.50 CANNON TYPE 3 PIN LINE MALE WIRE WRAP Save a fortune on expensive throw away batteries with these quality Nicads and Rechargeral Size AA '50mAH D TYPE IDC PLUGS CANNON TYPE 3 PIN CHASSIS MALE 1-9 111-98 100+ P10962 $3.50 $2.95 $2.50 MONITOR& SWITCH BOXES only $69.50 ,.·• GREEN YELLOW CANNON PLUGS AND SOCKETS 2 WAY................ $59.95 4 WAY................ $69.95 ::~:!~ ~:~7n :::: :::~~ ,]/rn') :l'!!!-.•...............,......,....- . - ~ :,::r · P1O585 18pln SUS SUD P10587 1apln sus .,.ao ]' P1O510 20pln SUS $2.75 :} P1OH2 22prn sus S2.7O ... P1OH4 24pln ,ue S3,IIO P1O5H 28pln .3.H .3.50 P10H8 40pln •us '4,10 VOLTAGE REGULATORS BARGAINS DINripUon 1•1 10 ♦ 780SUC 7812UC 7815UC 710SUC 711 ZUC 711 SUC 78LOS 78L12 LM324 HS '''°°°•IO .so '°f(l,'553000 '°·110 f0,40 f0,40 .,.oo f0,40 741 f0,50 '°'41 ''°°''4415 '°•" '°•" '°·" $0.30 f0,30 f0,10 f0,38 f0,45 We have a great range of /:. panel meters at great :) prices! ::',:, 010500 MU4S 0-lmA $9.95 J g; ~:~ ~~:: ~~:~: ::::~ },:: :) :{ }':' :·::,:; 1-9 2155 240V ll-15V 1A M12155 .........$8,95 $7,95 2156 240V 6-15V A2 M12158 ........ $13.95 $12,95 2851 240V 12•6V CT 250mA M12851 ......... $4,15 .. S4,50 6612 240V 16 30vc 1A tapped M1111a ........ Cl __) 12V DC FANS 10 • 10 • aurnrn 12V DC, 1,7 WIii 0,14 Amp T124H................. 18,H 10• l1n1, only t17.H FANS Quality l1n1 for u ■a In 1mp1, oomput■ r hot ■pol ooollng ■to. Anywhere you nttd plenty pow ■ r ol ■ lr. 24OV 4 1/1" TI 2411 .. JI l.01 111V 4 Ill" T1Z413 .. J1UI 240V 3 1/2" T12481 .. J1 UI 111V 3 1/2" T1Z487 .. S1Ue 10♦ l1n1 (mlaod) Only 114.16. 10+ $2. 75 100+ $2.50 $9.95 $9.50 SizeD 12AH $9.95 $9.50 $8.95 HEATSINK COMPOUND ~ 010533 MUS2E 0-SUA $12.95 010538 MUSS 0,SOuA $12.95 010540 MU6S 0•1mA $12.95 Heatsink compound ia 0105S0 MU6S0-100uA$12.9S : applied to the baae and 010560 MU6S0-20V $12.95 : mounting studs of .:• transistors & diodes. It MOSFET '.: maintains a positive SPECIALS ,· heataink aeal that :. improves heat transfer · from the device to the heatsink, thus .:' increasing overall ~O+ •• efficiency. $9.50 $8.00 : H11800 .. 10g ...$2.00 $10.00 $9,50 $8.50 $9.50 ,1us •1us s 3.95 s 3.oo I/ ~ 1•9 $2.95 Size C 1 2 AH $8.00 $8.110 TOGGLE SWITCHES : H11810.150g. $29.95 - WIRELESS MICROPHONE Tuneable:92·104MHz Freq raaponH: so. 15kHz, R■nge: over 300 feet In open field, A10450 .......... $24.95 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. Scanning facility for a CB radio This circuit gives a scanning facility to an electronically tuned CB radio. In order to add this modification, the radio must have a PLL chip with either a single UP/DOWN channel control pin, or two individual pins to control channel selection. It can scan either up or down and will halt momentarily when it detects an audio signal. It will then continue scanning until it finds another signal. The circuit can be broken into four sections: audio detection, 555 oscillator, latches and the output interface. Let's start at the 555 oscillator which produces a 3Hz pulse signal which is fed to AND gates IC3b and IC3c. NOR gates IC5d and IC5d are connected as an RS flipflop with UP and DOWN buttons connected to their inputs. If the UP button is pressed, IC5c's output latches low and IC5d's output latches high which enables gate IC3c to feed the 3Hz signals through to the output interface consisting of Ql, Q2 , Q3 & Q4. The 3Hz signal then causes Ql, Q2 & Q3 to turn on and off and thus cause the radio to step up the band three times a second. Similarly, if the DOWN button is pressed, IC5d's output latches low and IC5c latches high. AND gate IC3b now feeds through the pulse signals to Q4 . This causes the radio to step down the band at three times a second. When the radio comes to a channel with an audio signal present, audio detector stage ICl is driven hard into clipping. The clipped output signal triggers monostable IC2a which produces a pulse to disable the 555 oscillator for one second. In practice, while ever a strong audio signal is present, the 555 will be disabled and scanning will stop. One second after the audio signal ceases , the 555 will be enabled and scanning up or down the band will continue. NOR gates IC5a & IC5b are connected as another RS flipflop. One input is connected to the STOP button while 12 SILICON CHIP + 5 v - - - . - - - - - - - - -.......- - - - - - - + - - - - - - . 01 1N4001 AUDIO INPUT ~-·;,01 2 100kr >'!..-......- ~-T AC 06 + SV IC2a 4· +T 4538 iil-'7--4---'-r R 10n 3Hz +SY IC4: 555 .sv-~-----, STOP! S3 I 3300 +13.SV 211 N4148 02 5.1k 03 DOWN,T S2 TD PLL 33011 04 BC547 330\l the other input conn_ects to a diode OR gate (D2 & D3). If the radio scans through to a channel you want, pressing the STOP button causes the output of IC5a to go low and thus causes the output of IC3a to go low. This disables the 555 until the UP or DOWN button is pressed. In use , the radio's volume is set to the normal listening level and the squelch control backed off so it is just about tripping. You then adjust VRl until the output of the LM386 begins to clip, then wind the squelch back to suppress any background noise. When a signal just breaks the squelch, a nearly-clipping waveform will appear at the output of the audio amplifier. A strong input signal will produce a well pronounced clip, which is the desired result. Two types of PLL chips can be used with this design. The first is the C5121 which has a single UP/DOWN pin. The other is the SM5123A/SM5125B which has separate pins for UP and DOWN. If the latter PLL IC is present, the transistor interface is not required, and the outputs of IC3b & IC3c can be connected directly to the PLL chip itself. The relevant pin connections are to pin 20 (Up/Down) for a C5121 and to pins 23 (Up) & 22 (Down) for an SM5123A/SM5125B Steven Merrifield, Newlyn, Vic. ($35) +20V +SV 20 10~ A2 A3 A4 +10V 10k: D1 IC2 74LS374 .01 1k ENABLE 1k .01 ~ .,; ,.; DIRECTION STEP LENGTH .,. 0 11 0 0.1 .,. 10 CLOCK · I 89mm STEPPER MOTOR GREEN MOTOR COIL PHASE 2 +20V . 0.1I D3 _ 1N4001 10k 4.7ll ,ow. 10k .01 1k 1k .01 - .,. D4 1N4001 •SEE TEXT T This is the circuit for the stepper motor driver, together with its state machine. The bubbles in the state machine describe the output sequences from the EPROM, while the arrows joining the bubbles show the possible paths that the state machine can move to on the next clock cycle. EPROM-based stepper motor driver A stepper motor operates by energising different coils around the armature. There are four coils and when full stepping, each coil is energised in turn. In the half step mode, the armature is made to stop in between two steps by energising two adjacent coils. (Refer to "An Introduction to Stepper Motors", SILICON CHIP, August 1989 for a complete discussion of why this works). The circuit shows the state machine for half stepping the motor. Each bubble shows one energised state of the motor. The arrows connecting the bubbles show the possible paths the state machine can move to next. To full step the motor, every second bubble is in an energised state. If we were at state 0101 and were half stepping in a clockwise direction, 0001 would be next. If we were at state 1000 and were full stepping in an anti-clockwise direction, 0001 would be next. The EPROM is programmed with the state machine. Any EPROM could have been used, but 2732s and 2764s are currently the cheapest and the easiest to obtain. The address pins are used as inputs to the system. The outputs from the octal D-flipflop are fed into the EPROM as a feedback. The EPROM thus knows the current state of the state machine. The inputs, direction, step size and enable, together with the current state, determine the next state for the machine. When the octal D-flipflop is edge triggered by the clock, the data from the EPROM is loaded into the flipflops and the state machine moves into its next state. An edge triggered flipflop was chosen over a bus transceiver as the circuit could race if the clock pulse to the transceiver was too wide. Using edge triggering, the possibility of this occurring is reduced to a minimum. Each time the clock is pulsed, the motor will step according to the inputs. If the enable is high, all outputs will go fow when a clock pulse is received, effectively turning the motor off. The outputs of the flipflops feed the inputs to the LM380s that provide the actual drive for the coils. This part of the circuit was originally published in Circuit Notebook in July 1990. The 4. 7Q 10W resistors provide current limiting and may need adjusting to suit the stepper motor used (the coil current should not exceed 1A). Virtually any state machine could be constructed in this way. If more inputs or outputs are needed, several EPROMs can be cascaded together. The program can be constructed by drawing the state machine and working out what the inputs will be. These will form the addresses and the desired output becomes the data to be stored. Marque Crozman, SILICON CHIP. Program For EPROM-Based Stepper Motor Driver 0000 09 09 09 09 04 06 01 09 02 0A 04 05 06 02 05 01 0010 08 09 02 06 00 00 00 00 0A 08 06 04 00 00 00 00 0020 01 05 08 0A 05 04 09 08 00 00 00 00 00 00 00 00 0030 09 01 0A 02 00 00 00 00 00 00 00 00 00 00 00 00 APRIL 1992 13 The new digital oscilloscopes are rapidly changing the way we think about measuring equipment. They offer a stunning range of measurement options, have large bright screens and can be hooked up to a computer for data acquisition. We recently took a look at Yokogawa's model DL1100 and came away impressed. By LEO SIMPSON Yokogawa's 2-channel 100MHz digital CRO okogawa's DLl 100 digital scope really doesn 't look like any scope you've used in the past. It's fairly tall but not very wide or very deep and it has a bigger than normal screen. The unit's dimensions are 204mm wide, 270mm high and 333mm deep. Its overall screen size is 140 x 110mm and the graticule area is about 110mm wide by about 93mm deep, which is larger than a conventional scope's screen. It weighs 8kg. But look at all those buttons. And only one knob. At first glance, there are so many buttons that it is a little off-putting. What do they all do? After you get over the first bit of culture shock, you realise that quite a few of Y 14 SILICON CHIP them have labelling which is more or less self-explanatory. But to initially display a waveform on the screen you don't have to fiddle with all the screen settings. You.just push the Auto Setup button (just underneath the round knob). This brings up an "Auto Exec" legend up in the bottom lefthand corner of the screen. Pressing the screen button immediately under the legend then causes the scope to click relays and things inside and within a few seconds it brings up a stable display together with the vertical sensitivity, probe division ratio and timebase setting. Also displayed is the date and time. From there, you can then push the "V/Div" button which allows you to use the front panel knob to vary the vertical sensitivity in the normal 1-25 sequence, (eg, lV/div, 2V/div, 5V/ div, etc). The range of sensitivity is from 2mV/div up to 5V/div, assuming a 1:1 probe. If you press the Input button for either channel, you nominate the probe division ratio (1:1, 10:1 or 100:1) and the correct vertical sensitivity and probe ratio will be displayed in the top righthand corner of the screen. Now suppose that you want to vary the timebase setting. To do so, press the "Time/div" button and again you can vary the settings in a 1-2-5 se- ~d -FEB- 199? ~Q:~7 T ICHJ =5v--~ DL1100 CONDITI ON REPORT Ver. 1. 00- 20H 10n s/ d AC P*lO : \ 2. TI ME/ di 11 I 10ns / d i vl SAMPLE RATE 3. TRIGGER 4. ACQUI SITION 5. SAMPLING 6. DATA l ENG TH +++ [IORMAL] ~MS ~~ InGc u r.: ?V RSHT: [REPEAT ' CE3Rl The amber screen is, as with other digital scopes, a raster scanned tube as used in computer monitors. Thus, the display is made up of very fine dots. Screen resolution is very high although this is not covered in the specifications. By close inspection with a weaver's pick (a magnifying glass used by printers to examine print quality), we were able to determine the horizontal resolution at 500 dots (actually 501). Proportionally then, vertical resolution must be close to 400 dots (actually 401). When related to screen size, this order of resolution is roughly ~ 17. 0V 1~- ~ ~ 8V - 1.0V 1 ., s: ]¼ '' :' : R!St, 20. 7n~ FAL L rD~ A --PER l KI D ------ -- ~~!R 1m ------ ------- - - '' ' : ' '' - These printouts apply to the same waveform measurement. The tabulated values on the left are printed out by asking for the measurement conditions. The waveform on the right shows the fall time (20.7ns) of the square wave available from the audio oscillator published in the January 1990 issue of SILICON CHIP. Dot matrix screen \ 10Msei P: -P MAX M JIM quence from 10 nanoseconds per division (lOns/div) up to 50 seconds per division. That last figure is not a mistake. At the lowest timebase setting, the trace does take 50 seconds per division and a total of 500 seconds (8 minutes and 20 seconds to creep across the 10 divisions on the screen. This is just one aspect where this digital scope is dramatically different from conventional analog scopes. Why would you want such long sweep times? Well, why wouldn't you? There are any number of occasions where it would be nice to be able to measure and record long term variations in signals. Now you can do it and better still, you can take a permanent record with the inbuilt printer that sits in the top of the unit. ' : equivalent to a VGA monitor. Suffice to say though, the display is very fine and most of the time you are not aware of the dot structure. Indeed, you have a bunch of options as to how the display is presented. Pressing the Display button brings up a menu at the bottom of the screen, with each menu option corresponding to one of the- six buttons immediately below the screen. The function of the softkeys naturally changes for each menu and each function button that is pressed, so the number of screen adjustable parameters runs into the many hundreds. So back to the Display menu: this has two options for interpolation, LINE or SINE and the option for dot connection, ON or OFF. In addition, there are menu selections for Grid Select and INTensity adjust, which we'll come to in a moment. As we have already indicated, the screen display is made up of dots and so the channel traces are also dots, with the number for a waveform cycle being determined by the sampling rate (up to 20 megasamples per second) and the timebase frequency. Most of the time though , you don't want to look at a waveform which is just dots so you choose one of the interpolation options which means "connect the dots". The LINE option connects the dots with short vertical straight lines while the SINE option uses an algorithm to connect the dots still with vertical lines but with a better approximation to sine waveforms. In practice though, unless the waveshape is critical and you have keen eyesight, you won't be able to tell the difference. Now to the Grid Select menu; this gives three possible graticule patterns: Frame, Grid 1 and Grid 2. Frame just encloses the screen area with an outline rule. Grid 1 divides the screen up into vertical columns 11mm wide; ie, 1 division. Grid 2 is the conventional crosshatch graticule pattern as shown on all the screen photos accompanying this article. Next, you have Tick and % Marker on or off. "Tick" is (are?) the central vertical and horizontal axes of the graticule but divided into fifths; ie, 0.2div. "% Marker" are the conventional 0%, 10%, 90% and 100% horizontal rules that you would use when measuring the rise and fall times of square waves and pulses. Finally, the INTensity option allows you to vary the brightness of the dis- · played waveform, the grid and the readout messages, either separately or all together. So you can see from all these functions, which are brought into play just with the Display button, that there are literally many hundreds of options you can play around with to best measure and display the waveforms you are interested in. On the rear panel of the instrument are a pair of BNC sockets, one for a trigger output and the other a TTL signal used for when the DL 1100 is configured as a GO/NO GO tester. Also present are sockets for the IEE-448/ GP-IB (general purpose instrument APRIL 1992 15 Worst case jitter can be easily captured on the DL 1100 using the Dynamic Accumulate mode. You just select the period of time for which you want to accumulate data & the jitter information is compiled on the screen. bus) and RS-232 interface so that the unit can be used for data acquisition or remotely controlled by a computer. One point about the fan should be noted. If you are using the scope in a quiet lab, the fan is noticeable and can be irritating. On the other hand, if you have computers, printers and other fan-cooled gear around, you probably won't notice the DLl 100 at all. Measurements The "Measure" button brings into play a lot of options. Pressing the button brings up the first menu which gives you options of AUTOmatic or Manual functions. Pressing the AUTO softkey then brings up a whole range of on-screen measurements which are superimposed directly over the displayed waveforms. This latter point can be an irritation at times because you may want to see the complete waveform and all the relevant readings, without any interference between the two. You can now use the softkeys to further select which automatic measurements you want and those to ignore. If you select all the AUTO measurements, you will have displayed readings for 13 waveform parameters, including peak-to-peak, maximum and minimum values, RMS, rise and fall times and frequency. If a waveform has a lot of noise or jitter, you can go to the Acquisition menu and select for normal, envelope, average smooth or decimate 16 SILICON CHIP This photo shows a pulse waveform with accompanying measurements for risetime & overshoot. Note that sampling has been stopped to get a stable waveform on the screen. modes and these will either capture or eliminate much of the hash, depending on what you want. You can also use Window and Zoom modes to extend the timebase by up to 1000 times to display glitches which may be only 1 nanosecond long. Make no mistake, this is a very powerful instrument. Alternatively, you may want to record and display all the jitter. In this case, you call up the Accumulate menu and you can display the jitter over a range of times. The Start/Stop button is also a very useful facility. Say you are displaying a pulse width modulated waveform with a lot of motor commutator hash on it. Such a waveform can be difficult to examine properly because the hash causes it to jump around a lot, even if it is properly triggered. In this case, you have several options. Just pushing the Start/Stop button will freeze the display so you can get a good look at it. Alternatively, you might decide to go into short or long single shot mode to capture a picture of the waveform and store it for later examination and reference. And this is where the exceptional storage capacity of this digital scope really impresses. With a 1 millisecond time record, you can print it out with a resolution of 1 nanosecond. You should see the length of the printout - it runs for metres and metres. You can use it to store and examine long data trains, infrequent glitches, you name it. And to go back to that difficult PWM waveform with motor hash on it, you can always take the easy way out at any instant and just take a printout. It will also print out the scope's settings (ie, those not already displayed on the screen readout) such as trigger, acquisition and sampling mode, sampling rate, data length and so on. The question of sampling rate has already been covered to some extent and it varies according to the measurement conditions. Maximum sampling rate is 20 megasamples/second (with two simultaneous phenomena). This results in a maximum storage (and display) bandwidth of 8MHz for a single shot display and 100MHz (-3dB point) for repetitively sampled displays. The maximum memory size is 32K words/channel for single shot mode and 10K words/ channel in normal mode. Compared to competing brands, this is quite an extensive storage capacity. Settings saved When you turn the scope off, it automatically saves all your control settings. In this way, if you have a particular measurement setup, you don't have to go through it all again when next you switch on. On the other hand, having all settings saved can put a crimp on proceedings if you weren't the last person to use the instrument. The machine may not be able to do an "Auto Setup" in these conditions and so the way out is to continued on page 55 AVAILABLE THE 1992 FORCE ELECTRONICS CATALOGUE Over 4000 Products stocked. 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"My Power 200" 12VDC to 240VAC Inverter Simply plug this amazing product into your cigarette lighter socket to get 240 Volt AC power. Fitted with Australian 240V mains socket. SPECIFICATIONS: -140 Watt continuous -200 Watt peak -400 Watt surge PROTECTION includes: over voltage, under voltage and overload, fused input and output. Low battery indicator and audible buzzer. LED indicators for in/output voltage. Robust black anodised aluminium case. size= 50 x 135 x 74mm . 12 MONTH WARRANTY MADE IN AUSTRALIA. ONLY $199 Studio Twin Fifty Stereo Amplifier, Pt.2 Last month, we introduced our new high performance stereo amplifier and described the circuit operation. This month, we present the construction and troubleshooting details. By LEO SIMPSON & BOB FLYNN Most of the construction of the new amplifier is quite straightforward. The work mainly involves mounting components on the three printed circuit board assemblies. These are for the power amplifiers, the phono preamplifier, and the tone control and headphone amplifier circuitry. There is relatively little wiring inside the chassis. This is because all the pots, the headphone socket and the pushbutton switches (but not the mains switch) are mounted directly 18 SILICON CHIP on the tone control board. Similarly, the rotary input selector switch is mounted on a small PC board which is then soldered at right angles to the phono preamp board. Mounting the switches and pots in this way eliminates the tedium of running separate leads to the terminals of these components. It also greatly reduces the possibility of wiring errors. We understand that at least two kitset suppliers, Altronics and Jaycar Electronics, will be selling kits for this project. Both the Altronics and Jaycar kits will come with a prepunched chassis and the front panel labelling will be silk-screened. Starting construction The first job is to assemble the phono preamplifier board. This board is coded SC01103921 and carries the parts for the phono preamplifier and the RCA input and output sockets. It also carries six sets of stereo tracks which run between the RCA sockets on the rear panel and the selector switch at the front of the board: An additional set of stereo tracks run from the Tape In sockets to three pins on the front of the PC board. Before mounting any of the parts, it is a good idea to carefully check the copper pattern on the underside of the board. You should especially check for shorts between the long parallel tracks to the selector switch. Don't just rely on a visual check .. • • PHONO CD TUNER VCR AUX1 M AUX 2 TAPE OUT TAPE INPUT Rt GND• TAPE IN L• Fig.5: the parts layout for the phono preamplifier board. Install the 23 PC stakes at the external wiring p~ints first, then install the remaining parts exactly as shown. The capacitors marked with an asterisk should be close tolerance types. here - switch your multimeter to a high Ohms range and use it to confirm that the tracks are isolated from each other. This test will quickly locate faults on any board that has not been correctly etched. You will need to go through a similar checking procedure with each of the other boards when you come to them. Fig.5 shows the parts layout for the phono preamplifier board. The first job is to install the 23 PC pins. Fourteen of these support the selector switch assembly and these should be installed from the copper side of the PC board; ie, so that the shoulder of each pin sits against its respective copper pad. Another three PC pins are required for the power supply connections near the centre of the board (+15V, 0V & -15V), while the six remaining pins are located at the left and right channel outputs and the tape inputs. No particular order need be followed when installing the remaining parts on the board but it's best to start with the smaller parts (resistors and wire links) first. Check the values of all resistors with your multimeter before installing them on the board- it's .all too easy to misread the colour codes. You'll also notice that four of the capacitors (two in each channel) are marked with an asterisk. These capacitors are in the feedback network of the phono preamplifier and, ideally, should be close tolerance (5% or better) types in order to obtain accurate RIAA equalisation. If you have a capacitance measuring function on your digital multimeter, you can specially select these capacitors. If you are buying a kit, the kitset suppliers may elect to supply 5% capacitors or may also hand select the capacitors. Take care with the orientation of the LM8 33 IC and the electrolytic capacitors. The two input inductors (L2) are made by Philips (type 4312 020 36760) and are soldered straight into the board. No fiddly winding is required. Construction of the phono preamp PC board can now be completed by soldering in the three 3 x 2-way RCA socket panels. One of these, adjacent to the LM833, is cut down to a 2 x 2way, so that a total of 16 RCA sockets is provided. Selector switch assembly Fig.6 shows the details of the selector switch board. Position the switch with the locating pin towards the top and push the body of the switch all the way down onto the board before soldering the terminals. The pads along the bottom edge of the switch board can now be soldered to the 14 PC pins on the phono preamplifier board. Tone control board Fig.6: the selector switch should be mounted on its board with the locating pin towards the top. Check the PC pattern carefully to ensure that none of the input pads are shorted together. The pads along the bottom of the board are soldered to the 14 matching PC pins on the phono preamplifier board. · Fig. 7 shows the parts layout on the tone control PC board (code SC01103923). Commence assembly by installip.g PC pins at the external wiring points , then install the wire links, resistors, capacitors and semiconductors. Check the orientation of polarised parts carefully when installing them on the board. These parts include the three !Cs, four diodes, four transistors and the electrolytic capacitors. The 6.8µF and 22µF capacitors are bipolar APRIL 1992 19 15mm tapped spacers and screws. Don't fit the dress panel to the chassis at this stage. It should be left in its protective wrapping for as long as possible, to protect it from scratches. When all the pot nuts are secured, use your multimeter to check that all the pot cases are electrically connected together, via the chassis. Ifnot, it might be necessary to remove the board from the chassis and then take a round file to lightly clean off any paint or oxide from around the pot mounting holes. The reason for making sure that the pots are properly earthed via the chassis is to keep hum and noise to the minimum possible. Power amplifier board This view shows the completed phono preamplifier board with the selector switch board soldered to it at bottom right. The input RCA sockets are soldered directly to the phono preamplifier board & consist of two 3 x 2-way panels plus a single 2 x 2-way panel (cut down from a 3 x 2-way panel). types and can be installed either way around. Note that a short length of shielded cable must be wired into the board, adjacent to IC3. The headphone socket, pots and pushbutton switches should be left till last. Be sure to push them all the way down onto the board but don't solder all the leads at this stage. Instead, tack solder diagonally opposite pins at either end of each component. 20 SILICON CHIP The tone control assembly can now be tested in the chassis to ensure that everything aligns properly. Adjust the alignment of the pots and switches as necessary before soldering the remaining pins. That completes the tone control board. It can now be mounted in the chassis and secured using the pot nuts and lockwashers. The rear of the tone control board is secured using two The power amplifier board is identical to the stereo module published in our February 1992 issue except for some minor details. The specified heatsink is a 3mm-thick aluminium angle extrusion, 60 x 60 x 290mm long, with a cutout in the horizontal section to accommodate the toroidal power transformer. The component diagram for the power amplifier board is shown in Fig.8. We suggest that you mount the PC pins, resistors, diodes and wire links Below: check the orientation of all polarised components carefully when installing them on the tone control board. The pots, switches & headphone socket must be pushed all the way down onto the board before being soldered. e GND• 1~i~\ L• .C!L). 1uF (Ll OUTPUT TO POWER AMPLIFIERS D.5W ~ ~ R• Fig.7 (above): follow this layout diagram when wiring up the tone control board. The circuit diagram published last month shows the pinouts for the transistors. Fig.8 at right shows the parts layout for the stereo power amplifier module. Note that transistors Q7-Q11 in each channel are bolted to the heatsink before being soldered to the PC board (see text). on the board first, followed by the capacitors. There are only two electrolytics on the board, apart from those in the power supply. Make sure they are mounted with correct polarity. Most of the remaining capacitors are MKT polyester capacitors which have a standard lead spacing (pitch) of 5mm. We recommend against greencaps as they won't fit. The fuses specified are M205 20mm-long types, as widely used in commercial stereo amplifiers. All the TO-92 transistors (Q1 -Q3, etc) are mounted with the flat side facing towards the front; ie, away from the heatsink. Similarly, the TO-126 transistors (Q4-Q6, etc) mount with APRIL 1992 21 When you have assembled the stereo power amplifier, go over the board carefully & check that the correct transistor has been used at each location & that it is correctly oriented. The board should initially be tested with the fuses removed & 5600 5W resistors soldered across the fuseclips. the metal side facing to the front. The exception is Q7 which mounts with its metal face to the heatsink (with a mica washer, of course). The 0.4 70 3-watt resistors are made by Philips and have been specified to save board space, being a lot more compact than the common SW cement "bathtub" types. Mount them so that they clear the board by about 34mm. The 6.8µH output inductors are each wound on a Philips 4322-02130330 or Neosid 60-601-72 coil former using 24.5 turns of 0.8mm enamelled copper wire. Clean and tin the ends of the inductor before installing them on the board. Output transistors The way to mount the output transistors is as follows. First, all the Darlingtons and the two BD139s were mounted on the aluminium heatsink. In each case, they are mounted using the specified mounting kit consisting of a mica washer and plastic insulating bush for the screw. Heatsink compound is applied sparingly to both sides of the mica washer before it is set between the transistor and heatsink. The details are shown in the diagram of Fig.9. With all the transistors mounted on the heatsink, set your multimeter to a low ohms range and check that the transistor collectors are isolated (ie, 22 SILICON CHIP infinity resistance) from the heatsink. That done, set the heatsink upside down on your workbench and fit the PC board over the transistor leads. You may need to adjust some of the transistors so that their leads line up with the board holes. Tack solder a couple of Darlington transistor leads at each end so that the top board surface is about 8mm from the bottom edge of the heatsink. You will also need to slightly crank the leads of the BD139s (Q7) to line them up with their respective PC INSULATING MICA WASHER w,~jl SCREW I llllllD(3 -......._HEATSINK t T0220 DEVICE Fig.9: transistors Q7-Q11 are each isolated from the heatsink using a mica washer & insulating bush. Smear the transistor tabs & mica washers with heatsink compound before bolting the assemblies together & use your multimeter to check each transistor as it is mounted to ensure correct isolation. board holes. When you are satisfied with the lining up of the board, solder all the transistor leads to the board pattern. You will also need to make some wire connections underneath the board, before it is installed in the chassis. These are shown in the diagram of Fig.10. First, run a length of hookup wire between the +38.SV power supply output and the +38.SV input to the left channel. Second, run two wires from the GND points to the main board earth point between the two 4700µF power supply capacitors. Twist the wires together as shown in the diagram. The next step is to install the phono preamplifier board which has the selector switch board and RCA socket panels soldered to it. Before doing that though, fit the earth binding post (near the phono inputs) and connect a 380mm length of green hook-up wire to it. The other end will connect to the chassis earth point near the transformer. Now fit the two tapped spacers, one 10mm long and one 15mm long to the phono board. The 10mm spacer will mount over the horizontal section of the heatsink for the power board: Now place the phono preamp board into the chassis and secure it to the rear panel by means of 12 small selftapping screws into the RCA socket panels. Do not fit screws into the underside of the tapped spacers at this stage. The power amplifier board and its Fig.10: these power supply connections must be run on the underside of the power amplifier PC board before it is installed in the chassis. Use insulated hook-up wire & twist the leads to the GND connections together as shown. J,: .·. +38.5V L +38.5V TO LEFT CHANNEL CONNECTION MADE ON UNDERSIDE OF BOARD LF.FT ANO RIGHT CHANNEL EARTHS MADE TO JUNCTION OF FILTER CAPACITORS ON UNDERSIDE OF BOARD heatsink may now be slid into the chassis so that the horizontal portion of the heatsink slides under the phono board. Fit two 6mm long hollow spacers under the board and secure it in place with screws and nuts. Chassis wiring Take great care with the mains wiring -your personal safety depends on it. Fig.11 shows the chassis wiring details. The mains cord enters through a hole in the rear panel and is securely clamped using a cord-grip grommet. Strip back the outer sheath of the mains cord by about 35mm before connecting the Active (brown) and Neutral (blue) leads to the mains terminal block. The Earth lead (green/ yellow) is soldered to one of the adjacent solder lugs. The second solder lug terminates the earth lead which is run along the rear panel from the binding post terminal adjacent to the phono input sockets. Don't alter the earth wiring you may get a hum loop if you do. The primary leads of the transformer are connected to the mains terminal block, while the 25V sec- Below: this view, together with the chassis wiring diagram (Fig.11) on the following page, shows how everything fits inside the case. Orient the power transformer so that its leads face towards the front panel this is important to achieve minimum hum). APRIL 1992 23 RESISTOR COLOUR CODES 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 No. 2 2 6 12 2 2 2 4 8 4 2 2 10 4 4 2 12 2 4 2 Value 4-Band Code (1%) 5-Band Code (1%) 1MO brown black green brown r;ed black yellow brown brown black yellow brown red red orange brown brown grey orange brown brown blue orange brown brown green orange brown brown black orange brown yellow violet red brown orange white red brown brown grey red brown brown green red brown brown black red brown blue grey brown brown brown grey brown brown brown green brown brown brown black brown brown blue grey black brown brown green black brown blue grey gold brown brown black black yellow brown red black black orange brown brown black black orange brown red red black red brown brown grey black red brown brown blue black red brown brown green black red brown brown black black red brown yellow violet black brown brown orange white black brown brown brown grey black brown brown brown green black brown brown brown black black brown brown blue grey black black brown brown grey black black brown brown green black black brown brown black black black brown blue grey black black gold brown brown green black black gold brown blue grey black silver brown 200kn 100kn 22kO 18k0 16kn 15kO 10kO 4.7kn 3.9kO 1.8kn 1.5k0 1kn 6800 1800 1500 1000 680 150 6.80 ondary and centre-tap leads are soldered to three PC pins on the power amplifier board. Be careful not to transpose the centre-tap lead with one of the 25V secondary leads. To make it easier to solder the secondary wires to the amplifier board, we shortened the leads back and then added short extensions oflight duty hook-up wire, soldered and sleeved for secure connections. Be sure to use mains-rated 240VAC cable for the connections to the power switch. We used heatshrink tubing to cover the switch lugs and then covered the whole switch body with a larger piece of heatshrink tubing. The other end of the leads from the mains switch go to the terminal block, along with a .0lµF 250VAC "antithump" capacitor. Make sure that this capacitor is rated at 250VAC. Testing the board CAPACITOR CODES (10%) 0 0 0 0 0 0 0 0 0 0 0 0 0 24 Value IEC Code 1µF 1u0 330n 220n 150n 100n 0.33µF 0.22µF 0.15µF 0.1µF 820pF 470pF 330pF 150pF 68pF 33pF 2.2pF 820p 470p 330p 150p 68p 33p 2p2 SILICON CHIP EIA Code 105K 334K 224K 154K 104K 821K 471K 331K 151K 68K 33K 2.2K When the AC wiring is complete, do not add the shielded signal cables. The next process is to power up each board in turn and check that it is operating correctly. First, we do the power amplifier board, since it is the most involved. Before making any connection to the power board, check all your work very carefully against the wiring diagrams of Fig.8 and Fig.11. This done, remove the four 5A fuses and solder a 5600 5 watt resistor across each of the on-board fuseholders. These are current limiting resistors which reduce the likelihood of any damage to the output transistors in case you have done something silly like swapped a TIP142 for a TIP147. Next, solder two 2700 1W resistors across the low-voltage supply outputs - ie, between +15V & GND and between -15V & GND. These protect the regulators from excess input voltage until the tone control and preamp board supply lines are connected. Now apply power and check the DC outputs at the lefthand side of the board. The outputs marked ~38.5V and -38.5V can be expected to be around +45V and -45V because they are only lightly loaded. However, the ±15V regulated outputs should be close to their nominal values (note: the left channel amplifier is powered up during this test procedure) . Now connect the positive and negative supply leads to right amplifier Fig.11 (right): the chassis wiring details. Exercise care when installing the mains wiring & sleeve all exposed terminals on the fuseholder & switch with heatshrink tubing to prevent accidental contact. The leads between the mains switch & terminal block should be twisted together & should also be sleeved in heatshrink tubing. REAR PANEL SPEAKERS RIGHT LEFT GNO + + GND \.__r ACTIVE (BROWN) L_ COROGRIP -GROMMET X \~ LEFT OUTPUT PREAMPLIFIER PCB 6-- 4--•15V GND 5--15V POWER AMPLIFIER BOARD RIGHT SPEAKER~ J\ '-· '~:~' GND• GND + SOURCE ,,~. TONE CONTROL PCB ~ S6 FRONT PANEL APRIL 1992 25 running all the shielded cable and the speaker leads, as shown in Fig.11. You will also need to fit the extension shaft to the selector switch. This extension shaft passes through a plastic bush fitted to the front panel. Troubleshooting If the above measurements are not OK, the most likely causes are broken This close-up view shows the plastic bushing that's used to support the selector switch extension shaft where it passes through the front panel. channel. Set VRl fully anticlockwise in both channels - this gives the minim um setting for . quiescent current through the output transistors. Apply power again and measure the positive and negative supply rails. They should be within a few volts of ±38.5V. Now measure the other voltages on the circuit. They should all be within ±10% of the nominal values, depending also on whether your 240VAC mains supply is high or low (it is above 240VAC more often then not). The voltage at the output should be within ±30mV of 0V. Now switch your multimeter back to the Z00VDC range and connect it across one of the 560Q 5W resistors. Now adjust trimpot VRl for a reading of 22.4V. This gives a total quiescent current of 40mA. Do the same in the other channel. After five minutes or so, check the quiescent currents again and readjust VRl if necessary to get the correct voltage across the 560Q resistor in each channel. (If you are doing power tests on the amplifier and the heatsink becomes very hot, you can expect the quiescent current to at least double. When it cools down though, the quiescent current should drop back to around 40mA). Measure the voltage across each 0.47Q 3W emitter resistor. They should all be about 9-lOmV, which means that each Darlington transistor is getting its rightful share of the quiescent current. If all is well, switch off, remove the 560Q 5W resistors and the 270Q 1W resistors, and fit the 5A fuses. Now connect the ±15V supply wires to the tone control board and check the voltages on it. This done, connect the supply wires to the phono preamp and check the voltages on it also. If all these checks are OK, you can complete the wiring of the amplifier by tracks or solder bridges between IC pins. For example, if you have the correct supply voltages on an IC but its output is close to +15V or -15V, it is most likely that there is a break in the feedback network or to the inputs to that IC. You can follow this up by measuring the voltage at the input pins of the ICs. Again, these should all be very close to 0V. If not, check for breaks in the copper track, poor solder joints, and that the IC is not in the wrong way around. Note: if you've put the IC in the right way around, it is most unlikely that any malfunction will be due to a faulty IC. What happens if one of the power amplifiers is not working? If the other channel is working correctly, then you have an ideal cross-check. Check the voltages in the good channel and then in the bad channel and you can usually get a fair idea of what the problem is. It is unlikely that you will get the same fault in both channels, unless you have made the same assembly mistake in both! And now we'll give you a few clues which may help you solve any problems. First of all, let's assume that most of the amplifier voltages are correct but that you have zero quiescent current. Look for a short across VRl or Q7. If you have lots of current through the 560Q resistors and cannot control it with VRl, look for an open circuit in the 680Q base resistor .. l i i ' -s,,,..,,_~:"· _ _· . - 'i . t'l 26 SILICON CHIP The rear panel carries the RCA input and output sockets, an earthing terminal, the spring loaded loudspeaker terminals and the mains cord grommet . The power amplifier board is fitted into the chassis by sliding the bottom of the heatsink bracket under the phono preamplifier PC board. A cutout in the bracket provides the necessary clearance for the power transformer. to Q7 or a defect in that transistor. What if the output of the amplifier is fully latched up at either +38V or -38V? The most likely cause of this is a defect in the first or second differential pair of transistors, or something silly like the wrong transistor, say a BF469 where a BF470 should be. Sol_der bridges between tracks can also cause this fault. The above are the more common problems with build-it-yourself amplifiers. Most times though, you can expect the unit to work perfectly at switch on. Listening tests No, we're not going to listen to music - yet. The idea of the next few checks is to make sure that everything is really working as it should. You'll need a pair of headphones. Plug them into the headphone socket, turn on the power and listen. With the Volume control at mini- mum setting you shouldn't be able to hear anything. If you now select the phono input and wind up the Volume to maximum, you will hear some hiss and a small amount of hum. That is normal. If you now switch to the other inputs (CD, Tuner, etc), the noise should drop to extremely low levels (we doubt you'll be able to hear anything, even in a very quiet room). If you now plug a pair of shorting plugs into the phono inputs, the noise on the phono inputs should drop to much lower levels. If it does, pull the shorting plugs, wind up the Volume control and check the action of the Bass and Treble controls. The Treble control should boost and cut the hiss and the bass control should boost and cut the low frequency phono noise. The Balance control should shift the noise from left to right and the Mono/Stereo switch should also work. When in the mono setting, the noise should appear from right in the centre of your head. Switching to Tape Monitor should kill the noise and the Tone Defeat switch should kill any boost and cut effect of the tone controls. Now if all of these things don't check out, it is pretty easy to localise the fault to a particular section. For example, let's suppose that .t here is no noise on the phono inputs, but very faint noise on the CD and other inputs. OK, that means a fault in the phono preamplifier but provided the voltage measurements here were correct, then you probably have an open circuit between the phono LM833 output(s) and the selector switch. Remember too that if you have a fault in.one channel, you can usually track it down by comparing the operation of the circuitry in the good channel with that in the malfunctioning channel. The front panel can now be mounted but be careful - one scratch and you'll ruin the appearance of the whole project. Fit the lid to the case and the job is finished. SC APRIL 1992 27 .,, Now's the perfect time to check out our new April arrivals! This month you'll find a great range of new kits, tools and switches. As well, there's old favourites like our sensational Shortwave receivers. 111,1111••· .............. •••••••••• CAR LED VOLTMETER l llllll#l.11 - ~~~ '!!!!!. • .....WJIIIIIII..W - l'IAYM.Ulli ■ ----------STIREOAMPUFIH 0 - -J ' -9 . J ,. , , , ,'-"J~ ,, ,,- , -ff " - - :.. .,,. \~/ ' >' / ::- ..,,---..,:: ~ --- .__ ,, ~ -DIIL. - ::-.,. , : . ' PLAYMASTER 30/30W STEREO AMP _JM,,, __ .... QQQ • [I] Q A simple voltmeter that can save you money. It gives a visual indication of the charging system of a l 2V battery. The three LED's show if battery voltage is low, correct or high. This way, you con tell if voltage is dropping or if your battery is overcharging. It's super easy to build, includes a small PCB you con fit unit into a 35mm film container, or your pocket. £:>. March '92 ~ Cat K-4205 $695 Exceptional performance and specifications make the Playmaster series a popular choice among kit builders. This classic 30 / 30W stereo amp is no exception; it's superbly engineered and designed to enhance the output of any music system. All components (including heotsinks) are mounted on one PCB so it' s easy to build . It comes complete as a full form kit with PCB, hardware, pre-punched rack-mounted case, pre-punched silk screened front panel and all components. Se !ember ,88 Cat K-5600 p ~ $249 <at> The Go Anywhere Receiver It's Portable! 16 BAND SHORTWAVE RECEIVER 10 BAND PORTABLE SHORTWAVE RECEIVER The Songeon SG-789 is a neat and compact receiver with the power to pull in radio broadcasts from around the worldl • Local AM/FM bonds (FM stereo with optional headphones) • Receives the 8 most popular international shortwove bonds • Bondspreod tuning & LED tuning indicator • Superb sound reproduction • Sockets for headphones & AC adaptor $7 995 Cal D-2834 A World Of listening $169 Cat D-2839 45 MEMORY SHORTWAVE RECEIVER MULTI BAND SHORTWAVE RECEIVER Hear the world news, as it happens, via shortwove, or your local AM / FM stations. Listen to Commercial communications, Amateur, Morine, HF aircraft and more. • Backlit 5 digit LCD frequency screen • Covers l 50kHz-30MHz, 87 .5 - l 08MHz • 9 pre-set station memories & 24Hr clock • 5 tuning functions including direct keypad entry • RF gain control plus BFO for SSB reception • Battery powered or optional AC adaptor Cat D-2831 Listen to the world direct ... Europe, Asia, America and Australia. It covers local AM / FM stations, longwove and 13 international shortwove bonds. • Incredibly compact & portable • Lorge LCD screen showing major city times • With dual alarms, sleep timer and tuning indicator • Electronic bond selection & volume controls • Pop out stand for desk use $2 9 6 Tune into the world via shortwove with the superb ATS-808 from Songeon. With 45 memori es, stereo headphones and more! • AM & FM-stereo bonds • LCD signal stren~th meter • 16 bond division with direct • • Longwove: 150-5 l 9kHz access buttons • Mediumwove: 520 - l 720kHz • Keypad, outo-sconnin~ or rotary • Shortwove: 1.711 -29. 999MHz tuning continuous or in l 3 bonds • Alarm, sleeptimer & dua l time • FM 87 .5- l08MHz settings cat D-2829 $ • External antenna socket & built-in whip antenna 299 rz1 LZJ Kits marked with this symbol involve mains power wiring . Take extreme care when working with this equipment . Degree Of Simplicity B1304/T1 Q Simple QQ Intermediate QQQ Detailed AND Old Favourites AUTOMATIC LIGHT SWITCH With this amazing automatic light switch,you won't be stumbling around in the dark. It uses a passive infrared detector to turn the lights 'on' the moment you enter the room. With manual and automatic modes, 90° field of view and a range of up to 5 metres. r:.s well, it has a light sensitivity adjustment (so lights switch on only at night) and a time adjustment, which determines how long lights remain on. CatM-7035 $6995 Come in and see our great range of home electricals today! ~ _,,..., _ ,..,---··'""_;_,---~~------·;.,•-"' TV TRANSMITTER FOR VIDEO RECORDERS QQ A great idea for when there's one VCR and two televisions. Now you can play a video and watch it from another television without connection leads from VCR to TV. All components for UHF & VHF modulator output are included. What's more, it's simple to construct and comes as a full form kit with PCB, all components and front panel label. You'll have to build your own antenna, but PCB's and instructions are also included. Cat K-5700 ffff..,i•['1.!.J~ ~;JJ DEC '91 $1 09 SINE/SQUARE WAVE OSCILLATOR A high performance yet inexpensive benchtop audio oscillator. It covers the frequency range from around 6Hz to 70kHz, in four ranges, with very low distortion. What's more, in terms of practical and general use, this oscillator really delivers. It comes as a full form kit with all components, PCB, case and pre-punched silk screened front panel. Cat K-7340 <at>MAR'92 $5995 • All new kits may not be available in some stores. Please check your local store for availability. DS XPRESS PHONE & MAILORDER SERVICE Outside Sydney (FREE Call) 008 22 6610 Sydney And Enquiries - 888 2105 FAX: (02) 805 1986 or write to OS XPRESS, PO BOX 321 N/RYDE NSW 2113 All Major Credit Cards Accepted . 0/Nite Courier Available. 24 HOUR DESPATCH OF ALL ORDERS DICK SMITH (WHOLESALE) PTY LTD A.C.N . 000 908 716 STORE LOCATIONS: NSW • Albury 21 8399 • Bankstown Square 707 4888 • Blacktown 671 7722 • Brookvale 905 0441 • Bondi 3871444 •.Campbe/ltown 27 2199 • Chatswood Chase 4111955 • Chu/lora 642 8922 • Gore Hill 439 5311 • Gosford 25 0235 • Hornsby 477 6633 • Hurstville 560 8622 • Kotara 56 2092 • Liverpool 600 9888 • Maitland 33 7866 • Miranda 525 2722 • Newcastle 611896• North Ryde878 3855• Orange618400• Parramatta689 2188 • Penrith 32 3400• Railway Square211 3777 • SydneyCity267 9111 • Tamworth 661711 • Wollongong 28 3800 ACT• Belconnen (06) 2531785 • Fyshwick 80 4944 VIC• Ballarat 31 5433 • Bendigo 43 0388 • Box Hill 890 0699 • Coburg 383 4455 • Dandenong 794 9377 • East Brighton 592 2388 • Essendon 379 7444 • Footscray 689 2055 • Frankston 783 9144 • Geelong 232 711 • Melbourne City 399 Elizabeth St 326 6088 & 246 Bourke St 639 0396 • Richmond 428 1614 • Ringwood 879 5338 • Springvale 547 0522 QLD • Brisbane City 229 9377 ·• suranda 391 6233 • Cairns 311 515 • Capalaba 245 2870 • Chermside 359 8255 • Redbank 288 5599 • Rockhampton 27 9644 • Southport 32 9033 • Toowoomba 38 4300 • Townsville 72 5722 • Underwood 341 0844 • SA• Adelaide City 223 4122 • Beverley 347 1900 • Elizabeth 255 8099 • Enfield 260 6088 • St. Marys 277 8977 WA• Cannington 451 8866 • Fremantle 335 9733 • Perth City 481 3261 • Midland 250 1480 • North bridge 328 8944 TAS • Hobart 31 0800 NT • Stuart Park 81 1977 ORDER BY PHONE: - SYDNEY AREA 888 22 6610 OUTSIDE SYDNEY (FREE CALL) 008 22 6610 STORES ACROSS AUSTRALIA AND NEW ZEALAND Builld the E,cecutive Thingie Exaoutiva Ihiugia Many executives often suffer from a complaint commonly referred to as "executive stress". If that fits you, then you need the fast-acting relief of the Executive Thingie! You simply tilt the box in any direction to produce four different and medicinal musical notes. How many times have you walked into the boss 's office to find him slowly sliding under the desk with his eyes spinning in a counter-clockwise fashion? Believe it or not, this is a definite case of "executive stress", the management version of "industrial disease". The question is, what can be done about it? We believe that the solution is as simple as a few ICs and a soldering iron: get · him (or her) to build the Executive Thingie. When tilted, this ingenious device closes one or more mercury switches, thus triggering a tone to calm those jangled nerves (or make them worse)! Apart from that, the device is completely useless although you may learn By DARREN YATES 30 SILICON CHIP a few things while building it. The unit runs off a 9V battery and uses easy-to-obtain parts. Indeed, by the time you have it up and running, your worries may be over! Block diagram Fig.1 shows the block diagram of the circuit. As can be seen, it uses four tone generators and these are made using a single 4093 quad Schmitt trigger NAND gate IC. Each generator output feeds one of four voltage-controlled resistive volume controls. These controls are based on the FETs found inside a couple of 4007 !;lual complementary pair ICs and are activated by mercury switches MS1-MS4. The output from each volume control is then resistively mixed with the others and fed to an audio output stage. In practice, the mercury switches are split into pairs, with one pair used to monitor the x-axis and the other used to monitor the y-axis. When the device is held perfectly level, all switches are open and all the voltage controlled resistors have a very high resistance. Thus, no tones are fed through to the loudspeaker. However, when the device is tilted, one or more of the mercury switches will close and their corresponding voltage controlled resistors will switch to low resistance. These in turn allow signals to pass from their corresponding tone generator stages to the amplifier stage. +gv---i--1--1------.! MS2 MS1 MS4 MS3 JQIIE. OSCILLATOR 1 TONE OSCILLATOR 2 TONE OSCILLATOR TONE OSCILLATOR 3 4 VOLTAGE CO~T.!ll!!J.!;I) RESISTOR DIVIDER 1 VOLTAGE CONTROLLED RESISTOR DiVIDER 2 VOLTAGE CONTR.OLLED RESISTOR DIVIDER 3 R ij R Circuit diagram OUTPUT DRIVER Fig.2 shows the complete circuit details. It's easy to identify the various circuit sections. ICla, IClb, IClc & ICld are the tone oscillator stages, while IC2a, IC2b, IC3a & IC3b are the voltage controlled resistors. Ql, Q2 and their associated components form the output driver stage. Note that the four combined tone oscillator/voltage controlled resistor stages are identical. To simplify the description, we'll just concentrate on SPEAKER Fig.I: the Executive Thingie consists of four identical stages which are activated by mercury switches (MS1-MS4). The various outputs are then mixed & fed to an audio amplifier stage. the stage based on ICla and IC2a, since the other three stages all function in exactly the same manner. NAND gate ICla is connected as a square wave oscillator. Its output frequency is set by the lOOkQ trimpot S1 <>--;]_ 100 + 16VWJ T, B1 MS1 9V MS4 ~ i VR1 100k 10k .022! 322! .022! 10 2.2 + 25VWr 10 + 390k 390k .,. .,. 10k 10k 10k 2.2 2.2 390k 25VWr .,. -:- 25VWJ_ 390k 10k 10k -:- ':' .,. ,--------•9V Ic2 1Ic3 100 16VW E ·1n B ELJc VIEWED FROM BELOW Bll SPEAKER 02 BC327 C .,. EXECUTIVE THINGIE .,. Fig.2: the four oscillator stages are based on a 4093 quad NANO gate IC (ICl). IC2a, IC2b, IC3a & IC3b function as the voltage controlled resistor stages while Qt & Q2 form the basis of the audio amplifier. APRIL 1992 31 The assembled PC board is mounted on the lid of the case using screws, nuts & shakeproof washers, while the loudspeaker is fixed in position using contact adhesive. Use a small piece of foam rubber to wedge the battery in position when the lid is attached. and the .022µF capacitor on pins 1 & 2. The resulting output signal appears at pin 3 and is fed via a 10kQ resistor to pin 5 of ICZa. ICZa is a FET (field effect transistor) and is part of a 4007 complementary pair IC (ICZb is the other transistor in the package). Its gate is controlled by mercury switch MS1, a 390kQ resistor and a 2.ZµF capacitor. When the mercury switch is open, the voltage across the 2.2µF capacitor is zero and so the FET is turned off. This means that the FET presents a very high resistance between pins 5 & 4 of ICZa and so no signal appears across the 10kQ resistor on pin 4. Conversely, when the mercury switch is closed, pin 3 of ICZa is connected to the positive supply rail and the FET turns on. The FET now has negligible resistance, which means that the two 10kQ resistors connected to pins 4 & 5 now act as a simple voltage divider for the tone oscillator signal. Chime effect The chiming effect is created when the mercury switch opens again. Initially, the 2.ZµF capacitor is charged to the full supply voltage (9V) and so, when the switch opens again, the FET is held on by the voltage across the capacitor. The parallel 390kQ bleeder resistor - This close-up view shows how the mercury switches are installed. Bend their leads at right angles about 2mm away from the glass bodies before mounting them & make sure that they are parallel with the edges of the board. 32 SILICON CHIP now discharges the 2.ZµF capacitor. As the voltage across this capacitor decreases, the FET resistance gradually increases, thus giving us a decaying signal amplitude on pin 4 ofICZa. The result is that the tone volume decreases to nothing over a period of about one second. This sequence of events occurs for each of the four sections of the circuit, depending on which way you tilt the case to activate the mercury switches. The output signals from each section are then mixed together via four 10kQ resistors and coupled to the audio output stage via a 0. lµF capacitor. Transistors Ql & QZ form a simple complementary class AB audio amplifier and this drives an 8Q loudspeaker via a 100µF capacitor. The two diodes, Dl & DZ, provide about Mount the mercury switches so that the ends with the leads sit slightly proud of the PC board. This is necessary to ensure that all the mercury switch contacts are open when the project is placed on a level surface. PARTS LIST =l uF Fig.3: install the parts on the PC board as shown in this layout diagram. Take care with component orientation & make sure that you don't transpose Q1 & Q2. The four trimpots (VR1-VR4) allow the tone frequencies to he adjusted. 1.2V of bias between the bases of the two transistors to reduce crossover distortion. Without the diodes, each transistor would be off for the first 0.6V swing of its half-cycle. Power for the circuit is derived from a 9V battery via switch S1. The current consumed is approximately 0.9mA with no tone and about 9mA with tone. Construction All of the components except for the loudspeaker, power switch and 9V battery are mounted on a small PC board coded SC08103921. Fig.3 shows the assembly details. When you first buy or make the board, check it thoroughly for any shorts or breaks in the tracks. If you find any, use an artwork knife or a dab of solder where appropriate to fix the problem. It's far easier td do this now rather than to track down faults after the board has been assembled. Begin the assembly by installing the wire links. It's important to keep these as straight as possible so that they don't short out any other components (you can straighten the link wire by clamping one end in a vyce and then stretching it slightly using a pair of pliers). Next, install the resistors and the four trimpots. If you are unsure about the resistor colour codes, check them using a digital multimeter or refer to Table 1. The two signal diodes are the next to go in, followed by the capacitors and the two output transistors (Q1 & Q2). Check the polarity of the diodes and transistors carefully and make sure that you don't transpose Ql and Q2 (one is an NPN type and the other is a PNP). Similarly, make sure that you install the electrolytic capacitors the right way around. Now for the three ICs. These are installed in the centre of the board and all face in the same direction. Be careful not to overheat the ICs and make sure that there are no solder bridges between adjacent pins. Finally, solder in the four mercury switches. These must all be installed so that the end with the leads sits up higher off the board than the other end. This is necessary to ensure that the project must be deliberately tilted in order to generate a sound output. As a guide, if you sit the board down on a flat table, the mercury should run away from the contact pins in each case. By the way, don't play with the mercury if you inadvertently break any of the glass envelopes. It's highly poisonous. Now that you have finished the board, check it carefully for solder splashes, shorts between tracks and 1 PC board, code SC08103921 , 106 x 58mm 1 plastic zippy box, 130 x 68 x 41mm 4 mercury switches (MS1 -MS4) 1 Dynamark front panel label 1 9V battery snap connector 1 9V battery 1 SPST toggle switch (S1) 1 8-ohm 57mm-dia. speaker 4 1 00kQ horizontal mount trimpots Semiconductors 1 4093 Schmitt trigger NAND gate IC (IC1) 2 4007 dual complementary pair/ inverter IC (IC2,3) 1 BC337 NPN transistor (01) 1 BC327 PNP transistor (02) 2 1 N914 diodes (D1 ,D2) Capacitors 2 100µ,F 16VW electrolytics 4 2.2µ,F 25VW electrolytics 1 0.1 µF 63VW MKT 4 .022µF 63VW MKT Resistors (0.5W, 1%) 4 390kQ 233kQ 12 10kQ Miscellaneous Screws, nuts, solder, hookup wire, tinned copper wire for links missed solder joints. Check also that all the components are in their correct locations and are correctly oriented. Testing When these checks are complete, you can connect the loudspeaker and battery to check that the circuit works correctly. Initially, it's a good idea to connect your multimeter (set to a milliamp range) in series with your power supply. If the current drain TABLE 1: RESISTORS I a a a a No. Value 4-Band Code (1%) 5-Band Code (1%) 4 2 12 3901(Q 33kQ 10kQ orange white yellow brown orange orange orange brown brown black orange brown orange white black orange brown orange orange black red brown brown black black red brown APRIL 1992 33 ...... - I ' ARGON LASER These cooled Argon Laser • .•. -_ .f Heads air have had relatively _ "low hours" of operation. They are guaranteed. They · produce a bright blue beam :. (488nM) and have a power ·· output in the 10-100mW range. Limited supplies, at a small fraction of their real value. The head includes power meter circuitry and · - ·• _ ' t. " ONLY saoo ~l~~i;~o~\dc~~,~~- ;ti~~~t/~i?~a~:;r;ig~~er supply. We can provide the major components for this supply. Enquire. I, I.R. BINOCULAR VIEWER Fig.4: this full-size artwork can be used as a drilling template for the front panel. Drill small pilot holes first, then carefully enlarge them using a reamer. Suit teachers, doctors, businessmen, and other professionals. Improve and enhance all your presentations. Not a kit, but a complete commercial pen sized laser pointer at ONLY ~~r~ndc~~~~~eprice~199 Small pen sized body. Runs on two small AAA battery. Battery life: 2-10 hours. Visible 5mW red (670nM) laser. Projects a visible red spot at more than 50 metres. As used for medical treatment by doctors and acupuncturists. Small black anodised metal body. Removable pressure switch . Vertical and horizontal adjustments. Battery life more than 10 hours continuous. SmW 670nM class IIIA laser. Range is about 150m, some would claim three times more. Shock tested to 2000g. One year warr'l5'~i.v 5 299 Price includes one rifle or pistol mount 3mW GAS LASER ~~~~7. 1 ~i~~c~ra~ i1Wi Self powered, and originally intended to be mounted on a helmet. Focus is adjustable from 1 metre to infinity. Requires some IA illumination. Powered by one single 1.SV battery. Original , ~~;:g~~~~i~:~_Y Limited stock. 5 649 I VISIBLE LASER • DIODE HEAD · , Save, by making your own laser pointer, laser gun sight, medical treatment laser, etc. Produces a well collimated beam. Designed to be powered directly from a 3V battery, or from higher voltages, if a simple constant squrce is added. Simple circuit included. 5mW (670nM). At an incredible $135 inr\~~d~f'ory ~or the head only: Add $8 for the extra "bits" needed to make a complete laser diode pointer. Case, switch, alkaline batteries, and battery holders. Everything you need to make a complete, self contained, visible laser pointer or gunsight. ~ l Includes high quality low divergence Siemens laser head with an output at about 3mW and one of our reliable and efficient 12V universal laser power supply kits. The tube is used but it is guaranteed. The kit comes with full instructions and it even includes a prewound transformer. The applications include high power laser pointers, surveying equipment, optical experiments, education, holography, medical ~f~~ia~~citc exceeds Z0mA, switch off immediately and locate the source of the problem before proceeding further. If everything is OK so far, try tilting the board in each direction. You should hear four distinct tones. If any of the tones fails to sound, check the circuitry associated with that particular mercury switch. Once you have the circuit working correctly, the four trimpots can be adjusted to produce the desired notes. You do this by tilting the board in one direction to close one of the mercury switches and adjusting the corresponding trimpot until you get the desired tone. Adjust VRl for mercury switch MSl, VRZ for MSZ, VR3 for MS3 and VR4 forMS4. Final assembly The PC board bolts directly to the lid of the specified case using four screws and nuts, with extra nuts used as spacers. Drill these four mounting holes first, using the PC board as a template, then attach the front panel label to the lid and clear the holes using a sharp artwork knife. This done, drill the holes for the loudspeaker and another hole in one end of the case for the power switch. In each case, it's best to drill a small hole first and then enlarge it using a tapered reamer. The loudspeaker can now be glued to the lid (behind its holes) using a suitable adhesive. Wait until the glue dries, then install the PC board and power switch and complete the wiring. The battery sits on the bottom of the case and can be held in position using foam rubber when the lid is attached. Don't forget to switch the unit off when it is not in use, to preserve battery life. All that's left now is to find that frazzled executive. The symptoms shouldn't be too hard to spot. SC As per EA Oct. 91 issue. Very small size! Complete kit includes an objective lens, an infra red image converter tube, an eyepiece, an electronics kit and sufficient plastics for the case. Very simple to construct. ONLi99 ONLY s299 Melbourne Distributor: Electronics World (03) 723 3860 or (03) 723 3094 OATLEY ELECTRONICS PO BOX 89, OATLEY, NSW 2223 Telephone: (02) 579 4985 Fax: (02) 570 7910 Certified p&p: S6 in Aust. NZ (Airmail) : S10 34 SILICON CHIP Fig.5: here is the full-size etching pattern for the PC board. TOOL BOX ALLEN KEYS 1:s=irmm 8" Sizes In Box ALLEN-KEY-HT6 cumRs HOT AIR GUN ·oua1 lleat Aof Air Gun ARLEC-EHG998 %\U ARLEC-DRILL~~h~~sA~itcD~~Hi DRILL-ME12 5-14V DC Dr111 DRILL·SET·T2330 Drill Set EZ-C7SC/1 0.70mm Carbide Dr111 EZ-CSSC/1 0.80mm Carbide Drill EZ-C9SC/1 0.90mm Carbide Dr111 EZ-CIOSC/1 1.00mm Carbide Drill EZ-C12SC/1 1.20mm Carbide Drtll EZ· HSS.70 0.70mm HSS Drill EZ·HSS.80 0.80mm HSS Drill EZ-HSS.90 0.90mm HSS Drill EZ-HSS1 .00 1 .OOmm HSS Drill EZ-HSS1 .20 1.20mm HSS Drill 10.95 46.25 50.60 44.10 55.05 47.50 15.40 45.80 16.60 8.95 9.95 69 .95 35.00 22.95 89.95 8.70 5.55 5.55 5 .55 3.50 HOLE-PUNCH 69.95 IC EXTRACTORS IC-EXTRCTN-TWZR 1o Pin"&traction IC-EXTRCTN-16 IC·EXTRCTN-PLCC IC-INSRTN-16 IC-INSRTN-28 IC-INSRTN-40 14/16 Pin Extrctn Tool PLCC Puller 14/16 Pin lnsnn Tool 24/28 Pin lnsenn Tool 40 Pin lnsnn Tool POWER DRIVER BITS 29.95 14.50 12.50 12.50 12.50 12.50 12.50 33.00 SD-T£ST-ES1 SD· TEST-B3226 2.50 29.75 12.50 12.50 NUT·DRIVER-HT11 r uJu~W~~o Smm 17.95 TY, PIN INS~RT~~S in lnsener or ype 115mm Long Nose Pliers SnIBe Nose 12 mm Flat Nose 145mm Needle Nose 120mm Round Nose 120mm Snipe Nose 150mm Snipe Nose 150mm Snipe Nose-Bent 3.35 25(lmm·n nsnips 32.50 STRIPPER-CS200 STRIPPER-CSSOO STRIPPER-CK3754 STRI PPER-KFLEX STRIPPER-KOAX2 STRIPPER-W,W f,T!JJf:1:i E1~ 3.5mm RG58/59 COAX Stripper 18.95 19.95 JO KARI Flex Strtpper JOKARI Coax Str1pper Wire Wrar, Strtpper ARLEC-SUPER~ ~RTqfil-DrlWG~~~,r ARLEC·ET612 Eraser ARLEC-ET625 Drill Bits Pack of 4 ARLEC-ET627 Grinding Bits Pack of 3 ARLEC-ET643 Erasers ARLEC-ET669 Eng raving Bits ARLEC-ET688 Diamond Engraving Bit ARLEC·ET689 Splitting Discs ARLEC·ET722 Wire Brushes Pack of 3 3.95 11.95 2t'l,9e~K/X~ Kit 16 Piece Tool Kit 28.90 32.00 32.00 27.80 89.95 4.50 7.95 2.95 3.25 10.95 18.95 15.95 16.95 4.25 TOOL-KIT-HT11 TOOL-KIT-HT17 us TWEEZERS-CK2302 n s-mm"""S"traight Tweezers 8.95 TWEEZERS-CK2312150mm Clamp Tweezers 19.95 TWEEZERS-CK2314150mm 45d Tweezers 15.90 TWEEZERS-CK2316110mm Straight Tweezers 19.95 PLIERS PLIERS-HT15 PLIERS-CK3767 PLIERS-CK3770 PLIERS-CK3783 PLIERS-CK3771 PLIERS-CK3772 PLIERS-CK3777 PLIERS-CK3769 TIN SNIPS . 2.45 SNIPS-CK4531 1 19.95 D PIN-INSERTION H Omm Neon Test Dvr Test Driver 12.50 NIBBLER·HT2049 NIIR~!NfirTOOL I b ng ool Spring Loade 3 Claw Tweezers+ Magnet TEST DRIVERS 9.80 a~if.s PEARL-CATCH PICK-UP-HT27 2x4mm XBlade Bits 2x5.5mm XBiade Bits 2 Nol Phl~s Bits ~ ~~~l~t, i~ Bits 2 No2 PO~IDRIVE Bits POZIDRIVE Bits TORX T· 10 Bit TORXT-15 Bit TORX T-20 Bit Extender 6 Assnd Bits+Hoider 7 Asr1d Bits+ Extender Watchmakers Drivers SD-SET-CK488f CREWDRIVER SETS SD·SET·HTT 6 Pee Jwlrs Dvr Set SD-SET-tff8 Jewellers Philips Set SD-SET-HT9 6 Pee Jwlrs Dvr Set SD·SET-W18970 1000V 6 Dvr + Tester SD-SET-W20130 2 Phlps & 5 XBiade KNIV-f EZ3108 - C~nd ONo. ades x 5 4.50 EZ3110 X-ACTO No.16 Blades x 5 4.50 EZ3141 X·ACTO CUT-ALL Knife 5.25 KNIFE-SET-HT23 Boxed Set of 3 Knives 19.95 PICK UP TOO~S StubbV XBlade 2.5x60mm XBlade Dvr 2.5x75mm XBlade Dvr m lnsltd Xblade m XBlade Dvr m XBlade Dvr m XBlade Dvr 4 m lnsltd Xblade 4xl50mm XBlade 4xl50mm XBlade Dvr 4x250mm XBlade 5.5xl25mm XBlade 5.5x300mm XBlade 6x25mm Xblade Stubby 6.SxlSOmm XBlade 00x60mm Philips lx80mm Ph ilips Ox60mm Phlps lnsltd lx80mm Phlps lnsttd 2xl00mm Phlps lnsltd 02x25mm Phillips Stubby 250mm Philips 2xlOOmm POZIDRIVE 1.SxlSOmm TOllC for Mac T.10 TORX Driver SD· BIT-W26724 SD-BIT-W26726 SD-BIT-W26720 SD·BIT-W26732 SD-BIT-W26721 SD-BIT-W26717 SD·BIT-W26716 SD-BIT-W26735 SD-BIT-W26736 SD-BIT-W26737 SD-BIT-W26703 SD-BIT-W27620 SD-BIT-W26713 SD-SET-CK4854P 89.95 FILES·CK124P 15.50 SCRtuEW bDRl VERSriv 5 ili y Ra1cne11l er SD-HT28 SD-W86252 SD-CK4880'2.5 SD-CK4880'3 SD-W73101 SD-CK4880'4 SD-CK4880'6 SD·CK4881·4 SD-W73104 SD-CK4880 SD·CK4881-6 SD-CK4975 SD-W74008 SD-CK4965 SD-W86982 SD-W74010 SD-CK4882 SD-CK4882· SD-W73501 SD-W73502 SD-W73503 SD·W94208 SD-CK4977 SD-W77003 SD-TORX-HT20 SD-TORX·W82010 4.95 RG58/RG59U COAXS!rtpr 19.95 BNC/F/Mlnl M/M/N/TNC 64.95 6 Tension Rtcht Crmpr 82.60 D-Sub Cr1mp Tool 18.00 RG58/59 Coax Cr1mper 18.00 4 Pin US Pig Cr1mper 29.95 6 Pin US Pig Cr1mper 29.95 BPin US Pig Crimper 34.95 CUffiRS-HT12 104mm Diagonal Cutters CUTTERS-CK3799 110mm Angld Fish Cir CUTTERS-CK3798 110mm Obfique Cutter CUTTERS-CK3773 115mm Side Cutters CUTTERS-CK3786 120mm Oblique Cutter CUTTERS-CK3780 110mm Side Cutters CUTTERS-CK3841 120mm Side Cutters CUTTERS-CK3775 135mm Side Cutters CUTTERS-CK3623 145mm Side Cutters CUTTERS·HT13 104mm Mini End Cutters CUTTERS-HT14 115mm Diagonal Cutters CUTTERS·MPC290 Heavy Dutv Cutter CUT-N-CLINCH Cut and Cfinch Tool CUTTERS· TRV·30'V End Cutters Tapered Reamer SCRIBER-HT25 CRIMPING TOOLS CRIMPER-CSSOO CRIMPER-CS600 CRIMPER-KTC1 CRIMPER-HDSUB CRIMPER-HX2 CRIMPER-TCT44 CRIMPER-TCT66 CRIMPER-TCT88 REAMER REAMER-M422 If you want to do a good Job, you need tile r1ght tools and we've got 'emf Call In and check your re~ulrements whether It's for your lo5 or your hobby, we II h.r,,e the best quality anlf the 6est price. 35.10 33.10 38.80 29.50 34.75 40.80 44.60 17.95 1U5 TWEEZERS VICE-MV3 ·-===== Pias~Sf:ce Suction U5 SERVIC 'SLOG Found dead in a motel room That heading was the gist of a garbled phone message from one of the motel employees, under instructions from the manager. Unfortunately, it wasn't immediately clear just what had been found dead. Fortunately, it wasn't the body I had momentarily envisaged; just one of the TV sets. And, of course, it was I who would have to track down the fault and bring it back to life. The motel manager is a long-standing customer. Most of his TV troubles are routine and I didn't expect that this would be anything unusual. But it was, in a couple of respects. For a start, it was almost a new set, a Samsung model CB5012Z, one of a recent batch bought by the motel and only about six months old. More to the point, it was a model I had never handled before. Second, it turned out be an extremely rare fault; the kind of thing that is investigated only because there is nothing left to suspect. As with most modern TV sets, it .. .best television antenna performance for less cost. Fracarro 10BL4, 10BL.5, 10BL45, 1Oelement yagrs that ~v.Qrk Peter C. Lacey Services Pty. Ltd. P.O. Box 678 (74Fulton Rd.) Mount Eliza 3930 Tel:03 787 2077 Fax:(03) 787 3460 ACN006893438 36 SILICON CHIP was fitted with remote control and this brings me to a point I have been meaning to mention for some time. This fault did not involve the remote control, so the following remarks are more of a general nature, although they are indicative of changing set design. Remote control is, of course, nothing new. TV manufacturers have now used it in their sets for many years. In most cases, they use a microprocessor which is operated via the front panel controls or by an infrared remote control unit. Until recently, when a customer brought a set in with its remote control unit, I would always hand the control unit back to him - unless, of course, the fault obviously involved a remote control function. Experience had taught me that it was just one more piece of paraphernalia to keep track of and that it could easily be temporarily misplaced or forgotten when the set was picked up, thus causing a deal of inconvenience. This is not good for PR and handing it back was the simplest solution. But not any more. With many devices these days - both video recorders and TV sets - it is essential to have the remote control unit in order to work on them. Some cannot even be turned on - at least in the normal way - without the remote control and they certainly cannot be programmed without it. And so, the remote control must now be left with the set and that means more bookwork and labels to keep track of everything. Anyway, after that little digression, let's get back to the body in the motel room. It was duly delivered to my workshop, complete with its remote control. I set it up on the bench and turned on the master (mains) switch. Nothing happened, so I tried operating one of the channel selector switches on the front panel. Still no joy. Finally, I tried turning it on via the remote control. Again no response; it was very dead. I pulled the back off and went through what is a fairly common routine: mains fuse; power supply; horizontal output stage for short circuit transistor, ICs, etc. This only takes a few minutes and is time well spent even though, in this case, it revealed nothing obvious. Brownie points Now, to award Mr Samsung a couple of Brownie points, he has made it possible to separate the receiver from the remote control unit to some extent: He has provided two pins on the chassis, complete with a printed caption: "To start set, bridge these two pins". Suitably intrigued, I wanted to know just what these two pins did. Unfortunately, reference to the circuit didn't help; they weren't shown. But a spot of tracing provided the answer. One pin goes to chassis and the other to pin 41 of the microprocessor IC, RIC01 (top right of IC). From there, it was easy to see what it did. The on/off function is controlled by transistor RQ11- to the right of the IC. This has its collector connected to the 16.5V rail, via resistor RR51 (2700), while its base is fed from pin 41. The collector of RQ11 provides another supply rail - called simply "POWER" -via a 100n resistor, RR52. When pin 41 is high, it turns on RQ11 and pulls its collector down towards the emitter, which goes to chassis. In other words, the POWER line is turned off. But when pin 41 goes low, QRl 1 is turned off and the collector rises towards the 16.5V rail, thus energising the power line. Fair enough, so what happened when I bridged the pins? Well, it did turn the set on - at least to the point where the screen lit up. But there was no sign of a picture; just a bright screen as when on a blank channel. There was no sound either, not even noise, but that was normal. This set features a muting circuit to turn the sound off when there is no signal. So, at least the major part of the set was up and running but that was as far as it would go. It would not respond to any of the user controls, such as channel selection, brightness, colour, etc. In short, the microprocessor was not working, either in itself, or because of some associated component. When a microprocessor fails, the most likely suspect - and the easiest to check- is its 5V supply, in this case at pin 42. But it wasn't going to be that easy; the 5V supply was intact. So what next? One of the disconcerting facts about the manual and the circuit - and for which I will have to recall those Brownie points - is that nowhere in either are there any voltage references or waveforms. Nor are there any indications as to the state of the microprocessor pins - ie, whether high (5V) or low (OV) - for any particular function or operating condition. Some makers do supply this information and it can be very useful. Component checks I went over the surrounding circuitry, checking individual components on the basis that a failure in one of them could have upset the microprocessor. But I found nothing and, in the absence of any more specific data, I was eventually forced to the conclusion that it was the microprocessor. Naturally, it was one that I didn't have in stock, so it had to be ordered. 0001/\0'S.,.. Or HIS iV ~ s ARE. 'ROUi"INE:- ~,-- ruts ONS:' WA."S UN\JSU~\.. \N A. C.OU'P\,....6:. Or ~s?~C-C-So .. It arrived in a few days and I went through the routine of pulling the old one out and fitting it. And a fat lot of good it did; the set was the same as before. I took another long hard look at the circuit and mulled over the problem while I attended to some routine work on the bench. This is a technique which sometimes helps to get the grey matter into gear and it helped on this occasion. A vital part of the microprocessor circuit is its clock and the pulses from it. In this case, the clock operates from a 10MHz crystal (RXOl) which is connected between pins 31 and 32. Could the crystal be at fault? That was a long shot; a very long shot because crystals are very reliable devices. In fact, I have never encountered a faulty one in any of the microprocessor controlled sets that I have handled over the years. Still, stranger things have happened. I reached for the CRO leads and connected them across the crystal. The result was somewhat inconclusive. There was something there but I needed maximum CRO sensitivity - down in the millivolt range - to produce it. More to the point, I couldn't resolve any waveform out of it, in spite of my best efforts at setting the timebase and sync controls. In short, it appeared to be nothing more than mush. Been there, done that Nevertheless, I felt that the time had come ·to seek some help. I rang the Samsung service department and contacted one of technicians, who I know fairly well. After identifying the set, I put the problem to him along the simple lines that the microprocessor seemed to be totally inoperative. His response was immediate: "Changed the microprocessor?" "Yeah Bill, been there; done that". "Bet you haven't checked the 5V rail". "Yeah Bill, been there; checked that". "Oh. Er, well ... " I could sense that he was puzzled. "What about the crystal", I prompted. "Could be, I s'pose; but not very likely. They don't usually give trouble". APRIL 1992 37 of all or part of a low voltage rail. The luminance amplifier transistor sometimes causes this symptom, or an open circuit luminance delay line can remove the picture, though this usually results in a white, rather than black, screen. Next, of course, the brightness control circuit might be faulty-that could cause a black screen. Anything else you can think of? Well, there is something else but I'll not reveal it until the end of the story. See if your guess is correct. The story concerns a Sony KV1830 TV set, one of the earlier versions of this model with mostly discrete components. The lady complained that the picture just disappeared suddenly. The sound was OK but there was no sign of a picture. SERVICEMAN'S LOG - CTD ' CIS DOI r,.,. ,.__+--'";.;•;..._+---,-l--::--:-,,---r-+----0-1 ... Brief flash : 110 .... " ......__ ... _____ RR3S ;..._.'.;;";__ ., .,.., IUllC. ~ - · - Fig.1: part of the microprocessor circuitry in the Samsung CB5012Z. Pin 41 of the microprocessor (top right) controls transistor RQ11 which in turn controls the POWER rail. It wasn't the transistor that caused the problems, however. "OK, but what waveform voltage should I be getting across the crystal?" He thought for a moment: "About two volts". ''.OK, I can't get anything like that; not even a readable waveform. Better send me another crystal". Well, that was it. The new crystal duly arrived, was fitted, and all the control functions snapped back into action. With hindsight, I suppose, I was a bit hasty in assuming that the microprocessor was at fault. But then, as my mate at Samsung agreed, crystal faults are very rare. And it might just have been a little easier had the manual supplied more details. It might at least have prompted me to check the crystal. Southern Sony And now, for a change of scene, here's a story from my colleague, J. L., in Northern Antarctica, who appears to have come out of hibernation after a long absence. His story is also about 38 SILICON CHIP a set that wouldn't produce a picture. Here's how he tells it. How many different ways can you think of to kill the picture - ie, create a black screen - on a TV set? First, and least likely, there's a tube failure. Next, there's an EHT or horizontal output stage failure. After that, one is getting into the odd faults: loss of luminance output voltage and loss lr In the workshop, I confirmed her story but with one minor addition. The screen was normally quite black but, when the set was switched off, it flashed briefly with a very distorted raster. It didn't last long enough for me to see whether there was any picture or colour on it but it was enough to indicate that the horizontal output stage was working. At this , I heaved a sigh of relief. The horizontal output stage in this Sony ·set uses an SG613 GCS (gate controlled switch) which is quite expensive and cannot be replaced with anything else. Knowing that this stage was alive and working took a great load off my mind. I went first to the picture tube neck board, designated board "C" by the manufacturer. This provides access to the picture tube operating voltages and also to the red, green and blue TETIA TV TIP AWA C620 (G chassis) Symptom: screen shows a small, bright raster with all four sides curved inwards. There is no sign of convergence anywhere on the screen. The bottom edge of the picture shows severe vertical foldup and the whole picture is covered with flyback lines. Cure: in spite of the complex nature of the symptoms, the fault is quite simple. It is caused by the loss of the 150V rail. The usual reason for the loss of this rail is that D575 (UF2) gees short circuit and takes out the safety resistor R581 (4.70 O.SW fusible) . A DYXSS/600 makes a good substitute for the UF-2. TETIA TV Tip is supplied by the Tasmanian branch of the Electronic Technician's Institute of Australia. Contact Jim Lawler, 16 Adina St, Geilston Bay, 7015. Fig.2: this diagram shows part of the "B" board in the Sony 1830AS, with the "C" (neck) board at right. The luminance chain transistors (Q451, Q452, Q453 & Q454) are approximately mid-way up the "B" board, while the RGB output transistors are at the bottom of the "C" board. output transistors (Q701, Q702 & Q703). The picture tube G4 and G6 voltages were close enough to normal but the three cathodes and the Gl voltages were quite wrong. The cathodes were each at 220Vinstead of the 170V nominated on the circuit. And the Gl voltage was lower than the specified 30V, which aggravated the effect of the higher than normal cathode voltages. It was quite apparent that the three output transistors were cut off and that this was the reason for the black screen. All that I had to do was find out why they were cut off. The first thing I found when I checked the transistors, was that they all had 200V on their collectors - the same as on the supply rail - rather than the 170V shown on the circuit. This simply confirmed - if confirmation was needed - that they were not drawing any current. The base voltages were wrong too (2.1 V instead of 6.3V), as were the emitter voltages (5.5V instead of 7V). This was more of a headache than a help, because either voltage could upset the other. So which one was at fault? I decided that ifI could make one of detector stages were all OK. Only the brightness control had no effect but that was not surprising, since the battery supply would o_verride any control from the brightness pot. Froin there, I started backtracking into the "B" board. As already mentioned, this carries the luminance drive transistor (Q453) and this, in turn, is direct coupled to, and driven by, the luminance amplifier, Q451. Unfortunately, because of the way the set is constructed, it is almost impossible to get at these transistors while the set is working. However, since the luminance am- the voltages right, by brute force, it might give me some idea as to which part of the system was working, even if it did not tell me which part was not. And the easier voltage to brute force was the one applied to the bases. This is common to all three bases and comes from the luminance (Y) drive transistor, Q453 , on the "B" board. It finds its way to the "C" board via pin 6 of plug B5. And pin 6 provided an easy access point to this line, where I could clip a battery box into the circuit and wind up the voltage . The idea worked quite well. As the battery supply reached about 6V, up came the brightness and there was a picture. Not that anyone would want to watch it. It was overbright, negative and covered with flyback lines. .., But it allowed me to ~ It.,~ determine that the colour and contrast con'40M0 S~RVU S, NOR"T1t&=.RN trols were working and AN-r'A.RCTICI\, e.U\E.ltGING that the tuner, IF and ~ M . '-' 1~E-~i.JPtTION •••.. ~v APRIL 1992 39 plifier is direct coupled to the luminance drive, and the luminance drive stage is direct coupled to the red, green, and blue output stages (the ones with the grossly incorrect voltages on them), it seemed safe to assume that varying the input voltage - ie, the voltage on the base of the luminance amplifier, Q451 - would vary the operating conditions on the "C" board. Or so I thought. The input to Q451 is via pin 4 of plug B2 on the "B" board, (left side of the circuit) and the plug pins extend through the board, making a very convenient contact point for the battery box lead. Unfortunately, varying the voltage at this point had no effect the screen remained dark. So what was the voltage at this pin? Getting a meter prod onto it wasn't quite so easy but an extension lead solved the problem. And it came up at 2.1 V, which was close enough to the 2V specified on the circuit. This suggested that the fault, whatever it was, was back along the chain, in the direction of the "C" board. In other words, I had probably overshot. So what about the brightness control? The brightness control works on the base of the luminance drive transistor, Q453. The control is a 20kn pot between the base and chassis. Its connection is made via pin 3 of plug B4. It was a simple matter to confirm that this control was properly connected and working. · Blanking circuitry There are two other transistors associated with the luminance stages on this board. They are an ABL (automatic beam limiter) transistor, Q452, and the BLK (blanking) transistor, Q454. (Initially, I took BLK to mean black, of which I had more than enough. It took me a moment to translate it as blanking!) And, by a process of elimination, it was looking more and more likely that the fault was in one of these two stages. I pulled the "B" board out and checked all the resistors and capaci- :t De:<::1t>~ ~AT lr I: COU'-D fv'W£. ONS: Or -me. vt'L-TAGEt S °RlGH,, 'S'( "B~ R:>~CS:ooo 40 SILICON CHIP tors associated with the ABL circuit. In particular, there were several low value electros, which are always suspect. I removed these from the board but they all tested as perfect. Nevertheless, I replaced them because I've been caught before with electros that test OK - at least as far as conventional test equipment is concerned - but simply will not work. But fitting the new ones was a waste of time and money; the screen remained as black as ever. That left the blanking stage, Q454. I pulled the board out again and checked this transistor and its associated components thoroughly. There was nothing wrong that I could find but I changed the transistor on the off chance that it might have been one of those funny ones that check OK but will not amplify properly. Next I tried measuring the base voltage on this transistor, using a clip lead from pin 6 on plug B3. This is shown as -lV on the circuit but my measurements were quite meaningless. Depending on which meter I used (analog or digital), the reading ranged from zero to 50V! I couldn't find a convenient point to break into the base circuit of this transistor, so I applied my battery box in parallel with whatever was supplying bias to the transistor. By adjusting the input voltage, I was able to produce a white screen, but without any trace of a picture. I wasn't sure whether this test was pointing me in the right direction but I decided to investigate the blanking drive to see if there might be something along that road. The horizontal and vertical blanking pulses are developed on their respective boards, and are combined in a network of resistors and capacitors on the "D" board. The resultant drive exits on pin 6 of plug D4 (not shown) and enters the "B" board via pin 6 of plug B3. The vertical pulses are taken directly from the vertical output, with very"little processing. This was easy to check and revealed nothing unusual. The horizontal pulses, on the other hand, arise on the "E" board and undergo considerable processing. The network (lower right quarter of the "E" board circuit) includes blanking rectifier D808; blanking zener D809; blanking amplifiers Q801 and Q802; Fig.3: the "E" board in the Sony 1830AS. The horizontal blanking components (transistors Q801 & Q80Z, etc) are in the lower right hand corner. three fusible resistors; and C816, a 4. 7µF 250V electro. There were plenty of opportunities for trouble in that lot. My first checks were on the diodes and transistors but in-circuit meter tests, while not conclusive, were not so unusual as to suggest that they should be replaced at this stage. I would not have been surprised to find one of the fusible resistors open circuit - except that these units were one and two watt types and I have yet to find one of these go open spontaneously. This brought me to C816, the 4.7µF, 250V electrolytic. An in-circuit test told me that it was not shorted and so I decided to remove it for a capacitance check. Funny thing though; as soon as I unsoldered the negative lead, C816 fell off the board. It had become a oneterminal device and the positive lead was still attached to the circuit board. And that was the cause of all the trouble. In one way or another it had turned the blanking circuit hard on. After I had finished the job, I realised that I had seen something similar 26 E A· I.U.!11-05.J,A once before. On that occasion, the set was an HMV CZ 11 and half the screen was blacked out because a faulty transistor couldn't switch fast enough. This Sony was a different story altogether but, from now on, I'll have to remember that there are more ways to black out a screen than I had previously considered. AUSTRALIAN MADE TV TEST EQUIPMENT N 10% discount on all test equipment. 15% discount on two or more Items. SHO I HIGH-VOLTAGE P DEGAUS5 Quantum 50-Meg SCSI Hard Drive (1 only) $295.00 ,11111 -••9';~>. /! Fujitsu 240V Coil Relays, DPDT 30A · Fujitsu 5V Relays, SPOT Subminiature 2764 Surplus Computer EPROMs, Erasable ~-- ~ , ·-..·. ~ . r~ . ,,.!) "" Vi Phone (02) 774 1154 · 27512 Surplus Computer EPROMs, Erasable $6.95 QC-1910 Super Tiger 5MHz Oscilloscope From $19 exchange plus post & pack Cheque, Money Order, Visa, Bankcard or Mastercard 216 Canterbury Rd, Revesby, NSW 2212, ' • • TUNERS:.,,J Australia. Fax (02) 774 1154 $3.95 27256 Surplus Computer EPROMs, Erasable $5.95 - / 7 ~ ---· ~~ $19.95 27128 Surplus Computer EPROMs, Erasable $4.95 ~...... E Designed to test infrared or ultrasonic . control units. Supplied with extension , infrared detector lead. Output is via a LED •·• and piezo speaker. $84.00 + $4.00 p&p • ~=----TUNER REPAIRS--~ $9.95 ea A Strong magnetic field. Double insulated for your safety with momentary switch operation. 240V AC 2.2 amps. As important as a soldering iron! $75.00 + $10.00 p&p REMOTE CONTROL CTRONICS 217 High Street, Preston, Melbourne Victoria 3072 (Cnr of Bell & High Street) Built-in meter to check EHT transformers including split diode type, yokes and drive transformers. $78.00 + $4.00 p&p Built-in meter reads positive or nega- _ HUFTl!!!·l l ive voltages from 0-50kV. For check- . ' -- • . ing EHT and other HT voltages. · · $98.00 + $5.00 p&p Thank you, J. L., for an interesting story and a useful insight into the workings of this circuit. I have had several of these models through the workshop recently but with nothing like the fault you described. Anyway, congratulations on an arduous piece of detective work and a successful outcome. SC $29.95 TEEPROM EPROM Writer Card/Cable + Software To Suit IBM-Compatible Computers $39.95 ff a11 raer at-Line /Card-Mast Card-Visa-Cheque Phone (03) 484 0191 APRIL 1992 41 AMATEUR RADIO BY GARRY CRATT, VK2YBX Receiving weather satellite signals - the hardware required Interested in receiving off-air pictures from the weather satellites? Here's a rundown on the equipment that you'll need & where you can obtain it. Ever since the advent of weather satellites , amateur radio enthusiasts have been involved in the reception of images from spacecraft. Apart from the meteorological aspects of weather satellite reception, there are a number of technical challenges to be overcome if successful reception is to be accomplished. Areas such as satellite antennas , receivers , data processing and storage techniques all add to the challenge of satellite reception. There are several levels of weather satellite transmissions that can be received and each level provides higher · resolution and more varied formats all at an increasing level of complication, as far as the receiving equipment is concerned. Some satellites produce high resolution imagery which is sent at high speed on microwave frequencies. Such signals require significant effort and investment to be received. Other satellites, such as the polar orbiting "birds", use a much slower rate of transmission, in the VHF bands, and can easily be decoded using relatively simple equipment. These satellites use APT (automatic picture transmission), a system devised to allow users in remote locations direct access to meteorological data at low cost. APT resolution is typically 2-3km, allowing definite identification of cities, rivers, lakes and other major land features and their proximity to cloud masses. APT transmissions are FM, with an audio subcarrier that has been amplitude modulated. The amplitude peaks on the subcarrier correspond to white areas, while the lowest amplitude corresponds to black. Pictures are transmitted at either 120 or 240 lines per minute. What's needed This German-made satellite receiver (model MR-137) & its companion decoder unit (model FX-666) are one way of receiving weather satellite signals. Other hardware options are discussed in the text. 42 SILICON CHIP In order to receive APT signals from a polar orbiting spacecraft, we need a suitable antenna, a receiver, a decoder and a display unit. These days, with the cost of PC-compatible computers reaching their lowest levels ever, most operators will choose this kind of hardware to handle the display and decoding functions. However, this still leaves the antenna and receiver, which must both have particular performance characteristics for good reception. · The antenna should be horizontally polarised and have a high angle of radiation to allow reception for the maximum amount of time as the satellite becomes "visible", then passes overhead and disappears over the horizon. We discussed the construction of a suitable turnstile antenna in the tained. Other frequencies sometimes. used are 137.06, 137.12, 137.15, 137.33, 137.45 and 138.8MHz. VHF APT transmissions from these polar orbiting spacecraft use wideband FM with no pre-emphasis. Because the maximum deviation (of NOAA spacecraft) is ±18kHz, the maximum modulating frequency is 4kHz and the maximum Doppler shift is ±3kHz, we need a receiver with an IF bandwidth of 50kHz. This will present a problem to anyone proposing to use a standard scanning receiver, as the typical NBFM bandwidth is 15kHz and the wideband FM bandwidth is 180kHz. Alternative receivers A J-pole antenna is ideal for weather satellite reception. You can either use a commercial unit, such as the unit pictured here, or build the design to be published in a forthcoming issue of SILICON CHIP. November 1991 issue of the magazine. The next requirement is for a good VHF FM receiver, capable of reception in the 136-138MHz band. Many enthusiasts use a suitable scanning receiver which, despite not having ideal IF bandwidth characteristics for weather satellite reception, can be used to produce fair results. Dedicated kit receivers are also available at moderate prices. Some older crystal locked 2-metre FM receivers could also be pressed into service, although the cost of crystals will often make the purchase of a scanning receiver a more attractive proposition. The accompanying table shows a list of current VHF channels and the spacecraft that use them. As can be seen, some satellites share the same frequency (one will be turned off by ground station command if there is any chance of interference), so that maximum frequency utilisation is ob- One solution, suggested by Paul Hayden VK4ZBV, is to use one of the old 60kHz crystal filters from an early commercial 2-way radio transceiver. He also suggests an alternative approach, which is to use a crystallocked converter in conjunction with a surplus ex-army transceiver, such as the C45/46 or PRC9/10. Both these transceivers have a receiver IF bandwidth of 50kHz and can be converted to solid state operation. It is also possible to purchase a custom made 10. 7MHz filter from Hy-Q Crystals in Melbourne. Considering the highest altitude a polar orbiting weather satellite is likely to attain is 3000km, and that the resultant path attenuation at 137MHz is likely to be in the order of -145dB or so, the receiver must be capable of producing 20dB of quieting for an input signal of0.5µV (based on the spacecraft transmit power of 5 watts). This level of performance is reasonably easy to obtain, particularly if using a FET preamplifier at the antenna. Users should be aware of the close proximity of TV channel 5A and the adverse affect such signals will have on VHF weather satellite reception. Software Because we have elected to use a computer and video monitor as the decoder and display (and memory) devices, the choice of a suitable software program is the next project to tackle. There is an enormous amount of weather satellite software available, ranging from barely adequate to brilliant. Computer programs to suit Amiga, IBM, Commodore 64 and STOCK SALE!! FANS 80 x 80 x 25mm 240VAC .... $16.84 120 x 120 x 38mm 240VAC $16.92 Fan Finger Guards for 80mm Fans .. ....... ....... ..... .. $1.43 Fan Finger Guards for 120mm Fans ..................... $2.12 MISCELLANEOUS Circuit Breakers 7.5A- Press To Reset ............................ $7.25 Mains Power Lead 10A 1.8m long ........................... $4.16 9V Battery Snaps .... ............ .. $0.20 2 x AA Battery Holder ....... ..... $0.28 12-Way terminal block 10A ... $1.60 SEMICONDUCTORS 1N4004 Diodes ..................... $0.07 1N4007 Diodes ................. .... $0.10 1N4148 Diodes ... .... .. ... ...... ... $0.04 MJ15003 Transistor ..... ... ...... $6.50 MJ 15004 Transistor .......... .... $6.50 MJ15024 Transistor ........... .. . $8.60 MJ 15025 Transistor ... .. ..... ... . $8.60 MJ13007 Transistor ......... ..... $4.87 MFR571 Transistor .. .. ....... .. .. $4.27 NE555 IC .. ... ... .. ............. ....... $0.30 TL494 IC .... .. .. ...... .... ... .. ..... ... $2.83 MC14514 IC .......................... $3.00 MC34063 IC ............ .............. $2.98 ALL ITEMS 10 PLUS 10% OFF HYCAL ELECTRONICS Unit 4, 62 Gt. Western Hwy, Parramatta, NSW 2150. Phone (02) 633 5477 Fax (02) 891 5640 Credit Cards Welcome APRIL 1992 43 terns, Wichambrook Newmarket CB8 8QA, England. Phone (0440) 82 0040 of fax (0440) 82 0281. Their US distributor is Spectrum International Inc, PO Box 1084, Concord, MA 01742, USA. Phone (508) 263 2145 or fax (508) 263 7008. A comprehensive range of receivers, decoders, antennas, and other hardware for both APT, GMS and HRPT reception is available from: Quorum Communications Inc, 1020 Main Street Suite A, Grapevine, TX 76051, USA. Phone (817) 488 4861 or fax 817 481 8983. For those sufficiently affluent, Mitsubishi Electric can supply a suitable Video Copy Processor, allowing black and white prints of any video screen to be made for posterity. Model P75E can produce high resolution prints at 640 X 580 dots resolution in handy 200 X 154mm print size - ideal for the family album! Next month, we will discuss hardware requirements for the reception of GMS and HRPT satellite signals. A turnstile antenna can also be used for weather satellite reception although the results are generally not as good as from a J-pole. This is a commercial unit but you could also use the build-it-yourself design published in the November 1991 issue of SILICON CHIP. Tandy COCO computers are available, and may also be for other types of computer. Perhaps the best way to evaluate available software is to contact a local user group or scan some of the available bulletin boards for information on such programs. Hopkins, 4 Handsworth Street, Capalaba, Qld 4157. The software is available from: Mr M. Delahunty, 42 Villiers Street, New Farm, Qld 4004. A complete weather satellite receiving system and all discrete components including software can be obtained from Timestep Weather Sys- Hardware guide A suitable weather satellite receiver kit is available from Stewart Electronic Components, phone (03) 543 3733 or fax (03) 543 7238. The kit was described in the February 1988 issue of "Australian Electronics Monthly" (which has now ceased publication). A complete standalone receiver and decoder is available from Mr Volker Wraase, Kronsberg 10 D-2300 Altenholz/Kiel, West Germany. The receiver model is "MR-137", while the decoder is the" FX-666". A suitable pre-assembled and tested 137MHz preamplifier is available from: (1) SCISAT Products, PO Box 307, Kenmore, Qld 4069. (2) Vanguard Electronic Labs, 196-23 Jamaica Avenue, Hollis NY 11423, USA. An IBM PC/XT/ AT plug-in decoder board is available from Mr David G. 44 SILICON CHIP VHF WEATHER SATELLITES Country Satellite Freq. (MHz) USA NOAA9 136.620 USA NOAA 10 137.500 USA NOAA 11 137.620 USA NOAA12 137.500 USSR Meteor 2-17 137.300 USSR Meteor 2-18 137.300 USSR Meteor 2-19 137.850 USSR Meteor 2-20 137.850 USSR Meteor 3-2 137.850 USSR Meteor 3-3 137.300 USSR Meteor 3-4 137.850 Further reading (1) Communications Satellites - A Monitors Guide. 3rd edition by Larry V. A. Horn. Published by Grove Enterprises, PO Box 98, Brasstown, N.C. 28902, USA. (2) US Department of Commerce, NOAA Technical Report NESDIS 44. NOAA Office of Constituent Affairs, Herbert C Hoover Building, Room 6815 A, 14th & Constitution Avenue, Washington DC 20230, USA. (3) "TIROS-N Series Direct Readout Services Users Guide" and "The WEFAX User's Guide"; both available from The Co-ordinator, Direct Readout Services, United States Department of Commerce, National Oceanic and Atmospheric Administration, National Earth Satellite Service, Washington DC 20233, USA. In addition, NOAA has a large range of technical publications (NESS61 to NESS115) relating to weather satellite reception. These can be obtained by 'Yriting to the National Technical Information Service, US Department of Commerce, Sills Building, 5285 Port Royal Road, Springfield, VA 22161, USA. Information on related subjects can be obtained from the Environmental Data Service, D822, 6009 Executive Boulevard, Rockville, MD 20852, USA. SC lN ICS lNICS >NICS >NICS >NICS JAYCAR JAYCAR JAYCAR JI\YCAR JAYCAR ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRO ICS JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS JAYCAR JAYCAR JAYCAR JAYCAR JAYCAH ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS f-1 f-C1RONICS >N ICS Jt,vr/\o 11 c:rToA,.urc ,,.v,.....-.o c:1 crTon,.,ur-c- itr.vr/\o c:1 i::r-Tcf"\f\ ,re: _ECTRO _EC TRO _ECTHO _ECTRO _fCTRO _ECTRO 1/\vf"'A o ELECTRON ICS FLfCTRONICS ELECTRONICS ELECTRONICS ELECTRONICS JAYCAR JAYCAH JAYCAR JAYCAR JAYCAR /4 nd '/ Cat XJ-2000 W35 ECTROI .ECTROI .Ecrno .Ecrno 1 ECTRO .- - - - - - - - ~g~:g: ·- - and black painted fini sh. Grille is supplied wilh 4 mounting .ECTROI lugs, heavy duly screws and T-nuls (cabinel fixing spiked nuts). Th e lour new smaller grilles 3, 4, 5 and 61/2' are two piece with lhe speake r munling on a lrame whi ch lhen slots in lo lhe grille as sembly. Sell tappers and clips supplied. -~g=g: .Ecrno 1 Ecrno1 .ECTRO .ECTROI .ECTROI .ECTROI .ECTROI .ECTROI EC TROI .ECTROI .ECTROI ECTROI .ECTROI .ECTROI ECTROI ECTROI Cat AX-3512 Cat AX-3514 Cat AX-351 6 Cat AX-3518 Cat AX-3520 Cat AX-3522 Cat AX-3524 for 3" speakers for 4• speakers for 5" speakers for 6-6 1/2" speakers for 8" speakers for 10" speakers for 12" speakers HUGE PRICE REDUCTIONS JAYCAI JAYCAI JAvcA1 JAYCAI $34.95 Suilable for medium signal reception areas. 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AA FI Fr.TRON1r.s JAYCA CalLT-3178 I 30 % Chearer lh an Olh er suppliers. Gri lles pressed oul .ECTROI JAY CA JAY CA JAYCA JAYCA JAYCA Frequency -470-862M Hz• BoomWidlh-20mm sq • Overa11Lenglh - 680mm ca1u-31a1 .Ecrno1 .E:CTR01 ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS JAYCA JJAAvvccAA•, ...~~!ft!llli. ol slrong, pertoraled steel to protecl Hi Fi or PA speakers in cabin els or cars , elc. Each ollhe 8, 10, 12 and 15' griles has harge pertoia lions 10 let lt,e sound out, a rubbe r edge band JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR Suitable for good to medium sign al reception areas, or where ghosti ng is a problem. Specifications• Ele men ts - 23 • Gain -11dB • Channe ls - 21-69 • Bands - 4 and 5 • Up O :~g:g: l:LLCl HONICS ELECTRONICS ELECTRONICS ELl:CTRONICS HECTRONICS We have been able lo reduce lhe price of UHF antennas by up lo 45%. If you are a TVanl enn a installer or retailer contact our wholesale dept tor resellers prices. They will be well below whal you are paying now. All ante nnas include water resistant ?Sohm balun in a casing. Anodised elemenls, boom and relleclors whi ch are melal, not plasti c. Square 20mm diameler boom tor ex Ira rigldily. Exce llenl gain ligures and th ey are designed lor easy assembly. Protector Grilles Ecrno: .ECTROI c:rTAru,urc:: JAYCAR JAYCAR JAYCI\R JAYCAR JAYCAR mcA JAYCA JAYCA JAYCA JAYCA JAYCA ,JAYCA .JIAAvvccAA, 43 Element Metal Speaker Cone ELECTRONICS ELECTRONICS ELECTRONICS ELEClHONICS ELECTRONICS ;ia 23 Element / . .111111 $14.95 Now $10.00 JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR UHF TV Antennas Whal a llop! Greal producl, bul no one is inleresled. Hol Jel is a hol water reservoir lor your car wind screen. The reservoir moun ts on the radiator hose, which heals lhe water. lnslall alion should lake all of 5 min utes and all parls are supplied. Made In Engla ELECTRONICS f:Ll:C r HONICS ELECTRONICS ELECTRONICS FI ECTRONICS c:1 c:: rTQf'\'-.11rc:: 1tivroo c::1 c: rTon,.,11rc:; 1avro.A c:1 HOT JET SELLOUT _Ecrno _ECTRO _ECTRO _ECTRO _ECTRO _Ecrno _Ecrn6 .Ec1 Ro1 .ECTROI _ECTROI _ECTROI .ECTROI ECTROI .ECTROI ECTRO, JAY CAR JAY CAR JAYCAR JAYCAR JAYCAR iiiiiiiiii■ EU:C I HUNll,;S JAYCAR 1:LECrRONICS JAYCAR ELECTRONICS JAYCAR FLFCTRONICS JAYCAR ELFClRONICS~R tLl:C I HUNICS ELE'CTRONICS ELECTRONICS ELECTRONICS l:LECTRONICS JAYCAR JAYCAR JAYCAR JAYCAR .IAYCAR l::Lf CTRONICS EL!: ClRONICS ELl:CTRONICS ELEClHONICS FI FClHONICS JAYCAR JAYCAR JAYCAR JAYCAR .IAYCAh JAYCAf JAYCAf JAYCAF JAYCAF "JAYCAF JAYCAF JAYCAf ,JAYCAF JAYCAf .IAYCAf JAYCAf JAYCAf JAYCAf JAYCAf .IAYCAF JAYCAF JAYCAF JAYCAF JAYCAF JAYCAF JAYCAfJAYCAF JAYCAF J1\YCAF JA,CAF JAYCAe JAYCAF J AYCAF JAYCAF JAYCAF JAYCAF JAY CAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR J AYCAR JAYCAR JAYCAR JAYCAR JAYCAR JA, CAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR JAY CAR ELEC TRONIC SJAYCAR ELECTRONICSJAYCAR ELECTl-iONICS JAYCAR ELECfRO/\ICSJAYCAR dtCTRO/\ICS IA'f!:Ml ----· · ..... , .. . . . .., .., ., . ..., .... ----- ···-· ··._,. . , ..,,,, '-' ' " ' R ELECTRONICS R ELECTRONICS R ELECTRONICS R ELECTRONICS R ELECTRONICS JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR .,_,_...,...,,,,,_,,~,..., ..... 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The Jaycar kil includes an improved and larger vers ion ol lhe lranslormer specified lor the 40W version, which gives an exlra 20 walls lo around 60 walls. Ideal for lax machines, elecl ric loolhbrushes, ballery chargers for mobile lelephones, incandescenl lamps, elc., elc. TheJaycar kil includes PCB, box, punched and screened Iron! panel and all specilied components including lhe larger lransrormer. R R R R R R , , , 'l ELE ELE ELE ELE ELE ELE ELE ELE ELE ELE ELE· ELE ELE· ELE• ELE· ELE ELE $99 ELECTRONICS ELE:CTRONICS ELFCTRONICS ELECTRONICS ELECTRONICS 1 11\J r-11n c, c rTO f""H,11/'"' C' IA Vr" I\O c:, c r ToA-.ur- c- JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS 1r.. v r-110 et Cf"'TOAt,.uf"'C JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR l/\ V r"'f\C Cl C:f"'TOl"'H1i11f"~ IA V rAA TV Colour Pattern Generator Kit Rei: Silicon Chip November/December 1991 Acolour TV patlern generator is an essenlial servicelool for lhe TV serviceman since ii provides known and slandard pallerns. On awell adjusled sel, each pallern will be close lo pertecl, while on a poor sel the pallerns will be far from salislaclory. This new kit produces seven separate pallerns: checkerboard, crosshatch, dot, greyscale, white rasler, red rasler and colour bars. II will enable you lo set you r TVs convergence and purily Im lhe besl possible piclures. The kil includes PC board, box, punched and screened Iron! panel, high qualily video modulalor and all specilied componenls. 12V AC pl ugpack is an oplional exlra Cal. MP-3020 $16.95. Cal. KC-5103 ·-·-·--------== $11 Q .... Infra Red Remote Control Kit for the Train Controller KC-5028 Cal. KC-5029 240V Power Relay Kit Rei: EA January 1992 This kit will monilor lhe power drawn from a ·masler" power poinl socket. and automalically swilch on a slave sockel. It's very versalile because ii can monilor one or several appliances plugged into the "masler' and switch one or several devices plugged inlo lhe "slave". An ideal use tor lhis projecl would be lo swilch on your Hi Fi syslem. Wilh a lour oullel board plugged inlo !he slave sockel, lurning on your amplilie r (in masler) will swilch on your luner, lape deck, CD player and lurnlable elc. The kil includes PC board, box, 240 voll sockels, lead and plug and all specilied compo~ enls. Cal. KA-1740 I ELEC l ELE( :)4 9. 5 Q - $139.95 $ El::LLEEcc ~t~) Do Iby Surround Sound Decoder Kit ELE( FLFC ELEC ELEC ELEC ELEC ELEC ELE( ELEC ELEC ELEC ELF( Rei: EA January 1992. Experience cinema sound in your own lounge room. T11e Dolby "Surround Sound" process increases Ille sensatioo ol "being lhere" by producing an eflecls channel lo creale su rround sounds which a convenlionals slereo syslem can'I produce. Hook lhis simple kil in conjunclion wilh your Hi Fi VCR or slereo TV and lake lull advanlage ol movies recorded wilh Dolby encoding. Shor! lorm kil - includes PCB, and all on boardcomponenls. Cal. KA-1741 • $39 95 Light Beam Relay Kit Ideal Shop Door Monitor Rei: Silicon Chip December 1991 II you are running a business you will know Iha! it's imporlanl lo keep an eye on the door al all limes. A properly inslalled door mooilor will lei you know lhal someone has enlered lhe shop ii you' re working out the back. This kil allows you lo monilor a doorway or a path ..using an inlra red lighl beam. When someone walks lhrough the beam, ii !riggers an alarm tor a 1 second period. The ki l ~ includes PC board, box panel, • buzzer and all specilied 4 semiconduclors. Oplional exlras are12V DC 300mA plugpack Cal. MP-3006 $15.95, Relay Cal. SY-4052 $9.95 Cal.KC-5106 $32.50 Low Voltage cutout Kit for cars and Boats Rei: EA January 1992 Build Ihis simple kit and avoid gelling caughl oul wilh a llal ballery. II simply connects inlo a 12 voll accessories power line and shuls off lhe flow if lhe balleries vollage drops lo a dangerously low level , where ii won't slarl lhe vehicle. The shul oil voltage is adjuslable over a nominal rangeof 10.9V lo 11 .9Vand lhe unit will reslorepower lo lhe load aulomalically when lhe ballery vollage has relurned lo around 12.6V. An exlremely uselul and practical kil. The kil incl udes PC board, box, relay and all specilied componenls. Cal.KA-1739 $22.95 ADJUSTABLE O • 45 VOLT 8 AMP POWER SUPPLY KIT Rei: EA November 1991 Karaoke is a IOI of fun. Wilh !his kil you can remove lhe lead vocal lrom almosl any recording, and replace ii wilh your own via a slandard microphone. ll's a greal way lo liven up a parly. Complele kil includes PC board , box, Iron! panel and all componenls. Requires 2 x 9V 216 lype balleries Cal. SB-2370 $2.85 each. Cal. KA-1738 2 7 •g 5 ELE( ELE< ELE( ELE( ELEC ELEC ELEC ELE( ELEC JAYCAR JAYCAR JAYCAR JA YCAR JAYCAR This remole conlrol uni I is used in conjunclion wilh our Train Conlroller kil and dupticales all Ihe lunclions of lhewalkaboul lhrollle. The receiver/conlroller box has LED acknowledgemenl and speed selling indicalion. II has an adjuslable inerlia run conlrol and adjuslable slop inerlia. The remole conlrol has a range ol 10 melres, and has 10 lunctions: slower, lasler, stop, reverse and lorward. Theremainder are auxi liary swilches lo swilch lighls or pcinls. The kil is · ..,_ ,. · supplied complele wilh remole conlrol and receiver cases, plus all specilied componenls lo Iurn lhe KC5028 conlroller inlo wireless remole conlrol. Karaoke Box Kit <Vocal canceller> ELE( ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS (Cal. KC-5028 $89) , , 'l 'l , , , 'l ELE , ELE , ELE , ELE• , ELE• 'l ELE , ELE , ELE 'l FLF'ELE , ELE , ELE i ELE• , ELE• , ELE• , ELE• , ELE• , ELE• , ELE• 1 ELE• 1 ELE• 1 ELEI l · ' ' JAYCAR JAYCAR JAYCAR JAYCAR JAYCAR 1 A v l"'11n c, c r-Tnf"\,-111"'c- &o watt 12 - 240V Cal. KC-5108 ELECTRONICS ELECTRONICS ELECTRO'JICS ELECTRONICS ELECTRONICS Reier EA March 92 This projecl is an addilion lo our range of low cos I bench gear and is relalively slraighttorward lo conslrucl. The kil covers lhe lrequency range ol around 6Hz lo 70KHz in lour ranges wilh very low dislorlion (lypically 0.07%). II is based on a Wien bridge circuil, due lo ils low cosl, high perlormance characlerislics. The Jaycar kil comes complelewith inslrumenl case, Iron! panel label, plus lhe PCB and all specified -· · · .. . " JAYCAR JA YCAR J AYCAR JAYCAR __ _ .., • • ,.., , ., ...., .., cLE CTRONICS ELECTRONICS ELECTRONICS ELf CTRONICS ~ T . o ~ r ,~ r , r • ,... .,.,. ... ,..._. · - - ELECTR ONICS t LE CTRO NICS ELt CTRO NICS ELE CTRONICS JA YCAR JAYCAH JAYCAR JAYCAR Telephone Call Timer Kit Ref Silicon Chip March 92 This limer can save you or your business big money. II keeps !rack of lime lor you - lor up lo 19 minules - and gives lour warning beeps 12 seconds belore lhe end ol every minule. II lhen lighls up one or more LEDs lo indicale lhe elapsed lime since lhe slarl ol lhe phone call. The Jaycar kil comes wilh lhe box, Iron! panel, PCB and all specified componEnls. 9V ballery nol included Cal SB-2370 $2.85 Cal KC-511 1 , $29 95 ~~"""..:;;:;~:.iiliioilll= ~ s • ••• ·.:: ..-:": id., • . - - <!I~ •'° •'·••.•·•·· '-' · 1' ' v •' ,...,,,.,..., .... .., ~, vru • '-'- l-.v, 1, v, -.,,._, ..., ..,n , v ,,, , '-'-Lv ,, , ....., , ., .._,'-' ., ,.., , '-- " ' 1 ... ... L v,, lV l <tlVV vM I v r1 n ELECTRONI CS lcLECTRONIC'S ELE CTR ONICS ELEC TRO NICS JAYCAR JAYCAR J AYCA R JAYCAR ELEC TR ONICS JAYC AR ELE CTRONICS ELECTRONICS JAYC AR ELEC TRONICS ELECTRONICS J AYCAR ELECTRONICS ELECTRONICS JAY CAB El ECIBONICS EL( EL:~ EL{1 ;g:= ~t[i' $59 95 v, • • ..,, " • ._ ... ._ ...., • • , .....,, ,.,..., ..., '-' ' • • '-'' " • '-'-L JAYC AR JAYC AR JAYC AR JAYCAR EL(~ >'CAR EL! 1 YCAR ELI TI >'CAR ELI T l~~::~-.:::~;..::.;~~~---~~~~~~~-------------~~-.J~======:::::::__ ELE( ELE( · -ELECTRONICS ELECTRONICS ELECTRONICS ELECTRONICS ~CARE~: \'CAR EL . l'CAR EL' YCAR EL'.. l'C AR EL'.. YCAR EL'.. / CAR EL '.. YC AR EL'.. l'CAR EL'.. YCAR EL,. >'CARE~. YCAR EL'., ·/CAR El'. YCAR EL'. / CARE~ YCAR E~l / CAR EL'l YCAR EL; l YCAR EL; l 1 YCAR EL: 1 YC AR EL' YCAR EL; l l'CAR EL:1 1 YCAR EL'. YCAR EL( ~ YC AR EL( 1 YCAR EL( 1 YCAR EL( YCAR EL( ~ YCAR EL( 1 YCAR EL( 1 YCAR EL( T YCAR EL(T ~g:= ~tlT componenls. Our kil is also supplied wilh 1% resistors and lhe ullra-low noise 5534 op amp. Cal KA-1 742 . YCAR ElJ YCAR EL[ YCAR Et'. YCAR Et.= YCAR ElYCAH EL: YCAR EL: YCAR Et, YCAR El( YCAR Et;: YCAR EL;: YCAR ELYCAR ELYCAR cl! i CAR El:' YCAR El! YC AR El! YCAR EL; f CAR EL; YCAR EL; f CAR a' YCAR EL_ f CAR Et,_ YCAR Et,_ f CAR El,_. YCAR FL: YCAR EL' YCAR EL;· YCAR YCAR vCAR YCAR ~--------------''------""';;;;;......,__ LOW COST SINE/ SQUARE WAVE OSCILLATOR KIT t::LECTRO( ~g:= ~t\1 Rei: Silicon Chip Jan/Feb 1992 This swilchmode power supply has an adjuslable oulpul lrom O- 45 VOii DCand ii can deliver currenls up lo 8 amps. The kit is complele with case, punched and silkscreened Iron! and rear panels, melers, loroidal lranstormer and al l specilied componenls. Specifications of prototype: Output voltage O- 45V • Output current SA below 35V, 6A at 40V • Load regulation 1% • Ripple and noise 5mVp-p al 6A 13V, 10mVp-p al SA 18V, 40mVp-p al SA 35V • Current llmll SOOmA lo 8.6A • Overcurrent llmll 9A • Foldback current <2A Cal. KC-5109 --------------------.. $399 ELECTRd ELECTROf ELECTROf ELECTRO' ELECTRO~ JAYCAR JAYCAR JAYCAR IAYCAH ELECTRONICS JAYCAR ELECTRONICS,JAYCAR ELECTRONICS JAYCAR H i:r1uor-ucs1 IAYCAR L. ... Lv, ,-,u,,.,1-..,v >'CAR 1CAR /CAR /CAR /CAR EUTI EU n EU TF EUTF EUTf /CAR ICAR /CAR /CAR /CAR /CAR t CAR EUTF Eun EUTf EU TF EUTf EU TF EL(n 1/CCAARR EELLlli; ;g:= ~tli; /CAR EUTf /CAR /CAR /CAR ICAR 1CAR 1CAR /CAR /CAR /CAR /CAR /CAR EUTf EUTf EU TF ELI Tf EU TF EU TF EU Tf ELI TF ELITF Elin EL!Tf ICAREL!Tf /CAR EUTf ICAREUTf J (CAR EUTf 'WM I'-''"'"' LLECTRONS ELECTRONICS JAYCAR ELECTRONS ELECTRONICS JAYCAR ELECTRONS ELECTRONICS JAYCAR ELECTRONS El c:cr □a,.ur~ c:, c r - T ~ I REMOTE CONTROL BY BOB YOUNG Switching frequencies in speed controllers - which is optimum? This month, we will be taking a close look at the topic of switching frequency and how it affects the design and operation of speed controllers. Some designers use 50Hz as the switching frequency while others prefer 2.5kHz As noted in an earlier column, it is most important to switch the FETs in the fractional throttle range to avoid overheating them and wasting undue power. What we have yet to discuss is the question of what frequency do you run the chopper at? Here we have a philosophical argument of the utmost subtlety and with far reaching consequences ifwe are to believe the proponents of the 2.5kHz school. Much ink has been spilled by the electric modelling fraternity arguing over the merits of 50Hz, 2.5kHz, quency we run at. If the FETs and motor are on 50% of the time and off for 50% of the time, the current consumption and thus FET and motor heating · should be a constant. The same applies for all other pulse widths and by definition this must be so, for this is exactly how the system works. A 50-50 duty cycle gives half power, 75-25 three quarter throttle and so on, regardless of the chopper frequency. Add to this the fact that most modellers have a desperate need for speed and jam the throttle wide open for "The basic argument runs that the 2.SkHz switching rate is more efficient than 50Hz switching in that the motor runs cooler. Also, at very small pulse widths (low throttle), the control is much smoother and more precise". or frequencies in between. Some stalwarts have even changed sides and renounced their earlier views and have thus added additional confusion to an already perplexing argument. 50:50 duty cycle So what is the argument all about? At first glance it appears a storm in a teacup for a 50-50 duty cycle is a 5050 duty cycle regardless of what fre- most of the motor run anyway. At this point, the controller moves out of pulse (or switch) mode into straight DC and one really must wonder just what the fuss is all about when, for about 90% of the time, there is no pulsing in the system at all. The motor is running flat out. The basic argument runs that the 2.5kHz switching rate is more efficient than the 50Hz switching in that the motor runs cooler and is therefore subject to less demagnetising from heat. Also, at very small pulse widths (low throttle), the control is much smoother and more precise. There is also some talk of the 50Hz pulsing being more destructive to the magnets than the higher frequencies. 50Hz advantages Against this, the proponents of 50Hz systems claim quite rightly a lower component count and therefore higher reliability, smaller size and weight, and lower cost. The lower component count derives from the fact that the 50Hz is generated by th~ Rx decoder, whereas in the 2.5kHz system the 50Hz must be converted into 2.5kHz by a separate 2.5kHz oscillator. It is safe to say that it is the choice between these two fundamentals that shapes the basic design of any speed controller and the argument rages on, still unresolved. So who is right? That is what I have been trying to establish for the past three months. I must point out here that the problem is a lot more complicated than you might think and I can understand why it has never been fully resolved. To begin with, the motor is an inductive load when running and thus subject to the effects of frequency on impedance. This is compounded by the fact that the armature is switching at a rate related to the RPM and the number of poles in the commutator. The net result is a complex network of switching transients, back EMF transients and spark generated noise, all of which are changing in relation to one another as the chopper pulse width modulation and motor RPM vary. APRIL 1992 53 This means that the analysis is well out of the domain of the average electronics buff as it requires some quite specialised test equipment. For my tests, I set myself up with some quite basic equipment and it was not until I attempted to analyse the very surprising results that I realized how difficult a full analysis would be if the job was to be done correctly. My initial test set-up involved a heavy duty battery (on float charge) , a pulse generator which could be varied over the full range of wanted frequencies, a tachometer, a moving coil ·ammeter to monitor the current, and a storage oscilloscope to monitor the various voltage and current waveforms. The pulse generator was checked carefully for pulse width against frequency and gave a consistent 52-48 duty cycle over the usable range of the FETs. The tachometer was a photocell type. Two IRFZ44 FETs were used without base stopping resistors to drive a Leisure 05 stock motor and an 8 x 4 propeller (direct drive). Straight DC drive current was 28 amps, at 10,500 RPM. You can now afford a sate II ite TV system For many years you have probably looked at satellite TV systems and thought "one day". You can now purchase the following K-band system for only: $995.00 Here's what you get: * A 1.8-metre prime focus dish antenna, complete with all the mounting hardware. * One super low-noise LNB (1.4dB or better). * One Ku-band feedhorn and a magnetic signal polariser. * * lnfrared remote control satellite receiver with selectable IF audio 30 metres of low-loss coaxial cable with a single pair control line. & bandwidth, polarity & digital readout. Your receiver is pre-programmed to the popular AUSSAT transponders via the internal EEPROM memory. This unit is also suitable for C-band applications. Test results Table 1 gives the test results. As you can see, the revs and current drain are reduced as the frequency is raised, being a minimum at a pulse switching frequency of lkHz. Above that frequency, the revs rise but the current stays lower than at 50Hz. I am at a loss to present a definite solution to the curious results shown. Call, fax or write to: AV-COMM PTY LTD PO BOX 386, NORTHBRIDGE NSW 2063. Phone (02) 949 7417 Fax (02) 949 7095 All items are available separately. Ask about our C-band LNBs, NTSC 0 to-PAL converters, video time date generators, FM 2 & EPAL & Pay TV hardware. I I II ----------YES GARRY, please send me more information on K-band satellite systems. Name .............................................. I I II .___________ . 54 Phone .............................................. ACN 002 174 478 SILICON CHIP 01/92 Frequency RPM Current (A) 50Hz 500Hz 1kHz 1.5kHz 2kHz 2.5kHz 3kHz 5kHz 7600 7500 6800 6900 7200 7400 7500 7700 16.5 12.0 7.0 7.3 7.8 8.0 8.5 9.0 the 5kHz point but it must be remembered that I was only using two FETs. Six FETs will provide a much greater input capacity which will cause problems at the higher chopper frequencies. There is little doubt that the efficiency improves with frequency. Reference to Table 1 shows the current at 2.5kHz is approximately half that at the 50Hz figure for virtually the same RPM. On the other hand, I am not sure that the meter reading is a true indication of the current drawn. It was similarly difficult to interpret the current waveforms taken at various frequencies and I will need to take more definitive measurements before I can be sure of the relative merits of switching at 2.5kHz. Temperature measurements In view of the doubts about the current meter, temperature measurements taken after four minutes of run- "So there you have it - just as the argument for 2.SkHz switching predicted. It gives greater efficiency, cooler running and smoother control. Just don't ask me to explain it". I Address........................................... I I I I ........................... P/code ................ I II I TABLE 1 II I Although I did not think it important at the time to record the battery terminal voltage, I did note it mentally and the higher currents were associated with a lower terminal voltage, longer run times and longer charge times between runs. I also made a measurement at lOkHz but the reading was to my mind suspect, in that FET gate capacity was starting to distort the input. There was however no sign of distortion at ning gave a case temperature of 51.4°C for 50Hz operation and 37.7°C for 2. 5kHz operation. These case temperatures (maximum) were measured after the cooling effect of the propeller wash stopped and the internal heat had soaked through to the case. So there you have it - just as the argument for 2.5kHz switching predicted. It gives greater efficiency, cooler running and smoother control. Just don't ask me to explain it. But in spite of the above results, I find myself leaning very heavily towards the concept of a 50Hz controller. The resulting controller will be simpler and much less expensive than a 2.5kHz design. In my experience, these are very important points and as I have pointed out above, the controller will spend most of its time flat out anyhow. Other approaches Now let us discuss the ways other designers have approached the problem. The first example is a simple 2.5kHz controller with no braking. This controller is very smooth and quite linear in operation. It has six FETs which provide ample current for most applications. A voltage tripler provides 12.5V at the gates from the 4.8V Rx battery. It is a very nice little controller. I also have a circuit of European origin using the least components I have ever seen in any controller. One wonders how well it works. This is an opto-coupled unit to minimize noise fed back into the Rx from the motor drive circuit. It is fitted with a backEMF brake (dynamic braking) and again one wonders just how well that brake circuit works. From bitter experience, I have learned that the ON resistance of the transistor across the motor must be less than 100 milliohms for any braking effect to be achieved, which means that it must be driven hard. It has no voltage tripler and the drive voltage for both the forward and braking FETs is derived from the motor battery which is in this case quite adequate, being in the range of 10-35V. The disadvantage is that as the motor volts fall, so do the drive and braking voltages. Noise is also a bigger problem as the motor battery is coupled into the drive electronics and so an optocoupler is almost mandatory. It was obviously designed with model aircraft usage in mind, as a 7.2Vbattery would not provide sufficient drive to turn "From bitter experience, I have learned that the on resistance of the transistor across the motor must be less than 100 milliohms for any braking effect to be achieved, which means that it must be driven hard". the FETs hard on. It is typically European in approach, showing concern over feedback noise but unusual in using 50Hz. Another circuit uses 50Hz operation and has several clever features, including braking. Separate decoders drive the forward and braking FETs so that the brake cannot come on whilst forward is energized and vice versa. If this did happen, it would provide a dead short through the braking and forward FETs and destroy the controller. The circuit also has a voltage tripler which provides heaps of drive to both sets of FETs. This unit has been designed specifically for cars and uses a battery eliminator. The problem with battery eliminators is that the Rx runs off the motor drive batteries which eventu- Yokogawa DL1100 Oscilloscope - continuedfromp.16 press the "Initialize" button. This brings up an "Initial Exec" message on the screen, prompting you to press one of the softkeys (by the way, they're called "softkeys" because their function changes with each new screen menu). You might wonder why you have to press two keys to initialise the scope when it would be easier to press one. The same comment could go for the Auto Setup routine . And for that matter, you might ask why the machine could not initialise itself automatically at switch on. The scope could undoubtedly have ally go flat and thus all control is lost - not good in an aircraft. This type of Rx supply must also be filtered very carefully if motor noise is to be kept out of the circuit. There are also reversing controllers but these have a fundamental problem. The drive motor is included in a bridge circuit (similar to the Rail power controller featured in this month's issue) and thus there is double the volt- been made to automatically initialise itself at switch on but then there would not have been the convenience of having the last used settings saved. And the idea of making you press a soft key after pressing a front panel button stops you from accidentally wiping out existing settings . If you do press the wrong button and it brings up a screen menu that you don't want, all you do is press "Menu Off" and that clears it. Pressing it again brings the last menu back. From the foregoing it should be clear that the Yokogawa DLl 100 2 channel 100MHz digital oscilloscope is a age drop across the FETs as there is always one set of FETs on either side of the motor. For this reason, reversing controllers are not popular with the speed fraternity. They are, however, a must where total control over the model is called for. The final design Note that none of these circuits has all of the features considered desirable by the modern modelling fraternity so there is plenty of scope for new designs. Drawing from the above , our proposed design is a now a little firmer in that it will use 50Hz switching, dynamic braking, drive electronics working from the Rx battery, a free-running voltage tripler and, as a result of this battery isolation, no optocouplers. SC highly flexible and powerful instrument. It takes some time to become familiar with all its features and use them to the fullest. We had only a few days with it but in that time we have been very impressed. It is a fine instrument. The DL 1100 is priced at $4900 which includes the GP-IB interface, while the optional built-in thermal printer is an additional $750, as is the RS232 interface. These prices do not include sales tax. For further information, contact Tony Richardson at Yokogawa Australia Pty Ltd, Centrecourt D3, 25-27 Paul Street North, North Ryde, NSW 21_13. Phone (02) 805 0699. SC APRIL 1992 55 I PRODUCT SHOWCASE I The Electronics Workbench This software package from Emona Instruments is designed to enable on-screen simulation of analog and digital circuits, complete with testing by simulated instruments. It could be highly effective as a teaching aid for schools and technical colleges. By LEO SIMPSON One of the major problems in teaching electronics is the need to spend large amounts of time in setting up circuit demonstrations for or during classes. Most circuit princi ,Jes are best taught using theoretic l examples which can then be bacJ....ed up by practical circuit examples. However, the time spent setting these up can often make this impracticable. This Electronics Workbench package , produced by Interactive Image Technologies of Canada, enables circuits to be simulated on the computer screen, giving lecturers and teachers more time to spend on other things. Our review copy was of the profes- sional version which provides a VGA display and unlimited components in a circuit. The software comes on four floppy discs and the auto-installation system makes loading the software into your computer simple. The Electronics Workbench comes as two modules: analog and digital. The analog section provides you with four test instruments, as follows: a voltmeter which can show volts , amps, ohms and dBs; a 2-channel oscilloscope which operates in a way similar to a real one; a function generator which produces sine, triangle and squarewave signals from lHz to 999kHz; and a Bode plotter for dis- playing frequency responses. Once the software is running, the right-hand column of the screen shows a 'parts bin' which contains the icons to all the available parts you can use in circuit. You have an unlimited number of each component so you don't have to worry about running out of circuit parts. In fact, the limit on circuit complexity is more a matter of computer speed rather than the allowable number of parts; larger and more complex circuits take longer to simulate. To lay out a circuit, you simply click on the desired component with your mouse and drag it to the desired location on the screen. To join up components, you move the mouse to one of the ends of the component until the connector of that component lights up as a small black box. You then click and drag a connecting wire between that component and the next component. Both the analog and digital sections use the same layout procedure. The digital section's parts bin contains all the basic gates and flipflops, again in lr Ji l 00 -r = = 1 (,(1 l I,,,~~: ~t .:~. oow,n ' . .f 1)0 l-< f \ : ·$_; 1 0 0 kO ;-,: ~c• ; -~ \.:..... __ This 3-stage common emitter amplifier is one of the sample circuits provided and has both the dual trace CRO and the function generator connected in circuit. Note that the CRO shows input and output traces. 56 SILICON CHIP i This circuit demonstrates the software's ability to provide Bode plots of a Wien bridge network. The right hand column shows the analog parts available. These are brought to the screen by clicking and dragging. unlimited quantity. The test instruments in this section include a word generator which can hold 16 8-bit words; an 8-channel logic analyser; and a truth table/symbol converter capable of turning truth tables into circuit representations. This allows you to set up a digital circuit and go through the analysis showing all the possible states. The package also includes what is called a Hypertext help system, which can be tailor-made to suit your requirements. All you do is to type the text you wish to appear on screen in an ASCII-format file on any wordprocessor. This feature makes it suitable for use alongside most textbooks. Components such as op amps and transistors are assumed to have standard parameters but you can customise these to simulate virtually any device. One point we should make is that this software package is not like some of the more expensive circuit simulation packages which have comprehensive libraries of most commercially available op amps and transistors. Instead, it is intended more as a teaching and tutorial package rather than for design testing simulation, although it can do this to a limited extent. It is not possible to link analog and digital components together. In a classroom situation, where analog and digital electronics tends to be segregated, this would not cause a problem but it makes it difficult, if not impossible, to analyse many of the circuits de- scribed in SILICON CHIP. Some of the supporting literature which comes the Electronics Workbench suggests that this software package is ideal for practical classes with students because it allows them to build. circuits without the need for components, test instruments and the like, saving the school or college money. We hesitate to fully agree with this because as useful as the package may be, it cannot fully demonstrate to electronics students the practical problems that come up in circuit design and layout; eg, earth loops in amplifier design or over-biasing a class AB audio amplifier so that the output transistors blow up. Interestingly though, if the input of the simulated oscilloscope is not grounded, 1 volt of 60Hz signal is added to the output waveforms. This simulated hum pickup by the circuit is a small but practical point which would often be overlooked by students. The Electronics Workbench comes in three versions: the personal version which has a monochrome display and can run circuits with up to 30 components, and costs $149; the personal plus version which has unlimited components, retailing at $299; and the professional version with both EGA and VGA capabilities for $429. Each comes complete with a useful reference manual which shows how to install and operate the software, as well as explaining briefly how the software simulates the circuits. - ii ····- • .. ~- . .... . - Our first full catalogue of our huge range of electronic components and kitsets is nearing completion and will soon be delivered to those requesting a copy - FREE! To secure your copy, please fill in the coupon (or copy details), send together with 3 x 45<1: stamps for postage and we'll send a catalogue, hot off the press! You'll also receive updates, bonus offers, specials, etc. during the year AND each month until June you will be in the draw for a free SCOPE PH20 soldering iron! .::, =:. Q 'eLJ / Please send me a FREE catalogue 0:;)t I have enclosed stamps for postage Name: . Address .. .. . .. Postcode ,\ ALL ELECTRONIC COMPONENTS l i 118 · 122 Lonsdale Street. Melbourne. V,c 3000 l:L.. Telephone (03)6623506 Fax (03)6633822 Our conclusion: this software could be very useful to students and lecturers in a structured electronics course. For further information, contact Emona Instruments, PO Box 15, Camperdown, NSW 2050. Phone (02) 519 3933. - - . .·.... . . ==~~~"';:=J;&c-~=:-, ~='.'- - - · ·;:'.::.::: ,:;-:=;0=2:s~:'.-;=:-·:- - - - - -~ ----··- C·---c_,--, ·· - -=---=-=:--: • >·=-•--:;___.,.,. l <at> .. 1jjl ·.jiiQ}~ · < . < -: 1 i: ..- i.!..51- -~~,:~~~-cc=~. -.·· ---l~;-~:8? ~~~~-·-~---r-:-·_ ,- - . . _J -~ _J·!··-11!,' ....-I.••.···.· .i.~ .,._·_:_···r· .·_ •..· i r - -> :::-' ------ . I .. +·· ·,,,..,--;:::;_--::>--.~·-t-~~ A logic analyser and word generator make it easy to step through a 7-segment display driver. These instruments are brought down by clicking and dragging them from the top screen row. -x-_,,...:::1-.,\.. ...._ '--_,..:-· ,,- ··-:=::,-~;;:, - 1: i v.,· -t'.· '.,:. ·r.· .~ l Complex digital circuits can be simulated by the Electronics Workbench. This circuit is a BCD decoder which is based on simple logic gates. The right-hand column shows the components "parts bin". APRIL 1992 57 PC-compatible prototyping cards Rod Irving Electronics has a new range of prototyping cards that are double-sided with plated-through holes. The range consists of three boards, the first two having 5-volt and ground rails around the outside of the board and access to all pins on the bus. One is designed for an 8-bit or XT bus and the other HP's basic instrument line for a 16-bit or AT bus. Both boards retail for $59.95. The third card is designed for a 16-bit bus but also has a bl!lilt-in address decoding circuit and data buffer. It sells for $84.00. All boards have provision for a DB socket with up to 37 pins for an external port. For more information, contact Rod Irving Electronics, 74 Parramatta Rd, Stanmore, 2048. Phone (02) 519 3134. products. The new line of basic instruments has the same philosophy but has been engineered to keep product costs and prices down without compromising performance. In the past 12 months, a general purpose voltmeter, an oscilloscope, a power supply, a dynamic signal analyser, an LCR meter and a milliohm meter have been released. The intent is to expand the range across the entire HP product line. For more information, contact the Customer Information Centre, Hewlett Packard Australia, 31-41 Joseph St, Blackburn, Vic 3130. Phone (008) 03 3821 or in Melbourne (03) 272 2555. New Digitor multimeters In response to customer need, HP has been working on a series of new test instruments under the banner of "the basic instruments program". The program's aim was to develop affordable test instruments with the same quality and reliability as the existing HP range. HP's traditional focus has been to develop state of the art test instruments, not only in design, but also in the manufacturing and testing of its 58 SILICON CHIP Dick Smith Electronics has recently released a new range of high quality Digitor multimeters. The meters are built to survive professional use under harsh conditions. A high impact Valox case protects against accidental damage and an 'O' ring seals the case against the ingress of moisture and dust. The multimeters comply with MIL STD 28800 Class 11 lA and IEC 348 specifications and have both fuse and transient voltage protection on the inputs. Additionally, the meters will give a loud beep should they come in contact with dangerous voltages. The range includes a true RMS digital unit with analog tone (Q1586, $215); a 29range digital unit (Q-1584, $179); an autoranging digital unit (Q-1582, $149); and a pencil style digital unit with data hold (Q-1580, $149). The latter is designed mainly for electricians and servicemen. For further information, contact Bill de Rose or Rex Callaghan at Dick Smith Electronics on (02) 888 3200 or see the range at your nearest Dick Smith Electronics store. Safe & effective video head cleaner The new Trackmate TM271 VHS maintenance cassette solves the problem of cleaning fragile and inaccessible VCR parts by using a system of three brushes rather than tape. Being much wider than a video tape, the brushes clean not only the areas of normal tape contact but other regions where dirt can accumulate, such as the drum cooling grooves. The brushes are made from thousands of flexible filaments which are claimed to absorb dirt six times more effectively than conventional cotton buds. , Using the cleaner is simplicity itself. Isopropyl alcohol is applied to the brushes via a special pen and the cleaning cycle is set by twisting a "timer" switch. The cassette is then inserted in the VCR and "played". The cleaning cycle automatically stops if there is a problem or if the user gives the VCR an incorrect instruction. A built-in counter notes the number of applications and after 10 uses it reminds the user to wash the fibre brushes, which are mounted on removable cartridges. The Trackmate TM271 retails for $39.95 . For more information, contact Chantal Dray at Trackmate Australia, PO Box 652, Avalon, NSW 2107. Phone (02) 973 1807. Electronics Workbench® Personal torches from Rod Irving Rod Irving Electronics has a nifty range of personal, go-anywhere touches. They are made of corrosion resistant, machined aircraft aluminium and are waterproof. All seals are fitted with o-rings to make the torch completely watertight. They come with a spare bulb in the battery compartment and feature a twist on/off switch. Turning the lens further adjusts the focus of the beam. Complete removal of the lens turns the torch into a mini beacon. Two sizes are available, the smallest containing a single AAA cell and the larger one, two AA cells. Both retail for $11.95. Also available is a rechargeable key ring torch suitable for finding your car and door locks at night. For more information, contact Rod Irving Electronics, 74 Parramatta Rd, Stanmore, NSW 2048. Phone (02) 519 3134. NW.OGCIRCUn,~ ;:;; GD ■ o- , .' D> • ......... CS) 0 66060000 """' Build and simulate both analog and digital circuits, complete with simulated instruments on your computer! FEATURES • Quick and simple circuit entry • Digital and Analog Modules included, complete with all components • Simulated instruments: dual trace scope, spectrum analyser, function generator, multimeter, digital word generator and logic analyser • Complete control over all component values and parameters • Print: circuit schematics, parts list, instrument readings, macros • Logic conversion -truth table to Boolean formula to logic gates • Customisable hypertext help system THREE VERSIONS Variable gain amplifiers for AGC The new AD600 and AD602 ICs from Analog Devices are monolithic, dual-channel, low noise variable gain amplifiers, featuring wide bandwidth and low distortion for use in AGC (automatic gain control) and programmed gain applications. Gain characteristics for the AD600 are 0 te +40dB and -10 to +30dB for the AD602. Each channel of the amplifier employs a patented variable attenuator and a high speed fixed gain amplifier. The signal to noise ratio for a 1V RMS output at 1MHz is -76dB for the AD600 and -86dB for the AD602. With relatively few additional components, amplifier sections can be cascaded for a total gain control range of 80dB. For applications such as analog weighing systems, each channel can be turned off by a TTL-compatible gating signal which prevents signal transmission and sets the DC output to ground. The AD600 and AD602 are available in either 16-pin DIP or SOIC. For more information, contact NSD Australia, 205 Middleborough Rd, Box Hill, Vic 3128. Phone (03) 890 0970. SC • Professional Version: EGA/VGA colour display; unlimited components • Personal Plus Version: Monochrome display; unlimited components • Personal Version: Monochrome display; limited to 20 ----------------I YES ■ I want ELECTRONICS WORKBENCH in my computer Professional Version Personal Plus Version Personal Version $429 $299 $149 Plus$7 Delivery Enclosed is my cheque/money order for $_ _ _ _ _ or Please debit my Ca rd No.j O Bankcard O Mastercard IIIIIIIIIIIIIIII Signature _ _ _ _ _ _ _ _ Expiry Date _. _ /_ _ Name _ _ _ _ _ _ _ _ _ _ __ _ _ __ _ Street _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Suburb/Town _ _ _ _ _ _ _ _ Postcode _ __ Send to: Emona Instruments, PO Box 15, Camperdown, NSW 2050. Tel: (02) 519 3933 Fax: (02) 550 1378 ·-----------------~ APRIL 1992 59 AL TRON/CS 24 HOUR EXPRESS DELIVERY 'Our customers are often amazed at the speed and efficiency of our Jetservice Courier delivery. Phone your order Toll Free 008 999 007 and presto we can deliver your order next working day (country areas 24-48 hours later). Our famous 14 day satlslactlon money back guarantee protects your hard earned $$$'s should ever a purchase be unsuitable for your needs. I invite you to try Australia's best electronics phone order service soon.' Regards, Jack O'Donnell The All New Powerhouse 1200W Inverter This new design of Power Inverter will provide 1200 Watts of power from a heavy duty 12 or 24V battery. Usln9 the latest Mosfet output stage and toroidal transformer this inverter is efficient and will deilver high surge currents. The Powerhousa has been designed not only for rugged bullet proof operation but for ease of construction, two PCB's hold all circuitry with one inter-connecting cable. (7 wires). Thll kit come, lo you In • luHy drilled, pre punched chUIII complete with lllk ICrH ned front panel. Auembly of the kit 11 1lmplllled e1 the majority of component, mount on e llngle PCB. Thul vlrtually e llmlnetlng all external termln1l1. Sulteble for UNI In camping, boetlng, ll1hlng, mining, remote Mlllement1 etc. F11lure1: • Massive 1200W continuous 2400W surge will run almost anything • 12 or 24V operation selected via internal wiring • Low battery cut-out • Over temp cutout • Circuit breaker for overload protection • Auto start circuitry for standby operation • Easy to construct Compact 40 Watt Inverter (SC Feb '92) - -- K8710 $79 -- - ~ .00 This fantastic little unit is ideal for use with incandescent globes, (note this model inverter will not run fluorescent lighting) electric shavers, small radios and some plug pack operated devices, ie charging cord less drills and other rechargeatle battery appliances etc. Feeturea: • Operates off 12V DC • Battery connection leads provided • Light weight • Uses Mosfet devices • High efficiency • Low heat dissapation Baby Room Monitor (S.C. Jan '91) (SC Dec '91) This TV transmitter enables you to transmit signals from the output of your VCR to a second TV set in the housa without messy splitters and cables. Two versions available for videos with UHF or VHF outputs. K 5880 UHF Version K 5885 VHF Version $74 .95 Digital Altimeter for Gliders and Ultralights (SC Sep/Oct '91) K11790 Kit Version $799.oo 6792 Built & Tested 12V Input $999 6793 Fully Fully Built Tested 24V Input K K 1180 $24.9s Using state of the art circuitry this supply will be a great asset to the enthusiast and professional alike. It uses switch mode principles which allows for smaller transformers, and heatsinking which means greater efficiency, less heat and lighter weight. Feature1: • Variable output • Variable current limit • Separate Earth Terminal • Individual Volt and Amp Meters • Constant 13.SV setting • Short circuit proof Speclllcatlon1: • Output voltage 0-45V • Output current SA <at> 35V, 6A <at> 40V • :e8~~~tb~~r~;;; ~i~/f~t ;~~l~~~scek~Ou~~~t~e~s8t~a3,,5~,'7 Current limit SOOmA- Low Voltage Cut-Out for Cars and Boats This Baby Room Monitor allows you to listen to your baby from a remote location using a conventional FM receiver. It runs from a single 1.5V AA battery and includes a muting facility so that it only transmits sounds above a certain level. (SC Jan '92) Build this simple little device, and avoid getting caught out with a flat battery duri ng your holidays. It simply connects into a 12V accessories power line, and shuts off the flow if the battery voltage drops to a dangerously low level. Ideal for battery powered camping fridges etc. Adjustable Cutout Variable from 10.9V to 11.9V. Includes Automatic or Manual Voltage Reset Function. K 4328 $24.ss Infra-Red Light Beam Relay 7 ·,1:::;. _--_;;_.,--.",,.En·....:-,- ~ ~ : ·\_~ ,-.'~ _vU#lf.-,•----- ---l This compact digital altimeter · can display altitude up to 19,990 feet with 10 feet resolution. Accurate to better than 3.5 percent. A must for hang-gliders, ultralights etc. Operates on 9V battery. (SC Dec '91) This simple project allows you to Low Cost 'Karaoke' Adaptor ~!ilfa!~!i~~~~~~: ~~:"b~:i:~ it triggers an alarm for a 1 second period. Ideal door monitor for shops or for security around home or office. Requires 12V DC plugback (M 9002). . .l1 _Kz_sao_$_2_9_9_.oo________-+-_K1_,2_0_$_3_2_.9_s----lh,;~~;:-;.Colour TV Pattern Generator is new colour TV ttern generator oduces saven parate patterns: • heckerboard • White ter • Crosshatch • Red ster • Dot • Colour bars Greyscale will enable you to set your TV's convergence and purity r the best possible pictures. Requires 12V AC plugpack 9020 $16.95. .00 Adjustable 0-45V, 8 Amp Bench Power Supply (SC Jan/Feb '92) $375 .00 K 3380 ~i~ K & 4 Channel Guitar Mixer and Preamp K5535 $49.9s (SC Jan 1992) This unit features saparate bass, midrange and treble controls, very low noisa and distortion, separate Input level controls plus an output level control. Ideal for usa with most musical instruments from keyboards to guitars to tape decks. In fact, you can feed it with just about any audio signal - it's not just limited to guitar outputs. • Dl1tortlon: (at lkHz and 100mV input) less than 0.0075% • F~uency Re 1po1111: 18Hz-35kHz (+/ -3dB) . The kit includes PC Board, potentlometres, input sockets and all specified components. The kit does not include the optional ground plane, nor the 1SV power supply board. It's time to bring out all those hidden vocal talents that you've al ways known were there. With this project you can remove the lead vocal from almost any recording, and replace it with your own via a standard microphone. It's a great way to liven up a party! .K 1110 $34.9s Hlah Power Car Alarm With" lrelest Remote Control 125dB siren. Flashes headlights and sounds siren when unauthorised entrance through the car doors, boot, bonnet (negative trigger inputs) or removal of the car stereo (normally closed input to earth). Automatically resets after 60 seconds. 10 watt, 8 ohm. Ideally suited to S 5460 siren cover and our alarm panels. This horn can deliver in excess of 120dB when driven by an appropriate driver circuit. Protects external siren from tampering, weather etc. Also ideal for mounting strobe. Suits C 2015 horn speaker. Tamper switch available. s5220$99.oo $29 S 5221 Anditional Remote Control .95 Economy Alarm System This system comes complete with the following components: • One Alarm Panel • One Passive lnfrared Detector (P.I.R.) • One AC Power Pack • One 8 Ohm Horn Speaker • Three pairs of Magnetic Reed Switches • One 12V/1.2AH Rechargeable Back Up Battery • Emergency Panic Button Alarm Panel Feature•:• 5 Protection Circuit Loops • Independent Connections for N.C. and N.O. Sensor Switches • Arm - Disarm by Digital Access Key-Pad • MultiStation Remote Control • Warble Tone - Steady Tone Siren Driver • Adjustable Timers for Entry Delay and Siren Duration • " Latch" and "Timing" Output Relays • Remote and Local Alarm Status indication This system is easily installed by the Home Handyman No special tools or equipment are required. Comprehensive mstallat1on 1nstruct1ons suppiled. s 5470 Normally $~00 Thlt Month Only $299.oo, Save $50.oo s 5480 Cl:28.s5 S 5180 Tamper Switch $1.85 Alarm Strobes Uses Xenon Strobe • tube for high energy flash . Output rate approx 1 per second. 12V DC, 320mA. Dimensions: 97mm diam, 50mm High. · $F"s5, Now S 5455 Blue S 5450 Red $20.oo C 2015 $15 .95 Super Small PIR 11 I sC11• Incorporates Pulse Count :C;edib \;. 1 Trig9ering which virtually eliminates false alarms. QI" Operates on 8-16V DC. Features : walk test LED, wide 12x12m detection, N.C. tamper switch, interfaces with most alarm panels. See AL TRON/CS '92 catalogue for f•JII details. S 5302 Normally $}4oo This Month $69.oo UHF Microprocessor ControUed .Wireless Security System . . Apart from the flawless operation of the system one of the great features Is its appl1cat1on with rented or leased premises - let's face It, money spent on installing a wired system in your home or office, factory, etc is irrevocably lost when you move on. With this system you simply take it with you. Ultra high-tech and push button operation makes this unit a bre,eze to install and operate. Features 6 sectors plus 2 x 24 hour fire and tamper circuits. The S 5240 system includes main controller, 1 Passive Infra Red Movement Detector, 1 window or door Reed switch, wired siren, power supply, back-up rechargeable battery, and a special personal remote. All sensors are radio transmitters which means no wiring is neccessary (except for the plug pack and siren) . The whole si·stem is coded so it can not be interfered with and can be changed any time by the owner. Each individual sensor can be easily set to operate on any sector. The main controller utilizes latest EEPROM technology which means things like selecting user on/ off codes, isolating sectors are a breeze. Includes a myriad of other amazing features, too many to mention . Call AL TRON/CS today tor a ,,.. colour brouchure. Wireless Remote Keypad Complete ay1tem lncludea: External Siren S 5255 $135.00 I Red Detector/Transmitter C 2015 $15.95 1 x Door/Window reed Switch/Transmitter 1 x Hand Held remote Control/ Transmitter 1 x Horn Speaker - 10 watVwired 1 x 240V AC adaptor 1 x 1.2Ah Back-up Battery Passive Infra Red 1 x Set of batteries for all transmitters i : ~~;;i~~ in~~: 12" Guitar Soeaker Attention all guitarists and keyboard musicians. Th is fine USA designed speaker is supplied as standard equipment to the \liorld famous brand name series of Guitar Amps. • Impedance: 8 Ohm • Sensitivity: 101dB/W (0.5m) • Weight: 2400'gm c 3102 $99.00 8" PECC Woofer 60 Wattt RMS, 100 Walla Max. These Poly Emulsion Coated Cone (PEGG) Speakers utilize the development of high grade driver components in Japan , such as Barium ferrite magnets and specially formulated paper cones impregnated with poly emulsion. The result is a driver of quite remarkable power handling , performance and extremely low distortion . Redford 4" Carbon Fibre Speakers These 4" Dual Cone drivers are built from the latest technology in magnets, voice coils and carbon fibre cone material. They exhibit quite outstanding reproduction from the low frequency register through to quite remarkable mid range performance. The Carbon Fibre Cone is lightweight yet rigid, greatly reducing cone breakup and distortion. Musically, carbon fibre reproduces sound with a much smoother frequency response. Available in 8 or 16 ohm impedances, making them ideal for multiple speaker applications. Rated Input Power. . . . . . . 15W Max. Input Power. . . . . . . . . 25W Freq. Response ....... FO-20kHz Resonant Frequency .... . . 110Hz Sensitivity . ............. 96dB/W Magnet ......... . .. . 226gm/8oz ~95, Now s 5245 $155.oo Redford PECC Woofers NEw FO R •92 50 \van, RMS, 100 Watt, Max. C 0641 8 Ohm C 0643 16 Ohm Movement Detector Door/ Window Reed Switch & Transmitter S 5247 $72.95 s 5240 complete System 79 Only $ 6 .oo $24 .95 12" PECC Woofer 80 Watts RMS 160W Max. Impedance (300Hz) . . . . 8 Ohm Frequency Response ...... FO-4kHz Resonant Frequency. 60Hz (+/ -12Hz) Sensitivity ....... 98dB/W(0.5m) Magnet.. . . . . 848gm Impedance (300Hz) .... 8 Ohm Frequency Response . FO-3kHz Resonant Frequency .. 25Hz (+/ -5Hz) Sensitivity . . . . . . . . . . . 98dB/W(0.5m) Magnet. ................. 1408gm c 3024 $68':oo, c Now $54.95 3030 $'125.oo, Now $99.95 10" PECC Woofer 15" PECC Woofer 80 Watt• RMS, 130 Wattt Max. Impedance (400Hz) .. 8 Ohm Frequency Response .. . ... FO-4kHz Resonant Frequency .. 28Hz (+/-5Hz) Sensitivity . . .... 97dB/W(0.5m) Magnet. . 1170gm 100 Watt, RMS 200W Max. Impedance (400Hz) . . . ... 8 Ohm Frequency Response ...... FO-3kHz Resonant Frequency .. 25Hz (+/ -5Hz) Sensitivity ............ 98dB/ W(0 .5m) Magnet.. . .... 1835gm c 3026 $90"95 , Now $79.95 c 3032 $)a5oo, Now $ 1 9 9 .95 Sensational New Dome Tweeter Ferro Fluid60 cooled voi ce coil. watts • power capability. smooth response Silky ·.. 1.5kHz to 20kHz. Wide ' angle dispersion. In comparitive tests we rate this fantastic new Dome Tweeter superior to the VI FA D19! (which costs $45 or more). Incredible low price! C 3018 Normally $~.50 Introductory :tee . NEW FO R '92 $ 2 7 .50 ea, or $ 5 2 pair Save your valuable CD's from finger prints and some fine scratches with this wet type cleaner. Includes brush and cleaner spray. A bargain at this price. Excellent Clarity And Performance A 9220 Normally $)'1'.95 Range: Depending on conditions approx. 300M Requires 8 x AA batteries. A 1980 Normally This month Only $9.95 This Month $ 9 9 .00 $1.Nf.oo Amazing Nicad Battery Bargain from $2.oo ., ~~ All full specification premium quality. Good for up to 1000 recharges. unm lf(lll ~~ 1-9 S 5020 S 5022 S 5023 A/B Computer Switch · · · Box $2.95 $8.oo $14.oo AA 500 MAH 'C' 1.8AH 'D' 4 AH Built in ignition cap • Uses standard butane gas • Comes with safety bench stand• Supplied with 2mm soldering tip and blow torch tip• Adjustable temperature from 400°C to 12000C • Can be easily refilled with standard butane lighter gas • Replacement tips are less than half price of some other brands! T 2452 Replacement 2mm Tip $4.95 T 2455 Replacement Exhaust Port $4.95 T 2450 .50 T 2448 Weller Butane Gas Refill $5.95 This universal infra-red remote control makes all other remote units superfluous. Will control CD players, videos, TV' s and stereos etc. Controls up to 6 different appliances. Easy to use and programme from an existing functional remote. With this simple device you can monitor any door in your house. This two piece alarm consists of control box and magnet. The magnet simply mounts onto the door frame while the unit is mounted on the door so that when closed, the magnet and control box are opposite. Easy to use on/ off switch. Built in beeping buzzer sounds when tripped. Requires 9V battery. s 5315 '92 u1ea elate ot the art ceramic healing element. T 2446 Normally $ ~ 5 Micron Mk II Soldering Station I Electronic Temperature Controlled, Temperature Selectable, Soldering Station. The MICRON T 2440 soldering station offers the ultimate in controlled temperature hand soldering. Feature,: • Variable Temperature Control • LED Temperature Readout• Zero Voltage Switching protects CMOS D<,vices • Grounded Tip • 48 Watt Element • Thermocouple lmbedded in Heating Element for Precise Temperature Control • 24V Low Voltage Element • Rubber Silicon Lead • Chrome Plated, Iron Clad Ultra Long Life Tips • New Improved Ceramic Element $139 T 2440 Normally $J.i9'.95, This Month Only .95 G pfllCE! $15 This Month $ 3 9 .95 ,-MAz.1N Thie le the 1992 model of our fantaatlc Labtech Dual Trace 20 Meg Scope. There are over 3000 now In ,.,.lca throughout Auetral/e - Our cu1tomera Include Unlvare/tlu, R-arch E1labll1hmenla and lnduetry Famous Labtech 20MHz Dual Trace Oscilloscope J The '92 model is a dual trace 20MHz oscilloscope using a high brightness CRT. The vertical amplifiers have high sensitivity of 5mV/ div and a frequency characteristic response with smooth roll off exceeding 20MHz. The TV sync. signal operator circuit is provided to ensure stable observation of video signals. Triggering is obtained by ' sampling the AC power waveform, external waveform or internally generated trigger . Highly recommended for \ Two Channel Pro Power Amp 90 Watts Per Channel SENSATIONAL VALUE NORMALLY $699.oo THAT's i100 OFF k«&w.JUJJIAA,, ,•~, ~~ i: _ '.'· --·- _!_.c-'c ' I < '\WW :r~J~- Thi• 1tereo amp 11 ldaal tor background/foreground appllcallon,. Fantattlc tor reetauranta, 1hop1, dleco'1, aerobic, , PA t0und 1y1tem1 and home. 5e,.1ce Wortlbench, De,lgn Laboratory, Manutacturero, Unlveroltle1 and the dedicated enthullHtlc. Q NO~ ~AC~ IN STOCKI Amazing value! 240V AC inbuilt neon glows red . Panel cutout 18.6 x 13mm. • 90 watts RMS per channel minimum into 8 Ohms from 20 to 20,000Hz with less than 0.05% THD • 2 large power meter indicators • EIA Panel with handle device • XLR socket for speaker terminal • Output relay to eliminate turn-on and off transients • Dimensions: (W x H x D) 482 x 92 x 295mm • Weight: 10.5kgs • Ideally suited to A 2210 stereo tuner. S 3218 $1.50 u, or 10up $1 A 2040 $~ Thie Month $599.oo 0156 This Month Only $599.oo Ideally ·suited to Q 0156 (2 required) . Superb quality. DC to 80 MHz, Max 600 Volts DC. Lead length approx 1.5m. Q Screwdriver temperature adjustable between 2500C and 450' C enabling very delicate soldering on low settings with surprising heat energy reserve on maximum setting. Relative temperature is indicated by LED lamp brightness. Now $39 Scoop Purchase On Door Alarms ► OR H 0236 Double $5.50.. :.,;rr ~ I .• H 0235 Single $ 4 .95 ea 11 rfb~~~~ c:t ~~~na~y~~ePe~~g ~r.a ~~wgas soldering iron. Feature•• See through gas chamber (no more guessing how much gas is left!) • Universal Remote Control NEW 25+ $2.oo $ 6 .oo $ 12.oo ~ t~ ~....J ·.: : ~ -, ~ ~~ All New IRODA Gas Soldering Iron Two way printer/ peripheral computer switch with D25 sockets. Allows two printers to be run off one computer and individually selected or allows one printer to be run off two computers and individually selected. NEW D 1570 Normally $J8".95 FOR '92 This Month $ 3 9 .95 A 1000 $69.95 10-24 $ 2 .50 $7.oo $1 3 .oo lnterlocklng Part, Drawer• Unique design allows units to be 'dove-tailed' together. Drawers will not stick or seize. Single or double drawers available. 0175 $49.95 ea Illuminated SPST Rocker Switches Auto-Ranging Multlmeter with Bar Graph Readout for Just $99.oo Compar~s Very Favourably to Fluket or Beckmant at a Fraction of the Cost! Feature,: • 42 Segment Bar Graph Display • Auto-ranging on Voltage and Resistance • Memory Mode • Low Ohm Range • Hold Facility • Automatically indicates negative inputs • Low Battery Indicator • Continuity check with Buzzer Speclllcallone: DC Voltage Ranges: 5 (200mV, 2V , 20V, 200V, 1000V) Input Impedance: 100m Ohm, 200mV Range, 10M Ohm. the other Ranges AC Voltage Range: 4 (2V, 20V, 200V, 750V) Input Impedance: 10M Ohm DC Current Ranges: 200mA, 10A AC Current Range: 200mA, 10A RHl1lance Ranges: 200 Ohm. 2K Ohm 20K Ohm 200K Ohm. 2M Ohm , 20M Ohm Ganeral Display: 3½ digit LCD Q 1075 Normally $1$.'oo Now $99.oo Q 1077 Protective Holster $12.50 Q 1078 Carry Case $12.50 t TM ea Our Top Selling 17 Range Dlgltal Multimeter for an Amazing $39.95 With quality and features you would expect only on expensive meters the Q -1 056 represents ex cellent value fo r money. Specltlcallone: DC Voltage: Ranges 2-2000V AC Voltage: Ranges 200V, 500V DC Current: Ranges 200mA, to 10A Re1l1tance: 5 Ranges 200 Ohm, to 2M Ohm Diode Teal: Test Current 1.0mA Test Voltage 3.2V Max Battery Te,t: Ranges 1.5V, 9V Loaded Current: 1.SV 100mA, 9V 6mA Q 1058 Normally ~ 95 Thi s Month $ 3 9 .95 Q 1057 Carry Case to Suit $12.50 ~ TRANSFORMER SALE Save Up To 30% All Altronics Mains Transformers are now wound on segregated nylon 66 flame retardant bobbins. Models M 2851 - M 2855 and PCB Transformers M 7112 - M 7130 are fitted with primary thermal fuses. All comply to the latest (and very stringent) Australian Standard Code AS 3108 Customers please note - ALL MAINS TRANSFORMERS PRIMARIES 240v SPECIFICATIONS LISTED REFER TO SECONDARY WINDINGS Torlod Power Transformers Multlpurpose SOVA 80VA Model• 160VA Modela 300VA Modela 500VA Model• Dlmenalona and Weight 9, 12, 15, 18, 21, 24, Volts at OOVA output M 2165 Normally $26.so Thla Month $2O.oo SOVA Multlpurpose 100VA Normally All $49.95 Now$45.ooaa 12, 15, 24, 27, 30, Volts at 100VA output Model M 31)20 M 3025 M 3030 M 3035 M 3040 M 2170 Normally $29.95 Thi• Month $ 2 2 .oo Multipurpose 120VA 12, 15, 24, 27, 30, Volts at 120VA output. M 2175 Normally $39.95 Thi• Month $3O.oo 12.6V CT 150mA M 2852 12.6V CT 300mA M 2853 12.6V CT 500mA M 2854 24V CT 150mA M 2855 30V CT 150mA M 2154 12V, 15V, 18V 1 Amp M 2155 6V3, 7V5,8V5 Norma lly All $65.oo M 2156 M6672 6, 9, 12, 15V Normally 1-9 ea 10+ea $7.30 $7.65 $8 .20 $7.65 $7 .65 $11.00 $6.00 $5.00 $6.00 $5.00 $6.00 $5.00 $6.0 0 $5.00 $6.00 $5.00 $9 .00 $8.00 $9.00 $8.00 2 Amps $10.95 $17 .95 $15 . 0 0 $13.00 1 Amp $16.50 $15.00 $13. 00 9V5, 12V6, 15V 1 Amp · Now $60.oo aa Model M 3055 M 3060 M 3065 M 3075 M 3080 SEC. 6+6 7.5+7 .5 9+9 12+12 15+15 Normally All $129.oo Now $110.oo ea Model M 3085 M 3086 M 3088 M 3090 M 3092 M 3100 M 3105 Model M 3120 M 3125 M 3130 M 3135 M 3140 M 3145 M 3150 M 3155 SEC. V 12+12 18+18 25+25 30+30 35+55 40+40 45+45 r t ~~ Normally $13 .95 i 28mm SEC 1 $1O.oo $9.oo SEC 2 240V Microphone Type Primary: 200 Ohm Secondary: SOK Ohm 1 •l ~•~• Ngrmally All $12.95 Thla Month 10+ MU Metal Shielded Audio •~~ ••• FUSE 1-9 M 0701 Normally $34.95 1O.oo aa Thi• Month $25.oo Or buy 10 or more for $ 8 .oo aach. 174 Roe St . Perth W.A. 0000 Phone (09) 328 1599 PHONE TOLL FREE 008 999 007 MAIL ORDERS C/ - P.O. Box 8350 Stirling Street PERTH W.A. 6849 STANDARD DELIVERY & PACKING CHARGE $5 .50 to 1Kg. $8 1 Kg-5 Kg AUSTRALIA WI DE_ we process your order the day received an d despatch via . Austra lia Po st. Al low approx g days from day you post order to when you rece ive goods. SEC. V 30+30 35+35 40+40 45+45 50+50 55+55 60+60 65+65 . .... Impedance: 600 Ohm line/600 Ohm equipment Tuma Ratio: 1:1 7VA PCB Mount Mains Transformers From $8.00 Model M 7112 M 7115 M 7118 M 7124 M 7130 SEC. V 18+18 25+25 30+30 40+40 45+45 Normally All $89 .95 Now$80.oo ea Telecom Type Line Isolating Transformer 15, 17V5, 20, 24, 25V5, 30V 300VA 160VA Mini/Medium Mains Power M 2851 SEC. V 12+12 18+18 25+25 30+30 35+55 -~' ~%::' ,_- ~ "' ~,'-''"''''"''""-% ~ M 1000 Bridging laolallng Type Used for coupling audio modules. Prevents earth loops, hums etc . Essential coupling device where DC isolating is required. Nominal Impedance ratio: 10K: 10K (1:1) M 0702 Normally $34.95 Thi• Month $ 2 5.oo HEAVY HEAVY SERVICE -All orders of 10Kgsor more must travel Express Road - Please allow 7 days for delivery . $12.00 to 10Kgs. $15.00 over ;QKgs . INSURANCE - As w ith virtuall y ever y other Australian suppl ier, we send goods at consignees risk . Should you require comprehensive insurance cover against loss or damage please add $1 .00 per $100 of order value (minimum charge $1) . When phone order ing please request "Insurance" TOLL FREE PHONE ORDER - Bankcard . Visa. Mastercard Holders can phone order toll free up to 6pm Eastern Standard Time . Remember with our Overnight Jetaervlce we deliver next day . AL TRON I CS RESELLERS you - Chances are there is an Altronic Reseller right near check this list or phone us for details of the nearest dealer . OVERNIGHT JETSERVICE Up to 3Kg is $10 .00, 3Kg to 5Kg 1s $23.00 - We proce ss your Blue· Ribbon Dealer, are highlighted with a ■ These dealers generally carry a order the day received and despatch via. Overnight Jetaervlce Courier for deliver y ne xt day Country areas please allow addit ional 24 -48 hours. comp rehensive range of Altronic produ c ts and kits or will order any required item fo r you . WA COUNTRY ALBANY BP Electronics ■ (098) 412681 Micro Electronics (098) 412077 BUNBURY Micro Electronics (097) 216222 ESPERANCE Esperance Communications (090) 713344 KALGOORLIE Todays Electronics ■ (090) 215212 MANDURAH Lance Rock Retravision (09) 535 1246 Micro Electronics (09) 5812206 PORT HEDLAND Ivan Tomek Electronics (09 1) 732531 ROCKINGHAM TV Joe's (09) 5271806 NT ALICE SPRINGS Farmer Electronics (089) 522388 DARWIN Ventron ics (089) 853 622 VIC All Electronic Components (03) 6623506 BORONIA Ray Cross Electronics ■ (03) 7622422 CHELTENHAM Talking Electronics (03) 5842386 CROYDON Truscott Electronics ■ (03) 7233860 PRESTON Preston Electronics ■ (03) 4840191 COUNTRY BAIRNSDALE LH & LM Crawford (051) 525677 BALLARAT Balla rat Electronics (053) 311947 BENDIGO KC Johnson ■ (054) 411411 MILDURA McWill iam Electronics (050) 236410 OLD Delsound PL ■ (07) 8396155 WEST END B.A.S. Audiotronics. (07) 8447566 WOODRIDGE David Hall Electronics ■ (07) 8082777 MAROOCHYDORE MALS Electronics ■ (074) 436119 MARY BOROUGH Keller Electronics (071) 214559 NAM BOUR NambourElectronics (074) 411966 PIALBA Keller Electronics (071) 283749 ROCKHAMPTON Access Electronics (East St.) (079) 221058 TOOWOOMBA Hunts Electronics (076) 329677 TOWNSVILLE Super Solex ■ (077) 724466 SA Force Electronics ■ (08) 2125505 BRIGHTON Force Electronics • (08) 3770512 CHRISTIE$ BEACH Force Electronics ■ (08) 3823366 FINDON Force Electronics ■ (08) 3471188 HOLDEN HILL Force Electronics ■ (08) 2617088 LONSDALE Force Electronics ■ (08) 3260901 ENFIELD Aztronics ■ (08) 3496340 COUNTRY WHYALLA Eyre Electronics (086) 454764 TAS HOBART George Harvey ■ (002) 342233 LAUNCESTON George Harvey ■ (003) 316533NSW David Reid Electronics ■ (02) 2671385 SMITHFIELD Chantronics (02) 0097218 COUNTRY COFFS HARBOUR Cofls Habour Electronics (066) 525684 NEWCASTLE Novocastrian Elect.Supplies (049) 621358 WARNERS BAY Vilec Distributors (049) 489405WINDSOR M & E Elect. and Communications (045) 775935 WOLLONGONG Newtek Electronics ■ (042) 271620, Vimcom Electronics (042) 284400. • • ••• •• A.UXlUAJJV =Sll:1.TJ111E \li FRAREl D/J{ ·-··- REMOTE R,._ILPOWER r I . TIU.CK M \ti MAX mm. • > • • OL INFRARED REMOTE CONTROL FOR MODEL RAILROADS This infrared remote controller is based on our veiy popular Railpower walkaround throttle. All the features of the original circuit, including pulse power, inertia, braking and full overload protection are retained, and a few more have been added to make this a really deluxe model railroad controller. By LEO Sll\1PSON & JOHN CLARKE 64 SILICON CHIP Over the years, we have seen a number of solid state throttles for model railroad layouts but none matches the circuit presented here for features and versatility. While our Railpower circuit, published in the April and May 1988 issues of SILICON CHIP, featured a walkaround throttle, this new circuit goes one better with full infrared remote control. Walkaround throttles are a great idea because they allow you to follow the train closely around the layout while you control it. The walkaround throttle concept is simple - just a small box on the end of a lead which has a knob to vary the speed and perhaps a couple of switches to provide direction (forward/reverse) and braking. So it is simple and inexpensive. But for some time now we have had requests for an infrared remote controlled version of the Rail power? Why? Well, apart from the fact that so many appliances these days have remote control (and therefore it is fashionable), it does have distinct advantages when applied to a model railroad controller. There are no trailing cables to trip over and there is no need to plug and unplug the throttle as you move around a large layout. Apart from remote control, the new circuit has an impressive range offeatures, as listed in a panel accompanying this article. Before we describe the features, we should note that this series of articles will present a complete model railroad controller and then describe what you have to do to upgrade our original Railpower controller to full remote control. You can retain virtually all of the earlier circuit and just build the remote control section. Pulse power The IR Rail power uses pulse power to control the model locomotive motor. This is essentially the same method as used in switchmode power supplies whereby a DC voltage is varied by rapidly switching it on and off. This means that the peak voltage across the track is always the same, regardless of the speed setting. Varying the width of the pulses applied to the loco varies the speed. In our circuit, the track voltage is about 17 or 18 volts peak. This relatively high voltage is better able to overcome poor contact resistance between the loco wheels and track and so gives much better low speed running and starting. Features • lnfrared remote operation with 10metre range. • Pulse power for smooth and reliabte low speed operation. • Excellent speed regulation. • Adjustable inertia (momentum) . • Adjustable braking. • Full overload protection including visible and audible overload indicators (short circuit duration: one minute). • Adequate power for double and triple heading of locos. • Track/direction LED indicator. So the circuit monitors the backEMF of the motor and if this voltage drops, as it tends to when the loco starts lugging up a slope or whatever, the circuit actually increases its output voltage to help maintain the selected speed. We haven't overdone this feature though, so that a loco will still tend to slow down as it is loaded, but the speed regulation is certainly better than if this feedback was not included. Inertia or momentum Real trains have inertia, hundreds or thousands of tonnes of it. When the driver opens the throttle(s) on his • Acknowledge LED. • Preset maximum and minimum track voltage. • Meter to indicate speed setting. • 2 momentary auxiliary outputs. • 3 momentary or latched auxiliary outputs. • Forward/reverse control lockout to avoid derailments. • Zero track voltage when first powered up. • Several different IR remote controllers can be used on the same layout. loco(s) very little happens at first. It may take many kilometres for the train to get up to operating speed and similarly, when he applies the brakes, the speed does not slacken very rapidly. By contrast, model trains have no inertia at all and when full power is applied to the track, they accelerate like drag racers. Similarly, if power is abruptly removed from the track, they skid to a stop, which is hardly what you'd call "prototype operation". For this reason, the Railpower controller incorporates inertia circuitry so that the track voltage builds up slowly when the speed control is wound full on and drops slowly when Speed regulation Another worthwhile feature of our circuit is its excellent speed regulation. This helps the loco to maintain its speed even though the gradient may change or the load may change, as in shunting. What happens is that the circuit monitors the back-EMF of the motor. This is the voltage that all motors generate to oppose the current through them and, as it happens, the back-EMF is proportional to the motor speed (EMF stands for electromotive force , another term for voltage). All the controls (except for the inertia control) are on the infrared remote control handpiece. These include the throttle (Faster & Slower), braking (Stop) & direction controls, plus five auxiliary outputs for switching relays. APRIL 1992 65 MAINS INPUT A N E FUSE, SWITCH AND TRANSFORMER SLOWER TRAIN CONTROLS FASTER 0 12VAC 0 STOP 0 CONTROL INERTIA CONTROL i-----OUTPUT INFRARED RECEIVER PCB , 0 AUXILIARY CONTROLS! 0 2 4 RAILPOWER PCB INFRARED SIGNAL 0 00 3 5 +12V MOMENTARY 3 4 5 Overload protection All model train controllers need some sort of short circuit protection because short circuits can occur quite frequently. Whether it's because a loco is derailed, or because points are faulty, or because someone deliberately shorts out the rails with a screwdriver, overloads do occur. The Railpower controller has "foldback" short circuit protection (we'll explain that later) plus a LED indicator and a buzzer to indicate that an overload has occurred. Thus, it will indicate even when momentary shorts occur, as can happen when a loco is crossing points. Power output While model loco motors rarely pull much more than one amp, some model locos can pull considerably more than this, depending on whether they have smoke generators, sound systems and lighting. So if you want to double or triple-head locos or have lots of track lighting, you'll want plenty of amps. The Railpower controller has plenty, around 4 amps or so with the specified 60VA transformer. In fact , we have tested the Rail power with as many as five locos pulling 60-plus wagons around a large layout. The Railpower SILICON CHIP OVERLOAD LED OVERLOAD BUZZER LATCHED OR MOMENTARY Fig.1: this block diagram shows all the control features of the new Railpower model train controller. The circuit has a current capacity of 4 amps, enough to power five or more typical locos to pull very long and heavy trains, and features track and overload indicator LEDs and a speed meter which indicates the throttle setting. the brake is applied. It makes the trains look a whole lot more realistic. You can adjust the amount of inertia with a knob on the front panel. TRACK INDICATOR LED OV AUXILIARY OUTPUTS WITH LED INDICATION 2 66 TRACK SIGNALS FORORO RE~SE handled it without a murmur and without even getting warm. Current output is not the only important parameter though. While most model locos are specified to operate at a maximum of 12V DC, some manufacturers specify less voltage and this should not be exceeded, to safeguard their motors. For example, Marklin Zscale (1:220) locos are specified for a maximum of 8V DC. Most N-scale locos run best with around 9V DC maximum. On the other hand, Lionel and LGB trains need around 15V to really perform. The Railpower controller can be easily adjusted for these specified maximum voltages. Transmitter and receiver Now let us look at some of the operating features of the Railpower. The features are depicted in the block diagram of Fig, 1. There are two separate units, the handheld IR remote control transmitter and the Railpower unit · itself which combines the infrared receiver PC board and the pulse power PC board. The pulse power board is identical to that used in the original Rail power described in April and May 1988. The handheld transmitter is just like the handheld remote for your VCR, CD player or TV set. It has 10 buttons which are in two groups of five. The top five buttons are for controlling the locomotive. There are buttons labelled Slower, Faster, Stop, For- ward and Reverse. The other five buttons are used to control five auxiliary outputs on the Railpower. These may be used for controlling lighting, signalling or points on the layout. Two infrared light emitting diodes (LEDs) protrude from one end of the handheld unit. When you press a button on the handheld unit, the Acknowledge LED on the front panel of the Railpower will flash or will light up for as long as you hold down one of the buttons. If you press the Faster button, the pointer on the meter will move up the scale. This indicates the speed setting for the loco. If the meter indicates full scale, then you are asking for full speed from the loco. Just how long it takes for the loco to reach full speed will depend on how you have set the Inertia control. If you have set the Inertia control to off (ie, fully anticlockwise), the loco will have no inertia at all and will respond immediately to any increase in the speed setting. You might want this when performing shunting manoeuvres. On the other hand, if you set the Inertia control fully clockwise, the loco will take three or four minutes to reach the set speed, depending on how much load it is pulling. If you press the Slower button, the meter reading will immediately begin to reduce to zero but again, the loco may take several minutes to reach the new speed you have set, depending on the Inertia setting. Pressing the Stop button will cause the loco to come to a complete stop and this will take between zero and about 10 seconds, depending on how you have set the braking adjustment. Forward/reverse lockout Pressing the Forward or Reverse buttons will cause the Acknowledge LED to light but you will get no other response unless the loco is stopped or running at a very low speed which is set by you. The reason for this feature is simple. If you switch any normal speed control from forward into reverse (or vice versa), it will usually derail the whole train. If your train consists of 60 wagons and several locos and the layout is a metre or more above ground level, such a derailment can be more than just a hassle - it can cause expensive damage to your rolling stock. Our IR Remote Rail power cannot cause these derailments. If you do want to change the direction of the train, the procedure is as Below: the circuitry in the Railpower unit is accommodated mainly on two PC boards: the original Railpower pulse power board at left (mounted on the lid) & the new Infrared Receiver board which mounts on the bottom of the case. The potentiometer on the front panel allows the amount of inertia to be adjusted. follows . First, hit the Stop or Slower button and allow the train to come to a complete stop. You must wait until the FR/OFF LED on the front panel is extinguished. When that happens, you can press either Forward or Reverse to change the direction of the train. You then briefly touch the Faster button and the train will build up to the previously set speed. A 2-colour LED indicates the track voltage and train direction. Green is used for Forward and Red for reverse and the LED glows more brightly as the track voltage increases. Auxiliary outputs As already noted, the new Railpower has five outputs and these are designed to operate external relays. Two of the outputs, 1 & 2, are momentary which means that they operate only while buttons 1 or 2 are pressed. The other three outputs, 3, 4 & 5, can be either latched or momentary. If they are set up as latched outputs, you press the appropriate button once to turn them on and once again to turn them off. Each output has an associated LED on the front panel which lights when the output is activated. Multiple remote controls Some readers will no doubt ask This is the board for the handheld remote control unit. The various linking options allow you to use up to three otherwise identical transmitters which all operate independently on the one layout (see text). whether they can have more than one of these infrared remote train controls on the one layout. After al( on a big layout divided up into blocks, you might want three, four or more controllers. The answer to the question is yes. In fact, the handheld remote control transmitter has three internal coding options which allow you to have APRIL 1992 67 PICK UP A. FREE RIE 1992 MAILORDER CATALOGUE FROM ANY OF OUR STORES NOW! , THE NEW PRODUCTS JUST KEEP COMMING AT ROD IRVING ELECTRONICS --~~~ WELLER SOLDERING STATION with temperature controlled soldering iron. !:~- ~ -~~ \ 11111) ~ ~ THE POWERMATE "GREAT 8" with Overload Protection. .. A tramsformer power~d soldering station, complete with a low voltage, temperature controlled soldering pencil. The special Wellar "closed loop" method of controlling maximum tip temperature is employed, thereby protecting temperature sensitive components while the grounded tip protects voltage and current sensitive components. 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Cat No. Description 1-9 10-99 100+ R15210 .001uF 1nF Polyester 100V $0.40 $0.30 $0.25 R15212 .0015uF 1.5nF Polyester 100V $0.40 $0.30 $0.25 R15214 .0022uF 2.2nF Polyester 100V $0.40 $0.30 $0.25 R15216 .0033uF 3.3nF Polyester 100V $0.40 $0.30 $0.25 R15218 .0047uF 4.7nF Polyester 100V $0.40 $0.30 $0.25 R15220 .0068uF 6.8nF Polyester 100V $0.40 $0.30 $0.25 R15222 .01uF 10nF Polyester 100V $0.45 $0.35 $0.30 R15224 .012uF 10nF Polyester 63V $0.45 $0.35 $0.30 R15226 .015uF 15nF Polyester 63V $0.50 $0.40 $0.35 R15228 .022uF 22nF Polyester 63V $0.50 $0.40 $0.35 CITIZEN™ PN48TM Notebook Printer W•loom"• <h• ,.. wo,10 ~ ,~•book Cat No. R15230 R15232 R15234 R15236 R15240 R15244 R15248 R15250 R15252 R15254 .R15256 .033uF .047uF .068uF .1uF .22uF .47uF 1.0uF 1.5uF 2.2uF 3.3uF 4.7uF Description 33nF Polyestor 63V 47nF Polyestor 63V 68nF Polyester 63V 100nF Polyester 63V 220nF Polyester 63V 470nF Polyester 63V 1000nF Polyester 63V 1500nF Polyester 63V 2200nF Polyester 50V 3300nF Polyester 50V 4700nF Polyester 50V 1-9 $0.50 $0.50 $0.55 $0.55 $0.80 $1.05 $2.10 $3.50 $5.95 $6.50 $6.95 10-99 $0.40 $0.40 $0.45 $0.45 $0.65 $0.90 $1.75 $2.95 $4.95 $5.50 $5.95 100+ $0.35 $0.35 $0.40 $0.40 $0.60 $0.80 $1.50 $2.75 $4.75 $5.00 $5.75 ~ ~ ,,..,,.::5®74 -•;;J The PN48 Notebook Printer is the first printer that is every bit as portable as the new notebook computers. 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JI I I I ,- ------:7 E 1k ~ 100k: INFRARED RECEIVER PCB 1 I I ~ 0 Is --.--.- ........ .... 220k +17V 100k PULSE-POWER BOARD OUT + 0.1 +12V TRIANGLE WAVEFORM VT RAIL POWER +. 2200 .J: 2.2 .J: 25VW"t!.25VW-,,!. .,. .011 47 ~ 16VW+ +12V L ________ J I o;c 15 13 I I I. I .r-1 F M2165 60VA + +12V ,----!-----,I MINIMUM~ ADJUST VR2 100k 12 11 MAXIMUM ADJUST VR1 100k 100k +1?V 8.2k r: +9.BV +12V I 27k 10k +1 _2V +12V +12V EOc VIEWED FROM BELOW 8 MOTOR BACK EMF 8 CE ~ ~ 10k GND ,~oo, re ~, Q1 '80650 SW ~ .,. +12V o.m MOTOR OVERLOAD BUZZER Q2 BD650 +11v---.---------, Fig.2 (left): the pulse power circuit is virtually identical to the Railpower circuit described in the April & May 1988 issues of SILICON CHIP. All the IC and transistor numbers correspond to those shown in Figs.2 & 4. IC2c and IC2d provide the foldback current protection while ICs 3 & 4 provide logic switching to the H-pack output stage (Q1-Q4). +12V +12V 100k VT VP 1\/V\ OSCILLATOR three otherwise identical transmitters all operating independently. And if you install different ceramic resonators in the circuitry, you could have virtually unlimited numbers of independent infrared remote train controllers. Pulse power principles Now let us describe the operating principles of the pulse power circuitry of Fig.2. This is virtually identical to the Railpower circuit published in the April and May 1988 issues of SILICON CHIP. The circuit of Fig.2 is pretty daunting at first so let's have a look at the core of the circuit which is shown in Fig.3. This depicts the two key op amps which provide the pulse power output or more specifically, pulse width modulation. IC1d is wired as a Schmitt trigger oscillator while IC2a is wired as a comparator. ICld oscillates by the following action. When power is first applied, Cl has no charge and the output ofIC1d is high. Consequently, Cl is charged via R1 until the voltage at pin 6 exceeds the voltage at pin 5. This causes the output at pin 7 to switch low and so Cl is now discharged via R1. So Cl is alternately charged and discharged via Rl and the resulting waveform is a triangle (sawtooth) waveform, shown as VT in Fig.4. This waveform has an amplitude of between two and three volts peak-topeak and a frequency of about 200Hz. This triangular waveform is applied to pin 13 of IC2a which compares it with the speed voltage Vs fed to pin 12. Since IC2a is wired as a comparator, its output can only be high or low, so when VT is above Vs, the output will be low and when VT is below Vs, the output will be high. The interaction of VT and Vs via IC2a is shown in Fig.4. Fig.4(a) shows .,. Fig.3: this is the basic pulse power control circuit. ICld is wired as a Schmitt trigger oscillator while IC2a is wired as a comparator. The output (Vp) is a 200Hz pulse waveform with pulse width determined by the setting of the speed control pot. VT n?WITT /'( /\ /\ VP- (a) HIGH VOLTAGE (b) LOW VOLTAGE Fig.4: how the output of IC2a varies with the setting of the speed control pot. At higher speed settings, the output pulses are longer. that when Vsis set for high speed, the output from IC2a is a series of fairly wide pulses. These give an average DC voltage across the track which is quite high, say around 9 or 10 volts. Similarly, in Fig.4(b), when Vs is set for low speed, the output from IC2a is Vp, a series of narrow pulses which have quite a low average DC voltage, say around 2 or 3 volts. H-pack output So th e pulse waveform Vp is eventually delivered to the track and loco motor via IC3, IC4 and output transistors Q1-Q6 , as shown on the circuit diagram ofFig.2. Again, comprehending how all th ese devices work together is not easy so we have reproduced the output circuit in Fig.5. This shows the four power transistors, Q1-Q4, in an "H" configuration with the motor of the loco connected between the two sides of the "H". IC3 and IC4 are depicted as a logic block with three inputs, one for speed which is Vp and two for direction (forward and reverse). Fig. 5 is really quite a lot more corn- plicated than it needs to be. Instead of using six transistors and two logic ICs, we could have made do with one small signal transistor, a power transistor and a heavy duty relay, which would have reversed the track voltage for the forward reverse mode. But while the circuit is a little complicated, it does have the advantage of being cheaper and more compact than the relay/transistor combination. It also has the advantage of having memory for the direction setting. This is important if the circuit is to be used with a walkaround control as originally described or, as now, when the circuit is married to the remote control board. The H-co.nfiguration of Fig. 5 is commonly used in industrial circuits for motor speed and direction control. To make the motor go in one direction, Q1 and Q4 are turned on while Q2 and Q3 are kept off. To reverse the motor, Q2 and Q3 are turned on and Q1 and Q4 are turned off. Putting it another way, for the forward motor direction, current passes through Q1 and Q4; for reverse , curAPRIL 1992 71 VP LOIIIC IC3, IC4 FORWARD o.m REVERSE CURRENT SENSE ... Fig.5: the H-pack output circuit. To make the motor go in one direction, Q1 & Q4 are turned on while Q2 & Q3 are kept off. For the reverse direction, Q2 & Q3 are turned on and Q1 & Q4 are turned off. spikes from their commutators and from the pulse waveform. The Darlingtons come in a TO-220 plastic encapsulation but have a collector current rating of 16 amps peak (8 amps DC). rent passes through Q2 and Q3. In practice, for the forward direction, Q4 is turned on fully and Ql is turned rapidly on and off by the pulse waveform Vp, to give speed control. Similarly, for the reverse function, Q3 is turned on continuously and Q2 is modulated by the pulse waveform Vp to give speed control. Natty, huh? Q5 and Q6 are there solely to provide voltage level translation between the logic block, IC3 and IC4, and the output transistors. This is necessary because the logic circuitry runs from +12V while the output transistors run from +17V. Q1-Q4 are Darlington transistors which incorporate flyback diodes connected between their collectors and emitters. These diodes are necessary when driving inductive loads such as motors which will tend to generate ;, Main circuit Now let us relate the circuits of Fig.3 and Fig.5 to the pulse power circuit of Fig.2. The circuit of Fig.5 can be seen at the righthand side of the main circuit while ICld and IC2a are roughly in the centre of the circuit. In the top lefthand side of the circuit is a box marked infrared receiver board. Signals from the receiver board are connected at the six points shown in the box. Now have a look at ICla and IClb, at the lefthand side of the circuit. These two op amps are connected as :il ~ - .,HJ=5 ~0mV w OG P*1 rr ~ & & T" ff 72 • FER - Hl <:I ? I •) :1 !'i ~ & " -~ 'I fl"' SILICON CHIP ·- ~ ~'f~ window 2ms/d ~ rn r ' & & I '~ Fig.6: this oscilloscope waveform shows the voltage across the track at a low speed setting. Note that the pulses have an amplitude of about 17V. The waveform between the pulses represents the motor back-EMF. The hash on the waveform is caused by the commutator of the loco motor. voltage followers. Their function is to buffer and reproduce the voltage from the wipers of VRl and VR2. VRl .sets the maximum voltage applied to the track. This is important, particularly for Z-gauge, as mentioned earlier. VR2 sets the minimum track voltage. This is necessary because all locos have some minimum voltage below which their motors will not run. So VRl and VR2 set the overall speed range which is provided by the infrared receiver board at terminal 6. The speed setting voltage from the infrared receiver board is fed to the 47µF capacitor at the non-inverting input (pin 3) of IClc. The voltage across the 47µF capacitor is buffered by voltage follower IClc which feeds IC2a, via pull-down diode Dl. So IClc and Dl provide the voltage Vs fed to IC2a, as shown in Fig.3. Back-EMF monitoring As already noted, the pulse voltage from IC2a is fed via logic circuits IC3 and IC4 to the H-pack output stage but let's ignore those for the moment. Instead, let's flick down to the backEMF monitoring circuit provided by diodes D4 and D5 and transistor Q8. What this circuit does is monitor the voltage across the motor when the output transistors are providing no power. In other words, the speed monitoring circuit looks at the motor in between each pulse delivered by Darlington transistor Ql or Q2. How does it do it? Well, remember that for the forward motor direction, Q4 is continuously on while Q3 is off. This means that virtually the full voltage appearing across the motor appears at the collector of Q3. So the motor voltage is fed via D4 and a 2.2kQ resistor to the non-inverting input of IC2b (over on the lefthand side of the circuit). But D4 feeds the voltage down the 2.2kQ resistor all the time so it gets the pulse voltage as well as the motor back-EMF which is not what we want. So every time a pulse is delivered by Ql, the pulse waveform Vp also turns on Q8. So the pulse voltage never gets to the input of IC2b. Similarly, for the reverse direction, Q3 is always on and the full motor voltage appears at the collector of Q4 and is fed via D5 to the 2.2kQ resistor and thence to the input ofIC2b. Again, whenever pulse voltage is present across the motor, Q8 is turned on, to The remote control unit is built into a standard plastic case which is cut in half to produce a slimline unit that's easily held in the hand. Note the two infrared LEDs protruding through the end of the case. shunt it to ground. So the voltage fed to ICZb truly represents the motor back-EMF and therefore is an indication of the motor's speed. It is a train of pulses, because of the switching action of Q8. ICZb is a non-inverting amplifier with a gain of 3.2, as set by its 220k.Q and lOOk.Q feedback resistors. Its output is a pulse waveform which is filtered by a 22k.Q resistor a'nd 2.ZµF capacitor. This smoothed DC voltage, representing the motor's actual speed, is fed to the reference input of ICld, the triangle waveform generator. This h&s the effect of raising the overall voltage level of the triangle waveform VT, while its amplitude and frequency remain the same. So what happens if the back-EMF generated by the motor for a certain speed suddenly drops? The effect is to lower the overall voltage level of VT, the triangle waveform. As can be seen from Fig.3, if VT is lowered in leve_l with respect to Vs, the pulses delivered by ICZa will be longer and so the power delivered to the motor will be increased and the desired speed will be restored. Overload protection Two op amps, ICZc and ICZd, provide the short circuit protection and both of these are wired as comparators. The current passing through the motor is monitored by the 0. 1.Q 5W resistor connected to the commoned emitters of Q3 and Q4. The voltage developed across the resistor is fed via a lOk.Q resistor to the inverting input, pin 2, of ICZc. The voltage at pin 2 is then compared with a reference voltage at pin 3, which is approximately 0.6 volts. Normally, the voltage at pin 2 will be well below 0.6 volts and so the output of IC2c will remain high, as will the output of IC2d. Therefore, operation of the controller continues as normal. When an excessive current flows in the controller output, a large peak voltage will be developed across the 0. 1.Q sensing resistor and the voltage at pin 2 will rise above the threshold of comparator ICZc. This will cause the output to go low which then pulls pin 12 ofICZa low, via diode DZ. This has the effect ofreducing the width of the output pulses and so the fault current is reduced. ICZc also turns on the overload LED to indicate the fault condition. ICZc's action in reducing the fault current tends to cause a "hunt" condition whereby as the current is reduced, the voltage at pin 2 reduces and so the controller again delivers the full pulse width. This causes the current to increase again and ICZc again switches on. This "oscillation" is slowed to some extent by the O.lµF filter capacitor at pin 2 of ICZc, so that the action of ICZc is adequate to cope with shortterm overloads and short circuits which may occur when a loco is crossing points. For longer term short circuits though, ICZd comes into play. This op amp monitors the output of ICZc via LED 2 (the overload indicator). When a long duration short circuit occurs, the capacitor at pin 5 is discharged so that its voltage is below the reference voltage at pin 6. This causes ICZd's output to go low which then also pulls pin 2 ofICZa low, via diode D3. So ICZc and ICZd together act to reduce the pulse width and thereby control the output current. ICZd thus provides a 'foldback" current limiting action. ICZd also drives Q7 which sounds the buzzer whenever a short circuit or overload occurs. This very effectively draws your attention to any overloads, whether momentary or otherwise, so that any faults can be corrected. Just a small point of explanation here: the reference voltage at pin 3 of ICZc is 0.6V which may lead you to conclude that current limiting will occur for currents in excess of 6 amps peak (ie, 0.6V across the O. 1.Q sensing resistor). In practice though, the O. lµF filter capacitor at pin 2 allows higher peak currents to pass before limiting occurs. The output Darlington transistors, Q1-Q4, are fitted with small heatsinks which normally stay quite cool. If a short circuit is maintained across the track for any length of time though, the transistors will rapidly become very hot. They can withstand this condition for several minutes although the overload buzzer will be sounding stridently and the short should be removed as soon as possible. Logic circuitry Now we come to the part of the circuit which looks quite tricky but isn't; if you have stuck with the description as far as this point you will have no trouble with the logic. IC3c and IC3d are the key to it all; they are coupled together as an RS flipflop which is controlled by the APRIL 1992 73 13 10_t 12 XXX01 11 XXX10 ,. + + 220 16VWI 0.1! 02 BD140 -: 9V: ..L B + lO XXX11 5 100XX IC1 MV500 OUT 010XX A,.-5=-----(:>--L._K3-c1.,.__._ _ +9V 1 Bt=-~--_,L.,,K4"-(')-___. LK2 .,. LK1 PLASTIC 0 ~ ':" B ELJc VIEWED FROM BELOW ~{ ECB ~- RAILPOWER INFRARED TRANSMITTER BOARD Fig.6: this is the circuit for the remote control transmitter. It uses an MV500 transmitter chip (IC1) to drive two LEDs via switching transistor Ql. The pushbutton switches connected to the row & column address pins select the output code. forward/reverse switch S2. When S2 is set to the forward condition, it pulls pin 5 low (normally held high by a 10kO resistor). This causes the output at pin 4 to go high while the output at pin 3 goes low. The flipflop will then remain in this condition until S2 is switched over to the reverse condition. When that occurs, pin 1 will be pulled low and the flipflop will change state. Pin 3 will now be high and pin 4 will be low. (If you want to better understand this type offlipflop, have a look.at our series on Digital Electronics, in the February 1988 issue) . The flipflop determines which output transistor remains on continuously - ie, Q3 or Q4. For the forward setting of S2, pin 4 of IC3c will be high and pin 3 will be low. As a result, the outputs of inverters IC4c and IC4d will be low and Q3 will be off. Conversely, the outputs of inverters IC4e and IC4f will be high and so Q4 will be on. IC3a and IC3b gate through the pulse waveform (Vp) signals from IC2a, depending on the setting of the flipflop. Thus, ifQ4 is turned on continuously, pulse signals are fed via IC3a, inverter IC4a and transistor Q5, to turn Q1 on and off at 200Hz. Similarly, if Q3 is 74 SILICON CHIP turned on continuously, for the reverse condition, Vp signals are gated through IC3b, inverter IC4b and transistor Q6, to turn on Q2 at the 200Hz rate. Power supply The power transformer is a 60VA multitap unit available from Jaycar (Cat. No. MM-2005) or Altronics (Cat. No. M-2165). It is connected to provide a 12V AC output which feeds a bridge rectifier and two 2200µF 25VW electrolytic capacitors. This produces smoothed but unregulated DC of about 17-18V. This unregulated DC is fed to the output stage (Ql-Q4) and also to a 7812 3-terminal regulator to produce a regulated+ 12V rail which is used to power all the op amps and logic circuits. Remote control And now let's have a look at the infrared remote control side of the circuit. This is based on a 3-chip set from GEC Plessey. The remote control transmitter uses an MV500 while in the receiver we use an SL486 amplifier and MV601 receiver. The MV500 and MV601 !Cs are designed specifically for infrared or di- rect wire link transmission using PPM (pulse position modulation) signals. When connected to a suitable keypad, a maximum of 32 different codes can be transmitted. Each IC is set to the same transmit frequency, anywhere between 400kHz and 1MHz, with the frequency set by a ceramic resonator. For a given ceramic resonator frequency, it is possible to have three different transmitters and · each will have their own unique coding. The transmitter circuit ofFig.6 comprises the MV500 transmitter IC, the ceramic resonator (Xl) and infrared LED driver transistors Ql and Q2. The circuit operates from a single 9V battery and draws so little standby current (2µA) that an on/off switch is unnecessary. Ten pushbutton switches are connected between four of the row input pins (5, 7, 8 & 9) and either the column output pins (10, 11 & 12) or the +9V rail. When a button is pressed, a unique code is delivered from the output, pin 1. It drives transistor Ql via a lkO resistor. Ql then drives the base of transistor Q2 via a 1000 resistor. The 8200 resistor from Q2's base to the 9V rail ensures that Q2 turns hard off when Ql is off. Transistor Q2 drives infrared LEDs 1 and 2 via a 2.20 current limiting resistor. The peak current through the LEDs is around 1.3 amps although the pulses are very short at around 15 microseconds long and the duty cycle is quite low, at under 20%. The 220µF capacitor across the 9V battery supply helps supply the peak currents to the LEDs, while the 0. lµF capacitor provides supply decoupling for ICl. !Cl 's internal oscillator runs at close to 615kHz, as determined by the ceramic resonator (Xl) connected between pins 16 & 17. The l00pF capacitors at these pins provide the correct circuit loading for the resonator. The A and B inputs at pins 14 and 15 set the transmitter coding, as mentioned earlier. They can be independently connected to either the +9V rail or to ground. In our circuit, we show both inputs connected to the +9V rail via links LK3 and LK4. Note that the transmitter will not operate with both the A and B inputs tied to ground. Next month, we will continue with the infrared receiver circuitry and its interfacing to the pulse power circuit described above. SC Both drives include all cabling and adaptor card to suit most IBM Compatibles. Our current catalogue has details. "These drives are worth buyinl{ for the mechanisms alone. ' Now $199.00 Save $130.00 ~~: i[ !!I a_ '< .;~~ "Clil-~~ g#~ ~3!1>!:B S-&~.~~ ;I g.~~Q <ii" l!l-3 i -•CD :g I!!~ i $ll Cl) Cl) '-t Cl) ::,-' ct)OOCl)iiru,rop, ,...z s88"11l::rg,s~ ~ ~ ~ <' ~ oq g § a.2 '"::,-&oo ,._,, p... (") (') O O ~ -o - .,-1- l:j (I) n~ > ., ~ t,;"' "CI} § e fO 3 ~ 1f e g.' 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Front Panel Kit $135.00 • Voice recording and reproducing LSI using an ADM algorithm. • Capable ot record ing and reproducing up to a maximum of 16 phrases. • 4 different bit rates can be selected. (8K, 16K, 22K, 32Kbps). • Pausing function . • Beep sound output. • Mute Circuit. • Built-in DRAM refresh circuit.• Built-in band pass filter.• Builtin microphone amplifier. • Built-in 10 bit DAC. • Built-in DAC output buffer. • Uses a 640K resonator. • +SV single power. • Clocked CMOS for low power consumption.• Variabledebouncing time for start, stop and pause by the CPU terminal. Features: The CMOS chip used in thi s kit is a surtace mounted device, and so we have had these premounted to the board. The kit comes complete with a full set of instructions and 1MB of RAM . Prefined CMOS Surface mount Chip The CMOS LSI chip used tor this project uses a minimum of power. Recording and reproduction of the signals is processed through the CMOS chip using an (ADM )Adaptive Delta Modulation algorithm. This provides a clean clear recording. An electret microphone is used, and the CMOS chip has abuiltin microphone amplifier as well as a muting circuit. A 57mm speaker is provided to ensure quality reproduction. A 5mm LED is included to show the unit is recording . Low power consumption This digital voice project has hundreds of uses and will only take you a couple of hours to build. You can also install upto4MB of RAM tor longer recording times. Power is supplied from a low voltage plug pak (optional) . A Voice recorder you can build in a afternoon Easy to build Digital Voice Recorder Ilifferential input buffer for oscilloscopes This simple circuit will allow you to measure mains waveforms on your oscilloscope and to observe signals which cannot be connected to earth. It has a differential input and it provides 7 .5kV isolation between the input & output by means of linear optocouplers. By JOHN CLARKE Measuring mains voltages on most general-purpose oscilloscopes is a dangerous and inaccurate procedure. Unfortunately, it's not simply a matter of connecting the CRO probe to the mains, selecting the appropriate voltage division ratio and observing the waveform on the screen. Instead, there are at least two problems that must be overcome. First, you must connect the probe earth clip to Neutral. Connecting the probe the wrong way around, with the earth clip to Active, will not only blow a fuse but could also give you a nasty shock. In addition, the Neutral is not necessarily at earth potential which means that a large current may flow in the earth lead, even if the probe is connected correctly. The second problem you will probably run into is that the CRO lacks sufficient voltage division ratios. Most general purpose oscilloscopes can only be switched to a maximum of 5V/division, which corresponds to 50V/division when the probe is set to a 10:1 ratio. Because there are only eight divisions on the screen, it follows that only waveforms up to 400V p-p can be displayed in their entirety. A 240V mains waveform is about 680V p-p which means that it is much too big to fit on the screen. Of course, the variable VOLT/DIV control can be used to reduce the size of the waveform so that it does fit. However, the waveform then becomes uncalibrated and no worthwhile voltage measurements can be made. Difficulties also occur when measurements are to be made on Triac and SCR phase control circuits, or where you wish to monitor the current through a mains appliance (via a suitable shunt). Because the earth lead of the probe can no longer be used in these cases, the oscilloscope must be used in differential mode. This involves using both inputs of the CRO to measure a single waveform (ie, we must use a dual-trace unit). However, the waveform will again be too large to fit on the screen unless we are prepared to settle for an uncalibrated display. Differential input buffer The Differential Input Buffer divides the input signal by 1000, which means that you can now monitor calibrated mains waveforms. The unit also makes it possible to measure signals which cannot be referenced to earth. 76 SILICON CHIP This Oscilloscope Differential Input Buffer solves all these problems. Because it has a differential input, no earth lead is required on the probes and so it is impossible to incorrectly connect the earth to Active. In addition, the circuit divides the mains voltage by 1000, so that the vertical attenuator can be set to 1V/DIV to provide a fully calibrated waveform which easily fits on the screen. The input buffer also allows measur.ements of mains AC waveforms and __ •• --"-'- .,,~ The assembly of the unit is straightforward since most of the parts are mounted on a single PC board. Power is derived from two internal 9V batteries & this, together with the use of linear optoisolators in the signal paths, provides a nominal 7.5kV of isolation between the input & output sockets. other signal waveforms which cannot be referenced to earth. These include measurements at the outputs of bridged amplifier circuits and across motors driven by H-pack output circuits. Fig.1 shows how the Differential Input Buffer is used in a typical situation, in this case to monitor the output of a bridged audio amplifier. The unit has two inputs, one inverting(-) and the other non-inverting (+), and these are simply connected across the output'. The output of the input buffer is then connected to the CRO input in the conventional manner, leaving the second input of a dual-trace CRO free for other measurements. To ensure operator safety, the metal case of the input buffer is earthed back to the oscilloscope case earth and the rated isolation between the inputs and the output is 7.5kV. This isolation is provided by using optocouplers in the signal paths and by running the circuit from 9V batteries. Note that this figure is based on the rated isolation of the optocouplers and is a nominal value only. In practice, the true isolation is likely to be somewhat less than this figure due to the BNC input and output sockets. The complete circuit is housed in a metal case measuring 95 x 52 x 151mm. The front panel carries the OSCILLOSCOPE + DIFFERENTIAL INPUT OSCILLOSCOPE BUFFER • OUTPUT FRAME Fig.1: this diagram shows how the Differential Input Buffer can be used to monitor the output of a bridged audio amplifier, where no earth can be connected. two BNC input sockets and an on/off switch, while the rear panel carries the BNC output socket. Also on the back panel is an earth socket and this is connected to the earth terminal on the CRO via a banana plug lead (see Fig.1). Note that conventional CRO probes are connected to the two BNC input sockets and these should be set for 1:1 division. However, the earth clips on the probes are no longer used. In fact, depending on your application, it would be better to remove the clips altogether (or at least tape them up) to avoid accidental contact with the mains. How it works We've used a very interesting new device in this circuit - an 11300 linear optoisolator from Siemens. In fact, the circuit uses two such devices, one for each input. In addition, there are five op amps, two transistors and a handful of minor parts - see Fig.2. Before we get fully immersed in the circuit description though, we'll first take a closer look at the 11300. There's a very interesting twist to this device, as we shall explain. In the past, optocouplers have been used mainly to isolate digital control circuits from Triac circuits operating APRIL 1992 77 ~ - - - - - 4 t - - - - + - - - V 1 +, V+ TP5 INVERTING' "itlPUf T 0.1 TP4 VR3, VR4 CALIBRATE V- 4.7k 0.1T LINEAR OPTOISOLATOR IC2 IL300 ;t"'" V1- GAIN VR3 10k 8.2k 6" 1.1k TO OSCILLOSCOPE INPUT 5- ! +1000' VR1' 2oon- v- .,. IC5 LM334 CURRENT SOURCE 0.1! 10k V1- 680Q V+ V- V+ TP7 0.1T l NONINVERTINf INPUT "j_ V- TP6 VR3, VR4 CALIBRATE 10k V+ B1 9V. l"™ 6· -T 1 :!:.L.. v10 + 16VW• - 10~ 1.1k V- 5 1/2 SUPPLY AMPLIFIER ), +1000 VR2. 200n v- 'f" *PHILIPS VR37 0.5W 1500VAC Sl 8 v-<at>.v. ELJc l ,. B2 9V VIEWEO FROM BELOW 16VW -T : V1+ + 10k 10k :!:.L.. V1- DIFFERENTIAL INPUT BUFFER FOR OSCILLOSCOPES Fig.2: the differential input signals are first divided by 1000 & then applied to buffer stages ICla & IClb. These op amps in turn drive linear optoisolators IC2 & IC3 via current amplifiers Ql & Q2. Finally, the outputs of the optoisolators drive differential amplifier IC6a which produces the output signal. at mains potential. These optocouplers usually contained an internal LED and a photodiode detector. To activate the device, the LED was simply driven at a level sufficient to fully saturate the detector, which meant that the device was either on or off. We cannot use this type of optocoupler in an analog circuit however - at least, not if we expect good performance. That's because their output characteristics are far from linear and are subject to wide variations with changes in temperature. We cannot apply feedback either, since that would defeat the purpose of the optoisolator. And so we come to the 11300. Here's the twist: it overcomes the above problem because it has not one photodiode but two. One photodiode (on the iso78 SILICON CHIP lated side) is used to provide the output as before, while the second is used to provide the feedback to the LED driver circuit that's so necessary to ensure good linearity. In fact, the output sensor can be driven with a linearity of .01 %. Now let's get down to the circuit details. Op amps ICla and IClb are used to buffer the differential input signals. In each case, the incoming signal is.attenuated by a factor of 1000 using a voltage divider network consisting of a 1.ZMQ input resistor, a 1. lkQ resistor and a ZO0Q calibration trimpot. ICla and IClb drive optocouplers ICZ and IC3 via buffer transistors Ql and QZ. These transistors are wired as emitter followers and ensure sufficient current drive for the optocou- 1/2 SUPPLY AMPLIFIER pler LEDs via series ZZ0Q resistors. Feedback from the optocouplers is derived from the non-isolated detectors and is applied to the inverting input of each driver op amp. Since we want each optocoupler to operate with an AC signal, it is necessary to bias them so that their internal LEDs are at about "half-brightness" when no signal is applied to the inputs. This bias is derived from a constant current sink (IC5) which pulls 50µA via each of the 10kQ resistors connected to the inverting inputs of ICla and IClb. Essentially, ICla and Ql operate as a class-A amplifier, with the emitter of Ql sitting at close to half-supply (ie, 0V) under no-signal conditions. As the signal increases, Ql turns on harder and increases the drive to the LED. Conversely, as the signal decreases, Ql throttles back and the LED output decreases. IClb and QZ operate in exactly the same fashion. This CRO screen photograph shows the waveform across a 'Ii:iac 'in a typical phase control circuit. The vertical attenuator was set to 0.lV/ division and this, combined with the 1000:1 attenuation of the Differential Input Buffer, gave a display calibrated to lO0V/division. IC5 (the constant current sink) is an LM334 3-terminal device. Its operating current is set by the 680Q resistor between its "R" input and V-. In this circuit, the current is set at lO0µA and is equally divided between the inputs of ICla & IClb. IC4 is used to derive a half-supply rail from 9V battery BATT1. This op amp is wired as a voltage follower and derives its input from a voltage divider consisting of two 10kQ resistors. The resulting mid-point voltage is then decoupled by a l0µF capacitor and buffered by IC4, the output of which connects to the signal ground. The positive terminal of the battery thus becomes the +4.5V supply (V+), while the negative terminal becomes the -4.5V supply (V-). These rails power all the circuitry on the non-isolated side of the 11300 optocouplers. The outputs from the isolated detectors in IC2 and IC3 are used to drive differential amplifier IC6a. VR3 and its series 8.2kQ resistor set the voltage between the inverting input (pin 2) and the output (pin 1), while VR4 and its series 8.2kQ resistor set the voltage on the non-inverting input (pin 3). In operation, IC6a acts as an inverting amplifier for signals from IC2 and as a non-inverting amplifier for signals from IC3 . VR3 sets the overall Specifications Frequency response: DC to 100kHz Input impedance: 1.2MQ Input attenuation: 1000:1 Isolation: 7.SkV Power supply: 2 x 9V batteries PARTS LIST gain of this stage, while VR4 is an offset adjustment that's used to compensate for the extra gain in the noninverting path. IC6 is powered from 9V battery BATT2. In this case, voltage follower stage IC6b and the 10kQ voltage divider resistors on its input are used to derive a half-supply rail. This stage works in exactly the same manner as IC4. The output of IC6b connects to the signal ground and also to the case. The positive terminal of BATT2 thus becomes the +4.5V rail (Vl+) for IC6, while the negative terminal becomes the -4.5V supply rail (Vl-). Double-pole switch S1 provides power on/ off switching. S la switches the BATT1 supply while Slb switches the BATT2 supply. Construction The circuit is assembled on a PC board coded SC04204921 and measuring 121 x 84mm. This fits neatly into a standard metal case (see parts list) that's also large enough to accommodate the various input/output terminals and the on/off switch. Fig.3 shows the parts layout on the PC board. Start construction by installing PC stakes at the six test points and all external wiring points. Once this has been done, install the passive components (links, resistors, capacitors & trimpots), then the transistors and ICs. The LM334 can also be installed at this stage. Make sure that you don't confuse this device with the two transistors. The board assembly can now be completed by installing the two battery holders. Secure them using 2mm screws and nuts, then check the board assembly carefully against Fig.3 be- 1 PC board, code SC04204921, 121 x84mm 1 Dynamark front panel label, 92 x51mm 1 K&W instrument case, 95 x 52 x 151mm 2 216 9V PCB-mount battery holders 2 216 9V batteries 1 double pole rotary mains switch (must be mains-rated) 1 knob for switch 3 BNC panel sockets 1 banana earth terminal 4 6mm standoffs 5 3mm x 9mm screws plus nuts & shakeproof washers 6 2mm x 6mm screws plus nuts 1 solder lug 15 PC stakes 1 150mm-length 0.6mm tinned copper wire 1 250mm-length blue mains wire 1 250mm-length brown mains wire 1 100mm-length green/yellow mains wire 2 10kQ miniature horizontal trimpots (VR3,VR4) 2 220Q miniature horizontal trimpots (VR1 ,VR2) Accessory leads 2 oscilloscope probes 1 BNC to BNC plug lead 1 banana plug to banana plug earth lead Semiconductors 2 TL072 dual op amps (IC1 ,IC6) 2 IL300 linear optocouplers (IC2,IC3 - Siemens) 1 TL071 op amp (IC4) 1 LM334 3-terminal current source (IC5) 2 BC548 transistors (Q1 ,Q2) Capacitors 2 10µF 16VW PC electrolytic 4 0.1µF monolithic 2 10OpF ceramic Resistors (0.5W, 1%) 2 1.2MQ Philips VR37 0.5W 610kQ 21 .1kQ 2 8.2kQ 1 6800 2 4.7kQ 2 220Q Note: do not substitute for the Philips VR37 resistors as these are necessary to ensure an adequate voltage rating. APRIL 1992 79 SOLDER LUG FRONT RTH ~TERMINAL REAR Fig.3: install the parts on the PC board as shown in this wiring diagram & be sure to use the specified 1.2MQ input resistors (see parts list). All external wiring from the board must be run using mains-rated cable. fore moving on to the next stage. Once you are satisfied with the board assembly, the adhesive label can be attached to the case and holes drilled to accept the two BNC input sockets and the on/off switch. This job is best done by drilling small pilot holes first and then carefully enlarging them to the correct size with a tapered reamer. You will also have to drill holes in the rear of the case to accept the output BNC socket, earth terminal and earth screw, plus four mounting holes in the base for the PC board. Position the PC board towards the back of the case as shown in the photograph, to provide clearance for the OSCILLOSCOPE DIFFERENTIAL INPUT BUFFER ·- . ~N= ·.·c_ __ + (+) OFF + + (-) on/ off switch on the front panel. The various items can now all be mounted in position and the wiring completed as shown in Fig.3. Note that the earth lug is secured to the case using a screw, nut and shakeproof washer. The PC board is mounted on 6mm spacers and secured using screws, nuts and washers. Use mains-rated cable for all the internal wiring. Checkout & calibration Before applying power, doublecheck your work to make sure that there are no wiring errors. When you are satisfied that all is well, install the two 9V batteries and apply power. Use your multimeter to check that there is 9V between pins 4 & 8 of both IC1 & IC6 and between pins 7 & 4 of ON OUTPUT AT REAR 1V:1000V; 7.SkV ISOLATION CAPACITOR CODES o Value IEC Code EIACode D D 0.1µF 100pF 100n 100p 104 101 Fig.4: this artwork can be used as a drilling template for the front panel. RESISTOR COLOUR CODES D D D D D D D D 80 No. Value 4-Band Code 5-Band Code 2 6 2 2 2 1 2 1.2MO 10kO 8.2kO 4.7kO 1.1kO 6800 2200 brown red green yellow brown black orange brown grey red red brown yellow purple red brown brown brown red brown blue grey brown brown red red brown brown not applicable brown black black red brown grey red black brown brown yellow purple black brown brown brown brown black brown brown blue grey black black brown red red black black brown SILICON CHIP r. \ I -• el N 0, 0 N • 0 u en • 0 Fig.5: check your PC board against this full-size pattern before mounting any of the parts. IC4. The output ofIC4 at pin 6 should be at half-supply. You can check this by measuring between the positive terminal of BATTl and TP3, and between the negative terminal ofBATT1 and TP3. You should get readings of +4.5V and -4.5V respectively. The output of IC6b should also be at half supply. This can be verified by checking for +4.5V between the positive terminal of BATT2 and chassis and for -4.5V between the negative terminal of BATT2 and ground. To calibrate the instrument, first connect TP4 to TP5 so that a voltage is applied to the input of IC1a. Measure this voltage by connecting your multimeter between TP1 & TP3. Now connect your multimeter across the output BNC socket. Adjust VR3 so that the reading is the same as that just measured between TP1 & TP3. Next, disconnect TP4 from TP5 and connect TP6 to TP7 so that a voltage is applied to the input of IC1b. Check this voltage by measuring between TP2 & TP3, then connect your multimeter to the output BNC socket again. Adjust VR4 until the output voltage matches the previous reading (ie, the voltage between TPZ & TP3). VR1 and VR2 are now be adjusted to provide an exact 1000:1 division ratio for the input signals. These adjustments must be done with the power switched off. To make these adjustments, first use your digital multimeter to check the resistance of the 1.2MQ resistor between the inverting input and TP1. Note the value. This done, connect the multimeter between TP1 & TP3 and adjust VR1 for a reading which is 111000th the previous value. For example, if the 1.2MQ resistor measures 1.195MQ, adjust VR1 for a reading of 1.195kQ. This procedure is now repeated for the non-inverting input. Measure the value of the 1.2MQ resistor connected to this input, then connect your multimeter between TP2 & TP3 and adjust VR2 to the correct value (ie, 1/ 1000th the previous reading). The circuit is now calibrated and ready for use. As a final c}:ieck, connect the unit to an oscilloscope as shown in Fig.1 and connect the test probes to mains Active and mains Neutral. Check that the mains waveform can now be displayed on the oscilloscope screen with the vertical attenuator switched to the 1V/DIV setting. If you are not going to be checking mains voltages, you can modify the input attenuator circuit so that you can observe low-level signals in differential mode. For example, to divide the input signal by 100, increase the 1.1kQ resistors at TP1 & TP2 to 10kQ and increase VR1 & VR2 to 5kQ. Finally, exercise great care when measuring mains voltages. Make sure that the input probes & leads are in good condition and are rated for mains operation. Remember - contact with the mains can be fatal! SC .1.~~.r..1;ti:.~: RCS Radio Pty Ltd is the only company which manufactures and sells every PCB [, front panel published in SILICON CHIP, ETI and EA. 651 Forest Road, Bexley, NSW 2207. Phone (02) 587 3491. APRIL 1992 81 RITRON QUALITY RITRON ADD PRICE TO BASE SYSTEM COST. 512K VGA CARD .. $50 lM VGA CARD .. $150 TO CHANGE A B5M HARP PRTVE TO A 80286-16 CPU 1 MEG RAM EXPANDABLE TO 4 MEG 21Mhz LANDMARK SPEED TEST 1.2M JAPANESE BRAND F.D.D 85M HARD DISK DRIVE 28ms ACCESS 101 EXTENDED "CLICK" KEYBOARD MINI CASE & 200W POWER SUPPLY SUPA VGA COLOUR MONITOR (1024 x 768 Res) 0.28" DP 2 SERIAL, PARALLEL, GAME PORTS 3 YEAR PARTS & LABOUR WARRANTY 256K VGA CARD. 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ACN.005428437 HEAD OFFICE: 56 RENVER RD, CLAYTON. PH: (03) 543 2166. FAX (03) 543 2648 CITY 48 A•BECKETT ST. MELBOURNE. PH. 663 6351 I 639 1640. FAX: 639 1641. OAKLEIGH: 240C HUNTING DALE RD, OAKLEIGH. PH: 562 8939 NORTHCOTE 425 HIGH ST. NORTHCOTE, PH. 489 8866. FAX : 489 8131. SYDNEY:74 PARRAMATTA RD, STANMORE. PH: (02) 519 3134. FAX: (02) 519 3868 BLUESTAR COMPUTERS: 271 MAROONDAH HWY. RINGWOOD. PH: (03) 8701800 Postage rates $1 • $9.99 ...... $3.00 $10 • $24.99 .. $3.50 $25 • $49.99.. $4.50 $50 • $99.99 .. $6.00 $100 - $191i ... $7.00 $200 • $500... FREE $500 PLUS .. FREE Th•• pootag■ ,ate• arw bulc pootag• only up lo ~o::g'::lgh~ ltamo wih be chorgod •• • - • :~/1.y rot■ e TOLL FREE MAIL ORDER HOTLINE: 008 33 5757 VINTAGE RADIO By JOHN HILL The basics of receiver alignment There is little point in restoring an old valve radio unless the receiver is accurately aligned afterwards. If you don't, it's like putting a reconditioned engine into a car without fitting new spark plugs or tuning the carburettor. then convert the detected signal to sound. However, whereas a crystal set has only one tuned circuit, a multivalve receiver has many tuned circuits, all of which need to track accurately with each other if the set is to perform well. The alignment of these circuits is what this article is all about. The subject of receiver alignment has been "waiting in the wings" for quite some time, simply because it is a fairly difficult subject to cover in detail. Radios from different eras use different types of components and therefore require different alignment techniques. Some receivers require more alignment than others, while odd sets need no alignment at all. Perhaps the best way to approach the problem is to start at the beginning and work our way through. It looks like a project that will run over several months, so let's commence by studying the simplest of radio receiv- Tuned amplifier circuits ers, the humble crystal set. A basic crystal set consist_s of a coil of copper wire, a variable capacitor, a crystal detector and a pair of headphones. The coil and variable capacitor together form a tuned circuit. When tuned to a station, the radio frequency (RF) energy from the resonant coil is passed to the crystal detector, where it is rectified to audio frequencies which are then turned into audible sounds by the headphones. These same basic functions can be found in more elaborate receivers. All radio receivers select various radio frequency signals, detect them and It was discovered long ago that there were certain advantages if the feeble RF signals from the aerial were amplified (using valves) and selected by tuned stages before being fed to the detector stage. Early radios from the mid-1920s often had two or three dials on the control panel which indicated the number of tuned amplifier circuits. Unless these separate circuits were all tuned to the same frequency, the set would perform poorly because it . was out of alignment. To tune such a receiver from station to station required accurate adjustment of up to three individual tuned circuits. However, many operators were intimidated by these multi-dial receivers and three tuning dials were more than some people could handle. Naturally, the move to single dial tuning was a logical next step. No longer were there two or three separate tuning capacitors. Instead, they were "ganged" together to form a single unit. During the transition stage, there were various attempts at ganging by connecting single tuning capacitors together, using gearing, metal belts, or some other mechanical means. Ganged capacitors This simple crystal set is from the very early days of radio. It has only one tuned circuit and thus requires no alignment. 84 SILICON CHIP Around the 1930s, ganged capacitors made single knob tuning possible for as many as four tuned circuits. It was from this point on that receiver Trimmer capacitors are often built into the tuning capacitor. They can also be separate units installed elsewhere in the circuit. the aerial tappings can have a considerable affect on the set's selectivity. This old UDISCO receiver from the mid 1920s has three tuned circuits as indicated by the three tuning dials. Alignment of the three circuits was part of the "tuning" procedure. Failure to correctly adjust any of the three tuning capacitors would degrade the signal. Early receivers used only single tuning capacitors (left) and it was not until the late 1920s that single knob tuning became common. Single knob tuning required ganged tuning capacitors, as shown at right. From this point on, receiver alignment became important. pacitors were built into early tuning alignment became important. With the old setup of separate dials gangs, so that the capacitance could and tuning capacitors, it did not mat- be varied slightly on each section. In ter greatly if the capacitors were not later years, it became more common closely matched in value because each to fit the trimmers into the circuit tuned circuit could be peaked indi- · rather than to the tuning capacitor. As far as the TRF receiver is convidually to the chosen signal. However, with a ganged tuner, each cerned, the alignment procedure is section must be very closely matched limited to the adjustment of these trimto the others over the full range of its mers. This should be done at the high travel, otherwise it will not track ac- frequency end of the tuning range and curately. Even then, stray capacitance each trimmer peaked for maximum due to wiring and minor coil varia- audio output. The only other adjustments that can tions can upset tracking at the high be made to a TRF receiver are to the frequency end of the band. To correct this, small trimmer ea- tappings on the aerial coil. Changing Superheterodyne receivers With the advent of the superheterodyne receiver, alignment procedures became more involved and a really good job requires special equipment - namely an RF generator and an output meter. But before going on to a describe superhet alignment, there are a few things to discuss first. The superheterodyne circuit differs from the simple TRF receiver in that it converts each incoming signal, as selected, to the same frequency. This is called the "intermediate frequency" (IF) and is produced by a frequency converter stage which mixes the incoming RF signals with a frequency produced by an internal "local oscillator". The IF chosen varied greatly, depending on the design of the receiver, and ranged from 175-465kHz in domestic receivers. The intermediate frequency is the difference between the signal frequency and the local oscillator frequency. In theory, the local oscillator may be higher or lower than the signal frequency but, in practice, it is normally higher. Thus, a signal of 600kHz would need an oscillator at 600 + 455 = 1055kHz in order to produce a 455kHz IF. And a signal at 1500kHz would need an oscillator at 1955kHz to produce the same IF. The vital point about these figures is that, while the signal range is 2.5:1, the oscillator range is only 1.85:1. Yet these two frequency ranges have to be provided by two identical ganged tuning capacitors; one tuning the aerial circuit and the other tuning the oscillator circuit. APRIL 1992 85 This photo shows a selection of old IF transformers. The early types were adjusted by built-in trimmer capacitors while later versions used adjustable iron cores. This under-chassis view shows the aerial and oscillator coils (black objects) in a 1950-model Radiola. The larger of the two (at left) is the aerial coil. Many receivers have these coils encased in metal cans, which makes their identification more difficult. This is done by connecting a carefully chosen value of capacitance in series with the oscillator tuning capacitor, which reduces the capacitance range of this section. This capacitor is called a padder and may be fixed or made adjustable for alignment. Adjusting these two circuits - aerial and oscillator - so that each tunes exactly to the required frequency at each point across the tuning range is called tracking. It can be the trickiest part of the whole alignment procedure and must be done properly for best results. More about this later. In the majority of domestic receivers, the IF is amplified by one valve 86 SILICON CHIP (sometimes two) and this valve is coupled into the circuit by IF transformers. These IF transformers are (naturally) designed to work at the receiver's IF and can be adjusted to ensure that the transformer windings are peaked for maximum signal transfer. The type of IF transformer adjustments vary depending on the age of the receiver, so a quick look at these would be appropriate for those who are unfamiliar with old radios. Early IF transformers are adjusted by small trimmer capacitors which are built into their metal shields. Ac~ cess to the trimmer screws can be through holes at the top of the shield can, on the sides of the can, or from underneath. In all cases, adjustments are made using a non-metallic screwdriver, as the adjustment screws may have a high voltage applied to them. Apart from the possibility of an elec-: tric shock, a short circuit between the adjusting screw and the metal shield could damage the fine windings of the transformer. More recent IF transformers (from the late 1930s) feature adjustable ironcore tuning. The iron cores, or slugs, are attached to slotted brass screw threads which protrude from each end of the transformer. IF transformers made from around 1950 onwards are more likely to not have brass adjustment screws. Instead, these are adjusted via a slot in the iron core itself and these slotted slugs are easily damaged if they are stiff to turn. Once the slot has been gouged out it is impossible to adjust the transformer unless other techniques are used (see Vintage Radio, July 1990). Other parts of a superhet that need to be recognised are the aerial and oscillator coils. These are often open coils mounted on the underside of the chassis or they can be enclosed in a shielded can, which makes identification a little more difficult. If the coils are visible, then the aerial coil is usually the slightly larger of the two. If the coils cannot be seen, just trace the aerial through from the aerial terminal. The aerial goes to the aerial coil, which means that the other coil must be the oscillator coil. Most aerial and oscillator coils have adjustable iron cores but occasionally only the oscillator coil will be adjustable. However, very early receivers will have no slugs at all. (No wonder I have put off writing about receiver alignment for so long). Trimmer capacitors The next components to find are the aerial and oscillator trimmers and these can be found in a number of places. Some , as previously mentioned, are built into the tuning capacitor or soldered onto it. They may be fitted into the circuit close to the aerial and oscillator coils. They may even be bolted to the front, rear or top of the chassis with a small hole in the chassis for adjustment purposes. Sometimes they may even be labelled so that they are readily identified (but not often). RESURRECTION RADIO Vintage Wireless Specialists 'Irimmer capacitors come in all shapes & sizes. But regardless of their physical differences, they all perform the same basic function. Some trimmer capacitors don't even look like trimmer capacitors. One type consists of a central insulated wire with a coil of much finer wire wound around the outside. This type -which I understand was made by Philips - is inconvenient to work with because it is not easily adjusted. The capacitance of the trimmer is decreased by removing some of the outside coil. However, if the capacitance has to be increased, then wire has to be soldered to the outside coil and a few extra turns wound on. Another type consists of a long brass rod that slides in, but is insulated from, a metal tube, and is held in place with a locknut. While these are much larger than the compression type, they had much to recommend them. They were used by AWA, HMV and many other makers for many years. Unfortunately, without the proper tool, they can be difficult to adjust but, with it, they work well. The avail- able movement is quite large for a given capacitance range and, once adjusted, they are very stable - much more so than the compression type. The alignment tool used to adjust these was a composition rod with a box spanner at one end - to adjust the locknut- and a right angle hook at the other. The hook was used to engage a hole in the end of the brass rod, enabling it to be moved in and out of the insulator. It is unlikely that such tools would be encountered these days although it should be possible to make one with a little ingenuity. The final alignment component to identify is the padder capacitor. In early superhets, this takes the form of a compression type variable mica capacitor and is adjusted with a screwdriver. Many are made of white porcelain and these are easy to recognise. The padder capacitor is part of the local oscillator circuit and the correct value is important for accurate tracking. In later model sets , the padder capacitor was a fixed type, tracking adjustments being made by an adjustable iron core in the oscillator coil. So far, I have tried to keep this article as simple as possible and for good reason. Nearly all the vintPadder capacitors in old radios usually take the form age radio collectors I of a compression mica type which can be adjusted with a screwdriver. know cannot do their Repairs - Restoration - Sales Our skffied technicians offer QUALITY repairs and restoration. We also have a large stock of bakelite and timber radios fully restored and for SALE. Parts are available for the enthusiast, including over 900 valve types, high voltage capacitors, transformers, dial glasses, knobs, grille cloth etc. Circuit diagrams for most Australian makes and models. Send SAE for our catalog. WANTED : Valves, Radios, etc. Purchased for CASH Call in to our showroom at: 51 Chapel Street (PO Box 1116), Windsor, Vic 3181. Telephone: (03) 529 5639 own repairs. They have had little or no electrical or radio experience prior to becoming collectors and these people need precise directions if they are to align their receivers. It is pointless discussing alignment procedures if the reader is unsure of what he is doing. However, now that the preliminaries have been dealt with, I hope to be able to cover the subject more fully. From this point on, if I refer to the padder capacitor or the oscillator trimmer, I expect the reader to have some idea of what it looks like and where it might be found. Incidentally, there are two ways of doing an alignment job. One way is to use alignment equipment such as a radio frequency generator and an output meter; the other method is to do the job wjthout them. Although the right equipment makes the task easier, a reasonable job can still be done without it. In the next few months, Vintage Radio will cover both methods. So if you are about to tune up a recently restored receiver, then you will have to wait until then for the finer points on alignment. SC APRIL 1992 87 July 1988: Stereo Control Preamplifier, Pt.2; Fitting A Fuel Cut-Off Solenoid; Booster For TV & FM Signals; The Discolight Light Show, Pt.1 ; Tone Burst Source For Amplifier Headroom Testing ; What Is Negative Feedback, Pt.3; Amplifier Headroom - Is It A Con? August 1988: Building A Plasma Display; Universal Power Supply Board; Remote Chime/Doorbell; High Performance AC Millivoltmeter, Pt.1; Discolight Light Show, Pt.2; Getting The Most Out Of Nicad Batteries; Data On Insulated Tab Triacs. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice; Motorola MC34018 Speakerphone IC Data; What Is Negative Feedback, Pt.4. October 1988: Stereo FM Transmitter (Uses Rohm BA 1404); High Performance FM Antenna; Matchbox Crystal Set; Electronic House Number; Converting A CB Radio To The 28MHz Band; Queensland's Powerful Electric Locomotives. November 1988: 120W PA Amplifier Module (Uses Mosfets); Poor Man's Plasma Display; Automotive Night Safety Light; Adding A Headset To The Speakerphone; How To Quieten The Fan In Your Computer; Screws & Screwdrivers, What r You Need To Know; Diesel Electric Locomotives. December 1988: 120W PA Amplifier (With Balanced Inputs), Pt.1; Diesel Sound Generator; Car Antenna/Demister Adaptor; SSS Adaptor For Shortwave Receivers; Why Diesel Electrics Killed Off Steam; Index to Volume 1. January 1989: Line Filter For Computers; Ultrasonic Proximity Detector For Cars; Simple Computer Sound Repeater; 120W PA Amplifier (With Balanced Inputs) Pt.1 ; How To Service Car Cassette Players; Massive Diesel Electrics In The USA; Marantz LD50 Loudspeakers. February 1989: Transistor Beta Tester; Minstrel 2-30 Loudspeaker System ; LED Flasher For Model Railways (uses LM3909); Build A Simple VHF FM Monitor (uses MC3362), Pt.1; Lightning & Electronic Appliances; Using Comparators to Detect & Measure. March 1989: LED Message Board, Pt.1 ; 32-Band Graphic Equaliser, Pt.1 ; Stereo Compressor For CD Players; Map Reader For Trip Calculations; Amateur VHF FM Monitor, Pt.2; Signetics NE572 Compandor IC Data; Electronics For Everyone Resistors. April 1989: Auxiliary Brake Light Flasher; Elec- Ironies For Everyone: What You Need to Know About Capacitors; Telephone Bell'Monitor/ Transmitter; 32-Band Graphic Equaliser, Pt.2; LED Message Board, Pt.2. May 1989: Electronic Pools/Lotto Selector; Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference ; LED Message Board, Pt.3; Electronics For Everyone - All About Electrolytic Capacitors. June 1989: Touch-Lamp Dimmer (uses Siemens SLB0586); Passive Loop Antenna For AM Radios; Universal Temperature Controller; Understanding CRO Probes; LED Message Board, Pt.3. July 1989: Exhaust Gas Monitor (Uses TGS812 Gas Sensor); Extension For The Touch-Lamp Dimmer; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; NSW 86 Class Electric Locomotives. August 1989: Build A Baby Tower AT Computer; Studio Series 20-Band Stereo Equaliser, Pt.1; Use this handy form to order your back c opies l ---, Please send me a back issue for: 0 October 1988 0 November 1988 0 March 1989 0 April 1989 O August 1989 O September 1989 O January 1990 O February 1990 0 June 1990 0 July 1990 0 November 1990 0 December 1990 0 April 1991 0 May 1991 O September 1991 0 October 1991 0 February 1992 O March 1992 0 O 0 O O 0 0 0 0 July 1988 December 1988 May 1989 October 1989 March 1990 August 1990 January 1991 June 1991 November 1991 Enclosed is my cheque/money order for $___or please debit my: Card No. O 0 0 O 0 0 0 0 0 August 1988 January 1989 June 1989 November 1989 April 1990 September 1990 February 1991 July 1991 December 1991 O Bankcard I- I_ I~-~-~~~-I I_ Signature _ _ __ _ _ _ _ _ _ _ _ Card expiry date_ _ / _ _ Name _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Street _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Suburb/town _____________ _ Postcode _ _ __ __ O 0 0 0 0 0 O 0 0 O Visa Card September 1988 February 1989 July ·1989 December 1989 May 1990 October 1990 March 1991 August 1991 January 1992 O Master Card $5.00 each (includes p&p). Overseas orders add $1 each for postage. NZ orders are sent air mail. Detach and mail to: SILICON CHIP PUBLICATIONS PO BOX 139 COLLAROY BEACH NSW 2097 Or call (02) 979 5644 & quote your credit card details. Fax (02) 979 65o3 l I L--------------------------------------- ~-88 SILICON CHIP tributors; The Mazzie CW Transceiver; Waveform Generation Using A PC, Pt.3; 16-Channel Mixing Desk, Pt.4; What To Do When Your Computer Goes Bung, Pt.1. May 1991: Build A DTMF Decoder; 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1; Setting Screen Colours On Your PC. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protection Switch For Power Supplies; A Speed Alarm For Your Car; Design Factors For Model Aircraft; Fitting A Fax Card To A Computer; What To Do When Your Computer Goes Bung, Pt.2. June 1991: A Corner Reflector Antenna For UHF TV ; 4-Channel Lighting Desk, Pt.1 ; 13.5V 25A Power Supply For Transceivers; Active Filter For CW Reception; Electric Vehicle Transmission Options; Tuning In To Satellite TV, Pt.1. 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 ; What To Do When Your Computer Goes Bung, Pt.3; Weather Fax Frequencies. July 1991: Battery Discharge Pacer For Electric Vehicles; CD Error Analyser, Pt.1; 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; PEP Monitor For Transceivers August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Wave Generator, Pt.2; What To Do When Your Computer Goes Bung, Pt.4. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Error Analyser For CD Players, Pt.2; Tuning In To Satellite TV, Pt.3 ; Installing Windows On Your PC; Step-By-Step Vintage Radio Repairs. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; AlarmTriggered Telephone Dialler; High Or Low Fluid Level Detector; Simple DTMF Encoder; Studio Series 20-Band Stereo Equaliser, Pt.2; Auto-Zero Module for Audio Amplifiers (Uses LMC669). September 1990: Music On Hold For Your Telephone; Remote Control Extender For VCRs; Power Supply For Burglar Alarms; Low-Cost 3Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band. September 1991: Studio 3-55L 3-Way Loudspeaker System; Digital Altimeter For Gliders & Ultralights, Pt.1 ; Build A Fax/Modem For Your Computer; The Basics Of AID & D/A Conversion; Windows 3 Swapfiles, Program Groups & Icons ; How Glass-Mount antennas Work. October 1989: Introducing Remote Control; FM Radio Intercom For Motorbikes (Uses BA 1404 & TDA7000) Pt.1; GaAsFet Preamplifier For Amateur TV ; 1Mb Printer Buffer; 2-Chip Portable AM Stereo Radio, Pt.2; Installing A Hard Disc In The PC; A Look At Australian Monorails. October 1990: Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; The Dangers of Polychlorinated Biphenyls; The Bose Lifestyle Music System ; Using The NE602 In Home-Brew Converter Circuits. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders & Ultralights, Pt.2; Getting To Know The Windows PIF Editor. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY and Morse); Super-Sensitive FM Wireless Microphone; 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. November 1990: Low-Cost Model Train Controller; Battery Powered Laser Pointer; A Really Snazzy Egg Timer; 1.5V To 9V DC Converter; How To Connect Two TV Sets To One VCR; Introduction To Digital Electronics; Simple 6Metre Amateur Transmitter. November 1991: Colour TV Pattern Generator, Pt.1 ; Battery Charger For Solar Panels; Flashing Alarm Light For Cars; Digital Altimeter For Gliders & Ultralights, Pt.3; Build A Talking Voltmeter For Your PC, Pt.2; Error Analyser For CD Players Pt.3; Modifying The Windows INI Files. December 1989: Digital Voice Board (Records Up To Four Separate Messages); UHF Remote Switch; Balanced Input & Output Stages; Data For The LM831 Low Voltage Amplifier 'IC; Install A Clock Card In Your PC; Index to Volume 2. December 1990: DC-DC Converter For Car Amplifiers; The Big Escape -A Game Of Skill; Wiper Pulser For Rear Windows; Versatile 4-Digit Combination Lock; 5W Power Amplifier For The 6Metre Amateur Transmitter; The Great Green CD Pen Controversy; Index To Volume 3. December 1991: TV Transmitter For VCRs With UHF Modulators; Build An lnfrared Light Beam Relay; Compact Solid-State Laser Pointer; Build A Colour TV Pattern Generator, Pt.2; The Miracle Piano Teaching System; Windows 3 & The Dreaded Unrecoverable Application Error. January 1991: Fast Charger For Nicad Batteries, Pt.1; The Fruit Machine; Two-Tone Alarm Module; Laser Power Supply; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers When Servicing Microwave Ovens; Electric Vehicles - The State Of The Art. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1 ; Baby Room Monitor/FM Transmitter; Automatic Controller For Car Headlights; Experiments For Your Games Card; The GPS Satellite Navigation System . Garbage Reminder - A 7-Day Programmable Timer; Introduction To Stepper Motors; GaAsFet Preamplifier For The 2-Metre Band; Modern 3Phase Electric Locomotives. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Speeding Up Your PC; Phone Patch For Radio Amateurs; Active Antenna Kit ; Speed Controller For Ceiling Fans; Designing UHF Transmitter Stages. February 1990: 16-Channel Mixing Desk; High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs , Pt.2; PC Program Calculates Great Circle Bearings. March 1990: 6/12V Charger For Sealed LeadAcid Batteries; Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC. April 1990: Dual Tracking ±50V Power Supply; VOX With Delayed Audio; Relative Field Strength Meter; 16-Channel Mixing Desk, Pt.3; Simple Service Tips For Your Microwave Oven; Active CW Filter For Weak Signal Reception; How To Find Vintage Radio Receivers From The 1920s. May 1990: Build A 4-Digit Capacitance Meter; High Energy Ignition For Cars With Reluctor Dis- February 1991: Synthesised Stereo AM Tuner, Pt.1 ; Three Inverters For Fluorescent Lights; LowCost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages; Tasmania's Hydroelectric Power System. March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose 1/0 Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateurs & TV ; A Look At The Config.Sys & Ansi.Sys Files. 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; Playing With The Ansi.Sys File; FSK Indicator For HF Transmissions. February 1992: Compact Digital Voice Recorder; 50-Watt/Channel Stereo Power Amplifier; 12VDC/ 240VAC 40-Watt Inverter; Adjustable 0-45V 8A Power Supply, Pt.2; The Mobile Telephone Revolution; Designing A Model Speed Controller. March 1992: TV Transmitter For VHF VCRs; Studio Twin Fifty Stereo Amplifier, Pt.1 ; Thermostatic Switch For. Car Radiator Fans; Telephone Call Timer; Updating The Resistor/Capacitor Scene; Coping With Damaged Computer Directories PLEASE NOTE: All issues from November 1987 to June 1988 are now sold out. All subsequent issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tearsheets) at $5.00 per article, including postage. When supplying photostat articles or back copies, we automatically supply any relevant Notes & Errata at no extra charge. APRIL 1992 89 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. Audio expander might overdo it Having built the Audio Expander described in the May 1991 issue and checked its performance against your specifications (near as dammit!), I find it does not enhance the effect of much program material because of the "surging" or "rushing" characteristic it introduces. My assumption is that it relates to the attack and release times. The capacitors concerned have been tested and are within tolerance (10%). There has been no reference to this aspect since the project but it is very unpleasant. All being well, a second unit is to be built and incorporated in equipment having dynamic noise reduction, simulated stereo and dynamic range expansion when transferring early 78rpm recordings to tape. To this end, I will need to vary the degree of expansion as required. Several attempts to do this have been unsuccessful. The circuit presented in May was modified to control the audio input to pins 3 and 13 (IC2a & IC12b), assuming the resulting effect on the rectified DC control voltage would have the desired result. The original specifications could 24V operation for fluorescent inverters I am interested in the three inverters for fluorescent lights published in the February 1991 issue. I currently live on a ·boat and have decided to ditch most ofmy incandescent globes and put in fluoros, and would like to construct some different size inverters myself. The power on my boat is the problem. The DC supply is 24V and I do not want to tap half of my battery bank or run a separate DC to DC converter. Could you please supply me with the relevant 90 SILICON CHIP not be obtained at the appropriate setting of the potentiometers - in fact they were vastly different. Not having the internal IC circuitry, the resistive loading on pins 3 & 12 (ICla & IClb) or from pins 3 & 13 (IC2a & IC2b) must upset the "applecart". Another modification was to alter the circuit so that the pots were lifted from ground and used as a variable series resistances - none were satisfactory. Can you help? I'm obviously on the wrong track! (R. C. Narara, NSW). • From your description it does not appear that the attack and release times of the expander are incorrect but that perhaps the amount of expansion is too much for the program material you have. Furthermore, the relatively high residual noise of 78rpm records may make the "rushing" or "breathing" effect more noticeable. You can reduce the overall gain range by inserting a resistor in series with pin 7 (and pin 9) of IC2 . We suggest you try a value of 3.3kQ to start with. Speed control for model boats My son has been a model boat enthusiast for a few years now and is changes to the three inverters to run them from a 24V DC supply? I also have a few transformer pot cores (ferrite) - the round type with two halves and bobbins - and am wondering whether I could use some of these without too many changes other than the mountings. Would it be easier to buy the Siemens E cores? Seems a pity to waste the others. (R. T., Geeveston, Tas). • It should be possible to adapt the fluorescent inverter circuits to 24V operation merely by doubling the number of turns on the primary and feedback windings. You should be able to fit the extra turns on as setting a more exacting standard for himself with each model built. So far, he has failed to achieve reliability, economy of operation and light weight for radio speed control. I want to ask if you can advise as to the best approach and if a design can be obtained, or even a kit of the necessary bits. (A. M., Edgecliffe, NSW). • As you've probably noticed by now, the latest articles in Bob Young's Remote Control column are leading up to a design for a completely new R/C speed control. We hope to publish the final design soon. It will probably use some surface mount components to keep the size down. Combining the audio expander & compressor I have constructed the audio compressor described in the March 1989 issue and the audio expander described in May 1991 · and I am very happy with them. My problem is that I would like to put them into one box connected to one power supply and I would like to use one set of input/ output sockets. The only way to do this would be to use extra switches. Would you have any advice on hooking these up the the bobbin is not crowded in the original form. We must stress that we have not tried this although it should work. We don't think it would be easy to make the inverters function properly with the round ferrite cores. The inverters would certainly run but they would probably not produce sufficient spike voltage to fire the tubes. That is why the E cores have been specified; so they can be fitted with an air gap. This alters the saturation characteristic of the ferrite core and allows the transformer to produce a spike at the switch-off point of each transistor. correct way and can I insert a pot to control the signal on both the compressor and the expander? Regarding your comment in the articles about using the recommended PC boards, to avoid problems such as ground loops and hum, what is the cause of these - placing the components too close together or too far apart? Could you also please advise if it is wise to substitute 1 % resistors for 0.5% resistors in the circuit for the electronic-scale (project 1523) in the July 1984 issue in the magazine Electronics-Today-International. If I cannot substitute, where can I obtain them? I have contacted several stores in Melbourne. Are you going to publish a circuit for a digital recording amplifier with phono preamp and straight onto the recording head for normal reel/reel recorders. (F. F., North Box Hill, Vic.) • It is possible to connect the compressor and expander in the way you envisage. We suggest that you install both boards side by side in a suffi~ ciently large case. You will have to run shielded cables from the input sockets to the inputs of both the compressor and the expander. You will also have to substitute a 2pole 3-position rotary switch for Sl. This should be wired so that its three positions correspond to settings for Compress , Bypass and Expand. In effect, you will combine the 2-position switch S1 in each circuit into a single 3-position switch. And since both boards use the same ±lZV supply rails, you could eliminate the power supply components from one board and run it from the ±12V regulator outputs of the other. Our comment about using the recommended PC boards is a general one which applies especially to audio circuits. Ground loops are caused when currents from the output of a circuit are injected into the signal earth as can happen easily. That is why audio amplifiers commonly have star earth systems; they keep signal earths and output earths strictly separate. As far as your request for 0.5% resistors is concerned, we don't know of any retail output which has them in stock. But never fear. All you have ·to do is substitute 1% resistors. More than 75% of any batch of 1% resistors can be expected to fall within ±0.5% of their nominal value, so you could How to select polyswitches I want to provide effective loudspeaker protection for my 40 watt RMS guitar practice amplifier. I've decided to use a polyswitch protector device due to simplicity, space saving, etc. The problem I have is in correct selection of the polyswitch. According to data in the Dick Smith catalog, the "hold current" is the current the device will pass while maintaining a low resistance condition. Both hold and trip current are reduced by increased ambient temperature - hold current by as much as 20% at 40°C. Such a temperature is usual in a poorly ventilated instrument amplifier enclosure. Do these polyswitches go high in resistance above the hold current or when they reach the trip current, or somewhere in between? Are these figures RMS or peak values? Maximum transformer secondary current is 1.29A RMS. Maximum output current from the class AB push-pull output is 40 watts/45volts == 0.89ARMS, where supply voltage is ±50 volts and 10% voltage drop across the output transistors is assumed when saturated. Therefore, it would seem on the surface that I would need a device which will go high in resistance just install 1 % resistors and most of the time they would be within the required 0.5% tolerance. If you want to be sure, use a digital multimeter to check the resistor values before you install them into circuit. We have no plans to publish a circuit for a digital recording amplifier. Values should be marked on coils I am interested in quite a lot of your (smaller) projects and that is unusual for me to feel the urge to build; it only proves the quality of your magazine. I am a television technician and through my trade I know quite a lot of suppliers for parts. Why don't you simply between 0.9A RMS and 1.2A RMS. If my calculations are correct, then which device rating do I choose hold current, trip current, or something else? (J. S. , Thornlie, WA). • Picking polyswitches to protect amplifiers and speakers is a bit of a black art. The idea is that the amplifier should be able to be driven to clipping and a little beyond on normal program material into its lowest rated load, say four ohms. This may preclude full power on constant tone which would occur when testing for power output. Serious over-drive conditions should be protected against. In an over-drive condition, when the amplifier is driven far into clipping, it may deliver double its normal full power current and this can be enough to blow tweeters and even burn out voice coils in woofers in some circumstances. So if you pick a polyswitch with a hold current just above what the amplifier can deliver in normal program conditions, you should be right. In your case, your amplifier will deliver 2.2 amps into an 8-ohm load at the 40 watt level. On program material it could be expected to deliver a little more but only for brief periods. Therefore, we would suggest you use the 2.45A device (CatR-1792) from Dick Smith Electronics. put the value [µH) by a coil so that we know what it is. Too often this is not done. We then can try to substitute if the part is hard to get. A typical example is the Solar Charger in the November 1991 issue. I would really love to make this project and can do it cheaper than a kit. The only thing that lets me down is the Philips p0tcore 18/11-3B7 (4322 022 1500). Philips has never even heard of this number! Neither has Jaycar, Dick Smith, Altronics, Geoff Wood, Rod Irving, The Electronic Component Shop, RS Components, Digitell, Wes Components ... will I continue? Why not put the value by the coil? In this case I assume it is 220µH - as shown in Fig.2. I am thinking of getAPRIL 1992 91 Advance scope circuit needed I have recenVly acquired an" Advance Instruments" oscilloscope mode1 OS1000 - secondhand and am in need of an operating and service manual, including cir,cuit diagrams. I am wondering whether you know who the agents are for Advance Instruments i.n Australia or, failing that, whether you would be kind enough to publish my ting an air coil inductor as used in loudspeaker systems. Jaycar sells one for $3 .95 (LF-1310) with a wire of 0.8mm so I am sure it can handle the current. By the way, this will be cheaper too. Potcores range in price from $916 (FX series) and if you have to add postage on this then it can be unreasonably expensive. And what about the Siemens transformer ETD79 in the February 1991 issue (Fluorescent Inverter)? After long searching, I found it in the Farnell catalog under the Philips brand name! But how many people have access to this? Altronics is the only one who sells Siemens ferrite "E" cores and formers but the size and special price (up to $17.95) was far out of range. With toroids there is the same problem. Often only the type number is given and by cross reference we don't even know the dimensions. Finally, how about a simple inductance meter as an add-on to a multimeter? (C. K., Illawong, NSW). • Unfortunately, inductors and transformers, as used in inverters or converters, cannot be thought of as simple inductances. Their core saturation characteristics and frequency of operation are also very important and it is not possible to specify those in the same way as we can specify simple components like resistors or capacitors. All of this is a long way of saying that substitution is generally not easy. It is unlikely that an air-cored inductor could be made to work with the solar battery charger project. If you tried it, you might burn out both the transistor and the IC. The problem with ferrite cored inductors and transformers is that they 92 SILICON CHIP name and address in case any Tieader can help. I would gladly pay up to $50 for a good photocopy of the complete manual. (Greg Freeman, Harrogate Rd, Nairne, SA). • Unfortunately, we don't know iii there is a distributor for Advance Instruments in AustFalia but we have pubEished your name and address so that any reader who has the mam1al you want can contact you direcdy. are specialised components and they are always going to present a problem in terms of their ready availability and cost. Curing noise from fluorescent lights I have a query about your fluorescent light inverter which was published in the February 1991 issue. We live in an area that would be expensive to connect to mains power, so solar was the more viable option. We operate a mixture of 12V quartz halogen and 12V fluorescent lamps - the fluoros giving much more light per watt than the QH lamps. So fluoros get used to light large areas but no matter what type/make of inverter I use , I get radio interference on AM (broadcast or SW) radio. I assume that the inverter produces a fundamental or harmonic somewhere near the IF of the receiver. Due to the stability, or lack of it, in the fluoro inverter, the signal generated "comes and goes". Shielding the inverter is not a success. The fittings are metal; earthing them does not help. I assume the tube acts as an antenna. Question - how "stable" is your inverter and what frequency does it run at? Better still, can the inverter be crystal controlled to stabilise it? These little "broadband transmitters" have a good range too about 100 metres is the furthest point for total obliteration of signal from a local ABC station. The reason I'm asking is, I am doing a course on "media studies", and I want to compare the way overseas media cover our news and the way the local networks cover similar stories. As BBC, VOA and Radio Aus- tralia are all on AM shortwave, my current lighting system will have to be overhauled before I start. I'd like to stick with fluorescent lamps but I need to get away from RFI problems. (D. H., Beechwood, NSW) . • It is not the inverter which is the main source of interference but the tube itself. This applies to all fluorescent lamps whether they are mains powered at 50Hz or run from high frequency inverters. The reason is that the fluorescent tube is a gas discharge tube and the gas discharge itself is a potent source of radio noise that can span frequencies up to several hundred Megahertz. This radio noise is keyed or pulse modulated by the mains or inverter frequency so that what you hear via the radio is mainly the second harmonic. For example, a mains power fluorescent lamp gives a ragged sounding 100Hz buzz. This effectively destroys AM radio reception in weak signal conditions. Making an inverter crystal controlled is not likely to solve the problem of audible interference although if the inverter ran at a frequency well above 20kHz it may no longer be heard through your radio. This may only be a partial solution though , since a strong interfering signal can have the €ffect of desensitising a radio , via its AGC circuit. It is possible to obtain commercial inverter driven fluorescent lamp fittings which have low radio interference levels. We understand that these achieve their low RFI by virtue of being a constant current source and, secondly, by adding suppression capacitors across the tube. The fact that our February 1991 inverter design actually feeds the tube via a capacitor would effectively make it into a quasiconstant current source although we cannot vouch for its RFI output. And although we haven't tried it, we would not advise connecting a capacitor across the tube either as it may prevent the tube from starting. It may be possible to shield the tube itself using a wire mesh enclosure but the only really effective cure is to keep the antenna well away from the fluorescent lights and better still, use a noise cancelling antenna such as the one described in our June 1989 issue. This is fine for broadcast reception but would have to be made a lot bigger for shortwave reception. SC ORDER FORM Il11llr~P-~~ BACK ISSUES* MONTH YEAR MONTH YEAR YEAR MONTH MONTH YEAR *Back issues are $AS each (incl. postage). Overseas orders add $A 1 per issue for postage. BINDERS Please send me _ _ SILICON CHIP binder(s) at $A14.95 each (incl. postage). Overseas orders please add $A3.00 each for postage. TOTAL PRICE $A SUBSCRIPTIONS 0 New subscription - month to start 0 Renewal - Sub. 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Please have your credit card details ready Fax the coupon with your credit card details 24 hours 7 days a week Card expiry date I Mail coupon to: Freepost 25 Silicon Chip Publications PO Box 139, Collaroy Beach 2097 No postage stamp required in Australia APRIL 1992 93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. r-------------------------, CLASSIFIED ADVERTISING RATES ANTIQUE RADIO Advertising rates for this page: Classified ads: $10.00 for up to 15 words plus 40 cents for each additional word. Display ads (casual rate): $20 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on the form below or on a separate sheet of paper & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy Beach, NSW 2097. Or fax the details to (02) 979 6503. ANTIQUE RADIO restorations. Your one-stop radio repair shop. Specialising in restoring vintage radios including chassis rewiring, re-condensing, quality new parts, valves, valve sockets, speakers, power & audio transformers. Secondhand radio dials & parts for most brands & models. About 400 radios in stock for sale, restoration & parts. Every restored wireless is covered by a 2year warranty on parts & labour. We restore damaged woodwork & cabinets & French polish (approx. 40 coats). Vintage car radios available for sale or restoration. Repairs done on tape decks & amplifiers. Open Sat. 10am-5pm; Sun. 12.30-5pm. 109 Cann St, Bass Hill, NSW 2197. Phone (02) 645 3173 BH or (02) 726 1613 AH. FOR SALE TEST EQUIPMENT: (1) oscilloscope, Gosser 1049 double beam with service manual; (2) audio oscillator, AWA type 3A57150, 20Hz to 20kHz, metered output 0-15V, attenuator 5dB steps; (3) Patee VTVM; (4) RF oscillator, University Graham, 5 ranges 150kHz to 30MHz, attenuator. The lot $60 or will negotiate separately. Ring Don Clements on (02) 449 1992. Enclosed is my cheque/money order for $_ _ _ _ or please debit my 0 Bankcard O Visa Card O Master Card XI I I Signature_ _ _ _ _ _ _ _ _ _ _ Card expiry date_ _~/_ __ I I Name _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ I I Street _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ I Suburb/town _ _ _ _ _ _ _ _ _ _ _ Postcode_ _ _ _ __ I L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ JI WEATHER FAX programs for IBM XT/ ATs *** "RADFAX2" $35 is a high resolution, shortwave weather fax, Morse & RTTY receiving program. Needs CGA, SSB HF radio & Radfax decoder. Also "RF2HERC", "RF2EGA" & "RF2VGA", same as RADFAX2 but suitable for Card No. 94 SILICON CHIP FIX-A-KIT KIT REPAIR & CONSTRUCTION 3 MONTHS WARRANTY ON REPAIRS 12 MONTHS WARRANTY ON CONSTRUCTION TECHNICAL ASSISTANCE H·vcAL ELECTRONICS D es ign. M a nufacture & Re p a ir of t;.l ec tro ni c Equipme nt (02) 633 5477 Direct CAD PCB design from your schematic, rough PCB,to ink plot negative for prototype or one-off in sing I e or doub I e sided with s ii k screens & so I der resist. NC and photoplot options available on floppies. r Prices at February 12, 1992 SIMM 1MBx9 1MBx8 4MBx9 256 X 9 (For SIP Phone (02)807 6916 O or wr I te 0 ( ~ .C ~ G . F . & M. Hughes ~ PO Box 37, Ryde PCB ART NSW, 2112 1 J~ Hercules, EGA & VGA cards respectively. $35. *** "SATFAX" $45 is a NOAA, Meteor & GMS weather satellite picture receiving program. Uses EGA & VGA modes, needs EGA or VGA colour monitor & card, plus "WEATHER FAX" PC card. $45. *** All programs are on 5.25inch or 3.5-inch discs (state which) & include documentation. Add $3 postage. Only from M. Delahunty, 42 Villiers St, New Farm, 4004 Old. Phone (07) 358 2785. UNIVERSAL AT 1/0 CARDS: 2 x IDE Hard, 2 x HO Floppy, 2 x Ser, 1 x Par, 1 x Game, all cables & connectors. Enable/disable any feature - $55. XT/AT 102 keyboards $55. IBM printer cables $10. Plug packs 9.5VDC 1.1 A $14. Don McKenzie, 29 Ellesmere Crescent, Tullamarine 3043. Phone (03) 338 6286. INFRARED FILTER: a high-ql..(ality military grade deep infrared (IR) filter. For medium & high-power incandescent spotlights & floodlights. Approximately 130mm diameter & 6mm thick. High temperature pyrex-glass base material. Excellent for night surveillance equipment. Works with IR viewers & some video equipment. On special at $55.00. Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Fax (02) 570 7910. MINI INFRARED NIGHT VIEWER: as per EA, Oct. 1991 issue. A very small complete kit that includes a lens, an IR tube & an eyepiece. Simple to construct. The kit is now supplied with a high quality military inverter. Draws only 20mA from a 9V battery. Not only at the lowest price offered but we also include a free filter. $299.00. Includes the IR tube, lens, eyepiece, electronics kit, a 75mm round IR plastic filter & the case. Kit No. IRNW5. Limited stock. Certified "I MEMORY EXPANSION 100ns sons 100ns sons sons sons add $1) DRAM-DIP 1MBx 1 80ns 100ns 256 X 4 sons 41256 120ns 100ns sons 54.00 59.00 51.00 54.00 215.00 17.00 6.20 6.50 6.70 1.85 1.90 2.00 PELHAM \.. COPROCESSORS 80387-DX 25 80387-SX 16 8028710MHz 80287 To 20 240.00 145.00 100.00 130.00 FLOPPY DRIVES 3.5 Panasonic 1.44 5.25 Panasonic 1.2 80.00 92.00 EXPANSION CARDS LS 866N 32Mb OK 240.00 AST RAM plus 8Mb 375.00 BOCA AT plus 8Mb 240.00 SPECIALS Sun SLC Sharp 6220 Sharp 8081 PS/2(ALL) PS/2(ALL) Mac FX/NIX Laser Printers 4Mb 1Mb 1Mb 2Mb 4Mb 4Mb 2Mb 252.00 150.00 100.00 160.00 320.00 230.00 216.00 SOCKETS & PROC. Simm Sockets 30 x 2 Ang 6.00 Intel 80386/33 264.00 Intel 80486/33 790.00 Intel 80386/40 280.00 Sales Tax 20%. Overnight Delivery. Credit Cards Welcome 1st Floor, 100 Yarrara Road, Pennant Hills, NSW 2120. Tel (02) 980 6988 Fax (02) 980 6991 ~ , UNIDEN SCANNERS DON'T PAY MORE! 50XL ARP $299.95. Our price $211 10 memories, Lo-Hi VHF, UHF 1 OOXL T ARP $449.95. Our price $409 100 memories, Lo-Hi VHF, Air, UHF 200XLT ARP $549.95. Our Price $477 200 memories, Lo-Hi VHF , Air, UHF, 800 MHz DIGI-CART DSP BOARD For 16-bit IBM compatibles. Broadcast quality 44.1 KHz/16 bit stereo audio with audio recorder software. $1599 + Tax Custom software service for applications available. PC Computers (08) 3326513 36 Regent St Kensington SA All prices include delivery. Phone anytime today! (03) 883 9535; Fax (03) 432 0716 TopCom Communications PO Box 336, Greensborough, Vic 3088. \.. ~ TRANSFORMER REWINDS ALL TYPES OF TRANSFORMER REWINDS TRANSFORMER REWINDS p&p Australia $5; NZ (airmail) $10. Major credit cards accepted with phone & fax orders. Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Fax (02) 570 7910. SOLAR PANEL GIVEAWAY: brand new high-quality US-made amorphous glass solar panels. 150 x 150mm. Will deliver a full 1 watt whilst charging 6-8V batteries! Has weather protection film on rear. Reply Paid No.2, PO Box 438, Singleton, NSW 2330. Ph: (065) 761291. Fax: (065) 761003. Incredible pricing : $9 each or 10 for &75. Cert. p&p $5 on any amount. Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Fax (02) 570 7910. NIGHT VIEWER BARGAIN: a very small telescopic IR viewer (1/2 of a WANTED: YOUR CIRCUIT & DESIGN IDEAS Do you have a good circuit idea languishing in the ol' brain cells? If so, why not sketch it out, write a brief description & sena it to us Provided your idea is workable & original, we'll publish it in Circuit Notebook & you'll make some money. You'll also help save us from the dreadful "circuit burnout" syndrome which afflicts anyone who has to generate too many circuit ideas in too short a time. We'll pay up to $60 for a really good circuit (not too big please). So transfer your circuit to paper & send it to Silicon Chip Publications, PO Box 139, Collaroy Beach, NSW 2097. APRIL 1992 95 r----- --------------------, SILICON CHIP BINDERS l These beautifully-made binders will protect your copies of SILICON CHIP. They featu re heavy-board covers and are made from a distinctive 2-tone green vinyl that will look great on your bookshelf. Antique Radio Restorations ...... 94 Av-Comm ........... .... ................. .. 54 David Reid Electronics ..... ..... ..... . 3 Dick Smith Electronics .. ..... .. 28-29 Electronics World ......... ...... ....... .. 9 Emona Instruments ........... ... ..... 59 * 80mm internal width . * SILICON CHIP logo printed in goldcoloured lettering on spine & cover. Force Electronics ....... .. ...... ... .... 17 Geoff Wood Electronics ....... .. .. . 35 G. F. & M. Hughes ... ............ ... ... 95 Yes! Please send me _ _ _ SILICON CHIP binder(s) at $A11.95 plus $A3 p&p each (NZ $A6 p&p). Enclosed is my cheque/money order for $_ _ _ _ or please debit my 0 Visa Card All Electronic Components ..... ... 57 Altronics ....... ... ..... ... ..... ... ..... 60-63 * High quality. * Hold up to 14 issues O Bankcard Advertising Index 0 Hewlett Packard .... .. ..... ... ... .. .... IFC Hycal Instruments ...... ... ....... 43,94 Jaycar Electronics ...... ... ..... .. 45-52 J.V. Tuners .. .. ... .. .......... ... .... .... .. 41 Master Card KT Technology ... .... ... .... ......... OBC Oatley Electronics ................ 34,95 Card No. PC Computers ...... ... ............... .. 95 PC Marketplace ................... .. ... 75 Signature_ _ _ _ _ _ _ _ _ _ _ Card expiry date_ _~/_ __ Pelham ....... ............................... 95 Name _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ Peter C. Lacey Services ........... 36 Philips .. ... ........... .. .......... ..... .. .. IBC Street _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ __ _ _ __ _ Preston Electronics ... ........ .... .... 41 Suburb/town _ _ _ __ _ _ _ _ _ _ Postcode_ _ _ _ __ RCS Radio ..... ... ...... .... ....... ....... 81 Resurrection Radio ... .. ...... ..... ... 87 SILICON CHIP PUBLICATIONS PO Box 139, Collaroy Beach, NSW 2097, Australia. Phone (02) 979 5644 Fax: (02) 979 6503. L--------- ----------------J binocular viewer) with an objective lens and an eyepiece fitted. Supplied with a matching prefocussed IR tube that may have some minor blemishes. The scope has provision for a coaxial EHT connection and a small power supply kit will also be provided. Could be fitted into a small plastic case & fitted with a belt clip. Almost a complete partially constructed night viewer for only $199. Limited supply. Certified p&p Au stralia $5, NZ (airmail) $10. Major credit cards accepted with phone & fax orders. Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Fax (02) 570 7910. PCVOICE RECORDER SOFTWARE: turn your computer into an audio recorder, $25 + $3pp (VGA/EGA/CGA/ 96 SILICON CHIP Rod Irving Electronics .. .. ....... 1O, 11 68,69,82;83 Silicon Chip Back Issues ..... 88-89 Silicon Chip Binders ........... .... ... 96 Transformer Rewinds .. ...... ........ 95 MONO). MS-DOS required . Also available: PC TALKING VOLTMETER software. For project published in SILICON CHIP, Oct/Nov 1991. Plugs into the printer port of any IBM PC/XT/AT/386 or compatible. Displays voltages up to ±128V on screen, takes voltage samples over time, has 8-bit accuracy to within 1%. Combines with the PCVOICE RECORDER project to give a talking voltmeter. Available on 5¼-inch 360Kb disc plus documentation and instructions for $30 plus $3pp. Send your cheque or money order to Darren Yates , PO Box 134, French's Forest, NSW 2086. TopCom Communications .. ....... 95 VALVES: 653 Brand new valves for sale in original boxes including large quantity 6DQ6 etc. $1000. No offers. Phone (054) 94 3492. • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 587 3491 . PC Boards Printed circuit boards for SILICON CHIP projects are made by: • Electronic Toy Services, 2/111 Glynville Drive, Hackham West, SA 5163. Phone (08) 382 8919. • Jemal Products, 5 Forge St, Welshpool, WA 6106. Phone (09) 350 5555. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone 88 5730. We Only Skimped OnThe Price. Introducing The Fluke Series10. Fluke quality: Made in the USA by Fl uke, with the sarr1e rugged reliability that's made us the world leader in digital multimeters. Count on hard-working high performanceand a two-year warranty to back it up. Large, easy-to-read display: 4000 count digital readout. Actual size: Easy to carry, easy to use. New! Min/Max record with relative lime stamp and Continuity Capture™: Makes intermittent problems easier to find. Records highs and lows- and "time stamps" when they occurred. In continuity mode, opens or shorts as brief as 250 µs are captured and displayed . New! V Chek'": For fast accurate checks on power sources and supplies, set your meter on V Chekand let it do the rest. V Chek will determ ine continu ity/ohms; if voltage is present, it will automatically change modes to measure AC or DC volts, whichever is detected. For most initial troubleshooti ng checks, here's th e only setting you need to make. I Capacitance: Autoranging from .001 µFto 9999 µF. No need to carry a dedicated capacitance meter. I For high performance at Fluke's lowest price, get your hands on the new Series 10. Stop by your local Fl uke distributor and feel what a powerful difference the right multimeter makes- at th e right price. For a free product broch ure, contact you r local Fluke distributor today. Autoranging with manual option: Your choice, depending on your situation. Sleep Mode: Shuts itself off if you forget , extending long battery life even further. Fluke 10 4000 count digital display 1.5% basic de volts accuracy 2.9% basic ac volts accuracy 1.5% basic ohms accuracy Fast continuity beeper Diode Test Sleep Mode Two -year warranty New! Slide switch and a few pushbuttons control all functions: Designed for true one-hand operation . .Fast, accurate tests and measurements: AC and DC voltage measurements to 600 volts, ohms to 40 MQ; audible continuity test; and diode test. Fluke 11 V Chek™ Capacitance, .001 to 9999 pF 4000 count digital display 0.9% basic de volts accuracy 1.9% basic ac volts accuracy 0.9% basic ohms accuracy Fa~t continuity beeper Diode Test Sleep Mode Two-year warranty Fluke 12 V Chek'" Min/Max recording with relative time stamp Continuity Capture™ Capacitance, .001 to 9999 pF 4000 count digital display 0.9% basic de volts accuracy 1.9% basic ac volts accuracy 0.9% basic ohms accuracy Fast con tinuity beeper Diode Test Sleep Mode Two-year warran ty Optional holster with tilt-stand available. Safety- a Fluke standard: Designed to meet UL1244 , IEC 1010, CSA and VDE safety req ui rements; extensive overload protection built in. New! TL75 Hard Point'" Test Leads: Comfort grip with extra strong tips for extended service life. The New Series 10. A Small Price For A Fluke. Audible Continuity: To perform fast continuity checks, just listen for the beep; no need to watch the display. F L UKE AND PHIL I PS T HE T &M ALL I ANCE For fu rth er information contact: Philips Scientific & Industrial. Tel : (02) 888 0416