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Remote control for the Woofer Stopper Don’t get out of bed to press the Start button on the Woofer Stopper. Just press the button on a small hand-held trans­mitter instead. By DARREN YATES The Woofer Stopper in last month’s issue is a great idea. It zaps barking dogs with a high-level supersonic tone that’s beyond the range of human hearing. While we cannot guarantee that it will work with every dog, the device has been very effective on the mutts that have been zapped so far. In fact, a dog belonging to one of our staff members was stopped in mid-howl when the START switch was pressed. But there is one drawback 18  Silicon Chip to the Woofer Stopper. If the mutt next door starts making a nuisance of himself, you’ve actually got to get out of your chair or out of bed to press the START button on the front panel. This UHF remote control unit solves that problem. It uses a small handheld transmitter to activate a receiver module mounted inside the Woofer Stopper case. Basically, the receiver output is wired in parallel with the START switch. When the transmitter button is pressed, the receiver output goes high and this simulates the START switch action. Rather than re-invent the wheel, we decided to base the project on the UHF Remote Control that was featured in the Decem­ber 1992 issue. This used a small key fob style transmitter and a compact receiver unit based on a pre-built front end module. The transmitter circuit is identical but we’ve considerably simplified the receiver circuit, since we no longer require the relays or the latching circuit. All we require is a momentary output and this can be derived using just the RF front-end module and the decoder IC. The front-end module comes prealigned (to 304MHz) and uses surface mount components to give an assem- Fig.1: the transmitter is based on trinary encoder IC1. When S1 is pressed, IC1 generates a series of pulses at its pin 17 output to switch transistor Q1 on & off. This transistor is wired as a Hartley oscillator & operates at 304MHz due to its tuned collector load & the SAW filter in the feedback path. bly that measures just 35 x 25mm. It is fitted with a pin connector along one edge and plugs into the receiver PC board just like any other component. This eliminates alignment hassles and means that you don’t have to wind any tricky coils. So there it is; the answer to your prayers. Now you can zap the barking fleaball next door by remote control. Let’s find out how this miracle of technology works. How it works – transmitter The transmitter is based on an AX5026 trinary encoder IC – see Fig.1. When pushbutton switch S1 is press­ ed, this IC gener­ ates a sequence of pulses at its output (pin 17). The rate at which these pulses are generated is set by the 1MΩ timing resis­tor between pins 15 and 16 (R1), while the code sequence is set by the connections to the address lines (A1-A12). Each of these address lines can be tied high, low or left open circuit, giv­ ing more than half a million possible codes – 531,441 to be exact. Security is not a prime consideration in this project, however. The coded output from IC1 drives RF transistor Q1. This transistor is connected as a Hartley oscillator operating at 304MHz, as set by a tank circuit consisting of L1 (etched on the PC board), C3, C4 and C5. In addition, a SAW resonator is used to provide a narrow-band feedback path. Its lowest impedance is at its resonant frequency of 304MHz and thus the tuned collector load must be set to this frequency in order for Q1 to oscillate. The SAW resonator ensures fre- quency stability and makes the transmitter easy to align. That’s because the oscillator will only start and pulse LED 1 when the tuned circuit is virtually dead on frequency. This arrangement eliminates trial & error adjustments. C3 is used to adjust the centre frequency of the tuned circuit. This point corresponds to maximum current consumption and is found by adjusting C3 to obtain peak brightness from the indicator LED (LED 1). Power for the transmitter is derived from a miniature 12V battery (GP23 or equivalent) and this is connected in series with the pushbutton switch (S1). When S1 is pressed, the current drawn by the circuit is only a few Main Features Range .....................................................100 metres (line of sight only). Transmitter Frequency ............................304MHz (set by SAW filter). No. Of Code Combinations .....................531,441. Receiver Frequency �������������������������������Preset to 304MHz by a factory assembled front-end module. Receiver Dimensions ..............................33 x 64 x 30mm (W x D x H). Receiver Output ��������������������������������������High for as long as transmitter button is held down. June 1993  19 Fig.2: the receiver uses a pre-built RF front-end module to pick up the pulses from the transmitter. The resulting digital pulse train from the front-end module is then decoded by Tristate decoder IC1. When the transmitter button is pressed, pin 17 of IC1 goes high. milliamps, the exact figure depend­ing on the code word selected at address lines A1-A12. How it works – receiver Fig.2 shows the circuit details of the receiver. Its job is to pick-up the coded RF pulses from the transmitter and decode these pulses to generate an output. As already mentioned, the receiver is based on a complete “front-end” module. This processes the received signal via a bandpass filter, an RF preamplifier, a regenerative detector, an amplifier and a Schmitt trigger. Its input is connected to a short antenna, while its output delivers a digital pulse train to the input (pin 14) of IC1. IC1 is an AX-528 Tristate decoder and is used to decode the 12-bit pulse signal that’s generated by the transmitter. As with the AX-5026 encoder, this device has 12 address lines (A1-A12) and these are connected to match the transmitter code. If the code sequence on pin 14 of IC1 matches its address lines, and the code sequence rate matches its timing (as set by R1), the valid transmission output at pin 17 switches high. This output connects to pin 8 of IC5b in the Woofer Stopper and simu­lates the action of the START switch. Thus, when the transmitter button is pressed, pin 17 of the AX-528 decoder goes high and the Woofer Stopper is activated and begins its 9-minute timing cycle. Pin 17 of the decoder IC then switches low again as soon as the transmitter button is released. Construction Fig.3 shows the assembly details for the transmitter. All the parts, including the battery terminals and the switch (S1), are mounted on a small PC board. Before mounting any of the parts, you must first file the edges of the PC board so that it will fit in the case. This also removes two shorting strips. One of these strips runs along the bottom of the board, while the other runs down the righthand edge (as viewed from the copper side). Make sure that these two short­ing strips are completely filed away; if they are not, the bat­tery terminals will be shorted and the positive battery terminal will be shorted to C3. The most important thing to remember with the transmitter assembly is that all component leads should be kept as short as possible. Apart from that, it’s simply a matter of installing the parts exactly as shown in Fig.3. Be sure to orient IC1 correctly and note that the flat side of the trimmer capacitor (VC1) is adjacent to one end of the board. The SAW resonator and switch should both be mounted flat against the board, while the transistor should only stand about 1mm proud of the board. Take care when mounting the switch – it must be correctly oriented, otherwise it will appear as a short and the transmitter will be on all the time (the switch will only fit comfortably in one direction). The LED should be mounted with its top about 7mm proud of the board, so that it later protrudes about halfway through a matching hole in the RESISTOR COLOUR CODE ❏ ❏ ❏ ❏ ❏ ❏ No. 1 1 1 1 1 20  Silicon Chip Value 1MΩ 6.8kΩ 1kΩ 150Ω 82Ω 4-Band Code (1%) brown black green brown blue grey red brown brown black red brown brown green brown brown grey red black brown 5-Band Code (1%) brown black black yellow brown blue grey black brown brown brown black black brown brown brown green black black brown grey red black gold brown ANTENNA A K 82W .001 S1 D1 K 6.8k C3 6.8pF LED1 A 1k 1M .0033 Q1 RECEIVER MODULE 4.7pF SAW 1 12V BATTERY 150  IC1 AX528 .001 1M IC1 AX5026 1 12V BATTERY Fig.3: make sure that the shorting strips are removed from the transmitter PC pattern before starting construction – see text. Keep all leads as short as possible when installing the parts & take care with the orientation of the encoder IC. lid. Be careful with the orientation of the LED – its anode lead is the longer of the two. Check the board carefully when the assembly is completed – it only takes one wrong component value to upset the circuit operation. This done, slip the board into the bottom half of the case and install the battery. Don’t worry if the LED doesn’t flash at this stage when you press the switch – that probably won’t occur because Q1 will not be oscillating. To adjust the oscillator stage, press the switch and tune C3 using a plastic tool until the LED flashes. When this hap­pens, the oscillator is working and you can tweak C3 for maximum transmitter output (ie, max­imum LED brightness). The lid of the case can now be snapped into position and secured using the small screw supplied with the kit. 12V PLUG-PACK D2 D1 220  1000uF 78L05 100k 10uF 0.1 IC1 4060 SEE TEXT 10M 33pF  1 33pF Fig.4: this is the full-size etching pattern for the receiver board. Fig.5 shows the parts layout on the receiver board. Install the parts exactly as shown, leaving the receiver Fig.5: install the parts on the receiver board & connect it to the main Woofer stopper PC board as shown in this diagram. The prebuilt receiver module is installed with its component side towards the .0033µF capacitor. June 1993  21 module till last. This component must be installed with its component side towards the .0033µF capacitor. The antenna consists of a length of insulated hook-up wire and can be either 250mm or 500mm long. The latter will give slightly greater range if this is important. When the receiver assembly is complete, it can be linked to the Woofer Stopper PC board via a 3-way cable. This done, apply power to the Woofer PARTS LIST Transmitter 1 transmitter case 1 PC board, 30 x 37mm 1 miniature PC-mount pushbutton switch 1 12V battery, GP23 or equivalent 1 304MHz SAW resonator Semiconductors 1 AX-5026 trinary encoder (IC1) 1 2SC3355 NPN transistor (Q1) 1 1N4148 silicon diode (D1) 1 3mm red LED (LED1) Stopper and use your DMM to check that pin 17 of the AX528 switches high when the transmitter button is pressed (be careful not to short any of the pins on the IC). Alternatively, you can check that unit operates when the transmitter button is pressed by modifying the Woofer Stopper circuit to produce a 2kHz tone, as described last month. Coding Because this is not a securityrelated project, coding of the transmitter and receiver can be considered optional. That said, it’s still a good idea to program in a simple code to avoid any possibility of interference with other units. Initially, all the A1-A12 address lines will be open cir­cuit but you can tie selected address pins high or low by con­necting them to adjacent copper tracks. In both the transmitter and the receiver, a +5V rail runs adjacent to the inside edge of the address pins, while a ground track runs around the outside edge of the address pins. For example, you might decide to tie A1 and A8 high, tie A3 and A6 low, and leave the rest open circuit. Short wire links can be used to make the connections but note that you will have to scrape away the solder mask from the adjacent rail at each con­nection point on the transmitter PC board so that the track can be soldered Make sure that the transmitter code matches the receiver code. Finally, the receiver board can be mounted on the bottom of the case, adjacent to the power supply terminals. Use the board as a template for marking out its mounting holes and secure the board using machine screws and nuts, with additional nuts used as spacers. An additional small hole in the far end of the case serves as an exit point for the antenna. Footnote: when activated, the Woof­ er Stopper sounds for nine minutes before switching off. To reduce this period to one minute, cut the track to pin 3 of IC3 and connect pin 1 of IC4 to pin 15 of IC3 instead (or to pin 14 SC for a 30-second period). Capacitors 2 .001µF ceramic 1 6.8pF ceramic 1 4.7pF ceramic 1 2-7pF miniature trimmer Resistors (0.25W, 5%) 1 1MΩ 1 150Ω 1 6.8kΩ 1 82Ω 1 1kΩ Receiver 1 PC board, code 03105932, 64 x 33mm 1 front-end module (aligned to 304MHz) 1 AX-528 Tristate decoder (IC1) 1 .0033µF MKT polyester capacitor 1 1MΩ resistor (0.25W, 1%) Where to buy the parts A kit of parts for this remote control unit is available from Oatley Electronics, PO Box 89, Oatley, NSW 2223, Australia. Phone (02) 579 4985. The price is $39.95 plus $2.50 for postage (incl. transmitter kit, receiver PC board and all parts for the receiver). The original Woofer Stopper project is available separately from other kit suppliers. 22  Silicon Chip The receiver module is mounted on the bottom of the Woofer Stopper case, adjacent to the power supply sockets. Run the antenna across the inside of the case & through an exit hole in the opposite end (near the tweeter socket).