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The drive system for this garage door opener is based on a standard 12V windscreen wiper motor and a standard bike chain and sprockets. It raises or lowers the garage door fully within about 12-13 seconds and is powered by a 12V battery which is kept on permanent trickle charge. Note that a chain guard should be fitted, as a safety measure. 34  Silicon Chip How would you like to be able to drive straight into your garage without the hassle of having to get out of the car to open the door? Well, now you can have a remote-controlled garage door opener without having to pay big dollars. Do-it-yourself automatic garage door opener; Pt.1 Design by RICK WALTERS A LMOST EVERYONE who has a car and a garage wants an au-­ tomatic garage door opener. After all, who wants to get out of the car each time the garage door has to be opened or closed. As one of those fortunate people who now has an automatic garage door (this one), I can tell you it is bliss. You just roll up to the garage and drive right in, the door having just rolled up before you enter. And that’s on a fine sunny day. On a cold, wet winter’s night it is even better. Again, you just roll up to the garage and drive straight in. What more could you want? Problem is, automatic garage door openers are not cheap. Well, they’re not when you have a commercial unit installed but if you build your own you can save a bundle. The design presented here will drive a typical single (2.4m wide) roller door. It uses a 12V windscreen wiper motor and a bicycle chain as the drive system. Running from a 12V battery, it is proof against power blackouts too, something which cannot be said about most commercial door openers. Let’s just briefly describe the drive system. A standard 46-tooth pedal sprocket from a bicycle (approximately 190mm in diameter) is attached to the roller door drum spider. This is connected by chain to the 12V windscreen wiper motor which drives a standard 15-tooth rear wheel sprocket (62mm diameter). Since the wiper motor has a worm gear drive it automatical­ly locks the door in place when it is closed, giving good securi­ty. As with a commercial door opener, the wiper motor operates the door quite slowly, taking about 12 seconds to open or close the door. It doesn’t need to be any faster than this. If it was faster, the motor would need to be much more powerful and there would always be the risk of injury from a faster moving door. How could you be injured by a fast-moving garage door? Well, if you’re trying to escape from the garage before the door April 1998  35 The Q and Q-bar outputs of IC1a, together with the Q output of IC1b, drive two AND gates, IC2b and IC2c. If both the pin 1 (Q) and pin 14 (Q-bar) outputs are high, the output of IC2c goes high to turn on transistor Q1 and relay RLY1. This causes the motor to drive the garage door down. Alternatively, if both pin 1 (Q) and pin 15 (Q) are high, the output of IC2b goes high to turn on transistor Q2 and relay RLY2 and this causes the motor to raise the garage door. In both cases, the motor will continue to rotate until IC3b sees another input either from a limit switch, the local button or the receiver. When this happens the motor will stop. The next input will cause the motor to run in the opposite direc­tion. Fig.1: the circuit of the UHF receiver board. It uses a fully built UHF receiver module and this drives an A5885 trinary decoder. comes down, it is quite easy. The door is operated by a UHF remote control system and uses a standard keyring transmitter. The UHF receiver and motor drive circuitry is housed in a plastic case and this has a 12V light on it to illuminate the garage at night, after the car’s headlights are switched off. It turns off five minutes after the door is operated. There is also a “local” switch inside the garage itself so that the door can be raised or lowered without using the UHF key­ ring transmitter. So there you are. It offers all the features of a commer­cial door opener but you can build it yourself. Before we get to the mechanical details, let’s have a look at the circuitry in­volved. UHF remote control As already noted, the door opener is operated by a UHF remote control system. It uses a standard UHF keyring transmit­ter operating at 304MHz. This is supplied assembled and tested so there is no work on that score. Fig.1 shows the circuit of the UHF receiver and decoder while Fig.2 shows the circuit of the motor drive electronics. What we haven’t shown is the circuit of the keyring trans­ mitter. This is the same as that featured for remote central locking for cars, in the October 1997 issue of SILICON CHIP. This produces coded 100kHz bursts 36  Silicon Chip at 304MHz each time one of the two buttons is pressed. The UHF receiver and decoder has two principal parts. First, there is the UHF receiver itself which is a tiny fully-assembled and tested PC board. Its detector output feeds the 100kHz bursts to the input of IC1, an A5885 trinary decoder. As its name suggests, the trinary decoder looks for a valid code and when it receives it, one of its outputs at pins 12 and 13 goes low. So that either button on the transmitter can be pressed to raise or lower the door, we use both decoded outputs on the A5885 and these are ORed together by the diodes connected to the base of transistor Q1. When either pin 12 or pin 13 goes low, the collector of Q1 goes high and this signal is fed to the receiver input on the motor electronics board – see Fig.2. When the receiver is actuated by its remote control or when the LOCAL switch S3 is operated (inside the garage), the output of OR gate IC3b goes high, and this causes the output of IC2d to go high as well. IC2 is a 4081 quad AND gate package but IC2a and IC2d are merely used as non-inverting buffer stages. Anyway, the high signal from IC2d resets the 4060 timer IC5 and also is fed to the clock inputs of the 4027 dual JK flipflop IC1. The high signal clocks IC1a and if pin 10 (the J input) is high, IC1b will also be clocked. Limit switching So far we’ve given a general description of the circuit but to understand how the door is stopped when it reaches the top or bottom of its travel, we need to look at the circuit in a little more detail. Note that there are two flipflops in the circuit and these really control all functions. IC1a is the RUN flipflop and it determines wheth­ er the motor runs or not. IC1b is the UP/DOWN flipflop and it determines whether the door moves up or down. When power is first applied, the RC time-constant compon­ents at the input of OR gate IC3c apply a reset pulse to pin 4 of IC1a and a set (S) pulse to pin 9 of IC1b, via OR gate IC3a. This causes pin 1 of IC1a to go low (the door STOP) condition and pin 15 of IC1b to go high. This is the UP condition but the motor does not run because both inputs of IC2b must be high for this to occur. When the keyring transmitter button or the LOCAL switch is first operated, IC1a will change state and its pin 1 will go high but IC1b will not, so the motor will raise the door. The door will continue moving until it comes to the top of its travel whereupon the limit switch will close and take pins 1 & 2 of IC2a high. This takes pin 3 of IC3b high via diode D3 and causes a clock pulse to be delivered to IC1a and IC1b. Both flipflops change state so that IC1a reverts to the STOP condition while IC1a changes to the DOWN condition. The next time the LOCAL switch or transmitter button is operated, IC1a changes to the RUN condition and April 1998  37 Fig.2: the motor control board uses a dual flipflop and two relays to control the direction of the motor drive. A 1Ω resistor is switched across the motor to provide braking when both relays are de-energised. Fig.3: component layout for the receiver PC board. Fig.4: component layout for the motor control board. Make sure that all parts are correctly oriented. the door travels down until it hits the lower limit switch. This again causes a clock pulse to be delivered (via IC2a & IC2d) to IC1a & IC1b. Both flip­flops change state, IC1a to the STOP condition and IC1b to the UP condition. Note that the circuit shows two limit switches, both in parallel and both with contacts that are open while the door travels up or down. Our prototype used only one limit switch though, as we will see in the description of the mechanical installation. & 11 and this sets the total period of five minutes. Actually, IC5 is used in a slightly unconventional manner. When power is initially applied, the oscillator will run until pin 3 (the Q14 output) goes high. This output will then hold the input of the internal oscillator high, via diode D5, stopping it from oscillating. The voltage at pin 10, the oscillator output, is normally a 12V square wave (when the chip is not reset), and this is used to charge a 0.1µF capacitor at the gate of Mosfet Q3, via diode D4. So while the capacitor is charged, Q3 will be on and the lamp will be alight. By using this unorthodox scheme we were able to avoid the need to gate the various outputs of IC5 together in order to obtain the 5-minute operating time for the lamp. Lamp timer As already noted, each time IC2d’s output goes high it also resets and starts IC5, a 5-minute timer. IC5 is a 4060 14-stage binary divider with an inbuilt oscillator. Its oscillator fre­ quency is set to around 55Hz by the RC components connected to pins 9. Table 2: Capacitor Codes ❏ Value IEC Code EIA Code ❏ 0.1µF   100n   104 ❏ .01µF   10n  103 ❏ .001µF    1n  102 ❏ 470pF   470p   471 Each time the door motor runs (IC1a is clocked), IC5 will be reset by the output of IC2d, its Q14 output will go low, the oscillator will start and the lamp will turn on. Relay switching You may wonder why we have used relays to switch the motor in either direction instead of a 4-Mosfet Table 1: Resistor Colour Codes ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ ❏ No. 1 4 1 1 1 6 1 1 1 38  Silicon Chip Value 10MΩ 1MΩ 270kΩ 150kΩ 100kΩ 10kΩ 6.8kΩ 1Ω 5% 0.1Ω 5% 4-Band Code (1%) brown black blue brown brown black green brown red violet yellow brown brown green yellow brown brown black yellow brown brown black orange brown blue grey red brown brown black gold gold brown black silver gold 5-Band Code (1%) brown black black green brown brown black black yellow brown red violet black orange brown brown green black orange brown brown black black orange brown brown black black red brown blue grey black brown brown brown black black silver brown not applicable or 4-transistor H-bridge arrangement. The main reasons are the lack of suitable P-channel Mosfets (if Mosfets were used) and the power dissipation if Darlington power transistors were used. By using relays, we were able to keep the switching circuit quite simple. One further refinement that is possible by using relays instead of a H-bridge is the possibility of motor braking. This is provided by a 1Ω resistor which is switched across the motor when both relays are in the un­energised condition. This means that the motor stops abruptly when power is removed. If the door encounters an obstruction when it is closing, it will stop and then go back up. This is to prevent injury to people (you or your loved ones) or to your motor car. To achieve this, the motor current is monitored with a 0.1Ω resistor and the resulting voltage is fed to the non-inverting input (pin 3) of op amp IC4 where it is compared with a preset voltage from trimpot VR1 at the inverting input (pin 2). By the way, IC4 is connected to operate as a comparator. If the voltage across the sensing resistor exceeds that set by VR1, the output of IC4 will go high. This high signal is fed to IC3a, a 3-input OR gate and it “sets” flipflop IC1b so that its Q output goes high and Q-bar goes low. This turns off Q1 and turns on Q2, reversing the direction of the motor. Because the door operates quite slowly and then reverses if it encounters an obstruction there is little chance of injury to persons or damage to car bonnets etc. It goes without saying that the bottom of the door should be fitted with a rubber weather strip. In practice, trimpot VR1 is set so that the door closes normally but when it is restrained by slowing it with your hand, the motor reverses. On the other hand, if the door encounters an obstruction or jams when it is rising or if the current limit circuit fails to work (perish the thought), the resulting high current through the motor will blow the 10A fuse. Power for the whole circuit comes from a 12V car or sealed lead acid (SLA) battery which will need to be able to deliver around 5-6A each time the door is operated. At other times the current is very low, at just a few milliamps. The battery should be kept on Parts List - Electrical Main PC board 1 PC board, code 05104981, 112 x 76mm 2 DPDT or DPST relays, DSE P-8012 or equivalent 1 plastic case, 183 x 115 x 64mm, DSE H-2882 or equivalent 1 clear 12V reversing lamp with housing 1 3AG in-line fuse 1 10A 3AG fuse 1 8-way insulated terminal block 2 M3 16mm roundhead screws 10 M3 6mm countersunk screws 2 M3 nuts 2 M3 spring washers 5 M3 10mm tapped spacers 15 PC stakes 1 10kΩ PC-mount preset potentiometer (VR1) Semiconductors 1 4027 dual flipflop (IC1) 1 4081 quad 2-input AND gate (IC2) 1 4075 triple 3-input OR gate (IC3) 1 CA3130E or CA3160E operational amplifier (IC4) 1 4060 14-stage divider and oscillator (IC5) 2 BC548 NPN transistors (Q1,Q2) 1 BUK456/A/B/H Mosfet (Q3) 5 1N914 diodes (D1-D5) 3 1N4004 diodes (D6-D8) Capacitors 1 470µF 25VW PC electrolytic 1 100µF 16VW PC electrolytic permanent trickle charge, at around 50-100 mil­liamps. This current can be supplied by a 12V DC 300mA or 500mA plugpack. These typically deliver about 14-15V at no load and so could be connected permanently across the battery with no limiting resistor. If the battery voltage tends to rise above 14V under this permanent trickle charge, you will need to connect a limiting resistor in series with the battery. This may need to be found by trial and error and will probably require a 1W resistor with a value in the range from 22-47Ω. Electronics construction We mounted both the receiver and 1 47µF 16VW PC electrolytic 7 0.1µF MKT polyester 1 .01µF MKT polyester 1 .001µF MKT polyester 1 470pF MKT polyester Resistors (0.25W, 1%) 1 10MΩ 6 10kΩ 4 1MΩ 1 6.8kΩ 1 270kΩ 1 1Ω 2W or 5W 1 150kΩ 1 0.1Ω 2W 1 100kΩ Receiver PC board 1 2-channel keyring transmitter (Oatley Electronics) 1 UHF receiver module (Oatley Electronics) 1 PC board, code 05104982, 65 x 41mm 1 A5885M decoder (IC1) (Oatley Electronics) 1 BC548 NPN transistor (Q1) 1 78L05 voltage regulator (REG1) 4 1N914 silicon diodes 1 100µF 16VW PC electrolytic capacitor 2 0.1µF monolithic ceramic capacitors 1 100kΩ resistor 3 10kΩ resistors 1 18-pin IC socket 3 PC stakes Miscellaneous Solder, 24G tinned copper wire, hookup wire, heavy and light duty figure-8 flex. motor electronics PC boards in a plastic utility case measuring 183 x 115 x 64mm. This has the courtesy lamp mounted on its lid and an 8-way strip of insulated terminal block mounted at one end to terminate the various wires from the battery, limit switches, motor and LOCAL switch (S3). Both PC boards are quite straightforward to assemble. Fig.3 shows the component layout for the receiver board while Fig.4 shows the motor electronics PC board. Begin by checking both PC boards for shorted or open cir­cuit tracks. You can check the boards against the artworks of Figs.5 & 6. Make any repairs before starting assembly. This done, insert and solder the resistors and April 1998  39 Fig.5: the full-size artworks for the receiver PC board (above) and the motor control board (right). connections. Using a 12V car battery or a DC power supply set to 12V, apply power to the main board. The +12V goes to a PC pin adjacent to the two relays while the 0V goes to the GND pin adjacent to Mosfet Q3. Momentarily bridge the LOCAL PC pins with a piece of wire and relay RLY2 (UP) should energise with an audible click. Bridge them again and the relay should release. Bridging a third time should energise RLY1 (DOWN). Now bridge the limit switch PC pins and the relay should release. If you wish to test the timer operation, connect the lamp between the PC pins marked LIGHT+ and LIGHT-. Each time the LOCAL pins are bridged, the globe should light for about five minutes. This close-up view shows the receiver PC board with the pre-built UHF receiver module. It is connected to the controller board using just three links. diodes on the receiver board (Fig.3). Next do the IC socket, capacitors, regulator and transistor. Lastly, fit and solder the PC pins and the UHF receiver module. This has five pins which solder into the PC board. Plug in the IC, checking that pin 1 faces the regulator. Also check the polarity of the electrolytic capacitor. The same sequence of component assembly applies to the larger PC board, only this time fit the 16 links before starting on the resistors. Use IC 40  Silicon Chip sockets if you wish, but if you solder the ICs in place, double-check that pin 1 is correctly orientated on each one. Also double-check the polarity of the electrolytic capacitors. The last item to be fitted is the 1Ω 2W or 5W resistor on the copper side of the PC board. This is the resistor which provides motor braking when the power is removed. Testing The initial tests can be done without the motor or any other external Remote operation & encoding Turn the power supply off and solder wires between the three PC pins on the controller PC board and the corresponding pins on the receiver PC board. Reapply the power, press either button on the keyring transmitter and you should hear a relay energise. A second press should release it. Both the UHF transmitter and UHF receiver boards are sup­ p lied unencoded. This allows simple initial testing but once everything is working, both boards should be programmed with the same code. Pins 1-8 and 10 and 11 on the encoder and decoder ICs are used for this. Both PC Inside the control box are the two PC boards. The two relays provide the motor switching, while the lamp on the control box lid provides illumination in the garage after you have turned your car’s headlights off. boards have a track either side of pins 1-8 and each pin can be left floating, connected to the positive supply or connected to ground. Pins 10 and 11 will need jumpers to a supply if you use them. The most important step is to make sure that the corre­sponding pin on both the Transmitter and Receiver IC are connect­ed to a similar potential. For your own security you must not leave them un-encoded. If you do leave them unencoded, anybody with a similar unencoded transmitter would be able to operate your garage door and thereby gain entry to your home. Final assembly You will need to drill the lid of the plastic case to suit the lamp and two insulated wires 300mm long will need to be run to the PC stakes for the light. Having these leads long allows you to finish the wiring without the lid getting in the way. Each PC board was mounted on 10mm threaded pillars. This was mainly to provide clearance for the 1Ω braking resistor on the back of the control board. All the external connections from the PC board were run to an 8-way strip of insulated terminal block at one end of the case. With the plastic case mounted on the wall near the motor and battery, the terminal block is at the top end of the case. We used heavy duty figure-8 flex for the battery and motor connections and a lighter flex for the limit switch and remote connections. A small hole was drilled in the bottom end of the case to let the UHF antenna dangle through. Next month we will provide all the details of the motor/chain drive system, including drawings and photos. With the information provided, you will be able to build your own garage door opener. There is also the possibility of adapting the drive system to raise and lower canvas awnings or to SC drive sliding doors or gates. A standard 2-button keyring transmitter provides full remote control of the garage door opener. It’s great in wet and windy weather and in fine weather too. April 1998  41