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Semaphore Signal For OO Gauge Model Railways This realistic-looking OO Gauge Semaphore has been modelled on a real British semaphore. It has a red/white ‘flag’ that tilts down by 45° and lights a green LED to signal an oncoming train to continue, or is horizontal with a red light, indicating it should stop. It’s made from parts that are relatively easy to obtain, although it requires some machine tools and experience to build. S emaphore signalling was one of the first signalling systems used by railways. Semaphore signals were first patented in England in the early 1840s. They were so successful that they were adopted throughout the railway world. With the advent of coloured lights, they were slowly replaced, but a few remain in use. Adding them to a model railway makes it look very realistic. British signals come in two forms: lower and upper quadrant. Lower quadrant signals pivot the arm downwards for the off indication (trains can pass), while upper quadrant signals pivot the arm upwards for off. I decided to make a lower quadrant signal as most of the old signal photos I found showed this form. Current British practice mandates that semaphore signals, both upper and lower quadrant types, are inclined at 45° from horizontal to indicate ‘off’. 50 Silicon Chip The British semaphore signal arm consists of two parts: a timber or metal arm (or ‘blade’) that pivots at different angles and a ‘spectacle’ holding coloured lenses that move in front of a lamp so the signal is visible at night. To save having to make coloured lenses, the lamp is replaced with a 3mm red/green bicolour LED in the model. When the arm is horizontal, the red colour is switched on, and when it is down, the green colour is on. A miniature servo motor moves the signal arm up and down (see Fig.1). The servo collar is connected to the connecting rod (#10), which in turn is connected to the lever (#3). When the servo moves through 45°, the connecting lever does the same. As the connecting lever is joined to the signal blade by the pin (#4), the signal BY LES KERR Australia's electronics magazine blade follows the movement of the servo collar. In real life, the height of the signal blade above ground was determined by how far away it could be seen from an approaching train. If you only have a small layout, you can easily lower its height to make it look to scale. This is done simply by reducing the length of the connecting rod (#10) and the mounting pole (#11). We will present details of both the mechanical and electronic assembly. Just about any hobbyist should be able to assemble the control board as it is a simple single-sided design using all through-hole parts. However, note that making the parts for the mechanical assembly will require some machining experience and some advanced tools. Specifically, you will need a lathe; just about any small one will do, as long as it’s built to reasonable siliconchip.com.au Fig.1: this shows in detail what the Semaphore Signal looks like when it’s assembled and where all the pieces go. It’s essential to refer to this diagram during each construction step to make sure the parts go together correctly. tolerances. Most of the machining involves either brass or aluminium, both of which are relatively soft. You will also need a precise drill press and a good selection of drill bits. While you can probably get away without it, to produce an exact copy of the Semaphore presented here, you will also need a basic mill with an end mill tool, and the knowledge and ability to use it. A video showing the Semaphore in operation: siliconchip.com.au/Videos/ Model+Railway+Semaphore+Signal Circuit description The straightforward controlling circuit is shown in Fig.2. The speed at which a servo motor rotates is a function of the servo itself. In the case of the semaphore signal, we need it to rotate much slower than its maximum speed to make it look realistic. This is achieved by feeding a series of pulses to the servo’s control terminal, with a time delay between each pulse. When the up/down switch (S1) is siliconchip.com.au moved to the up position, digital input RB0 of microcontroller IC1 (pin 6) goes high, causing the microcontroller to produce a series of such pulses at its digital output RB1 (pin 7). The result is that the servo motor moves slowly clockwise by 45°. At the same time, digital output RB2 (pin 8) is brought high and output RB5 (pin 11) low, causing the red LED to light. The 100nF capacitor from pin 6 of IC1 to +5V stops any contact bounce produced by the switch. If the switch is returned to the down position, RB0 is pulled low by the 10kW resistor, resulting in another series of pulses from output RB1 that return the servo motor to its original position. At the same time, output RB2 goes low and output RB5 high, resulting in the LED changing colour back to green. Servo motors are not as accurate as stepper motors when moving through a specific angle, being out by as much as 10%. Similarly, any variation in the position of the signal blade hole, the LED plate or the connecting lever and Australia's electronics magazine The finished Semaphore will look like this, with wires connected to the PCB. April 2022  51 Fig.2: the control circuit, which runs from a 5V supply, is quite simple. Microcontroller IC1 monitors switch S1 and, depending on its position, sends pulses to the servo to control its angle while lighting either the red or green elements of LED1. Trimpots VR1 & VR2 fine-tune the angles of the flag in the horizontal and down positions, respectively. the servo collar can produce errors. To solve this, two 1kW trimpots are provided. The first varies the position of the signal blade in the horizontal position, and the second in the 45° down position. The trim potentiometers vary the voltage on analog inputs RA0 and RB7 of IC1 (pins 17 & 13, respectively). These feed into IC1’s internal analog-to-digital converter (ADC) which converts the voltages into numbers. The microprocessor uses these values to determine the pulse widths to produce in the two static positions. Mechanical assembly Many of the mechanical Semaphore parts need to be made, and the details of these are shown in Fig.3 (#1-9) and Fig.4 (#10-14). They are made as follows. #1 Cap and cap pin I turned the cap from a piece of 6mm aluminium rod by mounting the rod in the three-jaw chuck of a lathe, facing the end (ie, squaring it off) and turning down the diameter to 5.2mm for 5mm. I then cut the 127.6° taper. I reversed the job in the chuck and parted it off to 3mm, then used a centre drill followed by a 2mm drill to a depth of 2mm, taking care not to break through to the taper. I made the cap pin from an 8mm length of 2mm rod, glued in the hole I drilled in the cap using Loctite GO2 (available from Bunnings). The shape of this item isn’t critical, as it varied between different signal 52 Silicon Chip manufacturers. Paint the cap assembly red. #2 LED plate I made this from a piece of 1/32-inch (0.8mm) thick brass sheet. The distance between the holes is the critical dimension. Drill the holes, then cut the plate to size. Finally, clean up the edges. #3 Connecting lever This was made from a piece of 1/16-inch (1.6mm) thick, 1/4-inch (6.35mm) wide brass. Again, the distance between the holes is critical. Drill the holes first, then cut and file the lever to size. Paint the connecting lever blue-black. #4 Pin Cut a piece of 1/16-inch (1.6mm) diameter steel rod to a length of 11mm. Clean up any burrs on the ends. #5 Pillar (4 required) Similarly, I made these from 0.8mm diameter (1/32-inch) brass rod cut to 12mm in length. Again, clean up any burrs on the ends. #6 Railing This was also made from 0.8mm (1/32-inch) diameter brass rod. I turned a short length of scrap round to 11.2mm diameter and used that as a mandrel to form the curve. A small amount of heat applied by a gas torch makes bending easier. #7 Platform base This is made from a piece of 1/32inch (0.8mm) brass sheet. Drill all the holes, then cut the plate to size. Next, using a fine saw and file, cut out the square section so that it is a tight fit around the 1/8 inch square mounting Australia's electronics magazine pole (see #11 below). Finally, clean up the edges. #8 Ladder support This is made from a length of 0.8mm (1/32-inch) diameter brass rod. Use a piece of 1/8-inch (3.2mm) square brass as a mandrel to form the shape. Again, a small amount of heat applied by a gas torch makes bending much easier. #9 Support Place a piece of 12mm diameter aluminium rod in the three-jaw chuck of a lathe and face the end. Turn it down to 20mm to make it a slide fit in a 3/8-inch (9.5mm) diameter hole. Use a centre drill followed by a 4.3mm (11/64-inch) drill to bore it out to a depth of 20mm. Next, reduce the end to 5.25mm diameter for 8mm and part it off to length. Finally, drill and tap the hole in the side for the 2.5mm grub screw. Paint the support blue-black and when dry, then fit the 2.5mm grub screw. #10 Connecting rod I made this from 0.8mm (1/32-inch) diameter brass rod. Bend one end of the rod through 90° but only bend the other through about 20°. This is because the rod has to pass through the 2.6mm hole in the 5.5mm-thick base. We will bend it to 90° later in the assembly process. Paint the connecting rod blue-black. #11 Mounting pole The mounting pole is made from a length of 1/8-inch (3.2mm) square hollow brass tube. Drill the 1/16-inch (1.6mm) diameter hole at 92mm from the pole end. You can make the slot by drilling two 1mm holes 1mm apart siliconchip.com.au Fig.3: this shows the smaller parts (#1-#9) that need to be made. Some can be made on a lathe, while others require a saw, files and drilling. #6 and #8 are made by bending thin cylindrical bar stock on rectangular formers. Note that all dimensions are in millimetres. Fig.4: the remaining parts to make, including the larger items (#10-#12) plus a detailed view of the partially assembled Semaphore at right. siliconchip.com.au Australia's electronics magazine April 2022  53 and using a file to remove the remaining metal. Make sure that the insides of the slot and the insides of each end are free of swarf and are smooth, as when we insert the LED wires, we don’t want to cut their insulation. #12 Base My layout is made on a 2-inch (51mm) thick sheet of polyurethane foam. I buried the signal in the foam so that it was flush with the top of the base. This left a 0.5mm step down all around the Semaphore that I later filled with ornamental grass, so that the base was more in keeping with the scale. Depending on your layout, you might decide to leave out this step down. The base is made from 6mm aluminium plate. Cut it to size, then drill and tap the required holes. I made the step using an end mill in a milling machine. Paint the base blue-black and when dry, fit the 2.5mm grub screw. #13 Servo bracket This is made from 1/16-inch (1.6mm) thick aluminium sheet. Drill the two 3mm holes 29mm apart, then cut it to size. Clean up the edges with a file. #14 Servo collar Place a length of 12mm diameter aluminium bar in the lathe three-jaw chuck, face the end and turn it down to a diameter of 9.8 mm for 10mm. Bore it out to a depth of at least 5mm using a centre drill followed by a 4.8mm diameter drill. Part off a 3mm section, transfer this to the drilling machine and drill the 2mm hole for the grub screw. Thread the hole with a 2.5mm tap and fit the grub screw. Finally, drill the 0.8mm diameter hole exactly 4mm from the centre. Parts List – Semaphore Signal 1 single-sided PCB coded 09103221, 51 x 37mm (controller) 1 double-sided red PCB coded 09103222, 31 x 20.5mm (blade) 1 PIC16F88-I/P microcontroller programmed with 0910322A.hex (IC1) 1 5V DC power supply 1 DF9GMS 9g micro servo [Core electronics SER0006] 1 18-pin DIL socket (optional; for IC1) 2 1kW mini top-adjust trimpots (VR1, VR2) 1 3mm red/green LED, three-lead type (LED1) [element14 Cat 2148798] 1 miniature SPDT toggle switch (S1) [Jaycar ST0300] 2 M3 x 16mm panhead machine screws (for mounting servo) 10 1mm PCB pins 1 10mm length of 1mm diameter heatshrink tubing various lengths & colours of light-duty hookup wire 1 tube of Loctite GO2 adhesive 1 tube of Tarzan’s Grip or similar adhesive Capacitors 1 100μF 16V electrolytic 2 10μF 16V electrolytic 2 100nF 50V multi-layer ceramic Resistors (all 0.25W 1% metal film) 1 10kW 1 5.6kW 1 4.7kW 1 2.2kW 1 820W 2 680W Mechanical parts 1 300mm+ lengths of 0.8mm (1/32-inch) diameter brass rod 1 20mm+ length of 1.6mm (1/16-inch) diameter steel rod 1 20mm+ length of 2mm diameter aluminium rod 1 20mm+ length of 6mm diameter aluminium rod 1 40mm+ length of 12mm diameter aluminium rod 1 103mm length of 3.2mm (1/8-inch) square hollow brass tube [KS Metal] 1 20mm+ length of 1.6mm (1/16-inch) thick, 6.53mm (1/4-inch) wide brass bar 1 20 x 20mm rectangle of 0.8mm (1/32-inch) thick brass sheet 1 46 x 55mm rectangle of 6mm-thick aluminium sheet 1 35 x 7.5mm rectangle of 1/16-inch (1.6mm) thick aluminium sheet 1 OO-scale ladder [D.J.’s Models] 3 2.5mm grub screws 54 Silicon Chip Australia's electronics magazine Mechanical assembly With the parts now made, refer back to Fig.1 to see how they all go together. The LED plate (#2), platform (#7) and ladder support (#8) are all soldered to the mounting post. Clean, tin and flux the mating surfaces between the LED plate and the mounting post. Insert a temporary pin in the 1/16-inch (1.6mm) hole and use it to align the two pieces. Using a small blowtorch, heat the assembly until you see solder coming out of the joint. File off any excess solder. Now clean, tin and flux the mating surfaces between the platform and the mounting post. To align the plate squarely, use a small timber cube as a support and clamp it to the mounting post. Using a small blowtorch, heat the assembly until you see solder coming out of the joint. The next step is to solder the four 12mm pillars into the platform. Do this one at a time using a soldering iron. To keep them vertical in this operation, drill a 0.8mm hole vertically into a piece of scrap timber into which you insert the pin. The railing can then be soldered into place, making sure it is parallel to the platform. File off any excess solder. Next, clean, tin and flux the mating surfaces between the ladder support and the mounting post. To keep it level, make a small timber cube for it to rest on and clamp that to the mounting post. Using a small blowtorch, heat the assembly until you see solder coming out of the joint. File off any excess solder. The whole assembly can then be painted white. Signal blade The signal blade can be purchased as a PCB, coded 09103222 and measuring 31 x 20.5mm – see Fig.5. Using a small pair of side cutters, carefully remove the blade from the PCB. You can also snap it at the weak points deliberately created by holes drilled into the supports. Clean up the blade edges with a file. The PCB should already be coloured red/white, and you can easily paint the spectacle area (see Fig.6) by masking it and applying spray paint, painting it with a brush, or even using a black permanent marker. However, if you aren’t happy with the PCB colour, or you made the flag some other way, you can download the artwork (Fig.6) from the Silicon siliconchip.com.au Chip website, print it on a colour printer and cut out the front and back shapes. Use two-part five-minute epoxy to glue the front shape onto the face of the blade. Once dry, carefully clear the paper from the holes. Glue the rear label on and again remove the paper from the holes. should rotate 45° anti-clockwise while the LED should change to green. Add the short again and switch off the power. Leave the servo in this position as it will make the final assembly process easier. Now is a good time to give the bottom of the PCB a coat of clear varnish to protect it from corrosion. Control module Final assembly The heart of the semaphore signal is built on a single-sided PCB coded 09103221, which measures 51 x 37mm. Fig.7 is the PCB component overlay diagram. Start its assembly by fitting the PCB pins, then the IC socket. The reason for the IC socket is that there is no provision for in-circuit programming, although if you have purchased a pre-programmed micro, you could just solder it to the board. Alternatively, if you have a blank micro, download the firmware from the Silicon Chip website and program it using an external programmer now, before fitting it. Take care to orientate the socket/ IC correctly. Next, add the vertically-­ mounted resistors; you can replace the 0W resistor with a wire link. Follow with the capacitors; check that the electrolytic types are the correct way around, with the longer leads to the + symbols. Next, add the 1kW trimmer potentiometers and temporarily connect the servo motor and LED1 (as per Fig.8). Finally, connect the positive of the 5V power pack to +5V and the negative to 0V. Check that all the connections are correct and that there are no dry joints or solder bridges. At this stage, don’t plug in IC1 yet if you have used a socket. Refer back to Fig.1 during final assembly to see how the Semaphore goes together. 1. Push the red/green LED into the LED plate. Before trimming the leads as short as possible, note which is the shortest as this connects to the red LED. The centre lead is the common, and the other goes to the green LED. 2. The connecting wires must be very fine to fit through the mounting pole. I found suitable wires in an old computer mouse connecting cable. I selected red, yellow and black and made them about 300mm long. Using a fine-tipped soldering iron, connect the red wire to the red LED terminal, the yellow wire to the green LED terminal and the black wire to the common (middle) terminal. 3. Cut a 5mm length of 1mm diameter heatshrink tubing and slide it over the wires. Insert the wires one at a time into the post until they protrude from the end. Be very careful not to strip the insulation off in this process. Straighten up the wires and shrink the tubing down over the exposed portion of the wires using a heat gun. 4. Insert #4 (the 1/16in [1.6mm] diameter steel pin) into the signal blade and lock it into place using Loctite GO2. When dry, slide the assembly into the mounting pole (#11). 5. Push the support (#9) into the base (#12) with the grub screw in the support on the right-hand side when looking at the front of the signal. Tighten the grub screw in the base. 6. Push the three wires at the bottom of the post through the hole in the support, then push the post into the support and lock it temporarily in place using the grub screw in the support. 7. Take the connecting rod (#10) and push the end with the 20° bend up through the base and platform to the signal blade height. Use pliers to increase the 20° bend to 90°. 8. Insert the end of the connecting rod into the 0.8mm (1/32in) hole in the connecting lever (#3) and push Testing Switch on the power supply and connect the negative lead of a voltmeter to pin 5 of the IC socket and the positive lead to pin 14. The meter should read +5V. If it reads -5V then the IC socket or IC is the wrong way around. Switch off the power and insert the IC (if you used a socket), checking that it is correctly orientated. Switch the power on, and the LED should glow green. Short S1’s two terminals together and the LED should now glow red, while the servo motor should rotate 45° clockwise (looking at the shaft). Remove the short, and the servo siliconchip.com.au Australia's electronics magazine Fig.5: the semaphore flag is too small for most PCB manufacturers to make by itself, but they will make this larger PCB which can be snapped or cut apart (at the holes represented by black filled circles) to give you something very close to the correct flag shape. After cutting or snapping it out, all you have to do is file the top and bottom edges flat. Fig.6: this artwork can be printed, cut out and glued to the flag if it isn’t already coloured or you aren’t happy with the colour or surface finish. Fig.7: it shouldn’t take long to assemble the PCB as it only has a handful of parts on it. Make sure the chip is programmed first if you’re going to solder it directly to the board and watch the orientations of the electrolytic capacitors (the longer leads are positive). April 2022  55 the pin attached to the signal blade into the 1.6mm (1/16-inch) hole in its other end. With the signal blade horizontal, adjust the position of the connecting lever so that it is parallel to the axis of the signal blade. Lock the connecting lever temporarily in place with a blob of Tarzan’s Grip or similar glue. 9. Attach the servo bracket (#13) to the base using the two 16mm M3 screws. Align the servo motor as shown in Fig.1, and attach the servo collar to the shaft with the grub screw hole at the bottom. 10. Loosen the grub screw holding the mounting post in place. Slide the servo motor assembly under the retaining bracket. By adjusting the height of the post, you should be able to align the connecting rod with the 0.8mm (1/32in) hole in the servo collar. Push the end of the connecting rod into the collar. 11. Move the servo until the connecting rod is vertical, then lock it in place by tightening the screws. Adjust the height of the column until the connecting lever at the top of the signal is horizontal. Tighten the grub screw holding the mounting post in place and the grub screw in the servo collar. 12. Check that the signal blade is parallel to the front of the mounting base. If it is not, loosen the grub screw in the base and rotate the post until it is. Tighten the grub screw. Wiring Wire up the signal as shown in the wiring diagram, Fig.8. Check this before applying power, as reversing the supply polarity will destroy IC1. Then, with the switch closed, apply power. The LED should glow red, and the signal blade should be horizontal. Open the switch; the LED should light green and the signal blade should move down about 45°. Operate the signal several times to make sure it changes over smoothly and that nothing is binding. Check the tightness of the three grub screws and the servo screws. The two potentiometers on the PCB allow you to fine-tune the position of the two holes over the LED in the signal blade. The potentiometer closer to the LED connections on the PCB (VR1) adjusts the position of the signal blade in the horizontal position and the other (VR2) in the down (45°) position. Once you are happy with the blade position, use a drop 56 Silicon Chip Fig.8: once you’ve assembled the Semaphore and the control PCB, here is how to wire them up. Be very careful to get this right, especially the 5V power and servo wiring, or you could damage IC1 or the servo when you apply power. of Loctite GO2 to glue the connecting lever in place. Fitting the cap and ladder Attach the red cap and pin assembly into the top of the mounting pole using Loctite GO2. Take one of the supplied ladder lengths and paint it blue-black. When dry, lay the ladder up against the platform support and check that the top rung is level with the platform. Cut it to size and use Loctite GO2 to glue the ladder to the platform and support. I deliberately didn’t glue the ladder to the base, as that would stop the post assembly from being adjusted later. Using it The Semaphore could be combined with a level crossing, such as my design (July 2021; siliconchip.com. au/Article/14921), or you could use it on its own, such as before a switch or a station. The simplest method is manual control. Position a toggle switch at a convenient location in the layout. With the Semaphore in the stop (horizontal) position, manually stop the train in front of it. Then, switch the Semaphore off at an appropriate time, and the train can move away. There are also methods to automate it. For example, if used near a level crossing, you could arrange for the Semaphore to usually be in the stop Australia's electronics magazine (horizontal) position and then automatically switch to the down position when the level crossing boom gates are fully down. It could change back to the stop position as soon as the boom gates start to lift. All you need to organise this is to have a microswitch or reed switch arranged so that it is open when the boom gates are fully down and closed the rest of the time. If you can’t easily do that, the other option is to use a delay circuit that’s triggered by the same signal that activates the level crossing. Set the delay so that it closes a set of relay contacts or activates an open-collector/drain transistor after the boom gates have had a chance to fully lower. Use those contacts or that transistor to trigger the Semaphore into its off position, and arrange it so that the contacts open or transistor switches off as soon as the Level Crossing trigger switches off. You could also consider positioning a reed switch under the tracks and placing a magnet in the train. This way, when the train pulls to a stop in front of the Semaphore, it triggers a delay circuit that disables the Semaphore signal after a couple of seconds. It would need to hold it off until the train has passed, possibly sensed by a second reed switch. I’ll leave the details of that arrangement as an exercise for the reader. SC siliconchip.com.au