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PART 2: Last month, we presented the circuit details of our new Railpower Mk.II controller. We follow up this month with the construction details and a testing procedure for the completed unit. It can be run from a standard 12V battery charger or a model railway power supply. By RICK WALTERS L ET’S STATE AT THE OUTSET that the Railpower Mk.II is a highly flexible design and there is no reason why it has to be built up in the way we are presenting it in this article. We are featuring it in two plastic cases, one for the pushbutton control unit and a large case for the microprocessor-controlled pulse pow- 32  Silicon Chip er board. Many people will probably want to build the main board into a large console while others will want to conceal it underneath their layout. So be it. You can do it in several ways. Just remember that the basic circuit, as featured on the two PC boards, cannot be varied unless you really know what you are doing. Neither can you change any of the basic performance or operational features of the circuit, since virtually everything is under the control of the microprocessor; its Railp A Wa F internal program­ ming is fixed and immutable. With that proviso, let us now de­scribe the construction of our prototype. The main pulse power board is housed in a standard plastic instrument case measuring 204mm wide, 67mm high and 156mm deep. The front panel features the six board-mounted LEDs and the 8-pin DIN socket. The rear panel is bare except for a 5-way insulat­ed terminal block which carries the power input and track output wires. The hand control uses a small plastic case measuring 60mm wide, 30mm thick and 120mm deep. It connects to the main unit via a cable fitted with an 8-pin DIN plug. Before you begin assembly, both PC boards should be closely inspected for etching faults. Any broken tracks power MkII: alk -Around Throttle For Model Rail­ways should be re­ paired and any shorts cleared with a sharp knife. In particular, look closely at the two thin tracks between the pads of IC1 on the main PC board. and diodes. Next, fit the low profile capacitors and preset potentiometers. The four ICs are all ori­ented in the same direction, with the notched end facing the DIN socket end of the board. It is a good idea to solder the supply pins of each IC first, and then all the other pins. For IC1, the supply pins are 5 & 14, for IC2 & IC4, the supply connections are pins 16 & 8 while for IC3 they are pins 14 & 7. Main board assembly It is probably better to assemble the main board first. Its component overlay is shown in Fig.1. Fit and solder the five links, then the resistors Q11 TRACK 10uF 1k 10k BUZZER 10k 560  REG1 1.8k 2.2k D1 470  Q9 10k LED2 IC4 74HC42 LED4 IC3 74HC11 1 680  470  LED3 0.1 .047 10k 10uF 1 VR1 VR2 VR3 Q3 22k 10k D4-D7 VR4 470  ZD1 2x 22pF D2 4.7k 10k 1 180k 0.1 VR5 AC INPUT IC2 74HC051 X1 10k 10k 1 Q4 1k D3 IC1 Z86E08 Q8 10k 2200uF DIN SOCKET Q2 Q1 0.1  5W 10k LED1 Q6 Q5 Q7 LED6 LED5 TRACK 10k Q12 22k Fig.1: the component overlay for the main PC board. Note the heatsink assemblies for Q2 & Q6 and for Q4 & Q8. These have been drawn so as not to obscure the surrounding resistors although, in practice, they are mounted above these components. 22uF 0.1 10k Next, install the small signal transistors which are all BC338s except for Q12 which is a BC328. Then fit the larger components, ensuring that the electrolytic capacitors and the buzzer, are inserted with the correct polarity, as shown on the wiring diagram of Fig.1. The four power transistors are mounted in back-to-back pairs, Q2 with Q6 and Q4 with Q8. This physically 22k GND Q10 2200uF 0.1 October 1995  33 A bird’s eye view of the main PC board in the case. Note how the heatsink assemblies for the power transistors face outwards from each other. Don’t get the transistors mixed up when you’re mount­ing them otherwise they’ll emit smoke when you turn on the power. connects their collector tabs together with the heatsinks sandwiched between the metal tabs of the transistors. There is no need to use mica washers for the heatsinks but the metal collec- tor tabs should have a light smear of heatsink compound before they are assembled and bolted together. In practice, we suggest you bolt the tran­ sistor pairs together with their Q8 BD649 HEATSINK HEATSINK Q4 BD650 Q6 BD649 Q2 BD650 Fig.2: this diagram shows how the four power transistors are mounted in back-to-back pairs, Q2 with Q6 and Q4 with Q8. This physically con­nects their collector tabs together with the heatsinks sandwiched between the metal tabs of the transistors. There is no need to use mica washers for the heatsinks but the metal collector tabs should have a light smear of heatsink compound before they are assembled and bolted together. 34  Silicon Chip heatsinks and then insert and solder the transistor pairs to the PC board – see Fig.2. Take particular care to make sure that you pair up the right transistor types and don’t swap their connections around when mounting them on the PC board otherwise they will blow as soon as you apply power. The LEDs should be tested before the leads are bent, as it appears that there are non-standard ones around. Normally, the longer lead is the anode, which should go to the more positive side of the circuit. To test the LEDs use a 6V or 9V battery and the 560Ω resis­tor used in the hand control. Connect the resistor to the battery positive and the longer lead of the LED to the free end of the resistor. The other LED lead goes to the battery negative. If the LED lights it is a standard type; if it doesn’t, reverse the LED leads. If it now lights, cut a couple of VR1 MOUNTED ON COPPER SIDE METER 10k VR1 S1 2 2 4 1 S2 D4 6 D2 8 5 3 7 D3 LED3 8-PIN DIN PLUG SOLDER SIDE LED2 D5 D1 S3 Fig.5: this diagram shows the pin numbers of the DIN plug, look­ing at the solder side. Solder pin 8 first. S4 LED1 1 IC1 74HC42 LED4 560  S5 4.7k S6 4.7k 0.1 6 D6 4 7 3 5 TO DIN PLUG 10uF 8 1 Fig.3 (left): this is the component overlay for the hand control board. Trimpot VR1 is mounted on the copper side of the board, as indicated by its dotted outline. Note the orientation of each pushbutton switch. Seven of the DIN cable connections are shown at the bottom of the diagram while the eighth, marked “2” is at the top righthand corner. Fig.4 at right shows the full-size PC etching pattern. millimetres off the end of the longer lead, making it the shorter one. This way, all the LEDs will be similar when you come to bend them. If a LED still doesn’t light, it is faulty and should be discarded. While you have this test setup you should check the LEDs to be used in the hand control, but don’t bend their leads, as they stay straight. Looking at the LED leads with the longer one on the right, bend them both down, 8mm out from the LED body. The six LEDs on the main PC board should all have their leads bent this way. Front panel Before you solder the LEDs into the board, you need to check their alignment. Carefully affix the Dynamark label to the front plastic panel and drill out the six 5mm LED holes and the DIN connector hole. Insert LED6 (red) and LED5 (green) into the PC board and solder one leg of each, leaving about 8mm of lead above the top of the board. Insert the LEDs This photo gives a close-up view of the output transistor pairs. The collector tabs should have a light smear of heatsink compound before they are bolted to the heatsinks. through the front panel and slide the assembly into the guides at each end of the case. Screw the PC board into the bottom of the case using 6mm spacers to lift the board off the plastic pillars. Check the alignment of the LEDs through the front panel holes. If all is OK, unscrew the PC board, fit the other LEDs with similar spacing and solder all the leads. If you are not happy with the LED alignment make any neces­ sary adjustments. This completes the assembly of the main board. It cannot be tested without the hand control, so let’s build that next. The component overlay diagram for its PC board is shown in Fig.3. Hand control board After building the main board you will find this one much quicker and easier. Look carefully at the overlay and place the components as shown. Fit and solder the IC, resistors and diodes, making sure the resistors are bent over parallel to the board, or else they will be damaged when you mount the board in the case (see photo). Next fit the capacitors and push buttons making sure the flat side of each button faces the centre of the PC board. Run an insulated wire on the copper side of the board, from the pad adjacent to the 10kΩ resistor, to pin 16 on IC1. The preset potentiometer should be soldered last, as it is mount­ed on the copper side, so that you can adjust it without unscrewing the PC board. If you wish, you could drill a hole in the back of the plastic case, allowing you to make adjustments to this preset without removing the back. The LEDs can be soldered in now, although it’s best to leave them until the PC board is assembled into the October 1995  35 When you have finished assembling the hand control board the two 4.7kΩ resistors and the 10µF capacitor near the cable end must be laid flat, in order to fit into the case. This is the copper side of the board, after the cable has been terminated. Note the trimpot (VR1) at the top if the board. Leave slack on the cable leads, to avoid any stress. Some of the IC pins are unsoldered; there is no point in soldering unused pins. The completed hand control board is secured to the top half of the case which must be drilled to accept the meter, the pushbutton switches and the LED indicators. Note that the tops of the LEDs should just protrude through the case. plastic case. They can then be pushed right into the hole in the case front and their leads soldered. Now that both boards are finished, you can assemble the hand control. Hand control case The meter is mounted on the front of the plastic case (the half with the threaded brass inserts), at the end with the mould­ed recess on the front. Turn the case over and drill out the two plastic pillars. Start with a drill just big enough to remove the brass thread, then fit a drill two sizes larger and drill out again, repeating until the pillars are removed. Place the front panel template 36  Silicon Chip (Fig.7) on this half of the hand control and mark all the holes. Drill out the pushbutton and LED holes. Make the cutout for the meter either by drilling a series of holes, then cutting and filing the plastic or by using a small coping saw. Finally, drill the two mounting holes for the meter. Drill a 12mm hole centrally in one of the dark grey end pieces. Remove 100mm of insulation and screen from one end of the 9-way cable and clamp it in the end piece, using the cable clamp, leaving 5mm of the outer covering protruding through. Mount the control board in the case using the two 10mm metal thread screws and 5mm spacers to hold it in position. Check each button operation, making sure each operates without jamming. If a button is not free to move, slacken the mounting screws and readjust the board position, or ream out the offending hole. When all buttons are operating properly, mark the position of the top mounting hole for the PC board, through onto the front panel. Remove the PC board, drill the hole and countersink it in the front of the case to allow the 2.5mm machine screw to sit flush. Hold the board so that, when you look at the components, the red button is at the bottom right. Insert both the righthand LEDs into the PC board with the long lead on the righthand side. The lefthand LEDs should have their long lead on the lefthand side. The red LED goes above the STOP button, the green above the FORWARD button, The yellow above REVERSE and the orange above INERTIA. Replace the control board using the 12mm countersunk screw, 8mm spacer and nut, as well as the metal Design Philosophy For the Railpower Mk.II While last month’s article gave a comprehensive circuit de­ scription, we did not have the space to fully describe some of the operating features, especially as they related to our very popular Railpower design featured in April & May 1988. While that design was very effective, there were a number of features which we would have liked to improve upon but could not, without an excessive amount of extra circuitry. In particular, we have had comments from readers about the following points. When the Railpower was turned off, it inevitably caused any loco on the track to give a very slight lurch forward. At about the same time, the overload protection buzzer would briefly sound at a low level. This happens because the op amps in the circuit lose control once the supply voltage drops to a very low value. It’s a minor problem but a problem that would be nice to solve. While some examples of the Rail­ power with infrared remote control came on with Forward selected, most seemed to come on with Reverse selected and while this was easily corrected by pushing the Forward button before pushing the Faster button, again it was something we would have liked to fix. A more subtle problem involved the minimum speed setting. In order to make the controls more respon- thread screws and spac­ers, checking the operation of all the buttons again. Once all is OK, push the LEDs forward until they protrude satisfactorily through the front panel then solder all leads of the LEDs. Cable termination Slide the grey endpiece with the cable into the channels, at the end away from the meter, then cut and solder the wires as detailed in Table 1, leaving around 20mm of slack on each one. The terminations for the wires are marked on the copper side of the board. Pins 1-8, excepting pin 2, are all at one end of the board. Pin 2 is at the other end of the board. To make it easier to follow, we sug- sive, we provided a minimum speed trimpot and this was set to provide a low voltage across the track so that the locomotive was just on the point of moving. However, with many locomotives, the very narrow pulse output at the minimum speed setting caused an audible buzz. There was no way around this. In designing the microprocessor version of the Railpower, we were able to address all the above problems without any added circuitry – it was all done in the programming. Hence, when power is first applied, the Railpower controller always comes on with STOP selected. To make the loco go forward, just press FOWARD and the FASTER button until the desired speed setting is ob­ tained on the meter. The minimum speed buzz problem was solved in the following way. If the train is stationary and Forward or Reverse is select­ed, then the minimum speed voltage will be applied to the track and the loco will produce a background buzz. However, if the train is stationary and the Stop button is pressed, the track voltage is reduced to zero; the loco will then be totally quiet. Forward/Reverse protection In the infrared remote control version of the Railpower (presented in April and May 1992), we added pro- gest that, as far as possible, you use the wire colours corresponding to the resistor colour code. The braid (shield) of the cable should also be connected to the PC TABLE 1 Colour Pin no. Pink 1 Red 2 Orange 3 Yellow 4 Green 5 Blue 6 Violet 7 Grey 8 tection against throwing the train into reverse while it was going forward at speed. Normally, if you throw a model train into reverse it is highly likely it will be derailed and that could cause lots of damage to expensive models (if the loco and wagons fall off the layout onto the floor). In the remote control version of the Railpower, the for­ ward/reverse protection prevented reverse from being selected until the train had been brought down to a very low speed. In the new microprocessor version we have taken a different approach. Now if you press Reverse while the train is going forward, it will come to a stop and then the controller will switch to Re­verse. However, it will not move off until you use the Faster button. That way, the modeller will get a positive response when the Reverse button is pushed, even if that outcome had not really been intended. The train is still protected against damage though. We have taken this alternative approach because some users find it confusing when there is no response to persistent pressing of the buttons. This way, you learn to press the right buttons. Finally, because the microprocessor allows nothing to happen unless a button is pressed, there is no disconcerting lurch from a locomotive when the unit is switched off and nor does the buzzer sound briefly. board. Cover the braid with a piece of sleeving and con­nect it to the pad marked B(raid). The cable we used had two green wires so we used the dark green for the termination; the light green wire should be cut off as short as possible, as it is not used. October 1995  37 Fig.6: this is the full-size etching pattern for the main PC board. Check your board carefully for etching defects before installing any of the parts. The Dynamark label can now be affixed to the front panel and the meter mounted. Run two wires from the PC pads marked “meter” to the meter terminals, left pad to left lug, right pad to right lug. The other end of the cable can now be terminated into the 8-way DIN plug. To prevent the pins moving as you solder them, push the plug into the socket on the main board. Don’t forget to slide the outer rubber sleeve of the plug, small end first, onto the cable before you begin! Cut the insulation and sheath back about 30mm, cut off the light green wire, and using the previous table connect the wire colour to the corresponding pin number. We have shown the pin markings for an 8-pin DIN socket in the diagram of Fig.5 as some DIN sockets do not have the pin markings and even if they do, they can be hard to see even under good lighting. The braid should be threaded through the hole in one of the clamps that restrain the cable, then soldered. Check the colours against the numbers again, then reassemble the plug. Testing Set trimpots VR1 (Inertia) and VR2 (Brake) to mid position. Turn 38  Silicon Chip C C A A D B B A A B B A A HOLES: A = 9mm B = 3.2mm C = 2mm D = 2.5mm Fig.7: photocopy this diagram and use it as a template when drilling and cutting the holes on the hand control. the minimum speed control VR4 to minimum and the maximum speed control VR3 to maximum. Set the Meter adjustment VR5 to centre position. Set trimpot VR1, in the hand control, anticlockwise. Power input to the main board can be from a standard 12V battery charger or from a 12-15VAC model railway power supply. Either way, you connect to the two PC pins on the board marked “AC input”. Plug the hand control into the main board and turn on the power. The green power LED on the main board should light imme­ diately, followed by the red Stop LEDs on main board and the hand control. Pressing the Forward button should extinguish the Stop LED and light the green Forward LED on both units. Pressing Reverse should cause the green LED to go out, the Stop LED to light briefly, then the yellow Reverse LEDs to light. Hold down the Faster button and the meter should start creeping up the scale. Release the button and the meter should instantly drop back then begin to climb slowly. Press Slower and the meter should jump upscale then creep back as the button is held down. If everything is working so far, it STOP RAILPOWER Fig.9: the full-size artwork for the hand control label. is time to test the unit in situ. Turn off the mains power and disconnect the wires from the main board and then mount it in the case. Fit a 5-way insulated terminal block to the back panel, as shown in the photograph, to take the wires for the AC input and track output. Connect the Railpower to your layout and place a loco on it. Turn on the mains power and the green power LED should come on as before. Pick up the hand control and press FORWARD, then hold FASTER down and if the train moves forward, the polarity of the wires to the track is correct. Note that the train may not move immediately, as the minimum speed preset was set to 0V. If the train runs backwards, swap the wires connecting the controller to the track. Calibration It will take a few attempts to get the adjustment of the trimpots to your satisfaction. The minimum and maximum speed trimpots will undoubtedly need resetting several times, as well as those for inertia and brake. As we explained in the circuit description last month, the microprocessor normally only reads the values set on the trimpots when the power is first turned on. To save you from having to turn the power off and on after each adjustment, it is only necessary to hold down the FORWARD button and then press and release the INERTIA button. Fault finding There are two rules to follow if it doesn’t go when you turn it on. The first rule is don’t panic and the second is don’t assume that you have a faulty IC or crook transistor. While it may be a shock to your ego, the most likely reasons why the unit does not work are shorts due to solder splashes on the underside of the board, poorly soldered or unsoldered connec­tions, crossed wires in the DIN connector cable or components in the wrong way. So the first step in rectifying any problem is to very thoroughly inspect your work. As all the LEDs have been tested, there shouldn’t be any problems associated with them. If you wish to check the DIN cable, use a multimeter set to a low Ohms range and check for continuity between each pin and its respective pad on the hand control PC board. If the green POWER LED does not light you may have a prob­lem with your power wiring or a short on the +5V line. You should have +5V at the output of REG1, at pin 5 of IC1, pin 16 of IC2 & IC4, pin 14 of IC3 & IC1 in the hand control and at Q12’s emitter. If the green LED lights but the red Stop LED does not light at power-on, the first step is to unplug the hand RAILPOWER INERTIA OV E FORWARD R L OA D REVERSE ST OP FO R W AR D RE V E IN RS ER E T I A OF F FASTER ER SLOWER This tells the microprocessor to read the trimpot values again. So each time you want to readjust the trimpots, press these buttons to get the new values loaded into the microprocessor’s memory. If you readjust the minimum speed it will be necessary to stop the train to make this new value effective. Once you are satisfied with the trimpot settings, you can calibrate the meter. Slow the train with the SLOWER button until it comes to a complete stop. Adjust trimpot VR1, in the hand control, until the meter’s pointer is on zero. Press FORWARD, wait until the green LED lights, then press INERTIA and the orange LED will light. Take the train to maximum speed, then set trimpot VR5 on the main board for a reading of 10 on the meter. There is a small amount of interaction between these two adjust­ments and it may take several attempts to get them spot-on. Note that if you change the settings of the maximum or minimum speed trimpots, you will have to recalibrate the meter. PO W SPEED Fig.8: the artwork for the front panel label of the main board case. control. Turn the power off, wait for 10 seconds then re-apply power. If it now lights, the problem is most likely in the cable connections. If all the LEDs light in the way they should when the but­tons are pressed, but the loco does not go, then the microproces­ sor is working and the fault is in the area associated with IC3 SC or the transistor H-bridge. October 1995  39