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Control car burglar alarms with this . . . Dual channel UHF remote control This UHF remote control can control two devices indepen­dently of each other. It’s just the shot for controlling car burglar alarms & for switching other devices, such as house alarms, on & off. By BERNIE GILCHRIST Last month, we described a comprehensive car burglar alarm that you can build and fit yourself. In this article, we are present­ ing the companion remote control unit. It uses a commercial keyring transmitter plus a ready-made (and aligned) front-end receiver module so that it’s easy to build and get going. Although it’s mainly intended for 56  Silicon Chip controlling car burglar alarms, this unit can also be used for switching other electri­ cally-operated devices; eg, garage door motors, lights and model cars. The receiver board carries two relays – one for each chan­nel – and these have both NO (normally open) and NC (normally closed) contacts. They can be wired independently of each other in either latched or momentary (pulsed) mode to suit your appli­cation. Selecting latched mode simply means that the relay alter­nately operates and releases with each press of the corresponding transmitter button. Alternatively, if pulse operation is select­ed, the relay only operates while its corresponding transmitter button is held down. The companion UHF transmitter has one button for each chan­nel and transmits a coded signal to operate the receiver (and activate one of the relays) when ever a button is pressed. The code is selected using a combination of up to six wire links, which must be the same in both the transmitter and receiver (otherwise the unit will not work). Both channels can be operated at the same time, if required, by press- ing halfway between the two buttons on the transmitter. In all, there are some 4096 different code combinations and this should be sufficient to prevent interference from other users, particularly as the range is limited to about 20 metres. All connections to the remote control receiver are made via a single 9-pin nylon plug and socket. ANTENNA 12V CH1 (A) Q1 11 4TH GND 2 3 Circuit description The keyring transmitter uses an AX5026S-4 surface mount 4-state encoder IC which works with a complementary AX5027 decoder IC in the receiver. Note, however, that the decoder IC has 18 pins and provides seven address bit inputs (A1-A7) and four data bit outputs (D0-D3). By contrast, the encoder IC is a 16-pin device and only provides address bit inputs A1-A6 and data bit inputs D1-D3, with A7 and D0 not accessible. In this circuit (see Fig.1), address bits A1-A6 are used for code selection, while data bits D2 and D3 are used for channel selection. To set the security code, the six address inputs (A1-A6) can each be connected in one of four possible ways: to ground, to V+, to the 4th state pin (pin 1) on the IC, or left open circuit. This results in 46 or 4096 possible code combina­tions. (Note: a terminal has been provided to code A7 in the receiver in case a different keyring encoder is used in the future, thus giving 16,384 code combinations. However, for the transmitter used here, it must be left disconnected). The transmitter is activated by pressing either the CH1 or the CH2 button. If the CH1 button is pressed, for example, tran­sistor Q1 turns on and this does two things: (1) it lights LED 1 to indicate that the unit is transmitting; and (2) it pulls the D3 input (pin 11) of IC1 high to set the channel information Similarly, if the CH2 button is pressed, Q2 turns on, LED 1 lights (as before) and the D2 input is pulled high. The encoder IC has a single output (DOUT at pin 15) which generates a stream of pulses containing both the code and the channel information. These pulses then modulate (ie; switch on and off) a 304MHz transmitter stage. The data is sent continuous­ly while ever a button is being pressed. If both buttons are pressed, the code LED1 LED1 4 5 6 7 V+ A2 CH2 (B) Q2 16 VDD 4TH A1  IC1 AX5026 A3 VCC 11 D3 D2 10 DOUT 15 O/P 304MHz TRANSMITTER GATE OSC1 14 A4 A5 GND 470k A6 VSS 8 OSC2 13 TE 12 KEY-RING TRANSMITTER Fig.1: the transmitter is based on an AX5026 encoder IC, with data bit inputs D2 & D3 used for channel selection. Coding is achieved by connecting each address input (A1-A6) to V+, Gnd or the 4th state input, or by leaving it open circuit. information for both channels is generated by IC1 and transmitted. Receiver Fig.2 shows the receiver details. The pre-built UHF receiver front-end is a small module that uses surface mount devices. It is tuned to 304MHz and is supplied aligned and test­ed. In operation, the front-end module processes the received RF signal via a bandpass filter, an RF preamplifier, a regenera­tive detector, an amplifier and a Schmitt trigger. Its input is fed by a short antenna while the output (at pin 5) is a copy of the serial data stream that was produced by the encoder IC in the transmitter. Main Features • Dual channel – can control two independent devices • Good security – 4096 possible code combinations • Compact ready-made keyring trans­mitter • Ready-made & pre-aligned front-end receiver module for stable tuning & ease of construction • Latched or momentary relay output for each channel • A range of about 20 metres in open air The output from the front-end module is fed to the AX5027 4-state decoder (IC1) which then compares the transmitted code with the code on its own address pins (A1-6). If the codes are found to be the same, the VT (valid transmission) pin goes high, along with one (or both) of the two data terminals (D3 and D2). D3 (pin 13) goes high when channel 1 is selected, while D2 (pin 12) goes high when channel 2 is selected. Resistor R1 sets the data decoding rate so that it matches the transmis­sion rate. NAND gates IC2a-IC2d are used to decode the channel select outputs (D2 & D3) from IC1. Let’s assume that the CH1 button in the transmitter is pressed. In this case, D3 of IC1 in the re­ceiver goes high, which means that pin 3 of IC2a goes low and pin 11 of IC2c goes high. Similarly, pin 10 of IC2d goes high if the CH2 button is pressed, while both NAND gate outputs go high if both the CH1 & CH2 buttons are pressed together. These NAND gate outputs (pins 11 & 10) then drive the output stages of the circuit via one of two possible paths, to provide either latched or pulsed relay operation. Latched operation For latched operation on channel 1, the output from IC2c is fed to the clock input of 4013 D-type flipflop IC3a. This IC has its Q-bar output connected to its data (D) input to January 1995  57 +6V D3 1N4004 Q1 E BC547 C C3 0.1 V+ R4 1.8k B ZD1 1N4736 6.8V C1 0.1 +6V UHF 2 RECEIVER 5 MODULE 14 DIN 4TH GND 1,3,6,8, 10,11, 12 1 2 3 4 5 6 7 8 V+ 4TH A1 VT IC1 AX5027 A2 1 17 D3 13 A3 5 6 R1 470k OSC2 15 A6 3 IC2a 12 13 IC2c 4011 OSC1 16 A7 14 2 D2 12 A5 4 IC2b 4 14 R 1 D Q IC3a 3 4013 2 CLK Q S 6 LATCH PULSE 8 A 9 C K 4 2 E 3 1 8 V+ A 9 CH 2 LED2  6 D2 1N4004 LATCH PULSE 10 R6 R 13 1.5k D Q RLY2 R8 1.5k B IC3b 11 12 CLK Q S 7 8 B C R5 1.5k K R3 1M RLY1 R7 1.5k 7 C2 0.1 IC2d D1 1N4004 Q2 BC337 +6V 10 VIEWED FROM BELOW 11 7 9 VSS 9 E  5 18 VDD A4 A CH 1 LED1 K R2 1M 7 C4 10 C 9-PIN PLUG Q3 BC337 E RECEIVER Fig.2: the incoming RF signal from the transmitter is picked by a UHF frontend module & the detected signal fed to IC1 for decoding. IC2 & IC3 process the signals from IC1 to provide either latched or pulsed relay operation. Transistors Q2 & Q3 are used to drive the two relays. provide toggle operation. Each time IC3a receives a clock signal, its Q output at pin 1 chang­es state and remains in that state until the next clock signal is received. Assuming that the circuit has been wired in latch mode, IC3a’s Q output drives transistor Q2 via R5. Thus, if IC3a’s Q output goes high, Q2 turns on and activates relay RLY1 to operate a set of changeover contacts. At the same time, LED 1 lights to indicate that the relay is on. The relay now remains on until the transmitter button is pressed again. When that happens, IC3a’s output switches low and Q2, RLY1 and LED 1 switch off. D1 is there to quench any high-voltage spikes generated by the relay switching action. Momentary operation If the circuit is wired in pulse mode, IC2c’s output is fed directly to Q2 via 58  Silicon Chip R5, thus effectively bypassing IC3a. When the CH1 transmitter button is pressed, pin 11 of IC2c goes high and so Q2, LED 1 and RLY1 turn on as before. However, when the trans­ mitter button is released, pin 11 of IC2c switches low again and so Q2, LED 1 and RLY1 turn off. As a result, RLY1 only remains on for as long as the trans­mitter button is held down if the pulse mode linking option is selected. IC3b, Q3, LED 2 and RLY2 all function in exactly the same manner as their corresponding channel 1 components if the CH2 button is pressed. As before, either latch or pulse mode can be selected for the relay. Power supply Power for the circuit can be derived from any DC source capable of supplying 10-15V DC and 100mA (eg, a 12V car battery or a 9V plugpack supply). D3 provides reverse polarity protection for the circuit, while C4 provides supply decoupling. The result­ing +12V (nominal) rail is used to power the relays, transistors Q2 & Q3, and the LEDs. The remainder of the circuit, including the UHF front-end module, is powered from a 6V rail and this is provided by a series regulator consisting of Q1, ZD1 and R4. The circuit consumes about 5mA in the quiescent state (both relays off) and about 55mA when both relays are on. Note that when power is first applied to the circuit, IC3a and IC3b have their reset inputs pulled high via capacitors C1 and C2 respectively. This ensures that the circuit initially switches on with both relays off. The two capacitors then charge via R2 and R3 respectively and so the reset pulse ends after about 0.1 seconds, after which the circuit functions normally. Construction All the parts, including the frontend module, are mounted on a small 250mm LONG INSULATED WIRE ANTENNA 10uF 1.5k 7 NC D2 9 COMM 2 NO 3 COMM RLY1 0.1 LED1 D1 1M  P 1.5k 1 NC  P L IC3 4013 L 1 1 1M 0.1 470k 4TH GND V+ ANTENNA A7 A6 A5 0.1 Q1 1.5k IC1 AX5027 RLY2 Q3 1.8k 4 +12V 8 NO UHF RECEIVER MODULE ZD1 IC2 4011 LED2 D3 Q2 6 0V 1.5k PC board measuring 105 x 40mm. Fig.3 shows where the individual parts go on the board. Begin construction by installing the resistors (R1-R8). These can be mount­ed either way around but it is good practice to mount them with their colour codes all in the same direction as this will make them easier to check. Next, install the wire link that runs parallel to the IC2, then install the two wire links which determine latch (L) or pulse (P) operation for each channel. In fact, it’s a good idea to initially wire both channels for latch operation, just to make sure that the flipflops (IC3a & IC3b) are working. This done, install diodes D1-D3 and zener diode ZD1. These can be mount­ed in one direction only, with the stripe on the very end of the diode corresponding to the striped end on the overlay diagram. The three ICs can now be installed on the board. Make sure that you don’t get IC2 (4011) and IC3 (4013) mixed up and check that all the devices are correctly oriented. The next step is to mount the three transistors (Q1-Q3). Install each transistor so that its flat side is facing the direction shown on the overlay diagram and push them down onto the board as far as they will comfortably go before soldering their leads. Don’t press the transistors down too far though, as this stresses their leads and can damage internal connections. Note that Q1 is a BC547 device while Q2 & Q3 are BC337s, so don’t get them mixed up. Once the transistors are in, install the capacitors at the locations shown on Fig.3. The three 0.1µF (100n) MKT capacitors can be installed either way around but note that the 10µF electro­ ly­tic capacitor is polarised and must be correctly oriented. The two LEDs can either be installed directly on the board or con­ nected via long flying leads if you want to mount them at a remote location. Make sure that the LEDs are correctly oriented. In each case, the anode lead is the longer of the two while the cathode lead is adjacent to a flat edge on the body. Finally, complete the board assembly by installing the two relays and the front-end module. Note that the front-end module is oriented with its component side facing away from board. It comes fitted with a 12-pin header and these pins must be bent at A4 A3 A2 1A1 WIRE LINK FOR PULSE (P) OR LATCH (L) MODE Fig.3: the two wire links marked with an asterisk (*) are either connected to “L” for latched operation or to “P” for pulsed operation. The coding pads are at the righthand end but note that A7 must be left open circuit. The completed board assembly is mounted on the lid of the case using 12mm tapped spacers & machine screws. Note the coding links at the righthand end. right angles so that it mounts vertically as shown in the photos. In order to obtain a decent range, an insulated wire anten­ na must be connected to the EXT ANT input. This antenna should be 250-300mm long but can be increased to about 500mm to obtain a slightly greater range. Testing When the assembly is completed, connect the receiver to a 12V DC power supply and press the CH1 (A) transmitter button. If the unit is working correctly, relay RLY1 will immediately latch on. Check that this relay can now be turned off by again pressing the CH1 transmitter button. The second channel is checked out in exactly the same fash­ion (ie, RLY2 should toggle each time the CH2 (B) button is pressed). If everything is working OK, you can also check the effective range of the unit. It should operate reliably up to about 20 metres in open air. This range will be somewhat reduced if the receiver is placed inside a car, depending on the location of the antenna. Once these initial checks have been made, switch off and reconfigure the links (if required) to obtain the required relay operating modes (ie, either latch or pulse for each channel). Note that you will have to configure channel 1 so that it oper­ates in latch mode if you intend using this unit to control the Car Burglar Alarm described in last month’s issue. Coding As supplied, the transmitter comes with its A1-A6 address pins (pins 2-7) all open circuit (ie, the transmitter is not coded). Fortunately, the job of coding is fairly straightforward although you do need good eyesight and a soldering iron with a fine tip. An eyeglass or a magnifying glass will be handy for this job. January 1995  59 leaving the address pin open circuit. Note that address pin A7 must be left open circuit to suit the transmitter used here. Be careful not to link any of the three columns closest to the end of the board together, otherwise damage may result. Apart from that, it’s simply a matter of matching the re­ceiver’s code to that programmed into the transmitter. Check your work carefully here – if the two codes are different, the unit won’t work. Final assembly Mount the UHF front-end module with its component side facing outwards, as shown here. Note that the module is supplied pre-aligned to 304MHz & requires no further adjustments. 1 2 3 4 5 6 7 8 9 9-PIN PLUG ALLOCATIONS 1 CHANNEL 1 RELAY OUTPUT NC 2 CHANNEL 1 RELAY OUTPUT NO 3 CHANNEL 1 RELAY OUTPUT COMMON 4 +12V INPUT 5 NOT USED 6 0V INPUT 7 CHANNEL 2 RELAY OUTPUT NC 8 CHANNEL 2 RELAY OUTPUT NO 9 CHANNEL 2 RELAY OUTPUT COMMON 9-PIN NYLON PLUG VIEWED FROM BACK The transmitter case consists of two half sections which are simply clipped together. They are separated by lightly squeez­ing the sides of the bottom section, then prising the two sec­ tions apart. This done, remove the battery and the PC board from the case. All you have to do now is connect each A2-A6 address pin (pins 2-7) of the IC in one of four possible ways: (1) to a strip on the top surface of the board labelled 4TH; or (2) to a strip on the bottom surface of the board labelled V+.; or (3) to a strip on the bottom surface of the board labelled G; or (4) leave the pin open circuit. For example, you might decide to tie A2 to 4TH, A3 to G, A4 to V+ and leave A1, A5 & A6 open circuit. That’s just one possi­ble code combination – you should use a different combination to ensure that you have a unique code. The completed PC board can now be installed in a plastic zippy case measuring 41 x 68 x 130mm. As shown in the photos, the board is mounted on the lid of the case and is secured on two 12mm tapped spacers using four machine screws. You can use the board as a template for marking out the two mounting holes. An additional hole will also have to be drilled in one end of the case to provide an exit point for the 8-wire cable and for the antenna. The external wiring cable can be made up from eight 200mm lengths of medium-duty hook-up wire. Connect the leads to the PC board as shown on Fig.3, then sleeve them with a 170mm length of heatshrink tubing. The cable can then be passed through the hole in the plastic case and the various leads connected to a 9-pin plug. A plastic cable tie can be secured to the cable just inside the case to prevent the leads from being pulled out of the board. Fig.4 shows the wiring details for the 9-pin plug, as viewed from the back. Each lead is terminated by first soldering it to a special pin which is then pushed into its appropriate location from the back. Make sure that you install each pin in its correct location, as they are impossible to get out if you make a mistake. Fig.5 on page 40 of the December 1994 issue shows how to connect the unit to control the Dick Smith Fig.4: this diagram shows the pin allocations for the 9-pin plug as viewed from the back (or wiring side). Short links of fine wire can be used to make the connections. Be sure to keep a record of the code, since you will need to code the receiver with exactly the same combination. Import­ant: do not make any connections to pins 1 & 16 of the IC during the coding procedure. Once coding has been completed, the transmitter can be carefully reassembled by installing the parts and clipping the two halves of the case together. Make sure that you install the battery with the correct polarity – the positive terminal is indicated by a moulded “+” sign on the bottom section of the case. If everything is OK, the LED should light when one of the transmitter buttons is pressed. The same code can now be programmed into the receiver by linking each A1-A6 address pin of the decoder IC (AX5027) to 4TH, G or V+ at one end of the board, or by TABLE 1: RESISTOR COLOUR CODES ❏ ❏ ❏ ❏ ❏ No. 2 1 1 4 60  Silicon Chip Value 1MΩ 470kΩ 1.8kΩ 1.5kΩ 4-Band Code (1%) brown black green brown yellow violet yellow brown brown grey red brown brown green red brown 5-Band Code (1%) brown black black yellow brown yellow violet black orange brown brown grey black brown brown brown green black brown brown The transmitter is disassembled by carefully prising the two halves of the case apart. The 4TH state line is clearly visible to the right of the IC. Electronics Car Bur­glar Alarm. There are just four wire connections: the two power supply connections, a connection between the NO contact of RLY1 and the ARM/DISARM input of the alarm, and a connection between the common contact of RLY1 and the 0V rail. If you intend using the unit for some other purpose, note that it is suitable for switching low-voltage equipment only (up to 28V DC at a few hundred milliamps). Do not try to switch mains voltages using the on-board relays – the relays are not rated sufficiently to do this job, nor is the board designed to accommodate mains voltages. If you do need to control high voltage equipment, then this may be done by using the unit to control external heavy-duty relays which are rated to do the job. Troubleshooting If it doesn’t work, the first step is to check that the transmitter and receiver are identically coded. If this checks OK, check the supply rail to the frontend module and to the three ICs in the receiver. You should find +6V on pin 7 of the front-end module, on pin 18 of IC1, on pin 14 of IC2 and on pin 14 of IC3. If this voltage is incorrect, check D3, Q1 and ZD1. If the supply rail is OK, set your DMM to a low AC range and connect it between pin 9 of the front-end PARTS LIST 1 2-channel UHF keyring transmitter 1 PC board, code ZA1307, 104 x 40mm 1 UHF front-end receiver module 2 12V miniature SPDT relays, DSE Cat. P-8007 1 9-pin nylon plug & socket 1 plastic zippy case, 41 x 68 x 130mm 2 200mm lengths of mediumduty hookup wire (red & black) 3 400mm lengths of medium duty hookup wire (white, blue & yellow) 1 170mm length of 12mm-dia heatshrink tubing 2 12mm-long tapped spacers 4 3mm x 5mm-long machine screws 1 plastic cable tie Semiconductors 1 AX5027 decoder (IC1) 1 4011 quad NAND gate (IC2) 1 4013 dual D flipflop (IC3) 1 BC547 transistor (Q1) 2 BC337 transistors (Q2,Q3) 3 1N4004 silicon diodes (D1-D3) 1 1N4736 6.8V zener diode (ZD1) 2 3mm LEDs (LED1,LED2) Capacitors 1 10µF 16VW electrolytic 3 0.1µF (100nF) MKT ceramic This close-up view clearly shows the V+ & Gnd coding lines on either side of the A1-A6 address pins on the underside of the transmitter board. module and ground. Apply power and check that the DMM reading increases when you press one of the transmitter buttons. If it doesn’t, then either the transmitter is suspect or the front-end module is faulty. If the reading does increase as expected, switch off, set the DMM to measure DC volts and check that pin 17 of IC1 swings high when either button is pressed. Check the timing resistor (R1) and the coding if this does not occur. If the reading does go high, check that pin 11 of IC2 goes high when the CH1 button is pressed and that pin 10 goes high when the CH2 button is pressed. If either relay still refuses to operate, check its asso­ c iated driver Resistors (0.25W, 1%) 2 1MΩ 1 1.8kΩ 1 470kΩ 4 1.5kΩ Where to buy a kit A complete kit of parts (Cat. K3260) is avail­ able from all Dick Smith Electronics Stores or by mail order from PO Box 321, North Ryde, 2113. The price is $99.95 plus $7.00 p&p (includes one trans­ mitter). Additional transmitters (Cat. K­3261) are $39.95 each. Note: copyright of the PC board artwork for this design is retained by Dick Smith Electronics. transistor (Q2 for channel 1, Q3 for channel 2). If either relay works OK in pulse mode but not in latch mode, check the connections around IC3. Try changing the IC only as a last SC resort. January 1995  61