Silicon ChipJuly 1998 - Silicon Chip Online SILICON CHIP
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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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.dse.com.au Contents Vol.11, No.7; July 1998 FEATURES   4  Troubleshooting Your PC; Pt.4 Installing a modem and sorting out the problems – by Bob Dyball 12  How To Hold A Garage Sale Get rid of your junk and make some money – by Julian Edgar 40  Understanding Electric Lighting; Pt.8 Metal halide lamps and their properties 88  Special Subscriptions Offer Installing A Modem And Sorting Out The Problems– Page 4 Buy a subscription before end of September 1998 and get a bonus wallchart PROJECTS TO BUILD 18  Build A Heat Controller Use it to adjust your electric radiator or electric blanket to a comfortable level – by John Clarke 54  15-Watt Class-A Amplifier Module New class-A design boasts ultra-low distortion and noise – by Leo Simpson 66  Simple Charger For 6V & 12V SLA Batteries Easy to build unit features a 0-12 hour mechanical timer – by Branco Justic Build A Heat Controller For Electric Radiators – Page 18 80  An Automatic Semiconductor Analyser It automatically identifies the device and the leads – by Andy Wood SPECIAL COLUMNS 28  Serviceman’s Log It was only a piece of broken plastic – by the TV Serviceman 44  Satellite Watch What’s new on satellite TV – by Garry Cratt 69  Radio Control Radio-controlled gliders; Pt.3 – by Bob Young Low Distortion 15-Watt Class-A Amplifier Module – Page 54 72  Computer Bits Network cards and networking – by Greg Swain & Jason Cole 76  Vintage Radio Australia’s last valve radios – by Rodney Champness DEPARTMENTS   2  Publisher’s Letter 17  Mailbag 26  Circuit Notebook 32  Product Showcase 53  Order Form 90  Ask Silicon Chip 94  Market Centre 96  Advertising Index Charger For 6V & 12V Sealed Lead Acid Batteries – Page 66 July 1998  1 PUBLISHER'S LETTER Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager 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 Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Ross Tester Philip Watson, MIREE, VK2ZPW Bob Young 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: $59 per year in Australia. For overseas rates, see the subscription page in this issue. Editorial & advertising offices: Unit 8, 101 Darley St, Mona Vale, NSW 2103. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9979 5644. Fax (02) 9979 6503. ISSN 1030-2662 and maximum * Recommended price only. 2  Silicon Chip Measuring low level audio signals This month we’re very pleased to feature an ultra-low dis­tortion amplifier module running in class-A. The module is the direct result of readers’ letters asking for a state-of-the-art design over a number of years. Quite frankly, we haven’t been keen on the concept but having decided to do it, we were a little stunned at how good it has turned out to be. Sure, it has the usual drawback of class-A operation in that it is very ineffi­cient, using a lot of power for not very much power output – only 15W into 8Ω. But the distortion is a great deal lower than any amplifier we have produced in the past. And because the distortion is so low, it has caused us real problems in trying to determine just how low it is. Our audio distortion test set, made by Audio Precision, is perhaps the best commercially available equipment in the world but even it is not good enough to fully test this new amplifier module. And this caused us to use a new distortion monitoring technique, which was suggested by Doug Self in a recent issue of the English magazine “Electronics World”. Briefly, it makes use of the signal averaging facility in a digital sampling scope, to remove random noise from very low level repetitive signals. This is an interesting turn of events and shows how a digital oscilloscope, normally not regarded as ideal for observ­ing low-level analog signals, actually can be used with much greater effect than a conventional analog scope. By way of expla­nation, even though digital oscilloscopes are becoming widely used in laboratories around the world, designers still tend to turn to their trusty analog scopes when they want to look at low-level analog signals. The same situation occurs in our own lab. We use the digital scope all the time and often feature its recorded waveforms in our articles. But there are times when only the analog scopes will do. The reason is not hard to find. Digital scopes inevitably show even the cleanest of waveforms as having little wiggles all over them. But analog scopes show clean sinewaves when the wave­form is clean. Is that not true? Well, it all comes down to perceived reality and what we’re used to seeing on scope screens. Because analog scopes display repetitive waveforms as many hundreds or even thousands of sweeps of the beam across the screen, they filter out low level noise. Digital scopes don’t; their sampling method inevitably catches the noise and the glitches and so we see all the garbage on the waveform. We’re not used to this and it clashes with our normal perception of reali­ty. Most designers don’t like it. However, when analog scopes are called upon to display noisy waveforms they have a problem because the noise obliterates the repetitive signal buried under it. But it turns out that we can use the averaging mode of a digital scope to effectively remove the random noise from a low-level signal and allow the repetitive component to be clearly displayed. So the often-des­pised digital scope turns out to have unseen advantages. The problem with this averaging technique is that it again challenges our concepts of how signals should appear on a screen. Is this “filtered” version reality? The truth is that every method of measurement only gives us a partial view of what’s really happening in a circuit or piece of equipment. We become used to this “partial view” and accept it as the whole truth but again, it isn’t, is it? There will always be another way of measuring a circuit or producing a better result. There will always be something new; some new circuit technique, product or measurement method. That’s the challenge of electronics and it is very satisfying. Leo Simpson M croGram Computers Infra Red Serial Links Year 2000 BIOS Card support for 4 HDD’s and 2 FDD’s. Even Pentium motherboards are not immune to the Year 2000 bug! The Year 2000 BIOS Card solves the problem of progression from 1999 to 2000 as well as 21st century leap years. It is an 8-bit card which provides year 2000 support for motherboards with a BIOS which only stores the year with two digits. i.e. 97 instead of 1997. Cat. No. 2565 Cat. No. 3359 Cat. No. 2632 The IrJet is available in two models. Connect via standard serial port for computers without a builtin IR port or directly to a motherboard with built-in IR port pin outs. It communicates via an infra red signal between notebooks, desktop PC’s or other IrDA compliant infrared devices. A transfer rate of up to 115,200 bps is supported over $129 3.5 metres. Most file management software is supported and it is Win 95 compatible. Year 2000 BIOS Card Multi-PC Controller 4 Way 2 Control A controller with two control keyboards, monitors, mice and sound equipment which allow two operators simultaneous access to four computers (not the same computer). Auto scan or manual selection (key strokes or switch) of the PC’s is provided. This desktop model is designed for multi file server installations. A 19” rack mounted model is also available. Cat. No. 11636 Multi-PC Controller 4 way 2 Control $899 Uninterruptable Power Supplies Whether you require a line interactive or true on-line UPS, we have the right one for you. From entry level UPS’s for stand alone PC’s to intelligent microprocessor controlled UPS’s for professional high performance file server applications. Cat. No. 8645 Cat. No. 8646 Cat. No. 8574 Cat. No. 8591 UPS 500VA UPS 750VA UPS 1500VA UPS 2000VA $360 $470 $1120 $3060 Diagnostic Card - PCI & ISA Bus A dual bus diagnostic card! Simply invert the card to test the other bus. It identifies POST BIOS faultcodes & displays error codes. Diagnostic error codes are provided for AMI, AWARD & Phoenix BIOS. Suitable for 486 / 586 / 686 / Pentium II compatible systems. Cat. No. 8421 Cat. No. 8518 Infra Red Serial Link Infra Red Motherboard Link Compact Keyboard When desk space is at a premium an 80 key keyboard with full 101 key functionality will come in handy. It has dimensions of only 297(W) x 152(L) x 30(D) mm. Cat. No. 8238 Compact 81 Key $129 $89 HDD Cont ISA IDE BIOS Ultra DMA HDD IDE Controller Give your existing motherboard Ultra DMA support. This IDE controller for the PCI bus gives Ultra DMA performance to suitable hard drives and CD-ROM drives. Up to 33.6Mb/s. HDD Controller PCI Ultra DMA IDE 8 EIDE Device Card Cat. No. 2320 CD ROM Rewritable RICOH Kit ISA Quad-Channel EIDE Card Cat. No. 6378 Cat. No. 6412 Cat. No. 6379 Cat. No. 6358 CD ROM Rewritable RICOH Kit SCSI CD-ROM Rewitable RICOH Kit IDE CD-ROM Rewritable Media CD ROM Writable CD’s Blue/Silver TV Display on PC Monitor $985 $860 $40 $8 Cat. No. 2326 4 Port RS232 16550 COM 1-8 IRQ 3-15 sales<at>mgram.com.au $295 The dual port card is now available with 16650 UART chips with 32 byte FIFO buffers. Cat. No. 2333 Two Port 16650 Serial Card $159 Plug & Play PCI models also available. Hard Disk Drive Duplicators These hard disk drive duplicators offer a low cost, high performance solution whether you want high-volume 1 master to 8 drive copying or quick, low volume, 1 master to 2 drive copying. Features include: • FAT32 compatible • Track by track, file by file, whole or partial drive copying • Accepts different geometry drives including 2.5” and 3.5” drives • Copy Win 95 operating system in minutes Cat. No. 6426 Cat. No. 6427 E & OE Hard Drive Duplicator Two Drives $2899 Hard Drive Duplicator Eight Drives $6499 All prices include sales tax info<at>mgram.com.au Australia-Wide Express Courier (To 3kg) $10 We welcome Bankcard Mastercard VISA Amex Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261 FreeFax 1 800 625 777 $199 Avoid slowing down your hard drive access speed The Ricoh MP6200S CD-RW by putting your CD ROM on a separate controller. allows you to erase & rewrite a Cat. No. 6385 CD ROM IDE ISA Controller Card $31 CD-RW disc over 1000 times. Included in the kit is Easy CD Pro Serial Cards 95/NT & Direct CD software, 1 blank CD-RW rewrite- We have a large range of serial cards providing able CD & 4 blank CD-R write once CDs. Reads 6 x either 1, 2, 4 or 8 ports. Our most popular and speed & writes 2 x speed. Applications include data versatile single, dual & four port cards feature high backups & taping of music or video & audio clips. It speed 16550 UARTS, COM 1 to 8 and IRQ 3 to 15. is backward compatible with other CD-ROM media & Cat. No. 2297 1 Port RS232 16550 COM1-8, IRQ 3-15 $80 Cat. No. 2239 2 Port RS232 16550 COM 1-8 IRQ 3-15 $99 will function as a normal CD-ROM drive. Come and visit our online catalogue & shop at www.mgram.com.au Dealer Enquiries Welcome $169 This card supports up to 8 EIDE devices in a single slot. It has an on-board intelligent ROM BIOS that configures all drives automatically without need of additional software drivers. Other features include:• Provides 8 selectable I/O port addresses & IRQ’s • Supports DOS, Windows, Win 95, Windows NT, UNIX, SCO UNIX, Novell Netware 2.x,3.x,4.x, OS/2 2.0, Warp. $79 A computer monitor has much higher resolution and stability than a TV, hence you get a great picture with this item. It is an easy-to-use external unit which Cat. No. 3362 Diagnostic card for PCI / ISA $229 connects between your PC and monitor and displays Cat. No. 3128 Diagnostic Card for ISA $69 TV on your PC. It features an IR remote control and Computer Security Kit supports channel auto scan and memory. Ideal for preventing the kids from Cat. No. 3372 TV Display on PC Monitor $299 destroying your data! No software BIOS Upgrade required. A small keypad mounts in a If your motherboard BIOS does not support LBA 3.5in bay which allows an access (Logical Block Addressing) or hard drive capacities code to be entered. Two access greater than 528Mb, overcome these limitations codes distinguish the level of user so that the floppy with our BIOS card. Supports hard drives up to drive is automatically locked when accessed by the 8.4GB capacity & needs no software drivers. second user. The keyboard & mouse may be Cat. No. 2564 HDD ISA BIOS Card $59 locked/unlocked at any time. Also available, a BIOS controller card with Cat. No. 8493 Security Kit Hardware Access Lock $89 Phone: (02) 4389 8444 $107 Vamtest Pty Ltd trading as MicroGram Computers ACN 003 062 100 MICROGRAM 0798 Fax: (02) 4389 8388 Web site: www.mgram.com.au FreeFax 1 800 625 777 July 1998  3 COMPUTERS: Installing a Modem The Maestro Jetstream is a 33.6K external voice/data/fax modem. It’s available from Dick Smith Electronics for $99.00. Troubleshooting Your PC; Pt.3 Modems can sometimes be tricky things to get going but they needn’t be if you follow a few simple rules. Here’s a useful guide to install­ation and troubleshooting. By BOB DYBALL There are several things to carefully consider when buying a modem. One of the most important is whether to buy an internal unit or an external unit. Each option has its advantages and disadvantages. Because it is a plug-in card that fits inside the computer, an internal modem doesn’t need a plastic case, a serial cable or a power supply plug­ pack. As a result, an internal modem will usually be less expensive than 4  Silicon Chip the equivalent external version from the same manufacturer. On the other hand, users new to modems might find the front panel LEDs on an external model to be useful indicators as to what is happening. An external modem can also be less intimidating to install for the novice, since you don’t have to open up the PC’s case. If you have a 486 (or earlier) PC, check using MSD to see if you have a 16550 UART on a least one of the COM ports in your system. A 16550 UART has a 32-byte buffer and this alleviates the data bottleneck that the 1-byte buffer on an 8250, 82450 or 16450 UART can create in slower PCs. If you don’t have a 16550 UART, you should consider fitting a highspeed serial port with a 16550 UART if you wish to use an external modem. On the other hand, most newer PCs and almost all internal modems already have a 16550 UART fitted to them. Cables and adaptors Check the serial ports on the rear of your computer before buying an external modem. Some external modems are not supplied with an RS232 cable, while others include a cable that has only a 9-pin or a 25-pin connector. Some modems, however, include a cable that has both types of connector at one end, while others may come with an adaptor. If you have a 9-pin male D socket on the PC, try to avoid using a 9 to 25-way adaptor to connect the cable. It’s better to buy a cable that’s fitted with a 9-pin plug. This will reduce the weight on the back of the socket and ensure a more reliable connection. Getting it right the first time The way in which you set up an internal modem will depend on whether you have a PnP system or whether you have to configure the card manually for a non-PnP system. As you will have gathered from last month’s article, you need to put a little thought into the installation if you have a non-PnP system, in order to avoid resource conflicts. If an internal modem refuses to work, many people automati­ cally assume that the unit is faulty but that’s seldom the case. Instead, an IRQ conflict with some other device is the most common problem, while plugging the phone lead into the wrong socket on the back of the modem would be a close runner-up. If you are convinced that everything is correct, try using a terminal program (such as Windows Terminal under Windows 3.x or HyperTerminal under Windows 95). As a test, type AT&V and press Enter (in the terminal window) - the modem should display its current configuration. If it does, do this several times and check the output. If it varies, you might have a handshaking or serial port problem. By the way, if nothing appears in the terminal window as you type, it’s because local echo is turned off. To turn it on, type ATE1 and press the Enter key. Any commands that you enter in the terminal window will now be visible as they’re typed. Windows 95 users can also check the modem status by first double-clicking the Modems icon in Control Panel. You then click the Diagnostics tab, select the modem port and click the More Info button. If the modem is working OK, you should see a dialog box similar to that shown in Fig.9. Among other things, this shows the IRQ, the port, the port address and the UART type. If the modem isn’t working and you’re running Windows 95, double-click the System icon in Control The Spirit 56K internal modem plugs into an ISA slot on the motherboard ($179.00 from Dick Smith Electronics). Panel and select the Device Manager tab. This will show any resource conflicts that may be present. Common problems Now let’s take a look at some other common modem problems: (1). Windows for Workgroups 3.11 locks up, needs cold re­boot: this fault only affects WFW 3.11 when you have a fast 486 or Pentium-based PC and a serial port with a 16550 UART. To overcome this problem, the file “Serial.386” in the C:\Windows\System directory needs to be updated using Microsoft update WG1001. Many BBS systems distribute this as WG1001.EXE or WG1001.ZIP. All you have to do is unzip the file and copy the updated Serial.386 file over the old one and restart Windows. Note that you may have to use a DOS communications program to get the update, since Windows will usually lock up when using the modem until you replace the Serial.386 driver. (2). Modem dials out but programs do not respond after dialling: this symptom is often due to a COM port conflict. Usually, it’s due to two COM ports that have the same I/O port address – one on the motherboard and one on your internal modem card or extra serial card. In this case, the set- Fig.8: if you are using an external modem, use the MSD utility to confirm that it can be plugged into a COM port that has a 16550 UART. July 1998  5 Fig.9: double clicking the Modems icon in Control Panel (Win95), then clicking Diagnostics and More Info lets you check that the modem is responding OK. tings may allow you to get a dial-out response from the modem but that’s all, as the two COM ports will return different values. (3). Modem dials, sounds like it connects, but then drops out: if there’s a problem connecting to another modem, it may be due to the negotiation of error correction and data compression. Usually, it’s best to leave these on for best performance, as you can get between 20% and 400% better throughput if the connection is successful. To see if compatibility is a problem, try disa­ bling compression and then, failing that, error correction. Your modem’s manual will usually list the AT command codes and these can be tacked on the end of the initialisation string. Alternatively, in Windows 95, you can disable compression and error correction by double-clicking Modems in Control Panel, then clicking Properties, Con- nections and Advanced and deselecting the relevant boxes. (4). Modem dials, connects, stays on line for 5-10 minutes, then drops out: this is commonly caused by a Touchfone T200 (or similar) model telephone. What happens is that the telephone circuit is designed to “grab” power from the line every 5-10 minutes to maintain the last number redial and other memories. Try disconnecting all T200s from the line to see if the problem disappears. If the problem persists, try disconnecting any other phones. Some answering machines and cordless phones can also cause problems, as can someone picking up another phone that’s connected to the line. Don’t forget that it might be the other end that has the problem phones, particularly if you normally have no problems when connected to other parties. The current Touchfone 400 does­n’t cause any problems by the Some Useful Modem Commands ATE1 Turn on command echo. This lets you see what you are typing in the terminal window. ATE0 turns command echo off. AT&V Display active and stored configuration profiles. ATLn Control loudspeaker volume (n = 0-3). AT&Wn Store the active profile in stored profile n (n = 0 or 1). 6  Silicon Chip way but it is always advisable to turn off “call waiting” before using a modem, as the call waiting tones can cause a modem to disconnect. (5). Can’t dial out – no dial tone, or modem dials but no carrier: many modems have two telephone sockets, one usually labelled “line” the other “phone”. Unfortunately, many people confuse the functions of these two sockets but it’s really quite simple. The “line” socket connects to the “telephone line” (ie, it is connected to the wall socket), while the “phone” socket allows an optional telephone handset to be connected. This allows you to use the telephone (when the modem is not in use, of course) without having to unplug the modem or resort to using a double adaptor with long trailing cords. If there is only one socket on the back of the modem, then you have no option but to use a double adaptor on the wall socket if you wish to connect a telephone in parallel with the modem. Sometimes, a modem will have non-standard connections to the RJ-45 connector (the small click-in connector that goes into the modem). If you can’t get a dial tone and you are not using the cable that came with the modem, try going back to this cable - it just might be the answer. (6). Modem dials and gets wrong numbers, or there is no carrier, a voice message or a busy signal: this is a common problem for Windows 95 users. What happens is that Windows 95 automatically inserts a “0” in front of the area code that’s entered for the number to be dialled. So if you enter 02 for the area code, for example, the modem will actually dial 002. The answer is simple: just leave out the leading 0 when entering area codes. Note, however, that Windows 95 is only “smart” enough to add the leading 0 if it knows you are in Australia. This means that you must set the dialling properties up correctly in the first place. To do this, go to Control Panel, double click Mo­dems, and click Dialling Properties. Now enter your physical location in the box marked “I am dialling from” and enter Austra­lia in the box marked “I am in this country/region”. Finally, and most important of all, enter the area code without the leading zero. (7). Where is the modem driver?: when you use the Add New Hardware wizard in the Windows 95 Control Panel, Windows 95 attempts to automatically identify your new modem for you (pro­vided you select the autodetect option). It does this by sending a series of AT commands to the modem and then checking the re­sponses against a list. If you don’t get a match, use the driver supplied on the floppy disc that’s included with the modem. Alternatively, you can skip the autodetection routine and choose the brand and model yourself from the listed alternatives. If you can’t find a match, try choosing a “Standard Modem” of the appropriate speed from the list of generic modem models. If you have problems finding a Windows 3.x or DOS driver, that’s normal because there aren’t any. Instead, it is the commu­nications program that supplies the driver. If you cannot find an exact match for your modem, try choosing a Generic High Speed or Generic Hayes type from the list. Alternatively, for a fax-modem, try a Generic Class 1 or a Generic Class 2 type etc, depending on the modem FaxClass. You can check this by typing AT+FCLASS=? in a terminal program (eg, Windows Terminal under Windows 3.x, Hyper­Terminal under Windows 95, or Telix or QModem under DOS). (8). Problems detecting busy or dial tones: the noises that older telephone Fig.11: typing AT&V in a terminal program should force the modem to display its current active profile plus any stored profiles. If you do this several times and the output varies, then you may have a handshaking or serial port problem. exchanges make for the busy and dial tones are different to those made by the newer exchanges. As a result, you might find that an older modem will work in one area (ie, with an old exchange) whereas a new modem won’t. To add to the frustra­tion, you can often take the same modems to a different area and find that the new one now works (because it’s connecting to a newer exchange), whereas old faithful now doesn’t. If there is no check box to turn dial tone and busy tone detection on or off, you can use the additional settings box to add the appropriate commands. Use ATX3 (or simple X3 if it adds the AT command for you) to disable dial tone detection, ATX2 to disable busy tone detection and ATX1 to disable both). The de­fault is usually ATX4 which enables both dial tone and busy tone SC detection. Windows 98: A Few Useful Tips The new features of Windows 98 will be more apparent to users of older versions of Windows than to users of more recent versions such as Windows 95b (Win95 OSR2 or OSR250). Many of the “new” features were already in place in the OSR2 and OSR25 versions, such as (optional) FAT32 formatting for the hard disc drive. Some of the changes are available as add-ons to Windows 95 (eg, USB support and an updat­ed dial up adapter), while other changes are completely new to ’98. The FAT32 system is limited in usefulness for drives under 1Gb and cannot really be used under 512Mb. Above 1Gb, it offers speed improvements of up to 50% and effectively provides 28% more hard drive space through more efficient storage. A utility is included for FAT16 to FAT32 conversion. If you want to run a dual-boot system, then FAT32 might not be for you. That’s because you will not be able to access data in a FAT32 partition unless you have Windows 95b or Windows 98 running. It’s a good idea to have the INF file for your VGA moni­tor handy when you are upgrading to Windows 98. I can assure you that it is quite annoying to that find the default refresh rate of the VGA card doesn’t fit in with that of your VGA monitor after upgrading. If, after booting Windows 98 for the first time, you find that the display is out of sync, simply ctrl-alt-del a couple of times and when you get the “Starting Windows 98” message, hit F8 and select Safe-Mode. The computer should now boot into Safe Mode with the standard 640 x 480 16-colour view. You cannot normally add your INF file for the monitor using the Add New Hardware feature in Control Panel while in Safe Mode. The best procedure here is to double-click on System (also in Control Panel) and select Device Manager. Next, double-click the default monitor, then click Driver, Update Driver. You should now be able to install the correct drivers using the “Have Disk” option. July 1998  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: www.dse.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.dse.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.dse.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.dse.com.au How to hold a garage sale Want to make $500 for a day’s work and at the same time get rid of lots of junk that you no longer want? Here’s how! Text and Photos by Julian Edgar It sounds too good to be true, doesn’t it? You sell a lot of bits and pieces cluttering up your shed and home. In return you are given cash in hand and it’s all done by spending a pain­less day helping people cart away your junk! It’s called holding a garage sale and 12  Silicon Chip it’s a fabulous way of getting money for jam. Don’t just keep accumulating that electronic and mechanical stuff until the day you die. Don’t leave it in your estate. Turn it into money right now. We show you what to do. garage rt of any successful Signs are a vital pa are ich wh ns ke fancy sig sale. Many people ma car. ng i ss­ pa a m fro nce hard to read at a gla d signs effective - an nd You need to keep the spe u yo t tha r lla do ry cheap. Remem­ber, eve out ht aig e is taken str setting up for the sal n be p, effective sign ca ea ch A s. fit pro of your on ck bla ed ard box paint made from a cardbo fore be x bo the ide ins ick two faces. Place a br you seal it up. el their items, Some people don’t lab don’t clean their , ms ite ir don’t price the ny items! Make ma l sel n’t do d an – items rkling clean. spa is g hin ryt sure that eve st and dirt du in d This gauge was covere und in the shed. – it had been lying aro d the brass an The face was cleaned which is old ing yth An . polished a bit ”, “collectors’ ue tiq should be labelled “an or all three! – ” ing est item” or “inter On each of the black faces of the boxes paint the ‘garage sale’ signs. If you do n’t have a small paint writing, don’t buy one brush to do the ! That’s just money that you have to then make up in sales. Instead, a small pie ce of scrap foam rubber or cloth can be pressed into use as a temporary brush. It works well. If white paint around the you have any old white or nearhouse, use that. Ag saved! Place the sig ns at the nearest ma ain, it’s dollars jor lead the customers to your house with mo road and then re signs. Check the signs during the day; it’s not unusual for pranksters to change their orientat ion. This phone was clean ed of! Items which don’t until it looked like new . . . well, kind have an obvious use (who wants a dial telephone?) need to be imaginatively lab elled – hence, the “excellent 2nd phone ” tag. In fact, the young woman who bo this phone had anoth ught er use for it – she wa nted it for her daught­ er’s cubby ho use. This potential use a good label. would also have made July 1998  13 e lot”, or “the set” words “the pair”, “th the ce pri the in­cluded” (it’s ter af Adding el such as “hardware lab er oth els an re, He r think that the lab is encouraging. been useful. Don’t eve s than six of the 120 ve ha uld wo gs) ba in the no les ring this garage sale aren’t effective - du out and clear signs. lay nt lle ce ex the d on attendees commente This were placed together. for Here two ‘like’ items ir pa the e say “I’ll tak must encourages people to u yo t tha te No es. r lin sing pri five bucks” and simila sur A g. cin xible on pri e don’t be prepared to be fle opl pe of r be num !) yway (surprising to me, an d walking ing over the cash an bargain, simply hand price if the op dr ly, ral ne . Ge number away with the goods a g yin bu is ­r custome one. you’re desperate, the ive s n­ e item is a very expe of items, or the sal During the sale not one person looked at this item and ask ed what it was. You can be guarantee d that if it had only been price labell ed some people would have queried its purpose. Even more would have loo ked at the handle, wondered what it wa s, not asked, and then moved on. This group would have included potential bu yers. If people say “What’s this thing, mate?” then you have not labelled it appropriately. That applies particularly to electronic goods that the average pe rson is not familiar with. If you have two ite ms that are similar but one is of better quality than the other, place the m together with different pric­e s. That way, people are encouraged to say eit he or conversely “this one r “wow, this one’s a bargain” is more expensive be much better quality ­cause it is ”! Either way, they will view your pricing technique as reasonable. Note tha t even with the clear label, one gentleman asked wh at voltage the horn speakers work on! asuring instruments I seem to love all me tube and bought this pitot- hand store for ond sec a anemometer at e the instrument, $30. But while I lik if someone were So it. d I’ve never use it, I reckon I could to give me $150 for ­ity in my soul to ros ne ge find sufficient ting a very high let them have it! Put ich you (just wh ing price on someth lets you celebrate maybe) want to sell over a fistful of s nd ha when someone eve too much when dollars – and not gri one item that was s wa is they don’t. Th oom at the end of returned to my storer the sale. 14  Silicon Chip speaker This is a twin-cone Spice up the goods! (forgotten) a at w ne it t I bough with a big mag­net. n’t know do I it. ve never used as if bargain price and ha d ke loo e sur it t bu is that I what its power rating te No ! ay handling, anyw it has a high power the h wit e con er inn the deliberately covered for their after a sub-woofer label - most people this way t bu r ive dr e con twin car wouldn’t want a Then, you up! it k l at least pic those same people wil l happen! never know what wil It’s worth a try put ting out expensive ite ms. Some (rich) people walk aro und with $400-500 is their wallets, and I needed only one such person a burning desire to who had own an oscilloscope. Where you are selling large items bo publishes catalogs, see ught from a company that if you can find the ori and stick it to the pri ginal ad ce tag. That way, pe ople can be quite overcome by the massive price reduct at the same time ch ion and can eck out the equipme nt specs. akers were cessity. These old spe player. NoTurn virtue into a ne with an ancient record speakers given to me together record player and the record the y bu the one was going to nk eed. The solution? Ju “excellent were poor quality ind ing speaker boxes as be the sed to the player and label clo d ce pla s wa ir pa The a focal point for re-speakering”! me ca be y so that the entrance to the sale, d. wn the path. They sol to people walking do The words “never use d”, “brand new”, “m int condition” and so on have a magnetic att raction. If the product is in the original packagin g and complete with an ori ginal price tag, so mu ch the better. But make sur e that you have a goo d reason for selling the item, ready to trot out when the cynical cus tomer asks why you’r e getting rid of it! If you set your displa y the wall to mount lar tables against a wall, you can use ger, additional signs. You may feel slightly foolish when you’re writing out all of these signs, but they certainly ma ke a difference. If you have heavy items that you don’t want to move, you ca n announce these in this way. One ad ditional sign I used said “Datsun Skyline 5-speed gearbox, $1 50”. No-one even ask ed about it, so I was glad that I hadn ’t lugged it out! Howe ver, it is wise to place on display as ma ny of the goods as you can. Incidentally, have a rad there’s not an oppres io playing during the sale. That way sive silence as peopl e inspect the goods. July 1998  15 circuit boards high. These printed Don’t set prices too ct one is fa in ponents on them; each have good com if t Bu . $1 n tha like $5 probably worth more s at your sale are ce pri t tha ng eli fe too high, customers get the quickly. If prices are red texta a high, they’ll move on h wit crossing them out about midday start attendance reductions. The peak ce pri in u’ll catch and marking yo d an early afternoon will usually be in the s. ce pri uced this wave with the red hold the sale must The area where you No-one is going to lit. ll be clean and we rk place covered happily walk into a da and cobwebs. tts bu in dirt, cigarette ange the entrance In fact, how you arr vital if you are is e sal to the garage their money. You to part people from g, friendly and min lco we want the area are setting up, positive. When you down the entrance ck ba frequently walk all looks from the path and see how it tial buyer. en pot a perspective of 16  Silicon Chip A sale that has items to interest every sin gle person who walks in off the street will be much more successful that one that interests only a few. Get everyone in your famil y (and extended famil friends) to contribu y, and te items for sale. If you are selling on behalf of someone else, you mu st get a clear idea of the pri ces that they expect, Almost everything on though. these tables sold, alo ng with heaps of the other items that you have seen in the rest of this story. At this single Sunday sal total customer count e, the wa (all profit!) was $406 s 120 and the sales figure .50. Add to that an other sale 6 months ago that ha d a roll-up of 165 an d sales of about $600 and you can see that garage sales really do work! Lay out your goods carefully. Small items should go at the fro graduating to larger nt, items (especially tho se that need suppor back. As sales occur, t) at always move the ite ms around so that the the seem constantly full. Stick the signs down tables with Blu-Tac or a sim adhesive, otherwise the wind or inquisitiv ilar e children will move Always remember to them. remove the signs as people buy the goods don’t need a huge am . You ount of stuff to ma ke money - there’s $150 worth of goods nearly shown in this photo. That’s potentially $1 in hand! 50 cash MAILBAG Serviceman is a legend I have enjoyed reading the Serviceman’s Log for many years. But after my experiences getting repairs done to my TV and video I am beginning to suspect that it is a work of fiction. His contribution to the March 1998 issue reinforced my suspicions. No TV repairer I have heard of operates anything like him. My TV repairer saw no connection between an electrical storm and my visit to his store with my TV. He didn’t listen when I described the faults, so neither were fixed when I picked the set up. Now he can’t get parts for my TV and it’s been in his shop for 6 weeks! He tried to tell me my remote control was faulty (I had tested it with my scope), so I had to show him that the fault was in the TV. He has never offered me a loan set! I routinely insist (politely, of course) that we turn on the device before I leave the shop to see if it’s fixed. I also do this whenever I buy anything new after getting too many DOA products. When I mention my repair saga to friends they all have similar stories of repairers. I suspect that the demise of the service industry is possi­ bly due to customers sharing my unpleasant experiences of getting repairs done, so choosing instead to buy a new one. L. McConaghey, Umina Beach, NSW. Comment: Our Serviceman agrees that some of his stories have an air of unreality about them and even he has trouble believing some of them but they do happen. Perhaps he’s just a legend in his own mind. Seriously, he does exist, the stories are real and his workshop is every bit as chaotic as the cartoons suggest. Service manual wanted I wonder if any fellow readers of SILICON CHIP may be able to help me obtain a service manual. I own a Panasonic UF400 fax machine (circa 1984) and although it is working, I would like to be prepared for when it eventually does die. I have tried Prime, High Country, Panasonic and their agents and about 80% of fax repairers in the Yellow Pages. None have been able to help. Perhaps, amongst the readers is someone who has serviced this model in the past and still has a service manual or at least the circuit diagram. I can make a photocopy if required, and if anyone can help I’d be glad to pay any reasonable costs. On the now old subject of having 230V mains forced upon us, it’s obviously a multinational company request to our puppet politicians. The argument that it helps for import/ export doesn’t hold. Appliance manufacturers have solved the problem of differ­ent voltages in different localities since reticulation of elec­ tric power began; either by providing a voltage selector switch or altering the windings in the motor/element/transformer. Look through an appliance catalog of 50 years ago and it’s not uncommon to find many domestic appliances, of the same model, available in 32, 110, 200 and 240VAC. The manufacturers didn’t seem to find this any great hardship – and this for our low population at the time, too. What is going to happen is a de­crease in the efficiency of the distribution system and all heating and most lighting appliances. This can be easily demon­ strated with a Variac. J. Hunter, St Leonards, NSW. Don’t take voluntary redundancy I must congratulate you on your Publisher’s Letter in the May 1998 issue of SILICON CHIP. It was very refreshing to read such a high impact letter that is absolutely correct in every detail, especially in this day and age when there is so much misleading and often false information published. I am a victim of redundancy. In 1987, we in NZ were living in an environment where the Government of the day was hell bent on destroying people and the country as well. Redundancy to me is the dirty word of the 20th century. It has, in a single word, destroyed the very fibre of our society. It has also destroyed the hopes and aspirations of many people, good people; not many have been able to escape the gauntlet. An aspect that I wish to highlight is the arrogant way chief executives and branch managers went about applying the edicts of the government of the day. In 1988 I was a Communica­ tions Inspector for the New Zealand Railways, aged 52 years with 27 years active service. I had just completed a four year con­tract on the Electrification Project and late in 1988, I was faced with an excruciating decision of what to do and where to go. The Communications Branch had been dissolved. It was wait­ing for a restructuring that was about one year behind everyone else and management stated that redundancy payments would end as at 28th February, 1989. It was apparent the restructuring plans would contain a down-sizing of position numbers so somewhere along the way people were going to miss out. As I was already out of a position because of electrification completion, I found myself in a very vulnerable situation. So much so that at the end of the day I was left with no other choice but to declare myself redundant and take the money before the deadline. Ultimately, the redundancy payout deadline was extended for an indefinite period but I was made aware of this the day before I was to finish up. It was described as voluntary redundancy but I can assure you it was not like that at all. At the end of the day I realised my worth to my employer was not as great as I thought it was. I wonder if anyone can place a true value on such a deci­sion having to be made at my age, with my experience. To me, it was a million dollar monetary loss decision over the rest of my life which I had to make back there in February 1989. The true impact of your letter becomes very apparent to those that have been made redundant and to those that are probably cornered right now, with nowhere to go. E. McFadyen, Rotorua, New Zealand. July 1998  17 Adjust your radiator for comfort with this: Heat Controller Now that we are in the grip of winter, most people will resort to an electric radiator to keep warm. Trouble is, most radiators have no heat control. At best, you might be able to set for low, medium or high heat. Now with this new Heat Controller, you can set for any heat from zero up to full power. By JOHN CLARKE Unless you live in the north of Queensland or the Northern Territory, the chances are that you turn on an electric radiator or two on those cold days and nights during winter. Electric radiators are quick and convenient but they do have a drawback in that most models have no provision for heat adjustment – you turn ‘em on and they get hot. That’s great when you first turn 18  Silicon Chip them on in a cold room but after a while you find it would be nice to turn them down to say, half or quarter of their output. Now you can do just that, with this new Heat Controller. We like to think of this project as a “dimmer for radia­ tors”. You can adjust the heat output continuously from zero to maximum but there is no electromagnetic interference (EMI) which you would normally get from a conventional light dimmer. Other appliances which can benefit from this Heat Con­troller are vertical grillers and also electric blankets which are often either too hot or too cold when using their own primitive switch-type controllers. The SILICON CHIP Heat Controller is suitable for 240VAC resistive loads, such as electric radiators, rated up to 2400W. It is housed in a medium-sized aluminium diecast box which is not only robust but also provides sufficient heatsinking for the internal Triac which performs the power control. The power setting is adjustable by the control knob on the lid and is indicated by a bi-coloured LED which glows green when low power is selected and graduates up through orange and to red as the power level is increased. The SILICON CHIP Heat Controller provides another advantage when controlling 2400W radiators which normally have switching for two or three settings. The radiator switch bank works by switching the resistive elements in or out of circuit to vary the power. By setting the radiator switch bank to maximum and then using the Heat Controller to vary the power, you get the advan­tage of a more diffuse heat from the radiator rather than having one or two elements running red hot. Zero voltage switching The Heat Controller adjusts the power applied to the load by switching the mains voltage on and off at a set rate. If the mains voltage across a radiator load is only present for 50% of the time, then the heat produced by the radiator will be half its normal output. As in other 240VAC mains power control circuits, a Triac is used to switch the voltage to the load. But unlike light dimmer circuits where the Triac is switched on part way during each mains half-cycle (ie, once every 10 milliseconds), in this cir­cuit, the Triac is only turned on at the start of a mains cycle and stays on for groups of half-cycles. Furthermore, by turning on the Triac at very close to the start of particular half cycles, the voltage across it at the point of switching is at a minimum; ie, close to “zero voltage” switching. This minimises electromagnetic interference due to the rapid switching of the Triac and does away with the need for any filtering components. Fig.1: at the maximum power setting, the full 240VAC is applied to the load. Fig.2: at medium power settings, the Heat Controller feeds even numbers of half-cycles to the load. Note the “zero voltage” switching action of the Triac which ensures a minimum of electro­magnetic interference (EMI) is produced. Features •  Suitable for resistive loads up to 2400W. •  Power control adjustable from zero to fully on. •  Power level indicated with bi-coloured LED. •  Housed in robust diecast aluminium case. •  Switched 240VAC mains outlet. •  Fused to protect against overload or internal failure. •  Minimum electromagnetic interference. Fig.3: at very low power settings, the Heat Controller feeds mains half-cycles of opposing polarity to the load, ensuring that no net DC appears. July 1998  19 The oscilloscope waveforms of Figs.1, 2 & 3 show how power control is achieved. Fig.1 is the 240VAC 50Hz mains waveform which is applied to the load at the maximum setting. Fig.2 shows the voltage waveform applied to the load at a medium power set­ting. Note how only full cycles of voltage are applied to the load and that some cycles are simply switched off. The cycles also always start at the zero voltage crossing point. At quite low power settings, only half cycles are connected to the load, as seen in the waveform in Fig.3. Note that consecu­tive half-cycles are of the opposite polarity and this ensures that there is no net DC voltage applied to the load which could otherwise produce galvanic corrosion in the mains wiring. 20  Silicon Chip Fig.4: the circuit uses a 555 oscillator operating at around 13Hz to control the switching of the Triac. The 3041 optocoupler incorporates “zero voltage” switching circuitry. WARNING: ALL PARTS OF THIS CIRCUIT OPERATE AT 240VAC Circuit details Fig.4 shows the full circuit of the Heat Controller which uses three ICs, a Triac and a few other low cost components. To run the ICs we need a low voltage DC supply rail and this is derived directly from the 240VAC mains supply via a 0.47µF ca­pacitor and the series 470Ω resistor. These limit the current to the following circuitry to about 33mA. The current is then full-wave rectified with the diode bridge D1-D4. Zener diode ZD1, limits the voltage to 15V, while the 1000µF capacitor provides DC filtering. IC1 is a CMOS 555 timer which is connected as an oscillator running at about 13Hz. It has a variable duty cycle which is adjustable with potentiometer VR1. This means that the pulsed output at pin 3 can be adjusted to be low (close to 0V) for most of the time and high (+15V) for a little of the time or alterna­tively, high for most of the time and low for a little of the time. And it can also be adjusted to any duty cycle in between these extremes. What happens is that the 0.1µF capacitor at pins 2 & 6 of IC1 is charged via the 4.7kΩ resistor at pin 7 and then via part of VR1 and diode D5. When the voltage across this capacitor reaches about +10V, it is then discharged via pin 7, diode D6 and the other section of VR1. So when the wiper of VR1 is at the D5 end, the capacitor is charged very quickly and discharged rela­tively slowly. This corresponds to a very short positive pulse from the output at pin 3, followed by a relatively long time with zero output. This is the low power condition of the circuit. The pulse output from pin 3 is fed to five sections of the 4049 hex inverter/buffer, IC2. Three of the inverters Parts List 1 PC board, code 10307981, 85 x 79mm 1 front panel label, 114 x 89mm 1 diecast box measuring 115 x 90 x 55mm 1 architrave 10A mains power point, HPM790, Clipsal NO.16N or equivalent 1 1MΩ linear potentiometer (VR1) 1 15mm knob to suit VR1 1 1m length of 10A 250VAC 3-core mains lead 1 200mm length of 7.5A mains lead 1 10A mains plug 3 crimp or solder lugs for earth connections 1 cord grip grommet for mains lead 2 3AG PC mount fuse clips (IC2a,b,c) are connected in parallel to drive the internal LED in IC3, a MOC3041 optocoupler with zero voltage switching circuitry incor­ porated. Each time the LED in IC3 is turned on, its internal Triac is turned on to provide gate current to the main switching Triac, a BTA41-600B, and this delivers the 240VAC to the load. The power level indication circuitry comprises inverters IC2d, IC2e & IC2f, transistors Q1 & Q2 and LED1. IC2d inverts the pulse signal from pin 3 of IC1 and its pin 2 output is filtered with a 10kΩ resistor and 100µF capacitor to provide a DC voltage which is inversely proportional to the duty cycle of IC1’s output signal. This DC signal drives the base of Q1 and its emitter output drives the red portion of the bi-colour LED via a 2.2kΩ resistor. Thus the red LED is fully driven when the pin 3 output of IC1 is low for most of the time. IC2e & IC2f perform two inversions of the pulse output signal from IC1 and IC2f drives a filter comprising a 10kΩ resis­tor and 100µF capacitor. The filtered DC voltage is directly proportional to the pulse duty cycle and it drives transistor Q2. In turn, Q2 drives the green LED in LED1 via a 2.7kΩ resistor. The green LED is lit when the pin 3 output of IC1 is high most of the time. Hence, LED1 changes from green to red as the setting of VR1 is increased 1 3AG 10A 250VAC fuse 3 M4 x 12mm machine screws 1 M4 x 9mm machine screw 4 M4 nuts 4 M4 star washers 1 5mm LED bezel 4 stick-on rubber feet 9 PC stakes 9 small cable ties Semiconductors 1 7555, LMC555CN, TLC555 CMOS 555 timer (IC1) 1 4049 CMOS hex inverter (IC2) 1 MOC3041 zero voltage crossing optocoupled Triac driver (IC3) 1 BTA26-600B or BTA41-600B insulated tab Triac (Triac1) 2 BC338 NPN transistors (Q1,Q2) 4 1N4004 1A diodes (D1-D4) from zero to maximum. The waveforms of Fig.5 demonstrate the operation of IC1 & IC2 at a medium power setting. The top trace is the waveform present at pin 2 of IC2 (also present at pins 10, 12 & 15 of IC2) and this shows the amount of time (70%) that the Triac is con­ ducting. The lower trace (channel 2) is the waveform present at pin 4 of IC2 (and also at pin 3 of IC1). Construction The circuitry of the Heat Control- 2 1N914, 1N4148 switching diodes (D5,D6) 1 15V 1W zener diode (ZD1) 1 red/green 3-lead LED (LED1) Capacitors 1 1000µF 25VW PC electrolytic 2 100µF 16VW PC electrolytic 1 0.47µF 250VAC X2 class polyester 2 0.1µF MKT polyester Resistors (0.25W, 1%) 2 10kΩ 1 680Ω 1W 5% 1 4.7kΩ 1 470Ω 1W 5% 1 2.7kΩ 1 330Ω 1 2.2kΩ Miscellaneous Heatshrink tubing, solder, etc. ler is mounted on a PC board which measures 85mm x 79mm and is coded 10307981. The compon­ent layout and wiring diagram is shown in Fig.6. You can begin construction by checking the PC board against the published pattern of Fig.7. There should not be any shorts or breaks between tracks or undrilled holes. If there are, fix these as necessary. The PC board may need to have the corners slightly rounded off to fit into the recommended case. Start assembly by inserting the PC Fig.5: these waveforms demonstrate the operation of IC1 & IC2 at a medium power setting. The top trace is the waveform present at pin 2 of IC2 (also present at pins 10, 12 & 15 of IC2) and this shows the amount of time (70%) that the Triac is conducting. The lower trace (channel 2) is the waveform present at pin 4 of IC2 (and also at pin 3 of IC1). July 1998  21 Fig.6: the component layout and wiring details for the Heat Controller. Note that all interconnecting wiring inside the case should be rated at 250VAC. WARNING: ALL PARTS OF THIS CIRCUIT OPERATE AT 240VAC Resistor Colour Codes ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 2 1 1 1 1 1 1 22  Silicon Chip Value 10kΩ 4.7kΩ 2.7kΩ 2.2kΩ 680Ω 470Ω 330Ω 4-Band Code (1%) brown black orange brown yellow violet red brown red violet red brown red red red brown blue grey brown gold (5%) yellow violet brown gold (5%) orange orange brown brown 5-Band Code (1%) brown black black red brown yellow violet black brown brown red violet black brown brown red red black brown brown not applicable not applicable orange orange black black brown stakes at the external wiring connection points on the PC board. Then insert the resis­tors, the diodes and the zener, taking care to place each type in its correct place and with correct polarity. Next, install the ICs and the transistors, taking care to orient them as shown on Fig.6. The capacitors can be installed next and note that the electrolytic capacitors must be oriented with the correct polarity. Next, fit the fuse and fuse clips. Clip the fuse into the clips first and then insert them into the PC board and solder in position. Triac 1 is mounted so that its leads protrude from the copper side of the board by about 1-1.5mm. Temporarily mount the PC board in the case and mark out the mounting hole position for Triac1. Note that its leads must be bent so that its metal flange makes contact with the side of the case. Now remove the PC board and drill out the 4mm Triac mount­ing hole plus holes for the cord-grip grommet and the earth lug screw. The hole for the Triac must be deburred, with a larger drill, to ensure that the flange sits in intimate contact with the case. Attach the PC board to the integral mounting pillars in the case with the supplied screws and secure the Triac to the case with a 4mm screw and nut and with a smear of heatsink compound between the mating surfaces. Note that the specified Triac is an insulated tab device and does not require an insulating washer. Attach the mains cord wires to the PC board and secure it in place with a cordgrip grommet. Be sure to connect the brown (Active) and blue (Neutral) wires to the correct terminals as shown on Fig.6. Mark out and drill the front panel for the mains GPO sock­et, potentiometer VR1 and the LED bezel, using the front panel label as a guide to hole locations. Note that it is important to drill a small hole for the locking tab on the pot, to prevent it from rotating when the knob is being turned. Attach the front panel label to the Capacitor Codes ❏ Value IEC Code EIA Code ❏ 0.47µF   470n   474 ❏ 0.1µF   100n   104 Note: cable tie passes through crimp lug to anchor LED leads to the case lid. This is the view inside the completed prototype. Be sure to lace the wiring with cable ties and note that the leads to the LED are anchored to the case lid by passing a cable tie through a crimp lug. Warning! (1) The entire circuit of this Heat Controller floats at 240VAC and is potentially lethal. Do not build it unless you know exactly what you are doing. DO NOT TOUCH ANY PART OF THE CIRCUIT WHILE IT IS PLUGGED INTO A MAINS OUTLET and do not operate the circuit outside its metal case. (2) This circuit is not suitable for controlling any type of lighting since its rapid switching action would cause very bad flicker. Nor is it suitable for use with any type of power tool or fan-assisted radiator. (3) If you are driving a 2400W radiator at maximum setting, the Heat Controller case will become quite hot to the touch and it probably should not be run in this condition for long periods. If you need to run a 2400W radiator at full power, you don’t need the Heat Controller anyway. On the other hand, if your application calls for this use, where a 2400W load needs to be run at full power, then you should use a larger case and a finned heatsink to dissipate the heat from the Triac. July 1998  23 from their terminations. We used a modified crimp lug to act as an anchor point to tie the wires from the LED to the case lid. This lug is secured to the second mounting screw on the GPO socket. Check your wiring carefully and please note that all of the circuit is connected to the mains supply and is potentially lethal. Do not touch any part of the circuit when it is plugged into a mains outlet. Always remove the plug from the mains before touching any part of the circuit. Testing the circuit HEAT CONTROLLER + + + WARNING Dangerous voltage inside. All parts operate at 240VAC. POWER Fig.7: here are the full-size artworks for the PC board and the front panel. Check the board carefully before installing any parts. lid and secure the mains GPO socket with 4mm screws and nuts. Also secure the pot and LED bezel in place. 10A 250VAC-rated wire must be used when wiring the GPO and earth connections. Solder or crimp the earth connection for the mains GPO socket to the solder lug using green/yellow mains wire. Similarly, solder or crimp the mains earth from the mains cord to a solder or crimp lug and connect both lugs to the case side using a 24  Silicon Chip screw, nut and star washer. The lid of the case is separately earthed by securing a solder or crimp lug under one of the architrave power point mounting screws. The green/ yellow wire is crimped or soldered to this lug and secured in the earth terminal of the power point. Use 7.5A 250VAC-rated wire for wiring from the pot and LED to the PC board and secure the wires with cable ties to prevent them breaking Testing the circuit is best done initially with the lid of the case securely closed. Apply power and see if the LED glows and can be adjusted from fully green to fully red. Connect up a 240VAC radiator and check that the heat output can be controlled from zero to maximum. If all is satisfactory there is probably no need to measure any circuit voltages. You can test for power voltage by connect­ing a multimeter across the zener diode, ZD1. Take care with this measurement since the whole circuit is floating at 240VAC. You should obtain somewhere between 14.5V and 15.5V DC when the unit is powered from the mains. Note that the supply voltage will differ slightly, depend­ing on the position of the power level potentiometer. When fully anticlockwise, the supply will be greater than when wound fully clockwise. This is because the current drawn by the circuit is higher with VR1 fully clockwise where the LED in IC3 is switched on for most of the time. Should you wish to monitor any of the waveforms on an oscilloscope, be warned that you cannot connect the earth probe to any part of the circuit. For maximum safety, you should only use an oscilloscope with differential inputs. Having said that, it is possible to safely check the operation of the low DC voltage part of the circuit by powering it from a low voltage DC supply (ie, the unit is not connected to 240VAC). With the supply set to around 20V, connect the negative lead to the anode of ZD1 and the positive lead to the junction of the 470Ω 1W resistor and the 0.47µF capacitor. That is how the waveforms of Fig.5 were SC recorded. SOLAREX BRAND SOLAR PANELS These are professional quality solar panels with aluminium frame and glass cover and 1 year guarantee. 30W: $290-80W:...........$650 NEW 12V SOLAR REGULATOR KIT Our new regulator suits up to 100W panels. Features a current limiter so it can be used with car battery chargers, generators etc. Low cost due to the use of some unused recycled components. complete kit inc. case $22... or $18 with the purchase of one of our solar panels.. *** FANTASTIC BARGAIN *** COMPUTER POWER SUPPLY PCB: New assembly. 45 x 108 x 200mm. 120 / 230V AC input. DC outputs are +5V<at> 6A,+ 12V <at> 1A,-12V<at>1A,-5V<at>1A. Data Inc.RU approval. Mains input . Be Quick: (Ps6) $12 ea. or 4 for $36 TWO CHANNEL UHF REMOTE CONTROL On freq. of 304MHz, transmitter is assembled, receiver is a kit, inc. 2 12V/12A relays, 1Tx + 1Rx kit:$45, additional Tx: $15 *** $2 ** YES ** $2 *** VHF VIDEO 1-2 MINI MODULATORS WITH EVERY CAMERA YOU BUY OR HAVE BOUGHT IN THE PAST. INC DATA SHEET:$ 2 (Rm2). This unit will fit neatly with our camera in our 50x 50x50mm case + swivel mount strong adjustable uni- versal bracket : $4 Bracket only :$1.50 *** TRANSISTOR SPECIALS *** BU-205 HIGH VOLTAGE $2.50 2SD-1554 HIGH VOLTAGE $5.00 MAJOR SALE / SATURDAY TRADING We will open some Saturdays. On these days you can pick-up orders & view advertised and bargain priced limited stock items, mixed orders should be placed prior. MAJOR SALE, More info 1 week before the sale on our Web Site or E-mail us " DECEMBER SALE " in the subject box. The next Saturday is 15 Aug. KIT OF THE MONTH *** PLASMA DISPLAY BALL KIT: A new HIGH POWER HIGH FREQUENCY EHT generator that will give an interesting and Exciting plasma discharge inside a standard Domestic light bulb or It can also be used to make a JACOBS LADDER or LADEN JAR & other EHT applications. Easy to modify primary coil, room for more secondary windings.Can be converted to a HV. DC. Supply with a HV diode. Inc. EHT transformer + PCB + all on-board Components & 1KV. fast Diode + application notes. To reduce the pricewe include some new recovered parts Requires 12V <at> 0.5-2A supply depending on application. Special introductory price $29.....16KV. Diode $1.50 Now updated weekly. If you haven’t looked at our Web page lately then you may have missed some of the great deals like the FREE OFFER plus lots more, most item quantities in our “Bargain Corner” are to small to advertise here www.ozemail.com.au/~oatley AUTOMATIC LASER LIGHT SHOW KIT: MKIII. Similar to the kit as published in Silicon Chip May 96 issue, The display changes every 5 - 60 seconds, the time is manually adjustable. For each of the new displays there are 8 different possible speeds for each of the 3 motors, one of the motors can be reversed in rotation direction, and one of the motors can be stopped. There are countless possible interesting displays which vary from single to multiple flowers, collapsing circles, rotating single and multiple ellipses, stars, etc. Now with no more mirror and motor alignment hassles with motor mounting on the PCB and mirrors now align with “Allen Key”. Kit includes PCB, all on board components, three small DC motors, mirrors, precision adjustable mirror mounts : (K83) $77 $50 PO Box 89 Oatley NSW 2223 Ph ( 02 ) 9584 3563 Fax 9584 3561 orders by e-mail: oatley<at>world.net http://www.ozemail.com.au/~oatley major cards with ph. & fax orders, Post & Pack typically $6 $29 Web Page and Bargain Corner MAGNETS: HIGH POWER NEODYMIUM RARE EARTH MAGNETS: Very strong You will not be able to separate two of these by pulling them apart directly away from each other. Zinc coated.---CYLINDRICAL 7 mm diameter x 3 mm thick: (G37) $2.50. --CYLINDRICAL 10mm dia- meter x 3 mm thick: (G38) $5.---TOROIDAL 50mm outer, 35mm inner, 5mm thick: (G39) $12.---ROD 10mm long, 4mm diameter: HIGH QUALITY DC MOTORS (G54) $2.50.--- CYLINDRICAL 3mm 3V - 8v DC motors with feedback winding for speed sensing ect. 40mm diameter diameter x1.5mm thick: (G58) 2 for $1 X35mm long $3 **SPECIAL**SPECIAL**SPECIAL** FOR $1 EXTRA WITH EACH ORDER MODEL TRAIN CONTROLLER KIT: WE WILL SEND A WIRING KIT !!! Ref: SC Jul 95. This allows two trains to Great for cars, radios mobile phones, fog be run on one loop of track, without hitting lights etc. 4 colours, 2 guages of wire, each other due to speed differences. Spade connectors, fuse holders, fuses. When the train breaks an infra red beam 17+ mtrs. of wire. Limited offer!!! just $1 it switches off the power to a portion of the track, until the other train catches up and HIGH RESOLUTION MONITOR breaks another beam at another location. Brand new 240V Circuit uses a relay to switch these two 30cm enclosed sections of the track. Main PCB: 96 x computer monitor 66mm, Infra Red Sensing PCB's: 59 x + video conversion 14mm: (K58) $28 kit. Gives better resolution than TV! *** CCD CAMERA SPECIAL *** Limited good qty. The best "value for money" CCD camera BARGAIN PRICE. on the market! 0.1 lux, High IR response & high res. Performs better than many SOLID STATE 4-6A PELTIER EFFECT cheaper models. WITH YOUR COOLER / HEATER CHOICE OF 1 OF 3 . 3 A <at> 1 4 V P E LT I E R : $ 2 7 , 6 A THESE LENS Pinhole <at>15VPeltier: $35, both are approx. (60deg.), 78 deg.; 92 deg.; 40X40X4mm, can be temperature 120 deg.; $89 or 150 deg: $99 controlled by reducing supply *** SPECIAL BARGAIN *** voltage/current, will even work from a 1.5V battery!! We supply Peltier Effect 12V/7Ah GEL BATTERY BARGAIN Fresh stock of NEW standard battery $22 device, data sheet, diagram & circuit for a small fridge / heater.. Other requirements; NEW ! 4Ch. UHF Insulated box, 2 large heatsinks, & a small LEARNING REMOTE aluminium block. This device is used in Can be programmed as the common 15Lr car fridge. Peltier effect a spare for your current Device + (G02) 12V DC Fan:(G11) remote or to replace up to 4 other units and combine into 1:(TX1) $39 OATLEY ELECTRONICS *** UHF DATA TRANSMISSION Stamp sized Xtal locked 433.9MHz superhetrodyne receiver module $25 Small matching transmitter kit: $12 UHF GARAGE REMOTE CONTROL RECEIVER: Ref:SC Dec 93. All the required electronics for UHF remote control of DC motors to operate garage doors, gates, and shutters. Provision for upper and lower limit switches, and has motor current sensing that will cause the motor to stop if the door hits an obstruction (this feature can also be used to eliminate limit switches). Circuit includes a 2 minute timer with a MOSFET switch for operating a 12V courtesy light. Security code has over 1/2 million combinations. Receiver uses the pre-aligned UHF receiver module. Use either 1 Channel Transmitter (K41) or 3 Channel Transmitter (K40). PCB and all on-board components kit for the receiver only: (K23)$70....12V wiper motor for only $8 IR RECEIVER FRONT END MODULE This device contains an IR receiver diode, an amplifier tuned to 38KHz, a bandpass filter, an AGC section & detector circuit. $2 Ea or 10 for $15 AMP-PREAMP & MORE A professional mostly Surface Mount PCB WITH a TDA1905 5W amp. IC & audio pre-amp section. We also provide a pre-wired high quality unidirectional electret mic. that has a wind filter & clip, A small speaker & hook up info. Appears to have been designed for a comms. system. Great applications including a two way intercom (2 req.) no switching require !: (Ap3) $10 each or 2 for $18. CCD IMAGE SENSOR: High quality "Thomson" brand, 2/3"CCD Image Sensor (part # TH7863-TBE1) 576 x 384 pixels. Inc data but no circuit suggestions available. Usable response 400 to 1100nm, 30dB S/N at 40 milli-lux, 2/3" optics compatible format: (D10) $35 MINIATURE FM TRANSMITTER (33 x 23 x 10mm) enclosed in a small black metal case. Built in switch & mic. Specs.: 88 to 108- Mhz (adj.), with a wire ant. bat. life 60 hrs, Range 50M:(G14) $39 (Std. watch battery LR44, inc.) FRONT SURFACED MIRRORS High quality mirrors 160x22x2.5mm. with some minor blemishes Ideal for laser & other optical projects $4 **********CLEARANCE SPECIAL******** UHF AUDIO-VIDEO TRANSMITTER . Send video from VCR's or $20 cameras to TVs in your home. Inc. Metal case telescopic antenna & leads: 12V operation, tunable (G01) *** GET THEM BEFORE THEY GO *** HELIUM - NEON LASER TUBE & SUPPLY KIT: Helium Neon 633nM red laser heads Great for light shows or holigraphy. 2-3mW. Inc. a special high voltage supply. Tube & supply: (L03) $60 This KIT requires 12V <at> 2A. WA R N I N G ! ! ! I N V O LV E S H I G H VOLTAGE & VERY BRIGHT NOT FOR USE BY CHILDREN!! ALL LASERS MUST BE USED UNDER COMPETENT SUPERVISION. *********CLEARANCE SPECIAL********* FLUORESCENT LIGHT HIGH FREQUENCY BALLASTS European made, new, "slim line" case high frequency (HF) electronic ballasts. Flicker free starting, long tube life, high efficiency, visual flicker during operation. Reduced radio frequency interference. Similar design to one published in the Oct. 94 Silicon Chip, although these are much more complex. Dimming requires external 100K pot or a 0-10V DC source. We have a limited stock 1 x 36W tube, 28 x 4 x 3 cm: (G09F) just $14 LASER DIODE POINTER ( Key-chain ) Very bright ( 650 nM ) pointer. supplied with 4 extra lens caps that produce symbols; CUPID, I LOVE YOU, LOVE HEARTS & A LADY. $29 LASER DIODE MODULE Same quality module that is used in the above laser pointer: $24 *************SUPER SPECIAL************ 60 NEW Flat NiCad FOR $10 Space saving batteries 16X48X5.5mm With solder tags **** TWO GREAT SPECIALS **** ***STEPPER MOTOR DRIVER KITS*** COMPUTER CONTROLLED STEPPER MOTOR KIT: can drive larger motors with optoisolation. Inc. software and notes: $40 or $50 with two used 1.8deg. motors!! 8 CHANNEL IR REMOTE CONTROL This kit converts a Magnavox IR remote into an IR remote with a SM5021 encoder IC. We use the case & 8 keys, and replace the PCB. The RX uses an IR RX module on 38KHz. There are 8 outputs. 2 of outputs toggle & 6 momentary outputs. To convert the TTL outputs to drive a relay, use our (K ) Dual Relay Kit. Tx PCB: 89 x 30mm. Rx PCB: 48 x 34mm: * TX Kit: (K65T) $20 * RX Kit: (K65R) $20 CFL AND BALLAST INVERTER KIT: Power efficient fluorescent 12V lighting. Unlike cheap commercial fluorescent tube drivers, our kit gets long life from tubes & is very efficient. It simply generates DC <at> around 250V-350V at up to 40W CFL's. (K111) $25 -Extra CFL's $11 STEPPER MOTOR DRIVER KIT Kit inc. a large used 1.8deg. (200 step / rev) motor & uses SAA1042A IC. Controls inc. ext. clock, on-board clock logic CW or CCW rotation, half or full step, enable/disable, clock speed1 motor: $20 or 2 motors:$30 Brand new motors coming soon. Low voltage, high efficiency, high res. low cost. NOTICE TO CFL KIT BUYERS PRIOR TO 18/5/98 In some kits that were sold before 18/5/98 one or both FETs run hot due to different tolerances of Ic1. please contact us for details on a mod to fix this problem. POWER MOSFETS: 2SK 2175 15A-60V N chn. Has diode clamp ie. not static sensitive. Suitable substitute for devices like BUZ71A or MTP3055E: 10 FOR $10 *** SPECIAL FREE OFFER *** BUY ONE OF OUR CMOS OR CCD CAMERAS & RECEIVE ONE OF OUR IO LED IR ILUMINATORS ( see in total darkness ) - ABSOLUTELY FREE PLUS $20 DISCOUNT ON OUR 4 CH A/V SWITCHER, This has to be the best "value for money" CMOS - CCD camera deal on the market!!! LED IR ILLUMINATORS KITS 10 LED:(K103) $14, 30 LED:(K102) $30 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. Bargraph auto tachometer This circuit provides an easy-toread indication of engine RPM at a glance, without needing to interpret numbers. The heart of the circuit is an MM5451 serially-fed LED display driver. Data is normally fed into pin 22 while the internal 35-bit shift register is clocked at pin 21. Each bit of the shift register drives one of the LEDs. There are two oscillators, one based on IC3c & IC3d and one based on IC3e & IC3f. Oscillator IC3c/d provides the “data” signal while oscillator IC3e/f provides the clock signal. What happens is that the gates and oscillator IC3c/d load a high signal into the 35-bit shift register. Just how many bits are loaded high depends on the engine rpm. Then as the signal from IC3c/d goes low, it shuts off IC2a 26  Silicon Chip and enables IC2d which then rapidly clocks in zeros to fill up the rest of 35-bit register. The number of bits high in the register then lights up the same number of LEDs. LEDs1-20 are green, LEDs21-30 are orange and LEDs31-35 are red, giving a visual indication of engine speed. Each LED represents 200 RPM, so with 35 LEDs the maximum reading is 7000 RPM which is sufficient for most engines. For a 4-cylinder engine, the oscillator output of IC3d needs to be set to 3.3Hz. The corresponding figures are 5Hz for a 6-cylinder engine and 6.67Hz for a V8. The circuit is designed to be powered at 5V, so a regulator such as a 7805 is required, with bypass capacitors at its input and output. This regulator will require a good heatsink as it passes close to 1A when all 35 LEDs are lit. S. Williamson, Hamilton, NZ. ($35) The circuit of this LED tacho is based on an MM5451 display driver. Phase/program indicator This circuit enables you to determine whether your audio source is actually stereo or mono, or whether you have a phase error somewhere along the line. When the signal to both inputs is the same, the output of IC1a stays at the same level as the output of IC1b, which is configured to provide a virtual ground at half the supply vol­tage. When IC1a detects a difference between the inputs, its output swings positive or negative relative to the virtual ground and causes either one of the 4.7µF capacitors to be charged, depending on which way the voltage swings. This causes the com­parator, formed by IC1c & IC1d to light LED1, to indicate correct phasing or stereo information. The input levels must be reasonably well matched or the LED will light with mono program material. The comparator sensitivity is adjustable with trimpot VR1. The input signal needs to be at least 100mV. S. Williamson, Hamilton, NZ. ($35) N-channel FET tester This Go/No Go indicator consists of a simple self- biasing N-channel FET amplifier, capacitively coupled to a PNP Darlington transistor which drives a LED via a 330Ω limiting resistor. A capacitively coupled output is provided to connect an oscilloscope for observation of the waveform. A 4-way socket (marked GDSG) is made from half of an 8-pin DIP socket salvaged from an old circuit board. To use the tester, connect 12V and 0V to the appropriate pins, insert the N-FET to test, switch on power and the LED should remain off. This is the “no signal” output condition. Now apply a 100mV 1kHz signal between the input pin and 0V. If the FET is OK, the LED will light. If the LED remains off, the FET is defective or wrongly connected. S. Foster, Orelia, WA. ($25) 1.5V DC-DC converter SILICON CHIP has published two versions of the TL496 1.5V to 9V DC-DC converter – in the November 1990 and August 1992 issues. While the circuit is quite handy, a number of readers have asked how to modify it for a higher output voltage. Since the internal feedback in the TL496 is fixed, there is no easy circuit modifi­cation to make it regulate to any output voltage other than 9V. However, by making it drive a step-up transformer instead of a choke, we can arrange for it to have any output. As shown, the TL496 produces a fixed output voltage at pin 8 but by connecting a transformer with its primary winding bet­ween pins 3 & 6, the output voltage across the 470µF capacitor is 9V multiplied by the turns ratio. In this case the turns ratio is 3:1 and so the output voltage will be around 27V DC. (SILICON CHIP). July 1998  27 SERVICEMAN'S LOG It was only a piece of broken plastic Sometimes, it only takes something as simple as a piece of broken plastic to stop a device dead in its tracks. And in some cases, this can mean consigning the device to the scrapheap unless one is prepared to use a little ingenuity. My first story involves a Sanyo VRH-5100 VCR which uses a P88 deck mechanism. The problem was lack of fast forward and rewind torque. Apart from the obvious symptoms, it was difficult to see what was causing the problem until I fitted a transparent dummy cassette, to discover that the reel brakes were on all the time. Getting closer to see what was causing that problem meant a fair bit of diagnostic surgery. After removing the front escut­cheon and ejector assembly, there was sufficient access to remove a slider block near the two take-up reels. Underneath, the prob­lem was obvious – two plastic axles, on which the reel brake levers pivoted, had broken. So much for the diagnosis. That had been relatively easy; fixing the problem was another matter. The plastic axles – bet­ween 1.5mm and 2mm in diameter – were part of larger plastic blocks which, apparently, had been moulded into openings in the metal chassis during manufacture. Don’t ask me how this was done; suffice it to say, that was the end result. It was no doubt all very clever on the part of the designer and manufacturer but it does pose servicing difficulties. In theory, the right thing to do would be to fit a new metal plat­form assembly, complete with the plastic mouldings, but that was much easier said than done. It would entail a major disassembly and reassembly exercise; a virtual pull-down and rebuild. Howev­er, this was out of the question; the cost in time and materials would be quite unacceptable. But even if I had wanted to, there was a more serious barrier. Subsequent investigations revealed that a replacement deck was no longer available; at least not from any sources to which I had access. All I could do was try to devise a way to make new axles and this turned out to be surprisingly simple in practice. First, the old axles were cut back to the plastic base and a small pilot hole drilled into the base. A small self-tapping screw of the appropriate diameter was then screwed into it to make a new axle. The result was as good as new. While I had the machine stripped down, I decided that it would also Fig.1: this diagram shows how new axles for the reel brake levers were fitted to the plastic blocks in the Sanyo VRH-5100 VCR. 28  Silicon Chip be a good idea to replace the loading motor belt. After that, it was simply a matter of putting it all back togeth­er again. The thing that took the most time was the ejector reassembly. This job is rather fiddly and its drive gears must be correctly aligned with the loading motor to ensure that the timing is correct. In the end, it all came out right and the customer was delighted that she could now play her tapes proper­ly. Yes, it was “only” a little bit of plastic. The old transistor set My next customer presented a complete change of scene. Not only was it a completely different appliance but it was also from a different era. It was a portable radio from the early period of transistor sets and was at least 25 years old – still in the age of large cabinets and reasonable size speakers. In greater detail, it was a Philips 4-Band 749, housed in a cabinet measuring about 30 x 18 x 7cm and featuring three AM bands (one B/C and two S/W) and the standard FM band. It operated from a bank of “D” cells or from the mains supply. All this added up to quite a substantial unit which, quite frankly, one would rather carry for a week than a fortnight! But it was a very good performer and the substantial speak­ er turned in a very impressive performance. And this was one of reasons that the owner was keen to get it fixed. Yes, he knew it was an old set but he liked the sound and the set had some senti­ mental value. So who was I to argue with that? As the customer put it, “it shouldn’t be hard to fix; it’s only a broken switch.” I hesitated a little at that; the word “only” can be a real danger signal. It often means that the owner considers the fault so trivial that I can fix it on the counter in a couple of minutes flat and more importantly, with little or no charge. It wouldn’t be the first time but as it turned out, I had misjudged him badly. He wasn’t worried about the cost; he was worried about the availability of the switch, or anything else that might be needed, in a such an old set. Well, there was no question about the ON/OFF switch; it was broken. It was mounted on the front panel and hopefully only switched a single lead from the power pack. But like the owner, I was worried about a replacement switch. I could see enough of it to realise that it was nothing like normal run of the mill types and was almost certainly a “special” designed by Philips. More than that I couldn’t say at that stage but said I felt sure that I could make the set usable one way or another, even if I had to fit a replacement switch on the cabinet back. But that would be a last resort. When I eventually opened the set, I realised just how “spe­cial” the switch was. Just reaching it was a fair exercise in itself and involved something like a dozen screws – a lot for a set of this size. The switch itself was nothing like anything I had ever seen and was supported by a small metal bracket. This in turn was fastened to the main PC board, which was mounted about 18mm behind the front panel. The switch featured a longish plastic shank (the part that had broken), with an actuating lever on the end protruding through the opening in the front panel. Behind the switch body, on the PC board, there was a small rectangular opening which provided access to the terminals on the rear of the switch. It was all very cleverly designed but it left little room for a replacement. No matter how I looked at it, there seemed to be no way out as the space was extremely limited. Even if I could find a way to mount a typical small toggle switch on the PC board, the actuat­ing lever would not reach the panel opening. Mounting it on the front appeared to be impossible but even if it was possible, the switch would be too deep for the space behind it. It looked like a switch on the cabinet rear was the only solution but I made one last effort. In the back of my mind I had an idea that I had seen a smaller switch which might just fit in the space. Perusing catalogs from the various component suppliers suggested that some of these might suit but the actual dimensions – or at least the ones I needed – were tantalisingly scarce. I finished up at the nearest Dick Smith Electronics store and found one that looked promising. Even then, I couldn’t be sure until I tried it. I took it anyway (it was only a couple of dollars) and went back to the pieces on the bench. And I was lucky; it could be used, the back of it fitting neatly through the hole in the PC board. Mounting it on the front panel was a tricky exercise and I had to make up a small auxiliary panel to support it. But it all came together in the end and the owner was delighted. Once again, it was “only” a piece of broken plastic. A frustrated customer Customers can sometimes be their own worst enemies. When one serviceman fails to fix a problem, they imme­ d iately go to someone else, sometimes changing technicians three or four times in a vain attempt to get the problem fixed. My next story concerns one such customer and this time the fault was purely electronic in nature. I could tell that the Johnsons were fed up the minute I walked in the door. They were very frustrated with their 1989 JVC AV-S290 AUT stereo television (BY-I chassis) and had lost pa­tience with it and with the army of July 1998  29 Fig.2: part of the Station Select Module in the JVC AV-S290 stereo TV receiver. The tuning voltage is controlled by IC002, which drives transistors Q013, Q014 and Q015. technicians they had pre­viously asked to service it. Personally, I felt that if they had stayed with just one technician, their problem would have been fixed more easily. Quite often, there are no quick 30  Silicon Chip fix solutions for intermittent faults and changing technicians midstream really means going back to square one each time the fault reappears. But try explaining that to some customers. The Johnsons complaint was that the TV was off tune and they couldn’t get sound or picture – only snow. What they appar­ ently failed to tell previous technicians was that it actually drifted off the tuned station after a while and that it was very intermittent, the set sometimes working perfectly OK for months on end. To give them some credit, they were the first to admit that they were not technical and didn’t know how to do the tuning themselves – even after owning the set for nine years! So, of course, every time they called a different service­man, he just reset the tuning and left, thinking that that was all the problem was. When they approached me in exasperation and mentioned the word “intermittent”, I mentioned a few unpalatable words like “workshop”, “weeks away” and “possibly costly”. I sweetened them with the offer of a loan set but they were reluctant to proceed until I pointed out that an equivalent new set would cost over $1000. Finally, they reluctantly agreed to let me have a look at it and so the beast appeared on my workshop bench a few days later. After what seemed like forever, I unscrewed all the self-tapping screws that held the back on like Fort Knox – whatever did we do before electric screwdrivers? I can never understand why some manufacturers require so many screws while others are just as successful with a few clips. Anyway, there I was, inside the beast, trying hard to acclimatise myself with its technology. Fortunately, I had man­ aged to obtain a service manual because I would certainly have been lost without it. The flat chassis consists of a twin switchmode power supply and a small signal board. The small signal board has half a dozen modules soldered into it and each module has surface mounted components and an awful lot of ICs. Because the problem was in the front end, I went straight to the tuner, or more precisely to the 32V rail that supplies the tuning voltage. This rail is derived from the main 115V B1 rail via a 15kΩ 2W resistor and integrated circuit UPCS74J (IC722). It is then applied to pin 24 of the SBY-M002A Station Select Module. The tuning voltage then comes out on pin 11 of the Select Module and is applied to the tuner’s BT pin. As I quickly discovered, the tuning voltage was rock solid going into the Station Select Module but intermittently unsteady coming out. This meant that either the module or the tuner was faulty, or possibly R006 (10kΩ) or C006 (47µF). My money was on the modu­le but there didn’t seem much on it that could easily be changed as it mostly consisted of surface mount large scale integrated circuits. It was also rather inaccessible. A check with a JVC agent proved that it was not designed to be serviceable and that a new one cost well over $100 (the tuner cost even more). The circuit for the Station Select Module (see Fig.2) shows that the tuning control voltage comes out of pin 37 of microcomputer IC002 and then goes to transistor filter stages Q013, Q014 and Q015 before arriving at the tuner on pin 11. What’s more, the critical 32V rail only went to these transistors and not to IC002. I decided to concentrate on this area and to start with I would try the heat and freeze treatment. My heater is an old hairdryer and isn’t too accurate where it blasts the hot air but the freezer can often pinpoint the component if it is heat sensitive because of its long nozzle. Anyway, it didn’t take too long to discover that I was on the right track as the tuning drifted dramatically with the freezer treatment. As near as I could tell, capacitor C010 (0.47µF) on the base of Q014 was the most sensitive to temperature varia­tions. This was a surface mounted component but it wasn’t too difficult to replace it with a conventional one. The problem with these tiny electros is that they are very prone to leaking their electrolyte and corroding the board below. The telltale clue is normally the smell of fish but this was not the case in this in­stance. Anyway, changing the capacitor and retuning the set proved to be successful. I then replaced C16, C17 and C13 as I felt that if one had died, the others would not be too far be­hind. The Johnsons were fairly blase about the repair as they had heard it all before (or so they thought). But the last time I contacted them the set was still going OK, with no sign of the fault! These surface mount electros can be a real problem in older equipment. They are difficult to remove as they are actually soldered from underneath and their markings are obscure if you are unfamiliar with them, the black mark signifying the negative side. In cameras, they are an absolute nightmare and they used to be very expensive, although the price has dropped in recent times. As I mentioned before, sometimes the capacitor just oozes its electrolyte onto the PC board and corrodes it. This sometimes happens with Sharp and NEC video capstan motors where it will often eat right through the track, causing the motor to fail completely. This is somewhat surprising as the capacitor is mounted upside down and you would have thought that the electro­lyte would have drained away from the PC board. SC July 1998  31 PRODUCT SHOWCASE Uninterruptible power supply for PCs Blackouts and computers definitely do not mix, especially these days now that so much software is Windows-based. If a blackout does occur and you have a lot of programs open, the amount of data loss can be substantial and it can take a long time to restore everything to where you were, even supposing that you had saved just before the blackout. The main reason for having a UPS in your computer is so that you can have an orderly shut-down of all programs before turning the computer off. After all, you don’t know how long the power may be off and in the meantime, your office is likely to be completely blacked out. There’s not much pleasure in working in the dark so, normally, you will just want to save your work, close down all programs and turn the machine off. The UPS needs to be able to run the video monitor as well as the computer itself and since a typical monitor has a power consumption of around 100W or so, that is a relatively large portion of the total power draw. The Apollo UPS consists of two parts. There is the UPS itself which PCB POWER TRANSFORMERS 1VA to 25VA takes the place of the normal switchmode power supply. It has the normal 3-pin IEC sockets for 240VAC input and switched output to the video monitor. The 24V 2.2Ah battery pack is enclosed in a case which fits into a standard 5.25-inch drive bay and it is charged from the UPS. The UPS is rated for a total output of 500VA which should cater for most computer and monitor combinations, although the maximum output from the switched socket to the monitor is rated at 140W. Installation is a straightforward matter: pull out the existing power supply, slide in the new one, together with the battery pack, hook it all up and away you go. The battery pack needs to be charged for 24 hours. After that it is ready to perform as a backup at any time. If the mains supply does fail, the UPS gives both audible (buzzer) and visible (flashing LED) indications of the battery status so that you can shut down in an orderly fashion. The actual operation time on battery will depend on the particular machine but is quoted as anywhere between 3 and 30 minutes. The battery recharge time is quoted as a minimum of 10 hours. The combined UPS/power supply is priced at $429 including sales tax and optional software for automatic shutdown is avail­able. For further information, contact Microgram Computers, Unit 1/14 BonMace Close, Berkeley Vale, NSW 2261. Phone (02) 4389 8444; fax 4389 8388. 4-channel learning UHF transmitter Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 32  Silicon Chip If you’ve ever had to replace a UHF remote control (for your car alarm, garage door opener, etc), you would know that genuine replacements are ridiculously expensive. For example, we were recently quoted $80 for a single channel Tilt-A-Dor controller. That’s one of the things that makes this $39 “Remocon” keyring-sized controller from Oatley Electronics so attractive. Another is that it will actually learn the digital code from an existing controller – anywhere in ELECTRONIC COMPONENTS & ACCESSORIES •  RESELLER FOR MAJOR KIT RETAILERS •  PROTOTYPING EQUIPMENT •  CB RADIO SALES AND ACCESSORIES •  FULL ON-SITE SERVICE AND REPAIR FACILITIES •  LARGE RANGE OF ELECTRONIC DISPOSALS (COME IN AND BROWSE) One of the banes of anyone who likes to do basic service on appliances are security screws. Some examples are Allen (hex) key screws with a central pin, Tri-Wing (similar to Philips but three slots instead of cross-slot) and Torx tamperpoof, again with a central pin. These are deliberately used by manufacturers to stop people from pulling appliances apart. So if something simple occurs like a switch failing or the power cord going open cir­cuit, you can’t fix it yourself; you must send it back to the manufacturer’s authorised service centre. Faced with a choice like that, many people just throw the appliance away and buy a new one but not the same brand – who wants to get caught a second time. Now you don’t have this un­pleasant choice because you can buy this set of security screw­driver bits. It contains 32 bits and a 50mm magnetic holder which fits into a standard hex-drive screwdriver or can be used with any electric screwdriver or battery-operated drill. Just recently, one of our staff members was faced with the above scenario. The power cord of his electric lawn trimmer had gone open circuit just where it entered the handle. This is exactly where you’d expect it to fail because this is where it is flexed and strained the most. But the handle and the whole ap­pliance was held together with Torx tamperproof screws (the ones with the small pin in the middle), making it impossible to disassem­ble using normal Torx bits. Not to worry though. He obtained a set of these security bits and had the lawn trimmer’s handle apart in a matter of moments. From there it was only a matter of cutting the defective section out of the power cord, resecur­ing it and he was back in business inside 10 minutes. He’d mended an appliance which would have otherwise cost over $150 to replace or possibly $40 and a week or so to have serviced. You can obtain this security bit set from any Jaycar Elec­tronics store at $29.95 (Cat TD-2035). the frequency range of 255-500MHz. Yet another is its tiny size: 65 x 35 x 13mm, not including its keyring atttachment. What’s more, it can handle up to four different codes so the one keyring-sized unit can replace the remotes for your car alarm, garage door, home alarm, etc, as well as replace multi-function remotes Teaching the Remocon is as simple as adjusting the frequency until its LED glows brightest (there are three jumpers to select basic frequency range and a fine frequency adjustment) and simultaneously pressing the required button on the Remocon and the button on the existing remote. A LED flashes to tell you the code has been learnt. In use, we found the Remocon had a range at least as great as the remote it replaced – and was less than half the size! It is available by mail/fax/email order from Oatley Electronics, phone (02) 9583 3563, fax (02) 9583 3561, email oatley<at>world.net Croydon Ph (03) 9723 3860 Fax (03) 9725 9443 Mildura Ph (03) 5023 8138 Fax (03) 5023 8511 M W OR A EL D IL C ER O M E Versatile security screwdriver bit set Truscott’s ELECTRONIC WORLD Pty Ltd ACN 069 935 397 30 Lacey St Croydon Vic 3136 24 Langtree Ave Mildura Vic 3500 Huge range of VIDEO Processors, Stabilisers, Mixers, Editors, TBC’s, Standards Converters, Switchers, Amplifiers, connectors, cables, adaptors, kits. PC editing cards & software:- FAST DV, AV Master plus, Miro DV300, DC30+, DPS Spark, Edit Bay, etc. SCSI cards & drives. PC Converters & Genlocks. Call for prices and information or ... Check our website for latest prices and MONTHLY SPECIALS http://www.questronix.com.au/~questav You can fax, post, phone or email your order. We accept AMEX, VISA, Master & Bank cards, cash and direct deposit, but not cheques. Ex-tax sales available to exempt buyers. Prompt delivery within Australia & overseas. 2/1 Leonard Street, HORNSBY, NSW, 2077 P O Box 548, WAHROONGA, NSW, 2076 Fax (02) 9477 3681 Ph. (02) 9477 3596 Email questav<at>questronix.com.au Visitors and demo's by appointment only. Resolution VCC3010 High Picture Corrector Adjust RGB/ Contrast/ Brightness/ Saturation/ Detail etc. 4 i/p Audio & Video selectors. Fade to black. Use Y/C & Comp. i/p's & o/p's in any combination. $679.00 The ultimate stabiliser E-D TBC/ Enhancer Totally eliminates 'piggy-back' signals! Full-frame 4:2:2 digital TBC. Adjust RGB, gain, black level, chroma, colour shift, etc. Freeze, enhance, bypass, four memories for settings, built-in Bars, Black Burst, etc, etc. $1,599.00 July 1998  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: www.altronics.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.altronics.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.altronics.com.au Silicon Chip Bookshop SUBSCRIBE   AND GET   10% OFF SEE PAGE 88 Guide to Satellite TV Installation, Recept­ion & Repair. By Derek J. Stephen­son. First published 1991, reprinted 1997 (4th 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. 383 pages, in hard cover at $55.00. 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 $90.00. Video Scrambling & Descrambling For Satellite & Cable TV By Rudolf F. Graf & William Sheets. First pub­lished 1987. This is an easy-to-understand book for those who want to scramble and unscramble video signals for their own use or just want to learn about the techniques involved. It begins with the basic techniques, then details the theory of video encryption and decryption. It also provides schematics and details for several encoder and decoder projects, has a chapter of relevant semiconductor data sheets, covers three relevant US patents on the subject of scrambling and concludes with a chapter of technical data. 246 pages, in soft cover at $50.00. 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 inter­ ested in audio design. 336 pages, in paperback at $70.00. Digital Audio & Compact Disc Technology 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 format and R-DAT. If you want to understand digital audio, you need this reference book. 305 pages, in paperback at $90.00. Surface Mount Technology By Rudolph Strauss. First pub­lished 1994. This book will provide informative reading for anyone considering the assembly of PC boards with surface mounted devices. Includes chapters on wave soldering, reflow­soldering, component placement, cleaning & quality control. 361 pages, in hard cover at $99.00. Radio Frequency Transistors 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 $95.00. Guide to TV & Video Technology By Eugene Trundle. First pub­lished 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 $55.00. Electronics Engineer’s Reference Book Edited by F. F. Mazda. First published 1989. 6th edition. This just has to be the best refer­ ence book available for electronics engineers. Provides expert coverage of Your Name__________________________________________________ PLEASE PRINT Address____________________________________________________ _____________________________________Postcode_____________ Daytime Phone No.______________________Total Price $A _________ ❏ Cheque/Money Order  ❏ Bankcard  ❏ Visa Card  ❏ MasterCard Card No. Signature_________________________ Card expiry date_____/______ Return to: Silicon Chip Publications, PO Box 139, Collaroy NSW, Australia 2097. Or call (02) 9979 5644 & quote your credit card details; or fax to (02) 9979 6503. Prices valid until 30th July, 1998 all aspects of electronics in five parts: techniques, physical phenomena, material & components, electronic design, and applications. The sixth edition has been expanded to include chapters on surface mount technology, hardware & software design, semi­-custom electronics & data communications. 63 chapters, soft cover at $160.00. 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 $75.00. Understanding Telephone Electronics By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. This is a very useful text for anyone wanting to become familiar with the basics of telephone technology. The 10 chapters explore telephone fundamentals, speech signal processing, telephone line interfacing, tone and pulse generation, ringers, digital transmission techniques (modems & fax machines) and much more. Ideal for students. 367 pages, in soft cover at $55.00. ✓ Title Price ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ Guide to Satellite TV $55.00 Servicing Personal Computers $90.00 Video Scrambling & Descrambling $50.00 The Ar t Of Linear Electronics $70.00 Digital Audio & Compact Disc Technology $90.00 Surface Mount Technology $99.00 Radio Frequency Transistors $95.00 Guide to TV & Video Technology $55.00 Electronic Engineer's Reference Book $160.00 Audio Electronics $75.00 Understanding Telephone Electronics $55.00 Postage: add $5.00 per book. Orders over $100 are post free within Australia. NZ add $10.00 per book; elsewhere add $15 per book. TOTAL $A Silicon Chip Back Issues 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 For Your PC, Pt.2; Build a Turnstile Antenna For Weather Satellite Reception. September 1988: Hands-Free Speakerphone; Electronic Fish Bite Detector; High Performance AC Millivoltmeter, Pt.2; Build The Vader Voice. 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. 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. 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. 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. 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; 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. 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; Guide 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. 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 1990: High Quality Sine/Square Oscillator; Service Tips For Your VCR; Phone Patch For Radio Amateurs; Active Antenna Kit; Designing UHF Transmitter Stages. February 1991: Synthesised Stereo AM Tuner, Pt.1; Three Low-Cost Inverters For Fluorescent Lights; Low-Cost Sinewave Oscillator; Fast Charger For Nicad Batteries, Pt.2; How To Design Amplifier Output Stages. February 1990: A 16-Channel Mixing Desk; Build A High Quality Audio Oscillator, Pt.2; The Incredible Hot Canaries; Random Wire Antenna Tuner For 6 Metres; Phone Patch For Radio Amateurs, Pt.2. 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. 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 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. 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. 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. April 1993: Solar-Powered Electric Fence; Audio Power Meter; Three-Function Home Weather Station; 12VDC To 70VDC Converter; Digital Clock With Battery Back-Up. June 1990: Multi-Sector Home Burglar Alarm; Build A LowNoise Universal Stereo Preamplifier; Load Protector For Power Supplies; Speed Alarm For Your Car. June 1991: A Corner Reflector Antenna For UHF TV; Build A 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. May 1993: Nicad Cell Discharger; Build The Woofer Stopper; Alphanumeric LCD Demonstration Board; The Microsoft Windows Sound System; The Story of Aluminium. July 1990: Digital Sine/Square Generator, Pt.1 (0-500kHz); Burglar Alarm Keypad & Combination Lock; Simple Electronic Die; LowCost Dual Power Supply; Inside A Coal Burning Power Station. 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. June 1993: AM Radio Trainer, Pt.1; Remote Control For The Woofer Stopper; Digital Voltmeter For Cars; A Windows-Based Logic Analyser. 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. ORDER FORM Please send me the following back issues: _____________________________________________________________________ _______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 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 ___________ 38  Silicon Chip Note: all prices include post & packing Australia (by return mail) ............................. $A7 NZ & PNG (airmail) ...................................... $A8 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. 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. April 1995: Build An FM Radio Trainer, Pt.1; Photographic Timer For Dark­rooms; Balanced Microphone Preamp. & Line Filter; 50W/Channel Stereo Amplifier, Pt.2; Wide Range Electrostatic Loudspeakers, Pt.3; 8-Channel Decoder For Radio Remote Control. January 1997: How To Network Your PC; 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. August 1993: Low-Cost Colour Video Fader; 60-LED Brake Light Array; Microprocessor-Based Sidereal Clock; Southern Cross Z80-Based Computer; A Look At Satellites & Their Orbits. May 1995: What To Do When the Battery On Your PC’s Mother­board Goes Flat; Build A Guitar Headphone Amplifier; FM Radio Trainer, Pt.2; Transistor/Mosfet Tester For DMMs; A 16-Channel Decoder For Radio Remote Control; Introduction to Satellite TV. February 1997: Cathode Ray Oscilloscopes, Pt.6; PC-Controlled Moving Message Display; Computer Controlled Dual Power Supply, Pt.2; Alert-A-Phone Loud Sounding Alarm; Control Panel For Multiple Smoke Alarms, Pt.2. 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. March 1997: Driving A Computer By Remote Control; Plastic Power PA Amplifier (175W); Signalling & Lighting For Model Railways; Build A Jumbo LED Clock; Audible Continuity Tester; Cathode Ray Oscilloscopes, Pt.7. September 1993: Automatic Nicad Battery Charger/Discharger; Stereo Preamplifier With IR Remote Control, Pt.1; In-Circuit Transistor Tester; A +5V to ±15V DC Converter; Remote-Controlled Cockroach. October 1993: Courtesy Light Switch-Off Timer For Cars; Wireless Microphone For Musicians; Stereo Preamplifier With IR Remote Control, Pt.2; Electronic Engine Management, Pt.1. November 1993: Jumbo Digital Clock; High Efficiency Inverter For Fluorescent Tubes; Stereo Preamplifier With IR Remote Control, Pt.3; Siren Sound Generator; Engine Management, Pt.2; Experiments For Games Cards. December 1993: Remote Controller For Garage Doors; LED Stroboscope; 25W Amplifier Module; 1-Chip Melody Generator; Engine Management, Pt.3; Index To Volume 6. January 1994: 3A 40V Adjustable Power Supply; Switching Regulator For Solar Panels; Printer Status Indicator; Mini Drill Speed Controller; Stepper Motor Controller; Active Filter Design; Engine Management, Pt.4. February 1994: Build A 90-Second Message Recorder; 12-240VAC 200W Inverter; 0.5W Audio Amplifier; 3A 40V Adjustable Power Supply; Engine Management, Pt.5; Airbags – How They Work. 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. 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. 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; 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: How Dolby Surround Sound Works; Dual Rail Variable Power Supply; Build A Talking Headlight Reminder; Electronic Ballast For Fluorescent Lights; Build A Temperature Controlled Soldering Station; Electronic 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; 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 Pre­ amp­lifier;The Latest Trends In Car Sound; Pt.1. February 1995: 50-Watt/Channel Stereo Amplifier Module; Digital Effects Unit For Musicians; 6-Channel Thermometer With LCD Readout; Wide Range Electrostatic Loudspeakers, Pt.1; Oil Change Timer For Cars; The Latest Trends In Car Sound; Pt.2; Remote Control System For Models, Pt.2. March 1995: 50 Watt Per 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. July 1995: Electric Fence Controller; How To Run Two Trains On A Single Track (Incl. Lights & Sound); Setting Up A Satellite TV Ground Station; Build A Reliable Door Minder (Uses Pressure Sensing); Adding RAM To A Computer. August 1995: Fuel Injector Monitor For Cars; Gain Controlled Microphone Preamp; Audio Lab PC Controlled Test Instrument, Pt.1; Mighty-Mite Powered Loudspeaker; How To Identify IDE Hard Disc Drive Parameters. September 1995: Keypad Combination Lock; The Incredible Vader Voice; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.1; Jacob’s Ladder Display; The Audio Lab PC Controlled Test Instrument, Pt.2. October 1995: Geiger Counter; 3-Way Bass Reflex Loudspeaker System; Railpower Mk.2 Walkaround Throttle For Model Railways, Pt.2; Fast Charger For Nicad Batteries; Digital Speedometer & Fuel Gauge For Cars, Pt.1. November 1995: Mixture Display For Fuel Injected Cars; CB Trans­ verter 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. 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 Diode 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; Build A High Voltage Insulation Tester; Knightrider Bi-Directional LED Chaser; Simple Duplex Intercom Using Fibre Optic Cable; Cathode Ray Oscilloscopes, Pt.3. June 1996: BassBox CAD Loudspeaker Software Reviewed; Stereo Simulator (uses delay chip); Rope Light Chaser; Low Ohms Tester For Your DMM; Automatic 10A Battery Charger. July 1996: Installing a Dual Boot Windows System On Your PC; Build A VGA Digital Oscilloscope, Pt.1; Remote Control Extender For VCRs; 2A SLA Battery Charger; 3-Band Parametric Equaliser; Single Channel 8-bit Data Logger. August 1996: Electronics on the Internet; Customising the Windows Desktop; Introduction to IGBTs; Electronic Starter For Fluores­cent Lamps; VGA Oscilloscope, Pt.2; 350W Amplifier Module; Masthead Amplifier For TV & FM; Cathode Ray Oscilloscopes, Pt.4. September 1996: VGA Oscilloscope, Pt.3; Infrared Stereo Headphone Link, Pt.1; High Quality PA Loudspeaker; 3-Band HF Amateur Radio Receiver; Feedback On Pro­grammable Ignition (see March 1996); Cathode Ray Oscilloscopes, Pt.5. October 1996: Send Video Signals Over Twisted Pair Cable; Power Control With A Light Dimmer; 600W DC-DC Converter For Car Hifi Systems, Pt.1; Infrared Stereo Headphone Link, Pt.2; Multi-Media Sound System, Pt.1; Multi-Channel Radio Control Transmitter, Pt.8. November 1996: Adding An Extra Parallel Port To Your Computer; 8-Channel Stereo Mixer, Pt.1; Low-Cost Fluorescent Light Inverter; How To Repair Domestic Light Dimmers; Build A Multi-Media Sound System, Pt.2; 600W DC-DC Converter For Car Hifi Systems, Pt.2. December 1996: CD Recorders ­– The Next Add-On For Your PC; Active Filter Cleans Up CW Reception; Fast Clock For Railway Modellers; Laser Pistol & Electronic Target; Build A Sound Level Meter; 8-Channel Stereo Mixer, Pt.2; Index To Volume 9. April 1997: Avoiding Windows 95 Hassles With Motherboard Upgrades; Simple Timer With No ICs; Digital Voltmeter For Cars; Loudspeaker Protector For Stereo Amplifiers; Model Train Controller; A Look At Signal Tracing; Pt.1; Cathode Ray Oscilloscopes, Pt.8. May 1997: Windows 95 – The Hardware Required; Teletext Decoder For PCs; Build An NTSC-PAL Converter; Neon Tube Modulator For Light Systems; Traffic Lights For A Model Intersection; The Spacewriter – It Writes Messages In Thin Air; A Look At Signal Tracing; Pt.2; Cathode Ray Oscilloscopes, Pt.9. June 1997: Tuning Up Your Hard Disc Drive; PC-Controlled Thermometer/ Thermostat; Colour TV Pattern Generator, Pt.1; Build An Audio/RF Signal Tracer; High-Current Speed Controller For 12V/24V Motors; Manual Control Circuit For A Stepper Motor; Fail-Safe Module For The Throttle Servo; Cathode Ray Oscilloscopes, Pt.10. July 1997: Infrared Remote Volume Control; A Flexible Interface Card For PCs; Points Controller For Model Railways; Simple Square/Triangle Waveform Generator; Colour TV Pattern Generator, Pt.2; An In-Line Mixer For Radio Control Receivers; How Holden’s Electronic Control Unit works, Pt.1. August 1997: The Bass Barrel Subwoofer; 500 Watt Audio Power Amplifier Module; A TENs Unit For Pain Relief; Addressable PC Card For Stepper Motor Control; Remote Controlled Gates For Your Home; How Holden’s Electronic Control Unit Works, Pt.2. September 1997: Multi-Spark Capacitor Discharge Ignition; 500W Audio Power Amplifier, Pt.2; A Video Security System For Your Home; PC Card For Controlling Two Stepper Motors; HiFi On A Budget; Win95, MSDOS.SYS & The Registry. October 1997: Build A 5-Digit Tachometer; Add Central Locking To Your Car; PC-Controlled 6-Channel Voltmeter; The Flickering Flame Stage Prop; 500W Audio Power Amplifier, Pt.3; Customising The Windows 95 Start Menu. November 1997: Heavy Duty 10A 240VAC Motor Speed Controller; Easy-To-Use Cable & Wiring Tester; Regulated Supply For Darkroom Lamps; Build A Musical Doorbell; Relocating Your CD-ROM Drive; Replacing Foam Speaker Surrounds; Understanding Electric Lighting Pt.1. December 1997: A Heart Transplant For An Aging Computer; Build A Speed Alarm For Your Car; Two-Axis Robot With Gripper; Loudness Control For Car Hifi Systems; Stepper Motor Driver With Onboard Buffer; Power Supply For Stepper Motor Cards; Understanding Electric Lighting Pt.2; Index To Volume 10. January 1998: Build Your Own 4-Channel Lightshow, Pt.1 (runs off 12VDC or 12VAC); Command Control System For Model Railways, Pt.1; Pan Controller For CCD Cameras; Build A One Or Two-Lamp Flasher; Understanding Electric Lighting, Pt.3. February 1998: Hot Web Sites For Surplus Bits; Build A Multi-Purpose Fast Battery Charger, Pt.1; Telephone Exchange Simulator For Testing; Command Control System For Model Railways, Pt.2; Demonstration Board For Liquid Crystal Displays; Build Your Own 4-Channel Lightshow, Pt.2; Understanding Electric Lighting, Pt.4. March 1998: Sustain Unit For Electric Guitars; Inverter For Compact Fluorescent Lamps; Build A 5-Element FM Antenna; Multi-Purpose Fast Battery Charger, Pt.2; Command Control System For Model Railways, Pt.3; PC-Controlled LCD Demonstration Board; Feedback On The 500W Power Amplifier; Understanding Electric Lighting, Pt.5; Auto-detect & Hard Disc Drive Parameters. May 1998: Troubleshooting Your PC, Pt.1; Build A 3-LED Logic Probe; A Detector For Metal Objects; Automatic Garage Door Opener, Pt.2; Command Control For Model Railways, Pt.4; 40V 8A Adjustable Power Supply, Pt.2. June 1998: Troubleshooting Your PC, Pt.2; Understanding Electric Lighting, Pt.7; Universal High Energy Ignition System; The Roadies’ Friend Cable Tester; Universal Stepper Motor Controller; Command Control For Model Railways, Pt.5. PLEASE NOTE: November 1987 to August 1988, October 1988 to March 1989, June 1989, August 1989, December 1989, May 1990, August 1991, February 1992, July 1992, September 1992, November 1992, December 1992 and April 1998 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 for $10 including p&p. July 1998  39 Pt.8: Metal Halide Lamps Electric Lighting Metal halide lamps are very similar in their design to mercury vapour lamps. However, metal halide lamps produce a crisp, white light that makes them well-suited to floodlighting sports arenas, especially when events are to be televised. By JULIAN EDGAR As we have previously seen (SILICON CHIP, February 1998), mer­cury vapour lamps have a poor colour rendering, with a typical Ra of 45. Using metals other than mercury in a discharge lamp was long recognised as a potential solution to this problem. However, the use of alternative metals in elemental form was not success­ful 40  Silicon Chip because their low vapour pressures prevented the efficient production of radiation at normal arc temperatures. The discovery by Dr Reiling in 1960 that metals could be successfully introduced into the arc in iodide salt form made the metal halide lamp feasible. Early metal halide lamps used indium, thallium and sodium iodides, while more recent lamps use a varie­ty of other metals including scandium, holmium, thulium and dysprosium (and no, these aren’t made-up names!). The basic requirements of the metal additive are as fol­lows: (1) the iodide of the metal must be stable at high bulb-wall operating temperatures; (2) the iodide vapour pressure must be relatively high; (3) the excitation levels of the metal must be lower than that of mercury; and (4) the metal must emit a high proportion of visible radiation when excited. Lamp design Fig.1 shows a typical metal halide Fig.1: the construction of a typical metal halide lamp. The discharge tube is suspended within an outer glass bulb. lamp. The discharge tube is usually made of pure quartz, although some lamps employ PCA tubes similar to those used in high-pressure sodium vapour lamps. The tube is filled with a mixture of inert gases (neon-argon or krypton-argon), mercury and the appropriate metal halides. In addition, a white layer of zirconium oxide is applied to the outside of the electrode chambers and this helps maintain the arc tube at a uniform temperature. The electrodes consist of rods of tungsten on which a double layer of tungsten wire is wound. They are impregnated with an electron emissive material and are very similar to those The Sylvania Super MetalArc metal halide lamps are avail­able in power ratings from 175W to 1kW. The lamp life is 20,000 hours and the lamps are available with colour temperatures from 3200-4700K. used in a mercury vapour lamp. The gas used to fill the outer bulb of the lamp depends on the discharge tube filling. If the discharge tube contains a neon-argon mixture, the outer bulb is filled with neon to main­tain the same neon pressure inside and outside the tube. Alterna­tively, if the discharge tube contains krypton-argon, the outer bulb is filled with nitrogen or it is evacuated. The inner surface of the bulb is coated with phosphor to convert the UV radiation of the discharge tube to visible radia­tion. However, unlike a mercury vapour lamp, a metal halide discharge tube radiates only a small amount of UV radiation and even this is mainly long-wave radiation whose conversion to visible radiation is Fig.2: this spectral output of a three-band metal halide lamp clearly shows the three lines. poor. By far the majority of the light output comes from the halides. Lamp performance The performance of a metal halide lamp is very much de­pendent on the halides used. There are three main groups of halide lamps: (1) three-band colour radiators; (2) multi-line radiators; and (3) molecular radiators. A three-band radiator uses halides of indium, thalium and sodium. Lamps of this type have an efficacy of 69-79 lumens/watt, a colour rendering (Ra) of 60 and a colour temperature of 4300K. They are available with ratings up to 2kW and are suitable for large scale floodlighting, especially for TV broadcasts. Fig.2 shows the Fig.3: a multi-line lamp radiates energy across a much broader spectrum, giving an improved colour rendering of up to Ra 85. July 1998  41 Total IR Radiation (237W) Visible Radiation (97W) Convection & Conduction (61W) UV Radiation (5W) Fig.4: the energy balance of a 400W metal halide lamp. It produc­es 97W of visible radiation and 237W of infrared radiation. spectral output of a lamp of this type, with the three lines clearly visible. The Philips MHN-TD lamp is a multi-line radiator that uses thalium and sodium. Its spectral output is shown in Fig.3. As can be seen, it radiates energy across a much broader spectrum, thereby giving an improved colour rendering of up to Ra 85 in some wattages. Its efficacy is 75 lumens/watt and it has a colour temperature of 4200K. This type of lamp is suitable for indoor luminaires and lower power floodlights. Compared with the tungsten halogen lamps often used in these applications, metal halide lamps have four times the efficacy and three times the life expectancy! The rare molecular radiator metal halide lamp uses SnCl2/SnI2. These lamps have a typical efficacy of 61 lumens/watt, an excellent colour rendering of Ra 85 and a colour temperature of 5500K. Fig.4 shows the energy balance of into just 5W of visible light). Metal halide lamps are very susceptible to mains voltage fluctuations. This is especially so with three-band lamps which display a colour shift if the mains voltage varies by more than 10% from the nominal value. The reason for this lies in the lamp’s operation. In a three-band lamp, the indium vaporises first, forming a blue sheath around the mercury arc. Next the thallium vaporises, forming a green sheath around the thallium. The sodium is the last to vaporise, producing a yellow output. It follows therefore that if the lamp power is lower than rated, too little sodium will be vaporised and the lamp will be deficient in yellow and red. Conversely, too high a lamp wattage causes a colour shift towards pink. Fig.5 shows the start-up characteristics of a typical metal halide lamp. Control circuits Fig.5: the start-up behaviour of a metal halide lamp. It takes about three minutes to achieve a stable condition. a three-band, 400-watt metal halide lamp. Of the 400W input power, 237W of infrared radiation and 97W of visible radiation are produced. Only a small amount of the UV light emitted from the discharge tube is con­verted into visible radiation (15 watts of UV light is emitted from the tube and this is converted by the phosphor coating Metal halide lamps use the control circuits that were originally developed for other lamp types. Threeband lamps employ the ballasts intended for high-pressure mercury lamps, while multi-line lamps use the ballasts originally designed for high-pressure sodium vapour lamps. The voltage available from a choke ballast is not suffi­cient to start metal halide lamps, so an external starter is used. Very high voltage (30-60kV) series starters are used where instant reignition after a power failure is requir­ ed. Normally, the pressure in the discharge tube is too high to permit instant re-ignition and a cooling-down period of 5-20 minutes is necessary. SC Fig.6: the spectral distribution of a typical metal halide lamp (Philips). Right: the Philips ArenaVision range of floodlights is designed specifically for metal halide lamps. It is used to illuminate medium to large stadia and uses a multi-line lamp rated at 1.8kW. 42  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. The advertiser, BBS Electronics, is no longer in business. SATELLITE WATCH Compiled by GARRY CRATT* New digital service on Intelsat 701 Intelsat 701 (180°E) The RFO analog signal at 4049MHz RHCP disap­peared on April 1st and was replaced with a digital service operating at 4095MHz LHCP SR 27500, FEC 3/4. The new service utilises a west hemi-beam, making it difficult to receive along the east coast of Australia without a 3.7m dish. We have had reception reports from Brisbane, Orange and Newcastle (NSW). RFO is part of a multi-channel package containing some free-to-air channels (RFO1 and RFO2) and several encrypted chan­nels for Polynesia and New Caledonia (Canal +). In addition, the previously un-encrypted Vidiplexed channel at 3930MHz has almost permanently adopted some form of cut and rotate encryption, possibly macrovision, making it unviewable for most of the time. PAS-2 (169°E) NHK commenced digital transmissions on 4035MHz SR26470 FEC 3/4 on April 1st, as previously reported. The analog service is now operating at 4060MHz vertical polarity, half transponder. TV Chile International has left this satellite. They are considering reappearing in some kind of subscription format. ABN (now NBC), previously carried with CTN and other CA Chinese services on this satellite, has disappeared. NBC contin­ues on 4093MHz, vertical polarity, SR 29473, FEC 3/4. NBC Asia will be replaced by a combination of NBC Network and the National Geographic Channel programming from 44  Silicon Chip July 1st. The service will be uplinked from Singapore. Gorizont 27 (96.5°E) ORT 1, normally seen on transponder 6 (3675MHz), has moved to 3825MHz, possibly due to transponder deterioration. Meanwhile the ex-Gorizont 30 satellite, presently located at 122°E, continues to beam a commercial Russian network HTB on 3675MHz LHCP. We have some customers who have successfully used a 1.2m dish to obtain entertainment quality signals along the east coast of Australia. Measat 1 (91.5°E) VTV4 Vietnam continues to operate at 3715MHz and RTM (TV1) ex Palapa C2 operates at 3880MHz. Apstar 1 (134°E) MGM Gold has disappeared from this satellite after a corporate decision was made to cease operations, a result of the Asian economic crisis. Apparently, the company had invest­ed around US$20 million in the project. The project was a joint partnership between Encore Media and MGM. Programming was dis­tributed in Hong Kong, Taiwan, Indonesia, the Philippines and Malaysia. Poor subscriptions from cable operators and strong competition have been quoted as some of the reasons for closure. affected an earthquake monitor­ ing system carried on part of one of the satellite transponders. APT issued a press statement on April 10th saying that they were trying to trace the signal as quickly as possible. Apstar 2R CNN has migrated from analog to digital on this satel­lite and can now be found on 3980MHz vertical polarity, SR 26000, FEC 3/4. Asiasat 3 Hughes Global Services has taken drastic action in an attempt to recover the Asiasat 3 satellite which was stranded in a low earth orbit after a launch malfunction last December. By firing the spacecraft’s on-board rocket motor several times, they have managed to obtain a steady increase in the apogee of the satellite. The aim of the exercise is to place the satellite in a slingshot trajectory around the Moon and then, by utilising lunar gravity, return the spacecraft to a usable Earth orbit. The engineers expect to use most of the on-board propellant during this exercise, thereby limiting the life of the satellite, which was expected back in Earth orbit by the end of May. Asiasat 3 was considered to be one of the most powerful satellites ever launched and may yet prove useful if this technique SC is success­ful. Interference In other APSTAR news, officials in China are attempting to trace the source of terrestrial interference which has, since March 14th, adversely *Garry Cratt is Managing Director of AvComm Pty Ltd, suppliers of satellite TV reception systems. Phone (02) 9949 7417. http://www.avcomm.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 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 ORDER FORM BACK ISSUES MONTH YEAR MONTH YEAR PR ICE EACH (includes p&p) TOTAL Australi a $A7.00; NZ $A8.00 (airmail ); Elsewhere $A10 (airmail ). Buy 10 or more and get a 10% discount. Note: Nov 87-Aug 88; Oct 88-Mar 89; June 89; Aug 89; Dec 89; May 90; Aug 91; Feb 92; July 92; Sept 92; NovDec 92; & March 98 are sol d out. All other issues are currently i n stock. $A B INDERS Pl ease send me _______ SILICON CHIP bi nder(s) at $A12.95 + $5.00 p&p each (Australi a only). N ot avail abl e elsewhere. 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Please have your credit card details ready OR Fax (02) 9979 6503 Fax the coupon with your credit card details 24 hours 7 days a week Mail order form to: OR Reply Paid 25 Silicon Chip Publications PO Box 139, Collaroy 2097 No postage stamp required in Australia July 1998  53 A Amplifier Modu CLASS- Here’s one for the “golden ear” brigade: an amplifier module with ultra-low distortion and noise and running in class-A mode so there’s absolutely no chance of the dreaded crossover distortion. By LEO SIMPSON Over the years we have had two common requests from our audiophile readers for amplifier designs. The first request, which we have always turned down, has been for a valve amplifier. As we noted in an editorial in the July 1994 issue, valve ampli­fiers are fine for people on a nostalgia kick but if you want real quality and value for money, a well designed solid-state amplifier wins every time, and by a mile! The second request which we have not agreed to, until this issue, has been for a no-holds-barred class-A amplifier. We have not been keen on class-A amplifiers for one very practical reason – they dissipate heaps of power and they get hot. They also 54  Silicon Chip have other drawbacks which we’ll talk about later. Now we’ve finally relented and have produced a 15W class-A amplifier with really low distortion – so low in fact that it is a real problem to measure, even with our state-ofthe-art Audio Precision distortion measuring system. Mind you, it only puts out 15 watts. That’s about par for a typical valve amplifier and it will get just as hot. We envision this amplifier will appeal to several different groups of readers. First, it should appeal to those who wanted us to design a good valve amplifier, one that wouldn’t have that despised “transistor sound”. Well, this one will have a very clean transistor sound but there won’t be any cross­over distor­tion which normally occurs to a slight degree, even in the best class-AB transistor amplifiers. So in effect, this could be the “valve amplifier you build when you’re not building a valve amplifier”. Since its power output is limited to 15W, your loudspeakers will need to be reasonably efficient and your listening room not too large. The second group of readers likely to be interested in this amplifier are those who want a really good class-A headphone amplifier. Sure it’s a bit of overkill if you just want to drive headphones but it could be easily modified if that’s all you want. Performance As you can see from the accomp­ anying performance panel and distor- The heatsink for this 15W class-A module may look ridiculously large but it has to be that size to safely dissipate 40 watts continuously. ule you are likely to use with it, whether it is a magnetic cartridge, tuner or any type of tape player. Noise filtering & distortion tion graphs, the harmonic distortion of this amplifier is a great deal better than any previous amplifier that we have pub­lished but the figures do not tell the whole story. Unweighted signal-to-noise ratio (22Hz to 22kHz) is -113dB while the A-weighted figure is -116dB. Those noise figures are pretty low but they’re not low enough to enable us to easily measure the distortion which is typically around .0006% or a lot less. That’s not a misprint. That figure of .0006% is around 10 times better than any ampli­ fier we have published in the past. This is much less than the typical rated distortion of .002% of a CD player and a great deal less than the distortion produced by a CD player over most of its dynamic range. By way of explanation, CD players produce their rated distortion only at their maximum output level of 2V. At lower levels, their distor­tion levels will be considerably higher. The same comment applies to Mini-disc, DCC and DAT players. It goes without saying that the distortion level of this amplifier is hundreds or even thousands of times less than any other program source Fig.1 shows the total harmonic distortion (THD) versus power at 1kHz for the class-A module. This has been taken with a noise bandwidth of 22Hz to 22kHz, the same as for the unweighted noise measurement referred to above. As you can see, the measure­ ment is around .0006% at 10W and then rises very steeply above 15W, which is where the amplifier starts to clip. When we look at the other part of the graph it shows the distortion rising gradually as the power level is reduced below 5W. In fact, while the THD reading is rising, it is rising only because the residual noise component July 1998  55 AUDIO PRECISION SCTHD-W THD+N(%) vs measured 10 LEVEL(W) 02 JUN 98 12:24:33 1 0.1 0.010 0.001 .0005 0.1 1 10 20 Fig.1: total harmonic distortion (THD) versus power at 1kHz, taken with a noise bandwidth of 22Hz to 22kHz. AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 02 JUN 98 12:21:45 1 0.1 0.010 0.001 .0005 20 100 1k 10k 20k Fig.2: THD versus frequency at a power level of 10W, taken with a noise bandwidth of 22Hz to 80kHz. of the signal becomes more significant as the level is reduced; the distortion itself is actually reducing. How do we know that? A new technique, using the averaging mode of a digital sampling scope, allows the noise to be effectively filtered out of the THD signal, to reveal the distortion products. In effect, the 56  Silicon Chip sample averaging mode removes the random (noise) components of the signal to reveal the repetitive component which is the wanted signal. This technique was suggested by Doug Self in a recent issue of the English magazine “Electronics World”. We applied this technique to the measurement of distortion at a level of 1W into 8Ω, at a frequency of 1kHz. On the graph of Fig.1, the THD result is ostensibly .001% but when signal averag­ing is applied with our Tek­ tronix TDA360 scope, the true level is about one quarter of that or around .00025%. This is all well and good but when we do a test of our Audio Precision THD meter it comes up with a test result around .0004% (taken with a measurement bandwidth of 80kHz). That’s higher than we’re claiming for the amplifier itself! However, when we apply the same averaging technique to the Audio Precision test set, we come up with an estimated harmonic distor­tion of around .00015%! While this is pretty low, it is only marginally lower than the result of .0002% which we achieved for the amplifier itself at a level of 1W. The true distortion of the amplifier may be a good deal lower but we can’t state what it is. For a valid dis­tortion measurement, the residual distortion of the test equip­ment must be at least 10dB below the amplifier to be measured. On that basis, if we want to reliably measure a distortion level of .0003% for example, the test equipment should be below .0001%. So all we can say with certainty is that the distortion at lower powers is probably less than .0002%. However, by any stan­dard, a distortion level of .0002% is remarkably low for a power amplifier. Fig.2 tells a different story and it also needs to be interpreted. It shows the distortion versus frequency at a power level of 10W, taken with a filter bandwidth of 22Hz to 80kHz. This wider bandwidth will tend to degrade the THD measurements at middle and lower frequencies but will tend to give better than actual results at frequencies between 10kHz and 20kHz. Taking the upper frequencies first, a measurement bandwidth of 80kHz means that we are only measuring up to the 4th harmonic of 20kHz and higher order harmonics are being ignored, hence the THD measurement may be better than reality, not that you can hear any harmonics of 20kHz. At middle and lower frequencies, a measurement bandwidth of 80kHz includes more noise in the measurement and so it will be higher than it otherwise would be. An example of this can be seen at 1kHz where the THD is just above .0009%, while on Fig.1, at 1kHz and 10W, the result is .0006%. The difference of .0003% is solely the extra noise bandwidth from 22kHz to 80kHz. Hence, when looking at frequencies below about 5kHz on Fig.2, remember that the extra noise bandwidth is making the figures worse than they actually are. Fig.3 shows the distortion versus frequency at a power level of 15W, which is just below the onset of clipping. Again, it is taken with a measurement bandwidth of 22kHz to 80kHz but the difference in the distortion figures between 10W and 15W is not due to noise. It is simply due the fact that the amplifier is closer to the point of overload. Fig.4 shows the frequency response of the amplifier at 15W. Amplifier configuration Cast your eyes over the circuit of the new class-A amplifi­er module in Fig.5. Superficially, it doesn’t look much different in the overall configuration from any other discrete component power amplifier we have described in the last 10 years or so, does it? Well, there are some important differences in the output stage arrangement but in general, it’s not much different from other amplifiers that we have published. The reason it doesn’t look much different is that the design principles for good class-A and class-AB amplifiers are in fact identical. The only practical difference is in the amount of quiescent current drawn by the output stage transistors. Now while a typical class-AB amplifier might draw a quiescent current of about 20mA per output transistor, a class-A amplifier must draw a much higher current. To see why this is so, we need to briefly explain the dif­ ferences between the various amplifier classes. In a true class-B amplifier, you essentially have a pair of output transistors driving the loudspeaker. The top transistor conducts for half the output signal and then the bottom transistor conducts for the lower half of the output signal. This means that the transistors switch on and off as the output signal swings high and low. It is that switching action which leads to the dreaded crossover distortion in a class-B amplifier. Crossover distortion is very unpleasant and is normally much more significant at the AUDIO PRECISION SCTHD-HZ THD+N(%) vs FREQ(Hz) 5 02 JUN 98 12:20:06 1 0.1 0.010 0.001 .0005 20 100 1k 10k 20k Fig.3: THD versus frequency at a power level of 15W, which is just below the onset of clipping. Again, it is taken with a measurement bandwidth of 22kHz to 80kHz. AUDIO PRECISION SCFREQRE AMPL(dBr) vs FREQ(Hz) 15.000 02 JUN 98 12:26:22 10.000 5.0000 0.0 -5.000 -10.00 -15.00 20 100 1k 10k 20k Fig.4: frequency response of the amplifier at 15W into an 8Ω load. lower power levels. It was “crossover distortion” that damned the early transistor amplifiers and which was responsible for much of the complaint about “transistor sound”. For this reason, pure class-B amplifiers are never used for any audio applications. Instead, the output transistors are biased on by a modest amount to “soften” the switching action of the output transistors. This has two effects. First, with the optimum amount of quiescent current, it can reduce crossover distortion to vanish­ ingly low levels. Second, it means that for low power outputs, the amplifier is effectively operating in class-A mode anyway. For example, a typical stereo July 1998  57 Fig.5: the circuit is a conventional direct-coupled feedback amplifier with current-feedback pairs in the output stage. The Vbe multiplier (Q10) is adjusted to provide a quiescent current of 1A. amplifier may be operating in class-A mode for power output levels up to 20 milliwatts or more, although that’s really of academic interest only. However, a typical amplifier operating in class-AB will never be as linear as a pure class-A amplifier. Special power supply OK. We’ve already stated that the circuit of the module looks pretty conventional and so it is but that is only part of the story. The power supply design and chassis/wiring layout is much more critical. In fact, if you decide to build the module presented here and install it in a chassis with a conventional power supply, you will be severely disappointed. Unlike a conventional 15W power 58  Silicon Chip amplifier which draws a quiescent (no-signal) current of less than 50mA, this class-A design draws 1A. Yes, that’s right, a whole ampere. With a stereo pair, the total quiescent current will be 2A. By comparison, a 15W per channel class-AB amplifier would only draw about 1.25A when driven to full power. When you consider the fact that the amplifier has balanced supply rails of ±20V, the total power drawn from the supply rails by two 15W class-A modules will be 80 watts. In fact, the total amplifier power dissipation will be around 100W. And that is all the time, regardless of whether a signal is present or not. At no signal, all that power is then dissipated in the heatsinks and so they need to be quite large if they are not to become excessively hot. That’s the other important requirement with this class-A module – it needs a big heatsink. Use a small one and you will cook it. Because the amplifier modules draw so much current from the power supply, the ripple voltage superimposed on the supply rails is quite high. The normal way of reducing this ripple is to add lots of capacitance to the power supply. But you could add as much as 50,000µF to the positive and negative supply rails and it still would not get anywhere near solving the problem of audible hum from the amplifier. And large electrolytic capacitors are very expensive so that is not a practical route anyway. The real problem is that typical direct coupled power amplifiers do not have particularly good power supply rejection (PSRR). This means that if there is a large amount of ripple (hum) and noise superimposed on the supply rails, then some of that signal will inevitably appear at the output of the amplifi­er. Our amplifier incorporates all the usual measures to maximise PSRR but it’s still not good enough on its own. In a typical class-AB amplifier, the ripple voltage super­imposed on the supply rails under no-signal conditions might only be a few millivolts peak-to-peak and that makes a signalto-noise ratio of better than 110dB a relatively routine figure. But in the prototype class-A amplifier, we were having difficulty in obtaining a signal-to-noise ratio of better than 50dB because the ripple on the supply rails was as much as 5V peak-to-peak. -50dB is a lousy S/N figure. We had to come up with an effective solution and quickly. The answer was to come up with a fully regulated power supply, based on standard 3-terminal regulators and power tran­sistors. These get the power supply ripple down to very low levels but hum is still a problem in the amplifier unless it is laid out very carefully. We’ll talk more about those aspects next month. For now, let’s give a brief description of the power amplifier circuit and its assembly. Parts List For 15W Class-A Module 1 PC board, SC01207981, 120 x 81mm 4 20mm fuse clips 2 2A 20mm fuses 1 coil former, 24m OD x 13.7mm ID x 12.8mm long, (Philips 4322 021 30362) 2 metres, 1mm dia. enamelled copper wire 1 200Ω trimpot (Bourns 3296W or similar) 11 PC stakes 1 single sided heatsink 300mm x 75mm x 49mm (W x H x D) (Altron­ics H-0545, DSE H-3406 or equivalent) 2 TO-3P insulating washers 2 small flag heatsinks (for Q11,Q13) 2 10mm standoffs tapped 3mm 2 3mm x 10mm screws 2 3mm x 20mm screws 2 3mm nuts 2 3mm flat washers Semiconductors 5 BC557 PNP transistors (Philips or Motorola) (Q1,Q2,Q3,Q4, Q7) 5 BC547 NPN transistors (Philips or Motorola) (Q5,Q6,Q8,Q9, Q10) 1 BC337 NPN transistor (Philips) (Q11) 1 MJL21194 NPN power transistor (Motorola) (Q12) 1 MJL21193 PNP power transistor (Motorola) (Q14) 1 BC327 PNP transistor (Philips) (Q13) 1 BZX55C3V3 3.3V 0.5W zener diode (ZD1) Capacitors 4 100µF 25VW electrolytic 1 47µF 16VW electrolytic 1 2.2µF 16VW electrolytic 1 0.15µF 100V MKT polyester or Philips MKC 2222 344 2II54 5 0.1 100V MKT polyester 1 .0012pF MKT polyester or ceramic 1 100pF NPO 50V ceramic Resistors (0.25W, 1%) 2 18kΩ 2 180Ω 1 8.2kΩ 2 150Ω 1 3.3kΩ 2 120Ω 1 2.2kΩ 6 100Ω 1 1.8kΩ 1 6.8Ω 1W 1 1.2kΩ 8 1Ω 0.5W 1 390Ω 2 1.8Ω 5W (for setting bias) Note: the module requires regulated supply rails of ±20V. Details will be included next month. Circuit description The most important devices in the circuit of Fig.5 are the output transistors – Motorola MJL21193 and MJL­ 21194. These plastic encapsulated transistors have been featured in a number of our high power amplifier modules in recent years. They are rated at 250V, 16A (30A peak) and 200W and are clearly far more rugged than they need to be for an amplifier module of this power rat­ing. So why did we use them? We used them because they are ac­knowledged to be among the very best transistors for linearity made by any manufacturer in the world. And by using them at much lower than their design currents and voltages we get even better linearity. Second, the output transistors Q12 and Q14 are not used as complementary Darlington emitter followers as has been standard practice with all of our bipolar amplifier designs. Instead, Q12 and its low power driver transistor Q11 are combined into a cur­rent feedback pair; the same comment goes for Q14 and its driver transistor Q13. In effect, Q11 & Q12 are connected as a feedback pair with 100% current feedback from the collector of Q12 to the emitter of Q11, by virtue of the 0.25Ω “emitter” resistor. To make it easier to understand, you could consider Q11 as a standard common emitter amplifier with a 180Ω collector load resistor. Q12’s base emitter junction is connected across the 180Ω resistor and so it becomes a current amplifier stage and its collector load is the common 0.25Ω resistor which provides the current feedback to the emitter of Q11. The result is a compound transistor which has considerably better linearity than a typical Darlington-connected transistor pair in emitter follower mode. The use of this “current feedback pair” connection for the output stage is one the major reasons why this amplifier produces such low distortion; the other major reason is use of the class-A mode. Before leaving the output stage, we should point out that the driver transistors are just the common garden-variety BC337 and BC327 types which are widely used as small signal transistors. The reason why we can use them here instead of much more rugged driver transistors is solely due to the fact that since the amplifier is only called upon to deliver 15W and the output transistors have a relatively July 1998  59 Fig.6: the component overlay for the PC board. Note that transis­tors Q11 and Q13 should be fitted with flag heatsinks. Take care to ensure that all transistors are correctly oriented. high current gain, the drivers do not have to handle much current. Now let’s move to the input side of the amplifier. The input signal is coupled via a 2.2µF capacitor and 1.8kΩ resistor to the base of Q1 which together with Q2 makes up a differential pair. Q3 & Q4 make up a constant current tail which sets the current through Q1 & Q2. The collector loads of Q1 & Q2 are provided by current mirror transistors Q5 & Q6. Using the current mirror load arrangement for the differen­ tial pair gives a very linear stage; ie, low distortion. Most of the voltage gain in the amplifier is provided by the cascode stage involving Q8 & Q9. The collector signal from Q1 is coupled to the base of Q8 and its collector load current becomes the emitter signal to Q9 which effectively acts as a ground­ed base stage. Q9’s base is anchored by ZD1, a 3.3V zener diode, and this sets the collector voltage to Q8. The combined effect of operating Q8 with a constant collec­tor voltage and Q9 in grounded base mode results in a stage with very good linearity and wide bandwidth. Also contributing to the good linearity of the stage is the constant current load provided by PNP transistor Q7. The output signal from the cascode stage is coupled to the base of the driver transistors, Q11 & Q13, via 100Ω resistors. Vbe multiplier The Vbe multiplier stage is provided by Q10 and it is exactly the same arrangement as in any classAB amplifier. A “Vbe multiplier” is a temperature-compensated floating voltage source and in this case it provides about 1.7V between the bases of Q11 and Q13. Q10 multiplies the voltage between its base and emitter, as set by trimpot VR1, by the ratio of the total resistance Noise Averaging & Distortion The scope waveforms on the opposite page demonstrate how noise can obliterate harmonic distortion measurements and how the averaging technique using a Tektronix TDS 360 digital oscilloscope remove the noise to reveal the distortion. The two Polaroid scope photos (taken from a Hitachi 100MHz analog scope) show the 1kHz funda­mental and distortion waveforms at levels of 10W (Fig.7) and 1W (Fig.8) respectively. The measurement bandwidth is 22Hz to 22kHz (-3dB points). Note how the 60  Silicon Chip distortion waveform at 1W is effec­ tively buried in the noise. Fig.9 shows the 10W test waveforms on a digital scope and here you can see that noise is a strong component of the distor­tion signal. Fig.10 shows the same signals but with averaging applied to cancel out the noise and reveal the true distortion waveform which is mainly second harmonic. By comparing the meas­urements of the distortion waveforms in Fig.9 & Fig.10, we can see that the averaging has reduced the RMS value by 25% and so the measured distortion of .0006% at 10W on Fig.1 can be realis­tically estimated to be less than .0005%. Similarly, Fig.11 shows the 1kHz <at> 1W waveforms and here we can see that noise completely obliterates the distortion wave­ form. Fig.12 shows the “averaged” waveform which is much smaller in amplitude. So instead of an indicated reading of .001% at 1W on Fig.1, the actual measured harmonic distortion is closer to .00025%. Fig.7: these analog scope waveforms show the amplifier on test at 10W. The lower trace is the distortion wave­ form. Note the high noise content. Fig.8: these analog scope waveforms show the amplifier on test at 1W. In this case the lower trace distortion waveform is virtually obliterated by noise. Fig.9: taken at the same time as Fig.7, these digital scope waveforms show the amplifier at 10W. Note the high noise content of the lower trace. Fig.10: the same conditions as for Fig.9 but with signal averaging ap­plied to remove the noise from the distortion waveform. Fig.11: taken at the same time as Fig.8, these digital scope waveforms show the amplifier at 1W. Note the very high noise content of the lower trace. Fig.12: the same conditions as for Fig.11 but with signal averaging applied to remove the noise and reveal a very low distortion content. July 1998  61 The PC board design is critical to the performance of the amplifier so don’t alter it in any way. Note that two pairs of transistors (Q1 & Q2 and Q5 & Q6) are thermally coupled together and don’t forget to fit flag heatsinks (not shown here) to Q11 and Q13. between its collector and emitter (390Ω + 150Ω + VR1) to the resistance between its base and emitter (150Ω + VR1). In a typical setting, if VR1 is set to 120Ω (note: VR1 is wired as a variable resistor), the voltage between the collector and emitter will be: Vce = Vbe x 660/270 = (0.7 x 660)/270 = 1.7V Note that this is considerably less than the 2V or so which would be provided in typical previous bipolar amplifiers we have published but this reflects the change to the current-feedback pairs used in the output stage instead of Darlington connected emitter followers; only two base emitter junctions need to be stabilised in the output stage. In practice, VR1 is adjusted not to Performance Output power ������������������������������������� 15 watts into 8Ω Frequency response ������������������������� -0.3dB down at 20Hz and -0.5dB down at 20kHz (see Fig.4) Input sensitivity ���������������������������������� 680mV RMS (for full power into 8Ω) Harmonic distortion ��������������������������� <0.004% from 20Hz to 20kHz, typically .0006% (see text) Signal-to-noise ratio �������������������������� 113dB unweighted (22Hz to 22kHz); 116dB A-weighted Damping factor ���������������������������������� >200 at 100Hz & 1kHz; >70 at 10kHz Stability ���������������������������������������������� Unconditional 62  Silicon Chip produce a particular voltage across Q10 but to set the 1A quiescent current in the output stage. This requires a voltage of 0.25V across the 0.25Ω “emitter” resistors. In previous bipolar amplifiers we have published, the Vbe multiplier transistor would be mounted on the same heatsink as the output transistors, to ensure that it is thermally coupled to these transistors. However, the bias stability in the current-feedback pairs depends only on the base-emitter junctions of Q11 and Q13 and consequently the bias stability is quite good, even without the tight thermal coupling. Negative feedback Negative feedback is applied from the output stage back to the base of Q2 via an 18kΩ resistor. The amount of feedback, and therefore the gain, is set by the ratio of the 18kΩ resistor and the 1.2kΩ resistor at the base of Q2. This gives a voltage gain of 16 times (24dB). The low frequency rolloff is set mainly by the ratio of the 1.2kΩ resistor to the impedance of the associated 47µF ca­pacitor. This has a -3dB point of about 3Hz. The 2.2µF input capacitor and 18kΩ SMART® FASTCHARGERS One charger for all your Nicad & NiMH batteries As featured in ‘Silicon Chip’ Jan. ’96 Designed for maximum battery capacity and longest battery life Charge: Power tools ✔ Torches ✔ Radio equipment ✔ Mobile phones ✔ Video cameras ✔ Radio controlled models ✔ Field test instruments ✔ Lap-top computers ✔ Toys ✔ Dust busters ✔ Others ✔ The REFLEX® charger is powered from a Power Supply (optional) or from 12 or 24V batteries. Fig.13: this diagram shows the heatsink mounting details for the power transistors. After mounting, use your multi­meter to check that there is an open circuit between the heatsink and the device collectors. bias resistor feeding Q1 also provide a 3dB rolloff at about 4Hz and the two time-constants combined give an overall rolloff of -3dB at about 6Hz. At the high frequency end, the .0012µF capacitor and the 1.8kΩ series resistor feeding the base of Q1 form a low pass filter which rolls off frequencies above 74kHz (-3dB). The over­all amplifier response can be seen in Fig.4. The open-loop frequency response of the amplifier is rolled off by the 100pF capacitor at the collector of Q9. This ensures stability of the amplifier. An output RLC filter comprising a 6.8µH air-cored choke, a 6.8Ω resistor and a 0.15µF capacitor couples the output signal of the amplifier to the loudspeaker. This isolates the amplifier from any large capacitive react­ances in the load and thus ensures stability. It also helps attenuate any RF signals (including computer switching hash) picked up by the loudspeaker leads and stops them from being fed back to the early stages of the ampli­fier where they could cause RF breakthrough. The low pass filter at the input is also there to prevent RF breakthrough and to attenuate any oversampling artefacts from CD players. Finally, before leaving the circuit description, we should emphasise that the PC board itself is a critical part of the circuit and is a major factor in the overall performance. The same comment applies to the regulated power supplies (to be described next AVOIDS THE WELL KNOWN MEMORY EFFECT. SAVES MONEY and TIME. Restore Nicads with memory effect to remaining capacity and rejuvenate many 0V worn-out Nicads. CHARGES VERY FAST plus ELIMINATES THE NEED TO DISCHARGE: charge standard batteries in max. 1 hour and the ‘fastcharge’ batteries in max. 15 min. Partially emptied batteries are just topped up. Batteries always remain cool, increasing both the total battery life and the useful discharge time. DESIGNED AND MADE IN AUSTRALIA For a FREE detailed technical description please Ph: (03) 6492 1368 or Fax: (03) 6492 1329 2567 Wilmot Rd, Devonport, TAS 7310 month) and to the chassis and wiring layout, so don’t alter anything here. Module assembly The component overlay diagram of the PC board is shown in Fig.6. Before starting the assembly, it is wise check the board carefully for any Australian Audio Consultants - Sole Australian Distributors P.O. Box 11, Stockport S.A. 5410 Phone or fax 08 85 282 201 CLIO Test System Professional Electrical and Acoustical Testing • Dual Channel, Measures Phase • Sinewave testing, Gating • MLS Analysis • FFT Analysis • Digital Signal Generator • Dual Channel Audio Oscilloscope • 1/3 Octave Analysis • Reverb & Decay • Measures THD, 2nd & 3rd HD, IM dist. • Provides Waterfall plots, ETC curves, Polar Plots etc. • Measures T&S parameters, Capacitors & Inductors Fully featured professional system System including microphone Only $1551.00 tax ex Automated Quality Control system also available Morel Loudspeaker Drivers Highest Quality Loudspeaker Drivers • Hexatech voice coils for prodigious power handling • 118mm (4.5” ) bass drivers 150 Watts • Drivers shielded for A/V use • Transient power to 1kW • Morel use Neodymium & double or triple ferrite magnets • Available in matched pairs • Miniature tweeters available • MW 168 162mm bass driver 150W 88dB $159.00 • DMS 37 horn loaded Tweeter 200W 93dB $111.00 • MDM 55 Dome Midrange 200W 90.5 dB $129.00 • MW 265 222mm Bass Driver 150W 90dB $172.00 Call or write for full specifications - wholesale enquiries welcome July 1998  63 Fig.14: drilling details for the heatsink. The two transistor mounting holes need to be positioned between the heatsink fins otherwise they will need to be blind-tapped. 64  Silicon Chip open or shorted tracks or undrilled holes. Fix any defects before fitting the components. Start by fitting the PC pins and the resistors. The 0.25Ω emitter resistors in the output stage each consist of four 1Ω 0.25W resistors in parallel. When installing the zener diode, make sure you get its polarity correct. The same goes for the electrolytic capacitors. Note that the 100pF ceramic capacitor at the collector of Q9 should be an NPO (zero temperature coefficient) type. Other types will change their capacitance markedly which is undesir­able. Choke L1 is wound with 24.5 turns of 0.8mm enamelled copper wire on a 13mm plastic former. Alternatively, some kitset suppli­ers will provide this choke as a finished component. When installing the fuse clips, note that they each have little lugs on one end which stop the fuse from moving. If you install the clips the wrong way around, you won’t be able to fit the fuses. The 1.8Ω 5W wirewound resistors can also be fitted at this stage. They are wired to PC stakes adjacent to each fuse­holder and are used when setting the quiescent current. Next, mount all the small signal transistors. Both Q11 and Q13 will need to be fitted with small flag heatsinks (not shown in the photos). Finally, you can install the two output transistors. They are mounted so that the lower edge of their encapsulated bodies are 9mm above the board. Fig.13 shows how the transistors are mounted, while Fig.14 shows the drilling details for the large heatsink. Each power transistor requires a mica wash­ er and should have heatsink compound applied to its mounting surface and the heatsink area covered by the mica washer. Alternatively, you can dispense with the mica washers and heatsink compound and use silicone impregnated thermal washers instead. Whichever method you use, do not overtighten the mount­ing screws. Finally, check with your multimeter, switched to a high Ohms range, to confirm that there are no shorts between the heatsink and the transistor collector leads. Next month, we will present the circuit of the regulated power supply and conclude with the chassis wiring SC and testing. MORE FROM YOUR EFI CAR! Own an EFI car? Want to get the best from it? You’ll find all you need to know in this publication EFI TECH SPECIAL Here it is: a valuable collection of the best EFI features from ZOOM magazine, with all the tricks of the trade – and tricks the trade doesn’t know! Plus loads of do-it-yourself information to save you real $$$$ as well . . . HERE ARE JUST SOME OF THE CONTENTS . . . n Making Your EFI Car Go Harder n Building A Mixture Meter n D-I-Y Head Jobs n Fault Finding EFI Systems n $70 Boost Control For 23% More Grunt n All About Engine Management n Modifying Engine Management Systems n Water/Air Intercooling n How To Use A Multimeter n Wiring An Engine Transplant n And Much More including some Awesome Engines! AVAILABLE DIRECT FROM SILICON CHIP PUBLICATIONS PO BOX 139, COLLAROY NSW 2097 - $8.95 Inc GST & P&P To order your copy, call (02) 9979 5644 9-5 Mon-Fri with your credit card details! FROM THE PUBLISHERS OF “SILICON CHIP” T HIS NIFTY little unit will charge 6V or 12V sealed lead acid (SLA) batteries at one of three constant current settings and has a mechanical timer which can be set any­ where between 0 and 12 hours. Design by BRANCO JUSTIC A constant current charger with mechanical timer Over the years there have been a lot of charger circuits published but many of them suffer from a big drawback: if you forget to turn the charger off the battery will be overcharged. This can lead to the battery being damaged and in the worst case, you will have to throw it out and buy a new one. Even battery chargers which automatically taper off their rate of charge can sometimes overcharge a battery if you leave it running too long. So you really want the insurance of a timed mechanical cutout which you can set and forget, knowing that it will automatically do the job for you. And that’s what this charger will do for you. The charger comes in two parts. There is an in-line 15V 650mA DC power supply (ie, transformer, rectifier and filter capacitor) which feeds the charger itself which is housed in a small plastic case together with the mechanical (clockwork) timer. The 66  Silicon Chip front panel incorporates the timer knob and a ganged three-way switch to select the three charging rates of 0.1A, 0.3A and 0.5A. There are also two LEDs, one red to indicate that the unit is charging and the other green to indicate that it has timed out. In use, you connect up the battery, select the charging rate, plug the transformer into the mains and turn on, and then rotate the timer knob to the setting you want, any time up to 12 hours. The red LED will come on and the timer starts ticking. Circuit details Fig.1 shows the detail of the circuit and as you can see it is a little unusual in its configuration. DC from the DC power supply is fed via diode D1 to the emitter of transistor Q1 and to one side of the 3-way switch assembly. The switch assembly is connected in series with three resistors, R5, R6 & R7, all of which connect to the source of Mosfet Q2. All of the charging current to the battery passes via the three resistors (depending on the current selected) and the Mosfet Q2. The base-emitter junction of Q1 monitors the voltage devel­oped across the resistors R5, R6 & R7 and normally maintains the voltage at around 0.6V. What happens is that Mosfet Q2 is turned on by the 4.7kΩ resistor (R2) between its gate and the negative supply line (-V). If Q1 was not present, Q2 would be turned fully on and there would be no charge current limiting for the battery. Howev­er, when the voltage across one or all of the resistors R5 to R7 reaches 0.6V, Q1 is turned on and bleeds gate voltage away from Mosfet Q2, via LED2. Hence, Q1 maintains a constant current through Q2 and the whole circuit can be regarded as a constant current source. Note that the three resistors R5-R7 WARNING! This charger does not have any voltage limiting so overcharging of batteries is possible if the selected charge period is too long for the battery under charge. are progressively switched in parallel to get the higher current settings. R5 on its own gives a current of 0.6V/5.6Ω = 0.107A. R5 & R6 in paral­lel give a resistance of 1.82Ω and this results in a current of 0.6V/1.82Ω = 0.33A. Finally, R5, R6 and R7 all in parallel give a resistance of 1.09Ω and this results in a current of 0.6V/1.09Ω = 0.55A. In practice, these figures will be affected by the tolerance of the resistors and the actual forward bias voltage (Vbe) of transistor Q1. Timer operation When the timer is set to the desired time by rotating the knob, its contacts are open circuit. Hence, diode D2 is reverse biased and no current flows through LED1. Eventually, when the timer reaches the selected time, its contacts close and diode D2 conducts to pull the gate of Mosfet Q2 high. This turns it off and so charging stops. LED2 is extinguished. At the same time, LED1 is lit to indicate the end of the charging time. Diode D1 is included merely to protect against inadvertent supply reversal, while the 1000µF capacitor (C1) is there so that the unit can be used with other battery chargers which have an unfil­tered DC output. Fig.1: Q1 & Q2 combine to provide constant current charging at 0.1A, 0.3A or 0.5A (nominal), depending on the setting of the three rocker switches. Building it All the parts for this design, including the DC power supply, are available from Oatley Electronics at a very attractive price. Assembling this project is not an onerous job by any means and the PC board does not have many components on it at all. It measures 70 x 38mm. Mount the resistors first, followed by the capacitors, diodes, transistor and Mosfet. The two LEDs are wired at the ends of flying leads about 60mm long, to allow them to be poked through the front panel. Make sure that the semiconductors and electrolytic capacitor are mounted the Fig.2: here are the wiring details for the PC board and switch assembly. Note that Q2 must be fitted with a flag heatsink. July 1998  67 Parts List 1 PC board, 70 x 38mm 1 plastic box, 120 x 84 x 30mm 1 12-hour clockwork timer 1 3-way rocker switch assembly 1 15V 650mA DC supply 1 3-pin 240VAC plug 1 1000µF 25VW electrolytic capacitor 1 0.47µF monolithic capacitor 1 flag heatsink for Q2 Semiconductors 1 BC558 PNP transistor (Q1) 1 IRF9530 P-channel Mosfet (Q2) 1 C9448 3A diode (D1) 1 GIG diode (D2) 1 3mm green LED (LED1) 1 3mm red LED (LED2) Resistors (0.25W, 5%) 2 4.7kΩ 1 5.6Ω 1W 1 1kΩ 2 2.7Ω 1W 1 22Ω 1 1Ω 1W Miscellaneous Hookup wire, solder, heatshrink tubing (for LEDs). The PC board nestles between the clockwork timer and the 3-way rocker switch assembly. correct way around, otherwise the circuit will not work. The Mosfet needs to be fitted with a small heatsink, as shown in the photos. When the board is complete, put it aside. The switch assem­bly and timer now need to be mounted inside the front panel of the case. The switch assembly requires a rectangular cutout and has integral tabs which lock it into place. It is mounted at one end of the front panel while the timer is mounted at the other end. The timer needs just an 8mm hole for the shaft and it can be glued into place. The space between the timer and switch assembly is a neat fit for the PC board. You will also need to drill two 3mm holes in the front panel to take the LEDs. When the timer and switch assembly is installed, you can complete the wiring to the PC board, including the wiring to the two LEDs. The DC input wires and the output wires to 68  Silicon Chip the battery come out through existing holes in the side of the case. Connect the DC supply to the mains and switch on, with no battery connected and with the three rocker switches set to OFF. With the timer set to zero, the green LED should light. Rotating the timer knob clockwise should turn off the green LED and the timer will start ticking. Switch the power off. Now connect a 100Ω 0.5W resistor across the battery termi­nals and reconnect the DC supply to the mains. Rotate the timer to set it running and push the rocker switch for the 0.1A set­ting. The red LED should now light and you should be able to measure about 10V across the 100Ω resistor. Pushing the other buttons to increase the current through the 100Ω resistor will increase the measured voltage but not markedly so because the DC supply does not have sufficient vol­tage. If you want to test the higher current settings you will need a 22Ω 5W resistor and you will not be able to connect it for long as it will quickly become stinking hot. If you do have access to a 22Ω 5W resistor, connect it up for a quick voltage check. On the 0.3A setting you can expect to measure about 7V across the resistor and for the 0.5A setting you can expect to measure about 11V or so across the resistor. At this stage, you have a working charger and you can put it into service SC charging a battery. Where To Buy The Kit All parts for this project are available from Oatley Elec­tronics who own the design copyright. Their address is PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3563; Fax (02) 9584 3561. The kit price is as follows: Complete kit (not including 240VAC plug) .............................................$18 RADIO CONTROL BY BOB YOUNG Radio-controlled gliders: Pt.3 In this issue, we continue the story of the Silvertone Stingray, an unusual 2-metre class glider with a high degree of blending between the fuselage and wings. This blending reduces turbulence as well as making for a very sleek-looking model. While it looks very sleek, the major benefit of the blended fuselage is structural. Modern wing section theory for model aircraft has pointed the way to very thin wing sections, particu­larly for models where speed is an essential parameter. Now the point here is that the formula for cantilever spar strength follows a cube law, so if we double the thickness of the wing section we increase the strength of the spar by a factor of eight. This might sound impressive but the corollary is even more so. If we halve the wing thickness, then we reduce the wing strength by a factor of eight. Modern trends in airfoil section design have pulled the thickness to chord ratio of wing sections down from typically 12-15% in the 1950s to 7-9% on very modern sections. The Eppler 205 used on the Stingray is a 10.48% sec­tion. This is why the trend to thin wing sections has gone hand in hand with the trend to exotic materials in the wing construc­tion. Any reduction in the depth of spar weakens the wing enor­mously and the need for carbon fibre and fibreglass becomes mandatory if we are to stop the wings clapping hands on the tow. Combine thin wing sections with high aspect ratio (further reducing the This view of the Stingray-2M shows the tailplane horns. depth of spar), stir in a liberal dash of the modern high power, high-tension launch and the structural problems become enormous. One of the photos in this article shows a very large sailplane with a high aspect ratio. Just consider the extreme bending stresses on a wing of this length and thickness. Anything we can do to minimise the need for high aspect ratio wings will help structurally with spar depth, and aerody­namically with the increase in Reynolds numbers. The blended fuselage helps here and the Stingray-2M uses a much lower aspect ratio than normal. The spruce and balsa “H” section main spar enclosed inside a “D” box leading edge has withstood some very fast launches with very little wing flex. I should comment here that I am very wary of modern hi-tech materials, because of their toxicity. At the end of my military target model exercise in the 1970s I became extremely ill and was told by the doctors that I would be in a wheelchair by the time I was 45. These models were all moulded in epoxy fibreglass and in the end, as soon as the lid came off the epoxy tin, I started to react to the fumes. I might point out here that I only worked on the finished models. I did not wallow in the glass and resin; that was done by another fellow. The military work was cancelled soon after, an event that possibly saved my life. I lost the use of my right leg for a few days and was badly affected in the legs for years but I dodged that wheelchair. So if I cannot design a successful aircraft using traditional materials I am not interested in proceeding with the model. Not all people react like this of course but you should be very cautious with these exotic chemicals and use safety gear at all times. July 1998  69 Fig.1: three airfoil sections, the Eppler E205 (top), the E211 (middle) and the NACA0010 (bottom). The Eppler 205 is used on the wing and the NACA0010 is used on the tailplane of the Stingray-2M. I have reluctantly shown an Eppler 205 wing section. This is an old section and is now completely outclassed by the more modern sections. Anyone choosing to build this model should realise that the choice of section depends on the task intended for the model and that is a matter for the builder. By the way, some readers may consider that last month’s article provided the bare minimum of a plan for the Stingray-2M, in spite of my comment that I believed that there was sufficient information for an experienced build­er. It is very difficult for the uninitiated to comprehend just how clever most modellers are at their craft. I have seen people build a fully detailed 2-metre scale model of a 6engine B36 bomber, complete with retracts, flaps, waving pilot etc, from a tiny little three-view drawing in some ancient aircraft recogni­tion book. Compared to this level of skill, the drawing presented last month contains a wealth of information. However, I was conscious that the freehand airfoil section was not useable and hence the notation on the drawing (on page 55) “Wing section not a true airfoil (do not use)”. As I stated last month, the original plan had disintegrated long ago and my only record of the Eppler 205 wing section went with it. Fortunately, since writing that article, I have managed to locate HPGL files for two Eppler airfoils (the E205 and E211) and for an NACA0010 (see 70  Silicon Chip Fig.1a, b & c). The Eppler 205 is used on the wing and the NACA0010 is used on the tailplane. The E211 is designed for F3B models and gives low drag at zero lift at low Reynolds numbers and is presented for interest only. These are old airfoils now and are completely outclassed by the more modern airfoil sections. For those interested in airfoils and wing design there is an excellent program (Wingmaster) available from ViaGrafix USA at www.viagrafix.com. Tailplane assembly All I have said about the wing section goes triple for the tailplane/fin assembly. A vertical fin sticking up on a flat tailplane is a major source of interference drag. This is why the “V” tail has been used instead on the Stingray-2M. The dihedral angle on the tailplane is set at 35°, which I feel is the minimum for adequate rudder control. This places the two halves at an angle of 110° to each other, a figure well above the 90° minimum. The original tailplane was bolted on but I wish I had taken the trouble to fix it and fair the roots into the fuselage. Stakes or large fairings should not be used here, to avoid the risk of inducing an early stall on the tailplane. The “V” tail does place some demands on the radio and a mixer is required. If your transmitter is not fitted with a mixer, then the Silvertone MX-2 in-line mixer published in the July 1997 issue of SILICON CHIP can be fitted to the receiver. The tailplane area is unusually large for the same reasons as the wing. It makes no sense to carry a tailplane that features a chord well below 20cm and thereby produces more drag than lift. By using a very large tailplane, the Reynolds number stays high and the model can carry a CG (centre of gravity) that is well back by normal standards. This has several advantages. First, it makes the bucking associated with entering the thermal more visible. Perhaps a word of explanation is needed here. When a model enters a thermal, the rising hot air tends to throw the model up and out, away from the bubble and usually throwing up one wing and/or the nose. The rule is to turn into (towards) the high wing immediately and establish a circle inside the thermal. A model with a rearward CG is more sensitive to this bucking and amplifies the movement, making it easier to spot from the ground. Second, the rearward CG tends to load the tailplane and make it work as a lifting device instead of a drag-producing de­vice. Most important of all is the fact that a large tailplane can handle the stress of a winch launch much more effectively than a smaller unit. Sailplanes being winch-launched operate at fairly high angles of attack and with greatly increased wing loadings, par­ticularly in gusty conditions. Small inefficient tailplanes can easily stall under these conditions, with catastrophic results. Anyone who has ever witnessed an F3B model experience a tailplane stall on a highspeed launch will know exactly what I mean by this. As soon as the tailplane stalls, the angle of attack on the wing increases rapidly and one tip will invariably stall first. The model then goes into a frantic gyration, sometimes wrapping the towline around the fuselage in the process. This is a very dangerous occurrence and one that happens all too frequently with the trend to small tailplanes on large gliders. Now the absolute key to successful sailplane operation is the launch and anything that helps to improve the reliability of the launch is worth doing. The Stingray goes up the line well and was very badly abused during my learning period. The only problem This is a very large sailplane with a high aspect ratio. The bending stresses on a wing of this length and thickness would be very high. that I have encountered to date was that one of the people helping me launch the model was releasing it with too much line tension. Being so clean and light, the model immediately accelerated past the winch speed and continually flew off the line. It took us a while to figure that one out. The model is quite tolerant of towhook position because of the large tailplane and it can be moved quite close to the CG, again improving the launch. The tailplane is made of foam sheeted with balsa and uses a symmetrical section of 10% thickness to chord ratio (NACA 0010). This is probably a little thicker than necessary but again I prefer safety and reliability above perfor­mance. One final advantage of the large tailplane is that it allows the fuselage (moment arm) to be much shorter, making it easier to balance the model. The Stingray should balance without any lead in the nose, provided the tailplane is built lightly enough. If the servos are positioned correctly (forward of the CG), there is sufficient room in the fuselage for a ballast box on the CG. Perhaps the most commented on feature of the Stingray-2M is its turning ability. “V” tail models are notoriously difficult to turn, especially without a polyhedral wing. The Stingray responds well to rudder and slips easily into a smooth turn which remains at a constant radius. In flight, the model is flown mostly on trim and will remain inside the thermal with few cor­rections required. The swept wing provides yaw damping in straight and level flight and prevents the fishtailing often associated with “V” tails. It also acts as dihedral once rudder is introduced, making rudder-only turns very smooth. When added to the 5° dihedral built into the wings, the sweep provides sufficient rudder control. When I first pre­sented the model on the field (with no dihedral) the reaction of the group was unanimous. “It will never turn”, they all howled in chorus. Many stated outright that they had never seen a 2-metre that turned well, even with dihedral; one without dihedral com­pletely horrified them. Cowed, I returned to my workshop without flying that day and added 5° on each wing and that figure seems about right. However, I still wonder whether it would have turned properly without dihedral. I tend to believe that it would. Finally, I have a few comments on the finish. The original was painted by Barry Ming and used brown paper covering on the fuselage. This was sprayed with black acrylic paint and black Solar Film was used on the wings and tail. The green self-adhesive trim patches were applied after covering. I always paint my aircraft black all over because I feel black is the best visibility colour. All models go dark under­ neath when seen against the sky, even white ones, so I long ago decided that I would make as good a job of making the underside as dark as I could. When confronted with my endless stream of black models, one fellow once asked me if I had bought a 44-gallon drum of black paint at some time! The coloured patches are added to aid visibility and to make distinguishing the top from the bottom as easy as possible at a distance. The wings have since been recovered with Ozcover to prevent the covering going slack in high temperatures. Overall, this model flies well. It is no lightweight float­er but a slick machine that loves to fly fast; thus, it pene­trates well in breezy conditions. It handles well on the tow and accommodates itself well to zoom launches. The smooth turns make thermal soaring easy and the model can be slowed right down in a thermal. The stall is gentle and controlled. So there you have the story of the Stingray-2M. If you want a model that flies well and attracts attention on the field, this is the one for you. As I have already stated, it is not an easy model to build. The alignment of the two wing halves is the all-import­ant point during construction. The model would lend itself well to fibreglass for this reason. Just don’t ask me to build in that material. I would be interested to see the design developed, using modern wing sec­ tions. The Stingray-3M is merely the 2M scaled 1.5 times but with 2.5° of dihedral instead of 5°. If anyone decides to build it, please send me SC a photo. July 1998  71 COMPUTER BITS BY JASON COLE & GREG SWAIN Network cards and networking Network cards enable you to communicate with other computers so that you can share data and other resources such as printers. You can also play games against other people instead of playing a machine. Once a network card is up and running, it’s quite simple to share your data with other users and to gain access to resources on other machines. You can “map” new drives on your computer that actually point to drives (or individual folders) on other computers, for example. Networking was around before Windows 95; it’s just that Windows 95 makes it easier to work with networks. The installation of a network card is simple, particularly if it is a Plug and Play (PnP) type. If the network card is not PnP compatible, you will have to check that any jumpers are set correctly. Alternatively, you may have to configure the card’s resources using a small utility program that’s supplied with the card on a floppy disc. The most common settings that you have to take care of on a non-PnP network card are: (1) IRQ setting: check to ensure that this setting is not con­flicting with any other card. The cards that most commonly cause IRQ conflicts with network cards are sound and video cards, so check the IRQ settings of these carefully before assigning an IRQ to your network card. Assuming that you’re using Win- This is all the hardware you need to network two computers: two network cards, two T-connectors, two 50Ω terminators and 50Ω coaxial cable. 72  Silicon Chip dows 95, a good way of check­ing the IRQ status of existing cards is via the Computer Proper­ties dialog box – see Fig.2. You get there by double-clicking the System icon in Control Panel, then clicking the Device Manager tab and double-clicking Computer (at the top of the devices list). If you’re not using Windows 95, try running the Microsoft Diagnostic program (MSD.EXE) from the DOS prompt. This will give most (but not necessarily all) IRQ settings. A look through autoexec.bat and config. sys will also often indicate the IRQ settings of individual cards. Look for lines that include a /In or /I:n entry, where n is the IRQ setting (eg, /I10 indicates an IRQ setting of 10). Note that no two devices can share the same IRQ setting. If they do, then either one or both devices will refuse to work. Be sure to reserve the IRQs for any non PnP devices in the system BIOS, as described in the article entitled “Troubleshooting Your PC” in the June issue. (2) The port address: this must also be unique for each device in your computer. Generally, you can use the default setting but check anyway just to be on the safe side. If you do get a resource conflict, it’s simply a matter of changing the settings and trying again. (3) The card output: many network cards have two outputs, one a BNC socket for connecting to 50Ω coaxial cable and the other an RJ-45 connector (similar to a telephone sock­et) for twisted pair cable. Only one of these outputs is used, so you have to decide ahead of time which type of network cable you intend to use. The one that’s most often used for small office and home installations is coaxial cable, as this is the cheapest This close-up view shows how a 50Ω terminator is fitted to one of the T-pieces at one end of the chain. Terminator Terminator Fig.1: in a 10Base2 network, the computers are daisy-chained together by fitting T-connectors to the BNC sockets on the networks cards and then connecting the coaxial cable. The open ends of the T-connectors at either end of the chain are fitted with a 50Ω terminators option. This type of network is known as 10Base2 and, in addition to the 50Ω coaxial cable, uses T-junctions (one for each computer) and two 50-ohm terminators. The computers on the net­ work are connected together in daisy-chain fashion and terminated at both ends of the chain – see Fig.1. Twisted pair cabling involves running the cable from each computer back to a central “hub”. This type of network is known as 10BaseT and the cables between the computers and the central hub have RJ45 modular connectors on either end. A basic 8-port hub costs about $150, with more elaborate units costing much more. Installing the card Before removing the cover of the computer, switch off the power and remove the power cord. Once the cover has been removed, you can install the network card – just push it firmly into the expansion slot on the motherboard and secure it to the backplane connector using a single screw. Make sure that it is correctly seated in the slot at both ends. If it isn’t, remove the card and try again. If it’s a PnP card and you’re running Windows 95, the system will automatically detect the new card during boot up and prompt you for a driver disc (either from the Win95 CD-ROM or on a disc provided by the card manufacturer). If it doesn’t work, check for conflicts by going to the Device Manager in the System properties dialog box. If everything appears to be fine but the network card still doesn’t work, try running the Add New Hardware Wizard again (just double-click the icon in Control Panel and follow the instruc­tions). This will give Windows 95 a chance to re-detect the new card and shuffle the IRQs around if required. If the card isn’t automatically detected by Windows 95, run the Add New Hardware Wizard again but this time select the card manually from the list. If it’s not listed, try selecting the Novell/Anthem NE2000 driver from the list (most network cards are NE2000 com­patible). If the card is an older non-PnP unit that’s configured using software (or is being installed in a non-PnP system), you will have to run the supplied set- Fig.2: check for free IRQs and other system resources before fitting a nonPnP network card. In Windows 95, you get to this dialog box by double-clicking the System icon in Control Panel, then clicking the Device Manager tab and double-clicking Computer. Fig.3: it’s a good idea to check for resource conflicts after the card has been installed, even in a PnP system. Fig.4: if Windows 95 doesn’t detect the new network card, install its driver manually using the Add New Hardware Wizard (double-click the icon in Control Panel). Fig.5: if your network card isn’t listed, try installing the Novell/Anthem NE2000 driver. Most network cards are NE2000 compatible, so this should work OK. July 1998  73 Network Logon if you don’t want to be prompted for a password each time you boot your computer. If you’re running Windows For Workgroups (WFW) you will also have to manually install the networking protocols and the driver for the network card. You do that through the Network Setup icon in the Network group. Sharing & connecting Fig.6: Windows 95 automatically installs Client for Microsoft Networks when a network card is installed. Use this dialog box to install additional protocols and to enable file and printer sharing. Fig.8: clicking Add at Fig.6 brings up this dialog box. You then select the component you wish to add from the list (eg, a network protocol). up utility to configure the card. This usually involves stepping through the on-screen menus to select the IRQ, port address and connector settings. The style of software varies somewhat but don’t worry as it’s always quite simple to use. In some cases, the software can automatically configure the adapter to a free I/O address and IRQ. The choice of output connector on older network cards can be set using either jumper or software selection. Alternatively, many cards auto-detect the output that’s connected to the network cable. If the setup program comes up with an error, try boot­ing the computer without loading any memory manager utilities. In fact, don’t load anything except DOS (just rem out the appro­priate lines in autoexec.bat and config.sys). Software setup When a network card is installed, 74  Silicon Chip Fig.7: each computer must be given a unique Computer Name but the same Workgroup name must be used for all computers on the network. Fig.9: you select the network protocol to be added using this dialog box. Windows 95 automatically installs “Client for Microsoft Networks” and the NetBEUI network protocol. If you want to add additional protocols such as IPX/SPX and TCP/IP, begin by double-clicking the Network icon in Control Panel to bring up the dialog box shown in Fig.6. Now click the Add button, select Protocol, click Add again, select Micro­soft from the list of manufacturers, and select the protocol you wish to add. Once the protocols have been added, the next thing to do is to click the Identification tab and enter a unique Computer Name (you do this for each machine on the network). Conversely, the same Workgroup name must be used for all computers on the network. Finally, click the File and Print Sharing button to choose whether you want to share your files and/or a printer. You should also choose “Windows Logon” as the Primary Before you can connect to any resources on another machine, those resources must first be shared. You do that in Windows 95 via My Computer. Open My Computer, right-click the resource you wish to share (eg, a drive, an individual folder or a printer), select Sharing from the drop-down menu and then set the various options (share name, access control, etc) as desired. Alternatively, you can right-click the resource in Explorer and go from there. Once the required resources have been shared, you should be able to see the other computers on the network when you double-click the “Network Neighborhood” icon on the desktop. After that, you can view the shared resources on each computer and “map” these to your own machine as individual disc drives and printers – see Fig.11. Users of Windows for Workgroups share resources and connect to them using File Manager and Print Manager. Networking protocols Which protocol is the best to use? For a small local area network (LAN) that doesn’t require routing, NetBEUI is the easi­est to set up and get going. Other popular protocols are IPX/SPX and TCP/IP, especially if routing is a requirement. TCP/IP is used by everyone who accesses the Internet and is also often used for large commercial networks. However, there’s no need to use the TCP/IP protocol for a small LAN that’s used at home or in the office, unless you want to learn how it works. When you use TCP/IP, you must assign a unique set of numbers to each computer on the network. Basically, four separate numbers with values ranging from 0-255 are used, so that a typi­ cal TCP/IP assignment looks something like this: 210.54.46.12. Fig.10: you can share a disc drive (or a folder) by selecting it in My Computer, then clicking File, Sharing. Note that the R: drive has already been shared here, as indicated by the hand holding the drive icon. Printers are shared in exactly the same fashion. This presents us with quite a few combinations and allows every computer that’s directly connected to the LAN or to the Internet to be given a unique identification number. However, when we use the Internet we don’t use numbers but type in the URL (Universal Resource Locator) address instead; eg, www.time.com.au Fig.11: double-clicking Network Neighborhood gives you access to other shared resources on the network. You can also map these resources as individual disc drives on your own machine and install network printers. The reason we can do this is because there are a couple of large servers on the Internet which hold all the TCP/IP numbers on the Internet and link each one to a name. For example, the site www.time.com.au is linked to 210.54.46.12. When we look for a site, your web browser asks a “naming” server for the corre­sponding TCP/IP address. Your computer then goes to that address. TCP/IP networking is quite easy to set up and use when you know the basics and have a good instruction manual on implement­ ing the system. It all depends on the size of your network and how you intend to SC implement it. Networking From The DOS Prompt Most people will set up their network connections from within Windows but did you also know that you can do it from the DOS prompt? The only provisos here are that you must be using old DOS and you must have WFW installed on the machine (so that you get the relevant networking utilities). The setup utility to use here is Net.exe which is installed in the Windows directory. When you run this utility (type Net, press enter at the DOS prompt and select yes to start the Workstation service), you get a popup dialog box similar to that shown in Fig.12. After that, it’s a relatively simple matter to connect network drives and printers. If you are only booting to the DOS prompt, you will need to type net start full each time you boot the computer in order to log on to the network. To make things easy, you could place this line in your autoexec.bat file. There’s just one wrinkle here – if you want to boot Windows, you should type net stop first. That’s because Windows itself automatically starts the network service and logs you on when it boots. Typing net /? at the DOS prompt gives you a list of options for use with the Net.exe utility. The use option allows you to temporarily connect to another drive for example. Let’s say that you want to connect to the games directory on a computer called PC2 and to map this directory as your x drive. In that case, you would type: net use x: | \\pc2\games This way, you can store all your DOS games on a Fig.12: you can connect and disconnect network drives and printers in DOS using the net.exe utility. This utility is placed in the Windows directory when you install Windows For Workgroups. second com­puter and access them at any time without cluttering up the hard drive on your main machine. Another useful command is net diag. This can be used to test the network, especially if you’ve just installed a new network card and you’re not sure whether it works or not. This will look for a “testing server” or can set your com­puter to act as a testing server to test other computers (and therefore network cards) connected on the network. July 1998  75 VINTAGE RADIO By RODNEY CHAMPNESS, VK3UG Australia’s last valve radios The last gasp for valve radios in Australia occurred around 1973, when Kriesler ceased production of its 11-99 mantle radio. This set and the earlier 11-90 model had some interesting features, as we shall see. It is hard to know exactly when domestic valve radios ceased being made, as manufacturers often put the date of the acceptance of a design on the circuit diagram and on any allied information. However, it would appear that valve sets ceased production in 1973 or within a year of that time. A few special­ist sets of various kinds may have been produced for some time after that but that is not what we are interested in here. There was still a number of manufacturers producing domes­tic valve radios during the latter years. The main Australian ones were Astor, AWA, Ferris, Healing, HMV, Kriesler, Operatic, Philips, Pye, STC and Stromberg Carlson. The Kriesler 11-90 It is possible that the last domestic valve sets were pro­duced by Kriesler. In this article, I’ll endeavour to follow the production of the last of their valve mantle sets. The last completely new design occurred at the end of 1961, this being the 11-90. Initially, it was designed as an economy set for the kitchen or workshop/garage The author’s Kriesler 11-99 mantel receiver. The unit was built into a plastic case with a fold-down carry handle. 76  Silicon Chip and was probably meant to persuade people that transistor radios weren’t a viable option for listen­ing around the house. What did Kriesler do to make this an economy set that was well-designed, reliable and able to perform adequately? First, the set was built into a cabinet that had a fold-down carry handle. This, together with its figure-8 power cable, made it easy to gather the set up and move to the next power point. The cabinet was made in two halves, such that almost all servicing (if required) could be done with just the back half removed. And although there were antenna and earth terminals on the back of the set, the small internal loopstick antenna was quite adequate for most suburban locations. Circuit design What did they do in the circuit design to keep costs down and yet still have a set that offered adequate performance? Many of the simpler designs in earlier years used relatively low high-tension voltages – generally around 100V or so. However, although the RF (radio frequency) and IF (intermediate frequency) sections of these sets performed quite well, the audio output was quite limited as 6V6GT valves don’t work well with low high-tension voltages. During this period, the 6BM8 triode-pentode was used exten­sively in television sets as an audio amplifier/ output stage and as a vertical oscillator/deflection amplifier. However, it had reached its limits and new valves were needed for the audio and vertical sections of such sets. In particular, more was required out of the vertical deflection valve for the latest wide angle (110 degree) deflection picture Fig.1: the circuit diagram of the Kriesler 11-90 mantel radio. It was a 4-valve design with some interesting features to cut costs. tubes and Philips designed and produced the 6GV8 to do the job. Whether by design or by good luck, the 6GV8 proved to be a very versatile valve. As well as working well in its intended role in television sets, it was also found to work well in small regulated power supplies and as an RF output valve in low-power HF and VHF transmitters. What’s more, the 6GV8 worked very well as an audio amplifier at low HT voltages and was quickly adopted by Kriesler for the 11-90 receiver. The 6GV8 drew quite a considerable amount of current (about 40mA) with 100V on the plate and screen and with about -5V of bias. This meant that at about 100V or a bit more, quite a rea­sonable amount of audio output could be obtained. Kriesler used the 6GV8 as an audio preamplifier and audio output stage, which gave between 1W and 1.5W into a 4-inch speaker. This would be more than adequate for the environment in which it was intended to operate. The RF section followed almost exactly the designs that Kriesler had found to be effective since the mid 1950s. After all, why change a proven formula? The set ended up with a loop stick antenna/aerial with a 6AN7A converter feeding a 6N8 as the IF amplifier on 455kHz. The diodes in the 6N8 were strapped together to form the second detector and a simple AVC/AGC (au­tomatic volume control/ automatic gain control) network. To keep the tuning system simple, a “hand-span” dial was used. These were cheap to produce and simple to maintain, but are not as easy to tune as good cord drive systems. The power supply had to be designed at this time too. In Australia, we have stuck fairly rigidly to designs that complete­ly isolate the mains from the chassis, so a mains transformer was a necessity. To keep costs down, the transformer has only a single untapped 115V HT winding and one 6.3V heater winding on the secondary side, plus an untapped primary winding for 220-250V input. A 6V4 valve with both plates strapped together was used as a halfwave rectifier. The use of a 6V4 as the rectifier seems a little strange when it is considered that an OA210 or similar solid-state rectifier could have easily done the job (they were used in the power supplies in some TV sets at this time). I sus­pect that the 6V4 was used as they probably had tens of thousands of them and needed to use them up. The Kriesler 11-99 The Kriesler 11-90 was up and running by 1962 and was no doubt doing the job that it was designed for. However, the in­roads that transistorised sets were making into the traditional valve mantle set market were soon to become apparent, with many people choosing to use transistor sets despite their inferior performance to valve sets at that time. The 11-90 also proved to be a relatively reliable set, mainly I suspect because of its low high-tension voltages. It used paper capacitors and these do become leaky over time, although this is less pronounced when the HT is relatively low. Even so, in both the 11-90 and the 11-99 receivers, capacitors C2, C9 and C10 (see Fig.1) should be replaced with polyester types to ensure proper circuit operation. The other paper capaci­tors are not in such critical locations so their replacement is optional if they don’t becomes warm during operation (an indica­tion of excessive leakage). Although the 11-90 was doing a good job, some extra features were needed to keep the set selling against transistor­ ised receivers. The 11-99 was the outcome of these deliberations. First, the set was modified so that it could tune to a few interesting stations that were just outside the normal broadcast band, at the 1600kHz end of the dial. To do this, the set was tweaked to get it to tune up to around 1750kHz (mine goes to 1790kHz). The stations “just off the end of the dial” of normal sets were the university stations like VL2UV July 1998  77 The 11-99 (and the earlier 11-90) featured an uncluttered chassis that’s easy to service. Late-model 11-99s used a solid-state rectifier instead of the 6V4 valve. and the inshore marine radio services between 1700kHz and 1750kHz. Although most of these stations no longer operate, there are now a number of different special interest stations in the 1600-1700kHz band. These include Greek, Italian and Turkish language stations, as well as some RPH (Radio Print Handicapped) stations. The cabinet of the 11-99, although basically the same as the 11-90 in shape and size, featured a different front grille and logo. And because it tuned higher in frequency than the 11-90, it had a new dial scale. Because the sensitivity of the 11-90 was only just ade­quate, it was necessary to jazz up the performance of the 11-99 to receive the (low power) special-interest stations. Indeed, my 11-99 is a superb performer – it is one of the most sensitive sets that I have and is able to (noisily) resolve signals as weak as 1µV. The circuit is virtually identical to the 11-90 so I am not really sure what they did to get such a dramatic lift in sen­sitivity. They may have redesigned some of the IF transformers, or perhaps it was just the increase in HT voltage due 78  Silicon Chip to the solid-state rectifier used in the power supply. A solid-state rectifier was only fitted in very late model sets and this increased the HT(2) voltage from 110V to 133V. It’s quite possible that this may have been enough to get the 6AN7A and 6N8 valves really firing. The HT current drawn by the 11-90 is 42mA, while the 11-99 draws 48mA. This represents an increase of nearly 1W in power consumption, however the power transformer is not overloaded as it no longer has to supply current to a 6V4 heater - a saving of nearly 4 watts. The result is a net saving of 3 watts in overall power consumption. The new set, like many from this era, used a twin tuning gang with dissimilar gang sections. The manufacturer of the gang, MSP (Manufacturers Special Products, a subsidiary of AWA), did a really good job with the plate shapes. The oscillator and signal circuits accurately track each other 455kHz apart right across the tuning range. In fact, the tracking is as accurate as I have seen, which made aligning the set a breeze and ensures uniform sensitivity right across the band. As an aside, some other tuning gangs made for padderless operation had incorrectly shaped plates. As a result, the oscil­lator and signal sections do not accurately track each other 455kHz apart, which means that it is impossible to get the tuned circuits accurately aligned for the entire broadcast band. This is very disappointing, as some potentially high-performance transistor sets are mediocre performers because of this. As can be seen by looking at the circuit of the 11-90 (Fig.1), it is quite basic. In fact, the same circuit diagram was supplied with both the 11-90 and the 11-99 receivers right up until production ceased, even though the 11-99 circuit is slight­ly different. The photographs of the set show that it is not cluttered and as a result, is easy to service. The back of the set is removed by taking out two screws and lifting it off. This allows access to all components that would normally require service. How many sets require so little work to gain access to the internals and also have a circuit diagram supplied with them to make it just that bit easier? It could be described as a serviceman’s dream - easy and quick to service, with the circuit supplied. The differences in components and My Kriesler 11-99 I came across my 11-99 in a small country town. It was up on a cupboard and the ticket on it said that it didn’t work. Because it didn’t work, the price paid for it was very reason­able, especially considering that “working” sets were 4-5 times the price. When I got it home, I removed the back and carefully checked it for any signs of major problems, such as a faulty power transformer. The critical capacitors were all replaced and I checked for any shorts on the HT line and tested the speaker transformer. When I turned it on, it behaved just as the ticket said – it didn’t work. In fact, there wasn’t even a peep out of it. The voltages were checked and they all appeared on the high side, the exception being the bias voltage which was -1.5V in­stead of -5.7V. The 6GV8 would normally draw most of the set’s current but it wasn’t hot to the touch, which suggested that it may be faulty and not drawing current at all. A replacement 6GV8 was installed and the set sprang into life. The alignment of the set was slightly out and so this was adjusted. It peaked up quite nicely and the sensitivity was very high. After that, the set was given a general clean up and al­lowed to run for some time. It proved to be a very good perform­er. Well, was Kriesler successful with the 11-99? I would say yes. It was a sensitive set that worked very well on a reasonable aerial and earth. The very fact that more than 40,000 sets were produced over a number of years, until around 1973, indicates that this little set prolonged the valve era in Australia, because it effectively tapped into a niche market. SC CORRECTION: Last month’s Vintage Radio was incorrectly attributed to John Hill who has now retired. The author was, in fact, our new regular columnist Rod­ney Champ­ness. 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. Notes & Errata: this file lets you quickly check out the Notes & Errata 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 any item. 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 TOTAL $A Disc size required:    ❏  3.5-inch disc   ❏ 5.25-inch disc 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). ✂ voltages between the 11-90 and the 11-99 are not great but as has been said, the perfor­ mance of the latter is better. In the 11-99, C12 = 47µF 160 VW, C13 = 47µF 160 VW, and a BY126 solid-state diode has been used instead of the 6V4 rectifier valve. The 11-99 high tension vol­tages are also higher, with HT2 = 133V, HT1 = 90V, RF screen volts = 53V and the bias = -5.7V. July 1998  79 Connect the three leads to the device to be tested and the result is displayed in the blink of an eye. This is the LCD version which, in addition to the standard features can also measure transistor gain and diode forward voltage. AUTOMATIC SEMICONDUCTOR ANALYSER Design by ANDY WOOD Ever wanted to test a transistor or other three-legged device and you didn’t know which leads were which? How do you test a transistor in those circumstances? You put it in this Automatic Semiconductor Analyser, that’s how. It will tell you whether it’s a PNP or NPN transistor, a diode, an SCR or a Triac and it will tell you which lead is which. And if it is a transis­tor, it will measure its gain. 80  Silicon Chip Fig.1: the circuit of the tester uses a PIC processor (IC2) to handle all the testing steps which are done via a crosspoint switch array (IC1). This project arose out of a letter in “Ask SILICON CHIP” in the February 1998 issue. A reader wanted a transistor tester that would tell you whether the unknown transistor was a PNP or NPN type and which pin is which. This design does that but will also identify diodes, SCRs (silicon controlled rectifiers) and Triacs. It’s surprising just how often you need a transistor tester with this sort of intelligence. Even when the transistor is clearly labelled with its type number, its pinout information may be unknown or it may be available with several different pinouts; eg, EBC, BEC or CBE. Even when you know the pinout it can be inconvenient to connect the transistor leads in a particular order or you might inadvertently make a mistake when you do make the connections. And what if you inadvertently test the transistor as an NPN rather than a PNP type? With this “Automatic Semiconductor Analyser” it doesn’t matter. You can connect the transistor or device leads in any order you like and as WARNING! The inputs to this tester are not protected against high voltages and currents. Do not attempt to test devices “in cir­cuit”. soon as you turn on the power, the tester will work out what type the transistor is, which lead is which, measure the gain (hFE), and tell you the results – all in a frac­ tion of a second. The result is shown on an alphanumeric liquid crystal display (LCD). For diodes, the tester will identify the anode and cathode leads and measure the forward voltage. In some cases, it can even identify SCRs and Triacs. The tester does have its limitations though. It is not suitable for FETs or Darlington transistors and is not very tolerant of transistors with high leakage, such as some old germanium types. The gain (hFE) figure should July 1998  81 of eight rows and eight columns, with a switch at the intersection of each row and column. The general concept of the switch is shown in Fig.2. Any one of the switches can be turned on or off by means of the address, data, and strobe lines. Note that the “on” resist­ance of the switches is lower than for some other analog switch­es, such as the common 4066, but is still too great to be ignored in some situations. How it works Fig.2: this shows the setup of the crosspoint switch array and how it is connected to the test resistors. not be taken as an absolute figure ­­­­­­–due to the measurement method and the low currents involved, it is only approximate, particularly for power transistors. Again due to the low test currents, many SCRs are not sensitive enough to be identified and Triacs are generally even less sensitive and may not be identified in some cases. Having said that, most of the small SCRs that might be confused with transistors are sufficiently sensitive to be recognised. Circuit details Really, there is not much to this tester. It has three main components: the liquid crystal display, a crosspoint switch array and in case you haven’t guessed by now, a microcontroller. The circuit is shown in Fig.1. The microcontroller is a Microchip PIC16C711, an 18-pin device which has a built-in 8-bit analog to digital converter, 1024 words of program memory and 68 bytes of data memory. It is an OTP device. OTP stands for “one time programmable” and this means that the program memory cannot be erased and reprogrammed. The operating frequency of the PIC device does not have to be accurately controlled, so it operates in “RC” mode, whereby an external resistor and capacitor set the frequency. The crosspoint switch array, a type CD74HCT22106, is in a 28-pin package. This device consists of 64 transmission gates (otherwise known as analog switches) with an addressable latch associated with each switch. The switches are arranged in an array Each small numbered box on Fig.2 represents a switch which can be opened or closed by the micro­ controller. The rows are identified as Y0 to Y7, and the columns X0 - X7. The first row, Y0, goes to the ADC input pin on the microcontroller while the next three rows, Y1 - Y3, are connected to the test leads, TL1, TL2 & TL3. The columns (X0 - X7) connect to various test resistors and to the 0V and +5V rails. Only the top half of the crosspoint switch array (Y0 - Y3) is used for testing purposes while the lower half, rows Y4 - Y7, is used to control four LEDs if the LCD is not used. Now suppose an NPN transistor is connected to the tester with test lead 1 on the collector, test lead 2 on the base and test lead 3 on the emitter. In order to measure the gain, switch­es 9, 16 and 26 are closed. Fig.3 shows the result. The base and collector currents are determined by closing switch 0 or 1 so that the ADC (analog to digital converter) can be used to deter­mine the voltage across R1 or R2. From these measurements, the gain can be calculated, knowing that R1 is 1000 times greater than R2. There are six different ways that the test leads may be connected to the transistor and with two possible transistor types, this makes a total of 12 Resistor Colour Codes ❏ No. ❏  2 ❏  1 ❏  1 ❏  1 ❏  2 ❏  2 82  Silicon Chip Value 330kΩ 12kΩ 10kΩ 1.5kΩ 330Ω 220Ω 4-Band Code (1%) orange orange yellow brown brown red orange brown brown black orange brown brown green red brown orange orange brown brown red red brown brown 5-Band Code (1%) orange orange black orange brown brown red black red brown brown black black red brown brown green black brown brown orange orange black black brown red red black black brown Fig.3: the basic transistor setup to measure gain (hFE). possibilities that the tester has to try to make a valid test of the transistor. Complicating the testing process is the fact that a tran­sistor with the collector and emitter interchanged may “work” but the gain will be lower, so the combination of connections which gives the greatest gain is displayed by the tester as the valid result. The tester tries for an NPN transistor first, then PNP, then for an SCR, and finally for a diode. For diodes, the assumption is made that test leads one and two will be used. A transistor with only these two test leads con- nected may, of course, behave like a diode and will be identified as such. Some of the microcontroller I/O lines serve more than one function. For example, the LCD data lines also provide part of the address for the crosspoint switch. The LCD is operated in 4-bit mode; in this mode data lines D0-D3 are unused. R7 and C7 set the operating frequency of the microcon­troller at approximately 2MHz. At this frequency most instruc­tions execute in 2µs. Normally, the testing procedure simply involves connecting the transistor and switching on the power. The micro then per­ f orms all the tests and displays the final result in less than the blink of an eye. If no transistor is connected and the unit is switched on, the display will show a quizzical “?”. If the tester fails to identify a particular semiconductor, it is possible to step it through all possible test conditions. These include the tests for SCR and diode con­nections. Assembly You can build two possible versions of this Automatic Semi­ conductor Analyser. The first version uses the liquid crystal display and is the one we would recommend. But if you want to save some money you This prototype has been wired with all components for the LED and LCD versions. Fig.4: this is the wiring diagram and component overlay for the LCD version of the tester. Note that the LCD module (shown dotted) mounts on the copper side of the PC board. Take care with component orientation. July 1998  83 This view shows how the LCD module is mounted on the copper side of the PC board. It is stood off the board using suitable spacers and is connected to the board via pins and a machine pin IC socket strip . This side-on view shows the completed prototype, mounted on the lid of the case. If you are making the LCD version, resistors R9-R14 and the six LEDs can be deleted (see text). Fig.5: this is the wiring diagram and part overlay for the LED version of the tester. You can save quite a few dollars if you don’t need the features of the LCD version, although the latter is the one that we recommend – see text. 84  Silicon Chip can dispense with the LCD panel and use six LEDs instead but note that they will not be able to give a read­ing of transistor gain or diode forward voltage. It will also give you less information about why a component cannot be identi­fied. Fig.4 gives the wiring details for the LCD version while Fig.5 shows the LED version. If you are building the LCD version, resistors R9-R14 and the six LEDs are not required. Alternatively, if you build the LED display version, trim­pot VR1, switch S2 and the LCD are not required. By the way, the photographs for the prototype show all components in place and it operated with both the LCD and LED displays. So to avoid confusion when you are building your version, follow either Fig.4 or Fig.5 and note that the photos do show extra components on the PC board. Note that the circuit of Fig.1 also shows all components, for both versions. The first step in assembly of the LCD version (Fig.4) is to install the 10 wire links. Since many of them are quite long, we suggest you use single stand insulated wire, such as found in telephone cable. That done, install low profile sockets or socket strips for IC1 and IC2. Next, fit the resistors, trimpot VR1, capacitors, diode D1 and the 3-terminal voltage regulator REG1. A 2-way insulated terminal block is used for the battery connection and a 3-way terminal block for the test leads. Two PC stakes can be inserted in the board to connect pushbutton S2 or wires Parts List 1 PC board, code 04107981 1 16 character 2-line alpha­numeric LCD, using HD44780 controller 1 SPST miniature toggle switch (S1) 1 momentary contact (NO) pushbutton switch (S2) 1 9V battery 1 snap connector to suit battery 1 plastic utility case 1 front panel to suit case 1 2-way insulated PC-mount terminal block 1 3-way insulated PC mount terminal block IC sockets for IC1 and IC2, or IC socket strips IC socket strip and strip of pins to fit for LCD1 connection 3 miniature test clips 1 10kΩ trimpot (VR1) The LED version is less costly to build but won’t give a reading for transistor gain or diode forward voltage. can be soldered directly to the board. The LCD panel is a 16-character 2-line type, using the common Hitachi HD44780 or equivalent controller (see the February 1998 issue for information about these displays). These displays usually have 14 connections in a row and the tester has been designed so that a display of this type can be mounted “back to back” with the main PC board. Sometimes the connections are numbered differently but are in the same posi­tions. Some LCD panels with built-in backlighting have an extra two connections in the row for the backlight supply and these displays can be used as well, although there is no provision for the backlight which is simply left disconnected. If the pinout on your display does not match what is shown in Fig.4, a short length of ribbon cable may be called for. Due to the fact that the LCD is operated in 4-bit mode, four of the LCD pads on the tester PC board, D0-D3 in Fig.4, are unused and do not have to be connected. Assuming that the connections for the LCD match those in Fig.4, it is recommended that a row of pins be soldered so that they protrude from the copper side of the tester PC board. A machine pin IC socket strip can then be fitted to the LCD so that the two can be plugged together. Suitable strips of pins that fit into the IC socket are a bit rare but with care, short lengths of stiff wire may be substituted. Again, only 10 of the 14 lines have to be connected. Other plug and socket combinations may be used but if the space between the tester PC board and the LCD PC board is too great then there may not be enough space in the box for the battery. The LCD’s PC board should be attached to the main tester PC board using thin screws and suitable spacers. The main PC board is mounted on the top panel of the box with screws, nuts and spacers. LED version If you are making the LED display version shown in Fig.5, proceed as described above but trimpot VR1, pushbutton S1, resis­tor R15 and the LCD are not used. Fig.5 includes five additional wire links, six 390Ω resistors and the six LEDs that are needed for this version. The LEDs are fitted on the top side of the board. Take care to get the polarity of the LEDs correct – they don’t all “point” in the same direction. The PC board will be mounted on the top panel of the box with suitable screws and spacers about 12mm long. One way to get the length of the leads on the Semiconductors 1 CD74HCT22106E crosspoint switch array (IC1) – available from Farnell Electronic Com­ponents; phone (02) 9645 8888 (order code 403-528) 1 PIC16C711-04P programmed microcontroller (IC2) 1 78L05 5V regulator (REG1) 1 1N4001 diode (D1) Capacitors 6 0.1µF 50V monolithic 1 22pF 50V ceramic Resistors (0.25W) 2 330kΩ 1% 1 1.5kΩ 5% 1 12kΩ 5% 2 330Ω 1% 1 10kΩ 5% 2 220Ω 5% Miscellaneous Screws, nuts, spacers, single-strand hookup wire, solder LED Version Add: 6 5mm red LEDs (LED1-6) 6 390Ω resistors Delete: 16-character 2-line LCD 1 momentary contact pushbutton switch 1 10kΩ trimpot (VR1) Where to Buy the PIC Processor The programmed PIC processor is available from the design­er, Andy Wood, for $25 (includes p&p). Send remittance by cheque or postal money order to Andy Wood, GPO Box 1936, Sydney, NSW 1043. July 1998  85 STEP POWER AUTOMATIC SEMICONDUCTOR ANALYSER SILICON CHIP Number of flashes indicates which test lead is connected NPN PNP E B C Transistor Diode - A K Diode SCR G A K SCR Triac G M2 M1 Triac Off SILICON CHIP POWER On SEMICONDUCTOR ANALYSER Fig.7: here are the actual-size front panel artworks for both versions (LCD version top, LED version immediately above). LEDs correct is to drill the required holes in the front panel, place the LEDs loosely in the PC board and then adjust their height after bolting the PC board to the top of the panel. The LEDs can then be soldered in place. For both versions, the power switch (S1) is connected between the battery posi­ tive lead and the positive terminal on the 2-way terminal block. Before fitting IC1 and IC2, connect the battery, switch S1 on and check that +5V is present at pin 19 of IC1 and pin 14 of IC2. The test clips should be prominently labelled “1”, “2” and “3”. The three test leads should be connected to the 3-way termi­nal block. The test lead numbers are shown in Fig.4 and in Fig.5. Trimpot VR1 is used to adjust the contrast of the LCD dis­play. Using the tester Attach the three test leads to the 86  Silicon Chip device to be tested. For a diode, use test leads 1 and 2. For a transistor, the type (NPN or PNP), connections and hFE should be displayed on the LCD as soon as the tester is turned on. The connections, “E”, “B” and “C” are displayed in the order corresponding to the number on the test leads. For diodes and SCRs, “A” is used to indicate the anode, while the letter “K” will indicate the cathode which is the normal convention. If the device cannot be recognised or is faulty, a question mark will be displayed. If you want to know why the device fails to be identified, the tester can be placed into “single step” mode using push­button switch S2. In single step mode, the tester stops and displays the result after each combination is tried and only advances to the next combination when S2 is press­ed. The information displayed may indicate a “short” but Fig.6: this is the full-size etching pattern for the PC board. this should not be taken literally, as it may simply indicate high leakage. Similarly, “open” may mean the forward voltage is higher than expected. A number will be displayed after the word “open” or “short”; this is the ADC reading across the test resistor. For transistors, this resistor is 330kΩ, for diodes it is 330Ω, and for thyristors (SCRs) it is 220Ω. The reference voltage for the ADC is the 5V supply so a value of 255 is equivalent to 5V. Numbers that may appear preceded by “B” and “C” are the ADC readings across the base (330kΩ) and collector (330Ω) resistors. The only way to get the tester out of single step mode is to turn it off and back on again. For a diode, the connections and the forward voltage will be displayed. The voltage is as measured with the diode connected in series with a 330Ω resistor and two crosspoint switches (typically 65Ω each) across the 5V supply. For a diode with a forward voltage of about 0.7V, this means that the test current is about 9mA. As with the hFE value, the forward voltage measurement is an indication only. For one thing, the ADC has only Using the LED version The LED display version has six LEDs – three in a vertical row and three in a horizontal row. The vertical row is simple enough to understand but the horizontal row may appear to flash in an odd way but is also quite easy to understand once you know the trick. The vertical line of LEDs displays the device type. The top LED will be on for NPN transistors, the middle one for PNP tran­sistors, and the bottom one for diodes. Two of these LEDs on means an SCR and all three a Triac. Note that, as pointed out previously, some SCRs and most Triacs are not sensitive enough to be recognised by this tester. The horizontal row of LEDs indicates the connections. For transistors, the left LED is for the emitter. Observe this LED and it will be seen to be flashing one, two or three times. The number of times it flashes indicates NORBITON SYSTEMS NS_PC101 card for XT/AT/PCs allows access to 48 I/O lines. There are 5 groups (0 to 4) available on a de-facto industrial standard 50-way ribbon cable used in STEbus and VMEbus 19" rack mount control systems. The board uses 2 x 8255 ICs. Multiple boards can be used if more I/O lines are required. NS_LED PCB gives visual access to five groups (0 to 4) of the NS_PC1OX. There is a total of 40 status LEDs. The board offers a 25-way “D” type female socket. The lines are driven by 74244 ICs & configured as a parallel printer port. This socket gives access to printer port kits, eg, stepper motors, LCDs, direct digital synthesis. NS_16_8 PCB is a system conditioning card with 16 optically isolated inputs set-up for either 12V or 24V operation. The board provides 8 single pole, double throw relays with 10 Amp contact rating. which test lead is connected to the emitter. Similarly, the centre LED identifies the base and the right LED the collector. For other devices, the basic principle is the same, so for exam­ple, if the device is an SCR, the number of times the LED on the right flashes will identify the test lead connected to the cathode. Troubleshooting If the tester does not function correctly, begin by checking carefully for missing or misplaced wire links. Next, examine the PC board for broken or shorted tracks, particularly around IC1 where the tracks are closely packed together. If the microcontroller oscillator is working correctly, the oscillator frequency, divided by four, should be present at pin 15 of IC2 and should be about 500kHz. To test this an oscilloscope, logic probe, or multimeter with an inbuilt frequency meter can be used but take care not to short adjacent pins while testing this. If nothing is displayed on the LCD, try adjusting VR1 which adjusts the contrast. If there is still no display, KITS & CARDS NS_DC_DC is a step down converter with an input range 11 to 35V DC and an output of 5 volts DC at 5 Amps, with an output ripple of approx 150mV. There is an IN/OUT 50-way connector isolating the 5V and 12V+ &12V- rails of the PC power supply. This segregates PC’s power when working on prototypes. NSDC_DC1 module used with NS_DC_DC & NSDC_DC4 converters is a 5V to 12V(+/-) step- up converter. The board utilises 743 switch mode IC with 2 x 12V regulators, with output ripple of approx 200mV. NS_UTIL1 prototyping board has 1580 bread board holes access to any 3 groups (0 to 4) on the 50-way cable pinout. Power is available from the 50-way cable format 5 volts at 2 Amps & 12V+ 12V- at 1 Amp. There is provision for array resistors with either a ground or positive common connection. For brochure write to: Reply Paid 68, NORBITON SYSTEMS, PO Box 687, Rockingham WA 6968 http://www.users.bigpond.com/norbiton KITS-R-US PO Box 314 Blackwood S.A. Ph/fax 08 8270 3175 FMTX2A Universal Stereo Coder $49 FMTX2B 30mW Xtal Locked 100MHz Transmitter $49 FMTX1 1-3 Watt Free Running Transmitter $49 FMX1 200mW Full Broadcast Transmitter, built & tested $499 FM220 10-18 Watt FM BGY133 Philips Linear $499 FM1525 25 Watt Discrete Linear FM Band $499 FM2100 110 Watt Discrete Linear FM Band $699 FM3000 300 Watt Discrete Linear FM Band $1499 Philips 828E/A VHF Receiver Boards (6 metres) $9 AWA 721 VHF Receiver Boards (2 metres) $9 AWA 721 VHF transmitter boards 1 watt (2 metres) $19 Philips 323 UHF transmitter boards 500mW (70cm) $19 AEM 35 Watt Little Brick Audio Power Amp $15 Digi-125 200W RMS Audio Power Amp $39 CA Clipper Compiler, new in box $49 6dBd Gain Colinear FM Band Antenna $999 Roll Smart-1 FM Station Audio Processor $999 Free catalog on disk of discounted surplus components Same day shipping, credit cards OK, circuits supplied. SPECIAL STEAM BOAT KITS $14 8-bit resolu­tion but more importantly, accuracy of this reading is dependent on the 5V supply voltage provided by IC3, as this provides the reference for the ADC. check the LCD “enable” line (sixth pin, labelled E in Fig.4). With nothing connected to the test leads, this line should be low most of the time but two bursts of positive-going pulses should appear at intervals of about 300ms. If the fault is still not evident and there is still no display on the LCD, try to determine if the rest of the circuit is working. Attach test leads 1 and 2 to a red LED. The test current should be sufficient to make it flash. The LED should also be recognised as a diode, so pin 13 of IC2 should go low (this controls the “diode” indicator, LED1, for the LED display version). SC Protect Your Valuable Issues Silicon Chip Binders REAL VALUE AT $12.95 P LUS P& ★  Heavy board covers with 2-tone P green vinyl covering ★  Each binder holds up to 14 issues ★ SILICON CHIP logo printed in gold-coloured lettering on spine & cover Price: $A12.95 plus $A5 p&p each (Aust. only). Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. July 1998  87 3 1 2 GREAT REASO SUBSCRIBE NO Every new or renewing subscriber* between now and June 30 gets a FREE copy of the superb SILICON CHIP/JAYCAR Wall Data Chart. THAT’S WORTH $10.95 ALONE! Every new or renewing subscriber* between now and June 30 qualifies for an EXCLUSIVE 10% discount on ANY SILICON CHIP merchandise: books, software, EPROMS & microprocessors, binders, back issues, etc 88  Silicon Chip * This offer applies to Australian subscribers only ONS TO OW TO 3 The best reason of all: you’ll actually save money! Not only will you get your copy of SILICON CHIP BEFORE it’s on the news-stands – it’s cheaper getting your copy mailed direct to you – and you’ll never miss an issue! HURRY! TAKE ADVANTAGE OF THIS STRICTLY LIMITED OFFER TODAY! Yes Please! I want SILICON CHIP delivered every month to my letterbox and I want to take advantage of the exclusive subscribers’ offers. Name............................................................................................. PLEASE PRINT Address.......................................................................................... ....................................................................Postcode..................... ❑ New Subscription (month to start....................................) ❑ Renewal (Sub No from wrapper.......................................) I want ❑ One Year <at> $59 ❑ Two Years <at> $112 or ❑ 1Yr with binder <at> $72 ❑ 2 Yr with binders <at> $138 This is a YES! This offer also applies to GIFT SUBSCRIPTIONS: Call SILICON CHIP to place your order for a gift subscription. Here’s how to order: or or Fax this coupon (or a copy) to SILICON CHIP on (02) 9979 6503 – 24 hours a day Post this coupon (or a copy) to SILICON CHIP, PO Box 139, Collaroy, NSW 2097 You can even order by phone with your Bankcard, Mastercard or Visa Card: Call SILICON CHIP on (02) 9979 5644 9am-5pm, Monday to Friday FAX or POST ORDERS: Card No: Expiry Date:_______/_______ Signature:__________________________ (Yes, we do accept cheques or money orders by post!) March 1998  89 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Write to: Ask Silicon Chip, PO Box 139, Collaroy Beach, NSW 2097. Timing light goes berserk I have purchased and assembled a Multi-Spark CDI kit, as published in the September 1997 issue, and have the board using the reluctor circuit. After testing it appears to work very well. But my timing light seems to go berserk with the MSD and I’m having trouble checking the timing. I have tried to disable the multi-spark feature as per the instructions but now after retesting, it no longer wants to trigger using the reluctor. I have rechecked the assembly several times and can’t fault anything. Is there an update or could you advise? (S. W., Hackham, SA). •  As far as we can determine, your timing light should work satisfactorily when the MSD feature is disabled, even though the light will be triggered only once for each spark plug firing. TV reception problems Your March 1998 article on Yagi antennas for FM reception has served me well, not for FM radio reception but for improving my TV picture. I live in Coledale which is in the northern sub­urbs of Wollon­gong. There is a 300-metre escarpment to the west of us and this can block some UHF signals transmitted from the Knights Hill transmitter. The channels affected are ABC & WIN but luckily these channels are also put out on VHF from a closer translator at Brokers Nose. From information provided by an old Dick Smith Electronics catalog, WIN Wollongong (Channel 4) transmits on 94-101MHz & ABC (Channel 5A) is on 137-144MHz. I realised that your VHF Yagi antenna would come in very useful. The 90  Silicon Chip If your CDI system does not work after disabling the MSD feature, it is likely that a solder splash has shorted between copper tracks or there is an open circuit on the board. No errata have been published on this project. Doubling the scan rate of composite video In reply to B. L.’s letter published in the December 1997 issue of SILICON CHIP, I am writing to ask if it would be ex­tremely difficult to build an adaptor that could double the scan rate of a composite video signal so that a VGA monitor could display it. This would not only be useful to allow one to cheaply watch television on a computer but it would be a godsend for users of Amiga computers. The Amiga was designed with home video editing in mind, so most of its screen modes have a scan rate of only 15.625kHz. While this does allow antenna was built but instead of the 3mm perspex I used 10mm plastic from a kitchen cutting board for strength, as cockatoos visit our area most days and cause havoc bending antennas! Only time will tell if the UV will affect this plastic. My system now has a UHF & VHF antenna, both individually amplified and diplexed. The picture on WIN is perfect and the ABC is very good but sometimes has a band of white speckles that move down the screen. I wonder if any of your readers could tell me how to eliminate this interference. The cost of building the antenna was well worth the $48 outlayed. (J. J., Cole­dale, NSW). •  Thanks for your comments on the 5-element Yagi antenna. The interference on the ABC may be due to electrical interference from a nearby power pole, perhaps made worse when the wind is blowing. for cheap computing using a TV, the resolution leaves a lot to be desired and it is very tiring to stare at such a flickery display for any length of time. Although Commodore did make its own brand of monitors, that company has been dead for many years, leaving thousands of loyal users stranded. I’m sure that many readers would have an old Amiga computer gathering dust in the back of a cupboard somewhere. What users need is an adapter that could double the 15.625kHz signal from the Amiga but allow VGA signals to pass through unchanged. This would also allow the old Amiga to share a PC’s monitor with a minimum of fuss. As an afterthought, a “scan-doubled” TV on a big VGA moni­tor would be a lovely rich flicker-free screen for home-theatre buffs. (N. W., Orange, NSW). •  Running a composite video signal at double the normal scan rate would not be an easy task. We assume that it would require video RAM to store several lines’ worth of signal so that it could be output at double the normal rate. It is not a project that we would normally consider but perhaps one of our readers has designed a circuit to perform the task. Getting good bass from vinyl records I am writing concerning the Universal Preamplifier in your April 1994 issue. Long ago, I made the ETI Series 5000 pre-power amps but was never happy with the magnetic preamp it us­ed. My records never sounded right and yet there was no fault with the units. Apparently, the magnetic pre­ amp was designed to comply with a then-proposed RIAA standard that was yet to be adopted by the recording industry. Consequently, I found my record collection had a different sound quality to what I was used to. The sound was just overly bright and lacking in bass. This was annoying and without Multi-spark CDI is holy grail Since 1961, I have built several capacitor discharge igni­ tion systems which have all done an excellent job. My only frus­tration is with the unit I built for my 70hp outboard motor. At a particular low throttle setting (which happens to be the speed setting needed to negotiate the moorings near the launching ramp), the engine runs roughly. Hence my holy grail has been to build a multi-spark unit like the one John Clarke described in the September 1997 issue of SILICON CHIP. Having built the unit, I find the outboard doesn’t like it at any speed and misses badly. I have built a test rig using an adjustable speed motor driving a Holden distributor. I measure 298V at the drain of Q6. Connecting a CRO as in Fig.4 of the article, I get a similar waveshape but of course a peak of 298V. When I look across the primary of the ignition coil I get a similar wave-shape to Fig.3 except that each pulse is slightly rounder and only has a peak of -150V and +140 pursu­ing it further, I soon found myself enthralled with CDs and left it at that. The turntable has been in storage ever since. But the time is now ripe to convert these records to CD. This I can do using software supplied with the SB16 sound card on my computer and a CD burner. My turntable is fitted with a Shure V15 type IV cartridge and therefore I want to optimise the per­form­ ance from my audio setup. Because I wasn’t happy with the original Series 5000 magnetic preamplifier, I set out to find one that did not use ICs (I suppose I believed that transistorised preamps work better). I could not find one and settled for the SILICON CHIP design already mentioned. However, after testing it, I soon found that the performance of this unit was similar to the one I am throwing out. I compared duplicate recordings I have on vinyl and CD and without doubt, the vinyl playback is lacking in bass content compared to the CD play- volts. I get a nice square 15V pulse on the gate of Q7 which appears to turn hard on. I have even gone to the trouble of running a 2 sq mm wire directly from the source of Q7 to the coil and the same sized wire from the positive side of the coil directly to C2. Can I increase the voltage from 298V to 398V without damaging Q6 or Q7? Would I have to increase the value of the 33kΩ resistors or can pin 1 of IC1 and IC2 sink the extra current. My reason for asking this is that all the units I have built for 2-stroke engines seem to work better around 400V. (F. T., Narra­ been, NSW). •  We are concerned that perhaps your missing problems may be caused by a fault in the coil or an intermittent open circuit rather than insufficient primary voltage. This suspicion is reinforced by the fact that you experienced missing at low revs with the standard ignition system. While we do not recommend it, it is possible to increase the primary voltage to 350V by inserting a 50V 1W zener diode in series with the existing zener diode string. back. The recordings I am comparing are Dire Straits “Love Over Gold” and Sade “Diamond Life”. I am satisfied that nothing else is wrong and that both of these magnetic preamps do not provide correct RIAA equalisation. I do not want to go out and buy a secondhand amplifier just to do this task. Hopefully, you may be able to enlighten me as to how I can modify the design of this unit so that I can utilise the original RIAA equalisation, rather than any proposed equal­isation of that time. I also noted that wire links (C3, R3) were shown in your photograph but should have been omitted. I could find no errata for this error in following issues! I know you may not want to concede any error for this design but I am still hopeful for some useful advice, to get this unit operating to my satisfac­tion. (P. D., Mount Colah, NSW). •  The equalisation provided by the April 1994 design is very close to the EVATCO TUBE SPECIALS While stocks last 12AT7WC JAN Philips ECG Mil Spec $12.00 12AU7A/5963 $11.00 12AX7WA JAN Philips ECG Mil Spec $14.00 12AX7WA Sovtek $10.00 300B Sovtek Dual Point Matched $125.00 807 AWV Australia E82CC/6189 Siemens Germany $19.00 $20.00 EL34/6CA7 Sovtek or Svetlana Matched $26.00 EL84/6BQ5 Sovtek Matched $17.00 GE Tube Data Manual 1973 473 pages $26.00 TUBE DATA 3.5 DOS Disk 27,000 tubes $53.00 SSAE DL size for CATALOGUE ELECTRONIC VALVE AND TUBE COMPANY PO Box 381, Chadstone Centre, Vic 3148 Tel/Fax: (03) 9571 1160   Mobile: 0411 856 171 Email: evatco<at>mira.net SILICON CHIP This advertisment is out of date and has been removed to prevent confusion. July 1998  91 Controller damaged by induction motor Would you please help me? Some months ago I built your speed controller as described in the November 1997 issue. I used a Jaycar kit and the controller worked fine until a “mate” of mine decided to try it out on a bench drill fitted with an induc­tion motor. The internal fuse exploded and the whole thing went dead. I have been unable to find any other damaged components. Could you please advise which parts are likely to need replacing? (B. V., South Granville, NSW). RIAA standard but as the text reveals, it does add in the recommended IEC rolloff below 20Hz. You can eliminate this simply by using a 1µF (or larger) capacitor in place of the 0.33µF capacitor at the output. If you feel that the sound is still overly bright, then we suggest that this may be more to do with the characteristics of the magnetic cartridge and the tone arm. On the other hand, many vinyl records do not have the same strong, tightly controlled bass content as the equivalent CDs. This was often the case as the recording lathes and magnetic cartridges have a definite limit above which further signal amplitude merely causes overload. We would suggest that you try the bigger output capacitor as we have suggested and then, if the bass is still not strong enough, you can provide further bass equalisation via your sound card when making dubs to CD. By the way, examination of the •  We can only speculate about the damage but since the fuse has been so utterly blown, we expect that Q1 and D1 are likely to have been blown, as well as the bridge rectifier and possibly IC2 as well. It is also possible that tracks may have been blown off the PC board in which case the whole project is a write-off. If the damage is somewhat less than this and you are able to replace damaged components, you would be wise to check the operation of the circuit at low voltage with an oscilloscope, before reconnecting it to 240VAC. photograph on page 32 of the April 1994 shows that no links are present in the positions for R3 and C3. There were no mistakes in this project that we know of. Constant current to discharge a battery I need to maintain a constant current from a battery supply source, although the voltage gradually drops off which is accept­able. I want the circuit to contain a minimum number of compon­ents. The input is 9V, the output is to remain constant until a voltage level of approximately 5V is reached. The circuit will then operate with less current down to 3V. The required constant current output should be 850-900mA and the load is resistive. What sort of computer board would I need to fit into my 486/DX100 computer so that I can monitor, store and print out (in either table and/or graph form) the voltage, current and watts from a device under test; eg, a small DC motor running on a set of batteries. This would save having to write down values every 10 minutes and then plot a graph. The computer would be able to monitor and plot the graph when the test is considered finished. Would you know where one could purchase such a plug-in board or would you be able to come up with a project? Could these boards be used for AC as well as DC circuits? Submarine films show a crew member indicating to the cap­tain that he has picked up an enemy sub on his radar and they are down “X” feet or metres. How does radar work under water or do they really mean sonar? I always understood that radar worked above the water not under it. If radar does work under water, then why not us it in one’s swimming pool to detect an object like a young child that has fallen in? (R. B., Miranda, NSW). •  While we have not published a constant current load which exactly satisfies your requirements, it would be possible to modify the design published on page 43 of the April 1998 issue of SILICON CHIP. You would need to change the load transistors in order to be able to dissipate the higher power and the circuit would need re-biassing to suit a 9V battery. As far as your need to monitor voltage and current is con­cerned, you may like to try the PC-based Nicad battery monitor published in the June 1994 issue of SILICON CHIP. This used the games port and employed software which is available from SILICON CHIP for $7 plus $3 postage and packing. We can also supply the relevant back issue at $7 including postage. As far as we know, radar still does not penetrate water to any appreciaSC ble extent. 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. 92  Silicon Chip MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FOR SALE C COMPILERS: everything you need to develop C and ASM software for 68HC08, 6809, 68HC11, 68HC12, 68HC16, 8051/52, 8080/85, 8086 or 8096: $145.00 each. Macro Cross Assemblers and Disassemblers for above CPUs + 6800/01/03/05, 6502 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. ____________ ____________ ___________ ___________ ___________ ____________ ____________ ___________ ___________ ___________ ____________ ____________ ___________ ___________ ___________ ____________ ____________ ___________ ___________ ___________ ____________ ____________ ___________ ___________ ___________ ____________ ____________ ___________ ___________ ___________ ____________ ____________ ___________ ___________ ___________ Enclosed is my cheque/money order for $­__________ or please debit my ❏ Bankcard   ❏ Visa Card   ❏ Master Card Card No. Signature­­­­­­­­­­­­__________________________  Card expiry date______/______ Name ______________________________________________________ Street ______________________________________________________ Suburb/town ___________________________ Postcode______________ 94  Silicon Chip and 68HC12 now combined at the new low price of $75. Debug monitors: $75 for 6 CPUs. All compilers, XASMs and monitors: $480. 8051/52 Simulator (fast, now incl. 80C320): $75. Try the C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo desk: FREE. All prices + $5 p&p. Atmel Flash CPU Programmer: Handles the 89Cx051, the 89C5x and 89Sxx series, and the new AVRs in both DIP and PLCC44. Also does most 8-pin EEPROMs. Includes socket for serial ISP cable. $189, $35 tax, $10 p&p. 20-pin SOIC adaptor only $70. Credit cards accepted. GRAN­TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph (02) 9896 7150 or Internet: http://www.grantronics.com.au RAIN BRAIN AND DIGI-TEMP KITS. Also 60 channel Moni-temp with alarms and PC Data logging. Mantis Micro Products, 38 Garnet Street, Niddrie, 3042. (03) 9331 4786. Fax (03) 9331 4782 http://www.home.aone.net.au/ mantismp ELECTRONIC ENGINEERING SOLUTIONS: No matter what problem what industry we will find you a solution that meets your needs. Specialising in schematic & PCB design, custom Windows based software, embedded control, Windows/PC based test equipment, turnkey solutions. Fast turn around with competitive rates. DAMUE PTY LTD, 46 Whitby Road, Kings Langley NSW 2147. Phone (02) 9624 2802. Fax (02) 9624 2651 or E-mail alovell<at>ibm.net A NEW address for Acetronics http://www.acetronics.com.au On-line PCB quotes, free software, DIY PCB supplies plus many other items & services. 02 9743 9235. SIMPLE PIC84 PROGRAMMER: various models available. Also PIC-driven moving message and digital displays. EST (02) 9789 3616. www.nettrade.com.au/sesame/ HOMEBUILT DYNAMO, engineering dreams into reality. “An absolutely marvellous book for the true ex­ perimentalist!” Elektor Electronics. (www.onekw.co.nz) VIDEO SURVEILLANCE & CCTV EQUIPMENT. PCB CAMERA MODULES: AWFUL-CMOS only $49.00. 380 line x 0.2 lux 32 x 32mm from $73. 400 x 0.05 PREMIUM SONY Chipset from $88. CAMERAS: 36 x 36 from $85. Dome from $94. DIGITAL COLOUR MODULES: 32 x 32 from $182. 330 x 2 lux from $212. 450 x 2 lux from $326. DIGITAL CAMERAS: 380 x 1 from $270. 450 x 2 from $367. ACCESSORIES: 30 + Lenses, Infra-Red Illuminators, IR LEDs, Polarising, Infra-Red Cut & Pass Filters for Exposure, Focus & Glare Control, DOME HOUSINGS only $10. ANCILLARY EQUIPMENT: Quads 4 pix 1 screen from $254. Switch­ers 4 or 8 Ch from $114. MULTIPLEXERS FULL-SCREEN FULL RESOLUTION VCR Recording from $748. ALSO: Monitors, Outdoor Housings, Brack­ ets, Dummy Cams, CCTV-TV/VCR I/F Modules, Motorised Pan Units etc. Modulator/Mixer/Amplifier TV/VCR Modules from $14. 52mm dia 50 LED DIY InfraRed Illuminators from $19. PACKAGED SETS! QUAD + FOUR CAMERAS + Power Supplies from $645. GREENCELL Battery Regen­ erator 4 x AA or AAA suit Alkaline, Heavy/Super Duty Zinc Chlo­ r ide & Nicads with Mains Plug Pack $15. UP TO 2 Year WARRANTY available for most items! DISCOUNTS available based on ORDER VALUE, BUYING HISTORY and for CASH! BEFORE you BUY ask for our Illustrated Catalogue/Price List with Application Notes. Allth­ings Sales & Services 08 9349 9413, Fax 08 9344 5905. TELEPHONE EXCHANGE SIMULATOR, SC February 1998. Test all sorts of equipment without the cost of extra telephone lines. Melbourne 9806 0110. CRO: TEKTRONIX 2205 DUAL CHANNEL 20MHz, as-new condition (recent model). 2MHz function/sweep generator. Both for $550. Ben (02) 4226 9531, ben<at>snrc.uow.edu.au ELECTRONICS TEST EQUIPMENT: Signal generator Rhode & Schwarz SMS 0.1-520Mz $1500; function generator Tabur Electro 20Mz $520; digital MAKE YOUR OWN PCB'S Positive pre-sensitised 100x150 150x300 300x450 Single sided - Phenolic PCB $2.20 $5.10 n/a - Fibreglass PCB $4.55 $10.85 $22.10 Double sided - Fibreglass PCB $5.10 $12.85 $24.00 Heated Etching Tank $65.00 (+22 % sales tax if applicable) Other sizes available. We also stock developer, etchant and UV light boxes PRESTON ELECTRONIC COMPONENTS Computronics Now at 172 HIGH STREET, PRESTON, VIC (Corner of Bell and High Streets) Phone: (03) 9484 0191 Specialising in a wide range of: TV Antennas – Resistors – Cables – Circuit Boards – Capacitors – Sprays – PCB Artwork – Instrument Cases – Relays – Kit Sets – Semiconductors (all types) – Trimpots – Photo Sensitive – Transformers – Switches – Alarm/Security Equipment – CB Radios & Accessories. We are approved resellers for Altronics, DSE and RPG Products! Corporation Ltd 6 Sarich Way, Technology Park, Bentley, WA, 6102 Ph. 08 9470 1177 Fax 08 9470 2844 Other sizes at www.computronics.com.au Need prototype PC boards? We have the solutions – we print electronics! Four-day turnaround, less if urgent; Artwork from your own positive or file; Through hole plating; Prompt postal service; 29 years technical experience; Inexpensive; Superb quality. 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 http://www.cia.com.au/rcsradio/ Printed Electronics, 12A Aristoc Rd, Glen Waverley, Vic 3150. Phone: (03) 9545 3722; Fax: (03) 9545 3561 Call Mike Lynch and check us out! We are the best for low cost, small runs. Silicon Chip Binders ★  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 REAL VALUE AT $12.95 PLUS P &P Price: $12.95 plus $5 p&p each (Aust. only) Just fill in & mail the handy order form in this issue; or fax (02) 9979 6503; or ring (02) 9979 5644 & quote your credit card number. multimeter Fluke 8050A $250; oscilloscopes, HP 1740A 100Mz two channel delayed time base $750; BWD 520 50Mz two chan­nel $390; Tektronix 434 25Mz two channel storage with probe $450; soldering station Royel with temperature control $50. Phone: (03) 9309 3581. Mobile: 0412 340692. KIT ASSEMBLY: Any size or complexity. 20 years experience. $20.00/h. Ph Richard (08) 8293 3085. KITS ASSEMBLED at reasonable prices. Phone Neville (07) 3857 2752. WANTED SERVICE MANUAL or circuit or copy. Sony transistorised portable fiveinch screen TV model 5-202. Fully Germanium. Also circuit for 100k# per volt analogue multimeter. Make TMK, model 100K. (02) 9603 8763 Campbelltown. July 1998  95 14 Model Railway Projects Shop soiled but HALF PRICE! Our stocks of this book are now limited. All we have left are newsagents’ returns which means that they may be slightly shop soiled or have minor cover blemishes. Otherwise, they're undamaged and in good condition. SPECIAL CLEARANCE PRICE: $3.95 + $3 P&P (Aust. & NZ) This book will not be reprinted Yes! Please send me _____ copies of 14 Model Railway Projects at the special price of $A3.95 + $A3 p&p (p&p outside Aust. & NZ $A6). Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Advertising Index Altronics................................. 34-36 Australian Audio Consultants.......63 BBS Electronics...........................43 Computronics..............................95 Dick Smith Electronics..................... .................................. IFC,OBC,8-11 Harbuch Electronics....................32 Instant PCBs................................95 Jaycar ................................... 45-52 Kits-R-Us.....................................87 Microgram Computers...................3 Norbiton Systems........................87 Oatley Electronics........................25 Preston Electronics......................95 Printed Electronics.......................95 Procon Technology......................95 Quest Electronics........................33 Card No. RCS Radio...................................95 Signature­­­­­­­­­­­­___________________________  Card expiry date______/______ Resurrection Radio......................91 Name Scan Audio..................................91 Street ______________________________________________________ PLEASE PRINT ______________________________________________________ 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). Silicon Chip Back Issues....... 38-39 Silicon Chip Bookshop.................37 Silicon Chip Binders/Wallcht........93 Silicon Chip Software..................79 Silicon Chip Subscriptions..... 88-89 Smart Fastchargers.....................63 Truscott’s Electronic World...........33 Circuit Ideas Wanted Do you have a good circuit idea. If so, why not sketch it out, write a brief description of its operation & send it to us. Provided your idea is workable & original, we’ll publish it in Circuit Notebook & you’ll make some money. We pay up to $60 for a good circuit but don’t make it too big please. Send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, 2097. 96  Silicon Chip Microprocessor For Digital Effects Unit This is the 68HC705-C8P pro­gramm­ed micro­pro­cessor IC for the Digital Effects Unit (see Feb­. 1995). Price: $45 + $6 p+p Payment by cheque, money order or credit card to: Silicon Chip Pub­ lica­tions, PO Box 139 Collaroy 2097. Phone (02) 9979 5644; Fax (02) 9979 6503. Zoom EFI Special........................65 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”