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Fluorescent light simulator for model railways The key word for any railway modeller and his layout is "realism", right down to the fluorescent street lights. This project "quickie" simulates the flicker you see when fluoros first start up, and it can power up to 30 mini lamps. By DARREN YATES This is one of those circuits for the model railway perfectionist. It's just the shot for controlling the lamps around your layout and will provide a realistic "fluoro-flicker " each time the lights are switched on - just like real fluorescent lights. This rapid flikering effect only lasts for a brief period, after which the lights come on and stay on. The circuit should appeal most to those who like playing "night trains"; ie, running their layout in a dimmed room to take full advantage of the When the circuit is turned on, the lamps flicker for a brief period & then stay on - just like real fluorescent lamps. It will add realism to your model train layout. 42 SILICON CHIP lighting. Best of all , the circu it is quite simple and uses just one IC and a handful of other components. It will only take you about an hour or so to build, so you'll have it up and running in no time at all. How it works Fig.1 shows the circuit diagram of the Fluorescent Lamp Simulator. When the circuit is first turned on , the lO0µF electrolytic capacitor at the base of transistor Ql has no voltage across it, so Ql is turned off. While the capacitor is charging up via the 680kQ resistor, pins 6, 9, 13 and 2 of ICl are all high. These pins are used as enable inputs for the four Schmitt trigger NAND gates (ICl a-d), which are connected as square wave oscillators. ICla is connected in a conventional manner, with a 680kQ feedback resistor from output to input, and a 0.15µF timing capacitor from input to ground. This gives an output frequency of about 8Hz. ICl b, c & d are also connected as oscillators but in a different manner. Instead of the feedback resistor going from each gate's output to its input, it is connected to the input of the next gate in the chain; eg, pin 4 of ICl b is connected to pin 8 of IClc via the feedback resistor, etc. This forms what is known as a ring counter. The reason for this arrangement is so that the outputs of the three gates, IClb-ICld, go high one at a time to produce a light chaser effect. These outputs are mixed with the output of ICla via diodes Dl to D6 , which form three OR gates. Dl and D4 form one OR gate, D5 and DZ another, and D3 and D6 the third. The result of all this jiggery-pokey is that ICla pro- 47!! r---+-----------4-------+-------''#No.----------4----.....- - - - - - - - - • 1 2 V ffJ J 1W 680k, LAMPS B 100 + 16VWJ 680k 01 1N914 .,. LAMPS 05 1N914 05 B0139 0.151 C .,. 680k B 02 1N914 .,. 4.7k 07 B0139 C B E .,. 0.15! B EOc VIEWED FROM BELOW 680k ECB FLUORESCENT LAMP SIMULATOR Fig.1: when the circuit is first turned on, Ql's collector is high & this enables a ring counter IClb-lClc & Schmitt trigger oscillator ICla. The outputs from the ring counter are OR'ed with the output from ICla using D1-D6 & the resulting signals then used to drive three Darlington transistor pairs to switch the lamps. vides a degree of randomness to the outputs, to give the lamps that flickering effect. The OR-gate outputs are then fed to three lamp driver transistor stages via 4. 7kQ isolating resistors. Each of these stages consists of a BC337 and a BD139 transistor connected in a Darlington arrangement to provide the necessary current gain. When each output goes high, its associated Darlington output stage turns on and current briefly flows through the associated lamp. During this time, the lO0µF capacitor on Ql 's base continues charging until it reaches 0.6V. At this point, Ql turns on, pulling the enable line connected to the oscillator inputs low and forcing the NAND gate outputs permanently high. The lamps now stay on continuously. The capacitor charges up in 2-3 seconds which Where to buy the kit A kit of parts for this project is available from Electronic Toy Services, PO Box 491, Noarlunga Centre, South Australia 5168 (Shop 2/111, Glynville Drive, Hackham West, SA). This kit includes the PC board & all on-board components, but does not include the lamps. The price is $14.95 plus $2.50 p&p. The PC board can be purchased separately for $5.95 plus $2.50 p&p. Payment may be made by cheque or money order, or by phoning (08) 382 8919 and quoting a credit card number. Note: copyright of the PC board artwork associated with this project is retained by Electronic Toy Services. PARTS LIST 1 PC board (available from Electronic Toy Services) 3 12V mini lamps (eg, Jaycar Cat. Sl-2639) plus additional lamps (up to 30) as required Semiconductors 1 4093 quad Schmitt trigger NANO gate (IC1) 1 BC549 NPN transistor (01) 3 BC337 NPN transistors (02,04,06) 3 8D139 NPN transistors (03,05,07) 1 12V 1W zener diode (ZD1) 6 1N914 diodes (D1-D6) Capacitors 1 100µF 16VW PC mounting electrolytic 4 0.15µF 5mm-pitch metallised polyester Resistors (0.25W, 5%) 5 680kQ 3 4.?kQ 1 2.2kQ 1 47Q MAY1991 43 ·- Fig.2: follow this diagram carefully when installing the parts on the PC board & take care to ensure that all parts are correctly oriented. The pinouts for the B0139 transistors are shown on Fig.1 (mount them so that their metal tabs face the edge of the board). Up to 10 mini lamps can be wired in parallel to each channel. UHF HIGH GAIN ANTENNAS antenn existing systems triangul powder coated receiving elements ensures excellent UHF reception compared to other UHF antennas of similar size and price. Two models are available: the for Band Four and the S for Band Five UHF • reception. Both models are supplied with back reflectors to prevent ghosting as well as a waterproof entry box designed to accept 75 ohm coaxial cable without the need for addittional baluns. They also have predrilled holes for securing the tilt adjustable metal mounting bracket in either a horizontal or vertical position. Imported and distributed by: Available through the following retailers: Bernys. Brldgepoint. Military Road. Mosman. 2088. NSW. (02) 969 1966. Ritronics. 56 Renver Rd. Clayton. Victoria. 3168. (03) 543 2166. means that the lamps only flicker on and off for this amount of time. Power for the circuit can be provided by the train controller supply. A 12V 1W zener diode is used to protect the CMOS IC against high input voltages. By the way, if you only intend using four or five lamps per output stage, you can do away with the BD139 transistors and just use the BC33 7 transistors to drive each set of lamps. Construction Is .Your Product Or Service G·etting The Exposure It Deserves? Nearly 30,000 consumers will read this page. They need to see your advertisment, if you want them to buy your product. Contact Paul today on (018) 28 5532 to reserve this space. 44 SILICON CHIP All components, except for the lamps, are installed on a small PC board measuring 73 x 63mm. Before you begin soldering, check the board for any shorted or broken tracks, particularly those running between the IC pins. Once you 're satisfied that the board is correct, start the assembly by soldering in the resistors and diodes. Fig.2 shows how the parts are installed. If you're not sure of the colour code of the resistors, use a multimeter or check the accompanying table. Be sure to match the polarity of each diode to the wiring diagram. Next, install the greencap capacitors. These all have the same value, so you shouldn't have any problems here. When you've done that, solder in the transistors. Again, check with the overlay diagram to make sure you insert them correctly. The circuit diagram (Fig.1) shows the pinout details for the transistors. Note that the BD139s are installed with the metal faces of their tabs nearest the edge of the PC board. If you aren't using the BD139 transistors (see above), install a wire link between the base and emitter holes where each BD139 would have gone. Finally, solder in the IC. Check again that you have inserted it correctly before you start soldering. When you have finished the board, check it carefully for solder splashes to ensure that there are no shorts between tracks or between IC pins. When you are connecting up the lamps, note that they all have a common line; ie, the connection to the +12V supply rail. It is then just a simple case of running the other leads from the lamps to the outputs provided on the board as appropriate. Finally, you can either install the board in a small zippy box or just hide it as is under the layout table the choice is yours. Be sure to connect the power supply the right way around. SC RESISTOR COLOUR CODES Value 4-Band Code (5%) 5-Band Code (1%) 680kQ 4.7kQ 2.2kQ 47Q blue grey yellow gold yellow violet red gold red red red gold yellow violet black gold blue grey black orange brown yellow violet black brown brown red red black brown brown yellow violet black gold brown