Fullscreen Med Res (?MB)Non Flash

A remote controlled throttle for model railways PART 2: By JOHN CLARKE & LEO SIMPSON BUILD THE RAILPOWER Last month, we presented the circuit details of our new Railpower model railway speed control. This month, we describe the circuit of the IR remote control and give the construction details. L AST MONTH, we completed the circuit description of the Railpower except for the infrared remote transmitter and this is shown in Fig.5. It comprises a single IC, two transistors, an infrared LED and a few passive components. The 80  Silicon Chip IC’s internal oscillator is set to 455kHz by ceramic resonator, X1, con­nected between pins 12 & 13. The 455kHz oscillator frequency is divided down by 12 to give a 37.9kHz carrier frequen­cy for the infrared LED (IRLED1). Current drive for the LED is provided by the Darlington-connected transistors, Q1 & Q2. When any pushbutton is pressed, it pulls the corresponding input of IC1 low and this causes the output at pin 15 to deliver a uniquely coded stream of pulses (at 37.9kHz). The pulse codes can be changed using different combinations of links LK1 and LK2 so that you have the option of using up to four separate Railpow­er controllers which operate independently on the same layout. This can be a boon to realistic operation on large layouts with cab (block) switching. Naturally the receiver coding on the main PC board must match the respective remote control transmit­ter in order to operate. However, if you only intend to use one Railpower controller on your layout, you can omit the two links on both the transmitter and the main circuit board. The transmitter circuit is powered by two AAA cells con­nected in series to provide a 3V supply. The IC draws only about 1µA on standby, when the switches are not pressed, so the batter­ies should last for virtually their shelf life. Construction The Railpower may have a relatively complicated circuit but it is very straightforward to build. All the circuitry in the case is installed on a PC board measuring 216 x 170mm and coded 09310991. Before you begin assembling components on to the PC board, check that it fits properly into the base of the instrument case. Enlarge the corner mounting holes in the PC board to 3mm or 1/8" if these have not been drilled to size. Check that the holes line up with the integral pillars in the case. Then check the PC board for shorts between tracks or for any breaks. Make any repairs now, if required. Check the holes for the 0.1Ω resistor and the power diodes (D15-D18) as these may need to be enlarged to accommodate their thicker pigtails. The component overlay for the PC board is shown in Fig.6. Start by installing all the links on the PC board using 0.8mm tinned copper wire. Most of the links are 12.5mm long so you could bend these over a suitable former about 12mm wide, to create a uniform appearance. There is a longer link near IC5 and more links adjacent to the power transistors Q16, Q17, Q20 & Q21. Install the PC stakes in position and then insert and solder the resistors. Use the accompanying colour code table as a guide to selecting the resistor values. Better still, use a digital multimeter to check each value before it is inserted. The 0.1Ω 5W wirewound resistor should be raised above the PC board by about 2mm before soldering the leads. Next, install the diodes. Several types are used although most are the small switching diodes (glass encapsulated). 1A types (black resin body with silver stripe) used for D7, D8 & D14 while the 1N5404 power diodes Fig.5: the transmitter encoder IC has an internal oscil­lator set to 455kHz by the ceramic resonator, X1, connected between pins 12 & 13. The 455kHz is divided down by a factor of 12 to give a 37.9kHz carrier frequency for the infrared LED (IRLED1). When any pushbutton is pressed, it pulls the corre­sponding input of IC1 low and this causes the output at pin 15 to deliver a uniquely coded stream of pulses at 37.9kHz. used for D15-D18 are larger again. Note that you only need to install diodes D15 & D16 if the trans­former is a centre-tapped 24V unit. The capacitors can be installed next, taking care to orient the electrolytic types with the polarity shown on Fig.6. Note that you should only Improving The Speed “Hold” Time Following last month’s article we have had a chance to do some serious testing of the new Railpower on a large HO layout and it came through with flying colours, except for one aspect: the speed “hold” time. When you set the speed with the remote control, you expect it to stay set indefinitely. In practice, that is not possible with the “hold” circuit involving IC4b but the circuit did need improving so that the speed setting did not drop noticeably after a few minutes. Therefore, we are recommending a change to the value of C1. Instead of using a 2.2µF tantalum or low leakage electrolytic capacitor, C1 should now be a 22µF tantalum type. At the same time, the 10MΩ resistor associated with IC5a should now be 1MΩ while the 4.7MΩ associated with Q3 should now be 470kΩ. In other words, C1 is now ten times larger and the associated charging discharging resistors are one-tenth of their original values. These changes have been incorporated into the component overlay diagram of Fig.6. With the new values, a given speed setting can be expected to drop by 36% after 15 minutes or there­abouts. This should be more than adequate, even for the lar­gest layouts where protracted running at a given November 1999  81 Fig.6: the component overlay for the PC board. Install C3 or C4 (not both) depending on whether you want the circuit to power up in the forward or reverse mode. For forward mode, install C3; for reverse mode, install C4. install C3 or C4, not both. Install C3 if you want the circuit to power up with the controller in the forward mode. 82  Silicon Chip To power up in reverse mode, omit C3 and install C4. Now insert and solder the ICs, tak- ing care to orient them correctly. Be sure that each is in its correct place before soldering the pins. Secure the mains wiring using cable ties and be sure to sleeve all exposed terminals with heatshrink tubing as detailed in the text. Install the transistors and regulators next, taking care to insert the correct one in each position. REG2 and transistors Q16, Q17, Q20 & Q21 are mounted at full height with about 1mm of their leads extending below the copper side of the PC board. Six trimpots need to be installed, Capacitor Codes  Value IEC Code EIA Code  0.1µF   100n   104  .01µF   10n  103  .001    1n (1000p or 102) Resistor Colour Codes  No.    1    1    1    1    1    8    1    1    3  35    1    2    3    7    6 Value 10MΩ 4.7MΩ 560kΩ 220kΩ 120kΩ 100kΩ 47kΩ 39kΩ 22kΩ 10kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1.2kΩ 1kΩ 4-Band Code (1%,5%) brown black blue brown yellow violet green brown green blue yellow brown red red yellow brown brown red yellow brown brown black yellow brown yellow violet orange brown orange white orange brown red red orange brown brown black orange brown yellow violet red brown orange orange red brown red red red brown brown red red brown brown black red brown 5-Band Code (1%) brown black black green brown yellow violet black yellow brown green blue black orange brown red red black orange brown brown red black orange brown brown black black orange brown yellow violet black red brown orange white black red brown red red black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown red red black brown brown brown red black brown brown brown black black brown brown November 1999  83 Fig.7: wiring details inside the case. The 240VAC mains wiring should be run in 250VAC-rated wire, with green/yellow striped wire for the Earth. The buzzer is fixed to the board with double-sided tape. and again, make sure that the correct value is installed in each position. Finally, the nine LEDs can be installed. These are all oriented with the Anode (longer lead) to the right and are mount­ed so that the cathode lead is about 1mm below the copper side of the PC board. This will allow the leads to be soldered and have the maximum height above the PC board. The LEDs will eventually need to be bent over at right angles so that they 84  Silicon Chip can be inserted into the front panel holes. Front and rear panels Mark out and drill the front panel to provide an access hole for the infrared detector, the LEDs, the power switch S1 and the analog meter. The meter is supplied with a cardboard template to assist in marking out its cutout hole. The front panel artwork should be used as a guide for the hole positions. The rear panel is aluminium and it needs to be drilled for the four transistors, REG2, the access hole for auxiliary cir­cuits and the IEC power socket. Before the rear panel can be drilled, you will need to mark the positions of the four power transistors and REG2. To do this, you need to sit the assembled PC board in posi­tion on the base of the case. You will need to shorten some of the integral pillars with a large drill bit so that the PC board can sit correctly on the corner mounting pillars. Now slide the aluminium The H-bridge transistors (Q16, Q17, Q20 & Q21) and the 3-terminal regulator are mounted on the rear panel, which provides the necessary heatsinking – see also Fig.8. rear panel into place and mark the mounting hole posi­tions for the power transistors and regulator. At the same time, mark out the hole positions for the terminals and the auxiliary output lead hole which will need to be fitted with a grommet. The IEC mains socket should be mounted as far to the side as possible to allow clearance for the leads around the trans­former. Mark out the holes required for this and also for the adjacent earth screw terminal. Place the transformer on the PC board and determine its optimum mounting position. The mounting hole positions for this should not encroach onto the track area on the board. Drill and file out the holes on the rear panel and do the same for the transformer mounting holes on the PC board. We mounted the transformer with rubber grommets inserted into the holes in its mounting feet. The holes may need to be reamed to a larger size for this. The transformer is secured to the PC board with a screw, a flat washer and a nut for each foot. The nuts are tightened down sufficiently to anchor the transformer but not so tight as to prevent free movement. Secure the PC board in the case with self-tapping screws. Attach the IEC socket to the rear panel using 3mm screws and nuts and Fig.8: mounting details for the power transistors and 3-terminal regulator. Use mica or silicone washers and insulating bushes to isolate the metal tabs from the metal panel. This close-up view shows how the PIC12043 IR receiver (IC1) is aligned with a hole in the front panel, so that it can pick up the IR pulses from the remote control unit. November 1999  85 The remote control transmitter board has just a handful of parts and should only take a few minutes to assemble. Note that this board is supplied by Oatley Electronics and is substituted for the existing board inside the transmitter case. fit the binding post terminals. You can also attach the meter and switch S1 to the front panel. Fig.7 shows all the wiring details inside the case. The 240VAC mains wiring should be run in 250VAC-rated wire, with green/yellow striped wire for the Earth. Use a plastic insulating boot for the IEC socket terminals and a length of insulating tubing for the terminals of switch S1. Some of the wires will need to be passed through this insulation boot before soldering them in place. The earth connection to the transformer is made by scraping away the coating on the transformer mounting foot and soldering the wire in place. Be sure it is soldered properly, with a hot iron, and check that the solder has flowed onto the exposed steel. The earth terminations to the rear metal panel are made using crimp lug eyelets or solder lugs, each secured in place with a 3mm screw, star washer and nut. Fig.8 shows the details of how the power transistors and regulator are mounted to the rear panel. Use mica or silicone washers and insulating bushes to isolate the metal tabs from the metal panel. Use heatsink compound between mating surfaces if mica washers are used but this is not necessary for the silicone types. Check that the transistor tabs and regulator are indeed isolated from the case by testing on the ohms range with your multimeter. The reading should show open circuit. The binding post terminals are wired with short lengths of heavy duty hookup wire as shown. Wire up the front panel meter with hookup 86  Silicon Chip wire and connect the buzzer wires in place. We se­cured the buzzer to the PC board with a piece of double-sided tape. Alternatively, it can be glued in place with silicone sealant, contact adhesive or similar. The transformer secondary is wired as shown in Fig.7, using the three connections on the PC board for the 24V centre-tapped transformer type or without the centre tap terminal on the PC board (CT) for the transformer with two 12V windings. Transmitter construction The transmitter is assembled into a small case which con­tains an existing PC board. This unit is supplied by Oatley Electronics. You first need to prise open the case and remove the board. You then have to remove the battery clips and 455kHz ceram­ ic resonator from this board and install them on a new PC board that comes with the transmitter. Fig.9 shows the component layout for this new board. Insert the supplied components as shown, taking care to install the correct transistor in each position. Do not forget the wire links and the insulated wire link from the positive supply up to the 4.7Ω resistor. Be sure to orient the IRLED correctly, with the longer lead being the Anode (A). It is placed so that its body sits comfortably over the integral moulding in the case. When completed, you can attach the front panel label and cut the holes out with a sharp utility knife. Insert the PC board into the case and clip the case together. You will need two AAA cells to power the transmitter. Testing Fig.9: this is the parts layout for the remote control transmitter PC board. Check all your work thoroughly before applying power. When power is applied, the neon in the power switch (S1) should light and some of the LEDs should light. In particular, the forward or reverse LED should be on as well as the Stop LED. Check the supply rails on the circuit. Connect the negative lead of your multimeter to the 0V binding post terminal and test the voltage on the positive terminal. It should be +12V. Now check at pin 14 of IC2 for a reading of +5V. If either voltage is low, you should suspect a short on the PC board somewhere. Find it and fix it before going any further. There should be 12V between pins Fig.10: use this actual size artwork to check for etching defects on your controller PC board. 4 & 11 of IC3 & IC8; bet­ween pins 4 & 8 of IC4; between pins 8 & 16 of IC5 and between pins 7 & 14 of IC6, IC7 & IC9. Now check the operation of the remote control. Pressing the control buttons should operate the front panel LEDs. The Aux1 & Aux2 LEDs should light when the relevant remote buttons are pressed, with Aux1 staying on or off, after each button press. The Inertia and Stop functions November 1999  87 RAILPOWER SPEED SETTING SC Fig.11: this full-size front panel artwork can be used as a drilling template for the front panel of the main control unit. D OVERLO A FORWA RD E REVERS UT LOCKO STOP INERTIA OFF AUX2 POWER AUX1 SILICON CHIP AUX1 INERTIA AUX2 STOP REV FOR SPEED RAILPOWER TRACK 88  Silicon Chip 0 20 40 60 80 10 0 SPEED Fig.12: here are the actual size artworks for the remote con­trol handpiece and the meter scale. also should go on and off with alternate pressings of the pushbuttons. The speed (+) and speed (-) buttons should alter the meter reading but with this yet to be calibrated you may not obtain good results. The lockout LED should also switch on as the speed setting is increased. The track LED should gradually light up as the speed is increased and show a different colour depending on whether the forward or reverse mode is selected. It may come up very slowly in brightness because of the inertia setting. You can switch the inertia out for a faster response to the Speed buttons. Note also that the forward or reverse mode can only be selected when the lockout LED is off. Now connect your multimeter to the track terminals. Adjust the speed up fully by holding the speed (+) button down for about 10 seconds, then adjust VR1, the maximum speed trimpot, for a reading of 12V. If you are running an N-scale layout in which the model locomotives normally run at a maximum of 9V, then use this as the maximum speed setting instead. Adjust trimpot VR2 fully anticlockwise. Use the speed (-) button to reduce the track voltage to its minimum setting and then connect the controller to the track on your layout. Place a locomotive on the track, select inertia out (LED lit) and rotate VR2 until the loco just begins to move. Then rotate VR2 slightly anticlockwise from this setting. Now use the speed buttons to start the loco and bring it to a halt again. If the loco still tends to creep at the minimum speed setting, adjust VR2 even further anticlockwise and then check the settings again. Next, adjust trimpot VR6 so that the meter shows full scale at the maximum speed setting. You may want to remove the loco when doing this. Trimpots VR4 and VR5 are adjusted for the required amount of inertia for starting and stopping. The Inertia function will need to be selected (Inertia LED out) to adjust VR4. Trimpot VR3 is adjusted so that the forward/reverse lockout LED lights at the train speed below which you consider it safe to suddenly reverse the track voltage. Next month, we will give the details of how to wire the Railpower without remote control. This will give you the ability to plug a handheld controller into any place on your SC layout to control trains.