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-ARO Last month we presented the first article on the Railpower walk-around throttle for model railroads. This month we give the constructional details and show how to customise it for your particular application. By LEO SIMPSON PART 2: MODEL RAILROADERS (or are they railway modellers?) cannot be dictated to. They each want to build their train controllers their own special way, leaving out or adding in the features that they particularly want. So be it. In reading the construction information for the Railpower walkaround throttle remember that you can vary things around, as long as you don't take liberties with the basic circuit design. By that we mean that you can incorporate or leave out control features as you wish but don't play around with the componentry on the printed circuit board unless you really know what you are doing. With that in mind, let's discuss the assembly of the printed circuit board. To do this you will have to refer to the printed board overlay diagram, Fig.6, which was also publisheo on page 39 of last 44 SILICON CHIP & JOHN CLARKE month's issue. In fact, the overlay was printed a little too dark last month, making it hard to follow. To correct that, we are running it again in this article. Fig.6 shows all the components mounted on the board itself. The components not on the board are connected via the multiway connector strips. The 6-way connector is for the handheld throttle and the sixteen way connector (actually two eight-way units) is for the rest of the connections. Heatsinks required Assembly of the board can start with the wire links, small diodes and the 0.25W resistors. When these have been installed, you can concentrate on mounting the four output transistors, the 3-terminal regulator and their associated heatsinks. Three heatsinks are required. Ql and Q3 are mounted on one heatsink while Q2 and Q4 are mounted on another. We made ours from 0.8mm aluminium (equivalent to 22 gauge) although the thickness is not important. For each two-transistor heatsink W\:l used a piece of aluminium 30mm wide and 55mm long, with a rightangle bend 9mm from one end, which becomes the foot. Four 3mm holes need be drilled in each heatsink, to take the two mounting screws for the foot and the mounting screw for each transistor For the 3-terminal regulator heatsink we used a piece of aluminium 20mm wide by 45mm long, with a rightangle bend 9mm from one end. Three 3mm holes need to be drilled in it, two for mounting screws and one to secure the regulator. The three heatsinks 'should be secured to the printed board before the transistors and regulators are soldered into place. Note that the two transistor heatsinks must not touch otherwise they will short out the DC supply. Attach the regulator and the power transistors to their respective heatsinks and then you can solder their leads to the printed board. Note that mica washers are not necessary for the transistors or the regulator. Once the transistors and regulator are in place, the rest of O'I*I'LE FOR MODEL ROADS l°FOR :i TO HANO HELD UNIT - "l · .. RUN ov +12V LED3 -BUZZER + TRACK LED1 BI-COLOUR LED2 0 0 REV STOP ~11~fr{1J.'~ rf,'//' RAIL POWER ~I~ //0~ L: .:.J SPEED Fig.8: front panel artwork for the handheld controller. Fig.6: parts placement diagram for the PCB. Be sure to use the correct part at each location and note that IC2 is oriented differently to the other ICs. VR1 and VR2 set the maximum and minimum track voltages (see text). the components can be mounted on the printed board. We suggest that you solder in the small transistors, then the two trimpots, the wirewound resistor, the four integrated circuits, the four rectifier diodes and the capacitors. Leave the connector strips till last, otherwise they tend to get in the way when you are soldering other components. Note that ICl and IC2, the two LM324s, are oriented differently on the board (ie, they point in different directions). Power transformer Fig.7: this is the wiring diagram for the handheld controller. The numbers on the leads correspond to the numbers on the terminal block at the top of Fig.6. VR4 and VR5 set the running and braking inertia. FROM MAIN BOARD There are several options for the power transformer. Some modelling enthusiasts may already have a suitable transformer in the form of an old controller (containing just transformer and rectifier) or perhaps a battery charger with an output capacity of several amps. Virtually any transformer with a MAY 1988 45 ,-----------7 CONSOLE UNIT CONTROLS I I I I I I I I I SPEE VR3 I I I I I I I I 14 I I I I I REVERSE I I I S2 TO AILPOWER CIRCUIT I FORWARD L -- - - - - ---- - - - _J .,. LOCAL rEt~TE 16 i-- - - - - 2 I , 5 FORWARD - j --- - 3 6-PIN DIN PLUG _ _ 7USOCKET j S2 m~~ I I j j 4 SPEED VR3 INERTIA VR 4 I I RUN j I I I ~m VHS I L__ - j 220k -~NOHEL~~-AROUNO'U~ _ _ _ _ _ I I j Fig.9: this diagram shows the circuit additions required for switching between the handheld controller and the console controls. secondary voltage of around 12 to 15 volts and a current capacity of two or more amps could be used, although the more current capacity, the better. Be wary of old transformers that may have lain around for years and years. Such trannys may be a doubtful safety proposition as they will have absorbed a lot of moisture over the years and may be prone to breakdown. Modern transformers with split bobbin construction are much safer. Remember that you have virtually direct access to the output of the transformer when ever you touch the rails of the layout. If you have to buy a transformer, a 60V A multi winding unit, available from Jaycar (Cat. No. MM-2005) or Altronics (Cat. No. 46 SILICON CHIP M-2165) is good value. Two windings are connected in parallel to provide 12VAC at up to 5 amps. For many users, this would be enough to power two separate controllers. We give a little more detail on this later. Bare board plus walkaround throttle Many enthusiasts will want to build this controller as a bare board unit, to be buried somewhere underneath the layout and then have a handheld walkaround throttle, as described last month. There is nothing wrong with that idea but we suggest that the transformer and printed board be mounted together on a small metal chassis which is connected to the mains earth. We also suggest that all mains wiring and connections be well shrouded, allowing no possibility of accidental contact, whether by you or your children. If you are going to use a walkaround throttle, you'll probably want to plug it in at more than one point on your layout. This will require one or more 6-pin DIN sockets and some sheathed 6-way cable such as that sold by Jaycar as 6-way computer cable (Cat. No. WB-15 75). You could use telephone cable for wiring up the sockets (3-pair, single strand) but it is more prone to breakage. The sockets can be wired in parallel, in "daisy chain" fashion. Wiring up the handheld control is a simple matter. Just follow Fig.7 and the photos on page 40 of last month's issue. Powering up Having completed the wmng, check all your work carefully and then apply power. A number of voltage checks should now be made. To make these easier, turn the main board around so that it is oriented in the same way as the diagram of Fig.6 and have last month's issue open at the circuit diagram on page 37. That way, it will be easier to find your way around the board. Switch your meter to a 20V DC range and check that + 17V is present at the IN terminal of the 3-terminal regulator (you can pick it up at the end of the adjacent 2.2k0 resistor) and at the emitters of Ql and Q2. Depending on the incoming mains voltage, the measurement is likely to be anywhere between + 17V and + 21V or even a little more, depending on your transformer. Now check for + 12V at the output of the 3-terminal regulator and on each of the supply pins of the ICs: pin 4 of IC1 and IC2, pin 1 of IC4, and pin 14 of IC3. Again, the actual voltage will vary between + 11.4V and + 12.6V, depending on the actual 7812 (or LM340T-12) used. The voltages around IC1 and IC2, as shown in Table 1, should now be checked with the handheld throttle disconnected. These voltages are "ballpark" figures only but should This is the view inside the completed console unit. Note that the PCB and transformer are mounted on an aluminium baseplate which is then connected to mains earth. Table 1 IC1 : pins 1,2,3 ... ... ... .... ... ... .... ... ... ...... ... ....... .... .. .. about +1.2 volts IC1: pins 5, 6, 7 .. ... ....... ........ ... .. . about +4.8 volts (triangle waveform at pin 9, square wave at pin 7) IC1: pins 8, 9, 10 ......... ....... .. ..... .. ...... ... .. .. .. ... . same as wiper of VR1 IC1: pins 12, 13, 14 .... ..... ... ..... ... ..... ... .. ......... same as wiper of VR2 IC2: pin 1 ..... .... ... ....... ....... .... ... .... ... .... ............... ... about+ 11 volts IC2 : pin 2 ...... .. ... .... .......... ... .. ...... ... .. ............... ....... .. .......... 0 volts IC2: pin 3 ... .... .... ...... ... .... ... ... ... ..... ..... ... .... .... .... ... ....... .. +0.6 volts IC2 : pin 5 .... .... .... ........... ..... ....... .... .. ............ .. ... .. ...... . + 10.1 volts IC2 : pin 6 ... ....... .......... .... ....... .... ... ... ...... ............. ...... ... . +9 .8 volts IC2: pin 7 ....... ... ..... .. .... .. ...... .. ....... .... ... .. ...... ... .. .. .. about + 1 2 volts IC2: pins 8, 9 , 10 ..... ... ...... .. ...... ..... ......... .. .... ....... close to zero volts IC2: pin 12 .... ,... .. .. ... ....... .. .. ... .... ..... .. .... ..... .. ....... . about+ 1.8 volts IC2 : pin 13 ...... ........ .. .... .......... ......... .... .. .... .. ... ... same as pin 6 , IC1 IC2: pin 14 ... ..... .... ...... ... .. ..... ........ ........ .... .. ...... ........ ... .. zero volts be a good guide to see that things are working. Now you can plug in the handheld control and check that the voltages at pins 3 and 4 swap from high to low or vice versa when the forward/reverse switch is operated. Check the voltages at pins 6, 7, 9, 10, 11, 12, 14, and 15 also change state when the forward/ reverse switch is operated. Now connect your multimeter across the output terminals of the controller and wind the throttle control up to maximum. Adjust VRl so that the voltage is 12 volts (or whatever is the maximum recommended operating voltage for your The handheld controller plugs into a 6-pin DIN socket on the side of the case while the pulsed DC output to the rails goes via banana sockets. locos). Rotate the throttle to the minimum and adjust VR2 for an output of 1.5 volts or thereabouts (you will want to "fine tune" this minimum setting once your start operating trains). Now note that the polarity of the output voltage changes when you operate the forward/reverse switch and that the colour of the track LED changes (from red to orange or vice versa). Now wind the throttle to about the half-way mark and briefly short MAY 1988 47 6' 5' I'i;/4 ✓ 3' TRACK LED1 ~~3A _K PO ANS M2 LOCAL/ REMOTE S4 EARTH LUG <at> 19 22 7 8 9 10 11 12 13 14 OVE B 15 METAL BASEPLATE 16 ~ ~. 17 18 19 20 1 2 FORWARD/ REVERSE S2 <at> r. Fig.to (above): how the console case is wired up. Be sure to shroud all mains connections with heatshrink tubing and note the earthing lug under the power switch S3. Fig.11 (left) shows the PC artwork. the output terminals. The overload LED should light and the buzzer should sound. You can also listen to the operation of the controller by connecting a loudspeaker to the output terminals via a 1000 resistor. (Don't connect it directly otherwise you'll probably blow the loudspeaker). At low throttle settings the loudspeaker will have a thin, reedy sound. At higher settings, the sound will be louder but more mellow. Building a console c:o c:o ~ T'9 I 0) u en ~ 48 SILICON CHIP Some model railway enthusiasts will not be happy with just a tiny handheld walkaround throttle. They will want a console unit instead, or with the handheld throttle as well. To cater for those people we have built such a unit and prepared the necessary diagrams and photos. The console case we recommend is a plastic sloping-front unit with an aluminium lid. It is supplied by Jaycar, Cat. No. HB-6240. It measures 170mm wide, 214mm deep and 82mm high at the rear. We have designed a front panel for it too, featuring the NSW class 44 diesel electric loco. Fig.9 shows the circuit additions needed for switching between the console controls and the handheld walkaround controller. Essentially, the only addition, apart from the doubling up of controls, is the 3-pole switch S4. This is called the local/remote switch on the front panel of the console. The console controls are shown at the top of Fig.9 while the handheld control is shown at the bottom. Note that VR4 in the console is now a control in its own right rather than just a trimpot, as in the handheld unit. The idea behind this is that you can vary the inertia to suit the train. If you are doing shunting operations, you can turn off the inertia altogether. If you are just running a loco and short train, you'll want a medium setting for the inertia; if you have long train you'll want maximum inertia. Fig.10 shows how the console case is wired up, with a number coding system used for clarity The numbers down the righthand side of Fig.9 refer to the 6-way connector on the printed board, as shown in Fig.6 and on Fig.10. Pins 3, 5 and 6 of this connector go to the centre poles of switch S4. One side of the switch then goes to pins 3, 5 and 6 (labelled 3-dash, 5-dash and 6-dash on Fig.10) of the 6-pin socket for the remote handheld controller. You can use light duty hook-up wiring for all the ea bling in the console, except for the mains wiring and the figure-8 cable to the output terminals. The terminals of the mains switch should be sleeved with heat-shrinkable tubing, to prevent accidental contact. We recommend the use of a metal chassis plate within the console box for mounting the transformer and printed circuit board. The chassis plate can be made of steel or aluminium sheet (say 18 or 20 gauge} or, as with our prototype, you can use copper-clad laminate as used for printed boards. Note that the overload buzzer is The console unit features a large knob to vary the speed and a smaller knob to vary the inertia. The local/remote switch (top-right) provides selection between the console controls and the hand-held controller (when plugged in). wired directly to the printed board terminals (pins 13 and 14} and can be fixed to the inside of the case using a small piece of double-sided adhesive tape. The three LEDs are held in the front panel using clip-in bezels. VR5, the braking trimpot, is soldered direct to one of the pins of brake switch S1. When the wiring of the console is complete, you should go through the powering up procedure listed above. To do this, switch the local/remote switch to remote and do not connect the handheld controller. Other options Other options are sure to have suggested themselves as you have read through this article. For example, a pair of terminals could be provided on the rear of the console box to provide a regulated 12V output for accessories. These terminals would be connected to pins 17 and 18 on the printed board connector strip. You could also provide a pair of terminals for 12VAC output (connected to pins 20 and 21 on the aforementioned connector strip). Ideally, this output should have a fuse (say 2A rating} to protect it from short-circuits. This 12VAC output could be used to power an additional Railpower controller. Just connect the 12VAC lines to pins 20 and 21 on the connector of the second controller board. The rest we'll leave to your imagination. Have fun! le MAY 1988 49