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Project by Les Kerr Dual Train Remote Control This add-on to the Battery-Powered Model Train allows two different model locomotives to be controlled wirelessly from a single box. I n the January 2025 issue, we described how to control the speed and direction of a single model train using a 433MHz radio link (siliconchip.au/ Article/17607). Since then, I have been asked by several people if it could be modified to simultaneously control the speed and direction of two trains. That would allow two trains to run together on the same track or track layout without the expense of installing DCC. Children love the concept, as they can have one train chasing the other. The system presented here controls two trains, but it could be enhanced to control up to ten trains and operate onboard sounds like whistles and brakes. However, those extra features are for a future article. To control the speed and direction of two trains at once, I have used the same Receiver hardware but have made two new versions of Receiver firmware, one for each train. The Battery Charger presented previously also remains valid. If you have already built the single 72 Silicon Chip train controller, you will need to build a second Receiver and the new dual transmitter. I have made another refinement while adding the multi-locomotive capability. The previously described train controller Receiver was switched off by inserting a 2.5mm jack plug. This was fine if you only had one carriage, but when you added a second carriage, there wasn’t enough space between the carriages to insert the jack plug. To solve this, I made a much smaller on/off plug out of plastic that fits between the two carriages. Inserting this into the train’s jack socket switches the power to the train off, and removing it switches the train on. Fig.1 shows the dimensions of the plug. You will need two of these, one for each train. The adjacent photo shows the Dual Train Controller, which is built into a standard UB3 Jiffy box. It has a speed potentiometer and a direction toggle switch for each train, together with a power off/on toggle switch. The LED illuminates when it is switched on. Circuit details Fig.1: this plastic plug can be made with hand tools or a lathe from a small plastic cylinder using a file. It fits next to the carriage more easily than a jack plug to switch the train off. Fig.2 shows the dual transmitter circuit. It is similar to the single transmitter circuit published in the January issue but it uses a 14-pin microcontroller. Two new inputs are added for the speed and direction controls of the second train. The two train direction toggle switch positions are monitored by the microprocessor (IC1) using its RC2 and RC3 digital inputs, with +5V (switch Australia's electronics magazine siliconchip.com.au Fig.2: the Dual Transmitter circuit is an expanded version of the original, with a 14-pin PIC16F1455 instead of an 8-pin PIC12F617, plus duplicated speed and direction controls. open, held at +5V via the 10kW pull-up resistor) giving one direction and 0V (switch closed to ground) the opposite. The 100nF ceramic capacitors on these pins reduce switch bouncing and stop electrical noise from affecting the taken readings. Each train has its own potentiometer that is used to vary its speed. IC1 uses its analog-to-digital converter (ADC) channels AN4 for train 1 and AN5 for train 2. It converts the voltage on the potentiometer wipers (which are directly proportional to their rotation) to 8-bit numbers between 0 (train stopped) and 255 (full speed). 100nF capacitors to ground prevent electrical noise from affecting these readings. These measurements are continually taken; if subsequent readings are identical, indicating the positions of the speed potentiometers and switches haven’t changed, no transmission takes place. If subsequent readings are different, the new speed is transmitted along with the direction. The same happens for both trains separately. When a transmission needs to be made, IC1 produces digital data from its RC4 output at 900 baud, which goes to the 433MHz ASK (amplitude shift keying) transmitter module. Each train has its own qualifier added to the transmitted data so that only that specific train is addressed. I chose 900 baud because I found that this is highest baud rate for reliable transmission with these modules. The whole transmitter is powered from a 9V battery, which is connected siliconchip.com.au to the circuit via an on/off toggle switch (S1) and a 1N5819 schottky diode. The diode prevents accidental battery polarity reversals from destroying the circuit but has a lower forward voltage drop than a standard diode, so the battery lasts longer. A small 78L05 regulator provides +5V for the microprocessor. 100μF capacitors at its input and output reduce any ripple to a negligible level and ensure stability; the 100nF capacitors help with stability too. Receiver The Receiver circuit (Fig.3) is identical to the one published in the January issue. Signals from the Transmitter are received by the 433MHz receiver module, and the demodulated serial data is applied to the RC2 digital input (pin 8) of the PIC16F1455 microcontroller (IC2). The 8-bit train speed data and the direction data are extracted and stored in memory, then used to generate the pulse-width modulated speed signal and the direction signal. Two logic inputs, IN1 and IN2, control the H-bridge driver (IC3). To turn the motor in one direction, we apply a pulse-width modulated (PWM) signal to vary the speed to IN1 while holding IN2 high. If the train is to run in reverse, the PWM signal is applied to instead IN2 while IN1 is held high. To stop the train, both inputs are kept at the same level (both low or both high). The battery supply voltage is halved by the two 10kW resistors and the resultant ~2.4V is monitored by analog input RA4 (pin 3) of IC2 using its internal ADC. If the voltage at that pin falls below 2V (ie, the battery is below 4V), digital output RC4 (pin 6) is taken low, switching on red LED2 The Dual Train Controller conveniently fits into a UB3 Jiffy box. The drilling diagram is shown in Fig.6. Australia's electronics magazine October 2025  73 Fig.3: the same Receiver is used as before except with updated firmware so that the two trains respond to different signals. The PIC sends signals to a DRV8871 module to control the motor. to alert you that the battery needs charging. The micro also provides signals to drive the DRV8871 H-bridge IC. To turn the motor in one direction, the PWM signal is applied to digital output RC3 (pin 7), while RC5 is taken high (+5V). To reverse the motor direction, the PWM signal is applied to RC5 and RC3 is taken high. The higher the speed value, the faster the motor turns. When the speed control is near its minimum position, both RC5 and RC3 are taken low (to 0V), causing the PWM module to go into sleep mode, reducing the current drawn from the battery. The +5V supply for the 433MHz receiver and micro is provided by the S7V7F5 high-frequency voltage up/ down converter (MOD4) that takes the 4-6V battery voltage and provides a regulated +5V output. If the battery has been recently charged (it could be as high as about 6V), MOD4 steps down the voltage to +5V; if it is discharged below 5V, it steps it up. The 100μF electrolytic capacitor and 100nF ceramic capacitor reduce any noise or ripple on the supply. Similarly, the U3V16F15 (MOD3) provides the +15V DC supply for the motor. We use 15V instead of 12V to overcome any voltage drop in the tiny cables connecting the carriage to the train motor. Pololu recommends in their data sheet that you add a 47μF capacitor across the battery input when using these inverters, which I have done. Both these modules are available locally for around $9 each. There is a 2.5mm switched jack socket (CON1) so the battery can be charged. It also allows the battery power to the Receiver to be switched off simply by inserting a jack plug. With the jack plug in the socket, the battery is connected to the Charger and disconnected from the Receiver as its positive side is disconnected. Charger circuit This is how we wired up the Dual Train Controller. See Fig.7 overleaf for a simplified view of the connections. 74 Silicon Chip Australia's electronics magazine The Charger (Fig.4) is also the same as before. The battery is trickle charged at C/10 (90mA) for 16 hours unless the charger output voltage exceeds 6V, indicating the battery is fully charged. In that case, the charge current is switched off. When the power pack is switched on, 9V is applied to the 78L05 voltage regulator (REG2), which reduces the voltage to siliconchip.com.au ◀ Fig.4: the Charger circuit is also the same, using REF1 and Q2 to provide a current-limited voltage source to charge the battery. IC4 and Mosfet Q1 switch the charger off after a set time to avoid damaging the battery. The 1N4148 diode (D3) prevents the ADC input from rising above 5.6V, although that is unlikely because the battery would have to be charged to over 11V. Still, it’s possible CON2 could accidentally be connected to a voltage source, so it’s better to be safe. Dual transmitter construction +5V to power the PIC12F617 microcontroller, IC4. The two 100μF capacitors smooth out any residual ripple, while the two 100nF capacitors provide high-­ frequency bypassing. On powering up, digital output GP4 (pin 3) of IC4 pulses the green LED at 200ms intervals, indicating it is in standby mode. Pressing the Start button (S3) pulls the GP2 digital input low (pin 5), causing an interrupt routine to be triggered that takes the Charger out of standby mode and puts it into charge mode. The 100nF capacitor reduces any contact bounce from the pushbutton. This results in the green LED switching off and the red Charge LED flashing at 500ms intervals. Mosfet Q1 (IRL540N) is switched on by digital output GP5 going high, and the 16-hour countdown timer starts. When on, the drain of the Mosfet goes low, connecting the 90mA constant current source to the battery. The current source comprises the BD136 transistor (Q2), an LM285 2.5V reference diode and a 220W resistor in parallel with a 22W resistor. It works by holding the PNP base 2.5V below the +9V supply. This sets the emitter at 1.8V (2.5V – 0.7V), which matches the voltage across the siliconchip.com.au parallel resistors. They have a resistance of 20W (220W || 22W). With 1.8V across 20W, Ohm’s law (I = V ÷ R) tells us the current must be 90mA (1.8V ÷ 20W). The battery voltage is halved by the two 10kW resistors and applied to analog input GP0 (pin 7) of IC4. Once per second, it measures the voltage; if it is above 3V (battery fully charged), charging stops and the Charger goes back into standby mode, shown by the green LED flashing. If the battery voltage doesn’t exceed 6V, the charging stops after 16 hours. The 1N4004 diode (D2) prevents the battery from discharging if it is left connected when the Charger is not powered. The new dual transmitter PCB is coded 09110245 and measures 57 × 40mm – refer to the overlay diagram, Fig.5. The boards we supply are double-­sided and include two topside links. If you make it yourself as a single-sided board, you will need to replace those tracks with wire links. Start by fitting the resistors and D1, ensuring its cathode band faces as shown, then the socket for IC1, with the notched end at the top. You could solder the IC directly to the board, but if you wish to remove it later for reprogramming, you will need to use the socket. There are various ways to connect the wires to the board, but the easiest is probably to solder standard headers to the board and use pre-made wires with DuPont connectors to plug into them. Now is a good time to solder the twoway and three-way headers in place. After that, you can fit the MKT capacitors (all 100nF, not polarised), then the two electrolytic capacitors. The latter are polarised and must have their longer (+) leads inserted into the pads marked with + symbols in Fig.5 and on the PCB. Then solder REG1 in place, with its flat side facing as shown. You may need to bend its leads to fit the PCB pads. The 433MHz transmitter module has a three-pin header that goes into three pads on the board. Make sure it’s orientated with the antenna terminal towards the edge of the main PCB, then solder it in place. Fig.5: fit the components on the new Dual Transmitter PCB as shown here. IC1, D1, the electrolytic capacitors and the 433MHz transmitter module must be orientated correctly. The transmitter module is fitted vertically; it’s shown laid over here for clarity. The antenna runs above the left-hand edge of the PCB. Australia's electronics magazine October 2025  75 Don’t plug in the PIC16F1455 microcontroller yet. If you have purchased it from the Silicon Chip Online shop, it will already have the firmware loaded. If you wish to do this yourself, the files can be downloaded from siliconchip.au/Shop/6/508 – you will need a suitable programmer and adaptor socket. Make the transmitter antenna by winding 0.4mm diameter enamelled copper wire around a 2.5mm diameter former, like the shaft of a drill bit. Wind 16 close turns and ensure there is sufficient length at either end to trim it as shown in Fig.5. Then strip the insulation from the shorter end (using a sharp hobby knife or emery paper), tin it and solder it to the antenna terminal on the 433MHz module. The antenna runs above the edge of the board (not as shown in Fig.5; it was drawn that way for clarity). Finally, check for any dry solder joints or solder bridges. Case preparation Fig.6 shows the holes to make in the lid of the UB3 Jiffy box. The four 2.5mm countersunk holes are for the PCB mounting screws (they should be countersunk on the outside of the lid). The 7mm holes are for the pots, 5mm holes for the switches and a 3mm hole for the LED. The PCB mounts to the inside of the lid on M2.5 tapped spacers. Ideally, they should be around 18mm long but that size is not readily available – I custom-made mine on a lathe. 17mm spacers are commercially available and should be OK. Deburr the holes, then fit the LED, potentiometers, their knobs and the toggle switches as shown in the Fig.7: the wiring is most easily made by cutting female/female jumper leads in half, soldering the bare ends to the chassis-mounting components and then plugging the other end into standard pin headers on the PCB. photos. Attach the spacers using four 6mm-long M2.5 countersunk head screws, then hold the PCB to those spacers using four M2.5 sized machine nuts. Solder the 220W resistors between one end of potentiometers and their case as shown. To make the connection to the potentiometer cases, you will need to abrade a small section of the pot body with emery paper, a file or similar (don’t breathe the resulting dust!). Next, cut female/female jumper leads in half, strip the cut ends, solder them to the lid-mounted components and then plug the DuPont plugs onto the appropriate headers using the wiring diagram, Fig.7, as a guide. Tape the free end of the antenna to the case. The battery is attached by double-sided tape to the inside of the case, on the opposite side to the antenna. Testing Make sure that the microcontroller is out of its socket, then check the wiring of the battery connector and the orientations of the 78L05 voltage regulator and the 433MHz transmitter module. Connect the 9V battery and switch the unit on; the red LED on the front panel should glow. Use a multimeter to probe pins 1 (red) and 14 (black) of the IC socket and verify that you get a reading very close to +5V DC. If not, check that the Fig.6: prepare the Jiffy box lid with the holes shown here. The four 2.5mm holes are countersunk on the outside. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au 5V regulator is the correct way around and there aren’t any solder bridges shorting the tracks. Switch off the transmitter and plug in the microcontroller; you may need to straighten its pins first. Push it in evenly, making sure that none of the leads fold up under the body when doing so, and ensure its notch is aligned with the socket’s. If you have an oscilloscope, connect it to pin 6 of the PIC16F1455 and the Earth connector to 0V. Switch on and you should capture a serial data waveform at 900 baud, similar to that in Screen 1. Attach the back of the case using the supplied screws. For the construction details of the Receiver and Charger, refer to the January 2025 issue. The PCBs are not difficult to assemble, so we have reproduced the PCB overlays in Figs.8, 9 & 11, which will be enough for an experienced constructor to build them. Also refer to the Receiver battery wiring diagram (Fig.10) and Charger case drilling details (Fig.12). Fig.8: this is the smaller Receiver, which uses mostly SMD parts. Programming the Receiver IC If you purchased the microcontrollers from the Silicon Chip Online Shop, they will already be programmed, so you won’t need to do anything further. However, if you build the Receivers using blank chips, you will need to program them before you can use them. To do this, solder wires to the +5V and 0V rails as well as pin 4 (MCLR) of the microcontroller, and the pads on pin 10 (ICSPDAT) and pin 9 (ICSPCLK). With those wires in place and the PIC16F1455 IC attached to the board, connect the wires to your programmer (check its pinout in the documentation). The Receiver firmware is available from the same link as before (from siliconchip.au/Shop/6/508). Use your PIC programmer to upload it to the chip (eg, using Microchip’s free MPLAB IPE programming software). Use the testing procedure from the January 2025 article (siliconchip.au/Article/17607) to test the Receiver but adapt it to use the Dual Transmitter that you just built. Final testing Fig.9: the slightly larger Receiver board uses mostly through-hole parts. Fig.10: the Receiver battery wiring. Fig.11: the battery Charger uses all through-hole parts and is straightforward to build. Switch on the Transmitter and set the speed controls to their Fig.12: the Charger also fits into a UB3 Jiffy box, with the required holes shown here. For full assembly instructions, refer to the January 2025 issue. siliconchip.com.au Australia's electronics magazine October 2025  77 minimum position. With engine 1 on its back and connected to its carriage, switch on its Receiver by removing the on/off plug from the jack socket. Rotate the speed control for train 1 on the transmitter; the engine wheels should start to turn, spinning faster as the control is rotated towards maximum speed. Turn the control back down and the speed should decrease to zero just before minimum rotation. Repeat this test with the forward/ reverse switch in the other position. If you change the position of the forward/reverse switch, nothing will happen until the corresponding speed control changes. To avoid damage to the train’s motors, always reduce the speed control to its minimum before operating the forward/reverse switch. Switch off the transmitter and insert the on/off plug to switch off the train, then repeat the above procedure for train 2. Testing the trains on the track Place train 1 on the track and remove its on/off plug. On the transmitter, rotate the speed controls for trains 1 & 2 fully anti-clockwise. Switch on the transmitter and slowly rotate train 1’s speed control clockwise. Train 1 should start to move in a direction depending on the position of its forward/reverse switch. Continue rotating the speed to maximum and the train should accelerate to maximum speed. Switch off the transmitter and the train should continue running at maximum speed. Switch on the transmitter again and rotate train 1’s speed control to minimum. The train should slow down and then stop. With train 1’s potentiometer in the minimum position, rotate train’s 2 potentiometer; you shouldn’t see any response from train 1. Repeat the above test after moving the reverse switch to the other position. Remove train 1 from the track and insert its on/off plug, then repeat the above test for train 2. If the red LED on the train lights, it is time to charge the batteries in the train. To do that, insert the Charger’s jack plug into the train’s socket and SC switch on the Charger. Parts List – Dual Train Remote Control 1 500mm length of 1.5mm diameter black or clear heatshrink tubing various lengths & colours of light-duty hookup wire (wire for the power to the engine can be from old USB and mouse cables) Dual Train Controller (Transmitter) 1 double-sided PCB coded 09110245, 57 × 40mm 1 black UB3 Jiffy box 1 3-pin 433MHz transmitter module, WRF43301R or XLC-RF5 (MOD1) [Little Bird, AliExpress, eBay] 1 9V battery snap with flying leads 1 9V battery (BAT1) 2 10kW linear (B-curve) 24mm potentiometers with nuts (VR1, VR2) 2 large knobs to suit VR1 & VR2 3 SPDT subminiature toggle switches (S1-S3) [Jaycar ST0300] 1 14-pin DIL IC socket (optional; for IC1) 1 40-way female header strip (cut into five 2-way and two 3-way strips using side cutters) 4 M2.5 × 6mm countersunk head machine screws 4 M2.5 nuts 4 M2.5 × 17mm tapped spacers [element14 1466854] 1 20 × 40mm (approximate) piece of foam-cored double-sided tape 1 200mm length of 0.4mm diameter enamelled copper wire 8 200mm female-female DuPont jumper leads (two red∎, two black∎, one blue∎ & three green∎) 1 PIC16F1455-I/P 8-bit micro programmed with 0911024D.HEX, DIP-14 (IC1) 1 78L05 5V 100mA linear regulator, TO-92 (REG1) 1 3mm high-brightness red LED (LED1) 1 1N5819 40V 1A schottky diode (D1) 2 100μF 16V low-ESR electrolytic capacitor 6 100nF 50V ceramic, MLC or MKT capacitors 4 10kW ¼W 1% axial resistors 2 220W ¼W 1% axial resistors Charger 1 single- or double-sided PCB coded 09110244, 63 × 32mm 1 UB3 Jiffy box 1 9V DC 150mA+ plugpack Screen 1: the waveform between pin 6 of the PIC16F1455 IC and ground is a 900 baud serial stream. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au That time of year is nearly here... 1 2.5mm mono jack plug (CON2) [Jaycar PP0100] 1 chassis-mount DC socket to suit plugpack (CON3) 1 chassis-mount SPST miniature momentary pushbutton (S3) 1 8-pin DIL IC socket 5 2-way pin headers, 2.54mm pitch 6 female-female DuPont jumper wires, ideally joined in a ribbon 4 M3 × 8mm countersunk head machine screws 8 M3 hex nuts 1 500mm length of single-core screened microphone cable 1 PIC12F617-I/P 8-bit micro programmed with 0911024C.HEX, DIP-8 (IC4) 1 LM285-2.5 voltage reference diode, TO-92 (REF1) 1 78L05 5V 100mA linear regulator, TO-92 (REG2) 1 IRL540N 100V 36A Mosfet, TO-220 (Q1) 1 BD136/138/140 45/60/80V 1.5A PNP transistor, TO-126 (Q2) 1 5mm green LED (LED3) 1 5mm red LED (LED4) 1 1N4004 400V 1A diode (D2) 1 1N4148 75V 200mA diode (D3) 2 100μF 16V low-ESR radial electrolytic capacitors 3 100nF 50V ceramic, multi-layer ceramic or MKT capacitors 4 10kW ¼W 1% axial resistors 3 2.2kW ¼W 1% axial resistors 2 220W ¼W 1% axial resistors 1 39W 1W 1% axial resistor (for testing) 1 22W ¼W 1% axial resistor CHRISTMAS Spice up your festive season with eight LED decorations! Tiny LED Xmas Tree 54 x 41mm PCB SC5181 – $2.50 Tiny LED Cap 55 x 57mm PCB SC5687 – $3.00 Tiny LED Stocking 41 x 83mm PCB SC5688 – $3.00 Receiver – two are required per Transmitter 1 4-pin 433MHz receiver module, WRF43301R or XLC-RF5 (MOD2) [Little Bird, AliExpress, eBay] 1 Polulu U3V16F15 15V output step-up DC/DC converter (MOD3) 1 Polulu S7V7F5 5V output step-up/down DC/DC converter (MOD4) 1 Adafruit DRV8871 motor driver module (MOD5) 4 1.2V 900mAh NiMH AAA cells [Jaycar SB1739] 1 2×2 AAA battery holder with flying leads 1 2.5mm mono switched chassis-mounting jack socket (CON1) [Jaycar PS0105] 2 4-way right-angle pin header, 2.54mm pitch (for MOD2 & MOD5) 2 female-female DuPont jumper wires, ideally joined together 1 red 3mm LED (LED2) available from Core Electronics 🔹 🔹 🔹 🔹 Receiver (TH version specific parts) 1 single- or double-sided PCB coded 09110242, 74 × 23mm 1 PIC16F1455-I/P 8-bit microcontroller programmed with 0911024S.HEX or 0911024T.HEX, DIP-14 (IC2) 1 14-pin DIL IC socket 3 100μF 16V low-ESR radial electrolytic capacitors 2 100nF 50V ceramic, multi-layer ceramic or MKT capacitors 3 10kW ¼W 1% axial resistors 1 1kW ¼W 1% axial resistor Receiver (SMD version specific parts) 1 single- or double-sided PCB coded 09110243, 23 × 30mm 1 PIC16F1455-I/SL 8-bit microcontroller programmed with 0911024S.HEX or 0911024T.HEX, SOIC-14 (IC2) 1 100μF 16V low-ESR radial electrolytic capacitor 1 100μF 6.3V radial electrolytic capacitor 1 47μF 16V X5R M3216/1206 SMD ceramic capacitor 2 100nF 50V X7R M2012/0805 SMD ceramic capacitors 3 10kW ⅛W 1% M2012/0805 SMD resistors 1 1kW ¼W 1% M2012/0805 SMD resistor siliconchip.com.au Australia's electronics magazine Tiny LED Reindeer 91 x 98mm PCB SC5689 – $3.00 Tiny LED Bauble 52.5 x 45.5mm SC5690 – $3.00 Tiny LED Sleigh 80 x 92mm PCB SC5691 – $3.00 Tiny LED Star 57 x 54mm PCB SC5692 – $3.00 Tiny LED Cane 84 x 60mm PCB SC5693 – $3.00 We also sell a kit containing all required components for just $15 per board ➟ SC5579 October 2025  79