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Remote controller for garage doors Wouldn't it be wonderful if you could operate your garage door, gates or other devices by remote control? This unit will do the job for you. By BRANCO JUSTIC This general purpose unit will enable wireless remote control of garage doors, gates , blinds, shutters and many other devices. It features a ready-made transmitter, high security, and all of the desirable features that one would expect of such a controller! Your job is to build and install the 16 SILICON CHIP receiver/controller board described here. To this, you need to add a geared DC motor (such as an inexpensive automotive windscreen wiper motor), a power transformer and a little mechanical ingenuity. We will offer a few tips and ideas to get you started. Most people of course will want to use this project as a garage door con- troller. So, to simplify matters from here on, we'll describe the project for that application. Main features OK, lot's take a look at the main features. First, the controller has provision for both upper and lower limit switches. In operation, one of these switches (eg, a microswitch) is closed by the door at the end of its travel and this trips the circuit to stop the drive motor. In addition , the circuit also features overcurrent sensing for both the DOWN & UP modes of operation. These can be used to detect obstructions and immediately stop door operation to prevent damage to the motor or drive mechanism. In many situations, the ANTENNA r---t"-----,--....-----..-----.---..---~----....---------<1>----+8V 220k 1M L1 100k 100n 220k 4.7M 220pF E sOc 15pF VIEWED FROM BELOW GARAGE DOOR OPENER RECEIVER Fig.1: the UHF receiver front end. Ql functions as a regenerative detector stage, while Ll & Cl set the resonant frequency. The detected output appears at Ql's emitter & is amplified by ICla & IClb. The signal is then fed to Schmitt trigger stage IClc & inverted by ICld before passing to the decoder circuit (see Fig.2). overcurrent sensor could also be used to sense the "open" and "closed" limits and can thus eliminate the need for limit switches. Of course, these's nothing to stop you from using both limit switches and overcurrent sensing if you so wish. In fact, we recommend that you do use both methods for garage doors. As we've already mentioned, the unit is supplied with a ready-made transmitter and this has more than half a million possible codes - 531,441 to be exact! Press the button on the transmitter and the door goes up; press it again and the door goes down. Simple! The "open-field" range of the transmitter is over 200 metres, so lack of range will not be a problem for any normal domestic application. In addition, there is provision for manual operation using a pushbutton switch. This switch would normally be mounted on the wall inside the garage. The manual switch controls the unit in exactly the same fashion as the transmitter (ie, the unit changes direction on each subsequent press of the button). You don't have to wait for the door to reach the end of its travel either. It can be reversed at any time whilst in motion simply by pressing the remote or manual pushbuttons again. OK, so you've just opened the garage door using your fancy new controller from the luxury of your car. But who wants to drive into a dark garage at night? Wouldn't it be better if a light came on automatically as well? Our circuit takes care of this problem by including a timed relay output which switches a 12V supply rail. This relay is closed each time the controller is activated and remains on for about 2 minutes before automatically switching off. Low voltage automotive lamps and fittings can be used for the lighting, or you can use the on-board relay to trip a mainsrated relay to switch on 240V lights. Since all the inputs are filtered, inexpensive unshielded wire such as telephone cable can be used to connect the UP & DOWN door limit switches and the manual pushbutton switch. The total cost for the control board plus the transmitter is $107. To get a complete motorised garage door, you also need to obtain a suitable motor and transformer, a chain or gear drive system, a case to put it all in and other sundry hardware. All up, we estimate that the total cost of this do-it-yourself garage door opener will be about $200 . Compared to that, the cost of a commercial installation will set you back $650 or more, depending on its complexity. Interested? Then read on. How it works - receiver The control circuit is built on a single PC board. This contains the UHF receiver front end, decoding circuitry, light timing and relay driver circuitry, door operation logic, motor UP & DOWN relay drivers, overcurrent detection and a power supply. Fig.1 shows the circuit for the receiver front end. This is built around transistor Ql and quad op amp ICl. The coded signals from the trans- mitter are picked up by the antenna and are inductively coupled into a parallel tuned circuit comprising 11 and trimmer capacitor CVl. This tuned circuit sets the resonant fre quency for the self-detecting regenerative UHF receiver stage based on Ql and Dl. The detected output appears at the emitter of Ql and is AC-coupled via a 4.7µF capacitor to inverting amplifier stage ICla. A low-pass filter consisting of a lkQ resistor and .00lµF capacitor is included to prevent any RF signals from being coupled into ICla. ICla operates with a gain of about 214, as set by the ratio of the 4.7MQ feedback resistor and the 22kQ input resistor. The 15pF capacitor in parallel with the feedback resistor rolls off the response above 2.2kHz. The output from ICla appears at pin 10 and is AC-coupled to inverting amplifier stage IClb. This stage operates with a gain of 47 and a rolloff above 3.3kHz. Its output is biased at close to ground potential and so the original digital signal appears at the output (pin 9) of this stage. Next, the signal is fed to Schmitt trigger stage IClc. This stage cleans up the signal from IClb and prevents false triggering due to noise and interference. The resulting signal is then inverted by ICld to give a digital pulse train (Data) which matches the data present at the encoded output of the transmitter. Tristate decoder The recovered data signal is now applied to the pin 14 input of Tristate decoder IC2 (AX-528) - see Fig.2. This device is used to decode the 12-bit pulse signal generated by an AX-5026 encoder chip in the transmitter. It has 12 Tristate address inputs which are MARCH 1991 17 This view shows the UHF receiver/controller board, together with its companion transmitter (which is supplied ready made). Although designed to control garage doors, the unit could also be used to control gates, curtains, blinds, shutters & other mechanical devices via a motor & chain drive assembly. connected to correspond to the transmitter code. Each address input can either be tied high or low, or left open circuit (O/C). When the transmitter code matches the code on IC2's address pins (ie, when a valid signal is detected), pin 17 switches high and this drives the remainder of the circuit via two paths. Light relay First, the high from pin 17 is applied via isolating diodes D2 and D4 to a monostable made up from IC3b and IC3c. This monostable is used to operate the light relay via switching transistor Q5. The time the light remains on is set to about 2 minutes by the 1MQ resistor and lO0µF capacitor connected to pins 1 and 2 of IC3c. The circuit works like this. Initially, the lO0µF capacitor is discharged (both sides high) and so pin 3 of IC3c is low and Q5 is off. At the same time, pins 5 & 6 are held low via a 56kQ pull-down resistor. When a valid code is detected, pins 5 & 6 are pulled high and thus pin 4 ofIC3b switches low. This means that pins 1 & 2 ofIC3c also switch low and 18 SILICON CHIP so pin 3 switches high and turns on the light relay (RL5) via transistor Q5. At the same time, pins 5 & 6 of IC3b are latched high via D5. The lO0µF capacitor now charges via the 1MQ resistor and, after about 2 minutes, pulls pins 1 & 2 of IC3c high again to end the timing period. This also releases the high on pins 5 & 6 of IC3b and so pin 4 switches high again to discharge the capacitor so that it is ready for the next cycle. D6 clamps the positive side of the capacitor to the supply rail when pin 4 switches high again, to prevent damage to IC3c. pass filter. Its job is to filter out any RF signals which may be picked up by long leads connected to S1 and which could false-trigger IC3a. Similar filter networks are also used for the LOWER & UPPER limit switches (S2 & S3), for the same reason. Door logic Manual control The valid transmission line is also connected to the clock inputs (pins 3 & 11) of two paralleled D-type flipflops based on IC4. These flipflops toggle (ie, change state) on each successive clock input because of the 1MQ feedback resistor connected between the Q-bar outputs (pins 2 & 12) and the data inputs (pins 5 & 9). A time delay of about 1 second is provided in this feedback path by the 1MQ resistor and the lµF capacitor on pins 5 & 9 to prevent unpredict- Inverter stage IC3a and pushbutton switch S1 form the manual control circuit. Normally, pins 8 & 9 of IC3a are held high via a 1MQ resistor and so pin 10 will be low. When S1 is pressed, pins 8 & 9 are pulled low and thus pin 10 applies a high to the valid transmission line via D3 (just as if a valid transmission had been received from the transmitter). The 100kQ resistor and 0.1µF capacitor associated with S1 form a low Fig.2 (right): the decoding & door logic control circuit. When a valid code is detected, pin 17 of IC2 switches high & toggles D-type flipflop IC3. IC3 in turn controls RS flipflops IC5a,b & IC5c,d & these drive the motor relays via Q3 & Q4. Comparator stages IC7a & IC7b provide overcurrent sensing. g ~ ~ .... cc ::0 .- ~ I I st5. 8 IN GND VIE1ffoW M 0 eOc E CB rn ~ I OUT I DATAFROM ~ RECEIVER - ,,,.,, . A11 - 12 11 A10 10 A9 B AB 7IA7 +8V .,. 1 I I I T M 10 1~ .,. .J.t 1 I o., .,. I I 1 00kf ., 5 I '""l 330kJ t ! 1M + 56 k r.-. .,. I 0.1 7 Q I ~ 2,12 I I I ...~L I I "~ 100k 100k 2-1 ... "" +BV 22k ,, Q 0. .J 1 I ,.,.,..... ei- ~, ~• ' l- 56ki * +BV .,. i LIGHT O -. 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When the transmitter button (S1) is pressed, ICl generates a 12-bit code at its pin 17 output & this switches Ql which is wired as a Hartley oscillator operating at 304MHz. able operation due to short breaks in transmission. Normally, the set inputs (pins 6 & 8) of IC4 are held low by a 10MQ resistor. However, when power is first applied, a pulse is applied to the set inputs via a O.lµF capacitor. Provided the motor is connected with the correct polarity (ie, as shown in Fig.2), this will ensure that the door will be in DOWN mode if power is restored after a power failure. The Q and Q-bar outputs from IC4 are used to control two separate RS flipflops, made up from the four NAND gates in IC5. The outputs of these flipflops (pins 10 & 11) switch high when their inputs (pins 8 & 13) are momentarily pulled low (ie, while the O. lµF capacitors charge). IC5a & IC5b form the DOWN flipflop and its output (pin 11) drives switching transistor Q4 to operate the DOWN relays (RLA3 & RLA4). Similarly, IC5c 20 SILICON CHIP & IC5d form the UP flipflop and this operates the UP relays (RLAl & RLA2) via switching transistor Q3. These four relays in turn switch the power to the motor, the polarity depending on whether the door is to go up or down. For example, when RLAl & RLA2 are closed, the door goes up. Conversely, when RLA3 & RLA4 are closed, the door goes down. Note that, in either case, the motor current flows to ground via a 0.22Q current sensing resistor. Let's take a closer look at how this circuitry works by considering the operation of the DOWN flipflop (IC5a & IC5b). Normally, pin 13 of IC5a is pulled high by a lMQ resistor, pin 11 is low, and Q4 and relays RLA3 & RLA4 are off. When the paralleled Q-bar outputs of IC4 (pins 1 & 13) toggle low in response to the receipt of a valid code or at power up, pin 13 of IC5a is also momentarily pulled low via a O. lµF capacitor. This toggles the flipflop , so that pin 11 now goes high and turns on Q4 and the DOWN relays to provide power to the motor. At the same time, pin 2 of IC5b also goes high and so pin 3 switches low, which means that the flipflop latches in thi s state . The door is now driven downwards by the motor until it closes the lower limit switch (S2). At this point, pin 1 of IC5b is pulled low via a 100kQ resistor and this resets the flipflop (ie , pin 3 high & pin 11 low). This in turn switches Q4 and its associated relays off again and stops the motor. The UP RS flipflop (IC5c & IC5d) operates in similar fashion when the paralleled Q outputs of IC4 toggle low. In this case, the flipflop drives Q3 which switches the UP relays (RLAl & RLA2). The flipflop is reset and switches off the motor when the door trips the upper limit switch (S3) . The two 22kQ resistors between the outputs of IC4 and pins 1 & 6 of IC5b & IC5d allow the motor to be reversed while the door is in operation. In practice, they reset one of the flipflops if IC4 toggles again before a door limit switch is closed. For example, let's say that flipflop IC5a & IC5b is in the set condition (pin 11 high) and that Q4 and its relays are on. If the transmitter button is now pressed while the door is at mid-travel, the Q outputs of JC4 will pull pin 1 of IC5b low via its associated 22kQ resistor and reset the flipflop, thus turning Q4 off. At the same time, the other RS flipflop will be set and Q3 will turn on. Transistor Q2 makes it impossible for the outputs of both RS flipflops to be high at the same time (eg, due to a circuit fault). The way in which it works is quite simple. If pin 10 of IC5 c goes high, QZ turns on and pulls the base of Q4 low. Thus the DOWN relays will be off, even if the output of the DOWN flipflop (pin 11, IC5a) is high. This is a worthwhile precautionary measure because if all four motor-drive relays closed, there would be a short circuit directly across the power supply. Current sensing Comparator stage IC7a provides the overcurrent cutout feature for the UP mode. The voltage at its non-inverting input depends on the setting of VR1 and this can be anywhere in the range of 4-4.5V. The voltage at the inverting input is at approximately ½Vee (4V) with the motor not connected. However, when the motor is running, the voltage applied to pin 2 of IC7a rises to 4V plus the voltage developed across the 0.22Q resistor. For example, if the motor current is 1A, the voltage on pin 2 would rise to 4.22V; if the current is 2A, the voltage would rise to 4.44V, etc. Thus, if the motor current rises above a certain value, the voltage on pin 2 of IC7a will exceed the preset bias on pin 3. And when this happens, pin 1 switches low and resets the UP flipflop to stop the motor. Thus, Q3 and the UP relays turn off and the door stops if the current through the motor rises above a preset level. This typically occurs if the door encounters an obstruction or when it reaches the end of its travel. Overcurrent detector IC7b functions in exactly the same way for the DOWN mode. Trimpots VR1 & VR2 allow the trip currents to be set to the desired values for the up and down directions. The 10µF capacitors at pins 2 and 6 and IC7a and IC7b are there to slow down the response time of the overcurrent detectors so that they are not unduly sensitive to varying friction in the door 's movement or to the motor starting current. Power supply The incoming AC voltage from an external 12 or 24V transformer is rectified by bridge rectifier D16-D19 and applied directly to the motor driver relay polarity switches and the light relay. The resultant unfiltered pulsating DC is used only for driving the motor and the light. If the unit is powered from a DC supply, such as a battery which is continually trickle charged, the bridge rectifier assures that the correct polarity is applied to the circuit, no matter which way the battery is connected. A voltage dependent resistor is connected across the motor in order to minimise the possible high back EMF voltages (from the motor) which would otherwise produce sparks across the relay contacts. A 470µF capacitor is used to filter the rectified supply to drive the relay coils and diode D15 is used to isolate this filtered supply from the motor. Diode Dl 1 and a 100µF capacitor provide further filtering of a supply which is fed to IC6 , a 7808 3-terminal regulator. This provides an 8V supply for most of the circuitry. How it works - transmitter The circuit of the transmitter is shown in Fig.3. It is based on an AX5026 trinary encoder IC. When pushbutton switch Sl is pressed, this IC generates a sequence of pulses at its output, pin 17. The rate at which the pulses are generated is set by the 1MQ resistor between pins 15 and 16, while the code sequence is set by the connections of the address lines A1-A12. The pulses generated by the IC are used to switch Ql which is connected as a Hartley oscillator operating at 304MHz. Note that the transmitter will be supplied ready made and will only need to be set to your own unique code. We'll discuss this next month, along with the construction and installation of the unit. Until then , you will have to be patient and keep opening and closing your garage door by hand. Where to buy the kit A kit of parts for this project will be available in early April from Oatley Electronics. The prices are as follows: transmitter, $27.50 (built and tested); receiver PC board and all onboard components, $79.50; 12V 6.5AH Gel battery, $29.90 (limited stock). Certified postage on any of the above items is $6.00. In addition, Oatley Electronics can supply the receiver PC board in ready assembled form and is also offering a repair service for any constructor who runs into difficulties. For further information, contact Oatley Electronics, PO Box 89, Oatley, NSW 2223. Phone (02) 579 4985. Note: copyright© of the PC bocJ.rds associated with this project is owned by Oatley Electronics. PARTS LIST 1 PC board, code OE90RG, 187 x 106mm 5 SPOT relays 1 VL275A40B varistor 2 100kQ trimpots (VR1, VR2) 1 2-1 0pF trimmer capacitor (CV1) 1 5A fuse 2 fuse clips Semiconductors 1 OA90 diode (for testing) 10 1N4148 silicon signal diodes (D1-D10) 51N4004 silicon diodes (D11D15) 4 1N5402 silicon diodes (D16D19) 1 BF199 NPN transistor (01) 1 BC548 NPN transistor (02) 3 B0437 NPN Darlington transistors (03,04,05) 1 CA3401 quad Norton op amp (IC1) 1 AX528 trinary decoder (IC2) 2 4011 quad NANO gates (IC3,IC5) 1 4013 dual D-type flipflop (IC4) 1 LF353 dual JFET op amp (IC?) 1 7808 +8V regulator (IC6) Capacitors 1 470µF 35VW electrolytic 1 470µF 16VW electrolytic 1 10OµF 35VW electrolytic 2 100µF 16VW electrolytic 5 10µF 16VW electrolytic 2 4.7µF 16VW electrolytic 1 1µF 16VW electrolytic 6 0.1 µF monolithic 1 .0033µF ceramic (for testing) 3 .001 µF ceramic 1 330pF ceramic 1 220pF ceramic 1 33pF ceramic 1 15pF ceramic 1 3.3pF cermaic Resistors (5%, 0.25W) 4 10MQ 1 4.7MQ 1 2.2MQ 7 1MQ 4 330kQ 4 220kQ 8 100kQ 5 56kQ 2 47kQ 1 39kQ 1 33kQ 3 22kQ 1 10kQ 1 6.8kQ 2 4.7kQ 2 2.7kQ 1 1kQ 1 100Q 2 0.22Q 5W MARCH 1991 21