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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au Contents Vol.10, No.2; February 1997 FEATURES 4 Computer Problems: Sorting Out What’s At Fault It pays not to jump to conclusions when your computer plays up. We take a look at a couple of typical problems – by Greg Swain 66 Cathode Ray Oscilloscopes; Pt.6 Digital oscilloscopes can give misleading results if not used correctly. Here’s how to interpret the on-screen display – by Bryan Maher PROJECTS TO BUILD 10 PC-Controlled Moving Message Display This easy-to-build moving message display plugs into your PC’s parallel port. You just type the message in on the keyboard – by John Western COMPUTER PROBLEMS: SORTING OUT WHAT’S AT FAULT – PAGE 4 16 Computer Controlled Dual Power Supply; Pt.2 This month, we describe the interface board that lets you control the supply from your computer – by Rick Walters 24 The Alert-A-Phone Loud Sounding Alarm This very loud ringer plugs in parallel with your existing telephone and is Austel approved – by Derek Diggles 40 Build A Low-Cost Analog Multimeter You can learn about multimeters and kit assembly by building this simple unit. And you’ll wind up with a useful test instrument – by Leo Simpson BUILD A PC-CONTROLLED MOVING MESSAGE DISPLAY – PAGE 10 56 Control Panel For Multiple Smoke Alarms, Pt.2 The full construction and installation details are in this month’s issue. Build it and control up to 10 smoke detectors – by John Clarke SPECIAL COLUMNS 30 Serviceman’s Log Don’t monkey with a VCR – by the TV Serviceman 53 Satellite Watch The latest news on satellite TV – by Garry Cratt 74 Radio Control THE ALERT-A-PHONE LOUD RINGER – PAGE 24 How models can be lost through interference – by Bob Young 86 Vintage Radio The combined A-B battery eliminator – by John Hill DEPARTMENTS 2 38 54 82 90 Publisher’s Letter Mailbag Circuit Notebook Product Showcase Back Issues 92 93 94 95 96 Ask Silicon Chip Notes & Errata Order Form Market Centre Advertising Index CONTROL PANEL FOR MULTIPLE SMOKE ALARMS – PAGE 56 February 1997  1 Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Editor Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Robert Flynn Rick Walters Reader Services Ann Jenkinson Advertising Manager Brendon Sheridan Phone (03) 9720 9198 Mobile 0416 009 217 Regular Contributors Brendan Akhurst Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed John Hill Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young Photography Glenn A. Keep SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. A.C.N. 003 205 490. All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Macquarie Print, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $54 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 34, 1-3 Jubilee Avenue, Warrie­ wood, NSW 2102. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. PUBLISHER'S LETTER Tariff reductions on cars may not be wise As this issue goes on sale, we can expect that the Govern­ment will be placed under intense pressure to speed up tariff reduction in the car industry. Just before Christmas, the Produc­ tivity Commission brought down a majority report that urged tariff reduction from 15% in 2000 to just 5% in 2004. Presently, tariffs on imported cars are at a level of 25% and to reduce them to 5% in less than 10 years is a huge reduction in anyone’s language. Many economists would argue that Australia should proceed down the path of tariff reduction for all economic activities and in terms of hard financial figures, they are undoubtedly right. When tariffs are removed or reduced, the products affected in­variably are reduced in price and consumers are better off. But will we be better off overall? We have already seen this happen with electronics consumer products and there is no doubt that they are much cheaper now than they would have been if tariffs had been maintained. The problem is that while all those goods are undoubtedly cheaper, we have also lost a great number of skills that went with the manu­facturing and servicing of those electronic products. Not only the skills but most of the jobs have been lost and in many cases the people directly affected have never got equivalent satisfying employment again, if they have managed to get jobs at all. The same thing will happen as tariffs are reduced on cars. New cars and sec­ ondhand cars will become cheaper. But then we will lose many thousands of jobs in manufacturing, not only in the car industry itself but in all of the support industries, and that includes some electronics manufacturing, surprising though it might seem. But it will go much further than that. If new cars are cheaper, then it will become uneconomic to repair cars. So we will inevitably lose huge numbers of jobs in repair shops – not only mechanical repairs but in smash repair shops as well. Many more cars will simply be written off and sent to the crushers after even quite minor accidents. It is fairly safe to say that most of the people working now in the car manufac­ turing and repair industries would never get equivalent jobs again. And youth unemployment which is unac­ceptably high now, will go even higher. No, while we would all like to buy cheaper cars and enjoy the safety and driving pleasure that a new car entails, we will be paying a huge social price if we go down that road too rapid­ly. Sure, we are paying a high price to effectively subsidise a lot of jobs in the car industry. But people and the general community are always better off if they are gainfully employed instead of being on the dole. Let us hope that the history of the Australian electronics consumer industry is not repeated in the car industry. Leo Simpson ISSN 1030-2662 WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 2  Silicon Chip SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Macservice Pty Ltd *!#$*&<at>* COMPUTERS Sorting out what’s really to blame If there’s one thing I’ve learnt about computers over the years, it’s not to jump to conclusions when something doesn’t work properly. When things go wrong, it’s all too easy to blame the obvious, without getting to grips with what’s really at fault. By GREG SWAIN How often have you heard that a par­ ticular operating system is unstable? Or that it doesn’t work on such and such a computer? Or that a particular item of hardware has a “bug” and should be avoided? Or that something just doesn’t work when your own ex­ perience indicates otherwise? When it comes to computers, there are enough real problems to sort out without having to also sift through a mine of misin­formation, straight-out even been told that PCs are no good in this role because “they just don’t work” and because “they have font problems”. Well, you could have fooled me. There we’ve been all those years, suc­ cessfully producing a magazine using PCs that don’t really work – at least according to the hearsay of several self-appointed experts. What rubbish! We’ve used PCs in the desktop publishing role for over “A computer is really a box full of grem­lins, just waiting to wreak all sorts of havoc at the user’s expense”. bad mouthing and old wives’ tales. I’d like a dollar for every time that someone has rolled their eyes to the ceiling when told that SILICON CHIP is produced using PCs, for example. I mean, everyone knows that Macs are the all the go when it comes to desktop publishing, don’t they? I’ve 4  Silicon Chip six years now with very few problems but try telling that to some people. Not that it’s ever really worth the bother – a few pointed questions in­ variably reveal that such people know very little about PCs, and are simply basing their opinions on “common knowledge”. It’s all the stuff of myths and legends but if it’s “common knowledge”, then it must be true. I’m not seeking to belit­ tle Macs here, by the way. I’m simply making the point that the PC is a valid alternative for desktop publishing, de­ spite what many ill-informed people will try to tell you. The most common misconceptions by far arise out of hardware and soft­ ware upgrades. The reasons are not too hard to find. Hardware upgrades, in particular, are often not straight­ forward for a variety of reasons. After several recent experiences of my own, I’m convinced that a computer is really a box full of grem­lins just wait­ ing to wreak all sorts of havoc at the poor user’s expense. OK, so I’m exaggerating somewhat but if you’ve ever at­tempted to add hardware to a PC, you’ll know what I mean. Even Windows 95’s much vaunted Plug and Play (PnP) system has problems in some circumstances. Let me give you a couple of examples of what can happen when even rela­ tively simple upgrades are attempt­ed. The not-so-crook RAM Recently, we decided to upgrade the RAM in a couple of our office machines from 32Mb to 64Mb. These two machines used iden­tical mother­ boards and in each case, the existing RAM consisted of two 16Mb SIMMs. As a result, we decided to purchase two new 32Mb SIMMs for the first machine and transfer its existing 16Mb SIMMs to the second machine. Installing the new 32Mb SIMMs was straightforward enough but when we We solved the problem by leaving the new SIMMs in the third machine and sharing its original four 16Mb 70ns SIMMs between the first two machines. So all three machines ended up with 64Mb of RAM – it’s just that the two new 32Mb SIMMs ended up in an unexpected location. But it’s easy to see how misun­ derstandings can arise in this sort of situation. We could have easily been fooled into returning perfectly good RAM to the supplier, demanding that it be replaced. And of course, the re­ placement RAM would have caused exactly the same problems. upgrades. Win95 cannot automati­ cally assign interrupts (IRQs) to nonPnP expansion cards (now referred to as “legacy” cards) and can easily get itself into a knot if left to its own devices. To explain, a standard PC has 16 interrupts (0-15) avail­able but most of these are taken by the system, leaving about six free for expansion cards (de­ pending on the configuration). Each expansion card must be as­signed a unique IRQ; if two cards have the same IRQ, there will be a conflict and the system won’t work properly. The “minimalist” approach usually works well when install­ ing Win95, particularly if you have a mixture of legacy and PnP cards. This involves removing all non-essential cards, such as sound cards and network cards, before installing the software. Once the system is up and running properly, you can add the expansion cards back in, one at a time. By the way, it’s best to add the legacy cards first, as the PnP cards are auto­ matically assigned the leftover IRQs. In addi­tion, the system assigns IRQs to PnP cards in ISA slots before those in PCI slots. Note also that you should reserve the appropriate IRQs for the legacy cards in the system BIOS, where this facility exists (ie, if the motherboard has a PnP BIOS). This will usually be found under a “Plug and Play Config­ uration” (or similar) menu. For exam­ ple, if you have a legacy card that’s set to IRQ10, then you must assign IRQ10 for use by an ISA card. The above step is quite important. If you don’t do it, Win95 may automat­ ically assign an IRQ that’s already in use to a PnP card. Operating system myths The suspect motherboard There are also plenty of myths floating around regarding operating systems. One that I’ve heard from a couple of people is that Windows 95 needs a Pentium processor and won’t run on a 486. Wrong! What they really mean is that they couldn’t get it to work on their particular 486 for some reason or other. To prove the point, we recently installed the Win95 upgrade pack on an old 50MHz 486 machine. It ran without a hitch and I’ve even heard of people running Win95 on a 386. Hardware conflicts are often the root cause of aborted operating system It’s not just hardware conflicts that can be a problem. Hardware bugs can also cause problems and lead to unfair criti­cism of an operating system or even individual programs. Consider my own experiences with Windows 95 which is in­stalled on my main office machine. This is one of the machines described above that didn’t like the 60ns 32Mb SIMMs and the problem I am about to describe is directly related to the memory upgrade. As mentioned earlier, this machine was originally config­ured with 32Mb of RAM (2 x 16Mb SIMMs). It is set up This new motherboard cured an unstable Windows 95 installation. The bus speed of the motherboard in the original machine had apparently been pushed beyond its design limitations – or, at least, that’s one theory. switched on, the machine refused to boot. Sometimes it would just hang after completing the BIOS checks. At other times, it would start to boot the operating system and then halt, with a screen full of obscure error messages. Our first thought was that we must have dislodged a cable when installing the new RAM but a quick check re­ vealed that all was as it should be. Our next snap diagnosis was crook RAM and this was seemingly confirmed when it also failed to work in the sec­ ond machine. Yet when we substituted the old RAM, both ma­chines booted without problems. That was it, of course – one of those new 32Mb SIMMs just had to be faulty! But was it? Perhaps the problem was in the two machines which, after all, were virtually identical. The only way to find out was to try the new SIMMs in a third machine with a completely different motherboard. When we did, it booted straight up and performed flawlessly. So much for our snap diagnosis of faulty RAM! Instead, it appears that the motherboards in the first two machines weren’t happy with the 60ns RAM on the new SIMMs (the older SIMMs used 70ns RAM). And there were no settings in the system BIOS that could compensate for this. February 1997  5 You can easily check for hardware conflicts in Win95 by double-clicking the “System” icon in “Control Panel”, then se­lecting the “Device Manager” tab. Doubleclicking on a specific device then gives you the “Resources” tab, which lets you view the resources allocated. as a dual-boot Windows 3.11/Win95 system but I was never entirely happy with the system under Windows 95 as it occasionally crashed when the going got heavy. My first inclination was to blame which ever program I happened to have running at the time but eventu­ ally I began to suspect Windows 95 itself. However, the pattern was too intermit­tent to really get to grips with the problem. The breakthrough came when 6  Silicon Chip the extra 32Mb of RAM was added. Windows 3.11 continued to work nor­mally but not so Windows 95. It now frequently crashed, generat­ ing “Unexpected Exception” errors in the process. And when it crashed, it would often refuse to boot again unless the addition­al RAM was removed. This meant that the problem was probably hardware related. Initially, I simply tried replacing the original RAM with the second two 16Mb SIMMs but this made no difference. I also tried swapping memory banks and substituting the memory from the machi­ne’s twin without result. By now, the finger of suspicion was pointing fairly and squarely at the motherboard. After all, it had previ­ ously failed to work with the 32Mb SIMMs, so it was definitely suspect when it came to handling mem­ory. And there was another thing. The machine ran a 133MHz Pentium processor but the manual that came with the motherboard only mentioned 75MHz and 90MHz processors. An 8-way DIP switch is used to set the bus and processor clock speeds but the manual gave no details of the settings. Fortunately, the settings were screen-printed on the moth­ erboard in a vacant area adjacent to the micro­ processor. But what was interesting was that the machine’s twin, which was purchased four months later, also showed an additional setting for a 100MHz processor. And both ma­ chines were set to this configuration. That aside, the motherboard was obviously originally de­signed to op­ erate at a bus speed of either 60MHz when used with a 90MHz processor, or 50MHz when used with a 75MHz (or 100MHz) processor. That’s because the processor always runs at some ratio of the bus frequency, the available ratios in this case being 1.5x and 2x (ie, 1.5 x 50MHz = 75MHz, 1.5 x 60 = 90MHz, and 2 x 50MHz = 100MHz). So what was going on? A 133MHz processor requires a 66MHz bus so the board must have been tweaked to run at this higher speed – probably by the simple expedient of substituting a different crystal in the clock circuit during manufacture. Fairly obvious­ly, this was an existing design that had been hastily adapted to cater for the faster processor but it appeared that it wasn’t up to the task – at least not with Windows 95. There was nothing for it but to change the board. It ain’t that easy Now if you thought that changing the motherboard in a Win95 system was a straightforward task, think again. The mechanical installation is easy enough but getting everything up and running again is a different matter. Windows 3.11 was OK (it’s too dumb to recognise the swap) but Windows 95 is too clever by halves, tying itself in all sorts of knots when it discovered SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. ORDER FORM PRICE ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏ 3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my Bankcard   ❏ Visa Card   ❏ MasterCard ❏ Card No. Signature­­­­­­­­­­­­_______________________________ Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ the new motherboard. This problem apparently stems from the fact that the param­eters of the new motherboard and its BIOS don’t match the exist­ing registry settings. In the end, the only way around the prob­lem was to clean off the existing installa­ tion and its associated applications and reinstall all software. If you’re ever in this situation, by the way, don’t be tempted to simply reinstall the operating system over the top of the existing installation. It’s best to clean everything off and go for a fresh installation. The Win95 reinstallation was not without a small glitch, however. I’d removed the sound card but left in a SCSI card and a PnP network card. Everything went fine until the first boot. Windows 95 made it past the logon dialogs but then announced that it was searching for new hardware. There followed a brief period of hard disc activity, after which it just “hung”. I tried switching the machine on and off several times but always with the same result. Eventually, I pulled the network card and tried again. And that was it – the system now booted correctly and I was able to reintroduce the sound and network cards. Windows 95 now recognised the network card, installed the correct driver for it and automatically as­ signed an available IRQ. Now why didn’t it do that in the first place? Did the new motherboard do the trick? Well, based on my limited obser­ vations so far, the answer is yes. I now have a stable Windows 95 installation but just think how easy it would have been to jump to con­clusions and badmouth the operating system. Strangely enough, the other ma­ chine with the identical motherboard operates perfectly with its 64Mb of RAM but then it’s running Windows NT. So is Windows 95 fussier than NT about the hardware company it keeps? Or was it just a matter of manufac­ turing tolerances between the two boards? Or was the problem caused by some subtle hardware conflict which is now resolved and nothing to do with the motherboard at all? Finally, could I have cured the prob­ lem by changing the DIP switches so that the motherboard ran at a slower bus speed (yes, this would have throt­ tled back the processor)? We’ll probably never know the an­ SC swers to those questions. February 1997  7 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au PC-controlled moving message display Have you got an old PC sitting around gathering dust? You can use it to control this moving LED message display which plugs into the PC’s printer port. All you have to do is type the message in on the keyboard. Design by JOHN WESTERN Moving LED message displays are common in shops and clubs and are very effective as advertising signs. Now you can have your own by build­ ing this unit. All you need to drive it is an old XT (or better) computer and you can easily set the unit up to repeat a message or a number of messages. While LED message displays use a variety of formats, this one employs characters which are seven LEDs high by five LEDs across and these move along the LED array at a fixed rate. As presented here, the display con­ sists of a 48 x 7 LED matrix arranged 10  Silicon Chip on a single large PC board. This board basically consists of three 16 x 7 LED modules: a master module which also contains the necessary parallel port interface circuitry, and two extension modules. Each module has enough LEDs to display three characters, which means that the basic unit can display up to nine characters at any given time. If you wish, you can increase the display width by adding another one or two extension modules. This will allow either 12 or 15 characters to be displayed at any one time. The additional extension modules are sim­ ply cut from a second PC board and connected to the lefthand end of the message display using 12 wire links. Conversely, you can reduce the display width by cutting off one of the extension modules, to give a 32 x 7 (6-character) LED display. Of course, the length of the message is not limited by the number of char­ acters that can be displayed at any one time. Basically, you can make the message as long as you like. In opera­ tion, the leading characters appear on the righthand side of the display and scroll across to the lefthand side before disap­pearing off the “edge”. The mes­ sage continues scrolling until all the characters have been displayed and can easily be set up so that it repeats. Our prototype was built to the stand­ ard 9-character config­uration; ie, a sin­ gle PC board with three modules. This is housed in a folded smoked-Perspex case to produce an attractive display. It is powered by a 12V AC plugpack and is connected to the parallel port of the PC via a DB25 socket mounted on one end of the board. How it works Each character to be displayed is produced by turning on all the appro­ priate LEDs in a row for a short period of time. This is repeated for each of the seven rows, to make up the character in a multiplexed fashion. Because this happens at a very high rate, all the LEDs appear to be turned on at the same time. Fig.2 shows the circuit diagram of the Moving LED Display. Each row of LEDs is driven by a Darlington tran­ sistor pair con­sisting of a BC549 and a BC639; ie, Q1 & Q2 for row 1, Q3 & Q4 for row 2, etc. These seven Darlington transistor pairs are in turn driven by the printer port data lines. Note that each line from the printer port is filtered by an RC network con­ sisting of a 47Ω resistor and a 220pF capacitor. These filters prevent noise pulses from disturbing normal opera­ tion of the display. The LED columns are controlled by separate BC549 transis­tors (Q15, Q16, etc), in turn driven by 74LS164 shift registers (one for each group of eight columns). These shift registers accept the serial data applied to their A & B data inputs and convert it to paral­lel format at their Q0-Q7 outputs. So each shift register con­trols eight transistors Fig.1: this diagram gives a breakdown of the basic operation just to light one LED. In this case, we want to light the LED at row 4 column 3 (ie, R4,C3). This involves clocking a logic 1 into the shift register and then moving it until the third output goes high, represented here by the closed switch between the shift register and C3. Switch SW3 is then closed to light the row and thus eight LED columns. Note that, for the sake of clarity, our circuit only shows the first eight LED columns, their corresponding transistors (Q15-Q22) and one shift register (IC1). The circuitry for each successive eight columns is identical, with pin 13 of IC1 clock­ing the data inputs of the next shift register, and so on down the chain. IC1 is driven by one of the parallel printer port data lines, while two other data lines drive the clock and reset pins (pins 9 & 8). Basically, data is shuffled into IC1 in serial fashion and its appropriate Q outputs go high, thereby turning on the corresponding column transistors. One of the row data lines is then briefly taken high to light the required LEDs. In greater detail, the character to be displayed is broken down into the required pattern of dots for each row. Initially, the shift registers are all cleared by applying a pulse to the MR line. This sets all outputs to a logical low condition, turning all columns off. The required data is then applied to the A & B data inputs and the CLK line pulsed to move the data into the first shift register. Successive data is sub­ sequently applied in a similar fashion until the required pattern of dots for a particular row is set up in the shift registers. Once the data is ready, the row is turned on for a short period of time after which the shift register is cleared (reset) and the process starts again for the next row. Fig.1 gives a breakdown of the basic operation just to light one LED. In this case, we want to light the LED at row 4 column 3 (ie, R4,C3). This involves clocking a logic 1 into the shift regis­ ter and then moving it until the third output goes high, represented here by the closed switch between the shift register and C3. Switch SW3 is then closed to light the row, in this case the single LED at R4,C3. February 1997  11 Where To Buy The Parts The parts for this design are available from Oatley Elec­tronics, PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3563; fax (02) 9584 3561. The options are as follows: Complete Kits (does not include case) (1) PC board, all on-board parts, software on 3.5-inch disc, a surplus plugpack & bright red, green or amber LEDs (you specify): $165 (2) Above kit with super bright LEDs (narrow viewing angle): $200 Shortform Kits & Accessories (3) PC board only plus software on 3.5-inch disc: $75 (4) 336 bright LEDs (red, green or amber – please specify): $45 (5) 336 super bright LEDs: $90 (6) Suitable small 10.6V 1.4A surplus switchmode power supply in case: $12 Note 1: none of the above options includes a case or the Perspex channel shown in the photos. Please add $6.00 p&p to any combination. Note 2: the PC board associated with this design is copyright Oatley Electronics. In addition, the software supplied is copy­right John Western and must not be altered in any way or used for other purposes without permission. Note, however, that the basic circuit of Fig.1 works in the opposite sense to the circuit of Fig.2. In reality, the shift registers drive transistors and these provide logic lows, while the printer port data lines and their associated Darlington transistors pull the rows high. To sum up, the printer port data lines pull each row high in succes­ sion to light the appropriate LEDs. And in between times, the shift reg­ isters are reset and new data appro­ priate for the next row is clocked in. Add to this the fact that the display moves from left to right and you can see that the timing process is quite complicated. Fortunately, that’s all taken care of by a machine language program which is called LEDs.COM. This program manipulates all the control lines from the printer port to control the LED dis­play. Power supply The display is powered from a 9-12V DC plugpack rated at 1A. The DC rail from the plugpack is applied to REG1, which delivers a regulated 5V rail to power the LED arrays and the shift reg­isters. The 10µF and 1µF capacitors at the input and output of REG1 are there to ensure regulator stability. In addition, the supply pins of all the 12  Silicon Chip shift registers are filtered using 0.1µF capaci­tors Construction This design is available as a com­ plete kit of parts from Oatley Electron­ ics, who own the copyright on the PC board (see pricing panel). The board is double-sided with plated-through holes which means that there are no links to install. It is also solder-masked and carries a screen printed overlay to make the job of assembly as straightforward as possible. As mentioned earlier, the basic con­ figuration is a 3-sec­tion board with a 48 x 7 LED array. Each section (or module) contains 16 LED columns plus a pair of matching shift registers. In addition, the master module carries the DB25 socket plus the Darling­ton transistors and power supply components. Fig.3 shows the parts layout on the PC board. Note that this only shows the master module plus part of the first exten­sion module. The pattern of LEDs, shift register ICs and other parts simply repeats towards the left. Begin the assembly by installing the resistors and capaci­tors, then add the transistors and the ICs. The use of IC sockets is recommended here, since a dud IC (rare) is very difficult to remove if it is soldered directly to a double-sided board. Take care with the polarity of the ICs – they are all installed with the notched end to­ wards the right. Similarly, take care to ensure that the transistors are all correctly ori­ ented and note that Q2, Q4, Q6, Q8, Q10, Q12 & Q14 (ie, the transistors immediately adjacent to the LED rows) are all BC639s. Now for the LEDs. There are 336 LEDs in all, so installing them will take some time. The main thing to watch out for here is to ensure that they are all correctly oriented. You can identify LED polarity in two ways: (1) the anode lead is the longer of the two; and (2) the cathode lead is adjacent to a small flat section on the bottom lip. Push the LEDs down onto the board as far as they will go before soldering their leads. Once all the LEDs are in, you can install the DB25 socket and the 7805 regulator (REG 1). The latter is installed with its leads bent at right angles and its metal tab bolted to the PC board along with a small finned heatsink. The prototype board was installed in a smoked Perspex chan­nel (470mm long x 150mm high) and secured using machine screws and nuts at the back. This Perspex channel was bent up by a local plastics supplier. Alternatively, you can make up a suitable wooden or metal case with a Perspex viewing window for the LED arrays. Software & testing The software for the Moving LED Display comes on a 3.5-inch floppy disc and consists of six main files plus a brief readme file. The files leds3.com, leds4.com and leds5.com are for dis­ plays with from three to five modules (including the master module), while the ledset.com file configures the basic setup. First, copy the correct leds_.com file to the hard disc (or to another floppy), along with the ledset.com file. Next, rename the copied leds_.com file to leds.com, then run ledset.com Fig.2 (right): the Moving LED Display is controlled via the PC’s parallel port. The rows are driven by Darlington transistor pairs, while the data in the shift registers (IC1, etc) controls the column switching transistors (Q15, Q16, etc). February 1997  13 Silicon Chip BINDERS These beautifully-made binders will protect your copies of SILICON CHIP. They feature heavy-board covers & are made from a dis­ tinctive 2-tone green vinyl. They hold up to 14 issues & will look great on your bookshelf. ★ High quality ★ Hold up to 14 issues ★ 80mm internal width ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 (includes postage in Australia). NZ & PNG orders please add $A5 each for postage. Not available elsewhere. Silicon Chip Publications PO Box 139 Collaroy Beach 2097 Or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number.  Use this handy form Enclosed is my cheque/money order for $________ or please debit my  Bankcard  Visa  Mastercard Card No: _______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ 14  Silicon Chip Fig.3: follow this diagram when installing the parts on the PC board. Note that only the master module and part of the first extension module are shown here. The pattern of LEDs, shift register ICs and other parts simply repeats. Note that a heatsink should be fitted to REG1 (see photo). The basic PC board includes a master module (at right) plus two extension modules to make up a 48 x 7 LED array. Up to two extension modules, each with a 16 x 7 LED array, can be added to the lefthand end of the board. Note the heatsink fitted to the 7805 regulator (REG1). Fig.4: the ledset.com program lets you configure the ledsx.com program to suit your computer. The values shown are good starting points for a 133MHz Pentium machine (see text). to configure the display driver to the required parameters. Fig.4 shows the setup that appears when ledset.com is run. There are three parameters that can be varied: (1) the printer Port address; (2) the Delay; and (3) the Duty cycle. The latter sets the speed at which the message move across the screen, while the Delay sets the period between messages. The up and down arrow keys select the parameter to be altered. In most cases, the default printer port address of 0378H will be cor­ rect. If not, the address can either be gleaned from the system BIOS or by running the Microsoft Diagnostics program (type msd at the command prompt). Often, too, the address will be dis­ played at some stage during the com­ puter’s boot sequence. If you are using Windows 95, double click the System icon in Control Panel, then click the Resources tab, select the printer port and click Properties and Resources to view the address. The numbers for Delay and Duty will depend on the speed of the PC used. A Delay of 00500 and a Duty of 001 are good starting points for an XT but these numbers should be increased for higher speed PCs. We found that a Delay of 02500 and a Duty of 250 produced good results on a 133MHz Pentium machine. Note that you have to type in each digit in an entry, start­ ing from the left­most digit, until the number is correct. The display can now be plugged into the PC and the leds.com program run from the DOS prompt. The mes­ sage to be displayed must be included on the command line; eg, to display the message DOES YOUR DISPLAY WORK?, you type leds does your display work? at the command prompt. Note that all characters are displayed in upper case, regardless as to how they are typed. The above command will display the message once before returning con­ trol to DOS. If you want the message to be displayed repeatedly, you simply use a full stop as the first character of the message. For example, the command leds .silicon chip will repeatedly cycle the message SILICON CHIP across the display. The display can be stopped at any time by pressing Ctrl C on the computer keyboard. Assuming that the unit works cor­ rectly, you can now experi­ment with the Delay and Duty values in the ledset.com program. If a row of LEDs fails to light, check the associated Darling­ton transistor pair. Similarly, if a column of LEDs fails to light, check PARTS LIST 1 double-side PC board with plated-through holes, 414 x 107mm (incl. three modules) 1 smoked Perspex channel case with Perspex window or (see text) 1 mini U-shaped heatsink to suit TO220 regulator, 19 x 19 x 11mm 1 PC-mount DB25 male socket 1 DB25 cable, male-to-female 1 9-12V DC 1A plugpack supply 6 14-pin IC sockets Semiconductors 6 74LS164 shift registers 7 BC639 PNP transistors 55 BC549 PNP transistors 1 7805 5V 3-terminal regulator 336 LEDs Capacitors 1 10µF 25VW electrolytic 7 0.1µF monolithic ceramic 10 220pF ceramic Resistors (0.25W, 5%) 10 10kΩ 48 68Ω 48 4.7kΩ 10 47Ω the associated column switching transistor. Finally, a batch file can be used to allow a sequence of messages are to be displayed continuously. An example of this is as follows: :start leds message 1 leds message 2 leds message 3 goto start These lines must be created in an ASCII text editor and the file saved with a bat extension; eg, message.bat. February 1997  15 Pt.2: adding the parallel interface board BY RICK WALTERS Computer controlled dual power supply Last month, we presented the standalone version of this power supply. By building & fitting the interface board de­scribed here, you will be able to control it from your computer. The power supply interface board connects via a 25-way cable to the parallel port of your computer. The interface allows your computer to perform two functions. The first is to set the required posi­ tive and negative output voltages and current limit which will be delivered by the power supply. The second is to display the actual voltage and current from the power supply on the comput­ er’s video monitor. 16  Silicon Chip Normally the voltages set by the computer will be the same as those displayed but if the power supply goes into current limit, the associated output voltage will be reduced. One good feature of the computer control is the ability to use the settings which were in use the last time the supply was turned off. These settings are stored in a file which is read each time the software is run. This gives you the option of using the same supply values and printer port as previously or selecting new values or a different printer port. Now let’s have a look at the circuit of Fig.1 and even the most dyed-in-thewool computer hardware enthusiast would have to admit that it’s not too inspiring. However, before you turn the page and give up, let’s note a few key points. First, if you refer to the circuit presented last month, you will note that there are four outputs labelled IN1, IN2, IN3 & IN4 and three inputs labelled D/A1, D/A2 & D/A3. The outputs from the power supply board become the four inputs for the A/D converter on the interface board. They are fed to IC7, a 74HC4051 1-of8 multiplexer. Depending on the BCD data at its ABC inputs, it feeds the selected IN value through to IC8, the ADC0804 analog-to-digital converter. The four IN values relate to the fol­ Fig.1: the circuit allows data from the computer’s printer port to set the sup­ ply’s voltage and current outputs. It also allows the voltage and current to be monitored on the computer screen. Octal latches IC1, IC2 and IC3 are used as D/A converters and are con­trolled by IC4, a 74HC137 latched one-of-eight decoder. February 1997  17 Fig.2: follow this parts layout diagram to assemble the interface board. The assembly is straightforward but take care to ensure that the ICs are all correctly oriented and that the correct IC is used at each location. lowing four power supply parameters: IN1 Positive output voltage (V+) IN2 Output current (I+) IN3 Negative output voltage (V-) IN4 12V supply All these IN values will be in the range of 0-5V and will be converted by the ADC0804 chip, IC8, to an 8-bit word (a number between 0 and 255) which is fed to the computer’s paral­ lel port, on pins 10-17. Note that the parallel port is bidirectional so it can accept data on these pins, as well as outputting data. Three of the IN values, IN1, IN2 and IN3, are displayed on the computer’s screen. As we just remarked, the parallel port also outputs data and in this case it delivers 8-bit data to control the volt­ age and current settings on the power supply. This 8-bit data is delivered on pins 2-9 (D0-D7) of the 25-pin socket. From there it is connected to the D0-D7 inputs of IC1, IC2 and IC3. These are used as three D/A (digital to analog) converters. Digital to analog converters IC1, IC2 and IC3 are octal (8-bit) latches under the con­ trol of IC4, a 74HC137 latched one-of-eight decod­ 18  Silicon Chip er. Depending on the data fed to its pins 1, 2 & 3, IC4 enables IC1, IC3 or IC3 (via their latch enable pin 11 and inverters IC5b, IC5e & IC5c) so that the data on their input pins 2-9 is latched onto their Q outputs, pins 19-12 (Q0 to Q7). Each 74HC573 has a ladder network consisting of 10kΩ and 20kΩ resistors connected to the eight outputs. These networks convert the 8-bit data at the output to a voltage with a value between zero and 5V. These analog voltages are D/A1, D/A2 & D/A3, corresponding to the positive volt­ age setting Vo+, current limit setting Io, and the negative voltage setting Vo-. We have just described the two main functions of the interface board: first, monitor the four IN values from the power supply board and provide the three control values for positive and negative voltage and the current limit setting. Apart from that, there is little point in going further with the circuit description since the interface board is entirely under software control. PC board assembly The interface board measures 178 x 100mm (code 04101972) and has a 25-pin D socket mounted at one end. Fig.2 shows the component layout on the board. The board assembly is reasonably straightforward. In es­sence, you have a few rows of equal value resistors and eight ICs to install, and not much else. As usual, before starting assembly, check the copper pat­ tern for open circuit or shorted tracks or undrilled holes. Make any repairs required and then fit and solder the 21 links and 10 PC stakes. Next, fit the resistors and diodes, followed by the IC sockets, capacitors and finally, the D connector. Check your soldering when you are finished to make certain that no IC pads are bridged. Interconnecting wiring Most of the interconnecting wires should have been taped up when you built the power supply. If you followed the colour code that we suggested last month, the brown wire will go to D/ A1, the red to D/A2 the orange to D/ A3 and the black to ground. There should be four other loose wires: the blue goes to IN1, grey to IN2, brown to IN3 and white to IN4. Two leads need to be run from the anode of D3 to TP14 and from the remaining PC stake to TP4 on the power supply board. Fig.3: the parallel port interface board is mounted at one end of the chassis, with the DB25 connector protruding through the rear panel. Use this chassis wiring diagram and the wiring table from last month’s issue to make the offboard connections. Because only low currents are involved, you can run the connections to the interface board using rainbow cable February 1997  19 to the positive output voltage. If you set the front panel voltmeter to read the positive supply voltage and short the positive output, the current reading on the computer should read .05 and the digit colour should change to red. Also the positive voltage should read 0 or .1 and again should be red, indicating that it is not the selected value. The current limit changes colour as the limit setting is reached to let you know that the power supply is in current limit mode. Voltage calibration The interface board mounts vertically on one side of the case and is attached to the rear panel via the rightangle 25-pin D connector. Mount the PC board to the back pan­ el using the hex head bolts to secure it, with the components facing the power trans­former. We stuck a mounting foot on the metal chassis to keep the board parallel to the case, and another on the plastic cover to keep the board firmly in place. Testing You will need a 25-way D female to 25-way D male cable to connect the computer to the power supply. This done, load GW Basic and SCREG.BAS and follow the on-screen instructions (see Fig.5). As there are no previous values saved, you should enter 10V for the positive voltage, 15V for the negative voltage, .05 for the current limit, and 1 or 2 for whichever printer port you plan to use. It is probably wise at this stage to use LPT1, the paral­lel port you have been using to drive your printer, as you know that this port works. When you switch the power supply to remote, the voltages you have set (or values very close) should be displayed as in Fig.5. Pressing the plus key should in­ crease the positive voltage and the minus key should reduce it. If you press the “T” key the negative volt­ age should reduce to the same value as the positive and follow it. This is the “tracking” condition whereby the negative output voltage is always equal Software Features  Positive and negative voltage setting in 100mV steps from 0-25.5V   Individual output voltages or negative supply tracking positive supply   Current limit setting in 10mA steps from 0-2.55A for both supplies  simultaneously  Computer screen readout of positive and negative output voltages   Voltage reading changes from yellow to red for out of tolerance voltage   Computer screen readout of positive supply current   Current reading changes from yellow to red at current limit   Selection of printer port 1 or 2   All settings are saved and can be restored at program start  20  Silicon Chip In spite of the fact that the power supply will have alrea­dy been cal­ ibrated for standalone operation, it needs to be recalibrated for computer control. The procedure is similar to that outlined last month. Set both supply rails for 24.5V out­ put and with your DMM across the negative output and ground, adjust VR4 until the voltage reads exactly -24.5V. Now set VR6 so that the posi­ tive output voltage is identical. If you can measure current with your DMM, find a 10Ω 5W or 10W resistor and connect it in series with your ammeter across the positive sup­ ply. Set the voltage to 22V and set the current limit for 1.95A. Disconnect your DMM, switch it back to volts and with just the 10Ω resistor for the load and using the front panel meter to check that the current is around 1.95A, adjust VR5 so that the voltage on TP8 is 3.82V (1.96 x 1.95). If your meter can’t measure current, wire the 10Ω resistor across the pos­ itive terminal and earth, then set the positive voltage to 22V and the current limit to 1.9A. Measure the voltage across the 0.1Ω resistor in the emitter of Q2, multiply it by 1.96 and adjust VR5 until you can measure this voltage at TP8. Be careful as the resistor will get very hot. This will not be quite as accurate as the previous method as it assumes that the resistor value is exactly 0.1Ω. The linearity of the power supply output voltage versus the computer setting is excellent, with the DMM reading precisely tracking the reading on the computer screen. The voltage fed back to the computer is not quite as line­ar. There are slight errors in the converted voltages due Fig.4: actual size artwork for the PC board. Check your etched board carefully against this artwork before installing any of the parts. to A/D linearity around half scale, resistor tolerances, etc. We have made provision in the soft­ ware to apply five cor­rection factors to these readings. The first is for values bet­ween 0 and 5.5V, the next between 5.6V and 11V, the third between 11.1V and 16.5V, the fourth between 16.6V and 22V and the last between 22.1V and 25.5V. This will be explained later in the software description. Parallel port Before we start discussing the soft­ ware we should give a quick rundown on the parallel printer port and its peculiarities. It was originally designed to drive an 8-bit parallel printer, with suffi­ cient additional lines to provide data transfer in both directions, such as a BUSY line to prevent the computer feeding data to the printer faster than it can process it and a PAPER OUT line to allow an intelligent message to be shown on the compu­ter’s screen if this should occur. Because the original interface was for a Centronics print­er, some bits are true high, others are true low. These signal lines are split over three addresses on the IBM interface. For LPT1 which is the normal (and often only) printer port supplied, the addresses are 378H (hexadecimal, 888 in decimal) for the eight data lines, 379H for the next five lines and 380H for the remaining four lines. These are often called ports A, B and C. The data lines of port A are unidi­ rectional, capable only of sending data to the printer. The other nine lines can be used as inputs and those of port C can be used as outputs. This gives us the capability of sending and receiving 8-bit data from an external device to the computer. Port B has the highest bit inverted and port C only has one of its four bits true high. A subroutine in the software (at line 3000) untwists the input value Parts List 1 PC board, code 04101972, 178 x 105mm 1 rightangle 25 pin D male connector (COON1) 4 20-pin IC sockets 3 16-pin IC sockets 1 14-pin IC socket 10 PC stakes 2 3mm x 15mm machine screws 4 3mm x 10mm machine screws 6 3mm nuts 8 3mm flat washers 6 3mm spring washers tinned copper wire hookup wire Semiconductors 3 74HC573 octal latch (IC1-3) 1 74HC137 latched 1-of-8 decoder (IC4) 1 74HC14 hex Schmitt trigger (IC5) 1 74HC147 decimal-to-BCD encoder (IC6) 1 74HC4051 analog multiplexer (IC7) 1 ADC0804 analog-to-digital converter (IC8) 4 1N914 diodes (D1-D4) Capacitors 1 100µF 16VW electrolytic 4 0.1µF MKT polyester 1 .022µF MKT polyester 1 .001µF MKT polyester 1 150pF ceramic Resistors (0.25W, 1%) 4 1MΩ 27 20kΩ 2 47kΩ 23 10kΩ February 1997  21 Only a few connections need to be made from the interface board to the power supply board. The wiring diagram (Fig.2) has the details. which is the sum of port B and port C and gives a true value (TIN) for any data placed on these lines. Software The control program has been written in GW Basic, using screen 9, the highest resolution (640 x 350 pixel) colour screen. Contrary to the statement in last month’s issue, the software will work with EGA and VGA monitors, not just VGA types. The software code is quite conven­ tional and will run in QuickBasic if lines 1-14 are removed. You will also have to create a separate program containing just lines 5100-5199 and run it to create the file before you run the main program. Space does not allows us to present the full software list­ing in this article but we have included the main section from lines 20-999. Lines 20-70, as you can see from the comments, define the functions to be 22  Silicon Chip used, paint the introductory screen, read the previous settings from the hard disc and give you the option of reusing them or entering new values. Should you wish to retain an exist­ ing value, just press ENTER. The value will be accepted and the program will step to the next item. This is useful should you just wish to change the printer port for example, but retain the previous voltage settings. The values you selected are now written to the screen (line 60) then sent to the power supply in line 70. By structuring your program in this way you can write and debug each subroutine individually. Then if you decide to include an additional fea­ ture, it is only a matter of writing the rou­tine, debugging it, then adding a gosub in the appropriate place. Main program The main program, after the initial­ isation and preliminary housekeeping (lines 20-70), consists of lines 80-160 which, while there is no keyboard key pressed, will run lines 100 and 110 continuously. That is, read the data from the power supply and write these values to the computer screen. As the standard 8x14 text numerals look quite insignificant on the screen, we produced some larger, chunkier numerals using a rectangular block (CHR$219), defined on line 1260 and drawn by subroutine 4000. Keyboard input When a key is pressed the program branches to line 10000 which is the keyboard service subroutine. If a key which it recognises is pressed it will carry out the command and send a new value to the power supply. If a non-programmed key is pressed, it will be ignored and the program will return to run­ning lines 100 and 110. If you read the comments at lines 10021 to 10028 you will understand which keys do what. We used both E and V for the positive voltage and A and I for current, accepting both upper and lower case characters, just so you don’t have to try to remember which keys to use. When you are typing the program there is no need to include the comments but if you come back to study it at a later date, they will help your understanding. As described previously we have two functions, read from and write (send) to the power supply. We read the power supply voltages and current and write values to the D/A converters. Writing to D/A converters The write function is carried out by first placing the value we wish to write to a particular D/A converter on PORTA, then writing its address to PORTC. These addresses are listed in lines 1330-1400. The address for the first D/A converter ODA1 is 9. We can’t call it DA1, as we have defined D as a string in line 1030. You will notice that all the addresses are odd numbers, which indicates that the strobe line will be low (as we have explained previously, the logic for this line is inverted). When the address is written to PORTC, pin 4 of IC4 (latch enable) will be pulled low but after a short delay will go high as the .001µF capacitor charges through the 10kΩ resistor. The strobe is then taken high again to prevent the A/D converter being enabled (see “reading power supply values”) and placing data on the POR­ TA bus. ODA1 is now deselected, as any changes to PORTA data would be transferred to IC1’s output. Now the data which was present on PORTA has been latched by IC1 and is available as an analog voltage at D/ A1 output. The other converters are loaded in a similar manner. When we write to the D/As we al­ ways update the three of them and this is done in subroutine 8000. Listing 1 20 GOSUB 1000 ‘Initialise 30 GOSUB 2000 ‘Write screen heading 40 GOSUB 5000 ‘Get previous saved values from file 50 GOSUB 6000 ‘Write old settings to screen with option to change 60 GOSUB 7000 ‘Write selected data to screen 70 GOSUB 8000 ‘Output data to power supply 75 ‘MAIN PROGRAM loop 80 - 160 starts here. Monitor power supply & keyboard 80 K$ = INKEY$ 90 WHILE K$ = “”: K$ = INKEY$ ‘While no key is pressed 100 GOSUB 9000 ‘Read data from PSU 110 GOSUB 7000 ‘Write data to screen 120 WEND ‘A key has been pressed 130 GOSUB 10000 ‘Service keyboard 140 GOSUB 6360 ‘Update preset values 150 GOSUB 8000 ‘Write new values to power supply 160 GOTO 80 ‘Loop again 900 GOSUB 5100 ‘Save power supply settings 999 CLS: SYSTEM Fig.5: the positive and negative output voltages are displayed on screen, along with the output current. Also shown are the instructions for varying the output voltages and for setting the current limit and tracking. Reading power supply values To read a value from the power supply we latch its address into IC4. This time we don’t take the strobe line high as we did previously, as we want to turn on the A/D converter, IC8. After the delay introduced by the resistor and capacitor between the output of IC5a and the input of IC5f, this will be the case as its chip select (CS) will go low. This connects its tri-stated output to the PORTB and PORTC bus. For the PORTB and PORTC lines to be used as inputs they must all be set high. Then they will either stay high or be pulled low by the A/D. This procedure is carried out by subrou­ tine 9000. The last area to cover is the line­ arisation of the readings returned by the power supply. Lines 1420-1440 list the correction factors we found satisfactory for our supply. These are imple­mented in subroutine 9000 on lines 9140, 9210 and 9280. These have been REMmed out and values of 1.0 substituted in lines 1411-1413. The procedure is to make a table of the output voltage at the terminals ver­ sus the voltage shown on the screen. You then cal­ culate the adjustment factor to give the correct reading for each range. Once you have the values, delete lines 1411-1413, remove the REMs from lines 1420-1440 and enter SC your values. February 1997  23 The Alert-A-Phone consists of a plastic box containing the electronics, a 12V DC plugpack and a weatherproof metal horn loudspeaker (not plastic as shown here). Essentially, it is a high-powered telephone ringer for noisy environments. The Alert-A-Phone . . . a very loud ringer for your telephone Do you work in a very noisy environment and you can’t hear the phone when it rings? Or are you hard of hearing? If so, this project is for you. It is the Alert-A-Phone Loud Sounding Alarm. It connects in parallel with your existing phone and it is Austel-approved. DESIGN By DEREK DIGGLES* 24  Silicon Chip The Alert-A-Phone Loud Sounding Alarm has nothing to do with burglar alarms – a point we want to clarify right at the start. It is intended for use in noisy environments where normal phones are just about impossible to hear. The Alert-A-Phone can be turned up to a level which is really loud; deaf­ ening, in fact. That is its main feature. The others are listed in a separate panel in this article. As well as a weatherproof horn loudspeaker, the Alert-A-Phone com­ Fig.1: two integrated circuits are used. IC1 is for AC ring signal detection and ringer tone generation while IC2 is a 20W bridged audio power amplifier which drives the horn loudspeaker. prises a small plastic case to house the electronics, a 12V DC plugpack and a standard phone plug with a 3-metre cord. While the phone and the Alert-APhone will normally be within three metres of each other, the horn loud­ speaker can be up to 20 metres away and can be mounted outdoors since it is weatherproof. Other features of note are anti-tinkle circuitry and it will work with the new distinctive ring patterns used by Telstra and Optus as well as the normal ring cadence. The ring tone is adjustable in pitch, so that more than one Alert-A-Phone can be used if required with different phone lines. The Alert-A-Phone is housed in a plastic case measuring 128 x 42 x 65mm and this has a label on both sides. On the topside is the volume knob which is removable, to stop unwanted fiddling with the control. The label on the underside has the supplier’s name, address and phone numbers: Telephone Technical Ser­ vices, PO Box 357, Cleveland, Qld 4163. Phone (07) 3821 1222; fax (07) 3821 2161. Now let us discuss the circuit which is shown in Fig.1. connected directly to the incoming telephone line and is powered from it. Fig.2 shows a block diagram of the circuitry within the LS1241 chip. The chip is powered from the telephone line by virtue of the bridge rectifier connected between pins 1 & 8 and the DC filtering is provided by a 22µF capacitor connected to pin 7. The AC ring voltage is detected (ie, when the phone rings) by the internal thresh­ old circuit and this enables the tone genera­tor. The tone generator then pro­ vides a ring tone in the same cadence as the incoming AC ring voltage. The ring tone is adjust­able in pitch by the 10kΩ potentiometer VR1. WARNING Operation of this device may infringe Environmental Noise Pollution Regulations and could DAMAGE HEARING if exposure is prolonged. It is the user’s responsibility to control the volume and to switch off the device if necessary to conform to local environmental guide lines. The output stage connected to pin 5 normally drives a pie­ zoelectric transducer but in this case, as shown in Fig.1, it drives a 2.2µF capacitor in series with an isolation transformer (T1) which couples the tone ringer signal to the volume control VR2 and Circuit description Two integrated circuits are used, one for AC ring signal detection and ringer tone generation and the other an audio power amplifier which drives the horn loudspeaker. IC1 is an LS1241 electronic two-tone ringer made by SGS Thomson Micro­ electronics. It is designed to replace the bell in telephone handsets. It is Fig.2: block diagram for the LS1241 electronic two-tone ringer. It is powered from the phone line by dint of the bridge rectifier between pins 1 & 8. February 1997  25 Fig.3: the waveforms that can be expected in the circuit. The top trace (channel 1) is the incoming AC ring voltage with an ampli­tude of just over 200 volts peak-to-peak. The bottom trace shows the signal generated by the tone ringer measured at the output of the transformer T1 and the amplitude is around 12 volts peak-to-peak. Note: the waveforms are taken from the screen of a Tektronix TDS 360 digital scope and because of the very low timebase speed of 0.5s/div there are symptoms of aliasing in both waveforms. the input of the power amplifier IC2. IC2 is a TDA7240 20W bridged pow­ er amplifier normally in­tended for use in car radios. It is a 7-pin package with a heat­sink tab. Its normal operating DC voltage is up to 18V. Its power output is quoted at up to 20W at 10% harmonic distortion. Con­trary to what you might expect, it will deliver fairly close to this power even though the DC plugpack is only rated at 1A con­tinuous; ie, 12W. The reason it can deliver such high power is that the ring signal is inter­ mittent, giving the supply plenty of time to recover between each ring. Another factor in the high power de­ livery is that harmonic distortion is not an important factor – what is wanted is lots of loudness! Since the TD7240 is a bridged pow­ er amplifier, the horn loudspeaker is directly connected to pins 7 & 5; no coupling capacitor is necessary. Zobel networks consisting of a 2.2Ω resistor and 0.22µF capacitor are con­ nected to both outputs at pins 5 & 7 to ensure amplifier stability, especially as long output lines are being used. Fig.3 shows the waveforms that can be expected in the cir­cuit. The top trace (channel 1) is the incoming AC ring voltage with an amplitude of just over 200 volts peak-to-peak. The bottom trace shows the signal generated by the tone ringer measured at the output of the transformer T1 and the amplitude is around 12 volts peak-to-peak. Note: the waveforms are taken from the screen of a Tektro­nix TDS 360 digital scope and because of the very low timebase speed of 0.5s/div there are symptoms of aliasing in both wave­forms. The bottom waveform is modulated in both frequency and amplitude to give the typical warbling tone of a modern tele­phone. Putting it together Since this is an Austel approved device, there is only one way you can build it. You must purchase the complete kit and no component substitutions or modifications are allowable. It must also be powered from the supplied approved 12V DC plugpack. If these conditions are not followed, the Austel approval will be null and void. All the electronic componentry is mounted on a PC board measuring 123 x 58mm. This board mounts upside down in the plas­tic case and it has large corner holes which fit over the inte­gral corner plastic pillars in the case. This method avoids any screw Fig.4: the component overlay for the PC board. This board mounts upside down in the plastic case. 26  Silicon Chip The small transformer in the centre of the board provides 3kV AC isolation between the telephone ringer IC and the bridged audio power amplifier. heads protruding from the case which would probably not meet Austel standards. For the same reason, the removable volume control knob and shaft is of plastic construction. Fig.4 shows the component layout on the board. The PC board has a screen-printed component overlay on the topside and the copper pattern side has a green solder mask. The first step is to install the resis­ tors and the capacitors, ensuring that the four electrolytic capacitors are correctly oriented. This done, install the diodes, potent­ iometers and the 4-way insulated terminal block. IC1 is soldered direct to the PC board while IC2 is soldered in and fitted with a small finned heatsink which is also soldered at two points on the board. Two spade lugs are soldered at one end of the board at points A & B for the telephone line connection. The last component to be installed is the isolating transformer. This is soldered in and secured to the board with a Nylon cable tie. The kit will include a 3-metre phone cable with a standard phone plug at one end and two spade connectors on the other end. These are pushed onto the spade lugs on the board, after the cable has been passed through the adjacent hole. At the other end of the board, you will need to connect the two wires from the horn loudspeaker and the two wires from the DC plugpack. Make sure that you connect the DC plugpack cor­ rectly; the positive wire must go to the positive terminal on the board, marked with a + sign on the copper pattern and on the screen-printed overlay. If you do manage to inadvertently swap the supply leads though, there will be no damage, by virtue of the protection diode D1. Initial test When all the assembly is complete, apart from putting the lid on the box, Features  Very loud alarm; up to 120dB at 1 metre  Volume control on front panel plus internal pitch control  Can be turned off at the power point (no need to disconnect from phone line)  Weatherproof horn speaker can be up to 20 metres away from the AlertA-Phone  Reverse polarity protection for DC supply input  Power amplifier has overload protection  Do-it-yourself installation  Austel approved: Permit A9601B/0017  Ringer equivalence number REN = 1 February 1997  27 Electronic Projects For Cars 5 $8.9 PLUS P & $3 P The PC board mounts upside down in the case and the large corner holes of the PC board fit over the integral pillars of the case. Available only from Silicon Chip Price: $8.95 (plus $3 for postage). Order by phoning (02) 9979 5644 & quoting your credit card number; or fax the details to (02) 9979 6503; or mail your order with cheque or credit card details to Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097. Final testing For the final test you will need to connect the unit to the phone line, in parallel with a standard telephone. Rotate the volume control almost fully anticlockwise (minimum setting) and have someone phone in on that line (or use a cellular phone to call the line). The horn loudspeaker should ring in unison with the phone. From here, you make an adjustment to the pitch control VR1 is desired. Finally, the unit can be permanently installed. If the horn loudspeaker is mounted outdoors, it should point downwards so that it does not catch the rain. The volume control should be adjusted for an adequate level. There is no point in having it too loud as it will only cause annoyance to people SC near and far. *Derek Diggles is the principal of Tele­ phone Technical Services.  Use this handy form initial testing can be performed, before any connection to the phone lines. Plug in the plugpack and check that you have about 14V across ZD1. Wind the volume control clockwise and put your finger on the junction of the volume control VR2 and the 300kΩ resistor. You should immediately hear a loud blurt from the speaker. If this does not occur, check all the compo­ nents around IC2. Enclosed is my cheque/money order for Where To Buy The Kit $________ or please debit my The design of the Alert-A-Phone is copyright. Kit pricing is as follows:  Bankcard  Visa  Mastercard (1). Complete kit, including 15W metal horn loudspeaker, 12V DC plug­pack, drilled and labelled case, fitted telephone cord and 5m speaker flex and telephone double adaptor plug, $131.50 plus $7.00 for air freight anywhere within Australia. Card No: ______________________________ Card Expiry Date ____/____ Signature ________________________ Name ___________________________ Address__________________________ __________________ P/code_______ 28  Silicon Chip (2). Kit service fee: $30 including return delivery, provided workman­ship is normal. (3). Fully built and tested Alert-A-Phone, $193.50 plus $7.00 for air freight anywhere within Australia. Payment may be made by cheque, money order, Bankcard, Visa or Master­ card to Telephone Technical Services, PO Box 357, Cleveland, Qld 4163. Phone (07) 3821 1222; fax (07) 3821 2161. VISIT OUR WEB SITE OUR COMPLETE CATALOGUE IS ON OUR SITE. A “STOP PRESS” SECTION LISTS NEW AND LIMITED PRODUCTS AND SPECIALS. VISIT: https://www.oatleyelectronics.com/ SWITCHED MODE POWER SUPPLY:Compact (50X360X380mm), enclosed in a perforated metal case, 240V AC in, 12V DC/2A and 5VDC/5A out: $17 ...HP POWER SUPPLIES: Compact (120X70X30mm) HP switched mode, power in plastic case, 100-240V AC input, 10.6V/1.32A DC output, slightly soiled: $14 ...LASER MODULE: Very bright (650nM/5mW) focusable module, suit many industrial applications, bright enough for a disco laser light show, good results with the Automatic Laser Light Show: $75 ...AUTOMATIC LASER LIGHT SHOW KIT: 3 motors, mirrors plus PCB and comp. kit, has laser diode reg. cct, could be powered by the above 12V switched mode power supply, produces many different patterns, can be used with the laser module: $70 ...LASER POINTER: Our new metal laser pointer (With keychain) is very bright, with 650nM/5mW diode: $65 ... LEDS SUPER PRICES, INCLUDING A SUPER BRIGHT BLUE!: All the following LEDS are in a 5mm housing ...By far THE BRIGHTEST BLUE EVER OFFERED, superbright at 400mCd: $1.50Ea. or 10 for $10 ... 1C red: 10 for $4 ...300mC green: $1.10Ea. or 10 for $7 .. MAKE WHITE LIGHT BY MIXING THE OUTPUT OF THE PREVIOUS 3 LEDS? ..3Cd Red: $1.10Ea. or 10 for $7 ... 3Cd yellow (Small torch!) also available in 3mm: 10 for $9 ... Superbright flashing LEDS: $1.50 Ea. or 10 for $10 ... PHOTOTRANSISTORS: Enclosed in clear 5mm housing similar to the 5mm LEDS, 30V/3uS/<100nA dark current: $1.30 or 10 for $9 ...CONSTANT VOLTAGE DIODES: 1.52-1.66V <at> 10uA: 10 for $7 ...MASTHEAD AMPLIFIER PLUS PLUGPACK SPECIAL: Our famous MAR-6 based masthead amplifier plus a suitable plupack to power it: $20, Waterproof box: $2.50, bottom box:$2.50 ...17mm MAGNIFIERS: Made in JAPAN by Micro Design these eyepiece style metal enclosed magnifiers will see the grain of most papers, used, limited qty.: $4 Ea. ...HF BALLASTS: Single tube 36W Dimmable high frequency ballasts: $18 Ea. ...12V SLA BATTERY CHARGERS: INTELLIGENT “PLUGPACK” 240V-12V GEL BATTERY CHARGERS, 13.8V / 650mA, proper “switching” design with LED status indicator: $8.80 ...LASER POINTER KIT: A special purchase of some 660nM/5mW laser diode means that we can reduce the price of our Laser Pointer kit, includes everything except the batteries: $29 ...SPECIAL BATTERY AND CHARGER OFFER: When our 7AHr/12V SLA battery ($30) is bought with the SLA battery charger the total price for both is: $33 ...USED BRUSHLESS DC FANS: 4"/12V/0.25A: $8, 24V/6"/17W: $12 ...100,000uF ELECTROLYTIC CAPACITORS: 30V/40Vsurge, used but in exc. cond.:$10 ...12Hr. MECHANICAL TIMERS: 55X48X40mm, 5mm shaft (Knob not supplied), two hours timing per 45deg. rotation, two 25V/16A SPST switches which close at the end of the timing period: $5 ...USED IEC LEADS: Used Australian IEC leads: $2.50 ...STANDARD PIEZO TWEETERS: Square, 85X85mm, 4-40KHz, 35V RMS: $8, Wide dispersion, 67X143mm, 3-30KHz, 35V RMS: $9 ...COMPUTER POWER SUPPLY: Standard large supply as used in large computer towers, +5V/22A, +12V/8.5A, -5V/0.5A, -12V/0.5A, used but in excellent condition, guaranteed: $30 ...MAGNIFIERS: Small eyepiece: $3, 30mm Loupe: $8, 75mm Loupe: $12, 110mm Loupe: $15, a set of one of each of these magnifiers (4): $30 ... NEW NICAD BATTERY BARGAIN: 6 PACK (7.2V) OF 1.2V / 800 mAHr. AA NICAD BATT’s plus 1 X thermal switch, easy to seperate: $4 per pack or 5 packs for $16, FLAT RECTANGULAR 1.2V, 400mAh NI-CAD BATTERIES with thermal switch, easy to seperate, (Each batt: 48x17x6 mm): $4 per pack or 5 packs for $16 ...UV MONEY DETECTOR: Small complete unit with cold cathode UV tube, works from 2 X AA batteries ( Not supplied), Inverter used can dimly light a 4W white fluoro tube: $5Ea. or 5 for $19 ...MISCELLANEOUS USED LENS ASSEMBLIES: Unusual lens assemblies out of industrial equipment: 3 for $22 ...USED PIR MOVEMENT DETECTORS: Commercial quality 10-15M range, used but tested and guaranteed, have O/C transistor (BD139) output and a tamper switch, 12V operation, circuit provided: $10 Ea. or 4 for $32 ...CCD CAMERA WITH BONUS: Tiny (32X32X27mm) CCD camera, 0.1lux, IR responsive (Works in total dark with IR illumination), connects to any standard video input (Eg VCR) or via a modulator to aerial input: $125, BONUS: With each camera you can buy the following at reduced prices: COMMERCIAL UHF TRANSMITTER for $15 (Normally $25), IR ILLUMINATOR KIT with 42 X 880nM LED’s for $25 (Normally $35), REGULATED 10.4V PLUGPACK for $10 (Normally $25) ...PIR CASE FOR CCD CAMERA: Used PIR cases of normal appearance, use to hide the CCD camera, plenty of room inside: $2.50 Ea. or 4 for $8 ...CAMERA-TIME LAPSE VCR RECORDING SYSTEM: Includes PIR movement detector and interface control kit, plus a learning remote control, combination can trigger any VCR to start recording with movement and stop recording a few minutes after the last movement has stops: $90 ...GEIGER COUNTER KIT: Based on a Russian tube, has traditional “click” to indicate each count. Kit includes PCB, all on-board components, a speaker and Yes, the geiger counter tube is included: $30 ...RARE EARTH MAGNETS: Very strong! 7X3mm $2, 10X3mm $4, Torroidal 50mm outer, 35mm inner, 5mm thick: $10 ...IR TESTER: Kit includes a blemished IR converter tube as used in night vision and an EHT power supply kit, excellent for seeing IR sources, price depends on blemishes: $30 / $40 ...ARGON-ION HEADS: Used Argon-Ion heads with 30-100mW output in the blue-green spectrum, power supply circuit provided, size: 350X160X160mm, weight 6Kg, needs 1KW transformer available elsewhere for about $170, head only for: $350 ...DIGITAL RECORDING MODULES: Small digital voice recording modules as used in greeting cards, microphone and a speaker included, 6 sec. recording time: $9 ...WIRED IR REPEATER KIT: Extend the range of existing IR remote controls by up to 15M and/or control equipment in other rooms: $18 ...12V-2.5W SOLAR PANEL KIT: US amorphous glass solar panels, 305X228mm, Vo-c 18-20V, Is/c 200mA: $22 Ea. or 4 for $70 ...MIDI KEYBOARDS: Quality midi keyboard with 49 keys, 2 digit LED display, MIDI out jack, Size: 655115X35mm, computer software included, see review in Feb. 97 EA: $80, 9V DC plugpack: $10, also available is a larger model which has mor features and has touch sensitive response keys: $200 ...STEREO FM TRANSMITTER KIT: 88-108MHz, 6-12V DC supply, 8mA <at> 9V, 25X65mm PCB size, PCB plus all on-board comp’s, plus battery connector and 2 electret mic’s: $25, plastic case to suit: $4 ...WOOFER STOPPER KIT: Stop that dog bark, also works on most animals, refer SC Feb. 96, Kit includes PCB and all on board comp’s, wound transformer, electret mic., and a horn piezo tweeter: $39, extra horn piezo tweeters (drives up to 4) $6 Ea. ...ALCOHOL BREATH TESTER KIT: Based on a thick film alcohol sensor. The kit includes a PCB, all on board comp’s and a meter : $30 ...CENTRAL LOCKING KIT (NEW): A complete central locking kit for a vehicle. The kit is of good quality and actuators are well made, the kit includes 4 actuators, electronic control box, wiring harness, screws, nuts, and other mechanical parts: $60, The actuators only: $9 Ea. ...CODE HOPPING UHF CENTRAL LOCKING KIT PLUS A ONE CHANNEL UHF REMOTE CONTROL: Similar to above but this one is wireless, includes code hoping Tx’s with two buttons (Lock-unlock), an extra relay in the receiver can be used to immobilise the engine, etc., kit includes 4 actuators, control box, two Tx’s, wiring harness, screws, nuts, and other mechanical parts: $109 ...ELECTROCARDIOGRAM PCB + DISK: The software disk and a silk screened and solder masked PCB (PCB size: 105 x 53mm) for the ECG kit published in EA July 95. No further components supplied: $10 ...SECURE IR SWITCH: IR remote controlled switch, both Rx and Tx have Dip switches for coding, kit includes commercial 1 Tx, Rx PCB and parts to operate a relay (not supplied): $22 8A/4KV relay $3 ...FLUORESCENT TAPE: High quality Mitsubishi brand all weather 50mm wide Red reflective tape with self adhesive backing: 3 meters for $5 ...LOW COST IR ILLUMINATOR: Illuminates night viewers or CCD cameras using 42 of our 880nm / 30mW / 12 degrees IR LEDs. Power output is varied using a trimpot., operates from 10 to 15V, current is 5-600mA ...IR LASER DIODE KIT: Barely visible 780nM/5mW (Sharp LT026) laser diode plus constant current driver kit plus collimator lens plus housing plus a suitable detector Pin diode, for medical use, perimeter protection, data transmission, experimentation: $32 ...WIRELESS IR EXTENDER: Converts the output from any IR remote control into a UHF transmission, Tx is self contained and attaches with Velcro strap under the IR transmitter, receiver has 2 IR Led’s and is place near the appliance being controlled, kit includes two PCB’s all components, two plastic boxes, Velcro strap, 9V transmitter battery is not supplied: $35, suitable plugpack for the receiver: $10 ...NEW - LOW COST 2 CHANNEL UHF REMOTE CONTROL: Two channel encoded UHF remote control has a small keyring style assembled transmitter, kit receiver has 5A relay contact output, can be arranged for toggle or momentary operation: $35 for one Tx and one Rx, additional Tx’s $12 Ea. OATLEY ELECTRONICS PO Box 89 Oatley NSW 2223 Phone (02) 9584 3563 Fax (02) 9584 3561 orders by e-mail: branko<at>oatleyelectronics.com major cards with phone and fax orders, P&P typically $6. SERVICEMAN'S LOG A tale of two Sharp VCRs VCRs can fail for all sorts of reasons but I recently had one that really takes the cake. Fortunately, not all jobs are like that one, with most being quite routine. Just when I’d thought I’d seen every­ thing in the servicing game, along comes something to really set me back on my heels. Spilt drinks or other liquids are common reasons for TV and VCR failures but monkey urine? –you’ve got to be kidding! Of course, out of the thousands of servicemen in Australia, it had to be yours truly that got saddled with the job. The story started out innocently enough. Some months ago, the local vet brought in a mid-drive Sharp VCR with the complaint that it stopped working after about two seconds on “play”. The set was a 1992 VCA34X which looked to be in good condition – at least from the outside. Unfortunate­ ly, it didn’t smell quite so good and had a quite distinct “pong” of stale urine about it. However, seeing that it had come from the animal surgery, I assumed that this “pong’ had been picked up from something in the air. The fault description turned out to be quite accurate and when I removed the top cover, I could see that fast forward and rewind were OK. The play mode was a different matter, however – the arms loaded the tape properly, the drum motor started and the capstan motor started but it only did a revolution or two before stopping and unloading the tape. It all looked OK, so why didn’t it work? Unfortunately, I don’t have the service manual for this model but the deck was a very common type; only the electronics were different. So the first question was “is this a mechanical or an electronic problem?” I decided to inspect the whole machine carefully 30  Silicon Chip and turned it upside-down to remove the lower cover plate. Immediately, it was obvious from the severe corrosion where the smell was coming from. It was also obvious that this was where the problem lay. Fairly obviously, the machine had been sitting in a pool of urine, perhaps up to 12mm deep. And although this had long been cleaned off by someone else, the corrosion was abundant to see up to the high level mark. I was about to phone the vet and tell him that all was lost and that he should get a new VCR but then I had a little think to myself. To fix or not to fix Perhaps this wasn’t a hopeless case after all. First, all the major motors were actually turning and secondly, someone else had already done a pret­ ty good job of cleaning up the mess in­side. Added to that, all the bottom printed circuit boards looked OK and so I concluded that the job was worth investigating fur­ther to see if the ma­ chine could be salvaged. At this stage, my main suspect was the drum motor as it seemed hesitant to start and its speed appeared to be intermit­tent when it was strobed under a neon mains light. I also discov­ered that, occasionally, when the video was switched from EE mode (ie, Tuner) to the Play mode, a picture could almost be seen although not always in sync. My next step was to fire up the CRO and check the output of the PG (pulse generator) head. This revealed a pulse generator signal but it was fluctuating. Also there was 12V on pin 3 of the plug to the drum motor. From this evidence, it seemed likely that the drum stator board or its com­ ponents had corroded and so I decided to remove it to see if anything could be done. The connection to this motor is via a special 6-lead flat printed circuit ribbon cable harness whose end is just pushed into a receptacle. When I removed this, I found it to be badly cor­ roded. I cut about 12mm off, scraped away the white varnish covering the tinned strands, cleaned the socket and reinserted the harness. When I powered up and pressed “Play”, the motor spun up quickly and continued to play correctly. I then checked the other sockets in this area but they were all OK. In hindsight, I should have suspected a cable connec­ tion but everything looked fine until the cable was actually removed. I returned the video to the vet with a warning that despite cleaning it, he would probably have further problems in the long term as it is very hard to prevent a chemical reaction of this type from continuing. He apologised for the state of the VCR – apparently a monkey (would you believe it) had had an “accident” in that corner of the room and even though he had got a friend to check the VCR out, he must have missed that particular socket. Just how long the machine will last is anybody’s guess and I didn’t press the vet for any further details on the monkey or what it was doing there. Let’s just say that it doesn’t pay to have a monkey monkeying around near a VCR. Another Sharp VCR I thought no more about this repair until a few months later when another similar Sharp VCR came in. This time it was a slightly older model, a VCA105X, and the complaint was that it wouldn’t play. The unit looked in good condition throughout and this time there were no unpleasant odours! As with the previous unit, this too would load up, the drum motor would spin and the capstan motor would spin a few revolu­tions before it would unload and stop. This time, I did have the service manual and it also had a troubleshooting guide for the exact symptoms being experienced. The first step is to check the head switching pulse applied to pin 3 of IC801 (IXO491) and the PG (pulse gen­ erator) signal applied to pin 4 of servo control IC701 (IX04313GE). Well, the PG pulse was there but there was definitely no head switching pulse (HSWP) . In fact, all the voltages and inputs seemed cor­rect going into IC701 but nothing was coming out of pin 28 and there appeared to be no short circuit on that line. In view of these symptoms, I felt that the problem had to be electronic and, at this stage, considered IC701 and/ or the system control microprocessor IC801 as the main suspects. Before replacing these devices however, I first checked out all the B+ lines and the various clock signals but could find nothing wrong. The HSWP also went to the Y/C module and onto the head preamp board. I tried disconnecting these boards in turn but there was still no sign of a pulse. With reluctance, I ordered IC701 first as I knew these ICs would be ex­ pensive. It arrived a few days later and I wasted no time in fitting it. Unfortu­ nately, it made no difference, so that was expensive mistake number one. I was now faced with the prospect of having to replace the main micropro­ cessor (IC801), which was even more expensive. Before ordering it however, I tried replacing the mode select switch in case it wasn’t engaging quite correct­ ly – to no avail. Finally, I went ahead and ordered IC801. It too arrived after a couple of days and I went about the laborious task of removing the old 64pin IC and soldering in the new one. And that was expensive mistake number two because it also made ab­ solutely no difference – there was still no head switching pulse. Murphy was really working overtime on this job! A new approach I was discussing my expensive folly with several colleagues when one said that he had recently obtained the same model as a trade-in. What’s more, he offered to lend it to me so that I could pinpoint the location of the faulty parts without spending any more mega­bucks on use­ less guesses. He was also of the strong opinion that it was an intermittent capstan motor that was caus­ing the problem as this occasionally occurs February 1997  31 Serviceman’s Log – continued on this series of decks and gives many similar symptoms. Well, this was indeed a stroke of luck and I started by swapping over the capstan motor but that too made no difference. By now, I felt that my original diagnosis – that the fault was electronic – must be correct. As a result, I began swapping all the electronic circuitry between the two machines, board by board, but again this made no difference. After changing the last board, I was forced to conclude that I was looking at a mechanical/motor problem. In fact, it had to be the drum motor, even though all the pulses and voltages from it were correct and it looked as though it was reaching the correct speed when viewed under the strobe light. I couldn’t be certain of this, how­ ever, as it was unloading as soon as it apparently reached the correct speed. In fact, the machine did not even have time to switch from EE mode to Play mode, so no picture was available. Anyway, I proceeded to replace the drum motor and try again. Unbelieva­ bly, it worked this time but I couldn’t under­stand why. Out of curiosity, I measured the output from the new motor and it matched the old one exactly. How could this be? To solve this mystery, I replaced the old motor and in the process noticed that the ribbon con­ nector cable had come away from its 32  Silicon Chip hardened plastic support and that the tracks were somewhat loose and frayed. I didn’t pay much attention to this until I retried the old motor which, to my amazement, was now working. So what was the answer? As it is not possible to prove, I can only speculate that the ribbon connector cable was either shorting or not making a proper connection with the socket. I guess I should have remembered the symp­ toms of the earlier repair and examined this connection more carefully first. Bread & butter The next morning, I faced up to two TV sets that were awaiting my attention. The first was a 34cm Toshiba 144R8A made by Samsung (a P54S) and it was quite dead. Often, a set of this size is not really worthwhile repairing as they are so cheap to buy. It all depends on how difficult the fault is to fix and sometimes it can be quite difficult to decide whether to go ahead or not. On the plus side, the faults in this chassis are fairly well known which does reduce the amount of time spent in diagno­sis. In the 34cm model, most of the problems are in the power supply, due to the electrolytic capacitors drying out. This causes the chopper power transistor Q801 (2SC3552/BU508A) in the switchmode power supply to blow, which also takes out the fuse and/or R801 (5.6W 7W). In this case, the transistor had tak­ en out the resistor and so I replaced these parts and four electros (C808, C813, C812 & C811) all at once. When I switched it on again, the set was ob­ viously struggling to fire up and was making funny noises in the power supply. I immediately switched it off again to prevent another failure of the chopper transistor and then started to check for shorts on the B+ rails. The line transistor Q404 and capaci­ tor C413, a common culprit, were both OK. In fact there were no shorts and no, or extremely small, output from the chopper transformer. Checking the voltage across C807 confirmed there was 340V out of the bridge rectifier and I checked and cleared resistors R806 and R807. The oscilloscope confirmed that the circuit was oscillating though the waveforms were incorrect and Q801 was getting hot. I changed IC801 which is the main IC in the power supply but that made no difference. And that really only left the trans­ former (T801). Removing it, I tested it with a shorted turns oscillator/tester which indicated that pins 1 and 3 were shorted. This test is not always conclu­ sive as I don’t know what frequency the circuit is designed to resonate at. However, I decided to take a punt – a new chopper transformer was ordered and it subsequently proved that my diag­nosis was correct. The repair cost really made it quite a margin­al exer­ cise, however. Sony KV2064 The second set was a Sony KV2064 and the customer thought that it had to be the on/off switch because it was intermittently dead. Of course, power switches can sometimes be faulty but it never ceases to amaze me that many people think that a TV set consists of a tube, a valve, a switch and a fuse. That’s it – it has to be one these items which is faulty if the set doesn’t go! As it turned out, the owner of the set was a very heavy smoker and there was a film of nicotine over every surface and component inside the set. The switchmode power supply had 240V AC coming into it, which cleared the on/off switch, and there were no fuses blown. This of course left only the tube and the valve! A close examination of the power supply circuitry revealed that the start­ up resistors were the likely culprits. There was over 300V on the collector the chopper transistor (Q602) and the four high-value 0.5W resistors were all discoloured, although only one (R602, 330kW) was open circuit. I changed them all for high voltage types, reworked the solder just in case and switched on. It was all an anti­ climax – everything worked perfectly and the set now started every time it was switched on. All I have to do now is explain to the customer that it wasn’t the on/off switch. The reluctant NEC Later that morning, a lady dropped in her NEC video with the symptoms that it wouldn’t fast forward or rewind and turned itself off. When I eventually got the chance to look at it, I found that there was virtually little or no take up torque, which suggested a reel idler problem. Being an N9083A, this machine was a later (1991) version of the N9000 series, with the reel drive being a sub-assembly which is fairly easy to remove from under­neath. The main problem is due to two tyres within this assembly which are supplied in the VBK83 tyre and belt kit. However, one of the tyres is an integral part of an idler assembly and the replacement will not stay on satisfactorily without gluing. You can either purchase the entire sub-chassis assembly for around $55.00 trade (part no. 016192683 – this not shown in the service manual) or forego replacing that one tyre. It’s a real nuisance that it is not available as a complete pulley idler on its own. It is also worth noting that earlier models also require a modification to the white CR slider – this part is now black (part no. 016457582) and costs around $2.00. One can only hope that the customer clearly understood that the cutdown repair would not last as long as the original. Still, I spelt it out as clearly as I could. This afternoon saw a dead IBM monitor arrive. It was PS/1, manufac­ tured in June 1993, series 028-004. I have seen quite a few of these units with blown mains fuses (F601 2.5AT), usually without any apparent cause. In one case, however, it turned out to be the chopper IC itself that intermit­ tently blew the mains fuse. This particular unit also had a dud mains fuse. I replaced it, checked the rest of the supply for any obvious faults and then, just to be on the safe side, switched the set on with a 200W globe in series with it. Initially, the globe went bright, then dimmed and came on again at half about luminance. The first current surge was obvi­ ously due to the degaussing circuit kicking in and there was obviously still quite a lot of current being drawn at the end of the degaussing cycle – at least 0.75A. However, the compliance plate said the full current drawn was 1.4A, so I tried it without the globe and the fuse held and the screen gave a good picture. For the rest of the day, I cyclically switched the monitor off and on for periods of 15 minutes, without further problems. In the end, I could only ad­ vise the customer that the cause was probably either due to a mains surge or fatigue in the old fuse. All we can do now is keep our fin­ SC gers crossed. February 1997  33 SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: dicksmith.com.au MAILBAG Doubts On Auto-Transformer Safety This is a quick note to express some strong concerns with the article entitled “Stop Blowing Incandescent Lights” in the January 1997 issue of SILICON CHIP. First up, I have to admit that I have not thought through all the electrical, insulation or failure implications of running mains through a secondary winding but initially I had the con­ cerns with this that I did some years ago with an amplifier project in ETI which did a similar thing. My concern is that we are running 240VAC mains through part of the transformer that has a much lower breakdown voltage than the 240V primary winding – figures of 500VAC as opposed to 4000VAC come to mind. This seems to be an enormous risk and if it caused a fire then the insur­ ance company would be in the right (if they knew) to oppose payment in view of the fact that a non-approved non-standard use was made of an electrical component (insurance com­ panies do this with motor car parts if it suits them). On a more pragmatic note the heat levels at which the transformers op­ erate are high and you are indicating that they are dependent on “free air flow unimpeded by any ceiling insula­tion material” etc. This is very tenuous. Let’s think about possible scenarios. In my area the average length of ownership of houses is about five years. So let’s suppose the original owner puts in this arrange­ment for his lamps and then five years later he sells. The new owner decides, in sunny Queens­ land, that he will insulate the roof. Will the previous owner have passed on a “House Circuit Manual” or “List of Precautions”? Not likely! Who will tell the contractor put­ ting in the insulation not to cover the transform­ ers? Will the new owner even know they are there? Not likely? Do you know with certainty how your house is done (if purchased from an­ other party)? What if this is installed 38  Silicon Chip by someone in a more northern area – hotter still? All in all, I was not impressed with the article although there was some excellent data in there about lamp life and the effects of UV etc which I am raising with our occupational health and safety staff. We have many halogen lamps in reception areas – this could be a simmering compensation issue for some time in the future! R. Grant, Chapel Hill, Qld. Comment: we can address your concerns as follows. First, as we understand it, the bobbin construction of the specified trans­former means that the secondary winding automatically has a high breakdown voltage. Second, the metalwork of the transformer is completely shrouded by the outer plastic housing so that even if the transformer winding did break down, there would be no hazard. We have warned about not surrounding the transformer with insulation because it is good practice and it is required by wiring standards in any case. Household wiring should not be covered by insulation and all electricians and insulation con­tractors should be aware of this. In any case, the specified transformer does have an inte­gral thermal overload cutout and so if the transformer did over­heat, it would cut out. If used as described in the article, the transformer will be running within its ratings and therefore should never be an issue in the event of an insurance claim. Indeed, we think there is a higher chance of fire from halogen light fittings themselves; they get extremely hot and again, should never be covered by ceiling insulation; nor should any flush-mount ceiling light fitting. As a final note, we consulted with the manufacturers of the transformer, Atco Controls Pty Ltd, to ensure that there were no problems with this mode of operation. Your comment about Occupational Health & Safety is inter­esting. We think that the UV output of the mercury dis- charge lamps used in many sporting complexes is particularly dangerous. It can cause “sunburn” after a few hours and could be a compensa­tion issue at some time in the future. In our opinion, such lamp fittings should have a UV filter as a standard feature. Marconi School of Wireless Reunion I am writing for your assistance in organising a reunion of ex-Marconi School of Wireless students to be held in Sydney some time next year. The school closed in 1981 and with it into re­tirement went Ces Bardwell who joined the school as an instruc­ tor in 1939. Ces became principal/ manager, I believe in 1949, and held that position until the school closed in 1981. Ces will be 80 next year and he will be guest of honour at this reunion. My task is to find out where all the “ex” Marconi students and instructors are today and ask them to express an in­ terest in attending this function. Information required from those interested in attending this function should include the year/years of attendance and whether full-time or part-time. I can be contacted as fol­ lows: fax (make attention to “David Hawksworth”) 044 210032 or email techfm<at>peg.apc.org David Hawksworth, 84 Duncan St, Vincentia, NSW 2540. Further Advice On Networking Computers Early in 1996 I networked a Pent­ ium 166 and an old 486 almost iden­ tically to the method you described in the January 1997 edition of SILICON CHIP. My experience, at least initially, was not quite as straightforward as laid out in your article. When I set up my network system, I was not aware that both sys­tems require the same “protocol” to communicate with each other. Win 3.11 defaults to NetBEUI while Win95 defaults to TCP/IP. Initially, NetBEUI was not installed in the Con­ trol Panel/Network/Configuration of my Win95 system. After some weeks of trial and error (mostly error) I installed (added) the NetBEUI protocol to my Win95 setup. The network was then up and running within 15 minutes. The above may be of some help to your readers if they have similar problems. The article itself was very well done and is a very useful and practical demonstration of what can be achieved with surplus equipment. Peter Lynch, Bayshore Park, Singapore. Windows Dual-Boot Success I had refused to have anything to do with Windows 95, as I dreaded having to learn another new system, until I read the “dual boot” article in the July 1996 issue of SILICON CHIP. I thought that was just what I wanted. It would allow me to contin­ue work­ ing with my current programs under Windows 3.1 but to have a peek at Windows 95 every now and then to see what it has to offer and to learn how to use it. So I bought a “95” upgrade and a 1.2Gb hard drive and installed it ac­ cording to the article. As time went on my peeks at “95” became longer until I am now transferring most of my programs over to it. What I would like to know now is, how can I make my “95” D: drive a self-booting C: drive? Is it just a matter of transferring the Autoexec.xxx and Config.xxx files across? For many years now I have been trading in my car on a new one about every four years. I did this so as to reduce the chance of being held up in the “sticks” by a major breakdown. But I had always been dubious about electronic fuel injection and shied away from cars fitted with it. As electronics is my trade I know how delicate electronic equipment can be and I was always con­cerned about it breaking down in an EFI car while out in the bush somewhere. Then I read your excellent series on Electronic Engine Management and learnt that EFI is fairly reliable after all and that if it did break down, it wouldn’t disable the car completely and leave you stuck in the wilderness. So my last new car was one fitted with EFI. It seemed to perform quite well. The thing I liked about it was how it started the same, hot or cold. But my new car did break down! With a broken timing belt! At 7000km! Luckily, I was able to call for assis­ tance with my CB radio and catch a bus home. Three days later I was on the road again and haven’t had any more prob­ lems. The warranty has just expired. So it just goes to show, you don’t know what’s going to happen. A timing belt can go at any time in any vehicle and here I was concerned all the time with the EFI. Keep up the good work with your magazine. T. Vieritz, Emerald, Qld. Comment: unfortunately, there is no easy way to make your Windows 95 D: drive into a self-booting C: drive. The only foolproof way is to reformat the drive, reconfigure your hardware setup as necessary, and then load everything back on in the way you want it. We suggest you wait until you are sure that you can do with­out Windows 3.1 and then make a complete change to Windows 95. Your comments about vehicle electronics are interesting. Apparently, by far the most common cause of modern car breakdowns is a flat battery. Power Supply Weakness For Smoke Alarm Control Panel I have just read the article on the Control Panel for Multiple Smoke Alarms in the January 1997 issue of SILICON CHIP. I feel this is a most dan­ gerous project, due to the fact that the loss of the 9V supply, due to a short anywhere in the field, complete­ ly shuts down the whole system. That is the reason that the 240VAC units require a 9V battery backup for mains loss, so detectors can still work. L. Hirning, Dee Why, NSW. Comment: while we agree that the loss of the 9V supply would disable the whole system, there is a visible indicator in every smoke alarm to tell you that it is being monitored. If you can’t see it flashing, you know it is dead. The same criticism could be applied to every burglar alarm – if the main supply is lost, the alarm is dead but again, there is visible monitoring. Our approach to the Smoke Alarm Control Panel is essential­ly the same as in large building installations where the individ­ual alarms usually are all connected to an RS232 line and have their own unique addresses and no backup batteries. Again, each detector has a visible LED indicator to show that it is being monitored. Flashing Lights Foil Hunting Cats In your response to a letter from K.F., of Albion Park Rail, on page 93 of your August 1996 edition, headed “Cat deter­rent not humane”, you invite comment. It was an interesting and perceptive observation that you made in reply to the reader’s suggestion that emitted sonics would not deter birds in pref­ erence to bells attached to cats’ collars. We are given to believe by the avian experts that sonics do not indeed have any deterrent effect on birds. Your thoughts that cats should not be let out at night are not without prec­ edence. In Victoria, there is a curfew placed upon them in cities and shires that have elected to enforce, what is now state law, and bird and reptile population is now on the increase in those areas. Because cats hunt, by preference during the hours of sunset to sunrise, so we have researched and developed a tiny battery driven unit which emits high intensity flashing light from a position behind the cat’s neck. It can thus be used by responsible cat own­ ers as a “Skare” for birds and other creatures. The cat is unaware of this and the “Skare” acts as a far more effective deterrent than tinkling bells but has added safety benefits for the cat in that it is illuminated if crossing roads in unlit areas. This device will shortly be market­ ed through our existing “K-9 Collar” outlets whose primary purpose is the humane and safe containment of dogs, by proven methods using sonics and avoidance therapy. John Foley, Canine Invisible Enclosures (Qld) Pty Ltd, Tugun, Qld. February 1997  39 Build this low cost ANALOG MULTIM Are you in the market for a low cost analog multimeter? They do have their uses in spite of the fact that digital multi­meters have taken over. So why not put this kit meter together? You’ll learn about multimeters in the process of assembling it. By LEO SIMPSON You wouldn’t build this little multimeter to save money although it is pretty cheap. No, the reason for building it would be to gain a little experience in kit construction and to learn about analog multimeters. We foresee that large numbers of these meters will be built as part of school and TAFE college courses. That is what happened with the last analog multimeter we de­scribed, in the November 1989 issue of SILICON CHIP. And even though we’re quite sure that virtually every reader of this magazine has a digital multimeter, there are times when an analog meter is more suitable than a digital type. This is especially the case when the reading you are taking is fluc­tuating. When this happens it is not easy to make any sense of rapidly changing readings on a DMM (digital multimeter) but the movement of the pointer on the analog meter will give you a clear picture of what is happening. Two examples of measurements where the reading can fluc­tuate will demonstrate the point. The first is when you are carrying out an alignment procedure on a radio – the analog meter allows you to easily tweak the coil slugs for a peak reading. The second is when you are using the “Ohms” range of a multimeter to judge the leakage of a capacitor, particularly an electrolytic type. Judging by the speed with which the pointer moves up the scale, you can tell whether the capacitor is good or bad, especially if you have a known good capacitor to make a comparison. One other really good point about an analog meter is that its battery does not go flat at the most inconvenient time – when you want to use it, of course. How often 40  Silicon Chip have you dragged out your digital meter only to find that it has gone off duty because its battery is flat. This happens quite often with the cheaper DMMs because they are a bit hungry on batteries. By contrast, while all analog multimeters have a 1.5V cell and possibly a 9V battery to run the Ohms ranges, it very seldom goes flat and anyhow, you can still make voltage and current measurements even if the battery is completely dead. No off switch As part of this battery eating con­ cern, you never have to worry about turning an analog meter off. Just leave it as you last used it and it will sit there contentedly, not using any battery power at all. Unless your DMM has an “auto-off” function, you can’t say that about a digital meter. So while analog meters have been superseded by digital multimeters for most work, they are still handy to have. Multimeter features The meter in question is quite a good size and measures 148 x 99 x 34mm thick. This means that the scales are reasonably large and easy to read – an important point with an analog meter. This one has no less than eight scales on the meter face. The meter movement has the stand­ ard DC sensitivity of 20,000 ohms/volt on DC ranges. What this means is that it will draw 50 microamps from the circuit being measured, for a full scale deflection (FSD) of the pointer. When measuring voltages in high imped­ ance circuits it is most important to take this loading effect into account, otherwise the readings will be very mislead­ing. Most of the relevant multimeter functions are listed in the accompany­ Fig.1: the circuit of this analog meter is passive; ie, there are no active devices to amplify signals. The four diodes are the only semiconductors. D1 & D2 enable the meter to read AC voltages and currents. D3 & D4 are there to prevent damage to the meter movement in the case of a severe overload. All the switch contacts and tracks are integrated into the pattern of the PC board. METER February 1997  41 SPECIFICATIONS DC VOLTAGE Ranges ...........................................0.1V, 0.5V, 2.5V, 10V, 50V, 250V, 1000V Sensitivity ........................................20,000Ω/V Accuracy .........................................±4% at FSD AC VOLTAGE Ranges ...........................................10V, 50V, 250V, 1000V Decibels ..........................................-10dB to +22dB on the 10V range (add +14dB, +28dB for the 50V and 250V ranges; 0dB = 1mW into 600Ω) Sensitivity ........................................9,000Ω/V Accuracy .........................................±5% at FSD OUTPUT TERMINAL Capacitor coupled to the (+) terminal for blocking DC voltage when making AC measurements Coupling capacitance .....................0.047µF Maximum DC voltage ......................100V DC CURRENT Ranges ...........................................50µA, 2.5mA, 25mA, 0.25A Voltage burden (drop)......................100mV (50µA range), 250mV (other ranges) Accuracy .........................................±3% at FSD RESISTANCE Scale ...............................................0 to infinity, 20Ω midscale Ranges ...........................................x1, x10, x100, x1k, x10k Maximum current ............................150mA, 15mA, 1.5mA, 150µA, 60µA respectively TRANSISTOR (ICEO) & DIODE (IR) LEAKAGE Ranges ...........................................150mA, 15mA, 1.5mA, 150µA Maximum voltage ............................3V TRANSISTOR CURRENT GAIN (hFE) (using hFE adapter) Range .............................................0-1000 (calibrated for silicon transistors) Base current ...................................100µA maximum Collector current .............................11mA maximum ing specifications panel. The circuit is shown in Fig.1 and is fairly conven­ tional as analog multimeters go. The multi-position range switch controls all functions, switching multipli­ er resistors in and out for the various ranges. Note the diode protection of the meter movement, with D3 and D4. These prevents the meter movement from being mechanically damaged or burnt out if it is connected to an exces­ sive voltage while switched to a low voltage or low current range. However, if an overload does occur the meter’s pointer will still slam hard against the stops and the relevant range multiplier resistor may be burnt out. Oh, and the fuse may blow as well. Output terminal Some readers may be unfamiliar with the function of the OUTPUT termi­ nal which is connected to the positive input connec­ tion via C1, a .047µF 100V capacitor. This has nothing to do with an output from the meter but is a traditional feature on analog multimeters, harking back to the days of valve amplifiers. It enables you to measure AC voltages at the plates of valve stages. The capacitor is there to block DC voltage while allowing the AC voltage to be measured. While the traditional feature is fine, it could be a trap for young players on this meter, if they do attempt to measure AC signal voltages in a valve amplifier. For a start, the voltage rating The assembly work mainly consists of soldering the components onto the PC board and putting the selector switch together. The only components to be assembled on the copper side of the board (see above) are the zero adjust trimpot (R25), the buzzer and the banana jack socket sleeves. 42  Silicon Chip of the capacitor is much too low for such measurements. We would prefer to see the capacitor rated for at least 600V DC. The only problem is that such a capacitor would not fit in the avail­able space. Analog meter construction When you open the kit, you will find a number of small plastic bags as well as the meter case with the meter movement already installed. Fig.2 shows the component over­ lay for the PC board and the wiring inside the case. This diagram shows the component values while the PC board is screen printed with compo­ nent numbers; eg, R1, R2 etc. When you install each component make sure that its value on the circuit is matched with the component number on the PC board. There are quite a few steps in the assembly, as follows: (1). Solder all resistors to the main board. Check the colour codes against the list or check the values with a digital multimeter. Note: place a link across one of the two positions marked R8, if only one resistor for R8 (ie, 15MΩ) is supplied or you may be supplied with one 10MΩ and one 5MΩ for the two R8 positions. (2). Solder all diodes into place. (3). Solder C1 & C2 in place. (4). Solder all precut wire links into place. Follow the dotted lines on the overlay diagram for their positioning. (5). Solder trimpot R1 into place. The circuit shows 1kΩ but the sup­ plied value is likely to be 680Ω. (6). Solder the buzzer onto the cop­ per side of the PC board. Space the buzzer 3mm above the PC board so that its leads can be soldered. Space the leads so that the body of the buzzer is flush with the edge of the PC board. (7). Solder the “zero adjust” poten­ tiometer R25 in place on the copper side of the board. (8). Solder the fuse clips to the board and then fit the 500mA fuse. (9). Insert the ‘B1’ battery terminals into the PC board and solder. Note; they are inserted from the copper side of PC board. (10). Insert the three banana socket sleeves into the copper side of the PC board and solder evenly around each one. Each sleeve will sit flush with the top of the PC board. (11). Now we are ready to assemble the rotary switch. First, take the rotary Fig.2: most of the components are wired on top of the PC board. The exceptions are the zero adjust trimpot (R25), the buzzer and the banana jack socket sleeves. RESISTOR COLOUR CODES Resistor R3 R4 R5 R6 R7 R8 R8 R8 R9 R10 R11 R12 R13 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R26 Value 5kΩ 40kΩ 150kΩ 800kΩ 4MΩ 15MΩ 10MΩ 5MΩ 3kΩ 102Ω 10Ω 0.99Ω 83.3kΩ 360kΩ 1.8MΩ 6.75MΩ 20kΩ 2kΩ 44.2kΩ 18.5Ω 200Ω 34kΩ 190kΩ 10kΩ 2.1kΩ 5-Band Code (1% tolerance) green black black brown brown yellow black black brown brown green black orange brown grey black black orange brown yellow black black yellow brown brown green black green brown brown black black green brown green black black yellow brown orange black black brown brown brown black red black brown brown black black gold brown black white white silver brown grey orange orange red brown orange blue black orange brown brown grey black yellow brown blue violet green yellow brown red black black red brown red black black brown brown yellow yellow red red brown brown grey green gold red black black black brown orange yellow black red brown brown white black orange brown brown black black red brown red brown black brown February 1997  43 Where To Buy The Kit The kit for this multimeter is available from all Dick Smith Electronics stores for $29.50. (Cat K-1050). The finished PC board clips into the back of the meter case. As can be seen, most of the components are multiplier resistors for the various ranges. knob and make sure it fits onto the selector plate. Make sure that, when pushing the knob onto the selector shaft, the keyway on the shaft lines up with the knob. • • • • • • Next, insert a small spring into the hole located on the side of the selector plate. Smear a little petroleum jelly (Vaseline) around the selector housing where the ball bearing will run and MULTIMETER SAFETY WARNING This meter must not be connected to high energy sources which have transient voltages greater than 1000V. This includes the 240VAC mains. Do not connect the meter to a circuit which is greater than 1000V peak above ground. Do not use the meter if it is damaged. Inspect the test leads for damaged insulation or exposed metal. Check test lead continuity. Damaged leads should be replaced. Select the proper function and range for your measurement. Do not change ranges while the meter is connected to live cir­cuits. 44  Silicon Chip place a dab into the end of the spring. This done, place the selector plate into the case housing and push the spring with its accompanying ball bearing into position. Now turn the meter over, at the same time applying pressure to the selector plate so that it doesn’t pop out. Line up the selector knob keyway and from the front of the meter, push the knob into place. (12). Position the rotary wiper on the selector plate, with the integral plastic pillar locating the metal tab. Use a hot solder­ing iron to melt the top of the plastic pillar so that the wiper is permanently fixed in place. (13). Solder the meter wires to the PC board (note polarity). (14). Solder the 9V battery terminal wires to the PC board (points B2+ and B2-; note the polarity). (15). Before clipping the PC board into position, clean and polish the circular tracks of the selector switch. Methylated spirits will help dissolve any flux residues from soldering. (16). Insert the batteries into their respective holders. Fit the back of the meter case and its retaining screw; do not overtighten it. Finally, fit the knob for the zero adjust trimpot (R25). Congratulations, you have finished the assembly. There’s one more step before you can make measurements. Zeroing the meter Before doing any measurements, always check that the meter pointer is on zero at the left end of the scale: (1). Put the meter in the position that it will be in when meas­urements are made; ie, normally horizontal. (2). Remove the leads from the meter and check that the pointer is not being deflected by stray electromagnetic fields. (3). If the pointer is not on zero then rotate the slotted plas­tic ‘screw’ near the pivot axis of the pointer. (5). Give the meter a light tap on the side to ensure that the pointer has settled properly. Now you are ready to make meas­ SC urements. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: www.jaycar.com.au SATELLITE WATCH Compiled by GARRY CRATT* Apstar 1A, 134°E longitude: The location of Apstar 1A has angered Indonesian satellite operator Pacifik Satelit Nusantara, who claim to have registered the orbital location in 1993 for their Palapa Pacific 1 satel­lite. The com­ pany intends to make a formal complaint to the ITU. As has been demonstrated in the past, orbital location conflicts are becoming more common with the squeeze for spots over Asia. Indonesia has been testing a new ground station, causing inter­ference to the Apstar signal. Asiasat 2, 100.5°E longitude: The Egyptian Telecommunications Union has signed a multiple year lease for one 36MHz transponder on this satel­ lite for the provision of Arabic language (and others) throughout the Pacific. The transponder should be operational by the time this column goes to press. Elsewhere on AS-2, the final partic­ ipant in the European bouquet, Italian broadcaster Rai International com­ menced opera­tion in early November. The 5-channel digital TV service is now fully loaded and carries German, French, Italian, Spanish and the European music channel MCM, as well as 10 European radio sta­tions. A further addition to this package is the projected feature of a 1-way Internet browser, to the Deutsche Welle service. By tuning a digital satellite receiver to the signal and through the addition of a simple decoder box between receiver and computer, selected Internet sites can be downloaded at up to 255kbp/s, a significantly better rate than through a tele­phone line. The service is due to commence on Asiasat 2 in March, fol­lowing successful trials on some of the Deutsche Welle analog satellite channels in Europe and the USA. A 2.3m satellite dish is required for the reception of this digital package, in both Australia and New Zealand. Panamsat 2, 169° E longitude: Chinese Television Corporation (CTN) has announced it will use this satellite to transmit news feeds from within Taiwan, Northwest Asia and the Western USA to studios in Taipei. Use of the transponder should com­ mence early in February. Few analog transponders remain on this satellite (CNN, NHK, TVSN), as Panamsat has elected to adopt the Scientific Atlanta MPEG PowerVu compression system exclusively, when a digital platform is required. The proprietary S/A PowerVu system is not immediate­ly capable of re­ ceiving DVB compliant MPEG-2 signals. Gorizont 30, 142.5°E longitude: Papua New Guinea broadcaster EM TV has now adopted Video­ crypt full time, based on observations made dur­ ing December last year. The motive for scrambling all programs (even four hours of test pattern every morning) remains unclear as the broadcaster had advised they would be scrambling selected programs only, to prevent unauthorised re-broadcasting. Tamil broadcaster “Raj TV” has now disappeared from this satellite. Many operators have shown concern at the increasing degree of orbital inclination of this class of Gorizont satel­lite. Equipped with only north/south atti­ tude correction, geosta­tionary operation can only be guaranteed for two years or so, before inclined orbit operation is necessary. The effect of this is to force all ground stations to adopt dish tracking which is often not practical. No doubt EM TV will be faced with the deci­sion to “ytrack” or change satellites during 1997. Gorizont 29, 130°E longitude: Although reported as being sold to a consortium in the Philippines and to be used for coverage of the Asia Pacific Economic Forum held in Manilla in No­ Italian broadcaster Rai International commenced opera­tion on Asiasat 2 in early November. vember last year, the satel­lite remained on station at 130°E instead of being moved to 153°E as previously advised. All television broadcasts on this satellite have ceased and the fate of the satellite, which still has several more years of active life (in an inclined orbit) remains unclear. Optus B1, 160°E longitude: Sky network New Zealand will com­ mence their long awaited satellite pay TV service in April. Initially, it will be operated in analog using Videocrypt scrambling (the same system used on the Sky network terrestrial pay TV system in New Zealand). As deregulation of the pay TV industry will occur on July 1 this year, the service could be available in Australia almost immediately after commencement. Measat 2, 148°E longitude: First signal reports of testing on this sat­ ellite were received in December last year. By the time this column goes to press, C band signals should be observable along SC the east coast of Australia. * Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TV reception systems. Phone (02) 9949 7417. http://www.avcomm.com.au February 1997  53 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. AC power supply for photographic flashgun This circuit has been used to power a professional flashgun of about 200 joules. It has capacitors of 1500µF rated at 500V with a maximum surge voltage of 530V. The power supply delivers a regulat­ ed 480V to the high voltage capacitors and allows for mains variation of ±9%. An Arlec transformer which had two secondary windings of 12.6V <at> 3.5A on a segmented bobbin was rewound to provide a secondary voltage of 395V AC. A full-wave rectifier gives positive half sinewaves of 560V peak and these are truncated at 480V, using four 120V zener diodes in series. This zener-reg­ ulated voltage is applied via diode D5 to the gate of SCR1. The SCR fires every time its gate is higher than the cathode by about 0.6V. The resultant pulses charge the capacitors until they reach 480V and then the SCR stops conducting and then fires intermittently to maintain 54  Silicon Chip the voltage. The fluctuation appears to be around ±1V. A neon lamp was used as a flashing “ready” indicator. It fires at around 85V and drops to 62V while con­ ducting. This range is increased by the divider action and was deemed unsatisfactory. A 0.1µF capacitor was connected in parallel with the neon, trans­forming it into a relaxation oscillator. Every time the capacitor reaches the firing voltage of the neon, it fires and discharges the capacitor. The cycle is repeated while ever the supply is above 450V. This is adjusted by the 100kΩ resistor (in parallel with the neon). The 470Ω 20W resistor limits the current charging the ca­pacitors when they are fully discharged and natu­ rally affects the time taken to reach full voltage. The system takes about six seconds to recharge the capacitors after each flash firing. When the flash extinguishes the capacitors still have about 100V when starting to recharge. The SCR is protected by diode D6 when the AC is switched off and the capacitors are still charged. Many modern flashguns of this ca­ pacity operate at 350V and the supply should be modified accordingly. Warning: this high voltage supply is potentially lethal. Only experienced persons should attempt to build it. V. Erdstein, Highett, Vic. ($40) Precision analog multiplier The National Semiconductor LM­ 13600 and LM13700 ICs, known as “dual output transconductance amplifiers” differ from ordinary IC amplifiers in two main respects. First, they produce output currents instead of output voltages and second, their gains (gm) are variable as functions of input (control) currents. These properties make these ICs useful in applications such as voltage controlled amplifiers and filters, auto­ matic gain control (AGC) amplifiers and voltage multipliers. Examples of the latter include RMS voltmeters, power meters and watt-hour meters. One problem with these ICs is that the relationship between gain and in­ put control current is not perfectly lin­ ear over their entire operating ranges. In some applications this may not be a serious problem but if these ICs are to be used in precision applications then it could be significant. That turned out to be the case with a project which was intended to measure the energy in high voltage pulses. The design concept involved us­ ing one of the two amplifiers in an LM13600 to generate an output voltage proportional to the square of an input pulse voltage. This voltage could then be integrated using an ordinary op amp to obtain the pulse energy. The circuit used was a “four quadrant multiplier” and was an adaptation of a circuit in the National Semiconductor data sheets for this device. The problem showed up as an asymmetry in the output wave­form for the positive and negative halves of a sinusoidal input. The degree of asymmetry in the waveform began to be significant for output voltages outside the range of 0-200mV peakto-peak. This effectively limited the basic operation within this range since gain symmetry was a critical requirement. The non-linearity problem was solved by a cancellation method: two identical circuits were set up but with the signal into one reversed in phase with respect to the other and the out­ puts of the circuits were combined, as shown in the accompany­ing circuit. In this mode of operation, the out­ put waveform was symmet­rical over the range of 0-3V peak-to-peak (a 15:1 improvement over the basic circuit). Also, the output distortion at frequen­ cies above 10kHz was significantly re­ duced at all signal levels. The circuit is usable for input signals up to 200kHz. Herman Nacinovich, Gulgong, NSW. ($50) February 1997  55 Control Multipl Last month, we featured the circuit details of this Smoke Alarm Monitor. It will control up to 10 smoke detectors with the ability to disarm and automatically rearm two detectors so you can cater for childrens’ parties, candlelit dinners and open fires in the winter. This month we give the construction and installation details. Based on cheap and readily avail­ able ionisation smoke detectors, this Smoke Alarm Control Panel solves the problems of maintaining contin­ uous monitoring of up to 10 smoke detectors. Why 10? As outlined in last month’s article, if you have only one or two monitors in the typical Australian home, you are not safe against fire. Fire 56  Silicon Chip could start in a room with a closed door and even if a smoke detector is ultimately triggered it may be too late to save your home or your life. As noted last month, you need a smoke detector for every bedroom which has any electrical equipment plus a detector for every other room with electrical gear, apart from the kitchen and garage. For more informa­ tion along these lines and the circuit description, you will need to refer to last month’s issue. In setting out the construction details, we will first discuss the as­ sembly of the Control Panel and then continue with the modification of standard smoke detectors which are available from any hardware store or supermarket. Finally, we will discuss the installation of a typical home system. Control panel assembly The SILICON CHIP Smoke Alarm Control Panel is housed in a plastic case measuring 180 x 260 x 65mm. This would normally be mounted on a wall and so the top cover of the case becomes the control panel. We fitted PART 2: By JOHN CLARKE l Panel For le Smoke Alarms Left: the finished Smoke Alarm Control Panel has 10 LEDs which cycle through as each smoke detector is polled. The smoke detectors are modified battery operated units which are much cheaper to buy than mainspowered detectors. our prototype with a Dynamark label measuring 127 x 144mm. Inside the case, the circuit compo­ nents are mounted on two separate PC boards. The main board measures 149 x 251mm and is coded 03312961. It is installed in the base of the case and has a number of multi-way terminal connectors for all the connections from the smoke detectors. Two large holes at the top of the main board are for cable entry for the smoke detector wiring, although these may not be used if the cables are brought in via one of the side panels. The second board measures 112 x 151mm. It is coded 03312962 and it carries all the LED indicators and pushbutton switches for the smoke detectors. Before you begin assembly of the The finished front panel board with all the LEDs in place. Note that they must be test-fitted in the front panel before they are soldered. PC boards, check each one for shorts between tracks or breaks in the cop­ per pattern. You may need to drill out some holes for mounting the PC boards, the transformer, REG1 and for cable ties to hold down the SLA battery. The component overlay for the main board is shown in Fig.1 while the second board is in Fig.2. Install all the links first and note February 1997  57 Fig.1: this is the parts layout for the main PC board. Take care to ensure that all polarised parts are correctly oriented and note that a heatsink must be fitted to REG1. The 12V SLA battery is secured to the board using two plastic cable ties. 58  Silicon Chip Fig.2: the component overlay for the front panel board. This board mounts face down into the front panel. that you must choose the appropriate link for the preset disarm period you require. Fig.2 shows the link for a 15-minute disarm period although we suggest that most people will want a longer delay – the choice is yours. Next, install the resistors, using the resistor colour code table as a guide to the values. Alternatively, use a digital multimeter to check each resistor be­ fore it is installed. This done, insert the diodes, taking care with their orientation. Note that diodes D1-D20 (see Fig.1) are installed with their cathode bands facing IC2. Similarly, on the second board, diodes D22-D29 are all oriented the same way, with their cathode bands away from the switches. Note that there are two types of diode used on the main PC board: 1A 1N4004s which have a black body and the smaller 1N914s which usually have an orange glass body. The 13V zener diode ZD1 is similar in size to the larger diodes so be careful to install it in its correct place. Five PC stakes are installed on the main PC board. Four of these are for the transformer secondary and the SLA battery terminals. The fifth is mounted at the end of the SLA battery position to stop it from moving along the board and encroaching on adjacent capacitors. Next, insert and solder in the ICs. Take care with the orientation of each and check that the correct type has been installed before soldering. The 3-terminal regulator REG1 is mounted horizontally on a small heatsink using a 3mm screw and nut. Bend its leads so that they insert into the holes pro­ vided. There are three transistors to be mounted on the main board; make sure they are oriented correctly. Take care with the polarity of the electrolytic capacitors when they are installed. Note that the electrolytics on the front panel board are mount­ ed horizontally to allow clearance between the board and front panel. Switches S1-S13 are oriented with the flat side towards the top edge of the board. We used grey switch­es for S1-S11 and S13. Green switches were used for S12 and S14. When installing the terminal strips RESISTOR COLOUR CODES – CONTROL PANEL  No.    2  10    3  25    3    3    1    1    1 Value 470kΩ 100kΩ 33kΩ 10kΩ 2.2kΩ 1kΩ 680Ω 120Ω 100Ω 4-Band Code (1%) yellow violet yellow brown brown black yellow brown orange orange orange brown brown black orange brown red red red brown brown black red brown blue grey brown brown brown red brown brown brown black brown brown 5-Band Code (1%) yellow violet black orange brown brown black black orange brown orange orange black red brown brown black black red brown red red black brown brown brown black black brown brown blue grey black black brown brown red black black brown brown black black black brown February 1997  59 Fig.3: the wiring details inside the case. Apart from the mains wiring, the interconnections are made using rainbow cables terminated to headers. on the main board, orient them with the wire entry side as shown on Fig.1. Also mount the 180Ω 5W resistor and the pin headers for the A, B, C and D connectors. If you use 8-way headers in the 7-way C and D positions, the end pin of each should be cut off. Transformer T1 is mounted on the main board using 3mm screws and nuts. The earth solder lug is secured on the trans­former mounting screw with a star washer and nut. The SLA battery is mounted on its side with the terminals facing the 180Ω 5W resistor. 60  Silicon Chip Secure the battery to the PC board using cable ties as shown. Drilling the case Because it is assumed that the Con­ trol Panel will be mount­ed on a wall, we have used the case unconvention­ ally. The main board is mounted in the case lid (recognised by the brass inserts in the four corner posts), while the front panel is mounted in the base of the case. This has been done so that after installation, the lid can be removed by undoing the four screws. You will need to drill a hole for the cord grip grommet adjacent to where the transformer will be positioned. The main PC board can be attached to the lid of the case using 3mm screws at the mounting standoffs. The front panel section of the case will need to be drilled for the switch­ es, LEDs and fuseholder. S15 and the fuse­holder should be located 17mm in from the lefthand edge of the case to provide clearance for the transformer body. Position the fuse and S15 at 25mm and 55mm respectively up from the bottom edge of the case. The disarm LED11 for alarm 1 is located 22mm in from the righthand edge and 22mm from the top edge of the case. Attach the Dynamark label with LED11 in the above position and drill out holes for the switches and LEDs and insert the 3mm LED bezels. Place the front panel PC board in position under the front panel and secure with 3mm screws and 6mm spacers into the inte­gral standoffs in the case. (The spacers can be held in place over the screw using “Blu-Tack” as an aid in assembly). Push the LEDs into the bezels and solder in place on the board. Then re­ move the front panel PC board which is now ready for wiring. Fig.4: one of these PC boards needs to be fitted inside each smoke detector. The board is designed to fit inside the battery compartment. This is a finished smoke detector PC board, about to be in­stalled in the battery compartment of a Kambrook smoke detector. Wiring All of the wiring details not shown on Fig.1 & Fig.2 are shown in the di­ agram of Fig.3. This should be closely followed, in conjunction with the circuit diagrams published last month. Cut a 220mm length of 6-way and a 160mm length of 6-way rainbow cable. You also need a 400mm length of 7-way and a 250mm length of 7-way rainbow cable. Strip one end of each cable and insert the 220mm 6-way length into the A bus of the front panel PC board. The 160mm length of 6-way cable is inserted into the B bus. The 400mm length of 7-way cable is for the C bus and finally the 250mm length of 7-way is for the D bus. Strip the other ends of each cable of insu­ lation and attach the header pins to each lead. Now slide the pins into the header shell and plug it into the main PC board. Use 250VAC rated hook-up wire for the mains wiring. Alter­natively, strip some wire out of the mains cord. The mains cord should be secured with the cordgrip grommet so that it cannot be pulled out of the case. The green/yellow striped wire should be soldered to the solder lug located on the transformer mounting foot. Use heatshrink tubing over the fuse and mains switch wiring to prevent accidental contact with the live ter­ minals. Similarly, the terminals to the trans­ former primary must be sheathed in heatshrink tubing after wiring. Con­ nect the short lengths of hookup wire from the transformer secondary to the PC stakes on the main PC board. The battery terminal wiring consists of short lengths of hookup wire with spade terminal clips attached to one end. Solder the free end to the PC stake on the board, taking care with the po­ larity when connecting to the battery. Apply power to the circuit and check that there is about 9V between GND and the + terminal on the ter­ minals strips. Initial­ly, LED1 should light and then LEDs 2-10 should light in sequence, taking 7 seconds to cycle through. Press the disarm switches and check that the associated LED11 or LED12 lights. They should extinguish when the associated rearm switch is pressed. If you find that the circuit does not operate as described, check that the rainbow connectors are terminated in the correct positions and with the right polarity. Also check the supply to all ICs. There should be 9V between pins 1 & 8 of IC1, IC4, IC5 & IC6; 9V between pins 16 & 8 of IC2 & IC7; 9V between pins 4 & 8 of IC3; and 9V between pins 14 & 8 of IC8. Smoke detector PC board The small PC boards for the smoke detectors can now be constructed. These measure 46 x 23mm and are RESISTOR COLOUR CODES – DETECTOR PC BOARD  No.   1   1   1   1   1 Value 1MΩ 100kΩ 33kΩ 10kΩ 1kΩ 4-Band Code (1%) brown black green brown brown black yellow brown orange orange orange brown brown black orange brown brown black red brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown orange orange black red brown brown black black red brown brown black black brown brown February 1997  61 This folded-out view of the Control Panel shows the wiring to the two PC boards. Take care to ensure that the mains cord is correctly anchored. coded 03312963. You will need one of these boards for each smoke detector. Install the five resistors and single diode and then the transistors; take care to use the correct type in each place. Insert and solder the four PC stakes on one end of the PC board and the 4-way terminal strip at the other end. The capacitors are mounted as close as possible to the PC board with the polarity as shown. The LED mounts with its leads bent at right angles so that it protrudes above the edge of the board. We used Kambrook SD28 smoke detectors as our prototypes and the PC board is mounted with a self-tapping screw through the battery holder side panel as shown in the photograph. It should be possible to mount the PC board in the battery compartment of the smoke detector but the LED may need to be con­nected to the lid with The front panel board is secured to the lid on 10mm standoffs. It is linked to the main board using rainbow cables terminated in header plugs. 62  Silicon Chip flying leads in some cases. Cut off the battery clip for the smoke detector and solder the supply wires to the + and GND terminals on the PC board. To make a connection to the ionisation chamber, we used an alligator clip soldered to a length of hookup wire. You can’t solder to the ionisation chamber because it is stain­ less steel and you can’t undo one of the screws because they are tamper proof. To make a secure connection, bend out one of the metal slots and attach the alligator clip to this. On other smoke detectors it is pos­ sible to make a connec­tion to a wire which is attached to the ionisation chamber. Finally, attach a length of hookup wire to the piezo termi­nal which has a red wire from the smoke detector circuit already connected. We drilled a hole in the side of the smoke detector case to allow access to the lower screw terminals on the addon PC board. You may have to make a different arrangement for other models of smoke detec­tor. We have produced a label to designate the external con­ nections and a copy of this should be affixed to the terminal block in each detector. Drill a hole in the alarm lid for the LED bezel, taking care to mark the correct place before drilling. Since the smoke detector has now been modified to be pow­ered from an external source, there is no need to access it once it has been installed. We have produced a label which states that the are “No user serviceable parts inside”. Copy as many as you need and affix them to each detector. This is to comply with Australian Standards AS3786-1993. Testing When you have finished modifying all the smoke detectors, they can be temporarily connected to the Control Panel. Make sure that the connections are correct before switching on power. Note that the “in” and “out” terminals on the smoke detectors connect to the “test” and “in” terminals on the con­ trol panel. To avoid confusion, they have also been labelled A and D. The A terminal (in) on the smoke detector should attach to the A terminal (test) on the control panel. Similarly connect the B to B, C to C and D to D. Apply power and check that the LED in each smoke detector flashes about once every three seconds. Press the disarm switches to check that the The modified Kambrook smoke detector. The LED on the PC board protrudes through the lid and flashes every three seconds as an indication that it is powered. Fig.5: this is the full-size etching pattern for the front panel PC board. Once again, check the board carefully before installing any parts. February 1997  63 Fig.6 (left): this is the artwork for the main board, reduced to 70% actual size. It can be reproduced full size on a photocopier set to 1.41x. Fig.7 (above): full size artwork for the smoke detector board. Up to 10 of these boards will be required, one for each smoke detector. 64  Silicon Chip No user serviceable parts inside Fig.8: copy this label on a photostat machine and attach it to the outside of each smoke detector. A B C D Fig.9: attach this label In + Gnd Out to the terminal block in each smoke detector. LEDs for smoke detectors 1 and 2 stop flashing. Press the rearm switches to reapply power. Before proceeding fur­ ther, use some “Blu-Tack” in the top of each smoke detector piezo siren to reduce the sound level. Now press the test switch on the Control Panel for one of the connect­ ed smoke detectors. Its siren should sound after a few seconds and when the LED on the Control Panel lights, it should remain lit for about four seconds. The alarm will then stop and the next LED will light. During this 4-second time interval some of the other sirens may sound. Make this test on all connected smoke detectors. If the test switch on one of the smoke detectors is pressed, then when the associated LED on the Control Panel lights (ie, when the detector is polled, all the other smoke detector alarms will sound. Next, disconnect the mains power and check that the SLA battery con­ tinues to power the circuitry. Do not forget to remove the “Blu-Tack” from the piezo sirens after all the checks have been completed. Installation As noted previously, the Smoke Alarm Control Panel is designed to mount on a wall and preferably in­ side a closet or cupboard. The smoke detectors should be mounted in ac­ cordance with the brochure supplied with each unit. Each detector should be linked back to the Control Panel via its own length of 4-way telephone cable and these cables should all be in the ceiling space. After all, it would be no good if a fire started and burnt out the cables before the alarm went off! Finally, note that the parts list pub­ lished last month should show four 1kΩ resistors (not three), while a 47kΩ resistor should be added to the circuit between pin 11 of IC5f and the +9V supply. In addition, one of the 100µF bypass capacitors should be 10µF. SC We made the connection to the stainless steel ionisation chamber via an alligator clip. Other smoke detectors are easier, as they have a wire connection to the chamber. ALARM TEST REARM DISARM 1 + + + + + 2 + + + + + 3 + + 4 + + 5 + + 6 + + 7 + + 8 + + 9 + + 10 + + SMOKE ALARM CONTROL PANEL Fig.10: this is the full-size front panel artwork for the control panel. February 1997  65 Part 6: Interpreting Digital Oscilloscope Displays We must learn to interpret what we see on the digital oscilloscope screen. The display is only a reconstructed image of the waveform which is sampled during a very small fraction of the total signal time. And incorrect operation can introduce alias “ghosts” – signals which don’t exist at all. By BRYAN MAHER While digital oscilloscopes are powerful instruments, they take some getting used to, particularly for peo­ ple who have used analog scopes for many years. In reality, there are significant differences between displays of the same signal seen on a digital or analog oscilloscope. And both displays are likely to be different from the real live signal. Each scope shows a different image, neither of which is a true representation of the actual electri­ cal waveform. For anyone who has used an analog scope for many years, there must first be the realisation that the screen display is not reality and that both analog and digital scopes 66  Silicon Chip give different “filtered” views of real signals. All of which is an admission that the signal seen on a digital scope can look quite different to the same signal on an analog instrument. Moreover, on a digital scope, it will probably look much noisier. Is that noise really there? Well, yes, in many cases it is and it is just not seen on the analog instrument. These noisy traces are in sharp con­ trast to the smooth traces of an analog scope. Together with the complexities of screen menus, they make some longtime analog scope users reluctant to invest in a digital storage scope. This aversion is unfortunate, for it denies those people access to the great signal processing advantages of the digital instrument. Why the trace wriggles The wriggly nature of the trace hits you in the eye, even on large amplitude signals, such as that shown in Fig.1. By contrast, the same signal displayed on an analog scope is likely to be as clean as whistle. What happens when we photo­ graphically enlarge a portion of the baseline trace seen in Fig.1? The result of an 8-times magnification is shown in Fig.2. The wriggles are a form of noise. But their large amplitude, even on signals as big as 8V, indicates some source other than random noise at the scope input. And because of the dig­ itising process the digital scope trace tends to have a characteristic “jaggy” appearance. This is very different from the nat­ ural random noise generated in high gain preamplifiers which we see on analog scopes. But some noise im­ pulses are too fast to generate enough light in the phosphor and so are not visible unless we turn up the bright­ ness. This means we are never sure of the true amount of noise when using an analog scope. The jaggies on all digital scope displays operating in simple mode Fig.1: a digital scope can find an elusive glitch but the trace is wriggly, even on 8V signals. Fig. 2: photographically enlarging the trace of Fig.1 shows an artificial jaggy waveform, characteristic of digital scopes used in simple mode. This jaggy waveform is independent of signal amplitude. stem from four sources. The first and predominant cause is inherent noise within the analog to digital (A/D) converters. Digitising rates Designers face great problems when digitising rates from 100MS/s up to 8GS/s are required. At this rate, even flash A/D converters are inadequate, because their speed is ultimately limited by the slew rate of the analog comparators used. A new technology is needed. In many Tektronix digital scopes an extra component is added. At a very fast sampling rate, one complete re­ cord (collection) of samples is passed into a proprietary line of special sem­ iconductor analog storage elements. Then the sampler pauses, while this temporarily stored analog record is shifted out at a slower rate to an A/D converter. The digital data so produced is concurrently recorded in the mem­ ory. This double shuffle achieves the complete digitisation at an apparent rate extending up to 5GS/s. Other manufacturers combine many digitising paths to achieve high speed. The Hewlett Packard HP54720/10 model contains 16 500MS/s 8-bit flash A/D converter channels. All the data outputs can be interleaved to produce an equivalent 8GS/s rate of A/D conversion, with an extremely short effective sampling period of one pico­second. Such speeds are way beyond the capabilities of any direct single stage A/D converter technology currently in existence. Digitisation in multiple stages, though necessary to achieve the required speed, unfortunately does generate noise. This is the dominant cause of the wriggly baseline and trace observed when any digital storage scope is used in simple mode. Digital oscilloscope manufacturers admit that the displayed baseline and trace always contains wriggles of two to three pixels in amplitude. One pixel is the smallest possible increment in vertical amplitude of the display and is equal to 1/256 or 0.4% of the screen height. Because the digitising section comes after the preamplifier and attenuator stages, this noise introduced by A/D conversion is the same at all signal levels. In stark contrast, analog scopes only show baseline noise on tiny signals, of much less than a millivolt. Averaging mode One way to reduce the apparent noise on a digital scope waveform is to operate in averaging or High Resolution mode. Averaging means the digital data from a number of suc­ cessive recurrent sweeps is averaged before being displayed. HighRes is an ingenious method wherein averaging can be done even on a oneshot. Be­ cause random noise averages out to Fig.3: to demonstrate quantisation noise, the lower trace sinewave signal was sampled, digitised and immediately reconverted back to analog, then displayed in the upper trace. Any imperfections not noticed in the lower trace are enlarged in the upper trace by the digitisation. February 1997  67 zero, the trace then seen on the screen is much smoother. We will investigate averaging and high resolution modes in the next chapter. Quantisation noise A second cause of the wriggly trace in digital scopes is the quantisation noise described in the previous chapter. Readers will recall that the A/D converter breaks down the continuous analog signal into 256 or more discrete decision levels. The A/D converter output data is a digital code representing the nearest decision level below the voltage of the analog sample. Quantisation noise arises from the difference between the actual voltage of each sample and the smaller voltage values represented by the corresponding digital words. A steadily rising analog voltage into an A/D converter produces a digital output rising in a staircase of discrete steps. The same applies for falling slopes. So the trace displayed on any digital scope is fundamentally a series of small increments, rather than a smooth continuous line. Quantisation also results in a secondary source of noise. If an analog signal is just below some particular decision level, any tiny fluctuation or noise spike can push the signal momentarily above that decision level. Thus the next higher digital data is generated by the A/D converter, lifting the display up one whole pixel each time this occurs. It is possible to demonstrate quantisation noise. In the analog scope photo of Fig.3, the lower trace shows a sinewave which was also fed into a sampler and A/D converter. The resulting digital data was immediately converted back to analog form by a digital/analog (D/A) converter and the result shown as the upper trace. Small irregularities are present in the lower sinewave but are too fast or too small to be noticed. And some noise exists in the reference voltage of the A/D convert­ er. Each fast noise impulse momentarily lifts the analog amplitude up into the next decision level, so producing a higher digital word. Thus lots of small step errors are produced. Pulse stretching This sequence of scope waveforms shows a sinewave signal at 10kHz displayed on a digital and an analog scope. The top waveform is from a Tektronix TDS 360 digital scope in sample mode at 2 megasamples/second while the middle waveform is at the same sample rate but in average mode (128 waveforms averaged). Finally, the bottom waveform is from an analog scope. Note the very smooth trace. 68  Silicon Chip A third effect which makes quantisation noise worse could be called “interference pulse stretching”. Many noise pulses are too fast to be seen on an analog scope but when captured by a digital scope’s sampler, it holds the signal voltage steady until the next sample is taken. Hence the sampler stretches fast noise pulses out to equal the sampling period, so they can be more clearly seen. A fourth very important contribution to the wobbly trace displayed on any digital scope is directly related to the waveform capture rate and screen update rate. This points up the vital difference between the dis­ play on any scope and the real live signal we wish to investigate. Using an analog scope, in many circumstances you will never see noise impulses, for two reasons, as illus­ trated in Fig.4. Firstly, they are usually not in synchronism with the scope’s horizontal sweep and so occur on a different part Fig.4: an analog scope may update its display every five microseconds, with about 500 sweeps superimposed. Individual asynchronous noise pulses do not overlay, so they are usually not seen. of the trace each sweep. Secondly, and this is of the utmost importance, very often the display on an analog scope is an overlay of hun­ dreds or thousands of superimposed sweeps. Suppose for example that you are looking at the 3MHz signal shown in Fig.4(a), with the sweep speed set to 0.1µs/div. The forward trace takes 1µs and the retrace and holdoff might occupy 2µs each, as illustrated in Fig.4(b). That is 5µs for each complete display cycle. Therefore, your scope trace will sweep across the screen 200,000 times each second. This is your update rate, the num­ ber of times your display is renewed each second. All these traces are being drawn on your screen, each one on top of the last. You are capturing and displaying only one out of every five microsec­ onds of the live signal. You could say your waveform capture rate is 200,000 waveforms/second, which in this case is 20% of the live signal. If you have turned up the brightness (intensity) such that the effective per­ sistence time of the screen phosphor is 2.5 milliseconds, then the display you see is the overlay of about 500 traces superimposed, each showing the same signal pattern. The display is really the average of 500 views of the input signal, with the noise averaging towards zero. Therefore you will never notice the noise that is present and the trace and baseline will be the smooth clean lines which analog scope users have come to expect. But this means that analog scope us­ ers are blissfully ignorant of noise and interference which could be playing Fig.5: a conventional digital scope may sample the real live signal for only one microsecond, then display that segment for perhaps 33,000us. You see only 0.003% of the live signal. February 1997  69 Fig.6: a 2kHz sinewave was sampled at 2200S/sec. This too-slow rate generated a 200Hz alias frequency which modulated the input sinewave, producing the false waveform displayed. havoc with the circuit or equipment they are measuring. When those same signals and inter­ ferences are fed to a digital scope as illustrated in Fig.5, the display will be quite different. Because of the effects listed above, noise pulses are recorded along with the wanted signal. Even though these interference pulses may be only nanoseconds in duration, they are liable to be dis­ played. That might be regarded as a disadvantage of the digital scope. But many digital scopes also have a big advantage – they can be programmed to find glitches. The scope waveform of Fig.1 is such a case. The scope was programmed to search for and trigger the scope display on any pulse which had a duration between 0.5 and 4.5µs. The instrument found one interfer­ ence pulse having a duration of 2.01µs within a collection of thousands upon thousands of clean signals. With the scope triggered on this glitch you can see and analyse it. Some digital scopes can be set up to be triggered on runt pulses or on specified glitches as short as 2 nano­ seconds. This is just not possible with analog scopes. sinewave you will see about two cycles of that signal, indicating a frequency of only 50Hz! But if you raise the sweep speed to 20ns, the scope will sample at 2GS/s. Then a little more than two cycles of the same input signal will be displayed, indicating the true fre­ quency, 13MHz. We should always use the scope to achieve the fastest sample rate possible, otherwise the display may show the wrong frequency reading. Or in other cases we may observe distortion on fast edges in a complex waveform, with the low harmonics re­ produced larger and out of proportion to the high harmonics. In other cases a signal may seem to drift across the screen untriggered, like some weird apparition. Alternatively the screen may display a signal component at a fre­ quency which does not exist at the scope’s input terminals, as illustrated in Fig.6. Here the input signal is a 2kHz sinewave and the digital scope is in­ correctly operated with an effective sampling rate of 2200 samples/second. The display of the 2kHz signal ap­ pears to be modulated with a slower component, which has a period of 5ms, representing a frequency of 200Hz. Yet no 200Hz signal was ap­ plied to the scope. Where is it coming from? We say the 2kHz real signal is also masquerading under an “alias” (a false name) at a lower frequency, 200Hz. You can see an apparent modulation pattern which has a 5ms period. It is important to understand what causes these strange phenomena and how to prevent them. Picturing voltage signals Normally, when we draw a signal waveform, we get something like Fig.7(a) which depicts a 1kHz sine­ wave signal. We say that this is drawn in the frequency domain because the horizontal axis of the diagram is time which can be seconds, milliseconds, microseconds or whatever. But there is another way of depict­ ing the same 1kHz sinewave signal and that is the frequency domain, as shown in Fig.7(b). In this case, the horizontal axis of the diagram is frequency and since we only have one frequency it is depicted as a vertical line at the 1kHz spot on the axis. The height of the vertical line is measure of the amplitude, just as it is in the time domain. When you connect a 1kHz signal to a digital scope it will be sampled at some rate, which we will call the effective sampling frequency, fs. Any sampling process generates harmonics and so the sampler output will contain the 1kHz input frequen­ Aliasing A completely different type of error is sometimes seen on a digital scope when incorrectly used. The effective sample rate achieved is approximately proportional to the sweep speed you select. For example, a scope which is ad­ vertised to sample at 2GS/s will only achieve that rate when you select the fastest sweep speed. But the same scope, when switched to a sweep speed of 5ms/div has an effective sampling rate of only 10kS/s! That difference is crucial. At that setting, if you apply a 13MHz 70  Silicon Chip Fig.7: a 1kHz sinewave (a) can be represented in the frequency domain (b) as a vertical line on the horizontal frequency axis. Its height shows its amplitude. Sampling (c) at rate fs produces extra frequencies at fs ±1kHz. Fig.8: complex waveforms (a) can be depicted in the frequency domain (b) by a sequence of vertical lines representing the fundamental and all significant harmonics. The sampler (c) generates extra copies of all harmonics at the sum and difference of the sample rate fs and each harmonic frequency. cy, the sampler frequency fs, plus the sum frequency (fs + 1kHz) and the difference frequency (fs - 1kHz). These frequencies are shown graphically in Fig.7(c). If the sampling frequency is 1MHz, then the diagram of Fig.7(c) will show the input at 1kHz, sampling frequency at 1MHz, and the sum and difference frequencies: (1MHz + 1kHz) = 1,001kHz; and (1MHz - 1kHz) = 999kHz This description is a simplification, for the sampling process also generates an almost infinite number of other multiples at still higher frequencies, which we choose to ignore. But most real life waveforms, espe­ cially digital signals, are more com­ plex and might be like the example depicted in Fig.8(a). Squarish wave­ forms like this can be represented as the sum of a fundamental frequency sinewave plus many harmonics. And each harmonic is a sinewave with an appropriate amplitude and a frequen­cy which a multiple of the fundamental. So the waveform shown in the time domain diagram of Fig.8(a) might be described in the frequency domain of Fig.8(b) as a fundamental frequency of 1kHz plus many harmonic multiples at frequencies 2kHz, 3kHz, 5kHz, 7kHz . . . 21kHz, etc. We have stopped at the 21st harmon­ ic on the assumption that harmonics beyond 21kHz will be insignificant. We say that the input signal occu­ pies a frequency spectrum extending from zero to the highest significant harmonic. In this case the bandwidth B ex­ tends up to 21kHz. We refer to 21kHz as fB, the highest frequency in the input signal. We imagine an envelope shown as a dotted line in Fig.8(b) as the boundary of this spectrum B. When the complex waveform shown in Figs.8(a & b) is sampled, the sampler output looks something like Fig.8(c). Here we arbitrarily chose the sampling rate fs = 1MHz, so that fs is much larger than fB. The sum components generated by the sampler include the frequency fs added to the fundamental and to each harmonic of the input. These extend from fs up to the frequency (fs + fB). The difference components extended from fs down to the frequency (fs - fB). That is, the spectrum of the sampling products extends from (fs - fB) up to (fs + fB). Low pass filter The A/D converter must only see the spectrum of the input signal up to fB but none of the products of sampling; ie, above 21kHz in this case. To achieve this rejection, digital scopes include a programmable dig­ ital low pass filter (LPF) between the sampler and the A/D converter. The lower part of Fig.8(c) shows this filter and its passband, drawn here just a smidgen wider than fB. This filter passes the input signal spectrum on to the A/D converter but blocks all other frequencies above fB. That desirable result depends on the sampling rate fs being much higher than the highest significant harmonic (fB) in the input signal. That point is vital! Just how much higher is enough? And what happens if fs is not high February 1997  71 Fig.9: if the sampling rate is too low (a) the spectrum (fs - fB) overlaps the filter passband, so alias frequencies are displayed. But (b) if fs > 2fB, all terms generated by the sampler are rejected by the filter LPF, so preventing aliasing. enough? Fig.9(a) illustrates a case where the input signals extend 21kHz but the sampling rate is only 22.5kHz; much too low. This could occur if you operate the digital scope at too slow a sweep rate. This figure shows just the outline of Fig.10: this diagram explains the alias frequency component seen mixed with the 2kHz signal in Fig.5. The alias frequency is: (fs - f(in)) = (2.2kHz 2kHz) = 200Hz. 72  Silicon Chip each spectrum instead of depicting each and every harmonic. The vital point Now here is the vital point. Because fs is so low, the sampler products in­ trude into the spectrum of the input signal. More importantly, many of those sample frequencies will pass through the low pass filter (LPF). So they pass to the A/D converter and are displayed on the screen! Frequencies generated by the sam­ pler which overlap the LPF passband include (fs - fB) = (22.5kHz - 21kHz) = 1.5kHz; then (22.5kHz - 19kHz) = 3.5kHz; then 5.5kHz, etc in steps up to 20.5kHz. These “false” signals will appear on the screen, mixed in with the real signal. With all those false frequency com­ ponents mixed into the input signal, the waveform displayed on the screen will be nothing like the true shape. Aliasing can make a signal look like something it is not! Nyquist criterion So what is the minimum sampling frequency needed to avoid aliasing? Fig.9(b) shows the situation where aliasing is just avoided. Here the lowest frequency produced by the sampler, (fs - fB), is just a smid­ gen higher than fB. The frequency clearance between fB and (fs - fB) pre­ vents any overlap of the two spectra. So under this condition aliasing is avoided. To put that into figures, we need: (fs - fB) > fB; meaning that fs > (fB + fB) or ultimately, fs > 2fB. In plain English, that means that the sampling frequency must be more than twice the highest frequency com­ ponent in the input signal. This requirement is called the Nyquist Criterion, which is invoked to prevent aliasing errors in any system which uses sampling. The foregoing discussion supposes that the response of the filter drops like a rock to zero at the end of its nominal passband; ie, a “brick-wall” filter. But the response of real low pass filters is never as steep as that and some harmonic components beyond the nominal passband will always pass through. Hence, to prevent aliasing distor­ tions, we prefer the sampling frequen­ cy to be at least five or even 10 times the input signal bandwidth. Weird modulation explained We can now explain the weird mod­ ulation of the waveform seen in Fig.6. As Fig.10 shows, the input in Fig.6 was a single frequency sinewave at 2kHz but the sampling rate was too low at 2.2kHz. Sampling generates the extra frequencies: (fs - fB) = (2.2kHz - 2kHz) = 200Hz and also: (fS + fB) = (2.2kHz + 2kHz) = 4.2kHz. 200Hz is the alias frequency which intrudes into the passband of the low pass filter and mixes with the 2kHz input signal. This produces the amplitude modulated waveform seen in Fig.6 even though no 200Hz component was present in the input signal. At very slow sweep speeds, you might only see the 200Hz signal, noth­ ing else; a real trap for young players! To avoid alias problems when using a digital scope, keep the sampling rate high by using either the auto setup facility or the highest possible sweep speed. To determine if a signal seen is an alias, raise the sweep speed or use the Peak Detect mode. Lastly, we observe that analog scopes, because of their linear vertical deflection systems, cannot produce SC aliasing errors. Acknowledgements Thanks to Tektronix Australia, Philips Scientific & Industrial and Hewlett Packard for data and illustrations. February 1997  73 RADIO CONTROL BY BOB YOUNG How radio-controlled models can be lost through interference This month, we will continue with the comparison between AM and FM and examine some of the ramifications of the two sys­tems. One surprising result is the ease with which a model can be lost through interference. In the last November 1996 article I mentioned that we re­ceived many letters and phone calls about the Mk.22 R/C system and that the most common query was why 29MHz AM? As a result we went into an in-depth analysis of the relative merits of AM and FM and concluded that both systems were incorrectly named and that “FM” was greatly oversold against “AM”. In the end we demonstrated that the difference between the two sys­ tems was much less than commonly believed. The 29MHz discussion we left in abeyance and we will have to deal with that another time. We also dealt briefly with capture effect in FM models which in my Fig.1: the scope trace at the detector of an FM receiver running off a 6-channel transmitter and with a 7-channel trans­mitter interfering on the same frequency at a signal level of approximately 1:2. 74  Silicon Chip mind is a very serious issue, especially when we come to single conversion receivers operating on 36MHz. Let me ex­plain. In our discussion on capture effect in FM receivers we noted that capture is a phenomenon that occurs when an interfer­ing signal on the same fre­ quency exceeds the wanted signal by a small margin. The actual point at which capture occurs depends on the capture ratio of the receiver and may vary from 1dB (1.12:1) to a maximum of 3dB (1.41:1), whereas capture in AM receivers occurs with signal levels of 100:1 or more. Figs.1, 2 & 3 show the sequence of events leading to cap­ture of a radio control receiver by an interfering trans­ mitter. Fig.1 shows the scope trace at the detector of an FM receiver running off a 6-channel transmitter and with a 7-channel trans­mitter interfering on the same frequency at a signal level of approximately 1:2. Fig.2 shows the same Rx with the two transmit­ters at approximately equal level. Note the severe disruption of the signal. Fig.3 shows that the signal from the 6-channel transmitter has gone bye-bye and it’s hello to the 7-chan­nel transmitter signal. Control has now passed over completely to the inter­ fering transmitter, which has exceeded the 1:1 signal level ratio. At this point, the interfering trans­ mitter now has complete control and the model could easily be flown away. Indeed, when FM first made its appearance in England, the press there reported on a spate of incidents where models were flown away by pirate transmitters. “So what?”, I can hear the “experts” Fig.2: the same Rx as in Fig.1, with the two transmit­ters at approximately equal level. Note the severe disruption of the signal. saying. Nobody is going to be silly enough to fly two models on the same frequency and in years of flying FM in Australia, there has never been a recorded incident of a model being pirated away. Well let me tell you there is still a very definite risk of running into strong interference every time you fly on a field using both ends of the 36MHz frequency allocation. There may be no intention of deliberate interference or pirating but you could still lose your model. When you see how this interference and capture can easily take place you will see that there is still a strong ar­ gument for operation on the 29MHz band. Interference on 36MHz For some time now, there have been rumblings amongst the technically inclined R/C modellers about the pos­ sibility of transmitters spaced 455kHz apart causing interference with each other. The significance of 455kHz is that it is the intermediate frequency (IF) used in all R/C receivers. This has been rein­forced by the number of glitches experienced on some flying fields. There have also been rumblings about AM receivers not being satisfactory on 36MHz and this has been put down to inter­ference from harmonics arising from broadcast FM stations. The problem arises on the 36MHz band due to the fact that it consists of 59 spots spaced 10kHz apart in a 600kHz block. The 27MHz, 29MHz and 40MHz bands are only 300kHz wide or less and therefore there can be no trans­ mitters spaced 455kHz apart in these bands. Hence we are looking at some­ thing relatively recent from an R/C point of view. Thus at each end of the 36MHz band there are a number of frequencies which are spaced either 450 or 460kHz apart. All of this has lead to a deal of con­ fusion on exactly how to handle the situation. It particularly affects me because as the designer and supplier of the Silvertone Keyboard system of frequency control, I am responsible for arranging the keyboards for safe operation on 36MHz. Up till now I have always recom­ mended that where single conversion receivers are used, they should be on frequencies in the middle of the 36MHz band, while dual-conversion receivers could be used with frequen­ cies at each end of the band. In other words, use dual-conversion receivers on channels 601-614 (36.010MHz to 36.140MHz) and channels 646-659 (36.460MHz to 36.590MHz) and sin­ gle conversion receivers on channels 615-645. The rationale behind this is that by using single conver­sion receivers in a band only 300kHz wide, a 455kHz difference signal would not arise in the mixer and therefore no interfer­ ence would occur. For the double conversion receivers, the first IF is 10.7MHz and therefore the possibility of the 455kHz difference would not be a problem. That’s as I saw it, anyway. How wrong I was! All of this as­ sumes that the only two channels being affected were the overlapping pair of transmit­ters. The situation is complicated some­ what by the fact that 455kHz falls midway between two frequencies. As long as we use only 20kHz keys (2inch), the key width protects us from this compli­cation. What has forced me to rethink this problem has been a host of discussion about the existing keyboard and its shortcomings in dealing with the new MAAA 10kHz frequency alloca­ tions. When I sat down to write the instructions for the new keyboard I thought that the 455kHz difference was not really a problem. But when I thought about it in detail I realised that maybe I was coming at it from the wrong angle. I needed to get the facts, so I warmed up the old spectrum analyser, signal generator and CRO and went to it. All of this of course was one day before the magazine deadline (as usual, I can hear Leo muttering). One hour later I finished my refresher course on mixer theory and realised we had all been thinking inside the square. What I rediscovered is this: Any pair of transmitters separated by 450kHz or 460kHz will generate a very high level of signal in the mixers of single conversion receivers, AM or FM! This will happen in every receiv­ er operating on that flying field, regardless of frequency! In other words one overlapping pair of transmitters will interfere with all 59 receivers operating on the 36MHz band. Now this is pretty startling stuff and needs some explana­tion but it is really quite simple. First of all, the receivers operating in the 36MHz band (or any other band for that matter) are wide open to all frequencies in that band. That means that a single conversion receiver which may have a crystal in the centre of the band still receives all the transmitted frequencies across that band – nothing too radical here, so far. What happens is that normally all of the difference fre­quencies between February 1997  75 Fig.3: here, the signal from the 6-channel transmitter has gone bye-bye and it’s hello to the 7-chan­nel transmitter signal. Control has now passed over completely to the interfering 7-channel transmitter, which has exceeded the 1:1 signal level ratio the incoming frequencies and the local oscilla­tor (crystal) frequency appear at the output of the mixer. How­ev­er, the IF amplifier is a very narrow filter which will only pass a 455kHz difference signal to the receiv­ er detector. That is why we change both the transmitter and receiver crystals when we change frequencies, so that the difference between the two is 455kHz. But if we also have two other trans­ mitter frequencies on the band which differ by 455kHz, they will be picked up by the front end of the receiver, will be fed through to the mixer and the same difference frequency will automatically appear at the output. So now we have an apparently legitimate signal at the output of the mixer which is very much an inter­ fering signal. Whether this becomes a problem or not depends on its strength in com­ parison to the wanted control signal. And this is where capture effect comes into its own. Capture effect usually works in our favour and tends to lock out the 455kHz interference in all but the worst cases. Thus, it is very difficult to simulate the problem in a simple three transmitter field test. The danger arises mainly in situations where the trans­mit­ter radiation patterns sudden­ ly favour the interfering pair. Now the effects on the flying field of all of this have yet to be verified and extensive testing needs to be put in train immediately. In practice, the lev­ SILICON CHIP BINDERS These binders will protect your copies of SILICON CHIP.  Heavy board covers with 2-tone green vinyl covering  Each binder holds up to 14 issues  SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A14.95 each (incl. postage in Aust). NZ & PNG orders please add $A5 each for p&p. To order, just fill in & mail the order form in this issue to: Silicon Chip Publications, PO Box 139, Collaroy 2097; Or phone (02) 9979 5644 & quote your credit card details or fax (02) 9979 6503. 76  Silicon Chip el of interference will vary depending on a whole host of factors including capture effect, mixer compression, re­ ceiver bandwidth, oscillator injection levels, relative signal level ratios and PC board leakage. The most probable effect is random interference showing up in the form of brief glitches as models move in and out of trans­mitter radiation patterns. Add to this the random nature of the pairing on any one flying field on any one day. Some days the club would have some overlapping transmitters, some days none, some days a large number. The more overlapping transmitters that are transmitting at any one time, the higher the level of 455kHz gener­ ated in the mixers of all receivers on that field. The effect is cumulative and impossible to predict. Now you can see why capture is so important. Nobody would be silly enough to fly on the same frequency but we are acciden­tally generating the same frequency every day on flying fields all over Australia, wherever overlapping pairs of transmitters are allowed to operate. The testing I have carried out to date is brief and incom­plete. I simulated the 3-transmitter scenario by removing the crystal from a single conversion receiver. I could then work the servos from my modulated signal generator using a second unmodu­ lated trans­ mitter 455kHz away to supply the mixing signal. In this mode, I could achieve the equivalent of normal re­ceiver sensitiv­ ity, depending on the relative strengths of the incoming signals. With a crystal in the receiver (any frequency) and no carrier from the wanted transmitter, this effect was still pres­ ent but diminished somewhat, probably due to mixer compression. I did not test with a carrier because capture would confuse the issue and it is here that extensive testing needs to be done. To reiterate, wherever single conver­ sion receivers are in use, transmitters overlapping by 450kHz or 460kHz must not be used. The foregoing is yet another reason for me to continue to push for 29MHz AM. It is simple, cheap and reliable. It is free of the complications and expense of 36MHz FM and is by far the most cost-effective system for SC sports fliers. SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Please feel free to visit the advertiser’s website: Rod Irving Electronics Pty Ltd SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings. Rod Irving Electronics Pty Ltd PRODUCT SHOWCASE WeatherVox – an automatic weather station with telephone access Sphere Communications has launched an innovative weather station system called WeatherVox. It has all the main features of a normal weather station except that you can phone it from any­where and get a voice report of the weather over the last 24 hours. Most of us rely on the Australian Bureau of Meteorology for the nightly weather report but more individuals and organisa­ tions, the Bureau’s re­ ports are insufficient or not localised enough. For example, a rural fire brigade may be responsible for a large region of rugged mountainous country which is heavily forested. Access may be vary difficult and the weather may easily vary between extremes on the one day and from one small area to another. The only way to know the weather in each location is to have a weather 82  Silicon Chip station in each area. That may be well and good but how do you access the weather information which is being recorded? This was the question that exercised the minds of the people at Sphere Communications. They could see many applications for this device, among rural fire brigades, boating organisa­tions, golf clubs, life savers, fishermen, farmers, foresters or anyone with a need for specialised weather information. Even people with holiday homes or boats on remote moorings could have an application for this device. What Sphere Communications did was to design a computer to interface to an Ultimeter 2000 commercial weather station made by Peet Bros Company, Inc, a company based in New Jersey, USA. The computer interface reads all the weather data from the weather station and stores it in RAM. Then, when ac­ cessed by phone, it will give a voice report on all the weather information that it has been programmed to give. The voice used to deliver the weather information is that of wellknown Sydney radio & TV announcer Grant Goldman. His voice, or rather, many words and phrases, are stored in two ISD 2590P 90-second voice recorder ICs (this device was featured in the February 1994 issue of SILICON CHIP). The WeatherVox is a actually a sin­ gle board computer with an RS-232 input for the weather station connec­ tion and a tele­phone interface, using American RJ-11 and RJ-12 telephone sock­ ets, respectively. A number of functions within the WeatherVox can be addressed or changed by pushing buttons of a standard DTMF tone phone. Three levels of voice report are available on the Weather­Vox: Brief, Intermediate and Detailed. The Brief report includes time of day, current outdoor temperature, overnight low tempera­ ture and time at which it occurred, wind speed and direction, peak gust today and time of occur­ rence, average wind speed over the last ten minutes, average wind speed over the last minute, barometric pres­ sure, relative humidity and this week’s rainfall. The Intermediate report includes all of the Brief report’s details and adds this week’s rainfall, this month’s rainfall, this year year’s rainfall, wind chill and dew point. The detailed report includes all of the Brief and Interme­diate reports and adds highest and lowest temperature today and times of occurrence, highest and lowest temperature this month and times of occurrence plus the high­ est and lowest temperature this year and the times of occurrence. The parameters can be measured in a choice of unit: Temper­ atures can be recorded in Fahrenheit or Celsius; Wind speed can be metres/ second, knots, km/h or mph; Rainfall can be in centime­ tres, millimetres or inches; Barometric pressure can be millime­tres or inches of mercury, hectopascals or millibars and finally, wind direction can be in degrees or Cardinal points. All of this information is obtained in raw data form from the Ultimeter 2000. It is a compact self-contained unit with a large LCD screen and 16 pushbuttons to display the various read­ings on the screen. It has inbuilt sensors for tem­ perature and barometric pressure and has external sensors for wind speed and direction, rain gauge, temperature and humidity. The WeatherVox unit itself is a grey plastic box about the size of a VCR tape housing. It measures 110 x 200 x 30mm. It contains a multi-layer PC board that accommodates all the circui­try. It has been wholly designed and manufactured in Australia. It car­ ries an Austel permit: A95/12/0464. For more information, contact Sphere Communications, 161 Bunner­ ong Road, Kingsford, NSW 2032. Phone (02) 9344 9111; fax (02) 9349 5774. New loudspeakers from Jamo Jamo has just released a new range of loudspeakers called the “8-Series”. This consists of three bookshelf and two freestanding models plus matching centre and surround sound speakers. All have similar styling with a moulded front baffle and they are available in black or mahogany finish. All have a nominal im­pedance of 6#. The details of Jamo 8-Series are as follows. The Jamo 28 is a compact bookshelf with a 130mm woofer and a dome tweeter. Its power rating is 55 watts and it is priced at $399 a pair. The Jamo 38 is a slightly larger bookshelf, again with a 130mm woofer and a dome tweeter. It is rated at 60 watts and retails for $499 a pair. The model 68 is the largest bookshelf with a 165mm woofer and a dome tweeter. Its rating is 80 watts and retails for $699 a pair. The model 98 is a 2-way floor-stand­ ing speaker with two 165mm woofers and a dome tweeter. Its rating is 90 watts and it retails for $999 a pair. AUDIO MODULES broadcast quality Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 BassBox® Design low frequency loudspeaker enclos­ures fast and accurately with BassBox® software. Uses both Thiele-Small and Electro-Mechanical parameters with equal ease. Includes X. Over 2.03 passive cross­over design program. $299.00 Plus $6.00 postage. Pay by cheque, Bankcard, Mastercard Visacard. EARTHQUAKE AUDIO PH: (02) 9948 3771 FAX: (02) 9948 8040 PO BOX 226 BALGOWLAH NSW 2093 THE “HIGH” THAT LASTS IS MADE IN THE U.S.A. Model KSN 1141 The new Powerline series of Motorola’s 2kHz Horn speakers incorporate protection circuitry which allows them to be used safely with amplifiers rated as high as 400 watts. This results in a product that is practically blowout proof. Based upon extensive testing, Motorola is offering a 36 month money back guarantee on this product should it burn out. Frequency Response: 1.8kHz - 30kHz Av. Sens: 92dB <at> 1m/2.83v (1 watt <at> 8Ω) Max. Power Handling Capacity: 400W Max. Temperature: 80°C Typ. Imp: appears as a 0.3µF capacitor Typical Frequency Response MOTOROLA PIEZO TWEETERS AVAILABLE FROM: DICK SMITH, JAYCAR, ALTRONICS AND OTHER GOOD AUDIO OUTLETS. IMPORTING DISTRIBUTOR: Freedman Electronics Pty Ltd, PO Box 3, Rydalmere NSW 2116. Phone: (02) 9638 6666. February 1997  83 Finally, the 128 is a large 3-way tower design with two 200mm woofers. It is rated at 140 watts and retails for $1499 a pair. Both floor-standing models have magnet­ic shielding of the drivers. All Jamo loudspeakers come with a 5-year warranty and are available from selected hifi dealers around Australia. For more information contact Scan Audio Pty Ltd by phoning 1 800 700 708; fax 03 9429 9309. Monolithic wireless IC converts both ways a range of phase-shift (PSK) half-du­ plex wireless digital communications transceivers. These includes wireless local area networks, time-division duplex quadrature modulated commu­ nications systems and time-division multiplex access packet protocol radios. Due to its power management mode, the HFA3724 is suitable for use on PCMIA cards and other portable ap­ plications such as wireless handsets. It comes in an 80-lead TQFP package. For further information, contact the Australian distributor for Harris Sem­ iconductor, BBS Electronics Australia Pty Ltd, Unit 24, 5-7 Anella Ave, Castle Hill, NSW 2154. Phone (02) 9894 5244; fax (02) 9894 5266. 1kV miniature ceramic capacitors The Harris HFA3724 is the world’s first monolithic IF/quad­rature mod­ ulator/demodulator which converts in both the receive and transmit di­ rections between baseband and inter­ mediate fre­quencies from 10-40MHz. The chip simplifies the design of KITS-R-US RF Products FMTX1 Kit $49 Single transistor 2.5 Watt Tx free running 12v-24V DC. FM band 88-108MHz. 500mV RMS audio sensitivity. FMTX2A Kit $49 A digital stereo coder using discrete components. XTAL locked subcarrier. Compatible with all our transmitters. FMTX2B Kit $49 3 stage XTAL locked 100MHz FM band 30mW output. Aust pre-emphasis. Quality specs. Optional 50mW upgrade $5. FMTX5 Kit $98 Both a FMTX2A & FMTX2B on 1 PCB. Pwt & audio routed. FME500 Kit $499 Broadcast specs. PLL 0.5 to 1 watt output narrowcast TX kit. Frequency set with Dip Switch. 220 Linear Amp Kit $499 2-15 watt output linear amp for FM band 50mW input. Simple design uses hybrid. SG1 Kit $399 Broadcast quality FM stereo coder. Uses op amps with selectable pre-emphasis. Other linear amps and kits available for broadcasters. 84  Silicon Chip Philips has recently extended its range of miniature ceram­ic capacitors with the release of a 1kV DC series. These are available in values from 0.47pF to 3300pF with tolerances of ±0.25pF or ±5% for SL types and ±10% or ±20% for class II types. The operating temperature range is PO Box 314 Blackwood SA 5051 Ph 0414 323099 Fax 088 270 3175 AWA FM721 FM-Tx board $19 Modify them as a 1 watt op Narrowcast Tx. Lots of good RF bits on PCB. AWA FM721 FM-Rx board $10 The complementary receiver for the above Tx. Full circuits provided for Rx or Tx. Xtals have been disabled. MAX Kit for PCs $169 Talk to the real world from a PC. 7 relays, ADC, DAC 8 TTL inputs & stepper driver with sample basic programs. ETI 1623 kit for PCs $69 24 lines as inputs or outputs DS-PTH-PCB and all parts. Easy to build, low cost. ETI DIGI-200 Watt Amp Kit $39 200W/2 125W/4 70W/8 from ±33 volt supply. 27,000 built since 1987. Easy to build. ROLA Digital Audio Software Call for full information about our range of digital cart players & multitrack recorders. ALL POSTAGE $6.80 Per Order FREE Steam Boat For every order over $100 re­ceive FREE a PUTT-PUTT steam boat kit. Available separately for $19.95, this is one of the greatest educational toys ever sold. -55°C to +85°C but types an extended operating temperature of +125 degrees C are also available. These latter types could be used in power sup­ plies, electronic ballasts and automotive applications. For further information, contact Philips Components, 34 Waterloo Rd, North Ryde, NSW 2213. Phone (02) 9805 4479. New colour printer from H-P has photo quality Hewlett Packard has released the HP DeskJet 690C colour inkjet print­ er for home and office use. The new printer in­ corp­o­rates HP’s Photo REt (Resolution Enhancement technology) for photo quality images and uses a new ink cartridge which quickly snaps into place along­ side the standard colour cartridge, when printing high resolution images. Naturally, for such images, the computer will need to be equipped with a colour scanner or CD-ROM drive to read photo-CDs. The HP Deskjet 690C will print at five pages a minute (PPM) for black and 1.7PPM for colour images. It has a recom­mended retail price of $654 including sales tax. The HP Photo Colour kit sells for $102 while HP photo paper is priced at $25 for 20 sheets of A4. Further information on HP products can be ob­ tained by phon­ing 131 147 (toll free). electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semicustom electronics & data communications. 63 chapters, in hard cover at $120.00. Silicon Chip Bookshop Radio Frequency Transistors Newnes Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1994 (3rd edition). This is a practical guide on the installation and servicing of satellite television equipment. The coverage of the subject is extensive, without excessive theory or mathematics. 371 pages, in hard cover at $55.95. Guide to TV & Video Technology By Eugene Trundle. First pub­lish-­ ed 1988. Second edition 1996. Eugene Trundle has written for many years in Television magazine and his latest book is right up date on TV and video technology. 382 pages, in paperback, at $39.95. Servicing Personal Computers By Michael Tooley. First published 1985. 4th edition 1994. Computers are prone to failure from a number of common causes & some that are not so common. This book sets out the principles & practice of computer servicing (including disc drives, printers & monitors), describes some of the latest software diagnostic routines & includes program listings. 387 pages in hard cover at $59.95. format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $55.95. The Art of Linear Electronics By John Linsley Hood. Pub­lished 1993. This is a practical handbook from one of the world’s most prolific audio designers, with many of his designs having been published in English technical magazines over the years. A great many practical circuits are featured – a must for anyone inter­ested in audio design. 336 pages, in paperback at $49.95. Components, Circuits & Applica­ tions, by F. F. Mazda. Published 1990. Previously a neglected field, power electronics has come into its own, particularly in the areas of traction and electric vehicles. F. F. Mazda is an acknowledged authority on the subject and he writes mainly on the many uses of thyristors & Triacs in single and three phase circuits. 417 pages, in soft cover at $59.95. Digital Audio & Compact Disc Technology Electronics Engineer’s Reference Book Hard cove Produced by the Sony Service Centre (Europe). 3rd edition, published 1995. Prepared by Sony’s technical staff, this is the best book on compact disc technology that we have ever come across. It covers digital audio in depth, including PCM adapters, the Video8 PCM Power Electronics Handbook Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order r Edited by F. F. Mazda. version now available First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of all aspects of electronics in five parts: techniques, physical phenomena, material & components, ❏ Bankcard ❏ Visa Card ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. Principles & Practical Applications. By Norm Dye & Helge Granberg. Published 1993. This book strips away the mysteries of RF circuit design. Written by two Motorola engineers, it looks at RF transistor fundamentals before moving on to specific design examples; eg, amplifiers, oscillators and pulsed power systems. Also included are chapters on filtering, impedance matching & CAD. 235 pages, in hard cover at $85.00. Surface Mount Technology By Rudolph Strauss. First pub­ lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­ soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Audio Electronics By John Linsley Hood. Pub­lished 1995. This book is for anyone involved in designing, adapting and using analog and digital audio equipment. Covers tape recording, tuners & radio receivers, preamplifiers, voltage amplifiers, power amplifiers, the compact disc & digital audio, test & measurement, loudspeaker crossover systems and power supplies. 351 pages, in soft cover at $52.95.   Title  Newnes Guide to Satellite TV  Guide to TV & Video Technology  Servicing Personal Computers  The Art Of Linear Electronics  Digital Audio & Compact Disc Technology  Power Electronics Handbook  Electronic Engineer's Reference Book  Radio Frequency Transistors  Surface Mount Technology  Audio Electronics Price $55.95 $39.95 $59.95 $49.95 $55.95 $59.95 $120.00 $85.00 $99.00 $52.95 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ & PNG add $10.00 per book, elsewhere add $15 per book. TOTAL $A February 1997  85 VINTAGE RADIO By JOHN HILL The combined A-B battery eliminator The year 1927 was notable in radio history because it marked a real change in the type of receiver being offered for sale. For the first time, radios that plugged into household power became practical and a number of makes and models were made available. While there were mains-operated receivers around before 1927, they were few and far between and not many could be de­ scribed as being really successful. But valves such as the 26, 27, 71A and 80 changed all that and made workable mains-pow­ ered radios possible. From that time onward, radio receivers became better and better. Prior to 1927, almost every radio was battery-powered and the cost of replacing those batteries was a major problem. To help counter this prob­ lem, special devices such as “B” bat­ tery eliminators and “A” battery trickle chargers were developed. Of course, these money saving accessories were only of use in elec­trified areas but that included most of the cities and big towns, even back then. For the benefit of younger readers, it may useful to clari­fy the terms “A”, “B” & “C”, as applied to batteries or associat­ed circuits. The term “A” bat­ tery was used for the filament battery The old Van Ruyten battery eliminator is shown here stripped, ready for repairs. Like most vintage radio equipment it was in a fairly sorry state. 86  Silicon Chip and, by usage, the filament circuit as a whole. The term “B” battery was used for the high tension battery and its asso­ciated circuitry, while the “C” battery was for grid bias cir­cuits. Of course, battery-powered valve receivers continued in use for a long time after 1927, in some cases until the late 1950s and early 1960s. It took that long for the electricity grid to reach some of the more remote regions of the country. The battery eliminator Electrification was a mixed blessing for some country folk in that, although their homes had electric power, its arrival meant the obsolescence of some existing household appliances, including the battery radio. In many instances, however, these radios were kept in use by the same device that powered many early battery receivers – the battery eliminator. The more modern versions were actually combined “A” and “B” elim­ inators. This type was never on offer in the 1920s because a satisfactory A battery eliminator was beyond the technology of the day. Such a device required large capacitors and a rec­ tifier capable of passing an amp or more of current. Although such things were available at the time, their large size and high price excluded them from being used in domestic radio applica­tions. As a result, the rechargeable “A” battery continued in use in combina­ tion with a trickle charger. This was the best that could be done at the time. The combined “A-B” battery elim­ inator of the post-war years solved this problem by using a copper oxide rectifier and large value electrolytic capacitors. Battery receivers made during this period used low consump­tion 1.4V These old electrolytic capacitors were next to useless. Three had virtually no capacitance while the fourth had an internal short. this month’s Vintage Radio will delve into its con­struction, operation and restoration. This particular eliminator uses a 5Y3GT valve rectifier for the high tension or “B” voltage supply and a copper oxide recti­fier for the filament or “A” voltage supply. Both voltages are well filtered using chokes and electrolytic capacitors. There is also a rheostat to adjust the output voltage of the “A” circuit. The copper oxide rectifier was an early solid state device and the one in the Van Ruyten is quite small. It provides full wave rectification in con­ junction with a centre tapped trans­ form­er winding. It was an interesting exercise to check it and com­pare its performance with a pair of 1A silicon diodes. In this particular setup, both recti­ fiers performed simi­larly, producing exactly the same voltage under load. And although the silicon diodes, which are quite small, ran warm under test, the copper oxide rectifier remained quite cool. Because it worked so well, the old rectifier was put back into service so as to keep the unit working with as many of the original components as possible. At least the comparison proved that a couple of silicon power diodes could be used to replace the copper oxide rectifier in this circuit if the need ever arose, without altering the output voltage of the unit. Output adjustment This view shows the copper oxide low tension rectifier in the foreground, with the replacement electrolytics to the left. The new electros were mounted on a piece of thick cardboard as they were too small to be held by the original clamps. valves and had considerably reduced low tension re­quirements compared to receivers from the 1920s and 1930s. A 4-valve set using 1.4V valves con­ sumes only 250mA of filament current. By comparison, a single old 201A valve pulled 250mA at 5V. An “A” battery eliminator circuit using a transformer (which it shares with the “B” eliminator), a copper oxide recti­fier, a choke and a pair of 500µF electrolytics could supply the filament requirements of a late-model battery radio quite easily. Combined “A-B” eliminators kept many battery re­ceivers working without the need to trade-in or modify the re­ceiver for AC operation. Restoring an eliminator Battery eliminators are not that com­ mon these days but that doesn’t mean that they are not worth finding. Any working “A-B” eliminator is a very convenient way to operate a vintage battery radio receiver. Recently, I was lucky enough to find such a unit, a Van Ruyten, and Now this old battery eliminator, like most other power supplies of that era, is unregulated in both the “A” and “B” cir­cuits. To counter this problem a 6-ohm rheostat is incorporated into the “A” circuit to help compensate for various loads that may be applied. This allows the correct voltage to be delivered to suit a particular current demand and there is enough adjust­ ment to allow use at 1.4V and 2.0V, although the latter situation is very marginal. The adjustment procedure for set­ ting the “A” supply is as follows: (1) with the eliminator hooked up to the receiver, connect a voltmeter to the “A” battery terminals of the set; (2) back off the rheostat as far as it will go before switching on; and (3) slowly advance the rheostat until the desired voltage is shown on the voltmeter. And that’s it! February 1997  87 to fit the new switch to vary the “B” voltage. Performance This view shows the power transformer, the 5Y3GT HT rectifier and the two Trimax brand filter chokes (beneath the chassis). The original “B” supply had no ad­ justment for altering the output voltage but this facility was added during the restoration procedure. There were a number of other items that needed attention and the old Van Ruyten was completely stripped so as to make the necessary repairs. These repairs included: replacement of the filter capacitors and the 5Y3GT rectifi­ er valve, a new power cord, repainting of the steel cabinet and, as mentioned above, alterations to the high tension circuit to permit the “B” voltage to be varied. The modification to the “B” cir­ cuit involved adding a multi-pole 3-position switch so that two pairs of resistors could be switched into the plate circuits of the high tension rectifier. The resistors used here were 10kΩ and 27kΩ and they reduced the “B” voltage to approximately 60V at 4mA and 45V at 2mA. The unloaded voltage without the resistors is 150V. This simple modification was nec­ essary so that the elimina­tor could be used on 1- and 2-valve regenerative receivers, which have much lower “B” voltage and current requirements. Another reason for incorporating the variable “B” voltage switch was to fill a hole in the control panel. Origi­ nally the power cord exited through this hole but a previous repairer has cut a new power cord hole (and a fairly ragged one at that) in a far better posi­ tion on the side of the cabinet. As a result, the leftover hole in the control panel was the logical place A close-up view of the two filter chokes prior to installation. The larger one at the rear is for the low tension supply. Because the low tension supply is unregulated, the supply vol­tage varies with the load. This wirewound rheostat is used to adjust the “A” voltage to suit the receiver. 88  Silicon Chip With the restoration completed, a couple of wirewound potentiometers were set up in conjunction with volt and amp meters to monitor the Van Ruyten’s output capabilities. The results only proved just how good modern regulated power sup­ plies really are compared to something from the Van Ruyten’s era. The “B” voltages can vary by as much as 50V, depending on the load, while “A” voltages varied by up to 2.5V. No wonder there is a rheostat in the “A” circuit so that the voltage could be adjusted to suit the load – see Table 1 for details. Table 1 shows that the “A” supply is capable of delivering no more than 340mA at 2.0V. Any additional cur­ rent is obtained at the cost of reduced voltage. These figures seemed to indicate that an average 1930s battery receiver with 2V valves would not work sat­ isfactorily since it would draw more filament current than the eliminator could supply. It was time to find out whether or not this was to be the case. The only 2V battery receiver availa­ ble for test was a 1937 4-valve Radiola with a valve complement of 1C6, 1D5, 1K6 and 1D4. All up, these valves draw about 540mA so it was fairly unlikely that the Van Ruyten would be able to fully power this particular receiver. And so it proved to be. Even with the rheostat fully ad­vanced, the “A” voltage was a meagre 1.6V and while the set worked, it certainly lacked performance. In fact, it sounded a bit sick! Fairly obviously, the old Van Ruyten power pack was de­signed for receivers with 1.4V valves. Replacing the “A” battery eliminator with a modern 1A regu­lated power supply showed that the 2V valves would work down to 1.75V. Below that, the performance starts drops off, with the receiver virtually ceasing to function at 1.5V. Not being the type that gives up easily, I checked all my spare battery valves to see if any were more suitable to the task. Valve filaments are made to tolerances so some must consume less current than others. Eventually, I selected another set of valves that con­sumed slightly less cur­ P.C.B. Makers ! If you need: P.C.B. High Speed Drill P.C.B. Guillotine P.C.B. Material – Negative or Positive acting Light Box – Single or Double Sided – Large or Small Etch Tank – Bubble or Circulating – Large or Small U.V. Sensitive film for Negatives Electronic Components and Equipment for TAFEs, Colleges and Schools FREE ADVICE ON ANY OF OUR PRODUCTS FROM DEDICATED PEOPLE WITH HANDS-ON EXPERIENCE Prompt and Economical Delivery • • • • • • • • The finished battery eliminator, or “Portapac” as it was called, includes a rotary switch on the front panel. This switch serves to fill the hole originally used for the power cord and allows the “B” voltage to be varied in three steps. The rubber grommet near the output terminals allows screwdriver adjustment of the “A” voltage rheostat. rent than the originals. This squeez­ed the operating voltage up to just over 1.7V and the old receiver fired up much better than before. This was mainly due to a particu­ lar 1D4 output valve which had a much more economical filament con­ sumption than the others. That extra tenth of a volt made a considerable difference to the set’s performance and another tenth would bring the set up to its full potential. (Editorial note: it has been suggested in the past that running valve filaments at less than their rated voltage, but with normal anode voltage applied, may shorten the life of the valves.) Incidently, the “B” voltage drops to around 125V when the old Radiola is working properly. The maximum “B” battery voltage rating for the receiver is 135V. Eliminator hazards Unfortunately, using an unregulated “A” supply can have serious repercus­ sions if one of the valve filaments fails. That’s because the voltage to the other valves immediately increases because of the reduced load. In the case of the 1D4 (with its 0.25A filament) failing, approximately 3V would be applied to the other valve fila­ments. While a minute or so of that sort of treatment probably wouldn’t do much harm, it mightn’t do 60-year Table 1 “A” Voltage 1.5V 2.0V 4.0V “B Voltage” 150V 120V 110V 100V Max. Current 400mA 340mA 60mA Current unloaded 10mA 15mA 20mA old battery valves much good either. So if you are contemplating rebuilding an old battery eliminator, a regulated supply is the way to go. Who knows or cares what’s inside when the lid is screwed on? However, such an approach is a marked depar­ ture from the original circuit and is an unacceptable restoration as far as some collectors are con­cerned. Trying out the old Van Ruyten eliminator on a 2-valve bat­ tery re­ ceiver also proved a disappointment, although the results were expected. What may be an acceptable level of hum in a loud­speaker is not acceptable through headphones. It mattered not whether the “A” or the “B” supply, or both, were used – the hum levels were distracting. Small regenerative receivers using headphones perform SC best on batteries. • KALEX 40 Wallis Ave E. Ivanhoe 3079 Ph (03) 9497 3422 FAX (03) 9499 2381 • ALL MAJOR CREDIT CARDS ACCEPTED TRANSFORMERS • TOROIDAL • CONVENTIONAL • POWER • OUTPUT • CURRENT • INVERTER • PLUGPACKS • CHOKES STOCK RANGE TOROIDALS BEST PRICES APPROVED TO AS 3108-1994 SPECIALS DESIGNED & MADE 15VA to 7.5kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 February 1997  89 Silicon Chip Back Issues September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. April 1989: Auxiliary Brake Light Flasher; What You Need to Know About Capacitors; 32-Band Graphic Equaliser, Pt.2; The Story Of Amtrak Passenger Services. May 1989: Build A Synthesised Tom-Tom; Biofeedback Monitor For Your PC; Simple Stub Filter For Suppressing TV Interference; The Burlington Northern Railroad. July 1989: Exhaust Gas Monitor; Experimental Mains Hum Sniffers; Compact Ultrasonic Car Alarm; The NSW 86 Class Electrics. September 1989: 2-Chip Portable AM Stereo Radio (Uses MC13024 and TX7376P) Pt.1; High Or Low Fluid Level Detector; Studio Series 20-Band Stereo Equaliser, Pt.2. October 1989: FM Radio Intercom For Motorbikes Pt.1; GaAsFet Preamplifier For Amateur TV; 2-Chip Portable AM Stereo Radio, Pt.2; A Look At Australian Monorails. November 1989: Radfax Decoder For Your PC (Displays Fax, RTTY & Morse); FM Radio Intercom For Motorbikes, Pt.2; 2-Chip Portable AM Stereo Radio, Pt.3; Floppy Disc Drive Formats & Options; The Pilbara Iron Ore Railways. December 1989: Digital Voice Board; UHF Remote Switch; Balanced Input & Output Stages; Operating an R/C transmitter; Index to Volume 2. January 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages; A Look At Very Fast Trains. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random 4-Digit Combination Lock; 5W Power Amplifier For The 6-Metre Amateur Transmitter; Index To Volume 3. January 1991: Fast Charger For Nicad Batteries, Pt.1; Have Fun With The Fruit Machine; Two-Tone Alarm Module; LCD Readout For The Capacitance Meter; How Quartz Crystals Work; The Dangers of Servicing Microwave Ovens. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. March 1990: Delay Unit For Automatic Antennas; Workout Timer For Aerobics Classes; 16-Channel Mixing Desk, Pt.2; Using The UC3906 SLA Battery Charger IC; The Australian VFT Project. April 1990: Dual Tracking ±50V Power Supply; Voice-Operated Switch (VOX) With Delayed Audio; 16-Channel Mixing Desk, Pt.3; Active CW Filter; Servicing Your Microwave Oven. June 1990: Multi-Sector Home Burglar Alarm; Low-Noise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car; Fitting A Fax Card To A Computer. 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. August 1990: High Stability UHF Remote Transmitter; Universal Safety Timer For Mains Appliances (9 Minutes); Horace The Electronic Cricket; Digital Sine/Square Generator, Pt.2. September 1990: Low-Cost 3-Digit Counter Module; Simple Shortwave Converter For The 2-Metre Band; the Bose Lifestyle Music System; The Care & Feeding Of Battery Packs; How To Make Dynamark Labels. October 1990: The Dangers of PCBs; Low-Cost Siren For Burglar Alarms; Dimming Controls For The Discolight; Surfsound Simulator; DC Offset For DMMs; NE602 Converter Circuits. November 1990: How To Connect Two TV Sets To One VCR; Build An Egg Timer; Low-Cost Model Train Controller; 1.5V To 9V DC Converter; Introduction To Digital Electronics; Build A Simple 6-Metre Amateur Band Transmitter. December 1990: The CD Green Pen Controversy; 100W DC-DC Converter For Car Amplifiers; Wiper Pulser For Rear Windows; March 1991: Remote Controller For Garage Doors, Pt.1; Transistor Beta Tester Mk.2; A Synthesised AM Stereo Tuner, Pt.2; Multi-Purpose I/O Board For PC-Compatibles; Universal Wideband RF Preamplifier For Amateur Radio & TV. April 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. May 1991: 13.5V 25A Power Supply For Transceivers; Stereo Audio Expander; Fluorescent Light Simulator For Model Railways; How To Install Multiple TV Outlets, Pt.1. June 1991: A Corner Reflector Antenna For UHF TV; 4-Channel Lighting Desk, Pt.1; 13.5V 25A Power Supply For Transceivers, Pt.2; Active Filter For CW Reception; Tuning In To Satellite TV. July 1991: Loudspeaker Protector For Stereo Amplifiers; 4-Channel Lighting Desk, Pt.2; How To Install Multiple TV Outlets, Pt.2; Tuning In To Satellite TV, Pt.2; The Snowy Mountains Hydro Scheme. August 1991: Build A Digital Tachometer; Masthead Amplifier For TV & FM; PC Voice Recorder; Tuning In To Satellite TV, Pt.3; Step-By-Step Vintage Radio Repairs. September 1991: Digital Altimeter For Gliders & Ultralights; Ultrasonic Switch For Mains Appliances; The Basics Of A/D & D/A Conversion; Plotting The Course Of Thunderstorms. October 1991: Build A Talking Voltmeter For Your PC, Pt.1; SteamSound Simulator Mk.II; Magnetic Field Strength Meter; Digital Altimeter For Gliders, Pt.2; Military Applications Of R/C Aircraft. November 1991: Build A Colour TV Pattern Generator, Pt.1; A Junkbox 2-Valve Receiver; Flashing Alarm Light For Cars; Digital Altimeter For Gliders, Pt.3; Build A Talking Voltmeter ORDER FORM Please send me a back issue for:  July 1989  September 1989  January 1990  February 1990  July 1990  August 1990  December 1990  January 1991  May 1991  June 1991  October 1991  November 1991  April 1992  May 1992  September 1992  October 1992  April 1993  May 1993  September 1993  October 1993  February 1994  March 1994  July 1994  August 1994  December 1994  January 1995  May 1995  June 1995  October 1995  November 1995  March 1996  April 1996  August 1996  September 1996  January 1997                   September 1988 October 1989 March 1990 September 1990 February 1991 July 1991 December 1991 June 1992 January 1993 June 1993 November 1993 April 1994 September 1994 February 1995 July 1995 December 1995 May 1996 October 1996                   April 1989 November 1989 April 1990 October 1990 March 1991 August 1991 January 1992 July 1992 February 1993 July 1993 December 1993 May 1994 October 1994 March 1995 August 1995 January 1996 June 1996 November 1996                   May 1989 December 1989 June 1990 November 1990 April 1991 September 1991 March 1992 August 1992 March 1993 August 1993 January 1994 June 1994 November 1994 April 1995 September 1995 February 1996 July 1996 December 1996 Enclosed is my cheque/money order for $­______or please debit my: ❏ Bankcard ❏ Visa Card ❏ Master Card Signature ____________________________ Card expiry date_____ /______ Name _______________________________ Phone No (___) ____________ PLEASE PRINT Street ________________________________________________________ Suburb/town ________________________________ Postcode ___________ 90  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A7 Overseas (airmail) ...................................... $A10 Detach and mail to: Silicon Chip Publications, PO Box 139, Collaroy, NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details or fax the details to (02) 9979 6503.  Card No. For Your PC, Pt.2. December 1991: TV Transmitter For VCRs With UHF Modulators; Infrared Light Beam Relay; Colour TV Pattern Generator, Pt.2; Index To Volume 4. January 1992: 4-Channel Guitar Mixer; Adjustable 0-45V 8A Power Supply, Pt.1; Baby Room Monitor/FM Transmitter; Experiments For Your Games Card. March 1992: TV Transmitter For VHF VCRs; Thermostatic Switch For Car Radiator Fans; Telephone Call Timer; Coping With Damaged Computer Directories; A Guide To Valve Substitution In Vintage Radios. April 1992: IR Remote Control For Model Railroads; Differential Input Buffer For CROs; Understanding Computer Memory; Aligning Vintage Radio Receivers, Pt.1. May 1992: Build A Telephone Intercom; Electronic Doorbell; Battery Eliminator For Personal Players; Infrared Remote Control For Model Railroads, Pt.2; Aligning Vintage Radio Receivers, Pt.2. June 1992: Multi-Station Headset Intercom, Pt.1; Video Switcher For Camcorders & VCRs; IR Remote Control For Model Railroads, Pt.3; 15-Watt 12-240V Inverter; A Look At Hard Disc Drives. July 1992: Build A Nicad Battery Discharger; 8-Station Automatic Sprinkler Timer; Portable 12V SLA Battery Charger; Multi-Station Headset Intercom, Pt.2. August 1992: An Automatic SLA Battery Charger; Miniature 1.5V To 9V DC Converter; 1kW Dummy Load Box For Audio Amplifiers; Troubleshooting Vintage Radio Receivers; MIDI Explained. October 1992: 2kW 24VDC - 240VAC Sinewave Inverter; Multi-Sector Home Burglar Alarm, Pt.2; Mini Amplifier For Personal Stereos; A Regulated Lead-Acid Battery Charger. January 1993: Flea-Power AM Radio Transmitter; High Intensity LED Flasher For Bicycles; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.4; Speed Controller For Electric Models, Pt.3. February 1993: Three Projects For Model Railroads; Low Fuel Indicator For Cars; Audio Level/VU Meter (LED Readout); An Electronic Cockroach; 2kW 24VDC To 240VAC Sinewave Inverter, Pt.5. March 1993: Solar Charger For 12V Batteries; Alarm-Triggered Security Camera; Reaction Trainer; Audio Mixer for Camcorders; A 24-Hour Sidereal Clock For Astronomers. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; Windows-based Logic Analyser. July 1993: Single Chip Message Recorder; Light Beam Relay Extender; AM Radio Trainer, Pt.2; Quiz Game Adjudicator; Windows-based Logic Analyser, Pt.2; Antenna Tuners – Why They Are Useful. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80Based Computer; A Look At Satellites & Their Orbits. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags - How They Work. Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. March 1994: Intelligent IR Remote Controller; 50W (LM3876) Audio Amplifier Module; Level Crossing Detector For Model Railways; Voice Activated Switch For FM Microphones; Simple LED Chaser; Engine Management, Pt.6. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. April 1994: Sound & Lights For Model Railway Level Crossings; Discrete Dual Supply Voltage Regulator; Universal Stereo Preamplifier; Digital Water Tank Gauge; Engine Management, Pt.7. November 1995: Mixture Display For Fuel Injected Cars; CB Transverter For The 80M Amateur Band, Pt.1; PIR Movement Detector; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.1; Digital Speedometer & Fuel Gauge For Cars, Pt.2. May 1994: Fast Charger For Nicad Batteries; Induction Balance Metal Locator; Multi-Channel Infrared Remote Control; Dual Electronic Dice; Simple Servo Driver Circuits; Engine Management, Pt.8; Passive Rebroadcasting For TV Signals. June 1994: 200W/350W Mosfet Amplifier Module; A Coolant Level Alarm For Your Car; 80-Metre AM/CW Transmitter For Amateurs; Converting Phono Inputs To Line Inputs; PC-Based Nicad Battery Monitor; Engine Management, Pt.9. July 1994: Build A 4-Bay Bow-Tie UHF Antenna; PreChamp 2-Transistor Preamplifier; Steam Train Whistle & Diesel Horn Simulator; Portable 6V SLA Battery Charger; Electronic Engine Management, Pt.10. August 1994: High-Power Dimmer For Incandescent Lights; Microprocessor-Controlled Morse Keyer; Dual Diversity Tuner For FM Microphones, Pt.1; Build a Nicad Zapper; Engine Management, Pt.11. September 1994: Automatic Discharger For Nicad Battery Packs; MiniVox Voice Operated Relay; Image Intensified Night Viewer; AM Radio For Weather Beacons; Dual Diversity Tuner For FM Microphones, Pt.2; Engine Management, Pt.12. October 1994: Dolby Surround Sound - How It Works; Dual Rail Variable Power Supply; Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Temperature Controlled Soldering Station; Engine Management, Pt.13. November 1994: Dry Cell Battery Rejuvenator; Novel Alphanumeric Clock; 80-Metre DSB Amateur Transmitter; Twin-Cell Nicad Discharger (See May 1993); Anti-Lock Braking Systems; How To Plot Patterns Direct To PC Boards. December 1994: Dolby Pro-Logic Surround Sound Decoder, Pt.1; Easy-To-Build Car Burglar Alarm; Three-Spot Low Distortion Sinewave Oscillator; Clifford - A Pesky Electronic Cricket; Cruise Control - How It Works; Remote Control System for Models, Pt.1; Index to Vol.7. January 1995: Sun Tracker For Solar Panels; Battery Saver For Torches; Dolby Pro-Logic Surround Sound Decoder, Pt.2; Dual Channel UHF Remote Control; Stereo Microphone Preamplifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. December 1995: Engine Immobiliser; 5-Band Equaliser; CB Transverter For The 80M Amateur Band, Pt.2; Subwoofer Controller; Dolby Pro Logic Surround Sound Decoder Mk.2, Pt.2; Knock Sensing In Cars; Index To Volume 8. January 1996: Surround Sound Mixer & Decoder, Pt.1; Magnetic Card Reader; Build An Automatic Sprinkler Controller; IR Remote Control For The Railpower Mk.2; Recharging Nicad Batteries For Long Life. February 1996: Three Remote Controls To Build; Woofer Stopper Mk.2; 10-Minute Kill Switch For Smoke Detectors; Basic Logic Trainer; Surround Sound Mixer & Decoder, Pt.2; Use your PC As A Reaction Timer. March 1996: Programmable Electronic Ignition System; Zener Tester For DMMs; Automatic Level Control For PA Systems; 20ms Delay For Surround Sound Decoders; Multi-Channel Radio Control Transmitter; Pt.2; Cathode Ray Oscilloscopes, Pt.1. April 1996: Cheap Battery Refills For Mobile Telephones; 125W Power Amplifier Module; Knock Indicator For Leaded Petrol Engines; Multi-Channel Radio Control Transmitter; Pt.3; Cathode Ray Oscilloscopes, Pt.2. May 1996: Upgrading The CPU In Your PC; High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1996: Making Prototype Parts By Laser; VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. March 1995: 50W/Channel Stereo Amplifier, Pt.1; Subcarrier Decoder For FM Receivers; Wide Range Electrostatic Loudspeakers, Pt.2; IR Illuminator For CCD Cameras; Remote Control System For Models, Pt.3; Simple CW Filter. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Build A Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. April 1995: Build An FM Radio Trainer, Pt.1; A Photographic Timer For Darkrooms; Balanced Microphone Preamplifier & Line Filter; 50-Watt Per Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. May 1995: What To Do When the Battery On Your PC’s Mother­ board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. December 1996: CD Recorders ­– The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. June 1995: Build A Satellite TV Receiver; Train Detector For Model Railways; 1W Audio Amplifier Trainer; Low-Cost Video Security System; Multi-Channel Radio Control Transmitter For Models, Pt.1; Build A $30 Digital Multimeter. January 1997: How To Network Your PC; Using An Autotransformer To Save Light Bulbs; Control Panel For Multiple Smoke Alarms, Pt.1; Build A Pink Noise Source (for Sound Level Meter calibration); Computer Controlled Dual Power Supply, Pt.1; Digi-Temp Monitors Eight Temperatures. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Door Minder; Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, May 1990, February 1992, September 1992, November 1992 and December 1992 are now sold out. All other issues are presently in stock. For readers wanting articles from sold-out issues, we can supply photostat copies (or tear sheets) at $7.00 per article (includes p&p). When supplying photostat articles or back copies, we automatically supply any relevant notes & errata at no extra charge. A complete index to all articles published to date is available on floppy disc at $10 including packing & postage. February 1997  91 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. 12V to 6V conversion It is common practice, when work­ ing on old cars, to upgrade the elec­ trical system from 6V to 12V. This is mainly for conven­ience because 12V batteries and light bulbs are far more readily available than 6V equipment and if your old car is running on 12V you can always use the battery from your modern car to start it. The bulbs and ignition system can be replaced with 12V types and a 12V dynamo or alternator can be fitted. The car’s starter motor can stand the extra voltage under normal use and there’s a bonus in that it spins the engine faster, making start­ing easier. Where the 6V to 12V conversion starts to get a bit tricky is when you have to deal with items such as fuel gauge senders, fan motors, wiper motors, original radios, solenoids, etc that can’t be replaced with 12V equivalents. One method sometimes adopted is to create a separate 6V source and wire it separately to the equipment that needs it. This can be messy, especially if you need both 12V and 6V feeds through the ignition switch. My purpose in writing is to ask if SILICON CHIP can design a small cheap 12V to 6V device that can be fitted to the supply wire of each 6V item that Mono output from stereo amplifier I have a 30W stereo amplifier and wish to run a mono exten­sion loudspeaker. I joined the left and right stereo active signal outputs but this just causes the amplifier to overload and cut out. How can I add a mono speaker to play both channels? Thanks for your magazine. I have every copy which I cherish. (K. A., Castle Hill, NSW). • As you have found, you cannot 92  Silicon Chip has to stay that way. This seems to me to be a fairly neat solution to the problem. If you can come up with such a device, it would be of great help to the old car movement. (R. W., Yeronga, Qld). • We have published two circuits which could form the basis of a 12V to 6V converter for use in cars. The first is the PCB Drill Speed Controller published in January 1994. This would be good for about one amp or so and is available as a kit from Dick Smith Electronics. Second, another drill speed con­ troller was published in August 1992 in the Circuit Notebook pages. Provided the output transistor had a suitable heatsink, it could supply sev­ eral amps. In either case, you would adjust the circuit to deliver about 6.8V, for good performance from 6V accessories. Solenoid-operated door strike I have built the magnetic card reader described in the January 1996 issue of SILICON CHIP and I am going to use it as a door lock. I need to know where to obtain a solenoid lock and the cost. And could you please tell me how to wire it up. (D. H., Como West, NSW). • It should be possible to purchase a solenoid-operated door strike from join the active left and right stereo outputs to drive a mono loud­ speaker. In effect, this connection would place a short across the two amplifier channels for the differ­ ence signal. Your existing left and right speakers would not work in stereo either. The only way to drive a mono speaker is to mix the left and right channel signals via isolating resis­ tors (say 22kΩ) and then feed the mixed signal to a separate power amplifier which will then drive your mono speaker. most locksmiths. Most are powered from 12V (for just short time) and could be operated by the relay on the Magnetic Card Reader. Make sure you purchase a solenoid strike to suit your particular door lock. Remote control for outdoor use I am trying to design and build a remote controller for outside use with a minimum of 10 buttons, all of which must be configurable as toggles or mo­ mentary action. I know I could adapt the IR remote train controller circuit of the Railpower design produced by yourselves but my first question is would the IR system be prone to erratic operation if used outside in any kind of weather ranging from hot sunlit days to rainy nights? I ask this because I realise that the Railpower unit and most IR control­ lers as used for TV etc are designed for inside use, not outdoors. My next question is that if no problems would arise from using this system in those conditions, then where could I source the ICs. (S. B., Sydney, NSW). • No infrared system can be expect­ ed to work outdoors in daylight. The only effective outdoor remote control will be RF-based, probably UHF, to obtain a small size. You could adapt the Railpower system to UHF, using one the UHF circuits featured in our February 1996 issue. Better still, why not adapt the 8-channel design fea­ tured in February 1996 to UHF. It is a rela­tively simple matter to swap the IR transmitter output stage to a UHF output. Protecting fragile loudspeakers My wife has a Mitsubishi hifi unit and up till now, keeps blowing up the speakers. Although a bit of a pain, I have been able to overcome this prob­ lem through the local electronic shops being able to supply same or similar. This time she has also put paid to one of the output power transistors, an NEC D587. Unfortunately, this has stumped the locals, who don’t require a lot of stumping, if I may say so. If you can help me in sourcing a supplier I would be most grateful. The only reason the speakers go is because my other half is getting hard of hearing. A hearing aid would be cheaper but this is a no-go area. Hope you can help. (H. F., Perth, WA). • We suggest that you consider in­ stalling PTC polyswitch thermistors in series with the speakers. These go temporarily open circuit if their current rating is exceeded. We suggest you try installing a type RXE090 or RXE110 PTC thermistor. These are available from Jaycar Electronics in Perth. Phone (09) 328 8252. As far as the output transistors are concerned, why not contact your local Mitsubishi service agent? They are at 329 Collyer Road, Bassandean WA 6054. Phone (09) 377 3400. Troubleshooting the Insulation Tester The Insulation Tester described in the May 1996 issue of SILICON CHIP is a very useful piece of equipment but I have found that the voltages produced are somewhat lower than expected. The 100V, 250V and 500V ranges all produce about 150V. The 600V and 1000V ranges both produce about 450V. This is an improvement upon the 19V, 148V, 465V, 540V and 290V being produced from the respective (lowest to highest) voltage ranges after first completing the project but still not optimal. I effected this improvement by replacing the CMOS oscillator chip as I had noticed that the CRO traces from the oscillator when the 100V range was selected were almost nonexistent. Could the replacement IC be faulty as well or is there a problem with the error amplifier? Keep those great projects coming. (N. P., Seven Hills, NSW). • Your problem is possibly due to incorrect transformer wind­ings. Check that the secondary is wound in the same direction as the primary wind­ ing as shown in the diagram of Fig.4 (page 35, May 1996). Try winding the secondary in the opposite direction to the way it was. In addition, check that the range Dud micro in Dolby decoder I have recently purchased the Dolby Pro-Logic Surround De­ coder, Mk 2, as described in the November & December 1995 issues. My problem is that, upon powering up the unit, the dis­play does not flash “—” at all and the relays do not change state. In addition, the noise LED does not light when the noise sequencer button is pressed. I have measured the voltages on the power supply module and all are ±5%. I have also measured the voltages on ICs 1-9 as indicated on page 78 of your magazine article (bearing in mind the errata previ­ ously advertised). I have identified that when the unit is powered up, the measured voltage at PC0 is 0V and remains at 0V; ie, it does not go high. Hence Q1 does not switch on to energise the relays. I have re­moved IC6 and applied 5V to each of the 7-segment LEDs and ascertained that the 7-segment displays are not burnt out but are in good working order. resistors on switch S2b are arranged on your PC board in the correct order. Flatpack transistor washers I am looking to use the new flatpack MJL21194/21193 tran­ sistors as fea­ tured in the April 1996 issue but am having trouble finding the isolating mica/silicon washers. The magazine article shows a washer bigger all round than the transistor. Where did you get yours? (R. G., Chapel Hill, Qld). • You can obtain these washers from Altronics in Perth. They have two types: silicone/fibreglass Cat. H-7220 x 4 or mica type Cat. H-7120 x 4. You can phone Altronics on 1 800 999 007. Trigger happy laser pistol user I am writing in regards to the laser pistol and electronic target described in the December 1996 issue of SILI­ CON CHIP. Could you please suggest a way to alter the circuit so that the Each of the switches S5, S6 and S7 produce 5V at pins 17, 18 and 19 of IC6 respectively when not pressed and 0V at the same pins when the respective switches are pressed. Pin 2 of IC6 remains at 5V all the time. I have noted that the voltage sig­ nals for “B, A, E, R, S, D” are 5.4V, 1.0V, 2V, 2V, 2V respectively and that they do not change under any condition. I have noticed, though, that IC6 was supplied as an MC­ 68HC705C8ACP, not an MC68HC­ 705C8P. I assume that this is just another variation of the MC68HC­ 705C8P microprocessor chip and is a valid substitute. Could you please help me identify what is the problem with this kit? (C. C., Leem­ing, WA). • It appears that the microproces­ sor (IC6) is either not programmed or faulty. If it is programmed it will be marked accordingly. Either way, the microprocessor should be replaced. The ACP version is slightly different to the P version but we have programmed them to accommodate this difference. laser will remain on constantly when­ ever the trigger is pressed down? It occurred to me to short the 1.5kΩ resistor but I figured this would still create a pulse because of the 100µF capacitor. Your help in this matter would be much appreciated. (J. N., Greenacre, NSW). • As you suggest, shorting the 1.5kΩ resistor will allow the laser to stay on while ever the trigger is pulled. The 100µF capacitor can then be omitted. Notes & Errata MultiMedia Loudspeakers, November 1996: the perspective diagram on page 61 shows the wrong enclosure depth; it should be 224mm. Control Panel For Multiple Smoke Alarms, December 1996: a 47kΩ re­ sistor should be added to the circuit between pin 11 of IC5f and the +9V rail, while one of the 100µF bypass capacitors on the +9V rail should be 10µF. Note also that the parts list should show four 1kΩ resistors (not SC three). February 1997  93 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. TOTAL $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. Buy five and get them postage free. $A SUBSCRIPTIONS  New subscription – month to start­­____________________________  Renewal – Sub. No.________________    Gift subscription  RATES (please tick one) 2 years (24 issues) 1 year (12 issues) Australia (incl. GST)  $A135  $A69.50 Australia with binder(s) (incl. GST)**  $A159  $A83 New Zealand (airmail)  $A145  $A77 Overseas surface mail  $A160  $A85  $A250 Overseas airmail  $A125 **1 binder with 1-year subscription; 2 binders with 2-year subscription YOUR DETAILS Your Name_________________________________________________ GIFT SUBSCRIPTION DETAILS Month to start__________________ Message_____________________ _____________________________ _____________________________ Gift for: Name_________________________ (PLEASE PRINT) Address______________________ _____________________________ (PLEASE PRINT) Address___________________________________________________ State__________Postcode_______ ______________________________________Postcode_____________ Daytime Phone No.____________________Total Price $A __________ Signature  Cheque/Money Order  Bankcard  Visa Card  Master Card ______________________________ Card No. Card expiry date________/________ Phone (02) 9979 5644 9am-5pm Mon-Fri. Please have your credit card details ready 94  Silicon Chip OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE A POWER AMPLIFIER: 500W 4/8/16, 50/70/100V 5 R.U. $250. 8-channel microphone mixers 600 in/out 1 R.U. $180. All excellent order, ex airport service. Several available, ship anywhere. Fax (070) 55 0371. AUSTRALIA’S BIGGEST FIELD DAY for Radio and Electronics enthu­siasts. Come to the Central Coast Field Day, Wyong Racecourse, 8.30 a.m. to 3.30 p.m. Sunday 23rd February for truck loads of new and used Radio and Electronic gear at bargain prices. Dis­plays, lectures, radio fox hunts and equipment demonstrations throughout the day. Enquiries phone (043) 40 2500. C COMPILERS: Ever ything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140.00 for the set. Debug monitors: $70 for 6 CPUs. All compilers inc ‘HC12, XASMs and monitors: $480. 8051/52 or 80C320 Simulator (fast): $70. Disassemblers for 12 CPUs only $75. Try the new C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo disk: FREE. All prices + $5 p&p. GRAN­TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www.mpx.com. au/~lgrant. WEATHER FAX DECODERS: for HF, VHF/UHF use with JVFAX, MAXISAT and SATFAX. Details D. G. Hopkins, 4 Handsworth Street, CAPALABA 4147. (07) 3390 3328. COMPLETE C BAND SATELLITE SYSTEM: 4.6m segmented mesh dish with pole and self install instructions, dual input receiver with low threshold and inbuilt dual axis positioner, 2 actu- CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $10.00 for up to 12 words plus 50 cents for each additional word. Display ads (casual rate): $25 per column centimetre (Max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly on a separate sheet of paper, fill out the form below & send it with your cheque or credit card details to: Silicon Chip Classifieds, PO Box 139, Collaroy, NSW 2097. Or fax the details to (02) 9979 6503. ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. ✂ Enclosed is my cheque/money order for $­__________ or please debit my Signature­­­­­­­­­­­­__________________________ Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ ators, multi-polarity feedhorn, 20 degree LNB plus all cables. Never used. Private sale. $3,800. (086) 32 1035. SATELLITE DISHES: international reception of Intelsat, Panamsat, Gori­ zont,Rimsat. Warehouse Sale – 4.6m dish & pole $1499; LNB $50; Feed $75. All accessories available. Videosat, 2/28 Salisbury Rd, Hornsby. Phone (02) 9482 3100 8.30-5.00 M-F. MICROCRAFT PRESENTS: Dunfield (DDS) products are now available exstock at a new low price; please ask for our catalogue. Micro C, the affordable “C” compiler for embedded applications. Versions for 8051/52, 8086, 8096, 68HC08, 6809, 68HC11 or 68HC16 $139.95 each + $3 p&h • Now on special is the SDK, a package of ALL the DDS “C” compilers for $399 + $6 p&h • EMILY52 is a PC based 8051/52 high speed simulator $69.95 + $3 p&h • DDS demo disks $7 + $3 p&h • VHS VIDEO from the USA (PAL) “CNC X-Y-Z using car alter­nators” (uses car alternators as cheap power stepper motors!) $49.95 + $6 p&h (includes diagrams) • Device programming EPROMs/PALs etc from $1.50 • Fixed price electronic design and PCB layout • Credit cards accepted • All goods sent certified mail • Call Bob for more de­tails. MICRO­CRAFT, PO Box 514, Concord NSW 2137. Phone (02) 9744 5440 or fax (02) 9744 9280. EASY PIC’n Beginners Book to using MicroChip PIC chips $50, Basic Compiler to clone Basic Stamps into cheap PIC16C84’s $135, CCS C Compiler $145, heaps of other PIC stuff, Programmers from $30, Real Time Clock, A-D. Ring or fax for FREE promo disk. WEB search on Dontronics, PO Box 595, Tullamarine 3043. Phone (03) 9338 6286. Fax (03) 9338 2935. RAIN BRAIN 8-STATION SPRINKLER KIT: Z8 smart temp sensor, LED display, RS232 to PC. Uses 1 to 8 DALLAS DS1820. Call Mantis Micro Products, 38 Garnet Street, Niddrie, 3042. P/F/A (03) 9337 1917. mantismp<at>c031.aone.net.au February 1997  95 BASIC STAMPS & PIC Tools Enhancements from Microchip Opto Isolators from Scott Edwards Electronics PIC Chips MICROMINT DOMINO PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (067) 722 777 – may time out to Mobile 014 036 775 Fax (067) 728 987    (Credit Cards OK) http://www.microzed.com.au OPTO 22 Micro Engineering Labs MicroZed Computers PICBASIC Compir and proto boards PicStic BLACKJACK Specialising in easy-to-get-going hard/software kits. Stamp kits now have a compiler for 16C58 Send 2 x 45c stamps for information package (most credit cards OK) Advertising Index Av-Comm.....................................33 Dick Smith Electronics..... 8,9,34-37 Earthquake Audio........................83 Emona.........................................73 Freedman Electronics..................83 Harbuch Electronics....................83 MEMORY * MEMORY * MEMORY SPECIAL! (Ex Tax) 1Mbx9 – 70ns $15 30-pin Simms 651 Forest Rd, Bexley 2207 makes all the project PCBs published in SILICON CHIP and other Australian magazines Tel +61 2 9587 3491 Fax 9587 5385 E-mail rcsradio<at>cia.com.au SIMMS (Parity/No Parity) 4Mb 30 PIN-70 $50 $42 4Mb 72 PIN-70 $44 $29 8Mb 72 PIN-70 $80 $50 16Mb 72 PIN-70 $144 $114 32Mb 72 PIN-70 $288 $216 EDO SIMMS 8Mb (1Mbx32) – 60ns $47 16Mb (2Mbx32) – 60ns $108 32Mb (4Mbx32) – 60ns $219 MAC MEMORY 8/16Mb DIMMS $63/113 32/64Mb DIMMS $252/488 16Mb P’BOOK 520/540 $258 LIFETIME WARRANTY!! Ex Tax Pricing – Delivery $8. Pricing as at 07/01/96. Phone for latest. Sales Tax 22%. Credit Cards Welcome. We Also Buy And Trade-In Memory. PELHAM Memory Pty Ltd C COMPILERS: Dunfield compilers are now even better value. Everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $140.00 each. Macro Cross Assemblers for these CPUs + 6800/01/03/05 and 6502: $140 for the set. Debug monitors: $70 for 6 CPUs. All compilers, XASMs and monitors: $400. 8051/52 or 80C320 simulator (fast): $70. Disassemblers for 12 CPUs only $75. Demo disk: FREE. All prices + $5 p&p. GRANTRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph/Fax (02) 9631 1236 or Internet: http://www.mpx.com.au/~lgrant MicroZed has16C84 at $8, 16C58A at $5, 1C71 at $7. JW versions too. Discounts start at 10 pieces. Add $5 post on IC orders. Available now: new Stamp book Ver. 1.7, $35 post $8.00. PCBs MADE, ONE OR MANY. Low prices. Hobbyists welcome. Sesame Electronics (02) 9554 9760. HOMEMADE GENERATORS: how to instructions. Eight pages free text and colour photos on the Internet at http:// www.onekw.co.nz/onekw 96  Silicon Chip LASER PRINTER MEMORY 4Mb HP 4&5 $53 COMPAQ 8Mb ARMADA 1100 $139 All other models available $Call TOSHIBA 8Mb Portege/ Sat EDO $134 16Mb Portege/ Sat EDO $229 16Mb Tecra 500/610 Sat $229 All other models available $Call CACHE 256Kb PIPELINE BURST $21 256Kb 7200/8500 $92 VIDEO MEMORY 256K x 16 70ns (SOJ) $12 1Mb 7200/7500/9500 $83 SO DIMMS 8Mb/16Mb $82/138 Suite 6, 2 Hillcrest Rd, Ph: (02) 9980 6988 Pennant Hills, 2120. Fax: (02) 9980 6991 Email: pelham1<at>ozemail.com.au B/W CCD CAMERA. Chinon CX103 miniature PCB-board 46 x 44mm, 25mm high. Automatic electronic shutter. 7V to 16V. 2 lux. $95. PELTI­ER MODULE 12V, 4.4A, $18. LCD 16 x 2, no b/l, $9. All prices include air postage & data sheet. DIY Electronics, Hong Kong. Fax: 852 2725 0610. Email diykit<at>hk. super.net. See web site for direct component buying www.hk.super.net/~ diykit MICROS: 68HC705C8ACFN PLCC $11.50. 68HC705C8ACFS DIL $11.00. Erased Chips 68705P3 $5.00. DISPLAYS: LCD 2 x 20 $15; LED HPDL­2416 $13; VFD 2 x 40 $50. Min qty 4 of $7.50 p+p. Michael (03) 9803 3535. CAR/RALLY COMPUTER KIT: including fuel sensor & speed sensor. 68HC05 & HC11 Development Systems: Oztechnics, PO Box 38, Illawong NSW 2234. Phone (02) 9541 0310. Fax (02) 9541 0734. http://www.oz­technics.com.au/ WANTED VALVES: new and used. All types required. Phone: 047 51 5620. Instant PCBs................................96 Jaycar ............................IFC, 45-52 Kalex............................................89 Kits-R-US.....................................84 Macservice....................................3 MicroZed Computers...................96 Oatley Electronics........................29 Pelham........................................96 Rod Irving Electronics .......... 77-81 Silicon Chip Back Issues....... 90-91 Silicon Chip Bookshop.................85 Silicon Chip Binders....................76 Silicon Chip Model Railway Projects Book..........................OBC Silicon Chip Software....................7 Tortech.........................................89 Zoom Magazine.........................IBC _________________________________ PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd, 651 Forest Rd, Bexley, NSW 2207. Phone (02) 9587 3491. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. R AUSTRALIA’S BEST AUTO TECH MAGAZINE It’s a great mag... but could you be disappointed? If you’re looking for a magazine just filled with lots of beautiful cars, you could be disappointed. Sure, ZOOM has plenty of outstanding pictorials of superb cars, but it’s much more than that. If you’re looking for a magazine just filled with “how to” features, you could be disappointed. Sure, ZOOM has probably more “how to” features than any other car magazine, but it’s much more than that. If you’re looking for a magazine just filled with technical descriptions in layman’s language, you could be disappointed. Sure, ZOOM tells it in language you can understand . . . but it’s much more than that. If you’re looking for a magazine just filled with no-punches-pulled product comparisons, you could be disappointed . Sure, ZOOM has Australia’s best car-related comparisons . . . but it’s much more than that If you’re looking for a magazine just filled with car sound that you can afford, you could be disappointed. Sure, ZOOM has car hifi that will make your hair stand on end for low $$$$ . . . but it’s much more than that. If you’re looking for a magazine just filled with great products, ideas and sources for bits and pieces you’d only dreamed about, you could be disappointed. Sure, ZOOM has all these . . . but it’s much more than that. But if you’re looking for one magazine that has all this and much, much more crammed between the covers every issue, there is no way you’re going to be disappointed with ZOOM. Look for the June/July 1998 issue in your newsagent From the publishers of “SILICON CHIP”