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IR Remote Control Build this general purpose unit for your stereo system or model railway Want an IR remote control setup for your stereo amplifier, lighting system, model railway or any other system? This cheap set-up offers a motor-driven dual-ganged 20kΩ potentiometer and two relays. By LEO SIMPSON Based on the 8-channel infrared remote control featured in our February 1996 issue, this setup could be expanded to control up to six relays, in addition to the dual-ganged 20kΩ potentiome­ter. This could be useful for mode and source selection in an audio system, for controlling a lighting system or possibly for selecting various functions in a model railway layout. As presented in the February 1996 issue, the 8-channel remote control was just a bare-bones transmitter and receiver board. Of the eight decoded outputs on the receiver board, six 14  Silicon Chip were momentary outputs and two were toggle or latching outputs. The momentary outputs were high only while the respective buttons on the remote control were pushed, while the latched or toggle outputs would latch high for one press of their respective buttons and then latch low for the next press; ie, they provided “toggle” operation. Now while this system was attractive for many users, quite a few readers wanted more functions, which is why we are present­ing this enhanced system. The enhanced system has a modified transmitter board and adds a PC board which controls the motor­ ised potentiometer and two relays. The board can be split so that the relay section is separate from the potentiometer section. The motorised potentiometer is similar to those used for the volume control of millions of remote controlled home sound systems. It consists of the dual ganged potentiometer itself, a 4.5V DC motor and a gear and clutch system. The clutch lets the motor keep running even when the potentiometer has reach the end of its travel and so no cutout switches are required. Note that you could run more than one motorised pot from the infrared receiver if you wanted to. We’ll briefly mention the details later. But first, as they say on TV news programs, let’s have a look at the transmitter and receiver sections. The transmitter handpiece measures 155 x 35 x 16mm and is branded Mag­ navox. The seven buttons are labelled Tuner, CD, Track, Standby, Stop, Play and Volume. The last button is elongated and can be pressed at either end to make the Volume setting go up or down. When the Tuner or CD button is pressed, it operates one of the latched outputs on the receiver board. To unlatch the respective output, you need to press the same button. We use both latched outputs to drive relays so to operate a relay, you press the Tuner or CD button and to de-energise the relay you press the same button again. The remaining buttons control momentary outputs on the receiver board; they each go high, for as long as the respective button is pressed. The transmitter circuit is shown in Fig.1 and consists simply of an SM­ 5021B encoder (IC1) together with two transistors which drive the infrared light emitting diode, IRLED1. IC1 uses a 455kHz ceramic resonator as the oscillator and this is divided internally to give a 38kHz carrier frequency which is gated on and off by the data, according to which button is pressed. The 38kHz data pulse train appears at pin 15 and is amplified by the Darlington-connected transistors Q1 & Q2 to drive IRLED1. When buttons are not being pressed, pin 15 is low so no current passes through the transistors and the chip itself has negligible current drain. There are two links marked on the circuit: LK1 & LK2. These are coding links and should normally be left open circuit. The only reason for installing these links would be if you were using Fig.1: the 8-channel infrared transmitter. We suggest that the coding links LK1 & LK2 be omitted unless you are going to use two remotes in the one area. more than one of these remotes in the same location. In that case, you might, for example, install LK1 in one transmitter and LK2, in another transmitter. If you do this, you must ensure that the respective receiver boards have the same links installed. Speaking of the infrared receiver board, the circuit is shown below in Fig.2. It is almost as simple as the transmitter. As can be seen, it consists of an infrared receiver diode and preamplifier (IC2) feeding an SM­5032B decoder, IC1. This has eight outputs, six of which are high while the relevant transmitter button Fig.2: the 8-channel receiver circuit. Outputs G & H are latching while the other six are high only while the relevant transmitter button is pressed. July 1997  15 Fig.3: the relay/potentiometer board circuit. The motor drive circuit is inherently fail-safe since even if both the UP and DOWN inputs are high, no damage can result. 16  Silicon Chip is pressed and two of which are latching, as already mentioned above. Actually, IC2 is a three-lead device and it is more than just a preamplifier. It contains the IR photodiode, an amplifier tuned to 38kHz, an AGC circuit and a detector. Its output is a digital pulse train identical to that generated at pin 15 of the transmitter IC but inverted in polarity. Transistor Q1 changes the signal polarity before feeding it to pin 2 of IC1. Transistor Q2 and zener diode ZD1 act as a simple regulator circuit to provide a 5.6V supply to IC1 & IC2. The eight outputs of IC1 can only provide a drive current of about a milliamp or so, so any circuit driven by these pins must be designed accord­ingly. This brings us to the add-on board which drives two relays and the stereo potentiometer. Relay & potentiometer board Fig.3 shows the circuit of this board and, as you can see, it is split into two parts. One part takes care of the relays and the other section controls the motor-driven potentiometer. Let’s discuss the latter part first. Transistors Q1 & Q2, together with 150Ω resistors R4 & R7, form a bridge circuit to drive the motor. Normally, only one transistor can be turned on at any time. If Q1 turns on, current flows via R4 which has almost the full 12V across it but current also flows via R7 and the motor, causing it to turn in one direc­tion. Similarly, if Q1 is off and Q2 is on, the full 12V is ap­ plied to R7 but current also flows via R4 and the motor, causing it to rotate in the opposite direction. Diodes D1D4 protect the transistors from damage which could be caused by voltage spikes from the motor. LEDs 1 & 2 light to indicate the motor direction. As la­ belled on the circuit, the input for Q1 is UP, corresponding to clockwise rotation of the motor. When Q1 is on, LED1 will be on. Similarly, the input for Q2 is labelled DOWN, corresponding to anticlockwise rotation of the motor. When Q2 is on, LED2 will be on. Note that this circuit has a built-in safety feature in that even if Q1 and Q2 were both turned on simultaneously, no damage would result. In that circumstance, both R4 and R7 would have the 12V applied but no voltage would appear across the motor. Relay circuit Now let’s have a look at the relay circuit, comprising Q3 & Q4. These transistors would normally be driven from the latched outputs of the receiver board (ie, G & H). There’s nothing magic about the circuit. When the input to Q3 goes high, it turns on and operates relay 1. Similarly, when the input to Q4 goes high, relay 2 operates. LEDs 3 and 4 come on when the associated relay is operated. Diodes D4 & D5 protect Q3 & Q4 against any voltage spikes generated by the relays when they are switched off. Building a remote control system In presenting this system, we are not proposing a cut and dried solution, so we are just featuring the three PC boards and not giving full details on how they should be hooked up to con­trol an audio system, lighting system or whatever. We’ll leave the details up to you and The IR transmitter board should only take a few minutes to assemble. Note that this photo shows an early version. The final version shown in Fig.4 differs slightly in a few respects. LED and a few of the other passive components. Do not lose the rubber keyboard mat because it mates with the new PC board. You now have to assemble the new transmitter board which uses the SM5021B encoder chip. Just assemble it as shown in Fig.4. The next step is to assemble the receiver board, with the details shown in Fig.5. Unless you intend operating more than one of these remote control systems, leave the coding links off the transmitter and receiver boards. Next, assemble the motor drive and relay board. This board will be supplied as one unit but it can be split into two boards, as shown in the lead photo. Mount all the small components first before installing the motor driven poten­tiometer. If you mount the potentiometer first, you will be unable to fit all the components which lie underneath it. Once the two relays have been mounted you will need to wire the two protection diodes, D5 and D6, underneath the board, across the relay coils. One of the photos shows these diodes in place. When all the boards are complete, you are ready to test each one in turn and this should be done before the receiver board and relay/potentiometer Fig.4: the component overlay for the transmitter PC board. just indicate how the boards should be connected to provide the control functions you want. Now let’s describe the transmitter assembly. As supplied, the transmitter is fully assembled and operational but it won’t work with the corresponding decoder chip. You have to pull the transmitter apart by unclipping the case halves. You can do this by inserting a screwdriver into the case join down the side and levering it apart. Don’t apply too much force when doing this otherwise you will damage the case. Now lever out the existing PC board with its surface mount encoder chip. You will need to salvage the battery clips, the ceramic resonator, infrared Fig.5: the component overlay for the receiver PC board. Fig.6: the parts layout for the relay/potentiometer board. Mount all the small components before the motor-driven potentiom­eter is installed. You will need to run two wires from the motor itself to the “motor” pins on the PC board. July 1997  17 PARTS LIST 8-channel IR transmitter 1 Magnavox handpiece (includes 455kHz resonator & IR LED) 1 PC board 2 AAA 1.5V cells Semiconductors 1 SM5021B encoder (IC1) 1 BC548 NPN transistor (Q1) 1 C8050 NPN transistor (Q2) Capacitors 1 10µF 16VW PC electrolytic 2 100pF ceramic Resistors (0.25W, 1%) 2 1kΩ 1 4.7Ω 8-channel IR receiver 1 PC board 10 PC stakes Semiconductors 1 SM5032B decoder (IC1) 1 PIC12043 IR receiver (IC2) 2 BC548 NPN transistors (Q1, Q2) 1 6.2V zener diode (ZD1) Capacitors 1 100µF 25VW PC electrolytic 1 10µF 16VW PC electrolytic 1 0.47µF monolithic ceramic 1 .001µF ceramic Resistors (0.25W, 1%) 1 39kΩ 1 10kΩ 1 4.7kΩ 1 1kΩ Relay/potentiometer board 1 PC board 20 PC stakes 1 motor-driven dual-ganged 20kΩ potentiometer 2 12V relays with SPDT contacts 4 C8050 NPN transistors (Q1,Q2,Q3,Q4) 4 GIG silicon diodes (D1,D2,D3,D4) 2 1N4004 silicon diodes (D5,D6) 4 red LEDs (LEDs1-4) 2 100µF 16VW PC electrolytic capacitors 4 .015µF ceramic capacitors Resistors (0.25W, 1%) 4 120kΩ 7 3.3kΩ 2 150Ω 18  Silicon Chip The relay/potentiometer PC board can be split into two parts, each of which can operate independently of the other. This is the potentiometer section. board are wired together. We suggest you test the relay/ potent­ iometer board first. You will need a 12V power supply and a short lead with alligator clips at each end. The relay and potentiometer sections of the board have their own supply pins so each section can be tested independently. Apply 12V DC to the potentiometer board and observe that nothing happens (ie, no LEDs light, pot shaft does not rotate). Now take your clip lead and connect the UP input pin to the +12V pin on the board. The potentiometer shaft should rotate fully clockwise and then the motor should keep running, with the gearbox clutch slipping. LED1 should also light. Now take the clip lead and connect the DOWN input pin to the +12V pin on the board. The potentiometer shaft should rotate fully anticlockwise and then the motor should keep running, Don’t forget to add the two diodes on the back of the relay PC board. as before. LED2 should also light. Now test the relay board. Apply 12V DC and note that noth­ing happens, then use your clip lead to connect pin 1 on the board to +12V. You should hear relay 1 click and LED3 should light. Similarly, use your clip lead to connect pin 2 on the board to +12V. KIT AVAILABILITY These remote control boards are available from Oatley Electronics, who own the design copyright. Their address is PO Box 89, Oatley, NSW 2223. Phone (02) 9584 3561; fax (02) 9584 3563. The prices are as follows: 8-channel IR transmitter...............................................................................$20 8-channel IR receiver....................................................................................$20 Relay/potentiometer board plus parts for motor drive section......................$16 Complete kit with suitable plugpack & RCA leads (includes all of above but does not include parts for relay section).................................................$55 Parts for relay section.....................................................................................$8 Please add $5 to all prices for postage and packing. You should hear relay 2 click and LED2 should light. Testing the transmitter SILICON CHIP SOFTWARE Now available: the complete index to all SILICON CHIP articles since the first issue in November 1987. The Floppy Index comes with a handy file viewer that lets you look at the index line by line or page by page for quick browsing, or you can use the search function. All commands are listed on the screen, so you’ll always know what to do next. Notes & Errata also now available: this file lets you quickly check out the Notes & Errata (if any) for all articles published in SILICON CHIP. Not an index but a complete copy of all Notes & Errata text (diagrams not included). The file viewer is included in the price, so that you can quickly locate the item of interest. The Floppy Index and Notes & Errata files are supplied in ASCII format on a 3.5-inch or 5.25-inch floppy disc to suit PC-compatible computers. Note: the File Viewer requires MSDOS 3.3 or above. CD pin H Tuner pin G Track pin E Standby pin B Stop pin F Play pin A Volume - pin D Volume + pin C ❏ Floppy Index (incl. file viewer): $A7 ❏ Notes & Errata (incl. file viewer): $A7 ❏ Alphanumeric LCD Demo Board Software (May 1993): $A7 Note that pins G & H are the latching pins and these drive the relays. ❏ Stepper Motor Controller Software (January 1994): $A7 ❏ Gamesbvm.bas /obj /exe (Nicad Battery Monitor, June 1994): $A7 ❏ Diskinfo.exe (Identifies IDE Hard Disc Parameters, August 1995): $A7 ❏ Computer Controlled Power Supply Software (Jan/Feb. 1997): $A7 ❏ Spacewri.exe & Spacewri.bas (for Spacewriter, May 1997): $A7 ❏ I/O Card (July 1997) + Stepper Motor Software (1997 series): $A7 Connecting up If you’ve got this far, making the board-to-board connec­tions won’t be a problem. Pin C on the receiver board is connect­ed to the UP input on the potentiometer board while pin D is connected to the DOWN input. Pins H & G are connected to input pins 1 & 2 respectively on the relay board. If you wanted to connect a second potentiometer board, you could use any of pins A, B, E and F for the UP and DOWN func­tions. Alternatively, you could use any of the same pins to operate additional relay boards, although they would only be energised while the relevant transmitter button was pressed. Finally, if you have previously purchased the 8-channel IR transmitter and receiver boards, the transmitter buttons will not provide the correct functions. On the previous transmitter board (February 1996), the Volume button controlled latching outputs which is not appro­ priate for controlling the potentiometer board. SC ORDER FORM PRICE POSTAGE & PACKING: Aust. & NZ add $A3 per order; elsewhere $A5 Disc size required:    ❏  3.5-inch disc   ❏ 5.25-inch disc TOTAL $A Enclosed is my cheque/money order for $­A__________ or please debit my ❏ Bankcard   ❏  Visa Card   ❏ MasterCard Card No. Signature­­­­­­­­­­­­_______________________________  Card expiry date______/______ Name ___________________________________________________________ PLEASE PRINT Street ___________________________________________________________ Suburb/town ________________________________ Postcode______________ Send your order to: SILICON CHIP, PO Box 139, Collaroy, NSW 2097; or fax your order to (02) 9979 6503; or ring (02) 9979 5644 and quote your credit card number (Bankcard, Visa Card or MasterCard). ✂ Testing the transmitter on its own is not practical unless you have a cam­ corder or some sort of video camera. If you do, you can use the camera’s viewfinder to see if light is emitted when any of the transmitter buttons are pressed. However, while that tests the infrared side of things, it does not indicate that the buttons control the right receiver outputs. The way around this is to first con­nect 12V DC to the receiver board, then check that around +5.6V is present at the emitter of Q2, at pin 14 of IC1 and at pin 3 of IC2. Now aim the transmitter LED at the receiver’s detector window and use your multimeter to check that each output pin on the board goes high when the relevant button is pressed. The outputs should be as follows: July 1997  19