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Modifying the circuit for a hard-wired “walk-around” throttle. PART 3: By JOHN CLARKE & LEO SIMPSON BUILD THE RAILPOWER As promised in part 2, here is the walk-around throttle version of the Railpower speed control for model railways. It uses four switches to control speed, forward/reverse, inertia and braking. W ELL, WHAT IS a walkaround throttle control any way? It is a little hand-held control that you can plug in on several places on your layout. It means that you don’t have to be tied down to one place on your layout. 70  Silicon Chip For example, for shunting manoeuvres you might want to be very close to the locomotive as you marshall up a train. At other times, you might want to be close to the straight, so you can see your train barreling down towards you. Or perhaps you have a turntable and you want to watch the locomotive closely as it comes on and off. Whatever the reason, you want to be able to plug the hand control into one of a number of sockets around the layout to closely observe and control your trains. You want to be able to plug it in, set the train speed and direction and then unplug, go to the new location and plug in again, all without the locomotive faltering in any way – it should just maintain the settings, as if you had not touched the controls. Of course, you have most of the advantages of a walk-around throttle with the infrared remote control version published in the previous two chapters. But perhaps there are parts of your layout which will not let you use the IR remote control – perhaps they don’t have a line-of-sight back to the control unit. Possibly, you don’t want the remote control version because it uses batteries and yes, the AAA-cells will need to be replaced from time to time. OK, so you want the walk-around throttle; here it is. It consists of a small plastic case with three toggle switches and a pushbutton. Note that there is no provision for the auxiliary switching although that could be done if need be. We leave those details to you. Of the three toggle switches, two are spring-loaded 3-position types with the centre-position being OFF (ie, centre-OFF). These are used as the up/down speed control and the Direction control (forward/reverse). The Speed switch is pushed to the right to make the speed increase (UP); push it the other way and the speed setting decreases (DOWN). The Direction switch is used in the same way: push it to the right to select Forward operation and to the left to select Reverse. Mind you, the Lockout feature of the circuit still works so that the locomotive must be virtually stopped before you can change the direction of operation. The remaining toggle switch is the inertia ON/OFF control. The pushbutton is a momentary push-on type. Pressing it once brings the STOP function into play. Pressing it again will release the STOP function and allow the locomotive to resume its previous speed setting. Alternatively, pushing the speed Inside the modified Railpower. The infrared receiver components have been replaced by a hard-wired connection terminated in an 8-pin DIN plug on the rear panel. The modification is quite simple. switch UP or DOWN will achieve the same result. The hand-held control is wired via a length of 8-way cable to an 8-pin DIN plug. Inside the Railpower itself, IC1, IC2, Q1, three resistors and a capacitor are omitted and a 14-pin socket is installed in place of IC2, to allow the circuit connections from the handheld control to be made via a 14-pin header plug. The circuit of the walk-around control is shown in Fig.1. What we have done is to reproduce the top lefthand corner of the of the Railpower circuit which previously involved IC1, the infrared receiver and IC2, the 8-channel decoder. Eight control lines run away from IC2 in the original Railpower circuit and we now control six of those lines (omitting the two for the Auxiliary outputs) via the hand-held control and the 14-pin socket. The circuit also involves the +5V rail at pin 14 and the 0V line at pin 1. The forward/reverse switch, S1, operates by pulling pin 3 or pin 8 A close-up view of the modified section of the PC board with the header connector shown in detail above. DECEMBER 1999  71 Parts List 1 plastic case 83 x 54 x 31mm 1 label, 80 x 50mm (see Fig.5) 2 centre-off spring return momentary SPDT toggle switches (S1,S4) 1 SPDT toggle switch (S3) 1 miniature pushbutton switch (S2) 1 8-pin DIN line plug 1 8-pin DIN panel socket 1 1.5m length of Cat 5 8-way stranded cable (cut to 1100mm and 400mm) 1 150mm length of 0.8mm tinned copper wire 1 small cord grip grommet 4 10kΩ 0.25W 1% resistors 1 22µF 16VW PC electrolytic capacitor 1 14-pin IDC header plug 1 14-pin IC socket 2 M3 screws and nuts pin high (ie, to +5V) when selected. The lines from these pins drive the bases of transistors Q10 or Q11, respectively. Pushbutton STOP switch S2 operates by pulling pin 7 high. When S2 is released, the 10kΩ resistor pulls pin 7 low again. The 22µF capacitor provides debouncing for the switch contacts. The inertia switch S3 pulls pin 9 high when it is set to OFF. When S3 is set to ON, pin 9 is pulled low via the associated 10kΩ resistor. Finally, Speed switch S4 operates by pulling either pin 5 or pin 6 high (+5V) for speed DOWN or speed UP. When released, the switch springs back to its centre-OFF position and the two 10kΩ resistors pull pins 5 & 6 low. Fig.1: compare this modified section of the circuit with the infrared circuit shown last month. Fig.5) as a template for drilling the holes. When the holes are drilled, attach the label to the lid and cut the holes out with a sharp utility knife. Fit the switches and then you are ready to start wiring. The wiring details for the handheld control and lead to the 8-pin DIN plug are shown in Fig.2. We used Cat 5 8-way stranded cable to wire up the switches. It consists of four twisted pairs. Pass one end of the 8-way cable through the hole prepared for the cordgrip grommet and strip back the outer plastic sheath by about 50mm before wiring to the switches. We used the colours as shown and note that there will be one wire spare (orange/white). You will need a common connection to the centre terminal of S1, S4 & S3 and one side of S2. This can be made using tinned copper wire. The 8-way cable is captured with a cordgrip grommet in the end of the case and the free end is cut to 1100mm long (or longer if you want but you will need more cable). The end is then stripped and terminated into the 8-pin DIN line plug. Do not forget to slide the plastic boot of the plug onto the lead before connecting the wires. Construction The walk-around throttle is housed in a standard plastic case measuring 83 x 54 x 31mm. The first step in construction involves drilling holes for the switches in the lid of the case and a hole for the cordgrip grommet in the end of the case. You can use a photocopy of the front panel label (see 72  Silicon Chip Fig.2: the wiring of the hand-held controller box and the DIN plug. The length of cable between the two can be as long as necessary (ours was 1.1m long). The inside of the handheld controller is shown in the photo at right. Fig.3: part of the PC board component layout from last month, with the components in red to be deleted from the hard-wired “walk around” version. The IC socket, though, is an addition. The Railpower itself requires a number of alterations from the wiring layout (Fig.6) depicted in last month’s issue. First, you will need to drill and ream out a hole for the 8-pin DIN panel socket at the rear panel. Secure this with screws and nuts. When assembling the PC board for the Railpower, leave out IC1, Q1, IC2, and the components associated with pins 2 & 13 of IC2. A 14-pin IC socket is installed in place of IC2. We have shown the relevant corner of the PC board with the omitted components dotted, in Fig.3. A 400mm length of 8-way cable needs to be made up with the 14-pin header at one end and the 8-pin DIN socket (on the rear panel) at the other end. The details of this are shown in Fig.4. Four 10kΩ resistors are connected between pin 1 and pins 5, 6, 7 & 9. A 22µF capacitor is connected between pins 1 and 7, with the positive lead going to pin 7. Fig.5: same size artwork for the front panel of the hand controller in the “walk around” Railpower. Testing Having finished assembly of your Railpower, do all the initial checks as described in last month’s article. Then plug in the handheld control. Check that the Inertia switch turns the associated LED on the Railpower panel either on or off and that the stop LED turns on or off with alternate pressings of the pushbutton. The speed up and speed down selections should alter the meter reading up or down. The track LED should gradually light up as the speed is increased and be of a different colour depending on the forward or reverse setting. It may come up very slowly in brightness because of the inertia set- ting. You can switch the inertia out for a faster response to the track voltage. Note also that the forward or reverse functions can only be made when the reverse lockout LED is off. You should be able to remove the plug from the socket at the rear of the Railpower unit without affecting the train’s motion. The only exception is that the inertia control will always return to the ON setting with the plug disconnected. If you want additional 8-pin DIN sockets around your layout, these can be wired in daisy-chain fashion using the Cat 5 cable. Fig.4: the DIN socket to header pin wiring which goes inside the RAILPOWER case. This cable should be about 400mm long. DECEMBER 1999  73 Installing a speed control knob Inevitably, someone always wants a variation to a design after we have published it and the Railpower is no different in this respect. No sooner had the October issue hit the streets than a reader wrote in to say that he wanted a walk-around throttle with a speed control knob instead of the UP and DOWN buttons. Could we please publish the details? Well, it is stretching the friendship but since other readers will probably want to do the same, we are publishing brief details here. We should point out right now that there are a few more modifications involved to the 74  Silicon Chip Railpower itself. Fortunately, the handheld control can still be wired up using 8-way Cat 5 cable. Note that while we have produced a prototype handheld walk-around controller as described in Figs.1 to 4, we have not produced a version with a speed control knob. In other words, we have not tested the following modifications. Fig.6 shows the relevant circuit modifications to the Railpower circuit. As before, IC1, IC2 and Q1 are omitted and a 14-pin socket installed in place of IC2. In addition, diodes D1, D3 & D4, transistors Q2 & Q3 and five resistors are left out. These omitted components are shown in red on the diagram of Fig.6. The 10kΩ speed potentiometer which is installed in the handheld control is wired via pins 11, 12 & 13 of the 14-pin header. Pin 13 of the header goes to pin 7 of IC3a and pin 11 of the header goes to the cathode of diode D2. The wiper of the 10kΩ potentiometer goes to pin 12 of the header and this, in turn, connects to C1 and thence to pin 5 of IC4b via a 1kΩ resistor. Two cuts must be made to the tracks of the PC board and again, these are shown on the diagram of Fig.6. First, the track between the cathode of D2 and pin 5 of IC5a must be cut and so must the track between pin 5 of IC5a and capacitor C1. These two cuts leave pin 5 of IC5a not connected to anything. A section of the PC board layout (Fig.7) shows where the cuts are to be made. The tracks can be cut with a sharp, heavy-duty knife (such as a “Stanley” knife) or they can be cut using a small drill bit. In either case, ensure the tracks are completely severed and no swarf shorts out adjacent tracks. (If in doubt, check with a multimeter). You will also need to place three long links between the cut tracks and the appropriate tracks near the IC header socket. Use fine insulated wire (single lengths cut from rainbow cable are ideal) and solder them to the back (copper side) of the PC board where shown. In wiring up this version of the walk-around handheld control, you can follow broadly the same procedure as described above and the testing procedure will be similar as well. However, there will be one difference in operating the Railpower and that involves the STOP function. In the 4-switch version described earlier, if you operate the STOP button to bring the locomotive to a halt or slow it down, you only need to push the Speed switch momentarily up or down to release the STOP function and allow the train to resume its previous speed setting. However, in this Speed knob version, that circuit feature has been disabled, because diodes D1 and D2 have been removed (there being no Speed switch to forward bias them). So to release the STOP function, the STOP button must be pressed again and this toggles flipflop IC6a to achieve that function. The Speed knob can then SC be used to vary the speed of the locomotive. Please note: there are two errors in the PC board component overlay on page 82 of last month’s issue. IC5 is identified as a 4052; it should be a 4053 (the circuit diagram in the October issue is correct. Also, IC8 (the IC closest to the 2000µF capacitors) is identified as IC3. IC3 (top right corner) is itself correctly identified. Fortunately both IC3 and IC8 are LM324 quad op amps. Figs.6 (opposite) and 7 (above): these modifications will allow the use of a 10kΩ potentiometer as a speed controller instead of push-button control. Again, the relevant sections only of both the circuit diagram and the component overlay are shown. Additional components are deleted in this version and you will also need to modify the circuit board as shown above with two tracks to be cut and three links to be inserted (the green, blue and purple wires). These should be soldered underneath the PC board (ie, on the copper side). DECEMBER 1999  75