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The main board at far left allows two trains to run automatically around a loop of track, each train alternately stopping as it comes to a short isolated section. It also provides LEDs for signalling & for flashing level crossing lights. The smaller board provides various sound effects, including level crossing bells. Run two trains on a small layout Do you have a small model train layout with just a loop of track? Would you like to run two trains on it at the same time? It can be done cheaply and easily with the circuits presented here. As a bonus, you can have level crossing lights and sound effects. By LEO SIMPSON Running a train around a small loop of track is alright for beginners but before too long it becomes boring. However, adding variety is hard unless you extend the layout with points, more track and so on. If that seems like too much of a challenge then consider the circuits presented here. They will enable two trains to safely follow each other around a loop of track. As 32  Silicon Chip a bonus, you can have flashing level crossing lights and the accompanying bell sound effects. Most people with a single loop of track will have probably tried running two trains or two locos on it simultaneously but it doesn’t work well. One loco will eventually catch up with the other and then they will play “push me, pull you” all around the track. A better way of doing it is to divide the loop of track into two sections. Then you place a train or a loco in each section and only have one section energised at a time. That way, one train will proceed around its section until it comes to the end. It will then stop and the other train will proceed around its section until it too comes to the end. Each train will alternate in running and stopping but they will both proceed safely around the track without ever catching up to each other. This applies even if one train or loco is substantially faster than the other. This idea sounds alright in theory but how does the con­trolling circuit know when to switch the power to each alternate section of the track? Well, actually, this simple idea doesn’t work in practice and the loop of track TRAIN DIRECTION TRAIN SIGNALS DETECTOR A TRAIN 1 DETECTOR RELAY TRAIN CONTROLLER DETECTOR B TRAIN SIGNALS Circuit details TRAIN 2 ISOLATED SECTION Fig.1: this diagram shows the principle of operation. There are two infrared detector beams which are broken by the two trains as they pass around the track loop. A relay switches the power on & off to an isolated track section & so one locomotive stops while the other loco proceeds. needs to be sectioned along the lines shown in Fig.1. This depicts a loop of track which has one small isolated section in it. This isolated section need only be long enough to accommodate your longest locomotive. As well as that, two infrared light detector beams are positioned across the track. As a loco breaks one of these light detector beams, it is detected and some logic circui­try operates a relay to energise or de-energise the isolated track section which we’ll call section A. detector beam A. The circuit also provides a simple lighting system to increase the realism. You can have train signals and level crossing lights, as we shall see. Not included in this article is a train speed control cir­cuit. We are assuming that anyone who has a small layout will already have a train control and so this can be employed in the setup described here. tion. Train 1 sets off in pursuit and breaks infrared detector beam B which kills section A again so that when train 1 arrives there, it stops. This sequence continues, with train 1 and train 2 alter­nately stopping at section A while the other one proceeds around the track. On a layout, section A could be a station platform while a level crossing can be positioned near Fig.2 shows the circuit which enables the two trains to run around the loop of track. There are two infrared detector beams, beam A provided by LED1 & Q1, and beam B, provided by LED2 and Q2. When beam A is broken, Q1 will turn off which will turn on transistor Q3. This will pull pin 1 of IC1a low. ICI is a 4011 quad 2-input NAND gate package. Two of the NAND gates, IC1a & IC1b, are connected as an RS flipflop. When Q3 pulls pin 1 low, pin 3 of the flipflop goes high. This will turn on transistor Q5 and energise the relay. Because an RS flipflop is employed, nothing can happen until beam B is broken. This will switch off Q2 and switch on Q4 which causes the RS flipflop to change state. This turns off Q5 and disables the relay. So the RS flipflop is set and reset as beam A and beam B are interrupted and section A is alternately powered or not, to stop the trains. How it works Fig.1 shows train 1 proceeding clockwise around the lefthand section of the loop while train 2 is stopped in section A which has no power applied to it. The rest of the track is permanently powered from the train controller. As train 1 moves around the loop it breaks infrared detec­ tor beam A which causes the relay to apply power to section A. Train 2, which had been stopped in section A, can now proceed and it passes through infrared detector beam B, so the relay removes power from section A. Both trains are now moving and train 1 eventually arrives at the dead section A and stops. Train 2 now continues around and breaks infrared detector beam A. The relay now energises the isolated sec- This close-up shows the locomotive about to break one of the infrared detector beams. Note the optotransistor which has been bent over backwards so that its lens faces the infrared light emitting diode. July 1995  33 VCC A LED3 R1 560  Q1 A K A LED4 Q3 BC548 C B R5 220k C   LED1 C1 .015 R6 68k R2 560  A  LED2 Q2 R10 22k Q4 BC548 C B R8 220k C  C2 .015 R9 68k 14 1 3 2 RELAY 1 K D1 1N4004 SECTION A SPEED CONTROLLER R14 1k E 5 Q6 BC548 C B R12 10k 4 IC1b 6 7 E B VCC E A E K  LED6 Q5 R11 BC548 C 10k B A VCC R4 120k K A  K IC1a 4011 DETECTOR A  LED5 R13 1k E E K  R7 22k R3 120k A C9 0.47 R17 4.7M 13 R21 2.2k R18 2.2M IC1d 11 12 R16 120k  LED7 DETECTOR B 8 IC1c 10 R28 10k 9 A Q7 BC548 R22 10k D6 1N4004 +12V R19 205  ZD1 10V VCC C10 100 8 R15 47k IC2 555 6 0V 2 C3 .001 D2 4 3 5 1 4x1N4148 D3 C5 4.7 D4 E C B Q9 BC548 E C8 4.7 C7 A 4.7 K C VIEWED FROM BELOW E IC1d and IC1c operate as a square wave oscillator with its frequency of opera­tion determined by resistors R17 & R18 together with capacitor C9. The oscillator is enabled whenever pin 12 of IC1d is pulled high. Depending on where you want to put the level crossing lights, pin 12 can be connected to point A or point B (pin 3 or pin 4 of IC1) on the circuit. The complementary outputs of IC1c & IC1d drive transistors Q7 and Q8 and these cause LEDs 7 & 8 to flash B E C4 .01 Fig.2: the train detector board is based on an RS flipflop (IC1a & IC1b) which controls the relay. The RS flipflop is set and reset by the locomotives breaking detector beama A and B. IC2 and the associated voltage multiplier provide a 30V supply for the high voltage relay. 34  Silicon Chip Q8 BC548 D5 TRAIN DETECTOR As well as driving the relay, transistor Q5 drives LED3 and LED4 which are in series. Q6, driven from the alternate output of the RS flipflop, drives LEDs 5 & 6 in series. LEDs 3 & 5 are red while LEDs 4 & 6 are green. These are placed on signals situated just before each infrared detector beam, so that when a train goes through the beam, the lights change state (eg, from GO to STOP and vice versa. IC1c and IC1d are arranged to provide a complementary LED flasher. C B E R24 10k C6 4.7 K R23 2.2k C B  LED8 K Q1 C alternately. These can then be used to simulate the flashing lights at level cross­ings. Interestingly, when pin 12 is pulled low, LEDs 7 and 8 will stop flashing but one LED will stay alight, due the high state of pin 10 or 11. To stop both LEDs from lighting when pin 12 is low, transistor Q9 is connected in series with the paralleled emitters of Q7 and Q8. The base of Q9 is connected to pin 12 of IC1 via a 10kΩ resistor. Now, when pin 12 is high, Q9 is on and the LEDs can flash merrily away. But when pin 12 is low, Q9 will be off and so both LEDs 7 & 8 will be dead. The rest of the circuit based around IC2 is there solely to provide a high Q1 BC548 C E +8-15V C1 100 0V R1 2.7k C4 1 B R4 150k 32W 2 C2 0.47 ZD1 5.6V R2 10k TRIGGER 1 4 C5 0.1 7 C 8 Q2 BC548 C3 .015 R5 330  B 9 5 B R3 4.7k COB MODULE E E 10 NO 1 47k LED3,4 LED5,6 205  D6 1k 4.7uF D5 4.7uF Q6 2.7k +12V TRIGGER 0V 10k Q5 .01 +12V D1 10k GND ZD1 RELAY1 1k 120k 10k 10k IC1 4011 22k B 4.7uF D4 IC2 555 NC COM OSC O/P 4.7uF D3 .001 1 A Q4 220k 68k 560  120k GND 22k 68k .015 LED2 0.47 Q3 D2 Q2 220k 560  120k LED1 Fig.4 (left): the LEDs shown here will normally all be mounted on the model train layout. LEDs 7 & 8 are the level crossing lights while the others provide the signalling. Q9 10k 100uF .015 Q8 Q2 SPEAKER Q1 100uF Q3 150k 2.2k Q1 Q7 2.2k There are four PC boards to be assembled for this project: one for the train detector circuit, one for the COB module and two for the infrared light detector beams. We’ll deal with the IR beam boards first. Each board has two components: LED1 (or LED2) and the opto­transistor Q1 (Q2). As can be seen from the photos, the LEDs for these boards have clear lenses and are installed with the longer lead connected to the “A” mark on the board. The optotransistors come in a much smaller rectangular package which has only two leads. Looking at the package with the small lens facing you, the emitter lead is on the left while the 1uF ZD1 LED8 4.7M 2.2M LED7 Construction .015 4.7k The COB circuit is little more than a power supply and a transistor which drives a loudspeaker. The COB module requires a voltage of 5V and this track, or the level crossing bells. It just depends on which of four pins is connected to pin 1. To obtain the level crossing sound, connect pin 1 to pin 7. 10k COB circuit C VIEWED FROM BELOW COB is provided by the simple regulator com­prising a 5.6V zener diode ZD1 and emitter follower transistor Q1. Transistor Q2 provides the trigger facility. If the trigger input is pulled high, transistor Q2 turns on and shorts the zener diode at the base of Q1. This kills the supply from Q1 and so the COB module is silenced. On the other hand, if the trigger input is held low, Q2 is off and the COB module is fed its 5V supply by Q1. Transistor Q3 acts as a buffer stage for the COB module and drives the 32Ω loudspeaker. Depending on when you want the level crossing sound to be produced, the trigger input of the COB circuit can be connected to point A or B on the train detector circuit of Fig.2. While we have yet to mention it, the COB module is capable of a variety of train sounds. You can have a steam train whistle, a locomotive chuffing, a carriage passing over a join in the Q3 C8050 B E voltage source for the relay which is a 48V type. IC2 is a 555 timer connected as a square wave oscillator. Its output drives a voltage multi­plier consisting of diodes D2-D5 and capacitors C5-C8. This produces a DC supply of around 30V which is adequate to drive the relay reliably. But there’s more. As well as the signalling and level crossing lights, this project offers a small module which produc­es the sound of a level crossing. This takes the form of a chip-on-board (COB) module which is effectively a bare integrated circuit die (the chip) on a small PC board and encapsu­lated in a blob of epoxy. The circuit to enable the COB module is shown in Fig.3. C 0.47 COB MODULE Fig.3: the COB module board is little more than a power supply (Q1, ZD1) which is turned on or off by Q2. Q2 is switched by the trigger lead which should be low for sounds to be produced. 0.1 330  Fig.5: the various sounds of the COB module are enabled by connecting a link between the stakes for pin 1 and pins 4, 5, 7 & 8. The connection shown here is for the level crossing bells. July 1995  35 PARTS LIST Train detector 1 PC board (Oatley Electronics) 2 detector beam boards (Oatley Electronics) 1 48V DPST relay Semiconductors 1 4011 quad 2-input NAND gate (IC1) 1 555 timer (IC2) 2 infrared LEDs (LED1,LED2) 2 optotransistors (Q1, Q2) 7 BC548 NPN transistors (Q3-Q9) 2 1N4004 silicon rectifier diodes (D1,D6) 4 1N4148 silicon signal diodes (D2,D3,D4,D5) 1 10V zener diode (ZD1) 4 red LEDs (LED3,5,7,8) 2 green LEDs (LED4,6) Capacitors 1 100µF 16VW electrolytic 4 4.7µF 63VW electrolytic 1 0.47µF monolithic 2 0.15µF ceramic 1 .01µF ceramic 1 .001µF ceramic Resistors (0.25W, 5%) 1 4.7MΩ 2 22kΩ 1 2.2MΩ 5 10kΩ 2 220kΩ 2 1kΩ 3 120kΩ 2 560Ω 2 68kΩ 1 205Ω 2W 1 47kΩ COB sound board 1 PC board (Oatley Electronics) 1 COB module 1 32Ω miniature loudspeaker 5 PC stakes Semiconductors 2 BC548 NPN transistors (Q1, Q2) 1 C8050 NPN transistor (Q3) 1 5.6V zener diode (ZD1) Capacitors 1 100µF 25VW electrolytic 1 1µF 50VW electrolytic 1 0.47µF monolithic 1 0.1µF monolithic 1 .015µF metallised polyester or ceramic Resistors (0.25W, 5%) 1 150kΩ 1 2.7kΩ 1 10kΩ 1 330Ω 1 4.7kΩ 36  Silicon Chip This is the COB module board which is supplied with a miniature 32Ω speaker which produces an adequate sound level. The COB module is butted to the end of the board and the pins soldered. collector lead is on the right; there is no base lead. Insert the optotransistor into the board and solder the leads. If you have soldered the leads correctly, the transistor’s lens will now be facing away from the infrared LED. That means that the transistor body needs to bent over backwards so that the lens faces the LED. Next, we’ll talk about the train detector board. This has two ICs and eight transistors. Its component layout is shown in Fig.4. Install the resistors and wire links first, followed by the small capacitors and diodes. The electrolytic capacitors can then be inserted, followed by the transistors and the ICs. Make sure that all the semiconductors and the electrolytic capacitors are installed the correct way around. If not, they could be destroyed when you first apply power. Finally, the relay can be installed. The LEDs can be wired temporarily into the board but eventually they will be installed on the layout. Note that the LED labelling on the diagram of Fig.4 is different from that shown on the PC board itself. Cur­rent production versions of the board show positions for LED3 & LED4 at diagonal corners. Our diagram shows the correct situation, with LED7 & LED8 mounted in the top lefthand corner of the board, while LEDs 3, 4, 5 & 6 are connected at the bottom righthand corner. LEDs 3 & 4 are connected in series, as are LEDs 5 & 6 and the commoned positive connection goes to the junction of the 10V zener diode ZD1 and the 205Ω resistor. Note that a link is shown on the underside of the board connecting pin 3 of IC1 to pin 12. This enables the level cross­ing lights, as discussed previously. The alternative is to con­nect pin 12 to pin 4 (point B). COB module assembly Another view of the COB module board, showing the five PC stakes which enable a choice of sound effects. The light board mounted at right angles is the COB (chip on board) module. The relevant component layout is shown in Fig.5. The main aspect of this assembly is connecting the COB module to the PC board. The two boards are butted at right angles and the 14 connections SATELLITE SUPPLIES Aussat systems from under $850 SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 This is the train detector board which provides relay switching to the isolated track section and various LEDs for track signall­ing and level crossing lights. are soldered between them. After that, the remaining work is to install the board components which comprise five resistors, four capacitors, two transistors, the zener diode ZD1 and the PC stakes. Make sure that the semiconductors and the two electrolytic capacitors are correctly oriented. To obtain the level crossing bell sound, connect a lead between two of the PC stakes as shown in Fig.5. Testing Let’s test the train detector board first. You will need to connect the two optocoupler boards first so that the operation of the RS flipflop can be checked. Apply power and check the state of the LEDs. With both detector beams unobstructed, either LEDs 3 & 4 or LEDs 5 & 6 should be on. If LEDs 5 & Where To Buy Kits Both these designs are from Oatley Electronics who own the design copyright.The train detect­ or board kit is available for $20 while the COB sound kit costs just $12. Packaging and postage is $4.00. Send a cheque, money order or credit card authorisation to Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985 or fax (02) 570 7910. 6 are on, LEDs 7 & 8 should be flashing alternately. If LEDs 5 & 6 are on, try interrupting detector beam A by placing your finger between the LED and the opto­ transistor. LEDs 5 & 6 should go out and LEDs 3 & 4 should light and LEDs 7 & 8 should stop flashing. The relay should also be energised at this time. Now interrupt detector beam B in the same way. The circuit should change state again so that LEDs 3 & 4 go out and LEDs 5 & 6 come on, as before. If all of the above occurs, you have a working circuit. Testing the COB board Testing this board is easy. Just apply power and the speak­er should immediately emit the characteristic bells sounds of a level crossing. If it does not, check the 5V rail at the emitter of Q1 and all the connections to the COB module. To turn the sound off, connect a lead from the trigger input to the 8-15V rail. If it doesn’t turn off, check the compon­ ents around transistor Q2. Well, there you have it: a couple of low cost PC boards which will add life and realism to a simple model railway loop layout. Not only that, you could incorporate a similar small loop into a much larger layout and thereby add an automatic section which will run itself and give greater SC visual interest. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 9553 1763; Fax (03) 9532 2957 July 1995  37