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Do you have an application for a remote control? If you do, then take your pick from these three units. Two operate at UHF, while the third is an infrared unit which can handle up to eight channels. All are inexpensive and easy to build. 3 Remote Controls The first of these units, operating in the UHF band at 304MHz, has been designed specifically for retrofitting central locking to a car but any project that requires a simple on-off control could use it. The second, also operating at UHF (304MHz), is a 2-channel unit. The compact keyring transmitter (50 x 35 x 15mm) has two buttons, each of which controls a latching relay in the receiver. The third unit is the 8-channel infrared remote control and it operates in the same way as the remotes for your TV, VCR or audio gear. Now to the nitty-gritty. Designs by BRANCO JUSTIC 76  Silicon Chip Remote Control 1 – Single Channel UHF T HE KEYRING TRANSMITTER case for the single channel transmitter is 57 x 30 x 12mm and has an 18mm dimple for your thumb. Very cunningly, there is no external pushbutton; you actually squeeze the two halves of the case together and this actuates the internal switch. A 3mm LED comes on when the unit is transmitting. The circuit, shown in Fig.1, consists of one IC, one transistor and a few small components. ly into the main PC board. Its output, pin 5, connects to the input (pin 14) of decoder IC1. For the receiver to acknowledge the transmitter, both units must be set to the same code; ie, the corresponding pins on the encoder and decoder ICs must be con­nected in the same way (high, low or open circuit). Provided they are identical the decoder output, pin 17, will go high (+5V) and clock IC2 whenever a valid code is detected. When power is first applied, IC2 is reset by C9 and R4, which causes pin 1 to go low. Conversely, pin 2 will go high, locking the doors. When IC2 is clocked, pin 1 will go high, oper­ating RL1 and RL3 for about one second and turning RL4 on. RL1 will unlock the doors and RL3 will flash the indicators if the relay is fitted and wired to these lights. RL4, if fitted, could be used to turn a car alarm on and off. It would be wired to turn the alarm off now. The next time a valid code is re- The keyring transmitter (above) is shown only slightly smaller than full size. This mates with the receiver (right). While intended for motor vehicle use, this remote control has many other applications. When SW1 is closed, power is applied via LED1 to encoder IC1 and also to L1, the feed to the oscillator. The code at IC1 pin 17 depends on whether the coding inputs are tied to pin 18 (high), pin 14 (low) or left floating. This code gates oscillator Q1 on and off, which results in bursts of 304MHz. If you look at the PC board pattern you will see that L1 is a conventional inductor but L2 is actually a loop of copper on the board. As well as being the oscillator tank coil, this loop is used as the antenna. L1 isolates the tank circuit from the bat­tery supply. The receiver (Fig.2) consists of a tiny pre-built, pre-aligned UHF receiver module with 12 pins that solder direct- Fig.1: the transmitter is based on encoding chip IC1 (AX5326) and a single transistor transmitter. It outputs a coded pulse stream which is interpreted by the receiver. The circuit fits neatly into the keyring case above. February 1996  77 Fig.2 (left): the receiver circuit may look complex but is mostly controlled by just three ICs. The various relays, along with their appropriate driver components, may be included or omitted to suit the application. ceived, IC2 will be clocked again. Pin 2 now goes high, pulsing RL2 for one second and locking the doors. R12 is a 2.2MΩ resistor and this will give a one second flash from the indicator lamps. PARTS LIST Single Channel UHF Transmitter 1 plastic case 1 PC board 1 12V alkaline battery 1 PC board mounting switch 1 AX5326 encoder (IC1) 1 BF199 NPN RF transistor (Q1) 1 3mm red LED 1 10µH choke Capacitors 2 .001µF ceramic 2 4pF NPO ceramic 1 2-10pF variable Resistors (0.25W 1%) 1 1MΩ 1 100Ω 1 22kΩ Single Channel UHF Receiver 1 PC board 1 UHF receiver module 2 or 4 SPDT 12V PC-mount relays Semiconductors 1 AX5328 decoder (IC1) 1 4013 dual D flipflop (IC2) 1 4093 quad Schmitt trigger (IC3) 5 C8050 NPN transistors (Q1Q5) 8 G1G diodes (D1-D8) 1 5.6V 500mW zener diode (ZD1) Capacitors 2 100µF 16VW PC electrolytic 6 0.47µF monolithic ceramic 1 .015µF ceramic Resistors (0.25W 1%) 5 2.2MΩ 5 4.7kΩ 2 1MΩ 1 3.3kΩ 4 10kΩ 1 22Ω 78  Silicon Chip If you want a longer indication, change R12 to 10MΩ, which will cause RL3 to operate for around five seconds when the doors are locked. With no voltage on the base of Q5 (as pin 1 of IC1 is now low), RL4 will be de-energised. This relay would now turn the car alarm on. The circuit shows the wiring for conventional locking systems with bidirectional motors. Fig.3 shows the method used to connect the relays for two wire motors. Assembly is reasonably straightforward, with some care being required when soldering the components on the rather small transmitter board. The transmitter overlay is shown in Fig.4 while the receiver layout is shown in Fig.5. Fig.3: if you intend to use the single channel remote in a vehi­cle with central locking, this circuit shows how the various connections should be made. Relay 4 in the receiver is not shown: this can be used to arm/ disarm the vehicle’s alarm system. This photograph clearly shows the mounting position for the pre-built UHF receiver module. While IC sockets were used in the prototype, they are not essential and, indeed, better reliability can often be achieved without them. Fig.4: compare this transmitter PC board layout with the photograph above when placing components. Fig.5: the printed circuit overlay for the single channel receiv­er, reproduced actual size. The antenna can be a short (say 250-500mm) length of insulated hook-up wire. Keep all component leads as short as possible, both on this board and on the transmitter. February 1996  79 Remote Control 2 – Dual Channel UHF T HE SECOND TRANSMITTER is shown in Fig.6. As mentioned previously, it has two momentary contact pushbuttons, either of which apply power to the encoder IC and the rest of the circuit. Note that the encoder chip used here is the same as for the single channel transmitter. Switch SW1 takes pin 13 (D3) of IC1 high, while SW2 takes pin 12 (D2) high. When a button is pressed, the IC outputs one of two different codes, depending on the linking of pins 1-8. The oscillator is similar to the one described in the previous transmitter. One button on this transmitter could be coded to operate the central locking unit previously described, while the other could operate an automatic garage door, using one channel of the receiver described below. Receiver circuit The circuit of the dual channel receiver is shown in Fig.7. This has a discrete component UHF receiver instead of the pre-built surface-mount receiver used in the single channel circuit of Fig.2. L1 and L2 are copper tracks on the PC board, with L1 being damped by resistor R1 to broaden its response. L2 is tuned to the trans­mitter frequency by variable capacitor VC1 and the signal applied via C3 to the base of Q1, a self-detecting regenerative UHF amplifier. The detected output appears at the emitter of Q1 and is coupled via the 4.7µF capacitor to the inverting input of IC1a. The 2.2kΩ resistor and the 470pF capacitor prevent any RF signals being fed into op amp IC1a. This has a gain of 214 and rolls off the Fig.6: the circuit for the dual channel transmitter is very similar to the single channel version but uses separate pushbutton switches to transmit two different codes. 80  Silicon Chip Fig.7: the dual channel receiver is more complex than the single channel version. It has two decoding circuits and a discrete component receiver is used instead of the pre-built UHF module. February 1996  81 PARTS LIST Dual Channel UHF Transmitter 1 plastic case 1 PC board 1 12V alkaline battery 2 battery contacts 2 PC board mounting switches 1 10µH choke Semiconductors 1 AX5326 encode (IC1) 1 BF199 NPN RF transistor (Q1) 2 1N914, 1N4148 diodes (D1,D2) 1 3mm red LED Fig.8: two switches, and therefore a slightly larger case, are required for the dual channel transmitter. Compare the PC board overlay above, to the photograph at right. Capacitors 1 0.1µF monolithic ceramic 1 .001µF ceramic 1 3.9pF NPO ceramic 1 2.2pF NPO ceramic 1 2-10pF variable Resistors (0.25W 1%) 1 1MΩ 1 100Ω 1 22kΩ Dual Channel UHF Receiver 1 PC board 2 SPDT 12V PC relay Semiconductors 1 CA3401 quad op amp (IC1) 2 AX5328 decoder (IC2, IC3) 1 4013 dual D flipflop (IC4) 1 BF199 NPN transistor (Q1) 4 BC548 NPN transistor (Q2-Q5) 3 1N914, 1N4148 diodes (D1-D3) 3 1N4004 diodes (D4-D6) 1 15V 1W zener diode (ZD1) Capacitors 1 100µF 16VW PC electrolytic 1 10µF 16VW PC electrolytic 2 4.7µF 16VW PC electrolytic 4 0.47µF monolithic ceramic 2 .001µF ceramic 1 470pF ceramic 1 330pF ceramic 1 220pF ceramic 1 33pF NPO ceramic 1 15pF ceramic 1 1.5pF NPO ceramic 1 0.5-5pF trimmer Resistors (0.25W 1%) 1 4.7MΩ 1 33kΩ 3 2.2MΩ 1 22kΩ 4 1MΩ 7 10kΩ 1 470kΩ 1 6.8kΩ 4 220kΩ 1 2.2kΩ 1 100kΩ 1 100Ω 2 47kΩ 1 15Ω 1.0W 5% 1 39kΩ 82  Silicon Chip Fig.9: when constructing the receiver board, ensure that the component leads are kept as short as possible. Some resistors mount end-on to the board. response above 2.2kHz due to the 15pF capacitor across the 4.7MΩ feedback resistor. The following op amp, IC2b, has a gain of 23 and rolls off the response above 3.3kHz. The signal is then fed to Schmitt trigger IC1c, which cleans up any noise and interference on it. The final operational amplifier, IC1d, inverts the signal, making it the correct polarity for the decoders. Thus, the signal at pin 5 of IC1 is similar to that generat­ed by the transmitter. This is fed to two identical de­cod­ers – IC2 and IC3. One of these ICs has pin 13 connected to the +12V rail, while the other has pin 12 connected to this rail. Thus, SW1 on the transmitter will be decoded by IC3 and SW2 by IC2. Each output (pin 17) is fed to the clock input of one half of a dual type “D” flipflop, IC4. Each time the clock input goes high, the output (pin 1 or pin 13) will toggle (low to high or high to low), causing relays RLA or RLB to alternately latch or release. The outputs of IC2 and IC3 are “ORed” by D2 and D3 so that when either receives a valid code, the collector of Q3 will go low for about half a second. This could be used to actuate a buzzer or if the values of C12 and R24 are increased, a 12V globe could be switched on for a reasonable time. Building it The component overlay of the transmitter board is shown in Fig.8. Once again, the transmitter board is fairly compact and extra care should be taken with its assembly. By contrast, the receiver board depicted in Fig.9 should not present any difficulties. Some of the resistors stand vertically and they should be pushed right down against the PC board. The alignment procedure for each board is covered in the instructions supplied with the kit. Remote Control 3 – 8 Channel Infrared T HE THIRD OF THESE remote controls goes from the exotics of UHF at 304MHz to a more mundane infrared (IR) transmitting LED and an IR receiver module. But while the UHF remotes had only one or two outputs, the IR system has six momentary and two latching outputs available for controlling devices. The transmitter handpiece, branded Magnavox, measures 155 x 35 x 16mm. The eight buttons on it are labelled Tuner, CD, Track, Stand-by, Stop, Play and Volume up/down. When any one of the first six transmitter buttons is pressed, the corresponding receiver output (A-F) goes high momentarily. The Volume buttons toggle the G and H outputs; ie, latching them high on one press, low on the next. The transmitter circuit is shown in Fig.10 and as with the UHF circuits, there is not much to it; just an encoder IC and a couple of transistors to drive the IR light emitting diode, IRLED1. IC1, an SM5021B, uses a 455kHz ceramic resonator as the oscillator. This is divided internally by 12, giving near enough to a 38kHz carrier frequency which is gated on and off by the data. The pulse train appears at pin 15 and drives LED1 through Darlington transistor driver Q1, Q2. If several of these transmitters were to be used in the same vicinity, the coding links LK1 and/or LK2 could be fitted but otherwise they are not necessary. Receiver The receiver circuit is shown in Fig.11 and is almost as simple as the transmitter thanks to the use of IC2, a PIC12043. This device contains an IR receiver diode, an amplifier tuned to 38kHz, a bandpass filter, an AGC section and a detector circuit. Its output is a digital pulse train identical to that generated by the transmitter but inverted. Q1 changes the polarity to make it suitable for IC1, the decoder. Q2 and ZD1 regulate the input voltage to +5.7V, to prevent damage to IC2. The coding links LK1 and LK2, if fitted, must match those in the transmitter. The outputs of IC1 can only supply around one milliamp, so a buffer or Fig.10: the infrared transmitter circuit. Links LK1 and LK2 are coding links and are only required if another infrared remote is used in the same area. February 1996  83 Fig.11: only one relay driver is shown here for simplicity but each of the receiver outputs (A-H) requires a driver. Outputs A-F are momentary action, while G and H toggle. PARTS LIST Fig.12: very little assembly is required on the transmitter board. Watch the polarity of the infrared LED: its anode leg is longer than its cathode. Compare the overlay with the photograph at left. 8-Channel IR Transmitter 1 Magnavox handpiece (includes 455kHz resonator & IR LED) 1 PC board 2 AAA 1.5V batteries Semiconductors 1 SM5021B encoder (IC1) 1 BC548 NPN transistor (Q1) 1 C8050 NPN transistor (Q2) Capacitors 1 10µF 16VW PC electrolytic capacitor 2 100pF ceramic capacitor 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 transistor (Q1,Q2) 1 6.2V 500mW 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 4.7kΩ 1 10kΩ 1 1kΩ 84  Silicon Chip Fig.13: the receiver board for the 8-channel infrared remote is very simple but take care to ensure that none of the outputs are shorted, as their holes are close together. relay driver (as shown on the receiver circuit) is necessary to interface each output to the real world. So if you want six momentary outputs, for example, you will need six relay drivers. The transmitter PC board is shown in Fig.12 while the receiver board is shown in Fig.13. These two PC boards are easy to build as there are very few parts. Additionally, there are no setting-up adjust­ments (apart from the SC coding links). Kit Availability These remote control kits are all available from Oatley Electronics, 51 Lansdowne Parade, Oatley West. Phone (02) 579 4985. The prices are as follows: Single channel UHF transmitter ..............$10.00 Single channel UHF receiver (2 relays) ...$36.00 (extra relays $3.00) Two channel UHF transmitter ..................$18.00 Two channel UHF receiver ......................$26.00 (only 1 channel: $20.00) Eight channel IR transmitter ....................$18.00 Eight channel IR receiver ........................$18.00