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Remote controlled gates for your home Don’t you just love the idea of remotecontrolled gates? There is your stately mansion, secure behind heavy wrought iron gates. You roll up in your Lexus ES400 and the gates slowly swing open as if by magic. As you pass through, the gates swing shut again and you are secure inside your domain. By PHUNG MAI Well, OK you might not have a stately mansion nor a Lexus ES400 for that matter but the idea of remote controlled gates is still pretty attractive, isn’t it? Even if you just have ordinary gates, someone, probably you, has to open and close them each time you pass through. That’s not too pleasant on a cold, wet winter’s night. Now 66  Silicon Chip you can add remote control. Just think of the extra prestige automatic gates will add to your home. It’s quite common for people to have automatic garage doors but you can go one better with automatic gates. Of course, anyone can have automatic gates fitted to their home but surprise, surprise, they cost big dol- lars. The system presented here can be obtained at a fraction of the cost and you will end up with the added satisfaction of building it yourself. Mechanical concept The basic mechanical parts required to motorise your gates are a pair of 12V DC wiper motors from a car and a pair of scis­sor jacks, again from cars. You can pick these up very cheaply from car wreckers. You can buy them more cheaply at trash and treasure sales because these people think they’re selling junk! But you know better. The wiper motors and scissor jacks for the gates shown in the accompanying photos cost just $12.00. Cheap, huh? Fig.1 shows the concept. The wiper motor is attached to the moving gate while one section of the scissor jack is attached to the gate post. The wiper Fig.1: this diagram shows the general concept for the motorised gates. The wiper motor is attached to the moving gate while one section of the scissor jack is attached to the gate post. The wiper motor drives the threaded shaft of the jack to pull the gate open or shut. You need one wiper motor and one scissor jack mechanism for each gate. motor drives the threaded shaft of the jack to pull the gate open or shut. You need one wiper motor and one scissor jack mechanism for each gate. The photos illustrate the concept. The prototype gates are in front of a carport but the idea can be used anywhere, in inner-Sydney Paddington or on a country property out the back of Bourke. Since DC motors are used to motorise the gates, it is a simple matter to open or close them by changing the current direction through the motors. Beside the scissor jacks and automotive wiper motors alrea­ dy mentioned, you will need a couple of universal joints as found in standard 1/2-inch drive socket spanner sets and a few pieces of steel and bolts to clamp the jack sections to the gate posts. The scissor jacks should ideally have a 1/ -inch shank to match the universal 2 joint – it will make your job a little easier later. Making the drive system OK; you’ve got the wiper motors, universal joints, jacks and some steel. Despite the fact that the job is involved with metals, it is not a massive task. You will be impressed when you see your little toy pushing and pulling the gates. Fig.2 shows the drive system in cross-section. The steps you must follow are: (1) Disassemble the universal joint. (2) Centre punch into the universal joint at the male end. (3) Drill and tap the square shank of the universal to fit the threaded section of the motor shaft. These steps will align the motor shaft to the universal joint before they are welded togeth­er. (4) Disassemble the scissor jacks to obtain the wanted parts. Use a hacksaw or an angle grinder to cut away the unwanted sections. (5) After you have removed the threaded shafts from the jacks, you need to make one end of the shaft square to fit to the female end of the universal joints. As noted above, some jacks come with a square drive so they are the type to go for. Also make sure that the screwed shaft has good “square section” threads. Some jacks are very flimsy and have a very shallow thread­ ed portion; they should be avoided. (6) Measure the depth of the female end. Mark one side of the universal joint at about half of the depth. Drill at the marked point into the female end through the shaft to fit a suitable split pin. (7) Reassemble the universal joint. Drive system assembly The next task is to assemble the various parts to make a workable drive. One section of the jack is used to hold the threaded bearing for the shaft to wind through. This section is welded August 1997  67 MOTOR SHAFT AND UNIVERSAL JOINT MALE SIDE ARE WELDED TOGETHER AT DRILLED HOLE SUPPORTER MANUAL OVERRIDE THROUGH FEMALE SIDE WIPER MOTOR MOTOR SHAFT, THREADED SECTION SQUARE END THREADED SHAFT THREADED BEARING Fig.2: the drive system depends on universal joint to couple the wiper motor to the threaded drive shaft. to a clamp attached to the gate post. The method of at­tachment is up to you. You can either weld or drill holes and fit bolts, depending on whether you have wooden or metal gates. The distance between the pole to the threaded bearing is approximately two-thirds the length of the threaded shaft. You will have to allow for movement of the threaded bearing in the supporter slot, to allow for the change in the angle of the threaded shaft. The steps are as follows: (1) Thread the shaft into the tapped hole in the universal drive shank and then weld them together. (2) Bolt the base of the motor to the gate, as shown in the photos. The distance between the position of the motor on the gate to the hitch should be approximately half the threaded shaft length. (3) Wind the shaft through the threaded bearing about half of the length, then open the gate toward the shaft, place the shaft into the female end of the universal joint and then fit the split pin to connect them together. PARTS LIST 1 single channel UHF transmitter kit; available from Oatley Electronics. 1 single channel UHF receiver module (Oatley Electronics) 1 PC board, code 15108971, 122 x 99mm 4 SPDT 12V PC-mount relays 2 12V DC wiper motors 2 10A fuses 2 scissor jacks 1 universal joint and split pin (see text) Semiconductors 1 AX5328 decoder (IC5) (Oatley Electronics) 2 74HC00 quad 2-input NAND gates (IC1,IC2) 1 74HC20 dual 4-input NAND gate (IC3) 1 74HC107 dual JK flipflop (IC4) 68  Silicon Chip 1 7805 5V regulator (IC6) 4 BC337 NPN transistors (Q1,Q2,Q3,Q4) 5 1N4004 diodes (D1,D2,D3,D4,D5) 1 1N914, 1N4148 small signal diode (D6) Capacitors 1 1000µF 16VW electrolytic 4 2.2µF 25VW electrolytic 1 1µF 25VW electrolytic 1 0.47µF metallised polyester (greencap) 5 0.1µF monolithic Resistors (0.25W, 5%) 4 2.2kΩ 2 1kΩ 5-pin resistor arrays (RN1, RN2) 1 1kΩ 1 100Ω Besides making the connection, the split pin is a vital feature of the system. If it ever jams or fails due to loss of power or other cause, you will always be able to open the gates by removing the split pins. (4) To test the gate, connect the motor to a 12V car battery. Make the motor run forward and reverse a few times by changing the polarity, making sure that it is not jammed. Normally a wiper motor requires about 5A or so and you will have two motors drawing this current. To power them, you will need a 12V car battery on permanent trickle charge, say at around 100mA or so. By using a car battery you will not be shut out of your home if there is a blackout and there is little chance of the circuit ever locking up in the case of voltage spikes on the mains supply. Note that most wiper motors these days have two-speed operation. Choose the speed to give the smoothest operation of your gates. Circuit details The circuitry to control your gates is built around the single channel UHF remote control featured in the February 1996 issue of SILICON CHIP. This used an AX5326 encoder chip in a keyring transmitter and an AX5328 decoder on a small PC board populated with surface mount components. Both these items can be obtained from Oatley Electronics – phone (02) 9584 3563 or fax (02) 9584 3561. The AX5328 receiver board is mounted on a large PC board with a few logic chips and four relays to control the two wiper motors. The circuit of this board is shown in Fig.3. While we show the circuit powered from a transformer with two windings, the whole circuit can be powered from a 12V car battery, as noted above. To do this, delete the transformer and the bridge rectifiers and connect the battery to the points marked +12V and VM+. Note that the whole circuit could also be operated without the UHF remote control by pushbutton SW3. You will need to refer to the February 1996 article for the details of the UHF transmitter and receiver circuits. When the transmitter button is press­ ed, the output of IC5, the AX5328, will go high. In essence, the circuit consists of two JK flipflops in IC4 and four RS Fig.3: the circuit depends on a UHF receiver and decoder which drive several RS flipflops based on IC1 and IC2. These in turn control four relays which switch power to the motors to operate them in either one direction or the other. flipflops based on NAND gate packages IC1 & IC2. All these flipflops are reset when power is first applied. IC4b is used to debounce push­ button switch SW3. Assuming the cir­ cuit has been power reset, all flipflops will be cleared (ie, all Q outputs low) with SW1 and SW2 opened (gates closed). If a valid signal is detected by decoder IC5, pin 17 will go high and this is inverted by IC3a to trigger flipflop IC4b. This makes flipflop IC4a toggle; August 1997  69 from high to low and the RS flipflops based on IC1c/1d and IC2b/2c will be toggled via C11. Relays RLY2 and RLY4 will operate and the gate motors will be driven in the opposite direction until the flipflops are again reset by the limit switches SW1 & SW2. PC board assembly Fig.4: the parts layout for the PC board. Take care to ensure all polarised parts are installed correctly. ie, its outputs change state, with Q (pin 3) going high and pin 2 going low. This causes the two RS flipflops based on IC1a/1b & IC2a/2d to change state after being toggled by IC4a’s Q-bar signal via capacitor C12. As a result relays RLY1 and RLY3 will operate. Both motors now run until the above RS flipflops are reset by the limit switches SW1 and SW2. These switches are installed on the gates so they can reset the flipflops when the gates are com­pletely opened (or closed). With the flipflops reset, relays RLY1 and RLY3 are opened to stop the motors. The output of 4-input NAND IC3b gate also resets flipflop IC4b so that it can accept another input signal for closing the gates. When the transmit button is pressed again, pin 3 of IC4a will change state You will need a wiper motor, a universal joint and a threaded shaft from a scissor jack to make each drive system. 70  Silicon Chip In describing this project, we will assume that you have the February 1996 issue and therefore will have the construction information for the UHF transmitter and receiver module. The motor control part of the circuit, as shown on Fig.3, is accommo­dated on a PC board coded 15108971 and measuring 122 x 99mm. The component layout for the PC board is shown in Fig.4. This has the UHF receiver module mounted at one end and the four relays at the other. Check the board for any open circuit tracks or undrilled holes and fix any defects before inserting components. This done, fit all the wire links and the PC stakes for external connections. Next, fit the resistors, the two resistor arrays and the diodes. The next step is to fit the capacitors, noting that the electrolytics must have the correct polarity. The four transistors, the ICs and the relays can now be installed. Note that the UHF receiver module should be left out until after the PC board has been fully tested. Testing To test the unit, first connect a 20cm test wire to the edge GND pin on the board. This wire will be used to trigger or reset the flipflops being tested. This done, connect 12V DC to the AC input connector, then check to see that +5V is present at pin 14 of IC1, 2, 3 & 4 and pin 18 of IC5. If all is OK so far then try grounding the SW3 pin with the test wire. This simulates a valid input signal being received. Two of the relays should operate. Assuming relays RLY1 and RLY3 did, then reset them by grounding the SW1A and SW2A terminals. This simu­lates the operation of the limit switches. Now ground the SW3 pin again and relays RLY2 and RLY4 should operate. Again, you can reset them by grounding the SW1B and SW2B pins. If the above steps didn’t work, then you have to check the individual flipflops and you can check to see that the The motor attaches to the gate and drives the shaft to pull the gate open or closed. Note the split pin which enables the univer­sal joint to be uncoupled. We suggest that a metal guard be fitted over each drive shaft to prevent the possibility of accidental injury. The wiper motors are weatherproofed by metal boxes which give a tidy presentation (see photo on page 66). The drive shafts will need to be kept well greased. A sliding rubber boot inside a metal guard would provide good protection for the shafts. flipflop outputs are high or low with your multimeter. If the flipflops are all working correctly, you may have to check that the transistors are all switching on when they should and finally, that there are no open circuits in the relay connec­tions. Assuming that all checks are OK, you can now install the UHF receiver module on the PC board. Finally, test the whole circuit once again with your remote control. Electrical installation The control box should be located near the battery and indoors or under cover, to keep it out of the weather. It is suggested that all cables be run through plastic conduits and fuses must be included, as shown on the circuit. You will need flexible conduit at the gates themselves. The cables should be 4mm auto wire or thicker, to avoid unwanted voltage drops when the motors are running. You have a number of choices when it comes installing the limit switches SW1 and SW2. Perhaps the easiest is to use a pair of microswitches each for SW1 and SW2 and have them operated by the gates when they are fully opened and fully closed. When the whole circuit is wired up, check the gate opera­tion carefully using the manual switch SW3 and then the UHF remote control. Finally, fit metal guards over each drive shaft SC to prevent accidental injury. Fig.5: this is the full size etching pattern for the PC board. PLEASE NOTE: although we have produced a PC board pattern for this contributed design, the circuit has not actually been built or tested by Silicon Chip Publications. August 1997  71