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SILICON CHIP If you are seeing a blank page here, it is more than likely that it contained advertising which is now out of date and the advertiser has requested that the page be removed to prevent misunderstandings.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.keysight.com Contents Vol.13, No.12; December 2000 Home Networking For Shared Internet Access – Page 4. FEATURES 4 Home Networking For Shared Internet Access Home networking is now so easy that anyone can do it. Here’s how to set up a small network with shared Internet access – by Greg Swain 26 Review: Agilent 54622D Mixed Signal Oscilloscope It’s a high-performance analog scope and 16-channel logic analyser all rolled into one. And it’s amazingly easy to drive – by Leo Simpson 78 Vintage Radio Special: Your First Restoration Looking for a start in vintage radio? The AWA 467MA 4-valve mantle radio is the ideal set – by Rodney Champness 92 Index To Volume 13 All the articles, projects and columns for the year 2000 PROJECTS TO BUILD 14 Build A Bright-White LED Torch You get high brightness, a cool white light and very low battery drain. And you’ll never have to replace the bulb again – by John Clarke 36 2-Channel Guitar Preamplifier, Pt.2: Digital Reverb Add life to your music with this easy-to-build digital reverberation board. It uses two digital delay chips to give realistic effects – by John Clarke 53 Driving An LCD From The Parallel Port Agilent 54622D Mixed Signal Oscilloscope – Page 26. You build the module, then use the software to display messages or to program a thermometer/thermostat chip – by Peter Crowcroft & Frank Crivelli 68 A Morse Clock – Look Mum, No Hands! If you want to know the time, you’ve got to learn Morse code – by Leon Williams 74 Protoboards: The Easy Way Into Electronics, Pt.4 Fun with comparators: this month we play with the LM393 “bog-standard” dual comparator – by Leo Simpson Digital Reverberation Board – Page 36. SPECIAL COLUMNS 60 Serviceman’s Log History, symptoms & observations – by the TV Serviceman 78 Vintage Radio The AWA 467MA: an ideal first restoration – by Rodney Champness DEPARTMENTS 2 32 34 65 84 Publisher’s Letter Mailbag Circuit Notebook Subscriptions Form Product Showcase 86 87 93 94 96 Electronics Showcase Ask Silicon Chip Notes & Errata Market Centre Advertising Index Driving An LCD From The Parallel Port – Page 53. December 2000  1 PUBLISHER’S LETTER www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc.(Hons.) Technical Staff John Clarke, B.E.(Elec.) Peter Smith Ross Tester Rick Walters Reader Services Ann Jenkinson Advertising Enquiries Rick Winkler Phone (02) 9979 5644 Fax (02) 9979 6503 Mobile: 0408 34 6669 Regular Contributors Brendan Akhurst Louis Challis Rodney Champness Garry Cratt, VK2YBX Julian Edgar, Dip.T.(Sec.), B.Ed Mike Sheriff, B.Sc, VK2YFK Philip Watson, MIREE, VK2ZPW Bob Young SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490 All material copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Dubbo, NSW. Distribution: Network Distribution Company. Subscription rates: $69.50 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. E-mail: silchip<at>siliconchip.com.au ISSN 1030-2662 * Recommended and maximum price only. 2  Silicon Chip Australia can do well in the new economy Over the last few months there has been much moaning and groaning from the economic com­ mentators about the state of Aus­tralia’s currency; the beleaguered Aussie dollar. For months now, it has been out of favour with the currency dealers and commenta­tors have been coming up with reasons why. One of the favourite arguments is that Aus­ tralia is per­ceived as an “old economy” and that since it does not have any large manufacturers of IT (information technology) or telecom­ munications equipment, no-one from overseas is interested in investing here. In a further development of this argument, some commentators go on to lambast the government for abolishing the Research & Development grant scheme. The theory is that this reinforces the perception overseas that Australia is stuck in the past as an “old” economy. Well, most of these arguments are utter rubbish. For a start, as far as most of the rest of the world is concerned, if they ever think about Australia at all, it is in terms of kangar­oos and koalas or worse, they confuse it with Austria. The truth is that, relative to the economies of Japan, the USA or the major economies of Europe, Australia just doesn’t get above the noise level. So in the current climate when everything American is seen as the place to invest, Australia is ignored and our dollar languishes. And isn’t that great? It represents the greatest opportuni­ty that Australia has had for many years to grow its economy really strongly. Because our dollar is low, it makes our exports much cheaper and many companies are making great profits because of it. At the same time, imports to Australia are dearer and that discourages companies and individual consumers from buying as much overseas-sourced products as they would have. And each month that translates into a current account surplus rather than the current account deficit we have been running almost forever. In the long term, that means that less of Australia’s gross national product (GNP) goes to servicing our overseas debt. All of which is good for our economy, in the long term. Remember that Japan grew enor­ mously in those decades while its currency was delib­erately under­valued. To my way of thinking, the longer Australia has an undervalued currency, the better. And what about the “old” economy versus the “new” economy? Anyone who has been following the sharemarket since April will know that most of the “new economy” companies, mainly based in the USA, are not looking too brilliant. And the picture in Asia, where they are strong in IT manufac­ turing, is not so rosy either; so much for the benefits of having a strong IT manufacturing base. Australia has the best of both worlds. IT equipment is generally cheap and Australian companies have invested heavily in it. We’re right up there with the best in the world in that aspect, regardless of what the commentators might say (most of them have never worked in real companies anyway). And we can use our broad-based knowledge of IT systems to enhance our ability to export goods and services to the rest of the world. So when you hear yet another news bulletin about the par­lous state of the Australian currency remember that it is good news disguised – it will do us good in the long run. Leo Simpson Infrared Data Suite for Mobile Phones & PDA’s The INFRARED DATA SUITE plugs into the serial port of a PC & the software provided enables you to • Import contacts & phone numbers from a contact manager such as Outlook, or any other program supporting export via CSV files • Create, edit & back up your personal phone book on the PC & transfer the data to the phone or PDA • Create, edit & organize your scheduler on the PC & download it to the phone • Create, edit & send SMS short messages from the PC to the phone ready for transmission The data suite interfaces with most major brands of mobile phones with IR capability. $189.00 Cat. 8912 Infrared Data Suite USB version without Data Suite software also $139.00 available as Cat. 8923 New! Programmable POS Keyboard Our new 111 key programmable keyboard for POS systems uses full travel Cherry mechanical switches. The keys are arranged in two pads and are programmable with multiple scan codes which are stored in 2KB of EEPROM non-volatile memory. Includes a track 1 & 2 magnetic card reader, other track combinations are available or alternatively without the mcr. Another PS2 or AT keyboard can also be attached. Cat. 8913 Keyboard $309.00 GST is here! Manage it with this great POS Hardware Bundle This latest bundle includes a very fast Samsung parallel dot matrix printer (as required by Digitill and Attache), a cash drawer and our very popular CCD bar code scanner. The cash drawer connects to, and is triggered from the printer. The CCD scanner connects between the keyboard and the computer (keyboard wedge). $799.00 Cat. 8937 Printer parallel port $799.00 Cat. 8938 Printer serial port POS Keyboard 55 Key Reprogrammable Optional MCR Telephone Line Auto-Connect Stylish POS keyboard with a moulded slot on the right hand edge of the keyboard for an optional magnetic card reader. All 55 keys are programmable and configurable. There is an additional port for a standard keyboard. $269.00 Cat. 8922 55 key Keyboard Look Mum - No Wires & 11Mbps! Scenario 1: Set up a LAN of wireless networked PC’s. Connect notebooks &/or PC’s in difficult to wire environments such as historic buildings or frequently changing environments in retail shops, etc. Scenario 2: Provide access to corporate facilities such as email and data bases for mobile workers e.g. doctors and sales staff. Scenario 3: LAN interconnection for point-topoint link e.g. building to building. $1,249.00 Cat. 11339 Access point Cat. 11340 PCMCIA station adapter $559.00 The missing link The Microgram 11808 audio-video RF link with infra red repeater allows you to send high quality colour video and stereo audio from one room to another and control the source with your existing remote without wires! Signal penetrates walls, doors, ceilings and floors with an A/V signal range of 100M. Three separate channels allows up to 3 transmitter/receiver pairs to operate simultaneously. Comes complete with 2.4GHz transmitter & receiver. $236.00 Cat. 11808 AV RF Link Affordable Web-Based Training A whole range of courses are available! Including WIN 2000, Lotus Notes R5, Home Business, Motivation, Internet Information Server 4 and MCSE Series. Full details at www.tol.com.au Allows 2 separate telephone devices to share a single telephone line. Both connected devices are able to send (make outgoing calls) & either can receive incoming calls. Operation is fully automatic & can be fitted to any existing fax or voice line. "Barge-in" protection is provided to ensure that one device cannot interrup the other. Cat. 22002 Auto-Connect $190.00 Remote Device Activators Allows electrical appliances to be switched on or off by using your normal telephone line. Cat. 19002 Activator for one device Cat. 19004 240V Power Control Unit Cat. 19005 Activator for two devices Cat. 19006 PC reset unit $182.00 $109.00 $229.00 $45.25 PC CardBus Sockets Transfer your PC CardBus (32 bit) and PCMCIA (16 bit) based data to your desktop PC. This "drive" has two slots and supports Type I, Type II and Type III PC Cards. Software support is included for Win 9X, NT and 2000. Please note that for technical reasons, the 32 bit slot is not available with front access. $259.00 Cat. 6523 PC CardBus Programmable Keypads Store multiple keystrokes or complex commands under one key. The keycaps are easily removable to allow custom legends. Connects to PS/2 or AT motherboards, or there is a USB model available. Connect as a keyboard wedge for programming. $251.00 Cat. 8904 20 Key for PS/2 or AT $289.00 Cat. 8933 20 Key for USB port $429.00 Cat. 8934 58 Key for PS/2 $429.00 Cat. 8935 58 Key for USB port See review in October issue of Electronics Australia Online catalogue & shop at www.mgram.com.au Phone: (02) 4389 8444 info<at>mgram.com.au Fax: (02) 4389 8388 Australia-Wide Express Courier...$11 (3kg max.) We welcome Bankcard Mastercard VISA - NO SURCHARGE! Unit 1, 14 Bon Mace Close, Berkeley Vale NSW 2261 FreeFax 1 800 625 777 Vamtest Pty Ltd trading as MicroGram Computers ABN 60 003 062 100 Web site: mgram.com.au FreeFax 1 800 625 777 MGRM1200 Dealer Enquiries Welcome! sales<at>mgram.com.au Home Networking Plus Shared Internet Access BY GREG SWAIN Networking is a great idea if you have two or more computers. It lets you exchange files, share resources such as printers and even set up shared Internet access via a single phone line. Here’s how to build your own home or small office network with shared Internet access. 4  Silicon Chip D ESPITE ITS OBVIOUS attractions, most people regard comput­ er networking as just too difficult. But while that may have been true once, it’s now so easy that almost anyone can do it. In the past, you had to know about tricky configuration setups for net­ work interface cards (NICs), to avoid clashes with other hardware. You also had to know about networking proto­cols, setting up file and printer sharing, assigning network addresses and “mapping” drives. And as for allowing computers on a network to use a single modem for shared Internet access ... well, forget it! Not any more! Home or small office networking is now almost a “no-brain­ er” thanks to plug and play (PnP) hardware and the networking wizards now included in Windows 98SE and Windows Me. What’s more, setting up shared Internet access via a single tele­phone line is child’s play. If you have more than one comput­ Fig.1: a typical small network setup. All the PCs on the network are connected to a central hub and the machine with the modem functions as the “gateway” to the Internet. Note that each PC is assigned a different IP address. er, a network makes a lot of sense. It allows you to easily exchange files and share re­sources such as printers, disk drives and modems. No longer do you have to transfer files between PCs using removable disks or swap cables about when you want to print something. As far as each “client” PC on a net­ work is concerned, it looks as though shared resources such as printers, folders and even entire disk drives are directly connected to it. You can even “map” drives on another machine so that they look like local drives. This can be very useful if you want to share a CD-ROM drive between two or more machines, for example. Installing The Hub & Network Cards 1 Switch off the power, remove the cover and install a network interface card (NIC) into a spare motherboard PCI slot on each machine. Make sure that the card is seated properly in the slot. When the machine is rebooted, you will be prompted to install the drivers for the network card. 2 Plug the Cat.5 cables into the RJ45 sockets on each of the network cards in the computers. The other end of each cable is then connected to the hub (see below), which forms the central point of the network Internet sharing OK, enough of the file and printer sharing stuff. For many people, the main reason for wanting a network is to provide a shared Internet connec­ tion via a single phone line (or cable modem). Until recently, this also required the purchase of addi­tional software or hardware. That changed when Micro­ soft included Internet Connection Sharing (ICS) in Windows 98 Second Edition (SE) and, subsequently, in Windows 2000 and Windows Me. ICS is easy to set up and allows two or more users on a network to access the Internet simultaneously via a single connection. Before setting up ICS, all the com­ puters on the network must have net­ 3 The cables from the network cards are plugged into the individual ports of the hub. The 5-port Net­Gear hub shown here is a little unusual in that the ports are all on the front panel – handy if you want fast access to the cables. Most hubs have the ports at the back. December 2000  5 Fig.2: click the Device Manager tab in the System Properties dialog box of each PC to confirm that the network card drivers have been correctly installed. A yellow exclamation mark indicates a problem. work interface cards installed. Internet Connection Sharing is then installed on the “host” machine (ie, the one with the modem). This configures the host machine and also creates a setup disk which is used to configure the “client” machines. Once this has been done, the clients can all access the Internet through the PC with the Internet Connection Sharing. Basically, the host machine acts as a “gateway” – when a client machine requests Internet access, the host machine automatically dials out, makes the connection to the Internet and then relays the data back and forth between the two (see Fig.1). Without getting too technical, Inter­ net Connection Sharing uses the TCP/ IP networking protocol. It assigns a fixed IP address (192.168.0.1) to the Fig.3: the Network properties dialog box shows whether or not Internet Connection Sharing (ICS) has been installed on the host machine. host machine and also sets up a DHCP (Dynamic Host Configuration Proto­ col) service that automatically assigns IP addresses to the client machines. Don’t worry if these terms don’t mean much to you – the ICS wizard does all the setup for the computers on your network, so you don’t have to know anything about IP addressing. Note that ICS is not installed on the client machines. This means that the clients can run earlier operating sys­ tems such as Windows 95, Windows 98 or even Windows NT on the clients, although an NT box will require man­ ual configuration. Installing the network To set up a basic network, you need a hub, a network inter­face card for each PC, and some Cat.5 cables Fig.4: the Home Networking Wizard in Windows Me is accessed via the Start menu. Alternatively, if you are using Windows 98SE, you have to run the Internet Connection Sharing Wizard. 6  Silicon Chip (fitted with RJ-45 connectors) for the connections between the cards and the hub. Fig.1 shows a typical network set­ up for a home or small office. This is known as a “star” configuration – the hub provides a central connection point for the network, with the con­ nections radiating out to the PCs. The advantage of this arrangement is that a problem in one device doesn’t affect other users on the network. If you’re just starting out, consider buying a network starter kit. This will include all the parts needed to network two PCs, including a couple of network cards, the cables and a 4-port or 5-port hub. If you want to connect more that two computers, it’s just a matter of purchasing additional network cards and cables. One thing to watch out for is the speed of the hub. For most small networks, a 10Mb/s hub will do the job but if you regularly move large amounts of data, a 100Mb/s hub will really speed things up. Note that most 100Mb/s hubs will automati­ cally switch down to 10Mb/s when communicating with 10Mb/s network cards. Want to save some money? Well, you don’t really need a hub for a 2-computer network. Instead, you can directly connect the two network cards together using a special Cat.5 cross­over cable. Provided you’re using 100Mb/s network cards, this really is the cheapest route to a fast network. Putting the network together is a breeze – it’s just a matter of installing a network card in a vacant slot in each PC and then connecting them to the hub. When the machines are reboot­ ed, the cards will be automatically detected (we’re assuming plug and play cards here) and you just follow the on-screen prompts to install the driver software. Once that’s done, it’s a good idea to verify that the driver has been correctly installed. You do that by double-click­ ing the System icon in Control Panel, clicking the Device Manager tab in the System Properties dialog box and then double-clicking on the “Network adapters” entry. If everything is OK, you should see an entry for the net­work card similar to that shown in Fig.2. That’s it – the network is up and run­ ning although you still have to share resources and set up shared Internet The Windows Me Home Networking Wizard Fig.5: the host computer is configured here to connect to the Internet via a dial-up adapter. Fig.6: here’s how to configure the host machine to share its Internet connection with the other computers Fig.7: you can let the host connect to the Internet auto-matically on demand from a client machine or you can choose to connect manually. Fig.8: each computer on the network is given a unique name but the same workgroup name must always be used for the machines to “see” each other. Fig.9: this dialog box lets you set up file and printer sharing. Fig.10: the wizard creates a setup disk which is run on the client machines. December 2000  7 100Mb/s Network Starter Kit from MicroGram IF YOU WANT your first network to be fast, this budget-priced 100Mb/s starter kit can deliver the goods. Branded Edimax, it contains all the parts required to network two PCs, including a 5-port hub, two network inter­face cards, two 4.5-metre cables, access. But first, you have to install ICS on the host machine. Installing ICS Internet Connection Sharing can either be installed on the host com­ puter when the operating system is installed or it can be added later using the Add/Remove Programs applet in Control Panel. If ICS has been installed, you’ll find several entries referring to it in the Network Proper­ties dialog box (Fig.3) – right click My Network Places (or Network Neighborhood) and select Properties to bring up this display. Fig.12: once the network is up and running, you can access shared resources on remote machines using My Network Places or Network Neighborhood. 8  Silicon Chip a plugpack supply and a detailed installation guide. Note that the hub runs at 100Mb/s only (ie, it cannot switch down to 10Mb/s) but that’s not a problem if you stick to 10/100Mb/s network cards. The fifth port can also function Alternatively, double-click the Add/ Remove Programs icon in Control Panel, click the Windows Setup tab, click Internet Tools in Windows 98SE or Communications in Windows Me and then click Details. There should be a tick in the Internet Connection Sharing check box. If not, select the check box and click OK to install ICS. Don’t install ICS on any of the client machines. If you do, you’ll get all sorts of conflicts between the various services that are set up and your net­ work won’t work properly. Basically, four key components are as an uplink port for connecting to another hub. The kit (Cat. 11900) is priced at $199.00 and is available from Micro­ gram Computers – ph (02) 4389 8444; email info<at>mgram.com.au; website www.mgram.com.au Fig.11: Network Neighborhood is renamed as “My Network Places” in Windows Me. installed as part of ICS: (1) the DHCP service; (2) a Domain Name System (DNS) for resolving computer names into IP addresses; (3) a Network Ad­ dress Translator (NAT) which is used to route the information between the clients and the Internet; and (4) an Autodialler. However, you don’t have to know anything about the technicalities to get the system up and running. It’s just a matter of installing ICS on the host machine, then running the Home Networking Wizard for Windows Me or the Internet Connection Sharing Wizard for Windows 98SE (or Win­ dows 2000). However, unlike the Home Networking Wizard, the ICS wizard in Windows 98SE doesn’t set up your network shares. In either case, you get to the wizard Fig.13: a folder or disk drive is shared by right-clicking it in Windows Ex­-plorer and selecting “Sharing” from the drop-down list. via the Start menu – click Start, Pro­ grams, Accessories, Communications. Figs.5-10 show some of the dialog boxes that appear. The Internet Con­ nection Sharing setup comes first, after which you move on to the local network settings. Each computer must be given a unique name but the workgroup name must be the same for all the computers on the network, otherwise they won’t be able to “see” each other – see Fig.8. The next dialog box (Fig.9) sets up file and printer shar­ing. By default, the wizard lets you share the My Docu­ ments folder only but you can share additional folders (or even an entire hard disk drive) later on. If you don’t enter a password here, a warning panel will appear when you click the “Next” button to go to the next dialog box. If you don’t want a password, just click OK to close the warning panel and then click the “Next” button again and the wizard will carry on as normal. Passwords can be a real nuisance if no security is required. Finally, the wizard prompts you to create the “Home Net­working Setup” disk so that you can set up the Win­ dows 95/98 client machines on the network. Using a network It doesn’t take rocket science to use a network. You access shared resources on other machines by double-clicking “My Network Places” in Windows Me or “Network Neighborhood” in Win­ Fig.14: Windows Me features a greatly-improved “Help and Support” utility, with a web-like interface. If you can’t get Internet Connection Sharing to work, click Help in the Start menu and search for ICS to bring up this dialog box. You can then use the troubleshooting wizard to solve the problem. dows 95/98/98SE (Fig.12). Alterna­ tively, you can access these resources via Windows Explorer. By default, the Home Networking Wizard gives other users full access rights to a shared My Documents folder. If you want to change this to read-only access, right-click the My Documents folder in Windows Explorer, select “Sharing” from the drop-down list and select the settings in the resulting dialog box (Fig.13). Additional folders (or disk drives) are shared in exactly the same man­ ner. By the way, it’s a good idea to keep other users away from sensitive system files, so avoid sharing an entire disk drive if these files are present. By sharing only selected resources, your Assigning Letters to Shared Disk Drives & Folders A useful “trick” in some cases is to map a shared folder or disk drive on a remote computer to a drive letter on a local machine. This can be very useful if you want to store files on a single “work” disk or if you Fig.15: mapping drives across a network. have only one CD-ROM drive and want to share it get an error message. This typically across the net­work. occurs because the other computer A network drive is mapped by has not been switched on. right-clicking My Network Places (or Fortunately, there’s an easy anNetwork Neighbor­hood) and select- swer to this problem: double click ing “Map Network Drive...” to bring up the Network icon in Control panel, the dialog box shown in Fig.15. You choose “Client For Microsoft Netthen choose an unused drive letter works” from the list, click the Properand click the down arrow next to the ties button and select “Quick Logon”. Path window and select the path to From now on, Windows will only log the shared re­source. you onto the network when you boot Note that if a machine cannot find a but won’t try to reconnect any network mapped drive during boot-up, you will drives until you use them. December 2000  9 NetGear Network Starter Kits – You’ll Want One For Christmas Sharing! NetGear’s network starter kits include a modem sharing utility that’s similar to ICS. The installation wizard also sets up your disk drive and printer shares. NETGEAR’S NETWORK STARTER KITS include everything you need set up a small network in the home or office. There are two models: (1) the budget-priced SB105 which comes with a 5-port 10Mb/s hub; (2) the FB105 which boasts a 5-port 10/100Mb/s switch (a switch not only functions as a hub but also filters unnecessary traffic from individual network segments to increase overall speed). critical system files will be invisible to other computers on the network. Checking ICS You can test the Internet sharing feature by launching Internet Explorer on one of the clients, entering a web address and clicking the “Go” button (or pressing Enter). If everything is working correctly, the modem on the host machine should au­ tomatically dial out after a brief delay. The system should then log onto your ISP and download the requested page in the usual manner. In short, it should all work as if the modem is di­rectly connected to the client machine. A proviso – the autodial feature will only work if you chose “Yes, connect to the Internet automatically” (see Fig.7) 10  Silicon Chip Both kits contain two 10/100MB/s PCI NICs (network interface cards), two 3-metre cables and an easy-tofollow fold-out guide. Also included is a Drivers & Diagnostics Disk and a CD-ROM which carries “FirstGear” – a network installation wizard and modem sharing program that’s similar to Internet Connection Sharing. This could be handy if you don’t have Windows Me or Windows 98SE. A feature of the NetGear hubs is when you ran the Home Networking Wizard. Alternatively, you can elect to manually connect the host computer before attempting Internet access from the clients, to prevent automatic dial-outs. Once a connection has been made, all clients have immediate access to the Internet. If it doesn’t work, check out Win­ dows Me’s “Help” utility. In fact, this is a much-improved feature of Windows Me, with all the informa­ tion arranged in web page format. To troubleshoot your ICS installation, click Start, Help and enter “ICS” in the Search window to bring up a list of topics – see Fig.14. The low-down on TCP/IP For most people, that will be the that the ports are at the front. This can be an advantage in some installations, as it provides easy access to the cables. In addition, port 5 can be switched to function as an uplink port, for cascading to another hub. NetGear Network Starter Kits are available from computer stores and electronics retailers. The suggested retail price (including GST) for the SB105 is $159.00, while the FB105 retails for $299.00. end of the story since they now have a network up and running with shared Internet access. However, it’s handy to learn a few networking basics so that you can customise your setup or just to understand how it works. By default, Windows 98 and Windows Me install the TCP/IP networking protocol. TCP/IP stands for “Transmission Control Protocol/ Internet Protocol” and it relies on each computer being assigned a unique number called an IP address. You can think of an IP address as being akin to a telephone number if you like. An IP address consists of four groups of numbers separated by deci­ mal points, with each number having a value between 0 and 255. In this case, the ICS utility uses IP addresses rang­ ing from 192.168.0.1 to 192.168.0.254. These addresses belong to a group that has been specifically reserved for local area networks and cannot be accessed via the Internet. Another number called a “Subnet Mask” is used in conjunc­ tion with the IP address to set the network ad­ dress. By default, ICS uses a Subnet Mask of 255.255.255.0 and this is the same for all computers on the network (otherwise, they won’t be able to “see” each other). In addition, a Subnet Mask of 255.255.255.0 means that the first three numbers of each IP address must be the same. If an IP address on one machine is different in this respect, it will have a different network ad­ dress and will be invisible as far as other computers on the network are concerned. When you install ICS, it automat­ ically gives the host ma­chine a fixed (or “static”) IP address of 192.168.0.1 which is bound to the network adapt­ er. At the same time, it also sets up a DHCP (Dynamic Host Configuration Protocol) service on the host machine. This DHCP service then doles out IP addresses to the client machines as they boot up. This means that the client machines must be configured to obtain IP ad­ dresses automatically (this is done by the networking wizards). Typically, the DHCP service issues the first cli­ ent with 192.168.0.2, the second with 192.168.0.3 and so on. Note that these are dynamic IP addresses. This means that a client com­puter can theoretically be issued with a different IP address each time it boots up. By the way, the Home Networking Wizard will guide you through the process of installing TCP/IP if it hasn’t already been installed on a client machine (eg, Windows 95 installs the NetBEUI protocol by default). If you’re not using the wizard, you will have to install TCP/IP yourself – double-click the Network icon in Control Panel, click Add, click Protocol, click Add, select Microsoft, select TCP/IP and click OK. Assigning fixed IP addresses For most people, using the DHCP service is the easiest way to go. The only wrinkle is that the host machine must always be started first, otherwise client computers will be unable to obtain a valid IP address. Checking Out The Assigned IP Addresses YOU CAN quickly check the IP address assigned to any client computer by using the winipcfg utility that’s automatically installed with Windows 95/98 & Windows Me. It’s started by clicking Start, Run and typing winipcfg in the Open field and clicking OK (for NT, type ipconfig at the prompt in a DOS window). You then click the down arrow and select the NIC (not the PPP adapter) to check the details. This utility is particularly handy for checking that a PC is correctly obtaining an IP address from the DHCP server. It also shows the address of the DHCP server, the IP address lease period, the subnet mask and default gateway, and the DNS and WINS server addresses. Alternatively, select the PPP Adapter if you want to check the corresponding The way around this is to give each client a static IP address. To do this, go to the TCP/IP Properties dialog box Look Before You Leap! Don’t try to set up ICS on a network that’s already running DHCP and DNS services. If you do, the services that are set up by ICS will conflict with the established services and the network will stop functioning correctly. The same comment applies if the existing network relies on installed gateways and/or fixed IP addresses. Similarly, ICS could cause all sorts of problems on a network that’s running a proxy server such as WinGate. Fig.16: the winipcfg utility lets you check assigned IP addresses. details for this adaptor when the host machine is connected to the Internet. on each client by double-clicking the TCP/IP entry for the network adapter in the Network dialog box and follow these steps: (1) Select “Specify an IP address” and enter a unique IP address in the range 192.168.0.2 to 192.168.0.254 – see Fig.17. Give each client a Subnet Mask of 255.255.255.0. (2) Click the Gateway tab and enter a gateway address of 192.168.0.1 on each client computer (Fig.18). (3) Click the DNS tab, select Enable DNS and enter a unique host name (the name of the computer is recom­ mended). Finally, enter an address of 192.168.0.1 for the DNS Server Search Order (Fig.19). Notice that both the Gateway ad­ dress and the DNS Search Order ad­ dress are simply the IP address of the What About Broadband Connections? Naturally, you can also use ICS if you have a broadband connection to the Internet; eg, via a cable modem or ADSL (Asymmetrical Digital Subscriber Line) device. This will give several users simultaneous access to the Internet without experiencing the dramatic slowdowns that occur with a dial-up modem. If you have a broadband connection, be sure to use two network adapters (NICs) in the ICS host computer. One of these adapters connects to your cable modem, while the other is con­nected to the network hub to provide the LAN connection. Do not connect your broadband device directly to the network hub as this will expose your network to the bad guys on the Internet. December 2000  11 Assigning Fixed IP Addresses To The Clients Fig.17 Fig.18 Fig.19 Step 1 – select “Specify an IP address” and enter a unique IP address in the range 192.168.0.2 to 192.168.0.254. The Subnet Mask is 255.255.255.0. STEP 2: Click the Gateway tab, enter a new gateway address of 192.168.0.1 and click the Add button install it. Do this for each client machine. STEP 3: Click the DNS tab, select Enable DNS and enter a unique host name. Enter an address of 192.168.0.1 for the DNS Server Search Order. host ma­chine; ie, the host functions as a “gateway” for the clients when they access the Internet. For this rea­ son, don’t change any of the network settings on the host computer, as this will stop the ICS service. Once configured with static IP addresses, the clients no longer go looking for a DHCP server when they boot. This can be handy if you don’t wish to start the host machine and will elim­inate annoying delays as the clients boot up. It also allows the client machines to be networked without starting the host ma­chine. Note, however, that the DHCP ser­ vice still runs when the host computer is on and will automatically issue an IP address to any machine that requests it. Fig.20: stopping the DHCP service involves a registry hack. Drill down to the folder shown here and change the “Enable DHCP” key from “1” to “0”. 12  Silicon Chip Stopping the DHCP service Going a step further, the DHCP ser­ vice could well prove a nuisance if you want to set up ICS on a network that already has a DHCP server. In that case, the two DHCP services will conflict with each other. Unfortunately, stopping the DHCP service involves a regis­try hack. This involves starting the Registry Editor, drilling down through the keys to HKEY_LOCAL_MACHINE\System\ CurrentControlSet\Services\ICShar­ ing\Settings\General and changing the “EnableDHCP” key entry from “1” to “0” (just right click the key, click Modify and type in the new value). When you subsequently restart the computer, the DHCP serv­ice will be disabled. Be warned though – you play with the registry at your own risk. For this reason, it’s always a good idea to back up the registry before making any changes. The new System Restore utili­ty in Windows Me should also get you out of any trouble. Finally, note that ICS does not work with some versions of AOL and even if the host does connect, the clients must have different AOL accounts for SC Internet access. ATENTION TEACHERS AND GET YOUR OWN PIECE OF THE EDUCATION INSTITUTIONS SYDNEY2000 OLYMPICS A GREAT CHANCE TO BY SCHOOL EQUIPMENT AT BARGAIN PRICES SCIENTIFIC CALCULATOR CASIO FX-39, old model calculator with a bright green 8 digit Fluorescent display!, works from 2 AA batteries, good quantity: $18 SCIENTIFIC CALCULATOR CASIO FX-D400, 16 digit, dot matrix LCD displays alpha characters along with values and indicators, has replay function, large quantity: $26 OLYMPIC COLLECTABLES SOME THING FOR THAT SPECIAL CHRISTMAS GIFT SHIRTS, HATS, FLAGS, BACK PACKS ETC. CHECK OUT OUR WEB SITE I EARLY DECEMBER WE WILL HAVE P C R E L A Y I N T E R F A C E K I T SOME NEW LOW PRICED CAMERAS Features include 8 relays (2 are high current contact ratting),Relay “ON” FROM $50 indicating LEDs, onboard relays and DBVIDEO CAMERAS The output of these cameras bellow is std 25 connector. Kit includes PCB, all video & can be plugged into the "VIDEO onboard components and software. $40 IN" socket of any Australian std VCR, ...Optional 5M DB-25 to DB-25 cable:$10 video monitor or TV, or via an RF Modulator to an Ant. Input. The B/W cameras are Infra Red responsive & can be used in total darkness with IR Illumination. CAMERA INTERFACE KIT This kit provides power for a camera and a RF modulated output for use with TV Ant. inputs. Kit includes case, PCB, all onboard components & therefore modulator.:$18 SUPER MICRO MONOCHROME CCD RADIO CONTROL CLOCK (350mm) CAMERA MODULE: As new. These clocks were used by the N E W M A G N E T I C S H I E L D E D 9 to 14.5V DC, CCIR (50Hz, 625 SOBO during the Olympics. There SPEAKERS lines interlaced) Horizontal res: extremely high accuracy is controlled by a 75mm 36W 8 ohm speakers with foam 380 TV lines, 1/3" CCD, radio signal from the pager network. edged poly cone 2 for $9 Sensitivity: 0.2Lux. DIARY - ORGANIZER Settings for all states. Ideal for use in radio Auto-Iris. 23 X 60mm , CASIO JD-5000BK “My Magic Diary", stations etc. where time keeping is FREE FREE FREE 20grams. Inc. 3.7mm displays messages in one of 5 languages, important. :$250 LIMITED STOCK!!! DICTATION SOFTWARE WITH lens: (AR717R) $99 English / Italian / Spanish / German / NEW PC POWER SUPPLIES French. Modes of operation include THE PURCHASE H I G H P E R F O R M A N C E include Telphone Directory, Schedule, OF ANY OF THESE M O N O C H R O M E C C D C A M E R A We have Huge stocks of PC power Calendar, Data Memo "Diary", Secret supplies. MOTHERBOARDS MODULE: 7.5 to 14.5V Memory area, Time Ranging Just ask for it when ordering. DC (1.16W), Output keeping, Alarm, Fortune CCIR (50Hz, in price IBM VOICE TYPE 3.0 KIT: Telling, Conversion, 625 lines interlaced) from $15 This is a complete kit for Calculator, Data ComCCD, Sensitivity 0.1 Check our Voice Dictation. Incs. munication. Has an easy available Lux, Auto-Iris. 32mm web site software, manual & a to understand main separately squ. x 27mm. 20grams. for more noise cancelling desktop menu with simple icons, 3.7mm lens: (AR732) $89 details microphone. Brand new . good quantity: $20 COLOUR CCD CAMERA MODULE FLIGHT FORCE PC JOYSTICK: Software incs. VoiceType SCIENTIFIC CALCULATOR WITH AUDIO: 12V DC (2W), PAL (50Hz, This analogue joystick features IBM Anti Virus & Jungle CASIO FX-350D, 8+2 625 lines interlaced) Res. 330 TV Book for Windows on CD.(IBMVT3) $16 4 fire buttons - with disable digits, huge quantity: lines, 1/3” CCD sensitivity function for 2 player comp$15Ea., PENTIUM II MOTHERBOARD: Recent 3Lux. Has Auto-Iris. atibility, Contoured handgrip, buy 10 or more for motherboard made for the latest CPU's. 38mm Squ. x 32mm auto centering, independent $13.50 Ea. Std ATX form factor. Has 3 x (16-bit) ISA high & unit weighs auto-fire & X & Y axis trim. MORE CALCULATORS slot, 4 x (32-bit) PCI slots, 1 x AGP slot & 3 20 grams. Inc. 3.7mm Has a durable metal base ON OUR WEB SITE x DIMM (memory) slots, On-board 1 x lens: (ARCB21) $180 with a large suction cup for PS/2 keyboard, 1 x PS/2 mouse socket, 2 x NEW 6 CAN COOLER H O U S E D M O N O C H R O M E C C D stability. This item is new & in USB, 1 x parallel, 2 x serial ports. With AS USED BY VOLUNTEERS DURING its original retail box: (ZA0098) $25 setup manual & CD, IDE & FDD cables. CAMERA: 12V DC (1.16W) Output: THE OLYMPICS. Soft, foldable $5 Brand new in original box. Accepts Intel CCIR (50Hz, 625 VHF-UHF TV ANTENNAS WITH NEW HALOGEN LAMPS Osram brand Pentium II & Intel Celeron CPU's (NOT lines interlaced) Res. ROTATOR 12V 5W $2.50 SUPPLIED) from 233 to 800MHz. The 380 TV lines, 1/3" New & complete in original box. CCD, Sensitivity: 12v 20W $2.50 CPU socket is SLOT-1, S-370 CPU could Features include high gain RF amp. 0.1Lux. Auto-Iris. This antenna would be ideal for homes, 8 O H M 7 5 m m M A G . - S H I E L D E D be use with a converter board (NOT 40 x 39 x 35mm high SUPPLIED). Selectable 66 & 100MHz units or caravans, weekenders and SPEAKERS. & unit weighs 13g (AR830M) $99 BUS speeds & a clock multiplier up to 8 camper vans where it can be setup or Foam edged poly cone :2 for $9 times. Should accept Pentium III CPU's, MONOCHROME CCD VIDEO CAMERA: stowed away quickly. These antennas JUMBO SERVO KIT...Use it with our on a 100MHz bus: (SP6XS) $90 B&W Camera built on a PCB with auto iris. come pre-wired with several meter of very "German Motor" or a motor / gearbox of (0.1 lux) 32 x 32 by 27mm. Input. Can be flexible co-ax ready to plug into there base your choice. This kit is designed to work KTX PENTIUM II HEATSINK & FAN: focused sharply down to a few mm(useful control unit. Features inc. Quick G-clamp just like a std R/C servo (with much greater Brand new in original for people with visual impairment). Spec.: style antenna mount and could be fitted to power) using 1-2mS pulse width. It has pack with clips & Power req.: 10V to 12V <at> approx. 50mA. a balcony rail in seconds, rotary control proportional control ie. if you move the power lead Res: 400 lines approx. CCD: 1/3" (320 000 from base control unit or its ultra-sonic joystick a little, the servo moves a little. It terminated with remote control from the comfort of your pixels). 30grams: with 60° can be used with a std. R/C receiver or with a 3 pin plug. armchair. The base control unit powered (Pin Hole) lens fitted: our servo controller kit. Some applications (HHSP2) $4.50 by 240Vac and comes with instructions for (CA41L60) inc... R/C models, Robotics, Gates & Others available. Check our web site simple $89, with 92° lens: Doors, Fly by wire control (with our servo conversion (CA41L92) $89, with controller) of things like Forward controls USED HAND BAR-CODE SCANNERS to 12V 120° lens:(CA41L120) for outboards (steering, throttle etc), Pan & Simply plugs operation $89, with 150° (Fish tilt of Cameras, Antenna dishes etc. Could between your as it dosn't Eye lens) (CA41L150)$99 be used as a winch keyboard and your have local 60 SEC VOICE RECORDER MODULE for sails etc. with the computer. Scanned barapprovals. This is a small pre-built module and can be addition of a multi code data appears on your We do not set from 1 long up to 8 short messages. turn pot & a winch screen as if typed in by your recommend connection Features include eight pushbuttons, one drum. Kit includes keyboard. Great for stock control to Australian Operates from for each message. PCB, all onboard parts, feedback pot & etc. Allow you to scan into any Windows, mains 6Vdc :$28....Optional speaker $1 suitable mini case. $35 Add $20 for DOS, or NT application. Options for hands supply!: geared German Motor. free auto-scanning, preamble & post- BATTERIES $29 amble addition are standard. Comes ready Used in the opening and closing DUAL SERVO CONTROLLER KIT This is designed to control R/C servos with to scan. The default settings have been ceremony to illuminate the props etc. We have too much test equipment. 1-2mS pulse with. Ideal for use with our pre-set for the most common bar code Limited stock. 2V per cell, all have Y2K we need to clear some to make way for Jumbo Servo kit or with std servos. configurations. Reads the most popular date codes. Ideal for fishermen etc. more. Check out our web site Great Applications include testing of R/C servos bar codes including: -Code39 -Code 128 bargains at a fraction of the new cost. If pan and tilt of cameras etc. Std. kit includes UCC-128 -UPC-A -UPCE: $27 it’s not on our web site then ring us. PCB all onboard components, suitable 30 SEC VOICE RECORDER MODULE case and pots. $14.... Std. Kit plus power 12V 8Aph $14 This is a pre-built module and is the size of supply suitable for powering 1 Jumbo a postage stamp. Ideal as a personal Servo $24 reminder or could be integrated into other MICRO SWITCHES kits like the shop minder to say "welcome 12V 3.6 Aph gel cell 3 mini micro switch assembly people to a shop", "mind your step", on a waist belt $15 on a 600mm cable "please close the door". with a small plug. Operates from 6Vdc : $16 12V 8Aph with military 3 assemblies for $5 Optional speaker $1 style waist belts $17 www.oatleyelectronics.com Orders: Ph ( 02 ) 9584 3563 or 64, Fax 9584 3561, sales<at>oatleyelectronics.com, PO Box 89 Oatley NSW 2223 December 2000  13 major cards with ph. & fax orders, Post & Pack typically $7 Prices subject to change without notice ACN 068 740 081 ABN18068 740 081 SC_DEC_00 Build a LED torch This is an idea whose time has come. No longer will conventional torches with incandescent bulbs be good enough. Now you can build a solid-state torch with a white LED. You get high brightness with cool white light, low battery drain and you will NEVER ever have to replace a torch bulb again. M OST TORCHES chew through batteries as if they own shares in Eveready (with apologies to Mr Mallory and co). This one won’t. In fact, with intermittent use, you could get a life approaching the “shelf life” of the battery. You’ll certainly get at least six times the battery life of a normal twoAA-cell torch . Our LED torch runs much, much cooler than any torch you've ever experienced. You’ve probably seen the warnings on those superbright bulbs that have the capacity to melt normal torches. We’re not claiming that this is anything near as bright but, by the same token, this one runs cold to the touch. Our LED torch uses just one “AA” battery. That’s right, one only. And what’s more, it will continue to shine brightly for the whole of the battery life – however long that is. Ordinary torches start to dim (actually the light gets more and more 14  Silicon ilicon C Chip hip 14  S Design by JOHN CLARKE yellow and loses intensity) as soon as the battery voltage starts to drop off and really “lose their bundle” at about 1.2V per cell. Ours works with virtually full brightness down to below 1V (at which time you could regard the battery as dead). Impressed? You sure would be if you could see this little beauty “in the flesh”. It has a brilliantly white light (not the yellow you’re used to from most torch bulbs). LED light is a completely different type of light. It’s softer, more diffuse – without the hot spots and shadows you get with normal globes. The torch uses just one of the high intensity white LEDs which have recently come onto the market. When we say “one of” that’s deliberate, because there’s a choice. You can get high intensity or much higher intensity, depending on how This looks just like a standard torch – mainly because we used a standard torch (or two) to house the project(s). The main photo shows a heavy-duty and high quality aluminium torch which turns the lamp on by screwing the lens assembly out (Dick Smith Electronics Cat Y-1103). The inset shows a much cheaper lightweight torch which has a rotary switch to turn it on and off (the blue knob on the end). We can fit the LED assembly into virtually any 2xAA-cell torch, albeit with minor “surgery”. much you want to pay for the LED. More on those choices shortly – and if you want to know more about these devices, see the separate panel “On White LEDs and White Light etc”. The other aspect which makes this project so interesting is the electronics side. Now you’re probably thinking that we mean the usual series resistor which “ordinary” LEDs use to limit current to safe levels. Not so! White LEDs have a minor dilem­ ma – they require a forward voltage of around 3V to 3.5V. Not even two brand new 1.5V batteries in series can deliver enough voltage to light a white LED – and our design uses just one “AA” cell (ergo, 1.5V). The solution? A tiny inverter cir­ cuit inside the torch which steps the 1.5V up to drive the LED at maximum efficiency. This inverter is built on a PC board which is very close to the size of a standard “AA” battery and in fact is designed to take the place of one of the AA cells in a 2-cell torch. Clever, what? We receive a lot of emails (and even some letters too!) here at SILICON CHIP asking for simple, easy-to-build pro-jects which are relatively cheap and above all useful . . . something suitable for everyone from beginners wanting to build their first real project to old-timers (the word used in the most affectionate way!) wishing to keep their irons hot! That’s usually a near impossible wish list. But what we have here is a project which is right up to date, is quite inexpensive and simple to build, unique (we haven’t seen a similar pro­ ject anywhere else) and is very useful. Could you ask for more? The circuit As we said before, driving a white LED is not quite as simple as it would seem, especially from a low voltage. That’s why we have included an inverter to step up the 1.5V from the AA battery to more than 3.5V to drive the LED. The circuit consists of an astable multivibrator (Q1 & Q2) which os­ cillates at around 11kHz, driving a transistor buffer (Q3). This then drives a switchmode boost converter (Q4) which drives the LED. When power is first applied, one of the two transistors in the multivibrator will turn on first. It matters little which one is first but let’s assume Q1 turns on, biased via its 82kΩ base resistor. Q2 will be turned off because as Q1’s collector goes low, the 330pF capacitor will pull Q2’s base low. However, that capacitor now charg­ es (via the 82kΩ resistor) until the point is reached where Q2 receives enough base bias voltage to turn on. Its collector then goes low, pulling Q1’s base low via the .001µF capacitor and therefore turning Q1 off. The .001µF capacitor now starts to charge – and so the process keeps re­ peating for as long as power is applied. The smaller capacitor in Q2’s base (330pF vs .001µF in Q1’s base) means that Q1 will be on for a shorter time than Q2. The result is a continuous series of pulses turning the buffer transistor, Q3, on and off at 11.64kHz, with a duty cycle (or on time to off time) of about 30%. When Q3 is off, Q4 is forward-biased and the inductor in its collector cir­ cuit (L1) is energised. When Q3 turns on, Q4 turns off and the collapsing magnetic field of L1 supplies a pulse of current to the white LED via diode D1, lighting it. This also charges the 4.7µF elec­ trolytic capacitor which effectively smoothes the current “bursts”. With­ out this capacitor, the LED would appear much brighter since the pulse current would be higher. But the LED would also be at risk of destruction as the current peak would be significantly higher than it could withstand. December 2000  15 Fig.1: the circuit diagram of the “works” which drives the ultra-bright white LED from a single AA cell. The three parts of the circuit, labelled here and described in the text, are the multivibrator (based on Q1 & Q2), a buffer (based on Q3) and a switch-mode boost converter (based on Q4). Q4 is turned off for just enough time to discharge the energy in L1 after which it is turned on again. The energy delivered to the LED can be calculated from the formula: Power = L x I PK 2 x f/2      where L is the inductance in Henrys, IPK is the peak inductor current and f is the operating frequency. The peak current is limited by the resistance of L1 (about 3Ω) and the 1Ω resistor in series with Q4’s emitter. As the current rises through the 1Ω resis­ tor the emitter voltage rises, reducing the base drive to Q4. This limits the peak inductor cur­ rent to about 220mA. The first oscilloscope trace (Fig.2 below), shows the base drive to Q4 at the top and the voltage across the 1Ω resistor at the bottom. Note how the current builds up to about 224mA when the base of Q4 is high. You will recall the operating fre­ quency, set by the multivibrator, is about 11kHz while the inductance of L1 is about 220µH. The power delivered to the LED (from the above formula) is about 64mW. Average LED current can be worked out from the formula: I=P/V, where V is the voltage drop across the LED itself (3.4V) plus diode D1 (0.6V), or 4V. Therefore the average LED current is about 64mW/4V, or 16mA. The LED is designed for a maximum average current of 20mA. The second oscilloscope waveform (Fig.3) also shows Q4’s base voltage at top but has the collector voltage at the bottom. This shows that the voltages reaches close to 5V as Q4 is turned off, releasing the charge in the inductor through D1 and LED1. Power for the circuit is delivered by a single 1.5V cell. The circuit will operate to below 1V. It is also protected against the bat­ tery being connected back-to-front, as no current can flow “backwards” Fig.2: the top trace shows the base drive to Q4 while the bottom waveform is the voltage across the 1Ω resistor. The peak current is 224mV/1Ω or 224mA. 16  Silicon Chip through LED1, D1 or any of the transis­ tors because the supply is well below the reverse breakdown voltage of any of these devices. In fact, we deliberately connected the battery back-to-front and measured the current. It was zero – 0.0µA! Incidentally, we mentioned before that the capacitor across the LED was there to protect it. But this capacitor could also be re­ sponsible for damaging or destroying the LED if the circuit was powered up with the LED disconnected, then connected. Without the LED load, the voltage across the capacitor would be very much higher than the LED could handle. If the LED was then connected with the capacitor charged . . . phht – one dead LED. While this is a remote possibility, it could happen if the torch is switched on with the LED disconnected and we have taken steps to prevent this Fig.3: the same trace at top but the lower trace is Q4’s collector voltage. This peaks out at almost 5V – enough to cook the LED without a capacitor across it. happening by hardwiring the LED in position. Construction The white LED torch is actually built inside a . . . torch! We’ll describe the mechanical side a little later but basically, any torch that takes two AA cells will be satisfactory. One of the cells is replaced with a small PC board measuring 49 x 14mm. The components for the inverter need to be assembled on this board so they occupy a space no larger than an AA cell. That means soldering compo­ nents to both sides of the board. Begin, as usual, by ensuring your PC board is correctly etched and agrees with the printed PC board pattern. Normally we insert semiconductors last but in this case, transistors Q1, Q2 and Q3 can be installed first. They are arranged so that they lean towards the centre of the board, at about a 45° angle. The collector leads insert fully into the holes, the base and emitter leads don’t. Solder all leads in and cut the excess off. Now insert the 330pF and .001µF capacitors, as far down as possible onto the PC board. Make sure the tops of these capacitors aren’t any higher than the tops of the transistors. While inserting capacitors, place the 0.1µF and 4.7µF capacitors at the other end of the PC board, again as far down on the board as you can. Note that the 4.7µF tantalum capacitor is polarised. The two 82kΩ and one 10kΩ re­ sistors are mounted next. These are mounted “end on” and laid over at about a 45° angle so they too are lower than the tops of the transistors. Diode D1 can be soldered in next – watch its polarity! Apart from the inductor, which we will look at short­ ly, the only other “component” on the top side of the PC board is a wire link. Because of the proximity of other parts, we suggest that this be a short length of insulated hookup wire. You could use a length of resistor pigtail but we would still be inclined to in­ sulate it – just in case. Fig.4: most of the components are soldered through the PC board in the normal way but there are five soldered on the bottom side, as shown in the lower view at right. Compare these to the photos of the boards below. At the bottom is the same-size PC board artwork. wound a new coil on it, about the right inductance. Of course, this means taking off the old windings; the outer insulation is removed, the primary (outside) layer is unwound, then the fine secondary winding is removed by slicing through the wire with a sharp knife and peeling it off (that’s a lot quicker than unwind­ ing several hundred turns!). The inductor winding consists of 150 turns of 0.16mm enamelled copper wire. Tin one end and solder it to one of the former’s connection points (on the end), then wind on the 150 turns in several layers. The windings don’t need to be side-by-side but try to keep them evenly distributed over the full width of the former. When all the turns are on, cut the wire to a suitable length, tin the end and solder it to the other end of the former. The winding should be pro­ tected by a layer of insulation tape. To help the inductor sit as low as possible on the PC board, we cut a flat section on each of the former’s ends, just clear of the tape covering the winding. Mount the former onto the middle of the PC board and solder the two ends to the board with short lengths of resistor pigtail. You’ll need to take one around the end of the 0.1µF capacitor – make sure it doesn’t short to it. The other side of the board The remaining components, four resistors and transistor Q4, all mount on the copper side of the PC board. You’ll need a soldering iron with a fine point to solder the components to the copper pads. The resistors mount as flat as possi­ ble, with one lead snaking back over the board to connect to the appropri­ The inductor We looked everywhere for a suitable ferrite core and former (ie, small!) for the 220µH inductor (L1) but couldn’t find what we wanted. Eventually, we raided the junk box and found a trig­ ger transformer for a Xenon flashtube. It was about the right size and if we Top and bottom views of the completed PC board, here shown with the LED already solderd in. This board is for the cheaper torch style (ie, one with a separate switch) but the other type is similar – the main difference is that the thumbtack (left end) is connected to the – supply line in the alternate version. December 2000  17 Fig.5: these drawings show how both types of torch are assembled. On the left is the cheaper, switchedtype torch, along with its LED soldered into the bulb base. On the right is the screw-out torch version. On some models of torch the hole in the reflector will be too small to allow the LED to poke through – this will have to be carefully filed out to about 5.5mm. ate place. These leads must be protected against shorting with short lengths of insulation. If you could manage to get hold of some of those really tiny 1/8W resistors, they could almost solder point-topoint on the board. Before you solder in R1, you need to determine how “hard” you want to run the white LED – and therefore how much current you are going to put through it. R1 can be either a 1Ω resistor or a link (ie, 0Ω). The latter will result in a brighter light but at the expense of battery life. Table 1 shows the difference in current: it’s not much but it could be significant with a flattening battery. If you elect to use a link, make sure it (like the resistor lead) is covered with insulation. Finally, solder in Q4, the only transistor which is NOT a BC548. It is mounted so that it bends over at 90° and actually lies flat on the insulation covering R1. Again, a fine-pointed iron will be a necessity to avoid any solder bridges. Choosing the LED There are currently three “brightnesses” of ultra-bright white LEDs available: 1500-2000mcd, 5600-6000mcd and 8000mcd. The more you pay, theoretically, the brighter the LED. But we’ll “led” you in on a little secret: we connected 5600mcd and 8000mcd LEDs to the circuit and measured the output on a very sensitive Minolta lightmeter – and got absolutely identical results (down to 0.1 “f” stops.) So to be honest, we’d stick to 5600mcd LEDs and save a few bob! Connections to the board Remember we said that this PC board replaces one of the AA cells; the board actually takes the place of the cell and it needs connections at each end simular to an AA cell. How do we do this? With a small washer for the + end and a drawing pin (minus the point) for the – end, that’s how! To hold these items in place we use PC stakes. On the positive (washer) end push the two stakes “upside down” through the board (ie, the longer end goes through the board from above) and solder them in position underneath. Cut each stake with sidecutters so that there is 3mm above and below the PC board surfaces and then carefully bend them inwards (towards each other) so they somewhat follow the curve of the 3mm washer. 18  Silicon Chip The washer is placed at the end of the PC board so that it is proud of the edge (see the illustration). It is then sol­ dered to both PC stakes, above and below the PC board. You should have no problems soldering the washer to the stakes as long as it is clean and bright. If it is at all dull (ie, oxidised) it will pay you to polish it first with a piece of fine wet’n’dry paper. The opposite end of the board is similar, except Parts List 1 2 x AA-cell torch (DSE Y1127, Y1103, Jaycar ST3000 or similar) 1 PC board, code 11112001, 49 x 14mm 1 M3 tin plated washer 1 12mm OD plated steel thumb tack 4 PC stakes or 2 PC stakes and 1 20mm length of 1mm tinned copper wire 1 40mm length of 2mm OD insulating sleeving 1 5mm LED bezel 1 100mm length of light duty hookup wire (blue or black) 1 60mm length of light duty hookup wire (yellow) 1 Xenon tube trigger transformer (8mm diameter x 11mm long bobbin) (DSE M-0104 or sim) 1 2.5m length of 0.16mm enamelled copper wire 1 50mm length of 8mm wide insulation tape Semiconductors 1 5mm white LED (LED1) – 1500-2000mCd (DSE Z 3980, Jaycar ZD 1786), or 5600-6000mCd (DSE Z3981, Jaycar Z 1780), or 8000mCd (DSE Z 3982) 3 BC548 NPN transistors (Q1Q3) 1 BC338 NPN transistor (Q4) 1 1N914, 1N4148 switching diode (D1) Capacitors 1 4.7µF low voltage tantalum 1 0.1µF monolithic ceramic 1 .001µF ceramic (5mm OD max) 1 330pF ceramic (5mm OD max) Resistors (0.25W, 1%) 2 82kΩ 1 10kΩ 2 1kΩ 1 220Ω 1 1Ω 5% (or link – see text) Here’s how the LED mounts in the bulb base, the glass bulb having first been (carefully!) removed. The anode (longer) LED lead solders to the contact on the bottom of the lamp base while the cathode bends up and over the lip of the base to be soldered to the edge. On the right is the LED and holder inserted into the torch lamp assembly. that we use a brass (or tin) plated thumbtack, with the convex surface pointing outwards, instead of the washer. First of all, hold the thumb-tack in a pair of pliers and break the pin off with another pair of pliers. Then proceed as before, except that in this case you won’t need to shorten the PC stakes at all – just bend them over towards each other. That completes the assembly of the electronics – but make sure the PC board slides into the torch body you are going to use and, if the torch is metal, that there are no exposed component leads, etc which could short to the case. Fitting to the torch There are two different types of torch and you need to determine which type yours is, because fitting is slightly different. One type has a switch on it, usually switching the negative battery connec­ tion (because the globe end normally contacts the + end of the top battery). The other type has no “switch” as such; the torch is turned on by screw­ ing the globe/lens assembly out. This removes the pressure holding open the battery off the torch end, allowing them to touch and thus turning the torch on. You may know of this torch as a “Mag” brand but there are others with similar switching arrangements. Ours was in fact an “Arlec” brand courtesy of Dick Smith Electronics. We’ll look at the switched-type first. Wiring a switched-type torch We need to break the globe so that the white LED can be mounted inside the metal globe base. Wear safety gog­ gles and break the glass with pliers wrapped in a small piece of cloth. Carefully clean any glass or glue res­ idue from the globe base and remove the excess solder from the bottom so you can see right through the base. Slide a 5mm LED bezel over the LED from the lead end (collar at front) so that the base of the LED sits on the collar. Bend the cathode (shorter lead) 90° so that it emerges from one of the slits in the bezel. Pass the anode lead through the hole in the globe base and push the LED and bezel in so virtually all of the bezel is inside the base. Solder the anode to the bottom of the base and clip off the excess lead. Now bend the cathode lead back down 90°, over the outside edge of the metal base. Centre the LED within the base if necessary then cut the cathode lead off so there is just the tiniest bit over the metal edge – just enough to Capacitor CAPACITOR Codes CODES Resistor Colour Codes         No. 2 1 2 1 1 Value 82kΩ 10kΩ 1kΩ 220Ω 1Ω 4-Band Code (1%) grey red orange brown brown black orange brown brown black red brown red red brown brown brown black gold gold (5%) 5-Band Code (1%) grey red black red brown brown black black red brown brown black black brown brown red red black black brown Value EIA Code IEC Code  4.7µF   4.7µ 475  0.1µF   100n 104  .001µF   1n0 102  330pF   330p 331 December 2000  19 to the LED anode. Solder these two wires respectively to the LED cathode and anode (- and +) positions on the PC board. You can now assemble the torch and give it the “Smoke” test – if it doesn't smoke and the white LED comes on when you turn it on, well done! Wiring a twist-type torch On the left is the standard bulb “as it comes” in the heavy duty torch, without reflector of course. On the right is the LED version – we’ve disassembled the torch to take this photo (for clarity) but you don’t need to do this. That’s fortunate because some torches are very difficult to pull apart! be able to solder the cathode in place. You now have a white LED assembly which is virtually equivalent in size to the original bulb – and one which will fit into the variety of bulb holders used in torches. Hard-wiring the LED Remember we mentioned before that the LED could be damaged if connected across the charged capac­ itor? For this reason, we’ve decided to permanently wire the LED in place – just in case. Place the LED bulb assembly in its torch holder and solder a short (2cm) length of black wire to the LED cath­ ode and a similar length of red wire This type of torch, with its integral reflector, is more efficient than the cheaper “bulb only” torch types. The downside is that it is a bit more tricky to work with. You could disassemble the whole thing but that’s not easy so we took an simpler route. This torch normally uses a globe which has two stiff wire legs which you push into a base (after you screw off the reflector head assembly!). The two contacts in the base normally connect to the torch case (– battery connection) and to the top of the bat­ teries (+ battery connection). We simply short both the base con­ tacts together so they form the “–” connection from the case back to the thumbtack on the PC board, then we solder the cathode (K) lead of the LED to this common point. On white LEDs and white light and colours and Kelvins… The idea of using LEDs for torch lighting is not new – we published a LED torch in February 1994 using a high brightness amber LED. The LED was simply driven via 2-AA cells with suitable current limiting. Even though red, green, yellow and even blue LEDs have been around for a while, white LEDs took a lot longer to become a comm ercial reality. For a long time they tried to make them work by combining the outputs of red, green and blue LEDs to produce white (similar to making white in a TV picture tube). The results were anything but satisfactory. We’re not sure if white LEDs happened exactly this way but hey, why spoil a good story for the facts . . . One day, the white-coated brigade who had been tearing what was left of their hair out over white LEDs looked towards the heavens for inspiration. Instead he/she/they saw the fluorescent tubes in the laboratory ceiling and like Archimedes, shouted “Eureka!” “Why not coat a blue LED with a phosphor, just like in a fluorescent tube,” they thought. Why not indeed? Now just in case you don’t know what happens inside a fluorescent tube, the ultraviolet electrical discharge in the tube makes the phosphors (the white powder inside the tube which goes everywhere when you smash one!) fluoresce, or glow. The result is light – and depending on the type(s) of phosphor, the light can be virtually any colour. If the phosphor produces light over a broad spectrum, the result is white light, more or less. 20  Silicon Chip White light has a “colour temperature”, measured in Kelvins. Low colour temperatures, say from 1500K to 2800K, are reddish to yellowish, such as from candlelight and most incandescent bulbs. The yellowish-white light of a halogen bulb would be about 3000K-3500K while at the top end of the spectrum (5000K and above) it is the bluish-white light of a “daylight” fluorescent tube. Average sunlight (as distinct from daylight) is regarded as having a colour temperature of 4100K.­ “Pure white” light in television is considered to be 6500K; the photographic industry uses 5500K; the printing industry uses 5000K. Part of the reason for different colour temperatures being used as standard is the mechanism by which each of the media produce colours. The overriding aim of all of them is to get skin tones looking as natural as possible because these are the most quickly judged as being “right” or “wrong” to the eye. In the white LED, the phosphor converts the blue light into a wide spectrum white light. Now where have we heard that before? As a bonus, white LEDs produce what is a virtually an ideal light source, because the colours of objects will appear close to what you would see in daylight. White LEDs, by the way, are made from an InGaN (Indium Gallium Nitride) chip (blue LED) which is coated with a YAG (yttrium aluminum garnet), an inorganic phosphor. So now you have a great piece of trivia to drop when the conversation at your next dinner party starts to wane… The anode lead of the LED will be connected via a short length of hookup wire to the appropriate point on the PC board. First of all, proceed with the assem­ bly of the PC board as for the other torch, with one difference: instead of connecting a length of hookup wire to the cathode connection point on the PCB, use a short length of tinned copper wire and solder that to the thumbtack. The anode connection is the same – a short length (say 25mm) of hookup wire. Push the completed PC board as­ sembly through the torch until that short length of hookup wire emerges from the front. You might have to jiggle it around slightly to get it through. Next, discard the globe by pulling it out. Make a small “U” shape from a 10mm length of resistor lead off-cut (or tinned copper wire), just wide enough to push into the two contacts in the base which you just pulled the lamp from (the legs of the “U” about 1.5mm wide). Put that aside for a moment. The LED has a flange moulded on its base which makes it too thick to fit through the hole in the torch reflector, IRECT OMPONENTS COMPONENT 1-9 PRICE 10+ PRICE AXIAL ELECTROLYTIC CAPACITORS 10uF <at> 450 volt $2.60 $2.00 22uF <at> 450 volt $3.35 $2.80 47uF <at> 450 volt $7.44 $6.30 22uF <at> 50 volt $0.55 $0.50 AXIAL POLYESTER CAPACITORS (630V) 1-9 PRICE 10+ PRICE 0.001uF $0.60 $0.50 0.0022uF $0.65 $0.55 0.0047uF $0.65 $0.55 0.01uF $0.70 $0.60 0.022uF $0.85 $0.75 0.033uF $1.40 $1.25 0.047uF $1.55 $1.35 0.1uF $1.70 $1.45 0.22uF $1.85 $1.60 0.47uF $2.50 $2.20 RADIAL POLYESTER CAPACITORS (630V) 1-9 PRICE 10+ PRICE 0.001uF $0.35 $0.32 0.0022uF $0.35 $0.32 0.0047uF $0.35 $0.32 0.01uF $0.38 $0.32 Table 1: Performance Cell Voltage R1=1Ω: 1.5V 1.2V 1.0V R1=0Ω: 1.5V 1.2V 1.0V LED Current 18mA 10mA 5.6mA 21mA 12.5mA 7.3mA Cell Current 120mA 83mA 54mA 130mA 92mA 55mA so this needs to be carefully filed off. Don’t damage the top surface of the LED as you do this. Now remove the U-shaped wire from the base and solder it to the cathode (ie, shorter) lead of the LED, right up close to the body of the LED. The “U” should be centred on the body but en­ sure that it’s not too close to the anode lead, risking a short. Cut off most of the LED anode lead (leave just a couple of mm) and solder the hookup wire emerging from the front of the torch to the anode. Ensure that you haven’t shorted out anode and cathode in the process. Push the U-shaped wire and white LED all the way into the holes in the lamp base. Obviously, the anode connecting wire goes back down into the torch 0.022uF $0.42 $0.38 0.033uF $0.65 $0.55 0.047uF $0.65 $0.55 0.1uF $0.90 $0.80 0.22uF $1.00 $0.90 0.47uF $1.25 $1.10 RADIAL ELECTROLYTIC CAPACITORS (16V) 1-9 PRICE 10+ PRICE 1uF $0.26 $0.22 2.2uF $0.26 $0.22 3.3uF $0.26 $0.22 4.7uF $0.28 $0.24 10uF $0.30 $0.26 22uF $0.32 $0.28 33uF $0.35 $0.28 47uF $0.38 $0.30 100uF $0.38 $0.30 220uF $0.40 $0.32 330uF $0.50 $0.45 470uF $0.55 $0.50 1000uF $0.70 $0.55 2200uF $0.90 $0.70 3300uF $1.35 $1.10 4700uF $1.50 $1.20 RADIAL ELECTROLYTIC CAPACITORS (25V) 1-9 PRICE 10+ PRICE 4.7uF $0.22 $0.18 10uF $0.22 $0.18 22uF $0.22 $0.18 33uF $0.33 $0.26 47uF $0.38 $0.30 100uF $0.42 $0.32 220uF $0.55 $0.45 330uF $0.60 $0.50 body – but check that it doesn’t foul anything as it goes and check once again that nothing shorts! Before final assembly, test the torch by putting in an AA cell and screwing on the back. With the connection now made between the LED cathode and the torch body, the LED should light. If it doesn’t, remove the PC board and check your wiring and compo­ nent placement. If it is necessary to work on the PC board out of the case, temporarily solder any standard LED across the anode and cathode points on the PC board, rather than trying to make contact with your white LED. Assuming all is well, fix the white LED in place with a dollop of neutral cure silicone sealant, hot melt glue, or other adhesive. Then carefully screw the reflector assembly back on, ensuring the LED comes through the hole in the middle. You may need to remove the assembly and reposition the LED slightly if the alignment isn't spot on. You can adjust the focus (wide or spot) by the position of the reflector with respect to the LED. Screwing the reflector all the way in should turn the torch off. SC 470uF $0.65 $0.52 1000uF $0.90 $0.70 2200uF $1.30 $1.00 3300uF $1.85 $1.45 4700uF $2.60 $2.00 RADIAL ELECTROLYTIC CAPACITORS (50V) 1-9 PRICE 10+ PRICE 10uF $0.22 $0.18 22uF $0.22 $0.18 33uF $0.38 $0.30 47uF $0.38 $0.30 100uF $0.60 $0.50 220uF $0.75 $0.60 330uF $0.80 $0.70 470uF $1.20 $1.00 1000uF $1.50 $1.20 2200uF $2.80 $2.00 4700uF $4.30 $3.75 MAINS CABLE – BROWN COTTON COVERED Per mtr 1-9 PRICE 10+ PRICE $2.80 $2.20 DIAL CORD – 0.6mm Per mtr 1-9 PRICE 10+ PRICE $0.75 $0.50 24-hour online ordering: www.direct-components.com Fax: (08) 9479 4417 Email: capacitor<at>bigpond.com Snail mail: PO Box 437, Welshpool, WA 6986 Aust. Post – $0-50 = $5.00; $51-100 = $7.50; $101-500 = $9.50 Air Express: <3kg = $11.00; 3-5kg = $16 ABN: 70-032-497-512 December 2000  21 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 This is the top model in the Agilent 54600 series. It has two analog input channels and 16 digital input channels so it can perform as a combination analog scope and logic analyser. Agilent 54622D Mixed Signal Oscilloscope Back in October 1991 we reviewed the first of the “new generation” digital scopes from Hewlett-Packard, the HP 54601. Now we review one of the successors of that unit, the Agilent 54622D, a 200 megasample/second “mixed signal” machine. But while the two machines might bear the same 3-digit prefix, the perfor­mance of the new series is radically better. REVIEWED BY LEO SIMPSON 26  Silicon iliconCChip hip This is the rear panel of the 54621A 60MHz 2-channel oscillo­scope. This is identical on the 54622D mixed signal scope except that the latter unit also has the trigger input socket on the back panel. I N NOVEMBER 1999, the instrumentation side of Hewlett-Packard was spun off into a new company called Agilent Technologies Inc and this company has finally released its new series of digital scopes. There are five models in the series, two 60MHz models and three 100MHz units: the 54621A 2-channel 60MHz; the 54621D 18-channel 60MHz mixed signal scope; the 54622A 2-channel 100MHz; the 54624A 4-channel 100MHz; and the mixed-signal 54622D which has two analog chan­ nels and 16 digital channels. Over a period of several weeks we had the chance to try out the 2-channel and 4-channel 100MHz models and the 54622D mixed signal oscilloscopes. Apart from the more comprehensive trigger­ ing facilities and 16-channel input capability of the 54622D, all the scopes have the same operating features so virtually every­thing in this review will apply to all models in the series. First up, we will state that the ba­ sic “spec” for the 54600 series seems pretty standard – 100MHz or 60MHz bandwidth and 200 megasamples/ second (for analog channels). How­ ever, this tells only a small part of the story because this series of scopes does not have the sampling rate tied to the timebase speed, giving low sample rates at low timebase speeds. Instead, the 54600 series run at a high sampling speed all the time and in fact, it runs at the maximum 200MSa/ sec speed for all timebase speeds above 1ms/div. This is a huge step up in performance compared to most digital scopes. And it has a large memory, with 2MB of RAM per channel or 4MB in single channel mode. These two factors make it a potent scope indeed. We’ll come back to the performance aspects later. For the moment, let’s look at the basic operating features. Compared with other brands of digital scopes with CRT screens, the Agilent 54600 series is quite compact, measuring 352mm wide (including handle), 172mm high (including feet but not accessory bag) and 317mm deep. It is quite light at 6.3kg. The scope screen is a nominal 7-inch CRT with a live screen area measuring 127 x 99mm while the screen graticule has the standard arrangement with 8 vertical and 10 horizontal divisions. Along the bottom of the screen are six “soft keys” and their functions all change, depending on what button has been pushed on the control panel. Below these soft keys is the 3.5-inch 1.44Mb disk slot, the power on-off switch and the intensity control. This latter knob only controls the intensity of the channel traces, not the graticule or the various screen labels. The screen labels are fixed in intensity but you can change the brightness of the graticule (the ruled grid on the screen) by pushing the Display button, the Grid soft-key and then rotating the multi-purpose knob to the right of the screen. The control panel has a number of control groupings which make it easier to use. For example, there are groupings for the analog (vertical) and digital inputs, the horizontal timebase, triggering and so on. In the analog group, there are two BNC sockets, one for each channel, a sen­ sitivity control and position control for each and three buttons, one to select each channel and one to select MATHematic operations. Each of these three buttons is brightly illuminated when it is press­ ed. Digital inputs Similarly, for the selection of digital (logic) channels, there are two buttons plus a “label” button and these are also illuminated when pressed. The 16 digital inputs are connected via a special 16-way connector and two 8-way woven ribbon cables each of which termi­nate in a “pod” which has nine leads – ground and eight probe leads which can be connected to header pins on PC boards, or when probe tips are attached, connected to individual IC pins. You can select either or both of the 8-channel banks which are labelled D0-D8 and D9-D15. Individual chan­ nels can be turned off and any or all channels can be separately labelled by using the “label” button. You can (laboriously) feed in your own labels or you can select from the scope’s own fairly comprehensive logic library. The digital channels can be set for TTL, CMOS, ECL or user-defined threshold levels and by setting dif­ ferent thresholds for the two-channel banks you can work on mixed logic circuits. This whole 16-channel digital fa­ cility means that you have the best of both worlds in the Agilent 54622D – a high perfor­mance two channel analog (well, digital storage) scope and a 16-channel logic analyser. Well, not quite but you get the picture. In the “trigger” panel there are five buttons and a level control. Again, four of these buttons (edge, pulse December 2000  27 Fig.1: this is the “help” screen you get when you press and hold down the channel 1 selector button. Similar help screens are available when you press any button on the Agilent scope, regard­less of whether it is a front panel button or one of the softkeys below the screen. These help screens would make it much easier for any novice to become competent in using an oscilloscope. width, pattern & more) are illuminat­ ed when pressed and they also bring up their associated softkeys below the scope screen. Four other buttons can be illuminated: run/stop, single (for single shot mode), cursors and “quick meas”. Finally, the knob below the main time­ b ase control has an adjacent anticlockwise arrow and when some function can be varied by this knob, the arrow is illuminated. This last fea­ ture might be simple but it indicates just how much thought has gone into making this scope easy to use. Overall then, the control panel of the new Agilent 54600 series is dis­ armingly simple. You immediately feel as though you can sit down and use it straight away without having to read through a manual. And just in case you do need help with any feature, all you have to do it hold down the relevant button and some text will immediately appear on the screen to give the information. For example, say you are looking at the channel 1 menu which has soft keys for coupling (GND, DC, AC), BW limit, vernier and probe. You want to know what BW limit is. Press the softkey and text will come up to tell you that this key sets the scope bandwidth to 20MHz (instead of 100MHz) and this can be used to remove unwanted high frequency noise from the signal. Bandwidth limiting has been around for a long time on scopes but if you were a novice user you may 28  Silicon Chip Fig.2: here is a 100kHz sinewave with a small amount of noise superimposed, as shown by the small amount of frizzle on the waveform. Note the vertical cursors which are brought into play when the frequency measurement is called for. not have an inkling of what it meant. By the way, while all the oscillo­ scope labelling and operat­ing features are in English, the help screens can also be in Chinese, French, German, Italian, Japanese, Korean or Spanish. Fig.1 shows the help screen you ob­ tain when you hold down the channel 1 selector button. Before we leave the channel 1 menu we should mention the probe soft­key. The 54600 comes standard with 10:1 passive probes and these will auto­ matically be sensed by the scope as soon as they are plugged in. The scope then changes the input sen­sitivity by a factor of 10. So if the sensitivity was 1V/div with no probe connected, it will automatically go to 10V/div as soon as the 10:1 probe is connected. On the other hand, if you are using a probe without the auto-sensing fea­ ture, the probe softkey will let you set the attenuation to suit, anywhere from a factor of 0.1:1 to 100:1, in a 1,2,5 sequence. Apart from using probes without auto-sensing, this feature could be useful when you are moni­ toring a circuit via a voltage divider and you want the appropriate factor to be used and displayed by the scope. Screen saver We mentioned the controls for screen brightness (intensity) previ­ ously and that brings up another good feature of these Agilent scopes – a screen saver. Many a time I have come across a scope with a bright display (with no-one watching it) and I in­ stinctively lean across and turn down the intensity. But these scopes have a screen saver which moves around the screen and thereby avoids burning any pattern into the screen, as well as increasing the life of the tube, as the beam current is reduced. There is a choice of three screen saver patterns (Agilent logo, etc) and you can set the time after which it cuts in, from one minute to 435 min­ utes (default time is 360 minutes or 6 hours). Anyway, this is another good idea from Agilent. Triggering If nothing else, the triggering facili­ ties on the 54600 series are outstand­ ing. If you can’t get a stable display with this scope, you’re not likely to do so on any other machine. We’ve already mentioned the illu­ minated buttons which bring up the triggering options: Edge, Pulse Width, Pattern & More. “Edge” triggering al­ lows you to trigger the scope timebase on the positive or negative edge of pulse waveforms. The “Pulse Width” button allows you to select triggering on positive or negative pulses and to select the pulse width, greater or less than a variable value or between two variable values. “Pattern” allows for triggering on a logical AND condition of selected channels and each channel may be high (H), low (L), don’t care (X) or a rising or falling edge. Thus you can Fig.3: this low level 90kHz burst signal is the source of the frizzle on the waveform of Fig.2. Expanding out the waveform and using the frequency measurement facility showed that it was ringing at frequencies up to around 100MHz. set up triggering on a whole range of pulse/channel combinations. By the way, you also have the option of inverting the channel 1 & 2 inputs, giving a further range of conditions. The “More” button brings up an advanced trigger menu encom­passing TV, Sequence, I2C (for I2C bus signals) and Duration. TV triggering is really impressive as you can set triggering on NTSC, PAL, PAL-M, SECAM or generic TV waveforms, using positive or negative sync polarity. You can trigger on field 1 or 2, all fields, all lines or you can select a particular line number in field 1 or 2. Inter­estingly, the maximum line count catered for in a generic TV waveform is 1024. Agilent have certainly catered for every pos­sibility. Sequence triggering is pretty fancy too. In this mode the scope looks for a specified pattern and then triggers on another specified pattern. You can even specify a reset event. Duration triggering lets you trigger on an AND logic combi­nation of in­ puts with a duration greater or less than a specified value, with or without a timeout and so on. If you think about it, the specified triggering possibilities are enormous. Measurement options As you might expect, the measure­ ment options on the Agilent 54600 series are pretty wide as well. You can initiate measure­ments by push­ ing the “quick meas” or “cursor”. In Fig.4: monitoring video waveforms is dead easy. Here we’ve fed in a signal from an NTSC colour camera and with line 238 selected from field one. The line frequency comes up as 15.65kHz but we assume that the error (15.65kHz versus a correct 15.75kHz) is due to noise in the measurement. cursor mode you can have vertical (X) or horizontal (Y) cursors. For vertical cursors, the scope displays the time difference between the two (ie, along the X (time) axis) and also displays the reciprocal value which is the frequency. When horizontal cursors are set, the scope displays the voltage difference between the two. By the way, you can also have binary and hex cursors – the mind boggles. Pushing the “quick meas” button allows you to select time (frequency, period, rise & fall times, etc) or am­ plitude measure­ments (RMS, average, peak-peak, etc) from five menu pages. Only three measurements can be dis­ played at a time though, which is a bit of a downer. Mathematics While it may not be thought of as part of the measurement features, the mathematics of the 54600 series are particularly strong. Not only can you do standard operations like multiply­ ing channel 1 by channel 2 or taking the sum or difference, you can also get a plot of the derivative (ie, dV/dt) or integral (∫ V.dt) of the analog channels. The integral is calculated using the “trapezoidal rule” (now there’s a blast from my distant past – I was surprised that I could even remember it!). And there’s FFT (Fast Fourier Transform) analysis which can be done with Hanning, Flat Top or Rec­ tangular window settings. The number of points in the FFT is fixed at 2048 while the noise floor ranges from -70dB to -100dB depend­ ing on the level of averaging. High resolution display On the face of it, the display of the new Agilent scope is not anything out of the ordinary; the screen resolution is quoted as 255 vertical by 1000 hori­ zontal points (for the graticule area) but, and it is a big BUT, there are 32 levels of grey scale. However, there are several factors which lead to a scope display which is far better than you would expect, even given that there are 32 levels of grey scale. First, there is the very high sampling rate, even at low timebase speeds, and second, there is the deep memory. Third, the acquisition system has a vertical res­ olution (linearity) of 12 bits. Combine all of this with Agilent’s so-called MegaZoom tech­ n ology and the result is a display which is far better than most digital storage scopes. Not only that but it is better on most signals then even the best analog scopes. No longer do you see jitter on “smooth” signals such as sinewaves, due to the sampling system being tricked by noise. Instead, if there is noise superimposed on a signal, you see a smooth trace with lower intensity “frizzle”. The waveform of Fig.2 is a classic example of this. Here is a 100kHz sinewave with a small amount of noise superimposed. Look December 2000  29 Fig.5: using the same signal as in Fig.4, we wound up the time­base to 1µs/div, and set the horizontal position knob to bring up the colour burst. A rock steady waveform is the result. closely and you will see the frizzle. We were a little puzzled when we first saw this frizzle because it came from our low distortion sine/square oscillator described in the January & February 1990 issues. And since Fig.6: to measure the colour burst frequency on the signal of Fig.5 we wound up the timebase setting on the Agilent to 100ns/div, took a single-shot trace and the result is at the bottom of the screen: 3.584MHz. we thought our oscillator was above reproach, we initially thought that the scope was wrong. Looking further, we turned the oscillator’s output down to zero and the signal was still there. Even when we turned the oscillator off, the noise was still there. Not only that but we were able to obtain a stable triggered display with all sorts of spikey noise on it. Fig.3 shows the result; a low level 90kHz burst signal which is apparently radiated by our 100Mbit/s Cat.5 network (and it has a CE mark too – so much for EMC compliance!). The point is that the Agilent scope had no trouble seeing this noise. By the way, we got that scope trace with an averaging setting of one; the Mega­ Zoom cleans up the signal while still leaving the noise detail in there. We also measured the waveforms from a 555 circuit recently featured in the magazine and it was interesting that the 54622D showed up the spikes at the crests of the sawtooth; these are not visible on other digital scopes. TV waveforms The 54622D mixed signal oscilloscope has a special input socket for the 16 digital channels and these are brought out to two pods, each of which has nine leads – ground and eight probe leads. These can be connected to header pins on PC boards, or when probe tips are attached, connected to individual IC pins. 30  Silicon Chip The 54600 is particularly good on TV waveforms, because of its com­ prehensive sync facilities, including line number selec­tor. Fig.4 gives an indication of this. Here we’ve fed in a signal from an NTSC colour camera and selected line 238 from field one. As you can see, on the scope picture, we’ve measured the line frequency and video amplitude. The line fre­ quency comes up as 15.65kHz but we assume that the error (15.65kHz versus a correct 15.75kHz) is due to noise in the measurement. Want to measure the colour burst frequency? Easy. Just increase the timebase to 1µs/div and wind the horizontal position knob to bring up the colour burst. Fig.5 shows the Fig.7: using a 100MHz analog scope on the signal of Fig.5, this was the best result we could get. Since the analog scope did not come with a TV line selector there was no way to get the rock steady and bright waveform which is so easy to obtain with the 54600 series. result. This ability to display TV wave­ forms was so good that I thought I might crank up our workhorse analog scope, a Kenwood 100MHz model which I’ve always regarded as being fairly good in the sync department (for an analog scope). Anyway I fed in the same waveform and by judicious use of the main and delayed timebases I was able to obtain the waveform shown in the photo of Fig.7. It’s not bad but since the old faithful Kenwood analog scope did not come with anything as fancy as a TV line selector there was no way I was going to get the rock steady and bright waveform which is so easy to obtain with the 54600 series. Oh, we wanted to measure the col­ our burst frequency, didn’t we? Wind up the timebase setting on the Agi­ lent to 100ns/div, take a single-shot trace and the result is Fig.6. There is the measurement at the bottom of the screen: 3.584MHz. It should be 3.579MHz (alright, 3.579545MHz, to be precise but who is count­ing?). We could go on but by now you should have the overall picture. The Agilent 54600 scopes are delightfully easy to drive and the overall features in the package are very comprehen­ sive. Sure, it doesn’t feature runt triggering but you could play with sync settings to achieve a given result if you want. We think the 54600 series will be a real winner. Agilent have had plenty of time to think through all the features on this scope and the competition will be scrambling to match them. For further information on the 54600 series you can check the web­ site at www.agilent.com or phone 1 800 629 485. Pricing on the 54600 series starts at $4300 plus GST for the 54621A 60MHz 2-channel model, ranging up to $8514 plus GST for the full-featured 54622D 100MHz mixed signal oscilloscope complete with two analog probes and the digital SC probing pods. Own an EFI car? Want to get the best from it? You’ll find all you need to know in this publication  Making Your EFI Car Go Harder  Building A Mixture Meter  D-I-Y Head Jobs  Fault Finding EFI Systems  $70 Boost Control For 23% More Grunt  All About Engine Management  Modifying Engine Management Systems  Water/Air Intercooling  How To Use A Multimeter  Wiring An Engine Transplant  And Much More Including Some Awesome Engines! AVAILABLE DIRECT FROM SILICON CHIP PUBLICATIONS PO BOX 139, COLLAROY NSW 2097 - $8.95 Inc P&P Call (02) 9979 5644 9-5 Mon-Fri with your credit card details! December 2000  31 MAILBAG Pool alarm sensor should be out of sight I have just finished reading the article on the Pool Alarm in the Sep­ tember issue of SILICON CHIP. The project revolves around a de­ vice which floats in the pool to warn if a child has fallen in or any distrac­ tion to the surface has occurred. If you take a look at the photo on the front of the magazine, it depicts the child checking out the ball that is in the pool. However, I can almost assure you that even if the ball was not in that pool, she would certainly be equally curious about the warning device floating in the pool. It’s the old case of keeping the gate locked, the fence up to standards and anything resembling a climbing aid out of eye­sight or locked down. It all boils down to the parents/guardians keeping an ever watchful eye over children of that age. I have an idea that might be worth­ while in keeping the device out of sight. Basically it involves making the sensing part of the circuit remote (away from the rest of the control unit) and keeping it anchored nearest a pool ladder or near the edge of the pool, just enough that the device will still function. Alex Gordon argordon<at>es.co.nz Trap in battery conversion of plugpack powered appliances There is a trap for the unwary when converting some plug­pack-powered appliances for operation on batter­ ies, as suggested in “Battery Backup For Cordless Phones” in the October 1999 issue. I found this out when I converted a General Electric an­swering machine for operation from 12V by replacing the 9VDC nominal plugpack with an external 9V regulator running from the 12V supply. This arrangement very nearly destroyed the answering machine. You see, the designers of the an­ swering machine had reduced the DC input voltage to the machine’s internal operating voltage by simply wiring a 5.6V zener diode across the 32  Silicon Chip DC input – with no dropping resistor! The plugpack used had a sufficiently high output impedance for this to work but my regulator circuit simply overpowered the poor zener. Fortunately, the zener remained faithful to the bitter end. It failed as a short circuit rather than going open and allowing the 9V to damage the voltage-sensitive circuitry in the rest of the answering machine. Equipment designed in this way may also fail if the unregu­ l ated plugpack is replaced by a regulated plugpack. Of course, none of this would have happened if the answer­ing machine had used a series regulator or even just a dropping resistor before the zener diode (but even this must be suitably rated for the eventuality of a low-impedance DC supply). To solve the problem, I simply changed the external regula­tor to 5V. I removed the zener and did not replace it, since I did not have a replacement available at the time. However, it would have been better to replace it, to protect the machine if it is ever used again with a 9V plugpack. Andrew Partridge, Kuranda, Qld. Health card a good idea I would like to congratulate you on an excellent editorial, on the sugges­ tion for a health record card, in the October 2000 issue. Recently August 26 I entered the Alfred Hospital in Mel­bourne for laser ablation surgery on a 4.8cm tumour on my liver. After admission and three hours before the surgery, I told the resident doctor who came to explain the surgery all my cancer history. It had never been requested from me and I had assumed that the surgeon (whom I had never met) would have all the de­tails on his computer. Very wrong. I told her of my unresectable large pheochromocytoma, how it had almost blocked my Inferior Vena Cava and that I was on Warfarin to stop blood clotting. I told her about my ‘moderate to severe’ aortic valve stenosis and regurgitation. I told her of previous atrial fibrillations where the pheochromocytoma had released catecholamines into the blood stream and how for years I had carried am­ pules of Lasix with me and a syringe to inject myself if it ever happened again. I suspect she did not believe me at first but after listen­ing to my heart and seeing my 12-inch scar, she went to see her superiors. It turned out that the Alfred Hospital had NO access to my medical records, even though they were held on a computer at The William Buckland Institute (where I had radiation treat­ment twice) within the SAME grounds as the Alfred. The surgery was cancelled. It was finally done about a month later after appro­ priate premedication. It is a dreadful thought that if I am ever admitted to any hospital uncon­ scious, they will not know my signif­ icant medical history which would be vital in my case for appropriate treat­ment. So yes, I fully support a smart health card. But even before that I would support the simple sharing of medical records between hospitals. It is ridiculous that my medical records at Cabrini Hospital and The William Buckland Institute were not accessi­ ble by the Alfred Hospital computers. Cabrini is only about 5km from the Alfred. Doctors at the Alfred had to ring these two hospitals and ask for the records. But there is another, more signifi­ cant problem working against a smart card which you did not mention. In Australia the patient is not legally entitled to the reports of their own medical examinations. I have found that different hospitals can and do make different interpretations of medical imaging tests. I have a CT scan where the possible lung and liver metastasis interpretation was made by one radiologist at one hospital, but was said to be an artifact and an unfilled (by the contrast medium) liver vein by another radiologist at a different hospi­tal. The problem of wrong diagnosis of medical tests I see as the real imped­ iment to having medical records put in digital black and white on a smart card. Fortunately, in my case I have read up fully on my conditions and I have had sympathetic doctors who have given me all the reports. I do not want to blame anyone for misinterpre­ tations. I recognise that the same glass can be half full or half empty, with both interpretations correct. What was an unfilled vein 1cm in diameter in December 1996 was inter­preted as a possible benign tumor 2.5cm diameter in September 1999 but in July 2000 this was a 4.8cm tumour requiring immediate attention. What doctor wants to have his name electronically signed on a diagnosis subsequently found to be in error? In fact, America is way ahead of Australia in this regard which I think is why the USA will develop the health card first. This year, franchised medical testing clinics are opening where anyone can go in and pay for any medical tests they want, with NO doctor’s referral needed. If you think you want a particular test you just go and have it. A CT scan is about $US730. The patient gets back a full report. Then they can take that report to a doctor if needed. The high cost of medical treatment and medica­tion in the USA means that there is much more financial incentive there for smart health card development and use. Like most (all?) technology today, Australia will only get it as a spin-off from the USA. Finally, let me say that the virtual­ ly free health system in Australia is about the best in the world, the above problems notwithstanding. (The ba­ by-boomers like us will be kept alive from diseases which only 20 years ago would have killed us.) I confidently expect to be running kitsrus.com for many years to come. Peter Crowcroft PhD, DIY Electronics (HK) Ltd, Hong Kong. Solar power bogged in bureaucracy Of late, concerns have been ex­ pressed in several publica­tions about the intrusion of the bureaucracy into every part of our lives. Now it appears that its clammy hand is touching those who have a hobby that is actually productive to society as well as being enjoyable: the electronic fiddlers! Al­ though I have a degree in electronic and electrical engineering I take the title “fiddler” as honourable as the “rats of Tobruk” took theirs. Also, we know how hard it is to play a fiddle. Being one of the first members of Greenpeace, I have seen with disgust how the bureaucracy has pulled the whole issue to the edge of imbecility with all the unrealistic and counter­ pro­ductive rules. I live in the country and I see the effect on the farmers scratching a living. Putting my deeds where my words are, I designed and installed a solar/wind system 11 years ago, even though connection to the electricity grid would have been cheaper at the time. Designed to, among other things, run a 100W computer it now runs two 350W+ computers (I also do program­ ming as a hobby). Although the battery capacity is quite sufficient I wouldn’t mind having another few solar panels. Thus I enquired about the solar rebate program that the Victorian State Gov­ ernment has in place at the moment. However, the convoluted process of obtaining the rebate, together with the invasion of privacy, is worse than that to obtain a shooter’s licence. And this last one is very obviously designed to keep you from having shooting as your chosen sport. Of course the bureaucrats expect you to use “SEIA (Aust) Accredited Renewal Energy Installers” and dare I mention it, electricians also suitably stamped by the bureaucracy as experts. One look at the enclosed system planner will have you in stitches at first, but then you sadly ask yourself if this will ever be the clever country as long as this clammy hand tries to smother any free thought or enterprise. In the “typical power” of the plan­ ner, a computer uses bet­ween 8W and 120W (most monitors have a 150200W power supply but never mind), toasters 600W (slow toaster), etc. Every bathroom with a woman worth her hair has a hairdryer taking around 1000W but that is left out altogether. Then, at the bottom of the page, is the biggest spark of brightness: “allowance for system losses: 50%”, yes, fifty. If that doesn’t put even the greenest conservationist off, I’ll eat my hat. Maybe I am unbelievably clever that I have the most efficient system in the world but somehow my friends and I dismiss this possibility out of hand. Needless to say, I am going to spend $2000 of my own money and not have bureaucrat-stamped experts snooping around my prem­ises. Any electrician would be horrified to find that all the wiring is single conductor, 500mm apart, so low capacitance and low fire hazard. And how can no-earth be much safer than earths all over the place? No, I don’t want the poor fellow spinning on his head. It is a pity that the fiddlers have to go underground. Lucky fiddlers like Bell, Ericsson, Marconi and their likes lived in a different time, otherwise it would be a very dark and quiet world. Politically incorrects will be tried one dark day, so please withhold my name if you publish this letter. Till that dark day I hope to continue en­ joying SILICON CHIP. Silicon Chip Binders  Each binder holds up to 14 issues  Heavy board covers with 2-tone green vinyl covering  SILICON CHIP logo printed in gold-coloured lettering on spine & cover REAL VALUE AT $12.95 PLUS P & P Price: $A12.95 plus $A5 p&p each (Australia only; not available elsewhere). Buy five and get them postage free. 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. December 2000  33 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. Multi-station intercom uses CB microphones This intercom unit can connect any number of units togeth­er, rather than the limit of two, as with most designs. In prac­tice, the number of stations required would normally number less then 10. The circuitry is based on the CHAMP LM386 amplifi­er published in the February 1994 issue of SILICON CHIP and the Pre-CHAMP two-transistor preamplifier pub­ lished in July 1994. Each intercom station comprises the circuit shown here, built into a CB microphone. Any station on the system can call any other station connected to the line. It has auto­ 34  Silicon Chip matic line-load protection for the power amplifiers and an auto-mut­ ing ability. It runs off any 12V DC source which may be a plugpack or battery. You can use any CB microphone provided it has a momentary pushto-talk (PTT) switch. All you have to do when all units are built and connected is simply press the but­ ton on the CB micro­phone and talk. Let go of the button to listen to the reply from the other station(s). In fact, you use this intercom exactly like you would a CB radio. The microphone PTT switch provides power (black wire) to the intercom and the relay. Each unit also has a normally off (NO) pushbutton that is used as a “Call” button. Simply press this button and the speak­ers at all stations will beep. The beep tone is generated by the 555 which is wired as an oscillator. Each speaker has a 3.9Ω 1W series resistor and each set of relay con­ tacts has a series 10Ω 1W resistor. These are included to protect any and all of the LM386 amplifiers, regard­ less of any combination of intercom stations being simultane­ ously connected to the line. The bypass switch (S1) on the speaker allows you to mute your station without upsetting the total line load for the other stations on the line. Graeme Rixon, Otago, NZ. ($45) Solar-charged battery regulator This design was developed to im­ prove the reserve supply on a solar/ battery powered communications site. Most solar regula­ tors charge the batteries to a nominal voltage of around 14V whereupon the charger is disconnected. The battery then discharg­es to around 13.5V and the charger is reconnected and so the cycle continues. But when the regu­ lator is disconnected, there is unused charging energy which goes to waste. This regulator system works in a similar way except that there are two batteries, main and reserve. When the main battery is fully charged, the solar panel is connected to charge the reserve battery, so that no solar energy is wasted. Op amps IC1a & IC1b are wired as comparators and these compare the charged battery voltage, via ad­ justable voltage dividers, to the 6.2V reference provided by REG2, a 7805 regula­tor “jacked up” by two diodes, D1 & D2. When the main battery voltage is between 13.5V and 14.5V, the output of IC1a is low while IC1b is high. IC1b turns on transistor Q3 which provides the negative supply (earth) to relay RLY1. However, since the output of IC1a is low, Q1 & Q2 will be off and the relay won’t operate. While the relay is not ener­gised, the solar array is connected to the main battery. When the battery voltage reaches 14.5V, the output of IC1a goes high, turns on Q2 & Q1 and energises the relay. The relay should be a DPDT having at least two sets of contacts. One set of contacts must be able to handle the full current from the solar panel. Alternatively, you could use a 4PDT relay and parallel three of the four sets of the contacts. The other set of contacts is used to latch the relay when it is energised. At the same time, the main battery is discon­nected and the solar panel is connected to the reserve battery. This is maintained until the main battery discharges to 13.5V and the output of IC1b goes low, turning off Q3 and unlatching the relay. Peter Howarth, Gunnedah, NSW. ($35) AT LAST! Electronics TestBench This is it: the one you’ve been asking for! SILICON CHIP’s ELECTRONICS TEST BENCH is a valuable 128-page collection of the best test equipment projects from the pages of Australia’s best electronics magazine. Available now from your newsagent or direct from the publishers ONLY $13.20 INC P&P AND GST Silicon Chip Publications, PO Box 139, Collaroy, NSW 2097 Phone Orders: (02) 9979 5644   Fax Orders: (02) 9979 6503   Email Orders: office<at>silchip.com.au December 2000  35 2-Channel Guitar Preamp; Pt.2 Digital Reverb This reverberation unit will add “life” to your guitar, making a small room sound much more spacious. It can be used with our 2-Channel Guitar Preamplifier, added to some other piece of equipment or even used as a freestanding unit. By JOHN CLARKE In a live performance, reverberation is naturally caused by the multiple echoes that occur in a concert hall long after the original sound source has died away. These multiple echoes are mainly caused by the sound reflecting off the walls, floor and ceiling of the venue. The sound absorption char­ acteristics of the reflecting surfaces determine the reverberation time; ie, the time it takes for the sound to die away to nothing. Without some reverberation, music can sound dead or flat. Just how much effect it has can be realised when we recall hear­ing the sounds produced by 36  Silicon Chip an organ or choir in a large auditori­ um or church. How lifeless would it be if there were no walls to reflect this sound and add reverberation? However, reverberation is not al­ ways a good thing and too much can affect the intelligibility of speech. Ideally, the amount of reverberation should be made adjust­ able, to suit the particular venue. However, you really don’t have much control over the natural reverberation that exists at a particular venue. What’s more, reverberation can be practically non­ existent in small venues and where there are lots of soft furnishings that absorb sound. As a result, a live performance can seem dull and lifeless but there is a way around this. By feeding the sound through an electronic reverberation unit, you can add just the effect you want to make your performances sound great. In effect, you can be transported to the concert hall of your dreams – figuratively speaking. Digital reverb The SILICON CHIP Digital Reverber­ ation Unit is based on two Mitsubishi M6580P digital delay ICs. These are set up to simulate the different echo effects that naturally occur within concert hall. The overall effect is similar to that produced by a dual-spring reverber­ ation unit such as the one described in our January 2000 issue. However, this new solid-state unit has several advantages over the electromechani­ cal types. First, unlike the spring-based units, it is not microphonic in any way. This can be a problem with spring-based units, since any movement of the unit Fig.1: the block diagram for the Digital Reverberation Unit. It includes two digital delay lines, the outputs of which are mixed with the direct signals in IC3. The delayed signals are also fed back to two input mixers (IC1a & IC1b) and then fed through the delay lines again to provide the decay feature. can cause “spring noise” and lead to unwanted sound. Second, you can alter the delay times to change the effect if desired, something that is impractical on a spring-based unit. Finally, the noise, distortion and frequency response characteristics are much better than the spring reverb units can deliver. As shown in the photos, the unit is built on a single PC board and is easy to assemble. The board measures 173 x 109mm and fits easily into the chassis of the 2-Channel Guitar Preamplifi­er, behind the preamplifier boards. Note that when used with the 2-Channel Guitar Preamplifier, the unit is in the effects loop. This means that the input is driven by the Effects Send output and the output from the Main Features • • • • Dual delay for added effect Direct plus reverb signal mixing Decay and delay time can be altered Reverb and direct signal mixing can be altered December 2000  37 reverb unit is then fed back into the Effects Return socket. The reverbera­tion signal is then mixed in with the main (or direct) signal from the preamplifier stages, as described last month. Alternatively, you can build the unit into a freestanding case on its own. You would have to add a power supply (this could be the same as the one used in the preamp unit) and a couple of RCA sockets for the input and output signals. You also need to add a couple of extra resistors (R3 & R3') to provide the direct signal components (more on this later). Block diagram Take a look now at Fig.1; this shows the block diagram of the circuit. What we’re doing here is first sending the input signal to two mixer stages. These then drive separate delays lines and the outputs from these are then mixed with the direct signals in another mixer stage to produce an output signal. In greater detail, IC1a and IC1b form the input mixers. IC1a then drives IC2 which provides a 32.8ms delay, while IC1b drives IC4 which gives a 20ms delay. The delayed outputs from IC2 and IC4 are then fed to mixer stage IC3. As well as going to IC2 and IC4, the undelayed outputs from mixer stages IC1a and IC1b are also fed directly to IC3. This undelayed signal is important because it provides the audience with the direct signal, before the delayed signals arrive. After all, this is how the sound arrives in a real environment – the direct sound is heard before the reflected signals. However, it’s not enough to simply provide a direct signal and a couple of delayed signals – that won’t provide reverb­era­tion. What we need is a series of delayed signals that gradually decay to nothing. These reverberation (decay) signals are produced by also feeding the outputs from the digital delay chips (IC2 & IC4) back to their respective input mixers. As the signals pass through the delays, they are fed back to the mixer inputs but at a slightly reduced level. As a result, the original signals are repeatedly delayed until they eventually decay to a very low level. The time taken for a signal to decay away (ie, by 60dB) is the reverberation or decay time. The decay rate and the various mixing levels can be easily adjusted by changing resistor values, to produce the required effect. In addition, the delay time for IC2 can be changed in approximate 0.5ms increments from 0.5ms to 32.8ms using 38  Silicon Chip Fig.2: the complete circuit diagram for the Digital Reverberation Unit. Digital delay line IC4 operates with the default 20ms delay, while IC2 operates with a 32ms delay due to the data clocked into its Data input at switch-on. This data is provided by the delay preset circuit (IC5-IC8). December 2000  39 Fig.3: the codes required for IC2. Data (lower trace) from IC8 is transferred to IC2 on each negative edge of the SCK signal (middle trace). During this time, the REQ line (top trace) must be low to enable the follow­ing 12 SCK clock pulses. The positive edge of REQ signals the end of the serial data stream and loads the data in IC2. different linking options for the delay preset control (see Table 3). Circuit details Fig.2 shows the complete circuit details for Digital Rever­beration Unit. It uses eight separate ICs, including the two digital delay chips (IC2 and IC4). Although the circuit sections for IC2 and IC4 may appear to be the same at first glance, there are important dif­ ferences between them. First, unlike IC2, IC4 has its SCK (clock), REQ (re­ quest) and Data inputs (pins 5, 4 & 6) all tied low. As a result, IC4 is reset at power-on to operate with the default delay period which is 20ms. IC2, on the other hand, has its SCK, REQ and Data pins connected to a de­ lay control circuit. This circuit is used to “program” IC2 at power-on so that it provides a 32ms delay. Once this has been done, the delay control circuit goes to “sleep” and takes no further part in the action; it only operates to program IC2 at switch-on. In greater detail, IC1a functions as an inverting amplifi­er. It operates with a gain of -1 for the input signal and has high-frequency rolloff above 19kHz Fig.4: these oscilloscope traces show the two delay times. The upper trace is the input signal while the lower trace is the output after being delayed. The first delay period occurs 20ms after the original while the second delay is some 32ms after the original. 40  Silicon Chip due to the 820pF capacitor between pins 1 and 2. The signal from IC1a’s output (pin 1) is fed to a low-pass filter stage con­ sisting of 56kΩ and 27kΩ resistors and 150pF and 560pF capacitors. This filter network in turn forms part of the feedback circuit of an internal op amp at pins 22 & 23 of digital delay chip IC2. In operation, the low-pass filter rolls off high-frequency signals above 15kHz at a rate of 40dB per decade or 12dB per octave. This is done to prevent high-frequency signals from being converted into digital data by IC2, which could cause errors. IC2 samples the filtered analog signal at its input and converts it to digital format using an A/D converter. The inte­ grator components for this A/D converter are at pins 20 & 21. Basically, this RC network provides feedback for another internal op amp. The converted digital data is stored in an internal memory, after which it is clocked out and converted to analog format using another internal op amp stage. The integrating capacitor for this stage is connected between pins 15 & 16 and the output signal appears on pin 15. Another lowpass filter stage on pins 13, 14 & 16 (consisting of 56kΩ resis­ tors and 560pF and 150pF capacitors) removes any digital artifacts. Fig.5: the decay rate is shown in this oscilloscope trace. The top signal is the input while the lower trace comprises the output and the decay of the signal down to zero. The decay is about 0.7 seconds. This was set using a 10kΩ resistor for R1, the decay setting resistor. A 1kΩ resistor and a .0047µF capac­ itor at the output of the filter provide a further rolloff for frequencies above 33kHz. The delayed signal is then fed to pin 2 of mixer op amp IC3 via mixing resistor R2 and a 1µF bipolar capacitor. Similarly, the delayed signal from IC4 is also fed to pin 2 of IC3, this time via R2'. In addition, the delayed signals are mixed back into the inverting inputs of IC1a and IC1b via R1 (R1') and series 1µF capaci­tors. As a result, the signal makes multiple passes through the digital delay chip, to provide the echo effects. The value of R1 sets the decay time; ie, the time it takes for the echoes to fade away. The larger the value, the shorter the decay time. Note that op amps IC1a & IC1b are biased at +2.5V via the 10kΩ resistors connecting to their non-inverting inputs (pins 3 & 5) from pin 19 (REF) of IC2 & IC4 (this is the half-supply voltage for IC2 & IC4). Crystal X1 on pins 2 & 3 of IC2 sets the internal clock frequency and de­ termines the rate at which the digital signal is clocked out of memory for D/A conversion. The associated 100pF capacitors and 1MΩ resistor are there to provide correct loading for the crystal, so that the clock starts reliably. Delay time As mentioned above, IC2’s delay time is set via the REQ, SCK and DATA inputs at pins 4, 5 & 6. To change the delay time, a serial data stream must be applied to the Data input at pin 6 and this is then clocked in at each negative transition of the SCK (serial clock) input. The data stream is then accepted on the rising edge of the REQ (request data) input and includes various mute, sleep and address codes, as well as the delay information. Normally, the SCK, REQ and Data inputs are controlled by a microcon­ troller but we’ve eliminated the need for this by using four low-cost ICs (IC5-IC8). These make up the delay control circuit mentioned above. OK, let’s see how this works. When power is first applied, a 3.3µF capacitor pulls the inputs of Schmitt NAND gate IC6d high and so its pin 3 output is low. When the capacitor subsequently charges via its associ­ ated 100kΩ resistor, the pin 3 output switches high and a short posi­tivegoing reset pulse is applied to pin 15 (Reset) of IC7 via a .001µF capacitor. IC8 is a 74HC165 serial shift regis­ ter with parallel load inputs (D0-D7). The first 8-bits of data are set by the logic levels on the D0-D7 inputs and these are loaded into the register when power is first applied. The loaded data is then clocked out on pin 9 but only when pin 1 (the shift load input) of IC8 is low. The clock signals are derived from IC5, a 4060 binary coun­ter which has a free running oscillator at pins 9, 10 & 11. This produces a clock signal at Q4 (pin 7) which runs at twice the fre­ quency of the signal at the Q5 output (pin 5). Q4’s output is inverted by IC6b which then clocks pin 2 of IC8 and pin 5 (SCK) of IC2. Q5’s output is inverted by Schmitt NAND gate IC6a which then clocks IC7, a 4022 divide-by-8 counter, at pin 14. After two counts, the “1” output at pin 1 of IC7 goes high and is entered into IC8 via the serial input at pin 10 (DS). This high appears at the pin 9 output of IC8 after 10 clock cycles on pin 2. When the “6” output (pin 5) of IC7 subsequently goes high, IC5 is reset and remains that way while ever pow­ er is applied. At the same time, the REQ input of IC2 also goes high, while pin 11 of IC6c goes low to reset IC8. The delay control circuit now remains in this “suspended” state and plays no further role in the circuit operation. The oscilloscope trace of Fig.3 shows the required codes for IC2. The Specifications Delay times ................................................20ms (fixed) and 32.8ms (adjustable) Decay time .................................................0.7 seconds (adjustable) Signal handling ..........................................1V RMS max Signal to noise ratio with respect to 1V ....-83dB unweighted (20Hz to 20kHz filter) Frequency response ...................................-3dB <at> 20Hz & 10kHz Harmonic distortion ...................................typically 0.3% at 1kHz and 1V RMS Data (lower trace) from IC8 is trans­ ferred to IC2 on each negative edge of the SCK signal (middle trace). During this time, the REQ line (top trace) must be low to enable the follow­ing 12 SCK clock pulses (ie, pin 12 of IC5 must be low). The positive edge of REQ signals the end of the serial data stream and loads the data in IC2. IC1b and IC4 operate in a similar manner to IC1a and IC2 but without the delay control circuit. Instead, IC4 Parts List 1 PC board, code 01112001, 173 x 109mm 2 2MHz parallel resonant crystals (X1,X2) 1 500mm length of 0.8mm tinned copper wire 7 PC stakes Semiconductors 2 M65830P or M65830BP (but not M65830AP) Mitsubishi delays (IC2,IC4) 1 TL072, LF353 dual op amp (IC1) 1 TL071, LF351 op amp (IC3) 1 4060 binary counter (IC5) 1 4022 divide-by-8 (IC7) 1 4093 quad Schmitt NAND gate (IC6) 1 74HC165 8-bit serial shift register (IC8) 1 7805 5V regulator (REG1) 1 1N914, 1N4148 switching diode (D1) Capacitors 2 100µF 16VW PC electrolytic 2 47µF 16VW PC electrolytic 5 10µF 35VW PC electrolytic 1 3.3µF 16VW PC electrolytic 10 1µF NP or BP electrolytic 7 0.1µF MKT polyester 4 .068µF MKT polyester 2 .0047µF MKT polyester 1 .001µF MKT polyester 3 820pF ceramic 5 560pF ceramic 4 150pF ceramic 4 100pF ceramic Resistors (0.25W 1%) 2 1MΩ 13 10kΩ 1 100kΩ 1 6.8kΩ 1 47kΩ 2 1kΩ 8 56kΩ 1 220Ω 5W 4 27kΩ 1 150Ω 1 22kΩ December 2000  41 IN OUT OUT 10F 10k 150 1F 56k 33 560pF 150pF 560pF 56k 33 .068F 47F 56k 56k 56k 27k IC4 M65830P 0.1F 0.1F 1 1M X2 56k BP 150pF 27k 100F 0.1F 27k 1k 820pF 10k 1k 0.1F 150pF .068F BP 150pF X1 1 2 x 10F 10k IC3 TL071 R2' R2 10k 820pF BP 1F .0047F 560pF BP 2x 100pF IC2 M65830P REG1 7805 10F 1F 10k 100F 1M IC7 4022B 22k BP 1 .068F IC5 4060B 6.8k BP .068F 47k 1N 4148 BP 1F 0.1F D1 BP R3' R1' .0047F .001F 1 BP 10k 1 IC6 4093B 1 1F 1F IC1 TL072 820pF 10k 10k IC8 74HC165 1 2x 100pF 10F 1F 10F 1 100k 1F 10k BP 0.1F 1F R1 SIG GND R3 1F 3.3F +15V 15V _ 0V IN SIG 220 5W  GND  0.1F 560pF 47F 56k 27k 56k 560pF Fig.6: install the parts on the PC board as shown on this wiring diagram. The ICs all face in the same direction. operates with the default 20ms delay period, as described previously. Mixing IC3 mixes the delayed signals with the direct signals from pin 1 of IC1a & IC1b. The delayed signals come in via R2 & R2', while the direct signals are applied via R3 and R3'. The values of these resistors set the amount of mixing in IC3, while R1 & R1' set the reverberation or decay time. The values chosen will depend on the application of the reverberation unit. When connected to the 2-Channel Guitar Preamplifier, only R1 and R2 are used because the Reverb Unit is in the effects loop. In other applications, however, you may want to include R3 and R3'. In this case, you must use a larger value for R2 so that there will be an audible effect at IC3’s output. Power supply The Digital Reverberation Unit re­ quires regulated supply rails of ±15V and a single supply rail of +5V. The +5V supply for IC2 & IC4-IC8 is derived from 3-terminal regulator REG1. A 220Ω 5W resistor at the input is used to reduce the dissipation in 42  Silicon Chip the regulator, while the +5V output is fil­ tered using several electrolytic capacitors and two 0.1µF ceramic capacitors. The circuit can also be operated from a single +15V supply rail (instead of ±15V rails) if the GND is connected to the -15V rail. In fact, you can use a regulated supply voltage down to 8V, although the 220Ω resistor at the input of REG1 will need to be replaced with a link. Construction The Digital Reverberation Unit is built on a PC board coded 01112001 and measuring 173 x 109mm. Begin the assembly by installing the links and resistors. The resistor colour codes and are shown in Table 2 or you can use a digital multimeter to check each value before soldering it to the board. Note that if you are building the unit to go in the 2-Chan­ nel Guitar Preamplifier, use 10kΩ resistors for R1, R1', R2 & R2' but don’t install R3 or R3'. However, if the board is to be built into other equipment or used as a standalone unit, you must include R3 and R3' (10kΩ) to get a direct signal component. In that case, use 18kΩ resistors for R2 and R2'. The seven PC stakes can now be soldered into place, fol­lowed by the ICs. Take care to ensure that each IC is correctly located and orientated (the ICs all face in the same direction). The convention is that pin 1 is always adjacent a small dot or notch in the plastic body. Diode D1 can be installed next, fol­ lowed by 3-terminal regulator REG1. Again, make sure that these devices go in the right way around. Finally, install the two crystals (X1 & X2) and the capaci­tors. Table 1 shows the codes for ceramic and MKT types. Testing If you have a suitable power supply, con­nect it to the board and check the supply voltages to the ICs. Assuming you are using a regulated ±15V supply, there should be +15V on pin 8 of IC1 and pin 7 of IC3. Also check for -15V on pin 4 of both IC1 & IC3. Pins 1 & 24 of IC2 & IC4 should be at 5V. Alternatively, if you are using a single supply rail (“-” input connected to 0V), there should be +15V on pin 8 of IC1 and pin 7 of IC3. There should also be 0V on pin 4 of IC1 and IC3. In Fig.7: this is the full-size etching pattern for the PC board. Check your board carefully before installing any of the parts. addition, check for +5V on pins 1 & 24 of IC2 and IC4, pin 14 of IC6 and pin 16 of IC5, IC7 & IC8. Note that if you use a supply voltage lower than 15V, the 220Ω 5W resistor will have to be reduced in value or shorted out completely. The input voltage to the regulator needs to be at least 8V. Test & adjustment You can test the reverberation board by connecting a signal to the input (at around 1V RMS) and the output to an amplifier driving headphones or loudspeakers. Check that the sound has the reverberation added and that the signal is undistorted. Alternatively, if the board is built into the 2-Channel Guitar Preamp­lifier, you can check its operation simply be wind­ing up the Effects control. Of course, you will have to feed a suitable signal into the CH1 or CH2 input first and monitor the output using head­ phones or an amplifier. If you wish, you can alter the rever­ beration characteris­tics by changing Table 1: Capacitor Codes o o o o o o o o o Value IEC Code EIA Code 0.1µF   100n   104 .068µF   68n  683 .0047µF   4n7  472 .001µF   1n0  102 820pF   820p   821 560pF   560p   561 150pF   150p   151 100pF   100p   101 Table 2: Resistor Colour Codes o No. o  2 o  1 o  1 o  8 o  4 o  1 o 13 o  1 o  2 o  1 o  1 Value 1MΩ 100kΩ 47kΩ 56kΩ 27kΩ 22kΩ 10kΩ 6.8kΩ 1kΩ 220Ω 150Ω 4-Band Code (1%) brown black green brown brown black yellow brown yellow violet orange brown green blue orange brown red violet orange brown red red orange brown brown black orange brown blue grey red brown brown black red brown red red brown brown brown green brown brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown yellow violet black red brown green blue black red brown red violet black red brown red red black red brown brown black black red brown blue grey black brown brown brown black black brown brown red red black black brown brown green black black brown December 2000  43 Table 3: How To Set Different Delays For IC2 Using Linking On IC8 Delay 0.5ms 1.0ms 1.5ms 2.0ms 2.6ms 3.1ms 3.6ms 4.1ms 4.6ms 5.1ms 5.6ms 6.1ms 6.7ms 7.2ms 7.7ms 8.2ms 8.7ms 9.2ms 9.7ms 10.2ms 10.8ms 11.3ms 11.8ms 12.3ms 12.8ms 13.3ms 13.8ms 14.3ms 14.8ms 15.4ms 15.9ms 16.4ms 16.9ms 17.4ms 17.9ms 18.4ms 18.9ms 19.5ms 20.0ms 20.5ms 21.0ms 21.5ms 22.0ms 22.5ms 23.0ms 23.6ms 24.1ms 24.6ms 25.1ms 25.6ms 26.1ms 26.6ms 27.1ms 27.6ms 28.2ms 28.7ms 29.2ms 29.7ms 30.2ms 30.7ms 31.2ms 31.7ms 32.3ms 32.8ms Pin 12 GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + 44  Silicon Chip Pin 13 GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND + + + + + + + + + + + + + + + + GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND GND + + + + + + + + + + + + + + + + Pin 14 GND GND GND GND GND GND GND GND + + + + + + + + GND GND GND GND GND GND GND GND + + + + + + + + GND GND GND GND GND GND GND GND + + + + + + + + GND GND GND GND GND GND GND GND + + + + + + + + Pin 3 GND GND GND GND + + + + GND GND GND GND + + + + GND GND GND GND + + + + GND GND GND GND + + + + GND GND GND GND + + + + GND GND GND GND + + + + GND GND GND GND + + + + GND GND GND GND + + + + Pin 4 GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + GND GND + + Pin 5 GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + GND + the delay of IC2 and the values of resistors R1, R1', R2, R2' and R3 & R3'. The table shown on the main cir­cuit (Fig.2) indicates the ranges that can be used for the resis­tors. As mentioned in the text, the re­ verberation decay times can be made longer by decreasing the values for R1 and R1'. However, these resistor values cannot be made too small, otherwise the feedback signal will exceed the input signal and the circuit will be­ come unstable. The R2 & R2' mixing resistors determine the reverberation signal levels applied to the final mixer (IC3). Similarly, R3 & R3' set the undelayed (direct) signal levels. Note that when used with the 2-Channel Guitar Preamplifier, the reverberation unit is in an effects loop, whereby the signal is mixed in with the main or direct signal. This means that R3 & R3' are not required in this situation. However, if the reverb unit is connected as an in-line effects unit, resistors R3 & R3' must be included to provide the direct signal. A value of 10kΩ works well with 18kΩ values for R2 & R2'. If you’re prepared to experiment, you can substitute trim­pots for these resistors so that you can adjust the reverberation unit to your liking. This done, the trimpots can be measured using a multimeter and replaced with fixed value resistors. Changing the delay Finally, the delay time for IC2 can be changed by alter­ing the connections to pins 3, 4, 5, 12, 13 & 14 on IC8. Table 3 shows the connections required for each possible delay time. Note that the initial setting has all these pins connected to +5V. To make changes here, you have to cut the thinned track sections connecting these pins to the +5V track (ie, the track connecting to pin 16 of IC8). You then have to apply a solder bridge to connect the disconnected pins to the GND rail (on either side of IC8) instead. Make sure that none of the pins connects to both +5V and GND or the supply will be shorted. That completes the PC board assem­ bly. In Pt.3 next month, we will show you how to install it in the 2-Channel Guitar Preamplifier case, along with the two preamp boards and the power SC supply. 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 abc LCD PC LPT ON Via PORT Liquid Crystal Displays are used everywhere these days. But how do they work? We’ll show you how to drive an LCD from your PC keyboard. Then we show how to use the LCD to display and program a temperature/thermostat chip. It’s a great project for beginners, especially if you want to understand more about your computer. By Peter Crowcroft and Frank Crivelli Y ou’ll find LCDs, or liquid crystal displays, in a huge variety of appliances, consumer electronics and so on. Usually driven by a microcontroller, they’ve become very popular over recent years for information transfer and instructions and (usually!) make complicated equipment easier to operate. But how do you get the message you want onto the LCD screen? It’s not difficult, as this simple project shows. Circuit description The circuit (Fig.1) is quite straight­ forward. In fact, most of the “work” is undertaken by the large integrated circuit hidden under the black blob on the rear of the LCD module PC board. All we have to do is provide that module with the appropriate ASCII codes and these come from your com­ puter’s LPT1, or parallel, port. The project could have been as sim­ ple as that but we’ve gone one step fur­ ther and added a temperature control chip, the DS1620, which we can use to make a simple but effective thermo­ stat/thermometer in conjunction with the LCD module. The remainder of the circuitry is mainly power supply – and even that is very simple. Power is supplied from a 12V DC plugpack, with diode D2 protecting against reverse polarity on the DC input jack (centre pin is positive). Due to the low current requirements of the kit, only a small (TO-92 pack) 5V regulator is required. Resistors R2 and R3 hold the DS1620 CLK and RST inputs low when the kit is disconnected from the PC. This allows the chip to work in “stand-alone” mode. Resistor R1 and diode D1 convert the separate data input and output lines from the PC to the single bidi­ rectional data line on the DS1620. When writing to the chip, R1 pulls DQ high when pin14 of the parallel port (AUTO) is high. DQ is pulled low via D1 when AUTO is low. When reading from the DS1620, AUTO must be set high first. This high is blocked by D1 so that the DQ output can drive pin 10 of LPT1 (ACK). The liquid crystal display LCDs come in many shapes and December 2000  53 Front view of the pre-built Liquid Crystal Display (LCD) module used in this project. It has 2 lines of 16 characters. All these pics are shown same size. sizes but amongst the most common is the type we have used in this project, a 16 character x 2 line display. It requires only 11 connections – eight bits for data (which can be reduced to four if necessary) and three control lines (we have only used two here). This particular display, an MC162-2, runs from a 5V DC supply and The same module viewed from the rear. Under that big black blob is a chip which does all of the work in driving the display. All you have to do is talk to it! only needs about 1mA. The display contrast can be varied by changing the voltage into pin 3 of the display, usually with a trimpot. The display requires eight bits of data, a register select line (RS) and a strobe line (E), which are supplied from Here’s what you get in the kit. On top is the preassembled LCD module, with the main PC board underneath. The software is on the 3.5-inch floppy while all the components are separately packed in plastic. Inset at top is the kit as supplied. 54  Silicon Chip the PC printer port. A third input, read/write (R/W), is normally used to read or write data to and from the LCD. In this kit the R/W line is tied low so only “writes” to the LCD are possible (more on this later). The eight bits of data are supplied from the printer port data lines and two printer port con­ trol lines are used for RS (‘auto’) and E (‘strobe’). Basically the LCD has two registers – a data register and a control register. Data is written into the control register when RS is low and into the data register when RS is high. Data is latched into the LCD register on the falling edge of ‘Enable’. The sequence for writing data to the LCD is: 1. To begin, E is low 2. Select the register to write to by setting RS high (data) or low (control) 3. Write the eight bits of data to the LCD 4. Set the Enable signal high then low again. There are certain minimum timing requirements that must be followed when writing to the LCD, such as data setup times and Enable signal pulse width. These are in the order of tens and hundreds of nanoseconds. Extra timing delays are also intro­ duced by the capacitance of the cable used to connect to the PC printer port. Delay routines may be needed when using fast PCs to meet these timing requirements. The software supplied includes these delay routines. LCD displays have a ‘busy’ flag that is set while it is executing a control command but in our case this flag is not accessible because the R/W line has been tied low (write). This is not such a problem because all commands have a maximum execution time. We simply wait for Unlike the LCD module, you have to assemble this PC board yourself. But as you can see, there’s not much to it. The most difficult bit is the D-25 socket at the bottom. this time to pass before accessing the LCD again, eliminating the need to check the flag and thereby saving on an I/O line! For example, the ‘Clear Display’ command has an execution time of approx. 1.6ms. After sending this command to the LCD we simply wait 2ms before continuing on. This en­ sures that the command has finished. Characters to be displayed are written into the LCD’s ‘data’ memory (RAM). The amount of RAM available de­ pends on the type of LCD. The LCD used in this kit has 80 bytes of RAM. An internal address counter holds the address of the next byte to write to. These 80 bytes are broken up into two blocks of 40 bytes. The address range of the first block is from 00H to 27H and the second block from 40H to 67H. After power up and initialisation, address 00H is the first character of the top line and address 40h is the first character of the bottom line. The address counter is set to address 00H and is automatically incremented after each byte is written. If we now start writing data to the LCD, it will be stored from address 00H on but only the first 16 characters will be visible. To display the rest of the characters we need to ‘scroll’ the display. Scrolling simply means changing the start address of each line. If we scroll left one position, address 01H becomes the first character of the top And here it is with the LCD module plugged in and running. Perhaps you’re wondering “how did they get a message on the screen when nothing is plugged in...?” Fig.1: the circuit is quite simple – just a 5V regulated power supply, a DS1620 thermometer chip and the LCD. The LCD and DS1620 are controlled via the parallel port of a PC. December 2000  55 pcb overlay line and address 41H the first charac­ ter of the bottom line. Scrolling right does the opposite – addresses 27H and 67H become the first characters of the top and bottom lines. As you can see, each block of ad­ dresses ‘wrap’ around in a circular manner. The next address after 27H is 00H; the next address after 67H is 40H. If we scroll left 40 times we will bring address 00H back into view as the last character on the top line. The address ranges of each block are not continuous. There is a gap of 24 bytes between the end of the first block (27H) and the start of the second (40H). So if we keep writing characters to the display, the first 40 will be stored in addresses 00H to 27H, the next 24 will be ‘lost’ and the next 40 will be stored at addresses 40H to 67H. The internal address counter is directly accessible so we can set the next address to write to. This is how the characters are written to the second line of the LCD. For example, we can send 5 characters to the first line, set the address counter to 40H and then start writing characters to the second line. The DS1620 chip The DS1620 is a Digital Ther­ mometer/Thermostat IC from Dallas Semiconductor. It measures temper­ atures from -55°C to +125°C (-67°F to +257°F) in 0.5°C increments and has 56  Silicon Chip Fig.2: there’s not much to assemble on the PC board. Just take care with component polarities – and don’t mix up diodes D1 and D2! Also note that the X3 “GND” and “V+” printed labels on the PC board were back to front on early boards: what is shown here is correct. three “alarm” outputs. It requires no calibration or external components. (If you want to know more about this chip you can download the data sheet from www.dalsemi.com). The three alarm outputs, designated THIGH, TLOW and TCOM function as follows: ·THIGH goes high when the meas­ ured temperature is greater than or equal to a user-defined upper limit (TH). ·TLOW goes high when the measured temperature is less than or equal to a user-defined lower limit (TL). ·TCOM goes high when the tempera­ ture exceeds the upper limit and stays high until the temperature falls below the lower limit. These three outputs can be used to directly control heating and cooling appliances via suitable drive circuitry (eg, relays and optocouplers). Data is read from and written to the DS1620 via a 3-wire serial interface (DQ, CLK and RST). The user-defined upper and lower trip points are stored in the IC in non-volatile memory. This means that the trip points are ‘remembered’ even when the power is removed. The DS1620 can be used in two modes – Three-Wire mode for in­ terface to a computer or Standalone mode. This last mode does not require a computer interface. With RST and CLK low, the chip will continuously monitor the temperature and set the alarm outputs accordingly. This means that once you have programmed the upper and lower trip points the kit can be disconnected from the PC and you can use the alarm outputs for monitoring or control functions. You can even remove the chip from its socket and put it in your own temperature controller, using the kit simply as a DS1620 programmer. Temperature registers in the DS1620 are nine bits long and can be positive or negative values. Each reading has a resolution of 0.5° C. For positive temperatures, the most significant bit (bit 8) = 0 and bits 1-7 hold the integer value. Bit 0, if set, adds 0.5°. For negative temperatures, bit 8 = 1 and bits 7-0 represent the two’s complement of the temperature. To get the actual value, invert bits 7-0 then add 1. The DS1620 is controlled via a set of 8-bit instructions. Depending on the instruction, an 8 or 9-bit data value is either read from or written to the chip. All instructions and data are transferred serially starting with the least significant bit D0. To read or write a value to the DS1620: 1. To begin, RST is low and CLK high. 2. RST high 3. CLK low 4. Set DQ equal to bit 0 of instruction 5. CLK high 6. Repeat steps 3, 4 and 5 for    remaining instruction bits To write to the chip: 7. Repeat steps 3, 4 and 5 for bits 0-7 or 0-8 of the data to be written 8. RST low for at least 5ms To read from the chip do Steps 1 through 6 above then: 7. Set the AUTO signal high so that data can be read from the DS1620 8. CLK low. DQ now outputs the data to be read (LSB first) 9. Read and store DQ 10. CLK high 11. Repeat steps 8, 9 and 10 for the remaining bits of data to be read 12. RST low As with the LCD, certain mini­ mum timing requirements must be observed between each of these steps. In particular, RST must remain low for at least 5ms after writing data to the DS1620 (step 8). This gives the chip’s internal EEPROM time to store the data. Also, the DS1620 needs one second to execute a ‘start-convert’ presence of parallel ports in order, according to Table 1. The first port found becomes LPT1, the second LPT2, and so on. The BIOS stores the base address of each port found in a table in the BIOS variable segment of memory, as follows: Table 3 -- LPT Base Addresses Here’s how the LCD module mounts to the main PC board. The back of the module has a 16-way header pin set which mates with a 14-way socket on the board. instruction. So, after starting a tem­ perature conversion, you must wait 1 second before reading the result. The PC parallel port There are three common address ranges used for parallel port interfac­ es, as follows: Table 1 -- Parallel Port Addresses 3BCh - 3BFh 378h - 37Fh 278h - 27Fh Parallel interface on monochrome or TTL video card Parallel interface 1 (LPT1) Parallel interface 2 (LPT2) The standard PC parallel port con­ sists of three registers, each referred to by their functional name. These registers occupy the first three ad­ dresses in the range. The first address in the range is referred to as the base address. Table 2 -- Base Registers Data register Base address Read/Write Status register Base address + 1 Read only Control register Base address + 2 Read/Write For example, for parallel interface 1, the data register would be at address 378H, status register at address 379H and control register at address 37AH. Note that the data and control registers can be written to and read from. This does not mean that they are bidirectional. It means that the outputs of these registers can be read back to check their status. During the system boot-up se­ quence, the BIOS tests for the ADDRESS 0040:0008H CONTENTS Base address of LPT1 0040:000AH 0040:000CH Base address of LPT2 Base address of LPT3 0040:000EH Base address of LPT4 (If address=0 then there is no port for that LPT number.) Every signal line on the port, whether it is used for read/input or write/output, is allocated one particu­ lar bit at one of the three addresses Base, Base+1 or Base+2. The logic state of the bit indicates the state of the wire (0V or 5V.) The following table shows each printer port sig­ nal used by the kit and the register, address and bit position associated with it. The last three signal names are preceded by a minus sign. This means that the signal is active low. Writing a high to the bit causes the signal to go low. Table 4 -- Signal Line Attributes Signal D0 D7 ACK -STROBE -AUTO INIT -SLCTIN Reg. Data Status Control Control Control Control Addr. Bit Direction Base 0 - 7 Base+1 6 Base+2 0 Base+2 1 Base+2 2 Base+2 3 Output Input Output Output Output Output Construction There aren’t very many components to place on the PC board so chances of errors aren’t high – another feature which makes this a great project for be­ ginners. On the negative side, though, your soldering skills will be tested! ­As with all projects, before placing or soldering components, check the PC board for obvious defects – bridg­ es or shorts between tracks which shouldn’t be there, broken tracks, etc. Start with the lowest profile compo­ nents – the resistors and the wire link (use a resistor offcut for this). The two diodes are next but take care that you not only get them in the right places Parts List – LCD Interface 1 PC board, K134, 83 x 71mm 1 Liquid Crystal Display module, 16 x 2 characters 1 2.5mm DC jack, PCB mounting (X2) 1 D25 male connector, rightangle PCB mounting (X1) 1 5-pin SIL header (X3) 1 8-pin IC socket for IC1 1 14-pin SIL socket for LCD 1 14-pin SIL header for LCD (16 pin supplied in kit) 2 screws, 2.6mm x 18mm long 6 nuts, 2.6mm 1 software floppy disk Semiconductors 1 DS1620 digital thermometer and thermostat (IC1) 1 78L05 +5V regulator, TO-92 package (IC2) 1 1N4148 (D1) 1 1N4004 (D2) Capacitors 1 100µF 25V electrolytic (C1) 1 10µF 25V electrolytic (C2) 1 0.1µF monobloc (C3) Resistors (0.25W carbon) 4 10kΩ (R1-4) 1 10kΩ trimpot (VR1) A complete kit of parts, including software, is available from all Jaycar Electronics stores for $69.95. (Cat KD-6082). but with the right polarity. The power diode is the larger black diode and it is the one which goes in the top right corner of the board. Place the capacitors next, again tak­ ing care with type and polarity. If you haven’t used electrolytic capacitors before, the negative lead is marked by a row of “–” symbols down the side of the capacitor adjacent to that lead. Now solder in the trimpot, voltage regulator and DC socket. The trimpot and DC socket can only go one way but the voltage regulator could be mounted back-to-front if you’re not careful: it must go in the same way as indicated on the board. Mount the 5-way header pin set and the IC socket – again, make sure that the IC socket is oriented the same way as indicated on the board. When soldering the D connector, December 2000  57 IC socket and header pins, you will need to be particularly careful not to form solder bridges between the pins. A fine-tipped, clean iron is essential –and if you don’t want to strain your eyes, some form of magnifying lens is very handy (especially for us older dudes whose close-up eyesight ain’t what it used to be!). You should now have only a couple of components left: a header pin set and matching socket and a 25-pin D connector. The D connector might cause you a little bit of angst because it has to be very carefully aligned to go into its holes. You cannot put it in at an angle – the pins at the opposite end will miss their holes. But it does go in! The last component to mount on the main PC board is the 14-way header pin socket. The 16-way header pin set has to be soldered to the display module. This needs to be exactly vertical and is soldered on the same side as the LCD (ie, the header pins emerge from the underside of the board. At the risk of boring you, we must repeat – these pins are very close together. Watch out for solder bridges! Just in case you’re wondering, no, we haven’t made a mistake with the number of pins in the header pin and sockets. The pin set has 16 pins, the socket 14 pins. Two pins are unused in this project and simply hang off the end of the socket when later as­ sembled. Don’t assemble it yet – nor, for that matter, insert the DS1620 IC. We’re going to check the board first. But even before that, give your board the once-over to make absolutely sure your component placement is correct and that you have neither missed any pins while soldering nor soldered any bridges. Obviously, if you find any mistakes, correct them first. It’s best to take your time and not make any mistakes in the first place. But if you do have to unsolder compo­ nents – especially things like PC header pins or IC sockets – you’ll find it almost impossible without using either solder wick (which soaks up the solder, free­ ing the pins) or a solder sucker (which does the same thing by suction). Power This project is designed to run from a 12V DC supply which is then regu­ lated to 5V by the 78LS05. An ideal supply would be a 12V plugpack – be­ 58  Silicon Chip cause the circuit draws so little power, just about any 12V DC plugpack you find should be OK. BUT! (Don’t you just hate those buts?) The DC socket on the board is designed to suit 2.5mm plugs and, try as we might, we couldn’t find a 12V DC plugpack in our junkbox with a 2.5mm plug. Plenty of 2.1mm – which don’t quite fit – but no 2.5s. If you’re in the same position, the obvious answer is to cut the 2.1mm plug off and solder on a 2.5mm plug. Just one thing – make sure the centre contact is the positive contact. If it’s the other way around you won’t do any damage (thanks to the protective diode) but it won’t work, either... Testing and final assembly This is simply a check that the project powers up as it should. With­ out the IC or LCD module plugged in, connect your 12V DC source and measure the voltage between pins 4 and 8 of the IC socket (see the diagram to determine which pins those are). You should get a reading very close to 5V (between about 4.9V and 5.1V). If not, disconnect the power and check your PC board once again. If you get 5V, disconnect power, wait a minute or so for the capaci­ tors to discharge, then plug in the IC (watch its orientation!) and the LCD module. As we mentioned before, the two pins closest to the middle of the module are not used and simply hang out in mid-air at the end of the 14-pin socket. Reconnect power and you should find a row of black squares on the display. If you don’t, adjust the pot until you do. (The other thing that affects the contrast of the display is Please Note On early versions of the PC board silk-screened overlay, the two end pins of header pin set X3 were labelled incorrectly. With the D25 connector at the bottom, the GND (ground) pin should be the left-most pin and the V+ pin the right-most pin. PC boards in new kits should be correct but check yours, just in case! Incidentally, that V+ is not the regulated 5V supply but the full supply voltage from the nominal 12V plugpack – which could be as high as 16V or so. the angle at which you’re viewing it. Best is straight on). Once you’re happy that it’s working, remove the display module from its socket and insert screws in the two uppermost corner holes. Place a nut on each of these and tighten fully. Now place another nut on each screw and move it to about half-way along the thread. Replace the module in its header socket, with the ends of the screws through the appropriate holes in the PC board underneath. Rotate the two nuts so that they lie on the top side of the PC board un­ derneath, with the two boards exactly parallel. Then insert the remaining two nuts on the ends of the screws and completely tighten. Screw holes are provided on the top side of the display PC board and the board underneath but they are redundant as the display board is held securely in place by its header socket. So far so good. You’re now ready to fire up the PC and drive the display. Connecting to the computer Here’s a couple of real traps for young players. And not-so-young, either, ’cos we wuz trapped! First of all, the cable: the module is fitted with a 25-pin D “male” connec­ tor and your computer’s parallel port (LPT1) will be fitted with a 25-pin D “female” connector. So all you need is a 25-pin D male-to-female lead, right? Yes . . . and no! There are two types of commonly available 25-pin D leads. One is sim­ ply a “straight through” connection (eg, pin 1 to pin 1, pin 10 to pin 10, etc) and that is the type of lead you require. The other lead is intended for serial ports (some of which also use 25-pin D connectors!) and they are NOT straight through wiring: some of the lines cross over to other pins. Guess which lead we grabbed from our box of various computer leads? Of course, Murphy’s law applied and we tried to use the serial lead. And just as “of course”, it didn’t work. So make sure the lead you use is the right one. There is a second, less obvious trap. And again, we got caught. The software is written to suit a computer with a parallel port (LPT1) at address 378H. Now 99% of computers will have their LPT1 at this address, set ex-factory. There are some comput­ ers, though, which have their LPT1 at 278H. In normal circumstances, it doesn’t matter – Windows for example will work fine with either. But this display won’t. It needs 378H. And guess which address our computer used? Yes, it was 278H. (To be fair, the PC is an old 486/50 “workhorse” which we use for all sorts of project development and testing, leaving our main networked system for magazine production. Someone at some time had a reason to change LPT1 and it had never been changed back again!). So if you fire up the software and it doesn’t work, those are the two most obvious reasons why not. The first problem is fixed by swapping leads. The second requires either a moth­ er-board jumper change or (in more modern computers) a BIOS change at boot-up. Software Two programs are supplied with the kit and are also available for downloading. Both are zipped into one archive and will need to be un­ zipped first. Create a directory on your hard disk and copy the zip file from the floppy to it. Then use one of the many unzip­ ping programs (eg, WinZip, PKunzip, etc) to restore the files. Along with several “jpg” images which show how the kit is put together (some of which are reproduced here) are two .exe files which are the demon­ stration files for use with the display. There are other files, including “C” files written under Borland Turbo C for DOS. The .exe files (which are compiled versions of the C files) are designed to run under DOS (remember that?) but also run quite happily in a DOS box under Windows 95 or 98. As most computers these days are Windows boxes, it’s probably easier to use them this way. Simply dou­ ble click on one of the appropriate .exe files and a DOS box will open, running the software. The two demo programs are: K134LCD.EXE – this simply allows the user to enter a message to be displayed on the LCD. The message can be up to 40 characters long. The message can be stopped or scrolled left or right and the scrolling rate can be varied. When the program is run, a menu Use this same-size PC board artwork to check the board supplied in your kit – just in case. is displayed on the PC from which you choose the required function. At the same time, the square boxes on the display change to a message “PC controlled LCD demonstration”. The message is only displayed on the top line of the display. If the message is scrolling and it is less than 40 characters long then a number of spaces will be displayed before the message starts again. You can enter a new message by selecting option 1 on the PC menu, change the scrolling direction (2 and 3), stop scrolling (4), change the scrolling speed (5) or exit the program (0). The full ASCII set available from the computer keys is echoed on the display. Disconnecting the display from the serial port while a message is being displayed freezes the display at that point but does not lose the information – reconnection will start the message scrolling again, if that is what has been selected. K134TEMP.EXE – a “thermostat” program that displays the current temperature as well as the upper (TH) and lower (TL) temperature ‘trip’ points, using the DS1620 IC mounted on the same PC board as the display components. The value of the trip points can be changed via the PC keyboard and the user can choose between Celsius or Fahrenheit display. The DS1620 is configured to per­ form continuous temperature conver­ sions. Current temperature and trip point data is continually read from the DS1620 and compared with the previous reading. If any of the three values have changed then the display is updated. At the same time, the outputs (via header pin set X3) will reflect the status, as previously explained. These three pins can be used to con­ trol external equipment – eg, an alarm or a heating element if the temperature goes too low. References These days the internet is the place to get information. But here are some magazine references on LCD’s: < “A Liquid Crystal Display Driven From A PC Printer Port”, SILICON CHIP, March 1998. = “A PC-Controlled Thermometer/ Thermostat”, SILICON CHIP, June 1997. > “Temperature Monitoring With a Synchronous Serial Link”, MicroCom-puter Journal March/April 1995. Some websites you might like to visit are: < beyondlogic.org (excellent, must-visit site) = geocities.com/ResearchTriangle/1495/ee_lcd.html > iaehv.nl/users/pouweha/lcd.htm woe/lcd ? pobox.com/~lcd_info Or simply do a search on your favourite search engine (eg, yahoo. com) for ‘LCD parallel’ and you will get hundreds of links to follow-up. You can email the author at peter<at> kitsrus.com if you have any problems or requests. Information on other kits in the range is available from his web page at kitsrus.com SC December 2000  59 SERVICEMAN'S LOG History, symptoms & observations These are the three basic rules behind any approach to a service job – whether we are conscious of them or not. But inter­rogating a customer is not always easy. Most are helpful, but a few adopt a defiant “you-find-out” attitude. And some are so vague and inept that they are more hindrance than help. My first story was a typical example of the last point, although I didn’t realise this immediately. Instead, I took the customer’s observations at face value. Mrs Edwards needed a house call for her TV set, since it was a 95cm (37-inch) model that was too big to bring in. And to help make the house call worthwhile, she also had another TV set which needed fixing. Both sets had sound faults. The larger set turned out to be a 1992 Grundig ST 95-775/9 PIP/TOP with a CUC7890 chassis. The other was a 1987 Philips KS786 with a KL9A-3 chassis. But how hard can a sound fault be? If nothing else, I could fix the Philips and bail out of the ageing Grundig, so I agreed to go. The lady had switched both sets on before I arrived and neither showed any problem at all. I was somewhat miffed at this but she insisted I stay until the faults occurred. Fortunately, the Philips didn’t take long – there was a crackling coming from the loudspeaker and when I removed the back, I could see the EHT had been sparking from a very dirty ultor cap. I removed and cleaned the EHT lead and made sure it was making good contact before sealing it with silicone. A piece of cake, I thought – now for the Grundig which was running in anoth­er room. This, too, was begin­ ning to play up with slightly dis­torted crackling but only in the left channel. Using the remote control and se­ lecting the audio menu, I moved the 60  Silicon Chip stereo balance to the right and the problem stopped. I told Mrs Edwards that if she wanted this fixed, she would have to wait while I ordered the circuit manual. I explained about the balance control and she seemed quite happy with this. The service manual duly arrived a fortnight later and I phoned to make an appointment. However, Mrs Ed­ wards said that the set was now work­ ing OK and that my services were no longer need­ed. Such is life – I filed the manual and moved on to other jobs. It didn’t last, of course. Mrs Ed­ wards was back on the phone three months later, saying the Grundig was “still playing up”. Patiently I asked her to be more specific. Well, she said, the sound was distorted in both speakers, as before! Because I now had the manual and the audio output ICs in stock, I decided to give it another go. But I was more than a little concerned about how vague Mrs Edwards was with some of her comments. When I arrived and checked the set out, the distortion was still only in the left channel – it was just that the Items Covered This Month • Philips KS786 TV set. • Grundig ST 95-775/9 TV set. • Panasonic NN-C855B microwave oven. • Akai CT2869AUS TV set. balance control had been returned to the centre. Initially, I decided to re­ place the left channel audio output IC (IC4200, TDA2502H) and solder any suspect joints I came across to see if that fixed the problem. The first obstacle I had to overcome was the need to swing the TV set away from the wall. Unfortunately, it was sitting on a stand that didn’t have castors, weighed about 100kg and had to be slid across thick shag-pile car­ pet. However, I eventually managed to achieve this and remove the back. The next problem was to figure out how to remove the sound output mod­ ule, which was held in with a series of ingenious plastic clips (the service manual doesn’t mentioned these). After a struggle, I finally managed to remove the module and replace the left-channel IC. I then put it all back together again and switched on but it was still distorted in the left channel. I then did what I should have done when I first arrived and that was to play around with the accessories on this rather complicated TV set. The problem was trying to familiarise my­ self with such a complex set without altering any settings that I might not be able to restore. I checked whether the TV system had been correctly set as B/G for Australia, which it was, but when I selected the video via the AV (Audio/ Video output), I found that the sound was fine in both channels. This proved the problem wasn’t in the audio am­ plifier stages at all. Next, I tried to determine wheth­ er the fault was the same in mono transmission as well as stereo but I couldn’t get any stereo reception! The stereo indicators on the display and in the menus wouldn’t alter at all. The problem seemed to be in the stereo decoder which was, as far as I could see, part of the multi IF module. By now, I had spent a lot of time on this set without achieving anything, so I decided I would go back to the workshop and have a good think. If only Mrs Edwards had been a little more observant and more detailed in her description of the fault – after all they watch the set all the time. And if only the set wasn’t so big and heavy, so that I could get it into the work­shop. Finally I contacted the agents to find out the price and availability of the ICs and modules. The parts were all available but expensive and I didn’t really have a clue as to what I might need. I asked if I could speak to technical support and was delightful­ ly surprised to find out that not only could I speak to someone but that he actually knew – or was pretty sure he knew – what the fault was. In this set, there are two surface mounted BC858 PNP tran­ s istors (CT2524 and CT2527) on the copper side of the sound output module PC board – one for the left channel and one for the right – and these were the nominated culprits. Armed with this sort of 24-carat knowledge, I decided to give it one more try in the house and made an appointment after the ordered transistors had arrived. Back at the Edwards’ residence, I re­ moved the sound output module and sat down with it at a table. The first problem was finding the two transis­ tors, as they aren’t marked and there is no component layout. Eventually, I found them under a metal screen soldered on the top lefthand side of the PC board. The next drama involved remov­ ing these surface-mounted devices (which are soldered and glued) with­ out damaging the tracks on the board. After that, I had to hold each of the tiny new transistors in position with a pair of tweezers while I sol­dered their legs into place without applying too much heat. Finally, I reassembled everything and was ever so relieved to hear clear stereo sound from both channels. Because the circuits don’t show the interior block diagrams of the associ­ ated ICs, I can only speculate on their roles. IC2530 appears to be part of the digital surround sound preampli­fier processor, while IC2350, IC2520 and IC2510 make up the stereo decoder (both Nicam and Zweiton) – this being a multi-system TV set. Why the two transistors failed I don’t know – I was just happy to get out of there with the job done. A spooky microwave Many electronic items are now so cheap that they are no longer econom­ ical to repair at all. Unfortunately, I am old enough to remember fixing 6-transistor AM radios, whereas a modern “boom box” – usually con­ sisting of a CD player, dual cassette and stereo AM/FM tuner – is no longer worth fixing. Video cassette players are border­ line too, with new VCRs retailing at just over $200 and the hifi models starting at about $300. It is hard ad­ vising someone who paid in excess of $1000 many years ago that a better performing machine is now available at a third of the cost. The same can also apply to comput­ ers and to microwave ovens. I recently saw a microwave oven advertised for just $120! One wonders how they can purchase the raw materials for December 2000  61 Serviceman’s Log – continued that! At the same time, the power output has increased in these ovens to almost double what it once was, although many are now so small that I wonder whether my coffee cup would fit inside. So what is all this leading up to? Betty Carver brought in her rather up-market Panasonic microwave oven, somewhat grand­ly called “The Genius Dimension 4”. This particular model (NN-C855B) also includes a convection oven, is about five years old and would cost in excess of $600 to replace. The problem, according Betty, was that it intermittently “cooks by itself” 62  Silicon Chip (ie, turns itself on) and sometimes she could­n’t set the clock. With all the safety circuits built into ovens, I found it hard to believe that it could turn itself on unaided and suspect­ed there were some two-legged gremlins in her house. But she swore that she had been woken in the mid­ dle of the night by the audible alarm noises that the oven makes when it has finished cooking. Apparently, she even went into the kitchen once to find it on and cooking! More spe­ cifically, the display read “7/8 Beef/ Pork”. Intrigued by this somewhat spooky story, I agreed to have a look at it. This oven has a “Word Prompting Display” with an operation guide built into the microprocessor. When I switched it on it said, “Welcome to Word Prompt­ ing”, and I found that every­thing from setting the time to convection cooking all worked perfectly for me. I left it on the soakbench and days later, when I was about to phone Betty and tell her that I could find nothing wrong, it finally started its tricks. I was in another part of the shop and suddenly I could hear the oven beep­ ing, followed by the noise of the relays cutting in, the magnetron powering up and the tray rotating. It was all very X-files stuff, as no one else was around. And why had it selected the food category “8 Pork”. I tried to stop it but it wouldn’t immediately. After four tries it did stop and then the oven would work normally. It didn’t play up for the rest of the day, and I was puzzled as to how this had happened. Normally, selecting “Pork” would require, as a minimum, someone to press the 7/8 button twice and then press Start. The next day, when powered up, it wouldn’t let me change the clock or do anything much. In the days that followed, I found that this apparition was also likely to occur when the oven was switched on in the morn­ ings, intermittently giving exactly the symptoms Betty had described. I opened the oven and found it to be exceptionally clean. I then decided to stop our “ghost” in his tracks by disconnecting the membrane switch panel from CN4 on the Digital Pro­ grammer circuit board. And this, at least, provided a clue. The oven no longer operated by itself but neither could I make it operate. I then left it connected and the next time it tried to cook by itself, I un­ plugged it before it could complete its sequence. Gradually, by plugging and unplugging it, I convinced myself that the source of the phantom cooker was indeed the switch panel itself. I ordered a new one and when it arrived, I dismantled the front panel and carefully pulled off the old switch panel. I tried to examine the internal parts of the switch membrane assem­ bly (visible through the transparent underside) but everything looked OK. Finally, I pulled the paper backing off from the new panel and glued it to the front escutcheon before reas­ sembling the unit. The unit was then soak tested for three weeks and it now worked perfectly. Intrigued as to what caused the problem, I checked for high resistance between the contacts on the flex cable but couldn’t find any problems. So what happened? I can only speculate that Betty used detergent and water to wipe the front panel and some had penetrated around the edge and crept inside by capillary action. After that, depending on the temperature and humidity, this would intermittently activate some of the switches, causing the oven to start cooking. A crook Akai Long, long ago (even before Star Wars), Akai Japan used to make up-market reel-to-reel tape recorders, then moved into VCRs and TV receiv­ ers. They became very big and other factories in Korea (Samsung) started making TV sets for them, after which they bought sets made in China. Most of these were for the small-screen budget market and Akai felt that there was a gap they could fill by also supplying upmarket large-screen TV receivers. Akai turned to Europe to produce these and they were made by ITT (also Nokia/Salora/Schaub Lorens/ NAD/Dual/Luxor, etc). Only a dozen of these sets were sold in Australia and these were early digital types (the term “digital” is used very loosely in TV technology and is mostly confined to the tuning and control end of the set – the scanning and audio is essen­ tially analog. Most use the Philips I2C bus system). The problem is that when I encoun­ ter these sets, I am intimidated by the often unrecognisable – so called – interna­ tional symbols, the sheer number of features and the need to figure out how to use them before the function times out. Often, I wish that they would print an instruction booklet for the instruction book – in English! Anyway, there I was behind Mr Smithfield’s Akai CT2869AUS TV set, grateful that this was only a ba­ sic “poverty-pack” model. The fault ticket said succinctly that the set was dead which was partially true – there was no sound or picture, just a ghastly expectorant sort of noise from the rear, as though the horizontal output transformer was dead or in the pro­ cess of dying. Connect­ing the CRO to the collector of the horizontal output transistor (T501) revealed significant ringing in the horizontal output trans­ former – that is before T501 decided to cark it, right in front of me. This was a not a good start. Convinced that the horizontal out­ put transformer was the main fault I ordered a new one, only to find it was no longer available. After a lot of searching, I found that an HR6160 or EHT3790 was probably an equivalent and ordered one. When it arrived, I duly slipped it in with supreme con­ fidence, along with a new horizontal output transistor, fully expecting that that would be the end of the matter. Well, I was wrong! – it made no Central Coast Internet • Full Service Dial Up Accounts. • Web Hosting • Server Hosting Services • E-mail and WAP solutions for all business sizes • Domain Registration and Hosting Services • Network consulting service on info<at>cci.net.au For connection details to your local internet provider contact Andrew and also receive 20% off our vast range of TrainingOn-Line services. Phone: (02) 4389 8755 Fax: (02) 4389 8388 e-mail info<at>cci.net.au December 2000  63 Serviceman’s Log – continued difference at all and the set was still dead and buzzing. I subsequently spent an lot of time checking the tuning capacitors around the collector of T501 and the deflec­ tion yoke, to see if any had changed in value. After all, it takes a lot to destroy a horizontal output transistor which is rated at 1500V and 5A. The horizontal pulses are normally 1200V but if a capaci­tor changes in value (either going lower or open circuit), these pulses can go a lot higher and exceed the collector-emitter rating of the transistor, destroying it instantly. Alternatively, if there is a short circuit and the current exceeds 5A, the transistor gets very hot and fails. However, the switchmode power supply normally senses the excess current drain and will reduce its out­ put – which was what was happening here. In fact, the 155V rail was down by about one third. After some hunting about, I found that D573, a 33V zener diode, was short circuit. This zener diode is in the collector circuit of the east/ 64  Silicon Chip west output transistor (T573) but not shown on the diagram. Another component not shown on the circuit diagram was C516, a 470pF 1.6kV blue capacitor, which appeared to be somewhat worse for wear. Unfortunately, replacing these two components had no significant effect on the symptoms. However, the situation im­proved when I removed the deflection yoke and I subsequently wasted a lot of time substituting the yoke from another set only to find it made no difference. In the end, I turned my attention to the power supply. This really hasn’t changed all that much in 25 years and is not all that dissimilar to that used by Sunbeam Graetz TV sets in 1975! The switchmode power supply is based on a TEA2164/G control IC (IC701) and chopper transistor T701. Among other things, the output from the transformer supplies the hori­ zontal output transistor (T501). This means that if anything happens to the power supply, it is likely to have some affect on the horizontal output stage. With this in mind, I decided to replace all the electrolyt­ ics in the switchmode supply, from C700 to C734 (about 10 capaci­tors in all; the others in the sequence are elsewhere in the circuit). None of the electro­ lytics on the primary side made any difference but when I replaced C732 (1000µF) on the 31V rail, the set was fixed – well nearly! Now you could have knocked me down with a feather at this point! Why should ripple on the 31V rail be so significant, especially as all this rail seems to feed are the audio output ICs? I wasn’t quite out of the woods yet, as the set still showed a picture that was distorted with what looked like hum. Hot on the trail now, I continued replacing the electros and eventually found that C722 (470µF) on the input to the 5V regula­tor (IC721) and C522 on the output of the 12V regulator (IC521) were the main culprits. Finally, I set the 155V rail exactly with R612, making sure there was no picture (ie, minimum contrast and brightness) during this procedure. I also touched up a few potential faulty joints before composing a suitable bill SC for Mr Smithfield. Order Form/Tax Invoice Silicon Chip Publications Pty Ltd ABN 49 003 205 490 PRICE GUIDE- Subscriptions YOUR DETAILS (all subscription prices INCLUDE P&P and GST) Your Name________________________________________________________ (PLEASE PRINT) Organisation (if applicable)___________________________________________ Please state month to start. 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Please feel free to visit the advertiser’s website: www.altronics.com.au Look Mum, no hands (or digits!)… dahdah dahdahdah di’dahdit di’di’dit dahdi’dahdit di’dahdi’dit dahdahdah Here is a novel clock that doesn’t have a readout. It’s a talking clock, but instead of telling you the time in words it sounds the time in Morse code. A maze your friends by being able to tell the time just by listening to some dots and dashes. If you are an amateur radio operator, it is sure to make a great addition to your shack. There have been hundreds of clock projects over the years but to my knowledge there has never been one like this. The clock features hourly chime, one second internal resolution with an announcement resolution of one minute, and you can also select 12 or 24 hour time and set the speed of the Morse! As with a lot of projects that have appeared in SIL­ ICON CHIP this clock uses a mi­ crocontroller – in this case a PIC chip – to do all the work. There are very good rea­ sons for this; PICs are amazingly ver­ satile and they turn what would have once been a complex project into a very simple one. Of course, the fact that we are not worrying about driving a LED or LCD display makes it even easier, with the output device being a small piezo buzzer. Using Morse code also makes the project simpler, just like a Morse code radio transmitter is a lot less compli­ cated than a voice transmitter. With Morse code we just have two states to worry about; either the tone is on and we can hear it, or it is off and we can’t hear it. Now if you haven’t 68  Silicon Chip learnt Morse code yet either through your work or as a hobby, don’t worry. To be able to tell the time with this clock only requires a rudimentary knowledge of the code. Indeed to get you started there is a slow Morse setting so that you can get in some practice before you move onto the fast Morse setting. The project is constructed on a small PC board and housed in a plas­ tic box. Power is normally supplied from a 9V DC plugpack, however the box incorporates a battery backup in case of power failure. The Morse clock has only two buttons, TIME and SET. The TIME button is used to announce the time and also step through the functions in program mode. The SET button is only activated in program mode and is used to select the options for by Leon Williams VK2DOB each of the functions. How to set the time and program the functions is described later on. Circuit description The full circuit is shown in Fig.1. As you can see there is not a lot to it, with the PIC chip (IC1) doing almost all the work. The PIC chip used here is a 16F84 and is very commonly used. Its major advantage is that it can be programmed with a cheap and simple programmer and can be re-programmed over and over. So if you make a mistake with the pro­ gram (it’s an unwritten rule that programs n e v e r work first time), you can simply rewrite the chip with­ out having to throw it away or erase it with UV light. Packed inside the PIC (amongst other things) is a general purpose timer, 13 I/O pins that can be individually configured as outputs or inputs and 1K of flash ROM and 68 bytes of RAM. Pins 15 and 16 of IC1 are the oscil­ lator pins, connected to a 3.2768MHz crystal and two 22pF capacitors. The crystal frequency is divided by four inside the PIC to give an instruction clock of 819.2kHz. This is further di­ dit dahdi’dahdit dahdi’dah* *(MORSE CLOCK) vided by 64 in a pre-scaler and this is applied to the clock input of Timer 0. Timer 0 counts from 255 down to zero, repeating at a rate of 50Hz. The PIC is interrupted each time Timer 0 reaches zero and the software counts these pulses and when 50 are counted, one second has elapsed. The second count is in turn used to increment the minutes and hours counters. Pin 4 is the reset pin and is tied to +5V by a 10kΩ resistor. The PIC has a built in intelligent reset circuit and this should prove to be adequate in this application. However, if the power supply is disconnected, allow enough time for the bypass capacitors to discharge before reconnecting the power, otherwise the reset may not work properly. The TIME button is connected to Pin 7 which is configured as an input to Port B and has an internal pull up resistor. When the button is not pressed the PIC reads the pin as high; when the button is pressed it is read as low. The SET button is connected to pin 8 and acts in the same way. The software performs a debounce operation on the buttons. When a but­ ton is first detected as being closed, it waits for a short period and tests the button again. If the button is still closed, the program accepts this as a valid press otherwise it treats it as a spurious input and ignores it. The remainder of the Port B pins are configured as outputs and so do not need to be tied to a rail. The Port A pins are all configured as outputs with pin 1 used to activate the piezo buzzer. When the output is high (+5V) the buzzer is on and when the output is low (0V) the buzzer is turned off. The timing of the dots, dashes, character and word spacing are all multiples of the interrupt period (20ms). The software simply counts the number of interrupt peri­ ods and holds the output pin high or low for the prescribed period. The clock is powered from a nomi­ nal 9V DC supply, such as a plugpack. Diode D1 provides protection from reverse polarity and the 100µF capaci­ tor helps reduce power supply ripple. Regulator REG1 is a 78L05 type and its output voltage is raised to around 5.5V by D2, with the 0.1µF capacitor guarding against instability. Diode D3 drops this voltage back to 5V to We think old Sam Morse would have approved . . . supply IC1 at pin 14 and also stops the battery current from flowing back into REG1. When the power supply is re­ moved, power for IC1 is supplied by a back up battery supply comprised of 3 AA cells. When normal power is applied from the plug pack, diode D4 is reversed biased and so no current is drawn from the batteries. Howev­ er, when the main plugpack supply is not available, diode D4 conducts because its anode is more positive than its cathode and current for IC1 is supplied by the batteries. The PIC chip draws around 1mA when in idle condition and about Fig.1: the circuit diagram is just a power supply and a PIC microcontroller. December 2000  69 Parts List: Morse Clock 1 PC board, code 06112001, 72 x 56mm 1 plastic case, 130mm x 67mm x 44mm 1 panel mount DC connector to suit plugpack 4 PC board stakes 1 3.2768MHz crystal (XTAL1) 1 piezo buzzer (Jaycar AB-3459) 2 PC-mount push button switches (S1,S2) 1 18-pin IC socket 8 No. 6 x 12mm self tapping screws 4 32mm plastic spacers (see text) 1 3 AA cell battery holder 4 self adhesive rubber feet Small piece of tinned copper wire Light duty hook-up wire Semiconductors 1 PIC 16F84-04P (IC1) (programmed with MORSECLK.HEX) 1 78L05 5V positive voltage regulator (REG1) 4 1N4004 power diode (D1-D4) Capacitors 1 100µF 25VW PC electrolytic 1 10µF 16VW PC electrolytic 2 0.1µF MKT polyester 2 22pF ceramic Resistors (0.5W, 1%) 1 10kΩ 10mA when the buzzer is operating. While the circuit could be re-arranged to operate solely from 4 AA cells, with the regulator components removed, the expected operating time from the batteries alone would only be about 2-3 months. The batteries are only included to prevent the time settings from being lost when the unit is re­ located or when there is a blackout. If you choose not to use the backup batteries and the plugpack power is lost the time will need to be reset. Disassembled view of the Morse Clock. The 3-AA-cell battery holder is a little unusual – if you can’t find one, use a 4-cell holder with a dummy battery. mounting the smaller, passive com­ ponents (ie resistors and any links) progressing through to the larger ones, then the active components (semiconductors) and any on-board hardware (IC sockets, etc). Leave the installation of the PIC chip until the construction and initial testing is complete. Refer to the component overlay to ensure all components go in their correct spots and that any polarised components are installed correctly. Note that the two electrolytic capac­ itors need to be laid on their sides to avoid fouling the lid. The crystal is also laid on its side and held down with a piece of tinned wire soldered to the pads underneath the board. When installing the buzzer, make sure it is mounted flat against the PC board so that the when the lid is in place, the pushbuttons protrude sufficiently out of the lid. The buzzer positive lead is the longer one and Construction Construction of this project is straightforward. Start by checking the PC board for faults, looking for bridges across tracks and open cir­ cuit tracks. While there is no “right” or “wrong” sequence to installing the components, we usually start by 70  Silicon Chip Fig.2: the PC board component overlay. Note that the two electroyltic capacitors and the crystal must be laid over to fit under the case lid. connects to pin 1 of the PIC. Once the PC board is completed, it’s time to mark and drill the holes in the case. The PC board is mount­ ed on four pillars made from 32mm plastic spacers. These are screwed to the bottom of the case and the PC board screws to their top, just far enough down from the lid to allow the push-buttons to poke through. Unfortunately the 32mm spacers are just too long for this so we have to cut them down a little. First, place the PC board inside the box on the right side, butting up against the integral pillars. Align the PC board so the buttons and the buzzer are placed on the centre line of the base. Mark the spots for the mounting holes with a pencil and drill clearance holes for the self-tap­ ping screws. Drill a suitable hole for the DC connector on the rear side. Mount the DC connector and solder two wires to the socket long enough to easily reach the PC board power pins. Take the four 32 mm spac­ ers and carefully cut each of them to a length of 28 mm with a fine toothed hack saw. The plastic spacers used in the prototype have holes in each end that allow a No. 6 self-tapping screw to be inserted. Screw the four pil­ lars to the inside of the case bottom and then place the PC board on top of the spacers and screw into place with the four remaining self-tapping screws. You will also need to drill three holes on the centre line of the lid for the switches This same-size view shows that all fits in quite nicely into a standard 130 x 67 x 44mm and the buzzer. The switch­ Jiffy box. The PC board mounts on 28mm spacers to place the push-button switches at exactly the right height when the box lid is screwed on. es have a round body and the hole needs to be just big the batteries and install the PIC chip for hourly chime turned off. Pressing enough to allow the switches into the socket. Note the orientation the SET button toggles between the to move freely. The hole for the buzzer – pin 18 is closest to the crystal. settings. needs only to be equal to the hole in Connect the plugpack supply and you (3). Press the TIME button to access the top of the buzzer body to allow the should be greeted with the wonderful the 12/24 hour function. The number sound of the buzzer to escape when sound of slow Morse sounding the 1 is sounded to indicate 12 hour time the lid is in place. and number 2 for 24 hour time. Press­ Solder the DC connector wires to letters OK. Press the TIME button and you should hear the time being ing the SET button toggles between the PC board supply pins and the the settings. battery holder wires to the battery announced. Don’t worry about what it (4). Press the TIME button to access pins, ensuring that the positive and says at this stage, because we haven’t the AM/PM function. AM is sounded negative leads go to the correct posi­ set the time yet. Install the batteries again and then for AM and PM for PM setting. Press­ tions. The battery holder fits neatly in remove the plugpack. Press the TIME ing the SET button toggles between the gap left in the lefthand side of the button and verify that the clock is the two settings case. You could add a small piece of (5). Press the TIME button to ac­ foam as a packer to stop the battery still working with only the backup batteries. You will probably notice cess the fast/slow Morse function. F holder moving if you wish. that the output from the buzzer is is sounded for fast Morse and S for To prevent the mounting screws lower in level. This is normal and as the slow Morse setting. Once again scratching your desk and to make the clock less likely to slip around, attach stated earlier, the back up batteries the SET button toggles between the four self adhesive feet to the bottom are really only included to keep the two settings. clock going if the main power is lost (6). Press the TIME button to access of the case. for a short period. the Hour function where H is soundTesting Install the lid, reconnect the plug ed. Press the SET button and a beep Once construction is complete, it pack and your Morse clock is now will be heard. Each beep represents an increment of one hour, starting from is time to apply power to the circuit. finished. zero. In this mode the SET button Leave out the batteries at this stage Setting the time automatically repeats. If you do not and connect the plugpack to the DC Setting the time with the Morse press the SET button the hour setting socket. Using your multimeter, meas­ is unchanged. If the hours are set to ure the voltage at the output of REG1. clock is very simple, because there are only two buttons to press. Follow an illegal number, that is over 12 or You should read about 5.5V, and also you should read about 5V at pin 14 of the steps below to set the time and over 23, they are reset to zero and start again. the IC socket. If not, remove the power program the functions: (1). Press the TIME and SET but­ 7. Press the TIME button to access source and check your wiring again the Minute function where M is and the installation of the polarised tons together. The letters PGM are announced in Morse code, indicating sounded. Press the SET button and components. you are in program mode. a beep will be heard. Each beep rep­ Assuming this is correct, remove (2). Press the TIME button to access resent an increment of one Minute, the plugpack supply and install the batteries. Measure the voltage at pin the hourly chime function. The cur­ starting from zero. In this mode, the rently set option will be announced, SET button automatically repeats. If 14 of the IC socket again and this time it should be about 4V. If so, remove either ON for hourly chime or OFF you do not press the SET button the December 2000  71 Learning Morse Code While Morse code is no longer used in most commercial activities, some knowledge of Morse is required, at least for the next year or two, to gain a full privelege amateur radio licence. (The requirements have recently been changed to allow those who pass the 5 words per minute (wpm) Morse test to have access to all amateur bands. In the past, 10 wpm was the standard). So why learn Morse code? It’s still a viable means of communication; it’s still used by the armed services (eg, where ships are in line-of-sight to each other and radio communication might be eavesdropped, “Aldus” lamps are still used which flash Morse messages via light). But perhaps more to the point, if you listen in to the amateur radio bands (particularly the HF bands) you’ll hear amateur operators communicating with each other solely in Morse – for the shear pleasure of it. If you want to learn Morse code, listening in to the amateur bands is one of the best ways to go. Not one of the 20, 30 or 50 wpm speedhogs but slow Morse, often used by Novice operators. Or you could obtain one of the many tapes available which teach Morse code. And there are even many computer programs around which generate Morse from either a keyboard or from ASCII text and sound it via the computer speaker. The point is that Morse is an aural language, not visual. And while we’ve printed the Morse alphabet and numbers below, you will notice we haven’t shown it below )as dots and dashes – it is shown as dits and dahs – and should always be spoken that way. So the letter “A” is not dot dash, it is di’dah. “F” is di’di’dahdit, not dot dot dash dot. Note that if a "dit" is followed by another element (either dit or dah) we don’t pronounce the “t” in that dit – the T and the following D become effectively the same sound. The other main thing to remember when learning Morse is NEVER to start trying to send letters before you have thoroughly learnt to receive the whole alphabet. It’s very tempting to grab a Morse key or even a push-button switch, connect it to an oscillator and start bashing away. But your timing will almost certainly suffer if you haven’t got a good knowledge of Morse from reliable sources - others will find your Morse difficult, if not impossible, to decipher. Some letters are recognised very easily – if only because they form parts of common words or phrases. Who doesn’t know SOS, for example? Or “V” for victory (also known as the start of Beethoven’s fifth symphony – didididah). Other letters are easy because, well, they ARE easy: A (didah), E (dit) H (didididit) I (didit), M (dahdah), N (dahdit), O (dahdahdah) and T (dah). Even R (didahdit) and K (dahdidah) aren’t too difficult. There are other letters which are recognised because they are part of commonly heard expressions – especially on radio. “CQ”, or a general call to all stations, is one example. “HI” is another. And the universal radio greeting, “73”, makes a seven and a three easier. It’s when you start getting into some of the more obscure three-sound and four-sound combinations that Morse gets a little tougher – and some letters, such as B (dahdididit), C (dahdidahdit), F (dididahdit) G (dahdahdit), J (didahdahdah), L (didahdidit), P (didahdahdit) Q (dahdahdidah) W (didahdah) X (dahdididdah), Y (dahdidahdah) and Z (dahdahdidit) are regarded as the most difficult to recognise quickly. So you might have to put a lot more effort into these. Some people find learning “opposites” helps them: eg, R and K. Others find putting letters into similar sets works – eg A, U, V. Others simply get stuck in and learn the lot! Numbers are easy to remember but harder to recognise. That’s because numbers follow a pattern – one is didahdahdahdah, two is dididahdahdah and so on, but they have five-sound combinations. So when you start to hear a “1”, it could be an “A”, then a “W”, then a “J” then finally it becomes a “1”. Fortunately, most of the time when numbers are sent you’re probably expecting to hear a number, rather than a letter, so you’re more attuned to it. OK, enough of the preamble. Here is the full Morse code, including some punctuation. Gee, we hadn’t even mentioned trying to learn punctuation, had we? A B C D E F G H I J di’dah dahdi’di’dit dahdi’dahdit dahdi’dit dit di’di’dahdit dahdahdit di’di’di’dit di’dit di’dahdahdah N O P Q R S T U V W dahdit dahdahdah di’dahdahdit dahdahdi’dah di’dahdit di’di’dit dah di’di’dah di’di’di’dah di’dahdah K L M dahdi’dah di’dahdi’dit dahdah X Y Z dahdi’di’dah dahdi’dahdah dahdahdi’dit 72  Silicon Chip 1 2 3 4 5 6 7 8 9 0 di’dahdahdahdah di’di’dahdahdah di’di’di’dahdah di’di’di’di’dah di’di’di’di’dit dahdi’di’di’dit dahdahdi’di’dit dahdahdahdi’dit dahdahdahdahdit dahdahdahdahdah di'dahdi'dahdi'dah dahdahdi'di'dahdah error di’di’di’di’di’di’di’dit . , Fig.3 (left): you can photocopy and glue the front panel artwork to the lid of your Morse Clock. It also makes a great drilling template. Fig.5 (right) is the samesize PC board pattern. SILICON CHIP A B C D E F G H I J K L M N O P Q R S T U V W X Y Z 1 2 3 4 5 6 7 8 9 0 minute setting is unchanged. If the minutes are set to an illegal number, that is over 59, they are reset to zero and start again. Each time a minute is incremented the internal seconds counter is reset to zero. In this way you can accurately set the time by using a reference clock with a second hand. Increment the min­ utes up to 1 less than the amount required, and select the desired minute at the moment the second hand reaches 12 on the reference clock. Obviously, setting the time will be easier if you select a time just after an hour has passed. 8. Pressing the TIME button again will return you to the hourly chime function. Pressing both but­ tons at any stage during program mode will store the settings, exit from program mode, sound the letters OK and return to normal mode. Software For those who program their own PICs, there are two files available for downloading from the SILICON CHIP website. The files are MORSECLK.ASM and MORSECLK.HEX, both zipped into a single file, morseclk.zip. While you do not need the ASM file to program the PIC, it will be of interest to those who dabble in programming. It is always interesting to see how some­ body else did it and maybe pick up a trick or two. The program runs in a small main loop that monitors the buttons for a press and also checks if the hour is up to chime the time. Each 20ms, an internal interrupt occurs that forces the PIC to update the time registers in the interrupt routine. The rest of the code looks after the sounding of the dots and dashes and setting the various functions. Have fun and hopefully your clock will prove both as well as being a novelty. While Morse code may be some­ what outdated in the modern tele­ communications world, it still holds a certain fascination and throughout its history has served us well in both SC peace and war. With one of these . . . ...you could have one of these in about 1 HOUR! Introducing The Quick Circuit 5000 If you want fast, no-fuss PC-board prototypes, take a look at the Quick Circuit 5000. This PC-controlled milling machine reads the standard files generated by popular PC design packages and mills away the copper on the board to produce the tracks. It then drills the holes and cuts out the finished product. You can go from design to finished product in about one hour – without using any messy chemicals. Check out the November 2000 issue of SILICON CHIP for a full review Phone SATCAM on (02) 9807 SC 7081 or email satcam<at>ozemail.com.au December 2000  73 Fun with comparators This month, we’ll have a play with comparators. Most people regard comparators as pretty basic and boring devices but they should be regarded as important building blocks. You can do all sorts of functions apart from comparators. Examples are Schmitt triggers, oscillators, timers, pulse generators, AND and OR gates and even zero voltage crossing detectors. By LEO SIMPSON We will have a play with a “bog standard” device, the LM393 dual comparator but remember that virtu­ ally everything we do will be applica­ ble to other comparators such as the equally “bog standard” LM339 quad comparator or other higher perfor­ mance comparators. OK. So what is a comparator? It’s 74  Silicon Chip very similar to an op amp. It has a differential input stage, with noninverting (+) and inverting (-) inputs. The two inputs are used to “compare” two signals or two voltages and then the output indicates whether one input is higher (or lower) than the other. Typically, one input will be tied to a reference (REF) voltage while the other input is fed with the signal or voltage to be monitored. Let’s do a typical setup with the LM393, as shown in Fig.1. BELOW: this photo features all the parts shown in Fig.1 and Fig.2, except for the 47µF capacitor. One of the potentiometers is not used. Fig.1: this is a basic circuit for a non-inverting comparator. To turn it into an inverting comparator, swap the inputs, pins 5 & 6. Pins 2 & 3 on the unused comparator should be tied high. The 47µF is not used initially. Because we are wiring this up on a Protoboard and want to make it as straightforward as possible, I’ve hook­ ed up the second comparator in the LM393 dual package; ie, involving pins 5, 6 & 7. But remember that ex­ actly the same circuit can be hooked up with the first comparator, or any number of variations on the theme. Since we’re not using the first com­ parator, its inputs should be tied high (+12V) or low (0V). This is done to prevent it from producing any spuri­ ous oscillations which it could do if its inputs were left to “float”. Pin 6, the inverting input, is con­ nected to the junction of two 10kΩ resistors connected across the 12V supply. The voltage at the junction will be half the supply or +6V (nom­ inal) and since this voltage is fixed, we regard this as the REF (refer­ence) input. Pin 5, the non-inverting input, is connected to a variable voltage obtained from the 50kΩ pot (VR1) which is con­nected in series across the 12V supply. By rotating pot VR1, we can vary the voltage fed to pin 5 from +12V down to about +2V. Why not hook up just the 50kΩ pot and the 10kΩ resistor across the 12V supply to begin with and check with your multimet­er to see if this voltage range can be obtained? Check also that you get 6V (or half the DC plugpack supply voltage) at the junc­tion of the two 10kΩ resistors. Now hook up the rest of the components on the circuit of Fig.1, as shown in the photo and in the Protoboard wiring diagram of Fig.2. So that we can see what the compar­ ator does in response to the variable signal conditions, I have hooked up a LED (light emitting diode) in series with a 1kΩ resistor, between the +12V supply and the comparator’s output at pin 7. Now, if we set VR1 so that +12V is fed into pin 5, the LED will not light. If we then wind VR1 back the other way, reducing the voltage to pin 5, at some point the LED will light. If we then measure the voltage at pin 5 we should find that it is just below the voltage at pin 6. In our case, on the afternoon I was writing this, the voltage on pin 6 was +6.18V and as I wound VR1 to the point where the LED came on fully, pin 5 was +5.93V and pin 6 was +5.6V; ie, a smidgin below pin 5. This demonstrates a number of interesting points. The first question might be, “Why did the voltage at pin 5 change at all?” but we’ll get to that later. No, the main point is that when pin 5, the inverting input, is pulled low, the output at pin 7 also goes low. And Fig.2: use this diagram to wire up the circuit of Fig.1. Winding VR1 back and forth will turn the LED on and off. December 2000  75 Fig.3: using the simple comparator results in poor switching behaviour. The upper trace is the input sinewave at 1kHz while the lower trace is the output waveform. when 7 goes low, the LED will light because it is hooked up to +12V via the 1kΩ resistor. So what we have here is a non-in­ verting comparator. We can summa­ rise its operation by saying that when the non-inverting input goes above the inverting input, the output will go high; when the non-inverting input goes below the inverting input, the output will go low. Inverting comparator Say we wanted to change the sense of the comparator? Say, we wanted the output to go high when the input goes low – ie, below the reference input? Easy. Just swap the reference and signal inputs. Go ahead and do it: swap the connections to pins 5 & 6. Now what happens? What happens is that when pin 6 is above pin 5, the LED is alight. Conversely, when pin 6 is low, the output at pin 7 is high and so the LED is not alight. So that’s how you make an inverting comparator. The thing is, you can tell what the comparator will do just by look­ ing at which input is inverting and which is non-inverting. If we vary the non-inverting input, the output will essentially follow the input; ie, when it goes above the REF input, the output will go high as well. In other words, the output is the same as the non-inverting input or to put it anoth­er way, the output has not been inverted (non-inverting, get it?). Conversely, for an inverting com­ parator, the output signal will be 76  Silicon Chip Fig.4: this is the cleaner switching result when a 47µF bypass capacitor is connected to pin 6. This stops the voltage at pin 6 from varying while the switching action is taking place. inverted compared to the input. We can use these basic compara­ tor circuits in all sorts of ways. For example, if we replaced VR1 with a thermistor we could produce a temperature-sensitive switch. Or the potentiometer could be a throttle switch in a car or any one of a number of transducers. So comparators do an important job in sensing all sorts of circuit conditions and then switching an output in response. AC signals What else can a comparator do? So far we have only consid­ered the situa­ tion where a comparator is monitoring static or slowly varying signals. What about rapid signals? To demonstrate, let’s feed an audio oscillator into the comparator of Fig.1. We’ll feed the signal in via a 0.1µF (100nF) capaci­ tor to pin 5, set VR1 to give +6.5V at pin 5 and see what happens. With no signal from the oscillator, the LED is off. We apply a 1kHz sinewave signal, wind up the signal to about 400mV and the LED lights, although not as brightly as it was when we manually varied VR1. So what is happening? The scope waveforms of Fig.3 show the results. The upper trace is the input 1kHz sinewave and the lower trace is the voltage at pin 7 and the LED. Some­ thing is wrong here because instead of switching cleanly, the comparator is obviously dilly-dallying on the output transition between high and low. Hmm, what if the reference voltage at pin 6 was varying up and down with the switching action? We saw that this was actually happening on the static signal test previously. OK. So let’s hang a 47µF capacitor off pin 6 to the 0V rail. That will stop any short term signal variations on pin 6 and should clean up the output signal. The scope waveforms of Fig.4 show the result and the output waveform now switches much more cleanly. The LED also runs a little brighter as well. So in practice, we would not use a simple voltage divider for the REF voltage. We would use a well-filtered voltage, prob­ a bly derived from a zener diode or a more precise voltage source. However, even with a well-filtered REF source for one of the inputs, the switching action of a comparator may not be what we want. Say we were us­ ing a thermistor to drive a comparator in a temperature controller. If we had the simple circuit of Fig.1 (together with the 47µF capacitor at pin 5) it would certainly work but it would be far too sensitive and the circuit would hunt back and forth (ie, switch on and off) continuously with small temperature variations. This would be unsatisfactory if you were controlling a heater or cooling unit. Adding hysteresis The answer is to change the points at which the comparator switches from low to high and then from high back to low. To do this, we provide positive feedback from the output to Fig.5: to demonstrate hysteresis this inverting comparator ver­sion of the circuit has a 22kΩ positive feedback resistor con­nected between pins 5 & 7. the non-verting input. By positive feedback we mean applying some of the output signal back to the input, so that a portion of the output signal adds to the input signal. This is the opposite of negative feedback where the portion of the signal fed back from the output subtracts from the input. The circuit of Fig.5 is similar to Fig.1 but we have swapped the way the inputs are connected and we have added a 22kΩ resistor from pin 7 to pin 5. This positive feedback resistor shifts the switching threshold up and down as the output switches high and low. To set up the circuit of Fig.5, dis­ connect the oscillator, swap pins 5 & 6, pull out the 47µF capacitor and then check that the circuit works as before. As you wind VR1 back and forth you will find that the LED Subscribe & Get this FREE!* THAT’S RIGHT – buy a 1or 2-year subscription to SILICON CHIP magazine and we’ll mail you a free copy of “Computer Omnibus”. Includes articles on troubleshooting your PC, installing and setting up computer networks, hard disk drive upgrades, clean installing Windows 98, CPU upgrades, a basic introduction to Linux plus much more. switches on over a very narrow range. Pin 6 only needs to be raised or low­ ered by a small amount near +6V to turn the LED on or off. Now connect the 22kΩ resistor between pin 6 & 7. You will find that you now have to wind VR1 over a wider range to turn the LED on and off. In fact, you will now find that you have to vary VR1 so that it shifts pin 6 above +7V to turn the LED on and below +5V to turn it off. In fact, if you measure pin 5 as the LED turns on and off, you will find that it is moving up and down over a 2V range as the output goes high and low. This is a fairly crude way of adding hysteresis but it demonstrates the principle. You might also notice that the LED does not fully turn off. This is not be­ cause the comparator is not switching correctly but is due to the current flowing through the 22kΩ resistor. This small current is enough to keep the LED glowing feebly. Well, that’s enough for this month. Next month we’ll have a further play with the LM393 and make it work in SC a few more cir­cuits. APOLOGY ATTENTION KIT CONSTRUCTORS Some K3130 Temperature Control Switch kits were supplied with metal end panels, instead of the plastic panels originally specified. Depending on how the kit was assembled, this may compromise electrical safety. Constructors are advised to disconnect the kit from mains power and check the panels on their kit. If plastic panels have been supplied, no further action is required. If metal end panels have been supplied, customers should stop using the kit and obtain replacement panels. *Australia only. Offer valid only while stocks last. Subscribe now by using the handy order form in this issue or call (02) 9979 5644, 8.30-5.30 Mon-Fri with your credit card details. To obtain replacement panels contact: Dick Smith Electronic Kit Department "K-3130 End Panels" PO Box 321 North Ryde NSW 2113 or Phone: 1800 618 459 or e-mail: kits<at>dse.com.au Dick Smith apologises for any inconvenience caused December 2000  77 Vintage Radio Feature While it was quite grubby, this AWA 467MA set was a good can­didate for restoration as its cabinet was sound and it had all three original knobs. The AWA 467MA . . . an ideal first restoration By RODNEY CHAMPNESS, VK3UG As the saying goes, we all have to start somewhere, and so it is with restoring vintage radios. But the restoration of a 1930s 7-valve, triple-wave, mainspowered, wooden console receiv­er with a tuning indicator and a complex dial cord arrangement would be an ideal project to attempt if you wanted to become disillusioned. 78  Silicon Chip S ELECTING A SIMPLER and more common receiver as the first project is much more likely to be a success, even if a small amount of help is needed in some areas. Your first restoration will be remembered long after the tenth and it is much better to remember it as a success rather than a costly failure. A friend expressed interest in an AWA plastic-cased mantle set. It was a model 467MA which is similar to the 449MA except it has a loopstick antenna. It was like his parents’ radio, hence the interest. While I was in the process of restoration, it struck me that here was an ideal set for a beginner in vintage radio to restore. There is nothing special about this receiver which is a rela­tively simple broadcast band 4-valve superhet. Sets of this type were produced in the tens of thousands, so it’s rela­tively easy to find a suitable receiver for your first restora­tion. Circuits and bits and piec­ es are not too hard to find and help with the project is often available from experienced restorers. Perhaps your long-term interest in vintage radio will not be 4-valve plastic-cased receivers. If they aren’t of interest, does it matter if your res­ toration isn’t perfect? The value of the set is probably only a few dollars and you will have had some practice for your next radio and a lot of fun into the bargain. There are a few important points that the first time re­ storer should consider before obtaining a set such as this to practice on: (1) The plastic cabinet should be in good condition, with no chunks out of it, or cracks (if possible), not dis­ coloured, no distortions due to valve heat or other reasons, and complete with all knobs. It doesn’t matter if the cabinet and knobs are dirty, as they can be cleaned. Check the knobs; some may be broken, loose or extremely tight on the shaft. (2) Look inside the cabinet. It may be dusty and have slight corrosion or discoloration of the chassis but that is OK. Howev­ er, sets from marine environments can be bad choices, as are sets that have had water through them. They will have major corrosion on the chassis, in the pots and tuning gang and most of the components are liable to be leaky. The smell of mice or the smell of something such as a transformer that has been too hot is enough reason for you to pass up the set for something more acceptable. (3) Are the valves all there? It is not absolutely essential that they are but if they are, it indicates that the set has probably not been fiddled with. Miniature valves are reasonably easy to obtain. However, you will need to know what valves are used in the set and which sockets to plug them into. Often there is a sticker in the set showing which valve goes where. Sometimes, would-be repairers change the valves around and the set will definitely not work then – and the valves may be damaged. (4) The radio should be a 240V AC Australian unit, certainly not AC/DC which can be dangerous. Look for a power transformer in the set. (5) Sources for such sets are second­ hand dealers, relatives and garage sales, etc. If you ask “does the set work” and are told “yes”, never as­ sume that the set does work properly, if at all. If the owner wants to demon­ strate it, get them to do this before you buy. If it starts to smoke, leave it. If it sounds distorted it could be OK, providing it is switched off pronto – if you really want that set (this can be Fig.1 (below): no, this is not the circuit of the AWA 467MA but the 449MA which is very similar. The 6BV7 is a double-diode pentode, with the pentode used in the audio stage. Its cathode uses “back bias” with about 4V being developed across the nega­tive supply return resistor, R14. December 2000  79 This was the under-chassis view before restoration. All the black “moulded mud” paper capacitors were replaced with ceramic and polyester capacitors. a bargaining point too). Don’t expect the dial lamps to work. (6) The set you select should not be a midget, as parts are crowded in them, making access for the new recruit difficult. (7) A “hand-span” dial on the re­ ceiver will mean that no dial cord stringing will be required. This is not essential but it does make the first job simpler. The set described in this arti­cle has a relatively simple dial-cord drive. (9) The set should be a broadcast band only set, with a maximum of three or four controls. (10) Once you’ve obtained a suit­ able receiver, it is desirable to get as much servicing data as possible, before you start work on it. This is available from the Historical Radio Society of Australia or the New Zea­ land Vintage Radio Society. Tools and instruments You will need a collection of basic tools and instruments for servicing and restoring receivers, although most electronic enthusiasts would already have these. You will need a soldering iron and solder and a digital multi­meter (DMM) with 10MΩ input impedance. Don’t go for the cheapest of DMMs as you really do get what 80  Silicon Chip you pay for. An analog multimeter with a sensitivity of at least 20kΩ/V is OK for most measurements too, although in high impedance circuits such as the AGC system its readings will be erroneous. You will need a small collection of hand tools, including small-to-large flat blade and Phillips head screw­ drivers, long nosed pliers, side cutters and small adjustable spanners. This is a basic list and these items will usually be all that you will require to get a receiver going, but not to its peak. Additional tools, instruments and bits and pieces will be required as you gain experience. Restoring the AWA 467MA The description that follows is a good procedure for re­ storing vin­ tage radio receivers. The methods described in this article achieve a reasonable end result with not too much effort. Time to start: I never turn on a radio before I have dis­mantled it and made a number of checks inside to ensure it is safe; smoke signals from the set may herald an expensive restora­tion. So take the chassis out of the cabinet and put the cabinet to one side. I had a problem getting the knobs off. They had been put on with some sticky green gunk which had become semi-solid. The knobs are a slide-fit with a circlip providing pressure to hold them on. I was able to put my fingers under the edges of the knobs and gently ease them up and off the shafts. Sometimes it isn’t possible to do this and I may resort to using two screwdrivers, one on either side of the knob to gently ease it off the shaft. Make sure that even pressure is applied on both sides or the knob may break – broken knobs are not easy to replace. Then it is time the carefully inspect all the electronic works. The dial cord was checked and found to be intact, however the cord is often broken. If it is broken, it may be evident how it was strung, sometimes not. Get help here as each set is dif­ferent. If your set has a “handspan” dial there is no dial drive system, which makes things easier. Cleaning & lubrication I dislike working on a dirty chassis, so I cleaned all the top and bottom of the chassis and the mounted compo­ nents with a small paint brush. If you have access to an air compressor you can blow most of the dust and gunk out but be careful around the tuning gang; close the vanes before doing an­ ything near it. Don’t blow compressed air into the gang at close quarters. It the chassis is really dirty, a kitchen scouring pad (not steel wool) soaked in household kerosene will do a good job of getting the grime off. If need be, cut the pad up into strips to get into awkward places. The kerosene tends to act as an anti-rust treatment. Wipe everything clean with a rag. I then lubricate the pulleys and the shafts of the various controls with sewing machine oil. All of the con­ trols must move freely. The figure-8 power cord fitted to most sets of this era is often quite dirty. To clean the cord I run a small screwdriver down each groove in the cord to loosen the gunk. I then clean the cord with a rag soaked in methylated spirits. Usually the power cord comes up OK but if not, it is not expensive to replace the power cord completely. It is a good idea to check the power plug at this stage too. It should not be damaged. Older plugs which allow ac­ cess to the live wires on the underside should be replaced – those older plugs are really quite dangerous. I remove all the valves and clean them. If they are min­iatures (ie, all glass construction), I clean them up with soapy water, rubbing the muck off with my fingers. Be careful not to rub off the valve identification. I rinse the valves under clean water and allow them to dry. Octal valves with Bakelite bases must not be immersed in water; soapy water residue in the valve bases is likely to cause trouble. Hence, only clean the glass top of octal valves and then let them dry. They come up looking like new. Underneath the chassis The next task is to see what things are like under the chassis. I have made up a stand to mount upturned radio chassis on and this has been described in a recent article. It does make ser­ vicing a whole lot easier. With the set mounted on the servic­ing jig, all the components were carefully inspected. The black “moulded mud” paper capacitors were replaced with ceram­ ic and polyester capacitors. It isn’t always easy to just desolder compo­ nents as they often have their leads wound around and through terminal points. If they can’t be desoldered Sitting the receiver on a servicing jig makes it easier to inspect and service. easily it will be necessary to cut them out, unfortunately. As a newcom­ er it is much easier to replace all units rather than try to test them. An important tip – remove and re­ place only one component at a time, as it is very easy to forget which lead goes where. It is not my usual policy to replace all paper capacitors, just those that are in critical locations and leaky – usually around half of them. Despite the physical damage to several of the capacitors in this radio, cracked ends in particular, they generally had much less leakage than normal as tested on a high-voltage tester. All replacement capacitors should have the same values and voltage rat­ ings as the originals, although I often use 50V ceramic ca­ pacitors in the AGC circuit, at the volume control and as cathode bypasses, as the voltage across them is quite low. The lowest voltage paper capacitors were 200V. The wiring will probably be in plas­ tic covered hook-up wire and should be in good condition. I tested all the resistors in the set and two were found to have gone high in value and out of tolerance. In most cases, the resistors can be tested in circuit. However, quite often there are parallel paths with other resis­tors which give erroneous readings. In these cases it is neces­sary to unsolder one of the leads from the circuit and test across the resistor. It is desirable to know the colour code for resistors or have access to a resistor colour code chart. I checked the dial lamps and re­ placed them. If they test OK but the glass is blackened, replace them any­ way as they won’t have a lot of life left. Checking for shorts Now an important test. With a DMM set to a high Ohms range measure be­ tween the chassis and the Active and Neutral mains leads. There should be a very high reading (many meg­ohms) or over-range. This is not the best method of checking that the power transformer insulation is good but it does check for direct shorts. Use a safety switch The DMM resistance check is handy but it is more practical to obtain a Safety Switch (RCD, earth leakage detector or whatev­er you like to call them) as it will quickly detect any dangerous leakage to earth in anything attached to it. Note too that dangerous voltages are present in valve receivers, so don’t touch any part of the circuit while a set is switched on. To test the receiver, attach an earth lead to it, connect it up via the Safety Switch and apply power. If there is dan­ gerous leakage the device will trip, removing power before damage is done to anything or anyone. I use one all the time and I strongly suggest that you do too. All being well, which it is 99.9% of the time, I then turn the power on December 2000  81 no increase in temperature. If there is, that capacitor has excessive leakage current and should be replaced. In this set, the capacitors formed up quite quickly, so none required re­ placement. However, they could still require replace­ment if hum becomes evident in the audio. To check if an electrolytic capacitor has lost its ca­pacitance, try bridging a similarly rated capacitor across the one that you are checking. Remember that electrolytic capacitors are polar­ ised and must be connected positive to positive, and negative to negative or the capacitor may be ruined. If the hum disappears when you bridge the suspect capacitor, it proves that it is defective and should be replaced. Checking the audio stage This above chassis view shows the modification which was necessary to peak the loop stick tuning at the low frequency end of the dial. with the dial lamps installed but no valves in the sockets. I run the set for perhaps half an hour and check the transformer for heat rise. It should just be above cold; certain­ly not hot. Testing the power supply I then switch off and check with the multimeter (using one or more ohms ranges) that there is no short circuit between the high tension (HT) line (the plus terminal of the first elec­ trolytic capacitor) and the chas­ sis. It should not be lower than around 47kΩ. If it is, I check to see why and correct the problem. A short­ed capac­ itor (eg, one of the electro­lytics) is a likely source, as the paper capacitors have already been replaced. Next, I set the multimeter to a high DC voltage range and connect it across the HT rail using insulated clip leads. I then fit the rectifier valve but leave all the other valves out. The next step is to turn the set on and observe both the rectifier and the multimeter, as the rectifier warms up. All being well, the hight tension (HT) voltage will rise quickly as the valve warms. If it doesn’t, look at the rectifier; if its plates are glowing red, you have a short that has developed with the application of voltage. The way to check this is to switch off and disconnect each of the elec­ trolytic capacitors and see what 82  Silicon Chip happens when power is reapplied. If there are still problems, the rectifier may be faulty or there is some other voltage-dependent short. It will even­ tually be found, by progres­sively dis­ connecting bits and pieces. Warning: make sure that the voltage on the HT rail has fallen to a very low value before disconnecting the electrolytics; ie, they must be discharged. Forming the capacitors Having sorted out any shorts, it is quite likely that the electrolytic capacitors may need forming – the more modern ones don’t need much attention in this regard. “Forming” is the devel­opment of an insulating dielectric layer in the capacitor with applied voltage. This layer deterio­ rates over a period through lack of use. Turn the set on again and observe the voltage rise until it nearly stabilis­ es. Now turn the set off and observe how quickly the voltage disappears. Initially this is fairly quickly. Leave it about a minute and go through the same procedure again. Do this several times, until such time as the voltage drops quite slowly – providing there is no bleeder resistor from the high tension to chassis. If all appears well, leave the set to run for a few minutes, turn off and then feel each of the electrolytic capaci­tors. There should be little or The AWA 467MA has only one audio stage, a 6BV7. I check that the speaker transformer primary has continuity between the plate and the high tension (HT) output of the sup­ ply. Make sure the set is off and that the HT voltage has dropped to zero before connecting your multimeter (switched to Ohms) across the trans­ former. The reading will usually be in the range 300Ω to 500Ω. If there is no continuity, the speaker transform­ er will need to be replaced. Faulty speaker transformers are common, unfortunately. Next, I reconnected the test leads across the HT to chassis and set the multimeter to a high DC volts range again. I fitted the 6BV7 valve with the set turned off and then turned it on. As expected, the DC voltage was not as high now, as the valve was drawing current. To check the current, turn off the power and connect the multi­meter across the back bias resistor – ie, the one from the transformer centre tap to earth. Most of the last valve sets used back bias and in this particular set, the bias voltage developed is around 4V. With a 6M5, it would have been up around 7V and with a 6V6GT or 6AQ5, it would be around 12V. All the tests so far had been quite success­ful. Alignment The next step I take is to install the remainder of the valves and connect an aerial and earth. Once the set warmed up, there were signs of activ­ ity and I was able to tune in a number of stations. I check the tuning range and the intermediate fre­quency (IF) response with a signal generator. As a newcomer, it is unlikely that you will have one, hence it is desirable to leave the alignment alone or if possible take it to another enthusiast and ask him/ her to align the receiver for you. In this receiver, I found that the IF response was slightly out and it was adjusted for optimum performance. I did run into trouble with the loop stick aerial coil adjustment at the low-frequency end of the dial. The coil is held in position on the rod with some sticky gunk. It had gone very hard and I could not shift the coil along the rod to get peak performance at that end of the dial. In one of the photos, it can be seen that I have added some wire and wound it around the rod to peak the performance. It was necessary to wind one turn of wire on the rod in anti-phase to peak the performance. This was a messy job but the end re­ sult was improved performance. The technique for doing this will have to wait until another time. A sparkling cabinet This set’s cabinet was in good order so it didn’t take a lot of work to make it look loved again. I usually wash the plastic cabinets in warm soapy water in the laundry sink. If the cabinet has any transfers in it such as valve place­ ment or simi­lar, try to make sure that they don’t get wet or they may disin­ tegrate. Often receivers of this vintage have had the odd sticky transfer put on them by the teenagers of the family and these need to be soaked off. A nail brush or an old toothbrush makes an ideal scrubbing tool to get the gunk off the surfaces. The knobs usually respond to a good scrub too. Once they’re thoroughly clean, rinse them in clean water and leave to dry. Once dry, the clean but dull looking cabinet and knobs need a dose of au­ tomobile cream cut and polish. Read and follow the instructions on the tin and the end result will be a sparking receiver cabinet. Summary You may have noticed over the time I have been writing these articles that I seem to have very few nasty faults in sets. I believe this is because the faults have been removed by replacing components that are usually faulty and not turning the set on until all of these things have been attended to. In the later period of valved equip­ ment, valves proved to be quite reli­ able. I average around none to one valve per set re­stored. The old saying in the valve days was “it’s probably just a valve”. However, I have found the most likely fault to be a leaky paper capacitor. With everything operating and clean, it is just a matter of putting the chassis back into the cabinet, putting the knobs on and standing back, admiring and listening to your first restora­tion success. As time goes by, you will become more venturesome and will restore some very elaborate pieces of our radio history, but you won’t forget your first restoration. SC ELECTRONIC VALVE & TUBE COMPANY The Electronic Valve & Tube Company (EVATCO) stocks a large range of valves for vintage radio, amateur radio, industrial and small transmitting use. Major current brands such as SOV-TEK and SVETLANA are always stocked and we can supply some rare NOS (New - Old stock) brands such as Mullard, Telefunken, RCA and Philips. Hard to get high-voltage electrolytic capacitors and valve sockets are also available together with a wide range of books covering valve specifications, design and/or modification of valve audio amplifiers. PO Box 487 Drysdale, Victoria 3222. Tel: (03) 5257 2297; Fax: (03) 5257 1773 Mob: 0417 143 167; email: evatco<at>mira.net New premises at: 76 Bluff Road, St Leonards, Vic 3223 Silicon Chip Binders REAL VALUE AT $12.95 PLUS P&P  Heavy board covers with 2-tone green vinyl covering  Each binder holds up to 14 issues  SILICON CHIP logo printed on spine & cover Price: $A12.95 plus $A5 p&p each (Australia only) Car polish and elbow grease result in a pristine appearance, adding to the satisfaction of a restored receiver. 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. December 2000  83 PRODUCT SHOWCASE Wireless networking from Microgram If you're looking for the ultimate Christmas present – for the person who really does have everything – how about this do-it-yourself Wireless Networking system from Micro-gram Computers. While wireless networking was first introduced for laptops and notebooks (and indeed this system is suitable for those) it has now come down to more affordable levels – to the point where it’s a viable proposition for home and small office PCs. It's the perfect answer when you don’t want to (or cannot) run network cables. We plan to present a full review of this system in the January issue of SILICON CHIP but thought we should at least mention it here – just in time for Christmas! 84  Silicon Chip If you liked the idea of the giant Santa & Rudolph Chrismtas deco­ ration last month* but didn’t like the idea of building it yourself, Jaycar Electronics stores have a huge range of Christmas lighting decorations – from tiny to huge – which is sure to get lots of “oohs” and “aahs” around December 25! Full details are available from Mi­ crogram Computers either by phone, fax or website. Contact: Microgram Computers Unit 1, 14 Bon Mace Close, Berkely Vale NSW 2261 Phone: (02) 4389 8444 Fax: (02) 4389 8388 website: www.mgram.com.au New Dick Smith Electronics PowerHouse opening at Warringah Mall, Brookvale Dick Smith Electronics will open its eighth PowerHouse store, at Warringah Mall in Sydney’s northern beaches area, this month. PowerHouse stores are divided into four main ‘zones’ – electronics, entertainment, communications and computers. Everything at a Dick Smith Electronics PowerHouse is plugged in, powered up and fully tuned for customers to try out. The new store, located on the ground floor of Warringah Mall, covers 2,000 square metres (about six times the size of an average DSE store) with over 30,000 products in its range. Since news of the PowerHouse store had become known, there had been some conjecture about the future of the current Dick Smith Electronics store at Warringah Mall, which itself had been tripled in size and refurbished only two months ago. A Dick Smith Electronics spokesper­ son said that the company was happy to keep both stores operating despite their close proximity. “We have oth­ Jaycar can really light up your Christmas! ers close together and operating very well, though none quite as close as in Warringah Mall." The Santa Sleigh shown above, for example, is a huge 184 x 181cm and sells for $458.00. If that’s a bit too much for you, other Christmas lighting designs start at less than $20. Most are designed to be used outdoors as well as inside. For more information visit your nearest Jaycar Electronics store. They're also displayed on the Jaycar Electronics website, www. jaycar.com.au * Kits for the Santa & Rudolph Christmas Lights Display, featured in the November issue of SILICON CHIP, are now available through Jaycar and DSE. World's worst manual contest Just a reminder for the holiday season: “when all else fails, read the manual”. Have you ever been so frustrated with a manual or set of instructions that you cursed the author and wished you had never bought the product? Do you remember the last time you used “Help” on your computer and every click of the mouse led to a new set of decisions? Does this sound familiar? How about $US500 for your frustration? Technical Standards, Inc. (TSI), a Southern California documentation services company, is offering $US500 for the winning entry in their ‘Worst Manual Contest.’ Send a manual or set of instructions that is hard to understand, poorly written, or just plain wrong. Send it if it has bad grammar, Free Data Analysis Reference Book & CD Tektronix has developed a reference book and CD-ROM aimed at teaching design en­ gineers and technicians how to use popular software to analyze oscilloscope data. The book, titled "Oscilloscope Connectivity Made Easy" covers programs such as Microsoft Excel, Mathcad and MatLAB. It is geared to­ wards those who need to quickly analyse and organise their oscilloscope data using standard PC-based analysis tools. Based on Tektronix' TDS7000 series of scopes, the book explains and illustrates how useres can easily capture, analyse and archive data automatically using off-the-shelf programs. The book and its accompanying Contact: CD can be ordered directly from the Tektronix Australia Pty Ltd Tektronix website or by phone (see Phone: 1800 023 342 details below). Website: www.tektronix.com/ It is valued at $US149 but it is scopes_accessories free of charge until March 31 2001. AUDIO MODULES broadcast quality Manufactured in Australia Harbuch Electronics Pty Ltd 9/40 Leighton Pl. HORNSBY 2077 Ph (02) 9476-5854 Fx (02) 9476-3231 Free organ concert invite Yokogawa 2GSa/s 500MHz DSO The new DL7200 Digital Storage Oscilloscope from Yokogawa offers up to 500MHz bandwidth and 2GSa/s sampling rate. It also offers up to 16MW of memory, fast screen updates (30 per second), all-points display and easy-to-use zoom and search functions. However, Yokogawa maintain that while wide bandwidth and fast sam­ pling are important, long memory is critical in reliably capturing high too much legalese, is poorly translated, or has missing steps. If it is the worst entry, you will win $500. “Everyone has had trouble with a manual,” said Michelle Wier, Director of Operations of Technical Standards, Inc. “That's why we started our company. People like products they understand how to use, and good technical documentation reduces the need speed events. This DSO can sample at 2GSa/s even with a time window of 8ms (or 16ms at 1GSa/s). The new pattern search function makes it easy to locate specific signal patterns (up to 64 bits long) anywhere in the long memory, making it ideal for debugging serial bus applications. The DSO also offers ethernet capability, making it simple to connect to a PC via a network, print to a network printer or even receive error information from remote instruments using the email function. GPIB and RS232C commu­ nication are also included. Contact: Yokogawa Australia Pty Ltd Locked Bag 29, Rydalmere NSW 2116 Phone: (02) 9805 0699 Fax: (02) 9888 1844 email: measurement<at>yokogawa.com.au for technical support.” You don’t have to send the whole manual; excerpts of the worst parts are OK. The deadline for submissions is January 15, 2001, so check those Christmas gifts for potential entries. Entries must be in English. For complete contest rules see the TSI Web site at www. tecstandards.com OK, so it’s not quite a product. But it’s certainly a showcase! We know that many SILICON CHIP readers are also theatre/pipe organ fans – so here’s a freebie which will be of interest to you. The Friends of Sydney Town Hall Organ (FOTSTHO) are inviting anyone and everyone to attend this year’s Christmas Concert in Sydney Town Hall. It will of course feature one of the most amazing, famous and exciting musical instruments in the world – the 110-year-old Sydney Town Hall Pipe Organ. Spectacular and massive to look at, this restored organ has nearly 9000 pipes, ranging from just a few centimetres long to almost 20 metres (a full-length 64-ft monster). There are six keyboards – five for the hands and one for the feet. (For more info on this beautiful organ visit http:/www. cityofsydney.nsw.gov.au) The concert is on Tuesday 19th December from 8 to 9.30pm and will also include the Castle Hill RSL Youth Band, Kevinwood Hand Bells, choirs and Robert Ampt (the City of Sydney Organist) on the keyboard(s). And again to remind you – admission is free. December 2000  85 TRONICSHOWCASELECTR EMC Technologies' internationally recognised Electromagnetic Compatibility (EMC) test facilities are fully accredited for emissions, immunity and safety standards. EMC Technologies Melbourne: (03) 9335 3333 Sydney: (02) 9899 4599 MicroZed Computers GENUINE STAMP PRODUCTS NEW! HC-5 hi-res Vi deo Distribution Amplifier DVS5 Video & Audio str Di ibution Amplifier VGS2 Graphics Splitter FROM Scott Edwards Electronics microEngineering Labs & others Easy to learn, easy to use, sophisticated CPU based controllers & peripherals. PO Box 634, ARMIDALE 2350 (296 Cook’s Rd) Ph (02) 6772 2777 – may time out to Mobile 0409 036 775 Fax (02) 6772 8987 http://www.microzed.com.au Most Credit Cards OK Five identical Video and Stereo outputs plus h/phone & monitor out. S-Video & Composite versions available. Professional quality. For broadcast, audiovisual and film industries. Wide bandwidth, high output and unconditional stability with hum-cancelling circuitry, front-panel video gain and cable eq adjustments. 240V AC, 120V AC or 24V DC High resolution 1in/2out VGA splitter. Comes with 1.5m HQ cable and 12V supply. Custom-length HQ VGA cables also available. Check our NEW website for latest prices and MONTHLY SPECIALS www.questronix.com.au Email: questav<at>questronix.com.au Video Processors, Colour Correctors, Stabilisers, TBC’s, Converters, etc. QUESTRONIX All mail: PO Box 548, Wahroonga NSW 2076 Ph (02) 9477 3596 Fax (02) 9477 3681 Visitors by appointment only Marantz SR-14EX “top of the line” home theatre receiver If you have an idle $6990, the allnew Marantz SR-14EX can take pride of place in your Home Theatre setup. For your money, you’ll get Dolby Digital and DTS surround sound along with Zoran's new format THX Surround EX capability. THX Surround EX format decodes an additional back surround channel from suitably encoded DVDs, providing a more realistic surround sound environment with smoother 360° surround effects and more pre­ cise localisation behind and beside the viewer. The SR-14EX also incl-udes THX post processing for the most accurate possi­ ble reproduction of movie soundtracks in the home. 24-bit 192kHz D/A con­ verters on all five main channels plus a separate DSP chip and 24-bit A/D converter to provide the highest resolution playback 86  Silicon Chip from multi-channel movies and 96/24 DVD audio discs. HDCD decoding and pro-cessing is included for HDCD-en­ coded compact discs. Three sets of component video in­ puts, an extensive array of digital and analog inputs, outputs and switching facilities, front panel A/V inputs and an RF input (for use with Dolby-Digital encoded laser discs) are just some of the processing capabilities. The am­ plifier delivers 140W (8Ω) into each of its five main channels. Tone controls operate in the digital domain on all main channels. A precision AM/FM tuner is also built in, as is an icon-based multi-lin­ gual on-screen display. The SR-14EX is somewhat “future proofed” by provid­ ing six channel direct output to accom­ modate future surround sound formats plus 7.1 channel pre-amp outputs for connection to external amplifiers or subwoofers. An RC-5000 Programmable Remote Control (which can be used with every component in a home entertainment system) is also included. Marantz equipment is dis­ tributed in Australia by Jamo SC Australia. Contact: Jamo Australia Phone: (03) 9543 1522 Fax: (03) 9543 3677 email: info<at>marantz.com.au R 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. Electronic brakes for model tram I would like to develop an electron­ ic braking system for my miniature trams, that is more efficient and less severe than just reversing the power, an action which usually results in the driving wheels spinning without traction. The circuit used to power the trams runs at 24V DC. The amperage is unknown but can peak at quite a bit more than 20A, as follows. With the driving wheels off the track, such that there is no load, the motor draws about 6.9A. With the tram travelling on the flat and no passengers, the motor draws about 14.9A and when the tram starts on a gradient, the cur­ rent jumps quick­ly to beyond 20A (which is the limit of my measuring equipment). Hopefully, the peak will be less than 50A. The motors are 12V generators which have had their field coils’ earth isolated from their brushes’ earth, such that re­verse motion is obtaina­ ble. Could the Railpower controller of April 1988 be modified to provide Metal locator adjustment problem I have built the Induction Bal­ ance Metal Locator from the May 1994 issue of SILICON CHIP and I’m having trouble balancing the coils. I can’t seem to get it much below 4V. I think I have followed your instructions to the letter. I have been fault finding the circuit but as yet have drawn a big zero. Any sugges­ tions would be appreciated. (R. S., Wodonga, Vic). • The output from TP1 should be closer to 1V rather than 4V. A reading of 4V suggests that either the .01µF capacitor at the wiper of VR1 is leaky or there is a problem on the PC board causing the volt­ age to be high. Check also that the reverse smooth pulse braking at 24V and up to 50A, such that the brakes can be applied smoothly? Plus, could it also have two sets of power transistors since I am likely to use two motor set-ups per tram due to the steep track gradient in use, and thus will need two separate brakes controlled by a single circuit? (B. B., St. Andrews, NSW). • The Railpower circuit could not easily be upgraded to 50A. In any case, the accepted way of braking is to short the DC output of the motor. Have a look at the 50A DC Speed Control in the May 2000 issue – it had braking incorporated. Controlling a regulator with an op amp I have been reading your recent “Electronics TestBench” magazine and noticed the Dual Tracking Power Supply. This has given me an idea for solving a problem I have. I need to be able to con­trol the output voltage of an LT1038 10A regulator (which is similar to an LM338 but heavier cur­ rent) from an external voltage supply 330kΩ resis­tor and 0.1µF capacitor between pin 5 of IC1c and ground are OK. Alternatively, the coil coupling between L1 and L2 may be incor­ rect. Note that the adjustment is rather critical and must be done away from any metal objects. So adjust the overlap cou­pling between the two coils very slowly and care­ fully so that the voltage at TP1 drops to a low value. This adjustment sets the sensi­ tivity of the search head to metal objects and a high vol­tage will give reduced sensitivity. The adjustment may take several attempts as you develop a “feel” for how the volt­ age changes with coil movement. The voltage should rise as metal is brought near the search head. (actually the output of a PC DAC card). The idea of using an op amp to do the control work is one which I think would work well. But I need it to control a posi­tive regulator with a positive control signal of 0-10V. The input to the regulator will be about 32V and the output from 1.25V to 24V. Can you think of a way to adapt the tracking negative side of the dual power supply to accomplish this? (C. H., via email). • The regulator can be controlled using an op amp. Since you want to provide a 1.25V to 24V output with a control voltage from 0-10V, the op amp’s gain would need to be 2.28. Using an LM358 op amp and the input voltage to provide the power supply rails, connect the op amp output to the adjust terminal of the regula­tor. Connect the op amp up as a non-inverting amplifier with a gain of 2.28. Thus the feedback resistor will need to be 1.28 times larger than the resistor from the inverting input to ground. This is because the gain of the non-inverting amplifier is 1+ the feedback resistor gain setting. (ie, use a 1kΩ resistor from the inverting input to ground and a 1.3kΩ resistor from inverting input to output). The non-inverting input then connects to the 0-10V control voltage. Fitting CDI to a Mazda rotary In John Clarke’s article on the Mul­ ti-Spark CDI system in the September 1997 issue of SILICON CHIP, he refers only to using the kit in vehicles equipped with a distributor. I would like to use this kit in a Maz­ da that has a 13B rotary. The 13B has no distributor but fires the four plugs directly from two coils – each coil having two plug leads coming from it. One coil fires the “leading” set of plugs while the other fires the “trailing” set of plugs. It is relative­ ly common on the 13Bs to use the American MSD 6A ignition amplifier running through the leading coil only. December 2000  87 Audio compressor design query I have found an apparent prob­ lem in the “1-Chip Microphone Audio Compressor” presented in the March 1999 issue of SILICON CHIP. In your article, on page 58 in the specifications section, the `Ratio control’ entry mentions a ratio of compression between 1:1 and 15:1, with a pot centre setting of 7:1. However, in the data sheet for the SSM2166, a table on page 4 indicates that a compression ratio of 15:1 is achieved using a 395kΩ resistor between pin 10 and ground, and your circuit on page 58 and the parts list both indicate use of a 50kΩ pot to ground, clearly suggesting a maximum compres­ sion ratio of around 3:1. Would you care to comment on this discrepancy? (C. A., Brisbane, Qld). • The data sheet that we have from Analog Devices concerning (Amplifiers on the trailing coil are not recommended). Any advice would be greatly appre­ ciated. (H. W., via email). • You will need two kits – one for each coil. Alternatively, you could just use one kit to fire the coil for the leading spark plug in each chamber. Questions on interfacing I have three specific questions which are basically simple but I can find no satisfactory reference to these in my technical library or on the “web”. First, how can the output of a microcon­troller be optimally inter­ faced to low current devices such as LEDs or higher current devices such as DC relays, in order to minimise sinking current from the MCU. Second, is there a “rule-of-thumb” method for determining the appropri­ ate values of capacitor (and perhaps resistor) re­quired to provide a “sparkquench” across the contacts of a DC relay? Third, is there any PC-based application/stationery avail­ able at reasonable cost to assist in artwork production for projects? It seems to 88  Silicon Chip the SSM2166 shows values from pin 10 to ground varying from zero ohms for 1:1 compression up to 49kΩ for a 15:1 compression at a 300mV limiting rotation point. For a 1V RMS rotation point, which would be the normal setting, the value of resistance for 15:1 com­ pression would be 32kΩ. These values are found on page 4 and Fig.5. Thus, the 50kΩ pot for VR3 is correct. Note that the compression ratio is somewhat interdependent on the rotation point setting (at pin 11) and the actual position of the compression knob does not show a precise compression ratio setting. The compression range was tested using the 50kΩ pot at pin 10 and we did obtain 1:1 up to 15:1 compression as stated. Use of a 395kΩ pot (500kΩ) would only produce a control which operates over the first 25% of travel. The final 75% of travel would have no effect and maintain the compres­ sion at the maximum 15:1. me that software such as CorelDraw would be suitable for the design but whether such stationery is available is a mystery! (A. L., Ringwood East, Vic). • Have a look at the Multi-Purpose I/O Board For PCs in the March 1991 issue. It will drive relays or LEDs. We can supply the issue for $7.00 including postage. We don’t know of any rules of thumb for RC damping circuits across relay contacts. A reverse-biased diode is simpler and more effective. As far as artwork production is con­ cerned, do you mean for PC boards or front panels? For PC boards you could use Protel Easytrax (public domain). For front panels you can even use a word processor such as Word. Motorbike CDI wanted Can you please advise where I might find a circuit design for a simple Capacitor Discharge Ignition system? I want to fit one to a motor-cycle. It has a charging coil, already in the alterna­ tor, a pickup coil, for triggering but it doesn’t have a battery. (J. P., via email). • The only CDI system we have described is the Multi-Spark CDI in the September 1997 issue but it does require a battery and it isn’t simple. We understand that you want a mag­ neto-charged CDI system (as on some modern bikes) but unfortunately we have not described a suitable circuit. If sufficient readers are interested in such a project, we’ll have a look at developing a suitable circuit. How to measure to 99,000 RPM I was wondering if you could help me with some info about the 5-Digit Tachometer project in the October 1997 issue. The specs say that the maximum RPM reading is 60,000. What are the factors limiting the reading to 60,000? I would like to measure up to 99,000 RPM. Is this possible? (C. W., via email). • The factors limiting the maximum rpm reading are the .056µF input filter capacitor and .056µF capacitor at the collector of Q1. The 100pF capacitor between pins 6 & 7 of IC, the phase lock loop, is another limiting factor. You could reduce these values to say .027µF and 68pF, respectively, to ob­ tain the required 99,000 RPM. High charge rates from battery charger I have just completed the Mul­ ti-Purpose Battery Charger described in February & March 1998. Having got it to go, I found to my amazement that the charge current was a whopping 3A and the discharge current 2.02A. I had plugged in four 1.2V NiCd torch cells that had a 1.2A.h rating and they charged and discharged OK but I’m a bit concerned at the charging rates. Also, the inductor buzzes. The big question is this: is your circuit designed to charge only big gel pack batteries, ie, radio batteries, car and bike batteries, and phone and drill battery packs? I wanted to charge NiCd AAA, AA & D cell types. (K. T., via email). • The Multi-Purpose Fast Battery Charger was designed to provide a nominal 6A of charge current and 2A discharge.This was stated in the specifications and should not come as a surprise. We stated that it is suitable for tools, camcorders, RC equipment and car batteries. It is probably not really suitable for AAA cells. However, the method of detecting the end-point for charging should prevent dam­ age to any of your cells or batteries whether AA or larger. We suggest using the thermistor for end­ point detection when charging the smaller NiCd types, to prevent overheating of the cells. Buzzing or squeal in the transform­ er is normal. It can be quietened by potting the windings in epoxy. Using the Champ as a preamp I wanted to ask if I can use the Champ, a 0.5W amplifier described in February 1994, as a preamplifier. What would the frequency response of this kit be? I want to install it between a Dolby receiver and a subwoofer amplifier, as the receiver’s pre-out signal isn’t enough for the subwoofer amplifier. Would I lose the low end using the Champ? (D. C., via email). • You can use the Champ as a preamp. Provided you don’t load the output of the little amplifier with 8Ω but couple straight into your subwoof­ er amplifier, the frequency response should be flat down to below 10Hz. However, you will probably need to set the on-board pot well down because you won’t need all the gain. Blocking capacitor in phone line I am working on a project that re­ quires me to connect to a telephone line. Wanting to “do the right thing”, I purchased a 600Ω isolation transform­ er (Austel approved). My application requires a telephone to be connected Amplifiers wanted for computer surround sound I have been looking for suitable kits to build to provide good sur­ round sound for my computer. My computer has a Sound­Blaster Live card which provides front and rear line outputs. Not a lot of power will be required – say 10-15W RMS per channel for the front and rear – but I have no idea how much power is required for a sub-woofer channel. in parallel with the project for engi­ neering/monitoring purposes before switching to the project. Having built the prototype, I con­ nected everything up and the phone worked fine (I heard dial tone). When I switched in the project, the phone died. I measured the line voltage and found 0.7VDC! When “on-hook” the phone line read 47V and 6V when “off-hook”. When I measured the transformer resistance, I got 21Ω! No wonder there was no voltage to drive the phone. So why do they quote 600Ω for the transformer when it clearly isn’t? As a footnote, I returned to Jaycar and checked out some other ones and came up with similar results. How can I use these so-called isolation trans­ formers and still have a telephone connected and operational? Do I put a 600Ω resistor across the line and use capacitors in series with the transformer leads? (I. B., Monash, ACT). • You need a blocking capacitor in I was thinking of using a couple of your “15W/Channel Class-A Stereo Amplifier” kits for the front and rear and I’m not sure what to use for the sub-woofer. • Have a look at our 50W module described in March 1994. If you don’t want the full 50W, just run it with reduced DC sup­plies. Kits are available from Altronics, Jaycar and DSE. We can supply the March 1994 issue for $7.70 including postage. Don’t use the 15W class A mod­ ule – it is too good and too expen­ sive for your application. series with the primary of the isola­ tion transformer. Try a 10µF 100VW bipolar capacitor. The transformer primary and sec­ ondary winding can be ex­pected to have quite a low DC resistance. The 600Ω rating refers to the impedance of the phone line circuit not the trans­ former. If the transformer winding re­ sistance was high, it would intro­duce large losses into the circuit. Notes & Errata 50W Amplifier Module, March 1994: the 22µF capacitor con­nected to pin 8 on the LM3876 is shown reversebiased on both the circuit and wiring diagram. The 220µF capacitor con­ nected to the negative supply rail is also connected the wrong way on the circuit but is correctly shown on the wiring diagram. Modules that have been running for more than a few hours should have the SC 22µF capacitor replaced. 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. December 2000  89 REFERENCE GREAT BOOKS FOR AUDIO POWER AMP DESIGN HANDBOOK NEW NEW NEW NEW INDUSTRIAL BRUSHLESS SERVOMOTORS By Douglas Self. 2nd Edition Published 2000 85 $ By Peter Moreton. Publ. 2000 From one of the world’s most respected audio authorities. The new 2nd edition is even more comprehensive, includes sections on load-invariant power amps, distortion residuals, diagnosis of amplifier problems, and much more. 368 pages in paperback. VIDEO SCRAMBLING AND DESCRAMBLING for If you've ever wondered how they scramble video on cable and satellite TV, this book tells you! Encoding/decoding systems (analog and digital systems), encryption, even schematics and details of several encoder and decoder circuits for experimentation. Intended for both the hobbyist and the professional. 290 pages in paperback. NEW 2nd TCP/IP EXPLAINED 99 AUDIO ELECTRONICS Satellite & Cable TV by Graf & Sheets Edition 1998 $ By John Linsley Hood. First published 1995. Second edition 1999. 65 $ This book is for anyone involved in designing, adapting and using analog and digital audio equipment. It covers tape recording, tuners and radio receivers, preamplifiers, voltage amplifiers, audio power amplifiers, compact disc technology and digital audio, test and measurement, loudspeaker crossover systems, power supplies and noise reduction systems. 375 pages in soft cover. By Philip Miller. Published 1997. $ 99 By Tim Williams. First published 1991 (reprinted 1997). $ LOCAL AREA NETWORKS: An Introduction to the Technology 65 Includes grounding, printed circuit design and layout, the characteristics of practical active and passive components, cables, linear ICs, logic circuits and their interfaces, power supplies, electromagnetic compatibility, safety and thermal management. 302 pages, in paperback. ELECTRIC MOTORS AND DRIVES By John E. McNamara. 2nd edition 1996. By Austin Hughes. Second edition published 1993 (reprinted 1997). 69 $ For non-specialist users – explores most of the widely-used modern types of motor and drive, including conventional and brushless DC, induction, stepping, synchronous and reluctance motors. 339 pages, in paperback. ESSENTIAL LINUX EMC FOR PRODUCT DESIGNERS 99 90  Silicon Chip Widely regarded as the standard text on EMC, this book provides all the information necessary to meet the requirements of the EMC Directive. It includes chapters on standards, measurement techniques and design principles, including layout and grounding, digital and analog circuit design, filtering and shielding and interference sources. The four appendices give a design checklist and include useful tables, data and formulae. 299 pages, in soft cover. 65 $ By Steve Heath. Published 1997. By Tim Williams. First pub­­lished 1992. 2nd edition 1996. $ 85 $ THE CIRCUIT DESIGNER’S COMPANION Assumes no prior knowledge of TCP/IP, only a basic understanding of LAN access protocols, explaining all the elements and alternatives. Combines study questions with reference material. Examples of network designs and implementations are given. 518 pages, in paperback. Want to become more familiar with local area networks (LANs) without facing the challenge of a 400-page text? . Gives familiarity with the concepts involved and provides a start for reading more detailed texts. 191 pages, in paperback. Designed as a guide for professionals and a module text for electrical and mechanical engineering students. A step-by-step approach covering construction, how they work, how the motor behaves and how it is rated and selected. It may only be a small book but it has outstanding content! 186 pages in hardback. $ 85 Provides all the information and software that is necessary for a PC user to install and use the freeware Linux operating system. It details, setp-by-step, how to obtain and configure the operating system and utilities. It also explains all of the key commands. The text is generously illustrated with screen shots and examples that show how the commands work. Includes a CD-ROM containing Linux version 1.3 and including all the interim updates, basic utilities and compilers with their associated documentation. 257 pages, in paperback. BOOKSHOP WANT TO SAVE 10%? SILICON CHIP SUBSCRIBERS AUTOMATICALLY QUALIFY FOR A 10% DISCOUNT ON ALL BOOK PURCHASES! ENQUIRING MINDS! (To subscribe, see page 57) ALL PRICES INCLUDE GST UNDERSTANDING TELEPHONE ELECTRONICS THE ART OF LINEAR ELECTRONICS By Stephen J. Bigelow. Third edition published 1997 by Butterworth-Heinemann. $ 59 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. By John Linsley Hood. First published 1993. NEW SECOND EDITION 1998. $ 88 00 This practical handbook from one of the world’s most prolific audio designers has been updated and amended to make it the leading practical source of information for those interested in linear electronics and its applications, particularly in the world of audio design. 348 pages, in paperback. DIGITAL ELECTRONICS – A PRACTICAL APPROACH By Richard Monk. Published 1998. 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 to date on TV and video technology. The book includes both theory and practical servicing information and is ideal for both students and technicians. 382 pages, in paperback. $ SETTING UP A WEB SERVER 59 By Simon Collin. Published 1997. $ O R D E R H E R E P&P 69 Covers all major platforms, software, links and web techniques. It details each step required to choose, install and configure the hardware and software elements, create an effective site and promote it successfully. 273 pages, in paperback  AUDIO POWER AMPLIFIER DESIGN...............................$85.00  INDUSTRIAL BRUSHLESS SERVO MOTORS..................$99.00  VIDEO SCRAMBLING/DESCRAMBLING..........................$65.00  TCP/IP EXPLAINED.........................................................$99.00  LOCAL AREA NETWORKS...............................................$69.00  SETTING UP A WEB SERVER..........................................$69.00  THE CIRCUIT DESIGNER’S COMPANION........................$65.00  ELECTRIC MOTORS AND DRIVES...................................$65.00  UNDERSTANDING TELEPHONE ELECTRONICS.................$59.00  AUDIO ELECTRONICS.....................................................$85.00  GUIDE TO TV & VIDEO TECHNOLOGY............................$59.00  EMC FOR PRODUCT DESIGNERS...................................$99.00  THE ART OF LINEAR ELECTRONICS ..............................$88.00  DIGITAL ELECTRONICS ..................................................$65.00  ESSENTIAL LINUX..........................................................$85.00               ORDER TOTAL: $...................... Orders over $100 P&P free in Australia. AUST: Add $A5.50 per book NZ: Add $A10 per book, $A15 elsewhere With this book you can learn the principles and practice of digital electronics without leaving your desk, through the popular simulation applications, EASY-PC Pro XM and Pulsar. Alternatively, if you want to discover the applications through a thoroughly practical exploration of digital electronics, this is the book for you. A free floppy disk is included, featuring limited function versions of EASY-PC Professional XM and Pulsar. 249 pages, in paperback. 65 $ SEE ELSEWHERE IN THIS ISSUE FOR: SILCON CHIP’s COMPUTER OMNIBUS SILCON CHIP’s ELECTRONICS TEST BENCH ZOOM EFI TECH SPECIAL SILCON CHIP BINDERS SILCON CHIP GIANT WALLCHART TAX INVOICE Your Name_________________________________________________ PLEASE PRINT Address ___________________________________________________ ___________________________________ Postcode_______________ Daytime Phone No. (______) __________________________________ STD Email___________________<at>_________________________________  Cheque/Money Order enclosed OR  Charge my credit card –  Bankcard  Visa Card  MasterCard No: Signature______________________Card expiry date PLUS P&P (if applic): $........................... TOTAL$ AU.............................. POST 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 FEBRUARY 2001  91 ALL TITLES SUBJECT TO AVAILABILITY. PRICES VALID FOR MONTH OF MAGAZINE ISSUE ONLY. ALL PRICES INCLUDE GST FEBRUARY 2001  91 Index to Volume 13: January-December 2000 Features 01/00 4 Protel 99: Much More Than A PCB Design Tool 01/00 11 Review: B&W Nautilus 801 Monitor Loudspeakers 02/00 4 HiFi Review: Marantz SR-18 Home Theatre Receiver 02/00 10 Review: The "Hot Chip" Starter Kit 02/00 42 Light Emitting Polymers For Flat-Screen Displays 03/00 4 Doing A Lazarus On An Old Computer 03/00 24 Inside An Electronic Washing Machine 03/00 33 Review: Multisim – For Circuit Design & Simulation 04/00 6 Review: Jamo Concert 8 Loudspeaker System 04/00 10 How To Run A 3-Phase Induction Motor From 240VAC 04/00 54 Atmel's ICE 200 In-Circuit Emulator 04/00 76 Mitsubishi's Diamond View DV180 LCD Monitor 05/00 4 The Smart Electronic Technology Inside A Furby 05/00 34 Dolby Headphone: Five Channels Of Surround Sound 06/00 4 Oooh, Aaaah! - Sony's New Digital Handycam 06/00 8 Review: PC-Controlled Blood Pressure Monitor 06/00 77 Review: TiePie Handyprobe HP2 07/00 4 Say Bye-Bye To Your 12V Car Battery 07/00 72 Review: Motech MT-4080A LCR Meter 07/00 80 Review: ADEM Compac II Security System 08/00 4 Drive By Wire: Electronic Throttle Control; Pt.1 08/00 26 Review: CircuitMaker 2000 Virtual Electronics Lab 08/00 70 Structured Cabling & The Krone MiliLAN 09/00 4 How They're Bringing You The Games 09/00 26 Network Troubleshooting With Fluke's NetTool 09/00 62 LA-CRO - A Must-Have For Students 10/00 4 DrDAQ: It Turns Your PC Into A Science Lab 10/00 10 Structured Data Cabling For The Home 92  Silicon Chip 10/00 70 Drive By Wire: Electronic Throttle Control, Pt.2 10/00 78 Review: Altronic's Aussie-Made PA Amplifiers 11/00 4 Quick Circuit 5000 PC Board Prototyping System 11/00 10 ShockLog: Monitoring The Things That Go Bump 11/00 72 Tektronix TDS7504 Digital Phosphor Oscilloscope 12/00 4 Home Networking For Shared Internet Access 12/00 26 Review: Agilent 54622D Mixed Signal Oscilloscope 12/00 78 Vintage Radio Special: Your First Restoration Computer Features 01/00 66 Project: Parallel Port Interface Card 03/00 4 Doing A Lazarus On An Old Computer 04/00 76 Mitsubishi's Diamond View DV180 LCD Monitor 06/00 8 Review: PC-Controlled Blood Pressure Monitor 09/00 26 Network Troubleshooting With Fluke's NetTool 10/00 4 DrDAQ: It Turns Your PC Into A Science Lab 12/00 4 Home Networking For Shared Internet Access Serviceman’s Log 01/00 18 Philips CR635 TV; Mitsubishi HS621 VCR; Mitsubishi HSM60 VCR; National M15L TV 02/00 75 Thomson RP46 Projection TV; Seleco SVT150 Projection TV; Dual Digital Concept TV4170 TV; Sony KV-X2931S TV 03/00 65 JVC HR-D750EA VCR; National TC1407 Portable TV; National NV-H70A VCR; Mitsubishi CT2584AS TV 04/00 42 Panasonic NV-F70A VCR; Sony KV-2964AS TV; Sony KV-C2911D TV 05/00 40 Pentium 133 Computer; Sherwood Home Theatre RV4070R Amplifier; NEC N3419 TV; Akai CT-21WA9AT; Philips 2SSP1788/75R TV 06/00 38 Akai VS765 VCR; Toshiba Bazooka Model 3408H TV; Teac MV1480MkII TV/VCR; Panasonic NV-HD100A VCR; Sharp VC-H85X Hifi VCR 07/00 54 Compaq Presario 4704 Computer; Compaq Armada 1573D Notebook; Panasonic TC29V26A TV; Grundig ST7075S TV; Philips 33FL1880/75R Matchline TV; AWA SC6341 (AS630) TV; Panasonic TC29V50A MX-2A 08/00 38 Philips KT3-A3 TV; NEC JC2002VM 5D Monitor; Brionvega TVC 9203 Stratos 2 TV; Sanyo VHRD-7770M VCR 09/00 38 Philips Matchline 28 DC2070/ 20R TV; Philips 20GR102S/ 75B TV; NEC N6361 63cm TV 10/00 34 Teac CTM-5928TXT TV; Teac CT-M488 TV; Sharp VC-H93X VCR; Grundig GCF404/ CUC2401 TV 11/00 54 Masuda MGV28AV TV; Blaupunkt IS70-33VCT TV; Mitsubishi CT-29ATS(A)TY TV 12/00 60 Philips KS786 TV; Grundig ST 95-775/9 TV; Panasonic NNC855B Microwave Oven; Akai CT2869AUS TV Vintage Radio 01/00 74 Building A Vintage Radio Replica 02/00 82 The Hellier Award; Pt.1 03/00 99 The Hellier Award; Pt.2 04/00 60 The Hellier Award; Pt.3 05/00 64 Making The Obsolete Useful Again 06/00 53 A Japanese 110V AC/DC Set 07/00 82 The AWA P1 Portable 11-Inch B/W TV Set 08/00 84 The Astor RQ Lady's Handbag Radio 09/00 84 HMV's Nippergram: A Classic 1950s Portable Radiogram 10/00 82 A Battery Eliminator & A Simple Servicing Aid 11/00 78 The Intriguing Philips "Philetta" 12/00 78 The AWA 467MA Circuit Notebook 01/00 78 Battery Charging From A 1V Or 2V Solar Panel 01/00 78 TTL Decision Maker 01/00 79 Paralleling The Output Of 3-Terminal Regulators 01/00 79 Buffered Virtual Ground Generator 02/00 68 Using A Photo-Interrupter As A Train Detector Projects to Build 05/00 16 Building The Ultra-LD Stereo Amplifier; Pt.2 05/00 56 LED Dice To Build 05/00 72 A Low-Cost AT Keyboard Translator 05/00 78 50A Motor Speed Controller For Models 06/00 14 Automatic Rain Gauge With Digital Readout 06/00 26 Parallel Port VHF FM Receiver 06/00 56 Li'l PowerHouse Switchmode Power Supply 06/00 62 CD Compressor For Cars Or The Home 07/00 10 A Home Satellite TV System 07/00 18 A Moving Message Display 07/00 30 Compact Fluorescent Lamp Driver 07/00 42 El-Cheapo Musician's Lead Tester 07/00 60 Li'l PowerHouse Switchmode Power Supply; Pt.2 08/00 16 Build A Theremin For Really Eerie Sounds 08/00 32 Come In Spinner: Message Wand 08/00 54 Loudspeaker Protector and Fan Controller 08/00 62 Proximity Switch For 240VAC Lamps 09/00 12 Building A Swimming Pool Alarm 09/00 32 An 8-Channel PC Relay Board 09/00 54 Fuel Mixture Display For Cars; Pt.1 09/00 69 Protoboards - The Easy Way Into Electronics: Build A Light Chaser 09/00 78 Cybug - The Solar Fly 10/00 22 Guitar Jammer For Practice And Jam Sessions 10/00 28 Booze Buster Breath Tester 10/00 38 Wand-Mounted Inspection Camera 10/00 53 Installing A Free-Air Subwoofer In Your Car 10/00 60 Protoboards - The Easy Way Into Electronics: Build A Siren And Alarm Timer 11/00 66 Fuel Mixture Display For Cars; Pt.2 11/00 13 Santa And Rudolph Christmas Display 11/00 30 2-Channel Guitar Preamplifier, Pt. 1 11/00 60 Message Bank And Missed Call Alert 11/00 66 Programmable Electronic Thermostat 11/00 86 Protoboards - The Easy Way Into Electronics: More Circuits Based On The 555 Timer 12/00 14 Build A LED Torch 12/00 36 2-Channel Guitar Preamplifier, Pt. 2: Digital Reverb 12/00 53 Driving An LCD From The Parallel Port 12/00 68 A Morse Clock 12/00 74 Protoboards - The Easy Way Into Electronics: The LM393 Dual Comparator 02/00 68 How To Cut Clean Holes In Plastic Front Panels 02/00 68 Monitor For 12V SLA Batteries 02/00 69 12V Fan Controller For Lower Noise 02/00 69 Constant Current Load For Power Supply Testing 03/00 38 PC Printer Port Controls I-V Curve Tracer 06/00 43 Adding LED Indication To 12V Trickler Charger 06/00 44 A Speed Controller For 240VAC Universal (BrushType) Motors 06/00 44 Low-Cost Logic Indicator For PICs 07/00 70 4-Wire Milliohm Tester For DMMs 07/00 70 Fine & Coarse Power Supply Control 07/00 70 Constant Voltage Charger Uses LM317 08/00 78 Soldering Iron Time-Out Circuit 08/00 78 Split Supply With Low Quiescent Current 08/00 79 Off-Hook Indicator Has Better Visibility 08/00 79 Mains Power For Battery-Operated Clock 09/00 76 Improved Engine Immobiliser Uses SCR 09/00 76 A Really Simple Transistor Tester 09/00 77 Adding A Timer To The NiCd Discharger 09/00 77 Different Colours From A Green LED 10/00 58 Opto-Electronic Version Of High Energy Ignition 11/00 76 Water Level Indicator 11/00 77 Do-It-Yourself Car Battery Charger 11/00 77 Hi/Lo Pulse Indicator Uses A 7-Segment Display 12/00 34 2-Channel Intercom 12/00 34 Solar System Regulator 03/00 107 Digital Voltmeter For Cars, February 2000 03/00 107 Remote Modem Controller, August 1999 07/00 92 RoomGuard Intruder Alarm, April 2000 07/00 92 LED Dice, May 2000 08/00 91 Simple Superhets, Vintage Radio, April 2000 08/00 91 Ultra-LD 100W Amplifier, March & May 2000 08/00 91 Digital Voltmeter For Cars, February 2000 08/00 91 Low Distortion Audio Signal Generator, February/March 1999 09/00 91 PC-Controlled VHF FM Receiver, June 2000 09/00 91 40V/1A Adjustable Power Supply, June/July 2000 09/00 91 Loudspeaker Protector & Fan Controller, August 2000 10/00 90 Structured Cabling Systems, August 2000 11/00 93 Opto-Electronic Ignition, Circuit Notebook, November 2000 12/00 89 50W Amplifier Module, March 1994 01/00 24 Spring Reverberation Module 01/00 38 An Audio-Video Test Generator 01/00 56 Build The Picman Programmable Robot 01/00 66 Parallel Port Interface Card 01/00 80 Off-Hook Indicator For Telephone Lines 02/00 14 Build A Multi-Sector Sprinkler Controller 02/00 24 A Digital Voltmeter For Your Car 02/00 38 An Ultrasonic Parking Radar 02/00 53 Build A Safety Switch Checker 02/00 58 A Sine/Square Wave Oscillator For Your Workbench 03/00 16 Build The Ultra-LD 100W Amplifier Module; Pt.1 03/00 40 Electronic Wind Vane With 16LED Display 03/00 72 Glowplug Driver For Powered Models 03/00 86 The OzTrip Car Computer; Pt.1 03/00 96 A Solution Waiting For A Problem: Aura Interactor Amplifier 04/00 14 A Digital Tachometer For Your Car 04/00 28 RoomGuard: A Low-Cost Intruder Alarm 04/00 48 Build A Hot Wire Cutter 04/00 64 The OzTrip Car Computer; Pt.2 04/00 72 Build A Temperature Logger Notes & Errata 01/00 93 The PC Powerhouse, December 1999 02/00 93 Switching Temperature Controller, August 1999 02/00 93 Refinements To The Computer Monitor Checker, Circuit Notebook, November 1999 December 2000  93 MARKET CENTRE Cash in your surplus gear. Advertise it here in Silicon Chip. FRWEEBE YES! Place your classified advertisement in SILICON CHIP Market Centre and your advert will also appear FREE in the Classifieds-on-the-Web page of the SILICON CHIP website, www.siliconchip.com.au And if you include an email address or your website URL in you classified advert, the links will be LIVE in your classified-on-the-web! S! D E I F I S C LAS EXCLUSIVE TO SILICON CHIP! CLASSIFIED ADVERTISING RATES Advertising rates for this page: Classified ads: $11.00 (incl. GST) for up to 12 words plus 55 cents for each additional word. Display ads: $27.50 (incl. GST) per column centimetre (max. 10cm). Closing date: five weeks prior to month of sale. To run your classified ad, print it clearly in the space below or on a separate sheet of paper, fill out the form & 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. Taxation Invoice ABN 49 003 205 490 _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ _____________ 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 FOR SALE RAIN BRAIN AND DIGI-TEMP KITS: 8-station sprinkler controllers. New Digi-temp and Moni-temp use DS1820 sensors. Feature PC data logging, 60 channels over 500 metres. www.mantismicroproducts.com.au Only $39 ! VCR Controller use a std VCR for Surveillance Event Recording Wireless IR Control * 4 Ch Switchers only ! $79 * COLOUR Bullet Cameras from $122 * Digital PC 4 Ch Video Recorder System from $159 * DOME VIDEO CAMERAS COLOUR from $77 ! Mono from $53 ! BULLET from $97 TWO YEAR WARRANTY * DOME 480 Line 0.05 Lux SONY CCD & ChipSet from $81 * COLOUR DSP DOME: 400 Line from $139 * 600 + Line from $164 * COLOUR DSP PIN in PIR CASE from $152 * MINI CAMS from $67 * DSP COLOUR from $133 * PC REMOTE VIEW, PAGING, WEB-CAM, DVR System High 768 x 576 Resolution from $219 * QUAD 1024 H-Pixels from $175 * COLOUR QUAD only ! $380 * MULTIPLEXER 4 Ch from $633 * DIY PLUG-IN 20 metre AV Cables from $20 BLEMISH FREE & LOW BLEMISH CCDs * UP TO 5 YEARS WARRANTY * OVERNIGHT DELIVERY * www. allthings.com.au RAINBOW POWER COMPANY: Sol­ar Panels 80W $660, Batteries, Inverters, Regulators, Rebates available – call (02) 6689 1430. COVERT VIDEO SURVEILLANCE Tiny Sub-Matchbox from ~ 6 grams Wireless Video & Audio TRANSMITTERS from $77 * Pinhole Cameras from $67. Easily concealed in: Mobile Phone Case, Clock, VCR Cassette, Toys, Teddy Bear (Nanny-Cam), Smoke Detector, Ornament, Cap, Cigarette Pack, etc. www. allthings.com.au TELEPHONE EXCHANGE SIMULATOR, SC February 1998. Test equipment without the cost of telephone lines. Melbourne 9806 0110. WEATHER STATIONS: Windspeed & direction, inside temperature, outside temperature & windchill. Records highs & lows with time and date as they occur. Optional rainfall and PC interface. Used by Government Departments, farmers, pilots, and weather enthusiasts. Other models with barometric pressure, humidity, dew point, solar radiation, UV, leaf wetness, etc. Just phone, fax or write for our FREE catalogue and price list. Solar Flair/Ecowatch phone: (03) 5968 4863; fax: (03) 5968 5810, PO Box 18, Emerald, Vic., 3782. ACN 006 399 480. KITS KITS AND MORE KITS! Check ‘em out at www.ozitronics.com SEE-in-the-DARK Camera with in-built IR LEDs in Water Resistant Case for disturbance-free Baby - Bird - Animal observation from $147 * DIY Plug-In 20 metre Cable & Plug Pack from $33 * www.allthings.com.au C COMPILERS: everything you need to develop C and ASM software for 68­HC08, 6809, 68HC11, 68HC12, 68­ HC16, 8051/52, 8080/85, 8086, 8096 or AVR: $170.50 each. Macro Cross Assemblers and Disassemblers for above CPUs + 6800/01/03/05, 6502 and 68­HC12 for $88. Debug monitors: $88 for 6 CPUs. All compilers, XASMs and monitors: $5280. 8051/52 Simulator (fast, now incl. 80C320): $88. Try the C-FLEA Virtual Machine for small CPUs, build a “C-Stamp”. Demo desk: FREE. All prices + $5.50 p&p. Atmel Flash CPU Programmer: Handles the 89Cx051, 89C5x and 89Sxx series, and some AVRs in both DIP and PLCC44. Also does most 8-pin EEPROMs. Includes socket for serial ISP cable. $220 $11 p&p. SOIC adaptors: 20-pin $99, 14-pin $93.50, 8-pin $88. Credit cards accepted. GRAN­ TRONICS PTY LTD, PO Box 275, Wentworthville 2145. Ph (02) 9896 7150 or Internet: http://www.grantronics.com.au HOME CCTV Mono / Colour PAKS only ! $119 / $151 Full DIY Plug-In to TV / VCR 20 metre Cable, Plug Pack & Camera www.allthings.com.au RCS HAS MOVED to 41 Arlewis St, Chester Hill 2162 and is now open, with full production soon. Tel (02) 9738 0330; Fax 9738 0334. rcsradio<at>cia.com.au; www.cia.com.au/rcsradio ROLA AUSTRALIA PH/FAX (08) 8270 3175 WEB SITE WWW.BETTANET.NET.AU/GTD CHECK OUR WEBSITE FOR DETAILS ON KITS AND COMPONENTS • • • • Silvertone’s RC Receiver Still the best little performer available! TRANSMITTER KITS AND MODULES AUDIO MODULES COMPUTER INTERFACE KITS RADIO STATION AUDIO SOFTWARE NEW: Our MP3-CD player in short form for $169 inc GST. Includes the following: processor board, front panel display and tactile keypad; just add a case, cables, 12V power supply and a CD-ROM drive. Play CDs and up to 2600 MP3’s from a CDR. Great for car or home. Satellite TV Reception International satellite TV reception in your home is now affordable. Send for your free info pack containing equipment catalog, satellite lists, etc or call for appointment to view. We can display all satellites from 76.5° to 180°. Still only $129.50 AM or $149.50 FM. May be used with most ppm transmitters. This and many other radio control products available from: Silvertone Electronics, PO Box 580, Riverwood 2210. Phone/Fax (02) 9533 3517. www.silvertone.com.au AV-COMM P/L, 24/9 Powells Rd, Brookvale, NSW 2100. Tel: 02 9939 4377 or 9939 4378. Fax: 9939 4376; www.avcomm.com.au Positions At Jaycar We are often looking for enthusiastic staff for positions in our retail stores and head office at Rhodes in Sydney. A genuine interest in electronics is a necessity. Phone 02 9743 5222 for current vacancies. www.procontechnology.com.au Fischertechnik robotic kits, interfaces and Atmel AT90S8535 microcontroller boards from $66. Starter kits with cables and software, ready to program in compiled BASIC or assembler from $99. Design service available. Credit cards accepted. Phone (03) 98306288. DIY CCTV PAKS 4 Cameras & Switcher .................$354 as above COLOUR .....................$466 4 Cams, Switcher/Monitor ...........$495 as above 14" Monitor ................$528 4 Cams & QUAD .........................$478 4 COLOUR & QUAD ....................$752 Time-Lapse 24hrVCR $710 with CCTV Systems 2 Year Warranty ! MORE at: www.allthings.com.au Fully Plug-In DIY Paks with Cables & Power Supplies. ALSO PC Digital Motion / Sound detection & activated Video / Audio Recording systems 08 9349 9413. SMD COMPONENTS, Resistor kit, 18 x 50 x 1206 popular values in case <at> $38.50 inc GST. Capacitor kit, 18 x 50 x 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. 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. 1206 popular values in case <at> $88.00 inc GST <at> www.lazer.com.au or call on 02 93 111 500. NEW PROFESSIONAL PAN TILT DOME CAMERA controlled via remote. SPECIAL PRICE: Colour $680, B&W $550. To be an agent, or for more info call GCS sales rep George on 0410 739 317. FPGA Prototyping Kits: Lowest cost, easiest to use. Altera, Atmel. Xilinx kit now with 200,000 gates (!) and free design software! www.BurchED.com.au LASERS, LIGHTING, SOUND and other technology surplus equipment plus general household and office items at the LASERVISION garage sale. See www.laservision.com.au, select “products” then “surplus” to see some of continued next page December 2000  95 DON’T MISS THE ’BUS Advertising Index Acorn Icon (Akhurst Calendar)....64 Altronics................................. 66-67 Av-Comm Pty Ltd.........................95 Do you feel left behind by the latest advances in com­puter technology? Don’t miss the bus: get the ’bus! Includes articles on troubleshooting your PC, installing and setting up computer networks, hard disk drive upgrades, clean installing Windows 98, CPU upgrades, a basic introduction to Linux plus much more. Dick Smith Electronics...... 22-25,77 Price: $12.50 (incl. GST) Order now by using the handy order form in this issue or call (02) 9979 5644, 8.30-5.30 Mon-Fri with your credit card details. Investment Technology................31 Direct Components......................21 EMC Technologies.......................86 Evatco..........................................83 Harbuch Electronics....................85 Instant PCBs................................95 Special subscription offer available only while stocks last. Jaycar ................................... 45-52 Mass Technology.........................86 the items in advance. Enquiries to info<at>laservision.com.au. Garage sale Saturday 2/12/00 at 50 Carters Road, Dural. Nev­ille Walker (07) 3857 2752 or email flashdog<at>optusnet.com.au RICOM – Electronic Components: LCD screens – from 16x2 characters to 128x64 graphics with backlighting. PIC micros – from 12C509 to 16F877. See our website for full lists & pricing. www.ricomelectronics.webcentral.com.au PERSON WITH EXPERIENCE / APTITUDE able to fault find & repair PCBs – without diagrams. GENEROUS PKG NEG. Tel John<at>AER (03) 9482 4958 0415 305 470. QUAD 4 pixs 1 screen from $247 * Real Time * High better than SUPER-VHS 1024 Pixel Resolution * Time * Date * Camera Title * Alarm Input / Output * Remote Camera Selection * FREEZE * www.allthings.com.au KIT ASSEMBLY ANY KITS assembled/repaired: professional, speedy service. Phone WANTED Circuit Ideas Wanted Do you have a good circuit idea. If so, 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 so send your idea to: Silicon Chip Publications, PO Box 139, Collaroy, 2097. Microgram Computers..........3,OBC MicroZed Computers...................86 Oatley Electronics........................13 Printed Electronics...................... 95 Questronix...................................86 Rall Electronics............................86 RobotOz......................................86 Rola Australia..............................95 R.T.N..........................................IFC Satcam........................................73 Silicon Chip Bookshop........... 90-91 SC Computer Omnibus...............96 Sc EFI Tech Special.....................31 SC Electronics Testbench..........IBC Silicon Chip Subscriptions...........65 HELP SAVE THE NIGHT SKY! Silvertone Electronics..................95 We are losing our heritage of starry night skies. Poor, inefficient outdoor lighting is causing glare and “light pollution”. This wastes energy and increases greenhouse gas emissions. Solar Flair/Ecowatch....................95 _____________________________ You can help by joining SYDNEY OUTDOOR LIGHTING IMPROVEMENT SOCIETY (SOLIS). SOLIS aims to educate and inform about quality outdoor lighting and its benefits. We also lobby councils, government and other bodies to promote good lighting practice. SOLIS meetings are held third Monday night of each month at Sydney Observatory. Individual membership is $20 pa. Donations are also welcome. Cheques payable to “SOLIS c/- NSAS”, PO Box 214, West Ryde 2114. http://sites.netscape.net/solislp/ 96  Silicon Chip PC Boards Printed circuit boards for SILICON CHIP projects are made by: • RCS Radio Pty Ltd. Phone (02) 9738 0330. Fax (02) 9738 0334. • Marday Services, PO Box 19-189, Avondale, Auckland, NZ. Phone (09) 828 5730. December 2000  97