Fullscreen HTML5Med Res (??MB)HTML4

IR remote control for the Railpower Mk.2 This remote control gives you complete freedom of opera­tion for the Railpower Mk.2 train controller. It has pushbutton control for everything & pulls negligible current when not in use. By RICK WALTERS As presented in the September & October 1995 issues, the Railpower Mk.2 is a walkaround throttle. It allows you to follow your trains as they go around the layout. As such, it performs very well. But perhaps you don’t like being tethered by a remote control cable. If so, you will want this infrared remote control. It operates just like any other remote and is based on 70  Silicon Chip the same microprocessor used in the Railpower Mk.2. The remote control handpiece has six pushbuttons but does not have the meter which was included in the walkaround hand control. Instead, we have designed a small PC board which has an array of 10 LEDs, to give an indication of train speed. This is mounted inside the main unit, along with a small PC board for the infrared receiver. The remote control uses the same plastic case as for the walkaround hand control. It contains a small PC board (coded 09101961) and a battery. The board contains six pushbuttons, three transistors, one IC, one crystal and a few other compon­ents. As you can see from the circuit of Fig.1, the battery is connected all the time, as is standard practice in all infrared remote controls. But instead of a dedicated IC as found in most remote controls, we have used a Z86E08 microprocessor. To conserve the battery, we have used a feature which was not previously exploited. The Z86E08 is a CMOS device and normal­ly does not draw much current but for battery operation, it can be put into a “sleep” mode, whereby the current it draws Fig.1: the transmitter circuit. This uses a Z86E08 microprocessor to produce coded IR pulses when the buttons are being pressed. When the buttons are not being pressed, the micro­processor goes into sleep mode to conserve the battery. is only 10µA. This greatly increases the battery life. When IC1 is put to sleep. it takes pins 16, 17 & 18 high (ie, to the battery positive line, +4.5V). Later, when any button is pressed, R0 or R1 (ie, row zero or row one of the pushbutton matrix) will go high, turning on transistor Q1 via diode D1 or D2. Q1 pulls pin 4 of IC1 low, to “wake it up”, after which it takes pins 16, 17 & 18 low and scans the buttons to see which one was pressed. C3 (column 3), the input to the INERTIA button, is high and if this is pressed, pin 9 of IC1 will go high. If this button is not pressed the processor then takes pin 16 (C2) high. As you can see from the circuit, the STOP or FASTER button, if pressed, will take pin 8 or pin 9 of IC1 high and the code for this button will be sent. Pins 17 and 18 are taken high in sequence and if any of the remaining buttons are pressed, their code will be trans­mit­ted. The pulse code appears on pin 3 of IC1 and turns Q2 and thus Q3 on and off. Q3 pulses two infrared LEDs (LED1 and LED2). Remember, only one button is press­ ed at a time and the code for this button will be sent many times before you can release it. With the jumpers set on 1,1 a burst of code takes 20 milli­seconds to be sent. Each time the processor finishes a scan, it takes all column outputs high (C0-C3) and looks at the collector of Q1. If it is low, indicating a button is pressed, it will scan the buttons again; if high, it will go into sleep mode to conserve the batteries. The RATE links A and B must be the same in the transmitter and the Below: this photo shows the completed IR receiver board being installed in the Railpower case. Note the mounting details for the Acknowledge LED and the LT536 infrared diode (PD1). January 1996  71 Fig.2: the IR receiver circuit. This uses two cascode transistor stages (Q1, Q2 and Q4, Q5) with AGC to provide the necessary large gain for the photodiode signal. The signal decoding is done by IC4, a Z86E08 microcontroller programmed for this purpose. receiver. These links could allow you to have one hand control with a 3-position selector switch and this could control three Railpower IR receivers, each with a different rate setting. Infrared receiver The infrared receiver consists of photodiode PD1, cur­ rent-to-voltage converter IC1, two cascode transistor amplifiers (Q1, Q2 and Q4, Q5) with AGC (automatic gain control), a comparator and AGC detector (IC2), a pulse stretcher (IC3) and a data decoder, IC4. These are all mounted on a PC board (coded 09101962) which is housed in the case of the 72  Silicon Chip Railpower controller. The circuit is shown in Fig.2. Photodiode PD1 sees the IR pulses emitted by the remote control and varies its current accordingly. This variation in current is converted to voltage pulses by op amp IC1 which drives the base of Q1 via a .015µF capacitor. The pulses from IC1 can vary from around 0.2V peak-peak when the remote control is close to PD1 to being lost in the noise when it is some distance away. For this reason, we need a lot of gain for weak signals but not very much for the stronger ones. We obtain lots of gain by using cascode circuits and then we use automatic gain control (AGC) on both to cope with large signals. Gain control The two cascode circuits are similar, the first using PNP transistors Q1 & Q2, the second using NPN transistors Q4 & Q5. AGC is applied to the first pair by FET Q3, while FET Q6 applies AGC to the second cascode pair. The gain of the first cascode stage, with Q3 turned off, is around 3.3 while the gain of the second stage, with Q6 turned off, is 2.2 giving an overall gain of 7.3 (3.3 x 2.2). With Q3 & Q6 turned on fully, the gain of each cascode stage can be in excess of 200, giving an overall gain of 40,000 or more for very small input signals. PARTS LIST Remote Control Transmitter 1 PC board, code 09101961, 85 x 50mm 1 plastic case (Jaycar HB-6032 or equivalent) 1 4MHz crystal (HC18, HC49) 2 yellow PC mount momentary switches (Jaycar SP-0722 or equival­ent) 1 red PC mount momentary switch (Jaycar SP-0720 or equivalent) 1 black PC mount momentary switch (Jaycar SP-0721 or equivalent) 1 white PC mount momentary switch (Jaycar SP-0723 or equivalent) 1 green PC mount momentary switch (Jaycar SP-0722 or equivalent) 1 single AA cell holder (see text) 3 L1154 alkaline batteries 1 18 pin IC socket (optional) 4 #8 x 10mm self-tapping screws 4 5mm untapped spacers 1 100mm-length red wire 1 100mm-length black wire 1 50mm-length 1mm sleeving Semiconductors 1 Z86E08 programmed TXA (IC1) 2 1N914 signal diodes (D1,D2) 2 BC338 NPN transistors (Q1,Q2) 1 BC640 PNP transistor (Q3) 2 CQY89A LED (or equivalent) Capacitors 1 100µF 16VW electrolytic 2 0.1µF 50VW monolithic 2 22pF ceramic In practice, the output signal from the collector of Q5 is monitored by IC2b which is connected as a peak rectifier. With no input signal present, pin 2 of IC2b is pulled high by the 47kΩ resistor connected to the +5V rail. Negative-going pulse signals at the collector of Q5 cause IC2b and its associated diode D1 to pull pin 2 towards 0V and hence discharge the 100µF capacitor. Thus, the gates of Q3 & Q6 tend to be taken high for small sign­als, to increase the gain. Conversely, large signals tend to result in the gates of Q3 & Q6 going toward 0V, to Resistors (0.25W, 1%) 4 100kΩ 1 470Ω 1 22kΩ 1 100Ω 1 10kΩ 2 1Ω 1 1kΩ IR Receiver Board 1 PC board, code 0911X951, 120 x 50mm 1 4MHz crystal (HC18,HC49) 1 18-pin IC socket (optional) 2 3mm x 15mm threaded spacer 2 3mm x 10mm screw 2 3mm x 6mm screw 1 200mm-length black hook-up wire 1 200mm-length red hook-up wire 1 200mm-length orange hook-up wire 1 200mm-length yellow hook-up wire 1 200mm-length green hook-up wire Semiconductors 1 TL071 op amp (IC1) 1 TL072 dual op amp (IC2) 1 74HC132 quad 2-input NAND gate (IC3) 1 Z86E08 programmed RXB (IC4) 2 2N2907 PNP transistors (Q1,Q2) 2 BC549 NPN transistors (Q4,Q5) 2 BS170 FET (Q3,Q6) 1 LT536 photodiode (PD1) 1 1N914 signal diode (D1) 1 5mm red LED (LED1) Capacitors 1 100µF 16VW electrolytic 3 10µF 50VW electrolytic turn them off and reduce the gain. In practice, the circuit continuously varies its gain so that the signal amplitude at the collector of Q5 is more or less constant. Q3 & Q6 are connected to the emitters of their respective cascode stages via 0.1µF capacitors. This means that the gain of the cascodes increases at high frequencies but not at 50Hz or 100Hz, to reduce any interference from incandescent or fluores­cent lights. IC2a is connected as a comparator and compares the signal from the collector of Q5 with the DC voltage at 6 0.1µF 50VW monolithic 1 .015µF 100VW MKT polyester 1 .01µF 100VW MKT polyester 1 .001µF 100VW MKT polyester 1 820pF disc ceramic 1 680pF disc ceramic 2 22pF capacitors Resistors (0.25W, 1%) 1 220kΩ 1 18kΩ 3 100kΩ 3 10kΩ 1 68kΩ 1 3.3kΩ 2 56kΩ 1 2.2kΩ 2 47kΩ 2 1kΩ 3 33kΩ 1 470Ω 3 22kΩ Speed Display Board 1 PC board, code 09101963, 65 x 50mm 1 5kΩ horizontal trimpot (VR1) 1 1kΩ horizontal trimpot (VR2) Semiconductors 1 LM3914 bargraph driver (IC1) 1 10-LED display (Jaycar ZD1700) Capacitors 1 10µF 50VW electrolytic 1 1µF 16VW electrolytic 1 0.1µF monolithic Resistors (0.25W, 1%) 1 100kΩ 1 4.7kΩ 1 15kΩ 1 820Ω 1 15kΩ 9-resistor array (10-pin SIP) Miscellaneous Hookup wire, PC stakes. its pin 5. It effectively squares up the signal pulses and removes any residual noise. IC2a drives IC3, a CMOS quad NAND gate which is used as a pulse stretcher. This allows us to supply a consistent pulse width to IC4, regardless of the output of IC2a. Data decoder IC4 is another Z86E08 microprocessor which has been pro­grammed to accept the IR data transmitted by the hand control and convert it to the correct code on pins 15, 16 & 17 to operate the Railpower functions. The January 1996  73 This topside view of the remote control transmitter board shows how the crystal is laid flat. Make sure that the two IR LEDs are correctly oriented. Fig.3: the component layout for the transmitter PC board. Note the three capacitors mounted on the underside of the board. These are shown dotted within the outline for IC1. microprocessor stores two consecutive codes from the transmitter and compares them. If they are identi­cal, it will send the information to the Railpower; if they differ, it will ignore them and compare the next two codes received. As mentioned previously, the rate links on the receiver must be the same as those on the transmitter. The three output lines from IC4 are This view inside the completed transmitter shows the mounting details for the three capacitors on the copper side of the board. Note the modified AA cell holder for the three button cells. Fig.4: the component overlay for the IR receiver board. Note that the rate links on this board must match the rate link settings on the transmitter PC board. 74  Silicon Chip This view shows how the IR receiver board is mounted vertically along one side of the Railpower Mk.2 case, while the speed board is mounted upside down, with the LEDs protruding through the front panel. RESISTOR COLOUR CODES ❏ No. ❏  1 ❏  8 ❏  1 ❏  2 ❏  2 ❏  3 ❏  4 ❏  1 ❏  1 ❏  4 ❏  1 ❏  1 ❏  1 ❏  3 ❏  1 ❏  2 ❏  1 ❏  2 Value 220kΩ 100kΩ 68kΩ 56kΩ 47kΩ 33kΩ 22kΩ 18kΩ 15kΩ 10kΩ 4.7kΩ 3.3kΩ 2.2kΩ 1kΩ 820Ω 470Ω 100Ω 1Ω 4-Band Code (1%) red red yellow brown brown black yellow brown blue grey orange brown green blue orange brown yellow violet orange brown orange orange orange brown red red orange brown brown grey orange brown brown green orange brown brown black orange brown yellow violet red brown orange orange red brown red red red brown brown black red brown grey red brown brown yellow violet brown brown brown black brown brown brown black gold gold 5-Band Code (1%) red red black orange brown brown black black orange brown blue grey black red brown green blue black red brown yellow violet black red brown orange orange black red brown red red black red brown brown grey black red brown brown green black red brown brown black black red brown yellow violet black brown brown orange orange black brown brown red red black brown brown brown black black brown brown grey red black black brown yellow violet black black brown brown black black black brown brown black black silver brown January 1996  75 Adding A Speed Meter To The Railpower Mk.2 Fig.5: the speed meter is a conventional LM3914 LED bargraph circuit. It takes the place of the analog meter in the original walkaround control for the Railpower Mk.2. If you wish to add a speed meter to the Railpower Mk.2, then use the LED bargraph display we have designed. It sits above the LED indicators on the front panel of the main unit and con­sists of a bar of 10 red LEDs. It is a standard circuit employing an LM3914 LED bar­graph display driver. The two preset potentiome­ters on this board are adjusted in a similar manner to the meter setup in the hand control. The circuit is shown in Fig.5 while the component overlay for the PC board (coded 09101963) is shown in Fig.6. Fit the IC, SIP and resistors, then the capacitors and potentiometers. If you wish, you can solder the potentiometers on the copper side of the board, as we have done, to make them easy to adjust. Connect a red wire to the +17V, orange to the +5V, black to the ground and yellow to the input terminal, as shown on the layout. The other end of the red wire connects to +17V on the main board (REG1 input), the orange to +5V (REG1 output) and the black wire to ground. The other end of the yellow wire should be sol­dered to pin 4 of IC1 (top of VR5). connected to IC1 in the Railpower unit. handpiece and the IR receiver board. As mentioned previously, we have also designed an optional LED bar­ graph speed indicator which takes the place of the speed meter in the original walkaround hand control. Let’s start with the remote control transmitter PC board. Its component layout is shown in Fig.3. Check the board for open circuit tracks or shorts, especially the track that passes between pins 7 and 8 of IC1. While you’re at it, check the other two boards for any etching problems and make any fixes as required. The first step is to mount the blank board in the plastic case. It goes in the half with the brass inserts (the front), with the copper side of the PC board facing up. A small hole has been drilled at the centre of each group of four pushbutton pads to allow you to drill pilot holes through into the case front for the six pushbuttons. When you have drilled them, remove the board from the case. (By the way, these pilot holes are not present in the photo of our prototype). Fit the two long and two short links Construction In discussing the construction, we will assume that you have already built the Railpower Mk.2, as described in the Sep­ tember & October 1995 issues. We will also assume that you have built up the original wired hand control and have made everything function as described in the setup procedure. To add the infrared remote control, you need to build the remote control 76  Silicon Chip Calibration Once the maximum and minimum speeds have been set satisfac­ torily on the main Railpower PC board, FORWARD should be se- This assembled speed meter shows nine discrete resistors instead of the specified SIP resistor array. lected and the minimum pot (VR2) on this board set so that the first LED lights. The controller should then be taken to full speed and the maximum pot (VR1) adjusted so that LED number 10 is lit. There is a small amount of interaction and the adjustments may have to be made several times to get it right. As an alternative to the speed bargraph, there is no reason why you could not mount the original walkaround control meter in the front panel, fitting a meter zero adjust control the same as in the handpiece and taking the positive meter wire to pin 2 on the DIN socket. at the LED end of the board and the two rate links. We suggest you initially code it 1,1 as shown on the overlay, as this gives the fastest transmis­sion rate. Next, fit and solder the diodes and resistors, followed by the transistors, capacitors and crystal. Push the transistors well down so that they are only about 2mm off the board. Bend the crystal’s leads at right angles and lie it down flat. The electrolytic capacitor should also lie flat on the board. Lastly, fit the pushbuttons, noting that all the flats face in the same direction (towards the rate links). Do not The two adjustment pots are mounted on the underside of the speed meter board for easy access. Fig.6 (right): install the parts on the speed meter PC board as shown in this wiring diagram. Check that all the LEDs are correctly oriented and note the mounting details for VR1 and VR2 (see photo above right). fit the LEDs as this will be done later. If you elected not to use an IC socket, fit and solder the IC marked TXA (this Z86E08 has been programmed as the transmitter); otherwise, solder in the IC socket. In either case, be sure to check the orientation of pin 1. As the PC board is rather small, we elected to mount three capacitors on the copper side. These can be fitted now. The 0.1µF monolithic type is soldered from pin 5 to pin 14, then laid flat against the board towards the pin 1 end. The two 22pF capacitors are soldered from pin 6 to pin 13 and from pin 7 to the pad on the copper track between pin 13 and pin 10. Both are laid flat, facing towards the other end of the socket. These details can be checked in the relevant photo. Battery holder The battery consists of three 1.5V button cells in series. These are held in a half-sized holder made out of a single AA cell holder. Cut the battery holder in half with a saw or sharp knife about 28mm from the spring end. Our holder had a moulded ridge at this point. Carefully cut the non-spring January 1996  77 plastic end out of the holder and locate it in the piece with the spring to make a half-size unit. The easiest way to retain the end is to melt the plastic with your soldering iron. If you do this inside and out, the end will be held firmly in place. Alternatively, you can do a neater job if you have access to ACC adhesive as used in plastic model making). Solder a red wire to the spring end and a black wire to the other end, then connect the red to the positive supply terminal on the PC board and the black wire to the nega­ tive terminal. Now drill one of the case end pieces to take the IR LEDs. Drill two 5mm holes on the horizontal centreline and 7.5mm either side of the vertical centreline. Slip 10mm of 1mm-dia. sleev­ing over each long LED lead, sit the PC board and LEDs in the case and bend the leads so that 2-3mm of each LED protrudes through the end piece. The longer sleeved lead should be on the right when viewed from the component side. Once you are satisfied, solder in the LEDs, insert the IC if you used a socket and fit the board in the case using the self-tapping screws and spacers. The battery holder can be kept in place with a dab of BLU-TACK® adhesive. Receiver board The component layout for the receiver board is shown in Fig.4. Start by fitting the one link and the resistors. Next, fit the ICs, using a socket for IC4 if you prefer. Make sure that all the ICs are correctly oriented. This done, solder in the MKT capaci­ tors, the transistors, electrolytic capacitors and finally the crystal. Don’t mount PD1 or the acknowledge LED yet. RAILPOWER SLOWER FASTER REVERSE FORWARD leads so that it protrudes satisfactorily through the front panel. Locate the sensor centrally behind the rectangular cutout. Both anodes (longer lead) are towards the top of the PC board. When you are satisfied with their positions, solder them both in place. Solder the black wire to the centre pin of REG1 (ground) and the red wire to the output pin of REG1 (+5V). The orange wire should be soldered to pin 1 of IC1, the yellow to pin 2 and the green to pin 3. Reassemble the unit and after applying power, check that the walkaround control still operates. If it doesn’t, the most likely cause is a short between pins 1, 2 or 3 on IC1. Testing INERTIA STOP Fig.7: the full-size artwork for the remote control front panel. Fit 200mm lengths of hook-up wire to the board, in the wire colours as shown in Fig.4, for the signal output and supply connections. This done, mount the PC board in the righthand side of the Railpower case, using two tapped metal spacers. Drill two 5mm holes in the front panel for the photodiode and acknowledge LED. File the hole for the photodiode to a 5 x 7.5mm rectangle, then replace the panel and bend the LED Clip the three cells into the holder on the IR remote con­trol unit, observing their polarity. They are back-to-front compared to standard cells, the small cap being the negative connection. Point the remote control at the receiver and press a button. If all is well, the acknowledge LED on the Rail­power should light and the corresponding function should be indicated by the Railpower LED. If it doesn’t work, the problem is knowing which unit is not operating correctly, the transmitter or the receiver. First, check that the battery voltage is around 4.5V on the transmitter. If you have an oscilloscope, hold a button down and check pin 7 of IC1 to see that the crystal is oscillating at 4MHz. Now check at the anode of one of the transmitter LEDs. There should be a pulse train output whenever a button is pressed. If the pulses are being sent continuously, RAILPOWER Fig.8: this is the full-size front panel artwork for the remote control version of the Railpower Mk.2. 78  Silicon Chip AC K ER PO W ST OP FO RW AR D RE VE IN RS ER E TI A OF F OV E RL OA D CUTOUT Fig.9: here are the full size etching patters for the IR receiver board (right), transmitter PC board (bottom right) and the speed meter PC board (below). Check the etched boards carefully before installing any of the parts. then one of the pushbut­tons has been inserted incorrectly. If an oscilloscope is not available, remove the batteries and connect a DC power supply set to 4.5V. When a button is pressed, the current should be around 9mA. As soon as the button is re­leased, the current should drop to about 5mA and after one second drop to 100µA. If this occurs, you can assume that the transmitter is working satisfactorily. If not check the capacitors on the crystal pins. IR receiver board On the receiver, check that pin 14 of IC3 is at +5V with re­spect to pin 7. If you have an oscilloscope, check pin 7 of the processor to confirm that the crystal is oscillating at 4MHz. Hold the transmitter close to the receiver with a button pressed. The output at pin 6 of IC1 should be a negative-going pulse of several hundred millivolts. It should be positive-going at Q2’s collector and 3-4V negative-going at Q5’s collector. The output of IC2a (pin 7) should be positive-going, while the signal into pin 9 of IC4 should be a negative-going 5V pulse 33µs wide. This close-up view shows how the leads of the infrared photodiode (PD1) on the receiver are bent over, so that the active surface of the device faces the hole in the front panel. If you don’t have an oscilloscope, the best approach is to compare the DC volt­ages measured in your receiver with those shown on the circuit. They should be within 10% of each other. If there is a discrepancy, check the component values around the relevant stage and also your soldering. Check also that the A and B rate links on the transmitter and re­ceiver match each other. If they don’t, the SC remote control won’t work. January 1996  79