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A Remote Telltale for Garage Doors If you have a perfect memory you won’t need this. But the rest of us could find it very handy! It lets you know if you’ve left the garage door open without stumbling out in the dark or the pouring rain . . . By JIM ROWE 58  Silicon Chip siliconchip.com.au siliconchip.com.au D ID YOU REMEMBER to shut the garage door when you got home? If you’re not sure, you might well go out in the morning to discover that your car, portable barbeque and mower have all been nicked. Perhaps you’d better go out and check now, just to make sure... What’s that – you don’t have to worry, because you have an electrically operated door? Fair enough, but you still have to press the remote or inside-the-house button to actually shut the door. Or maybe you did close it earlier and now you’ve just pressed the remote button to close it . . . and opened it? I won’t flog this any more, because I’m sure you get the idea. If you cannot see the garage door, it’s all too easy to either forget to close the door, or forget whether you did or not. That’s why we’ve come up with this project: a low-cost and easy-to-build remote sensing system. Based on of a pair of compact UHF transmitter and receiver units, the transmitter continuously monitors the status of your garage door via a pair of microswitches. Whenever that status changes (because you open or shut the door), it sends a short data signal back to the receiver unit, which uses these signals to update its LED door status indicators. This can be placed in any convenient position – where you can view it and see at a glance whether the garage door is fully open, fully shut or somewhere in between. Nifty, eh? Both units fit inside standard lowcost UB3 jiffy boxes and make use of very low-cost UHF data transmitter and receiver modules. You can build the complete ‘telltale’ system very easily and at low cost. By the way, the system would also be suitable for remote monitoring of other things beside garage doors. You could use it for monitoring security gates and doors, fire shutters and doors and so on – anything with an “open” and “shut” state. How it works To save you the near-impossible job of building and aligning transmitters and receivers (at least, not without some pretty specialised test gear and knowledge), we’ve based the system on a pair of UHF (433MHz) data transmitter and receiver modules which are sold by Oatley Electronics in kit form, with the catalog number K190. The four-channel modules include security encoding and decoding and the transmit and receive subcircuits are preset to frequency, so there’s no need for setup or alignment. The transmitter module uses an SM5162 security encoder chip, configured to provide four data inputs and eight Tri-state encoding inputs – so it can be set to any of 6561 different security codes. The receiver module uses a matching SM5172 decoder chip, again configured for four data outputs and eight Tri-state encoding inputs, so it can be set up to respond only to signals with whatever security code you have set on the transmitter. As a result the two modules provide a high degree of security and protection against false indications due to interference from other 433MHz signals. Another nice feature of the K190 transmitter module is the fact that it includes a simple circuit which only activates its transmitter circuitry when one of its data input lines is pulled ‘high’. We make good use of this feature. The circuit of the complete transmitter unit is shown in Fig.1, where the transmitter module is shown at centre right. The module’s power supply input +V is connected directly to the +9V line from the battery, so like the rest of the circuit it’s in ‘standby’ mode The inset shows one microswitch, mounted at the garage door “open” position. We had a fortunate bracket on the door on which to screw our microswitch actuating lever – a small piece of blank PC board. This has a little bit of spring and give to ensure that it makes good contact with the microswitch button. siliconchip.com.au January 2007  59 100k CON1 100nF 22k 100nF 13 NC 14 IC1d 100nF 9V BATTERY 470 µF 16V 11 12 K NO S1 9 100k UPPER LIMIT MICROSWITCH 22k 1M IC1c 8 14 3 IC3a IC1: 4011B 100nF 1 D1 10 A 1 2 470nF IC3: 4093B 3 IC1a +V D 2 K 5 D1–D4: 1N4148 K 6 A 1M 4 IC1b IC3d 7 11 7 LOWER LIMIT MICROSWITCH CON2 NC 100k 100nF A 13 13 B A 12 100nF 22k C D2 OATLEY K190 ANT UHF TX MODULE GND 470nF 10 µF 14 IC2d 11 12 S2 K 9 NO 100k 22k 1M IC2c 10 IC3b 8 4 A 5 6 IC2: 4011B 100nF 6 IC2b D3 470nF 4 5 SC  2007 GARAGE DOOR TELLTALE TRANSMITTER all the time. The total current drain is only about 100mA in this mode, so the battery should last for its full normal ‘shelf life’. Each of the transmitter module’s A-D data inputs is connected to the output of one of four identical pulseforming one-shot circuits. Each one-shot consists of a pair of cross-connected 4011B CMOS NAND gates forming a simple set/reset flipflop, set whenever a negative-going pulse is applied to its input via the 100nF capacitor. About 600ms after being set in this way, it is reset again 60  Silicon Chip K 2 1 1M IC2a 7 3 IC3c 10 D4 A 8 9 470nF automatically by means of an RC timing circuit coupled to a 4093B gate configured as a Schmitt inverter. The input of each one-shot is connected via a 100nF capacitor to a fixed contact of one of the two door-sensing microswitches, S1 and S2. The input of the ‘D’ one-shot is connected to the normally closed (NC) contact of microswitch S1, while the input of the ‘C’ one-shot is connected to the normally open (NO) contact of the same switch. The ‘A’ and ‘B’ one-shots are similarly connected to S2. The COM contacts of both S1 and Fig.1: the transmitter monitors the status (open or closed) of two microswitches which are mounted at the top and bottom travel of the garage door. The transmitter is based on a prebuilt module. S2 are connected to circuit ground, so that either the NC or the NO contacts are grounded depending on whether the switch is operated or not. The idea of these four one-shot circuits is that whenever either switch S1 or S2 is operated, a 600ms long pulse is generated by one of the one-shots A, B, C or D. This is fed to the transmitter module, so that it springs to life and sends the corresponding coded signal. Thinking about it another way, a different code pulse is transmitted whenever the garage door moves into or out of the fully shut position, or siliconchip.com.au REG1 7809 +9V OUT IN GND 10 µF Vdd A OATLEY B ANT K190 UHF RX C MODULE 5 6 D RXD 8 GND 4 IC1b IC1c 1 100k 13 B 100nF C 12 Q1 PN100 E 6 12V DC – IN 7 4 10k B DOOR OPEN λ LED1 λ C Q3 PN100 680Ω A POWER K K λ LED3 1N4004 K E A LEDS 3 11 IC2c 10 K 8 1 IC1d IC2b K 680Ω A 10 9 IC1a 14 5 2 10k DOOR A SHUT LED2 IC1: 4001B IC2: 4011B 14 9 TP1 + A 100nF 680Ω +V K 470 µF 16V +5V 100nF D1 1N4004 IC2a 10k 3 2 B C A Q2 PN100 E PN100 C B E 12 13 IC2d 11 7 SC  2007 GARAGE DOOR TELLTALE RECEIVER 7809 IN OUT GND Fig.2: the receiver consists of a pre-built UHF receiver mounted on an Oatley module with some logic gates and flipflops to control the status LEDs. into or out of the fully open position. For example, when the door reaches the fully shut position, the NO contact of S2 is grounded and the ‘A’ one-shot is triggered, sending a 600ms pulse to the A input, telling it to transmit the ‘door shut’ code. But as soon as the door begins to open again, the NC contact of S2 now becomes grounded. This triggers the ‘B’ one-shot, sending a 600ms pulse to the B input and causing a ‘door opening’ code to be transmitted. Then when the door reaches the fully open position, the NO contact of S1 becomes grounded and this triggers one-shot ‘C’, causing a ‘door open’ code to be transmitted. And finally, when the door begins to leave the fully open position to close again, the NC contact of S1 is grounded, triggering one-shot ‘D’ and the transmission of a ‘door closing’ code. By the way, the transmitter current drain rises to about 10mA only when a code pulse is being transmitted. So the battery only needs to supply this current for about 600ms, when the garage door’s status changes. Most of the time the transmitter will be in ‘standby’ mode, drawing only 100mA. So that’s how the Telltale’s transsiliconchip.com.au mitter unit operates. Now let us look at the circuit of the receiver unit (Fig.2), to see how it responds to these four possible codes from the transmitter unit. Receiver operation The four outputs from the UHF receiver module are each fed through one gate of a 4001B quad NOR gate, IC1. The inverted pulses from these gates are then used to trigger a pair of set/reset flipflops, each formed by a pair of cross-connected gates of IC2, a 4011B quad NAND gate. As a result, when a ‘door shut’ code is received and a pulse appears at output A of the receiver module, this produces a negative-going pulse at pin 4 of IC1b, and the upper IC2b/IC2c flipflop is triggered into its set state. Pin 4 of IC2b switches high, which turns on transistor Q3. This allows current to flow through LED2 – the ‘door shut’ indicator. Now if the door starts to open and a ‘door opening’ code is received, a pulse appears at the B output of the receiver module. This is inverted by IC1c, applying a negative-going pulse to pin 8 of IC2c and triggering the IC2b/IC2c flipflop into its reset state. Pin 4 of IC2b switches low, turning off Q3 and also LED2. Nothing then happens until the door reaches the fully open position, and a ‘door open’ code is transmitted. This causes a pulse to appear at the C output of the receiver module. Gate IC1a inverts this pulse and uses it to trigger the IC2a/IC2d flipflop into its set state. So this time pin 3 of IC2a switches high, turning on transistor Q2 and LED1 – the ‘door open’ indicator. Then when the door starts to close again and a ‘door closing’ code is received, a pulse appears at the D output of the receiver. This is inverted by IC1d and applied to pin 13 of IC2d, the reset input of the lower flipflop. So this flipflop resets again, turning off Q2 and LED1. Summarising, the receiver unit responds to the codes sent by the transmitter by turning on LED2 only when the garage door reaches the fully shut position, and turns it off again as soon as the door begins to open. Similarly it turns on LED1 only when the door reaches the fully open position, turning it off again as soon as the door begins to shut. So LED2 glowing indicates that the door is shut, while LED1 glowing indicates that the door January 2007  61 ANTENNA ANTENNA D C B OATLEY K190 UHF TX MODULE +V GND V+ OATLEY K190 UHF RX MODULE A 470 µF +V – D2 + 4148 4148 1M 1M D4 GND RXD VDD TP1 470nF 470nF + 9V BAT 100nF 4148 1M D3 10k 4148 100k D1 470nF IC3 4093B 470nF 26011130 6002 © GND GND B A GND D C ANT 100nF IC1 4001B 1M 100nF 100nF 680Ω IC2 4011B IC1 4011B Q1 PN100 100nF 100nF IC2 4011B 680Ω 680Ω CN 100k CON2 MO C CN ON 100k 100k CON1 MO C 100nF 100nF 100nF 100k ON 10 µF 100nF 22k + NC COM NO NC COM NO FROM S1 FROM S2 POWER 10 µF + DOOR FULLY PN100 OPEN Q3 10k 10k Q2 22k 22k 16011130 6002 © 22k LED2 LED1 LED3 DOOR FULLY PN100 SHUT D1 1N4004 REG1 470 µF 7809 12V DC IN Fig.3: the transmitter PC board component overlay and matching photo alongside. Top of page is a side-on, close-up view of the transmitter module mounted on the PC board. is open. When neither LED is glowing, this indicates that the door must be somewhere in between the two extremes – neither fully open nor fully shut. We make sure that neither LED1 nor LED2 lights when power is first applied to the receiver unit by applying a ‘power on reset’ pulse to both flipflops. This pulse is generated by transistor Q1, the collector of which goes positive for a short time after power is applied (until its 100nF base capacitor charges via the 100kW resistor). The positive pulse at Q1’s collector is fed to the second input of IC1c and IC1d, causing a brief negative-going pulse to be applied to the reset input of the flipflops. There is a third LED in the receiver unit (LED3), which simply indicates that power is applied. So when only LED3 is glowing, you can be reassured that this is because the door is neither fully open nor fully shut. The status LEDs in the receiver 62  Silicon Chip operate from 9V DC, derived from an external 12V DC supply using REG1. The rest (Including the receiver module) runs from 5V DC, derived from the +9V line via an L4949 LDO (low drop out) regulator IC on the receiver module. This arrangement allows the receiver to be operated from either a 12V battery or almost any plugpack supply delivering between 11.5V and 15V DC. The total current drain is quite low – about 25mA when only LED3 is glowing, rising to 35mA when either LED2 or LED1 is glowing as well. Construction Both the transmitter and receiver are built onto 57 x 122mm PC boards and housed in standard UB3 utility boxes. The transmitter board is coded 03101071, while the receiver board is coded 03101072. All of the transmitter components, apart from the door sensing microswitches, either mount on the board or fit into the box with it, while all of the receiver components mount on that board. The only items to emerge from the transmitter unit box are an antenna wire at the top and the leads to the microswitches at the bottom. Similarly, the receiver unit has its antenna emerging from the top and the power supply lead from the bottom. The location and orientation of all components on both boards are shown in the overlay diagrams of Figs.3 & 4. The wiring of each is quite straightforward, so if you follow these diagrams carefully you shouldn’t strike any problems. We suggest that you assemble both of the Oatley K190 modules first, before fitting either of them to their Telltale boards. But before you even start assembling the K190 transmitter module, its board needs to be shortened by cutting off the end strip where indicated by a dashed line on the overlay. This removes an optional part of the board which is only needed when the module is fitted with its own four input pushbuttons. After cutting this part off, use a small file to smooth off any burrs. One of the ‘components’ to be fitted to the K190 transmitter module board is another even smaller board, about 15mm square, already wired with the SMD components used in the UHF transmitter circuitry. This smaller board mounts on the top of the transmitter module board, with its three connection leads going down through holes and soldered to pads on the underside. The antenna and ground leads, at the righthand end of the SMD board, are NOT cut off short after soldering but are left intact so they can be connected directly to the main Telltale transmitter board later on. The only lead which is cut short after soldering to the transmitter module board is the siliconchip.com.au ANTENNA B A GND D C GND V+ 26011130 6002 © OATLEY K190 UHF RX MODULE GND RXD VDD 10k 100k TP1 100nF IC1 4001B 100nF Q1 PN100 100nF 680Ω IC2 4011B 680Ω 680Ω 10k Q2 POWER 10 µF + DOOR FULLY PN100 OPEN Q3 10k LED2 LED1 LED3 DOOR FULLY PN100 SHUT D1 1N4004 REG1 470 µF 7809 12V DC IN Fig.4: here’s the receiver PC board overlay and photo, again with the kit receiver module shown in situ top right. supply/control lead, which is at the lefthand side. After the SMD board has been fitted, solder in the 18-pin DIL socket for the SM5162 encoder chip and also the other components: six resistors (mounted vertically on-end), a 22nF capacitor and a C8050 transistor. Then solder seven short (~10mm+) lengths of tinned copper wire (eg, resistor lead offcuts) to the pads provided at each end for off-board connections. There are five of these pads at one end for the transmit inputs A-D and a V+ connection and two pads at the other end for a ground and +9V connection. Each of these wires needs to be perpendicular to the module board surface. Next, pass a 10mm M3 machine screw down through each of the module’s four mounting holes (from the top) and then fit an M3 nut on each screw. Tighten these nuts securely, because they are used as spacers. Once they are tightened the transmitter module assembly can be mounted siliconchip.com.au on the Telltale transmitter unit board, by passing each of the module’s connection wires through its matching hole in the main board, with the four mounting screws through their larger holes. Once the module is sitting above the main board on its M3 nut spacers, turn the whole assembly over and fit another M3 nut on each screw to hold it firmly in place. Then you can solder all of the module’s connection wires to their pads on the main board and cut off the excess. With the transmitter module in place, the remaining components can be fitted quite easily. Fit the four wire links first, then the two PC board terminal pins for the battery snap leads and the two 3-way terminal blocks for the microswitch lead connections. These are followed by the resistors, the MKT and multilayer monolithic capacitors, the polarised electrolytic capacitors and the diodes. After this you can fit the three ICs, or their sockets if you’re using them. Then, cut a 173mm length of singlecore hookup wire for the antenna and solder one end of it to the rectangular pad near the top centre of the board. Your Telltale’s transmitter board should be complete and ready to fit into its box, once the box is drilled to accept it. Drilling details for both the transmitter and receiver boxes are shown in Fig.6. The board mounts inside the rear of the box via four 15mm M3 tapped spacers, using four 6mm countersunkhead screws to attach the spacers to the box rear and four round-head 6mm screws to attach the board to the spacers. Just make sure that you pass the antenna wire out through its hole in the top end of the box, before you lower the board assembly into place and fit the fastening screws. Once the board assembly is mounted inside the box, you can solder the ends of the battery snap leads to the terminal pins at upper left on the main board (the pins marked ‘9V BAT’). Make sure that you solder the black wire to the outermost (minus) pin and the red wire to the inner (plus) pin (the one nearer the 470nF capacitor). Then you can connect the ends of the 2-core shielded leads you’ll be using to connect microswitches S1 and S2 to their terminal blocks at the bottom of the transmitter board. The inner wires of each lead are connected to the end terminals on each block (NO and NC), while the shield braids connect to the centre (COM) terminals. The transmitter unit can now be completed by attaching the 9V battery to the snap connector. You’ll find that the battery fits inside the box sideways above IC1 and IC2, with the snap lead wires coiled up above IC3. We placed the battery in a very small plastic bag to preclude the possibility of shorts. The box lid can now be fitted with January 2007  63 Parts List – Garage Door Telltale Transmitter Unit 1 ABS Jiffy box, UB3 size (130 x 68 x 44mm) 1 PC board, 57 x 122mm, code 03101071 1 Oatley Electronics K190 UHF transmitter module kit 2 3-way terminal blocks, PC mounting (CON1, CON2) 2 PC pins, 1mm diameter 4 15mm M3 tapped spacers 4 6mm M3 coutersunk-head machine screws 4 6mm M3 round-head machine screws 4 10mm M3 round-head machine screws 8 M3 nuts 1 9V alkaline battery with snap lead 2 SPDT microswitches 2 lengths of shielded cable for microswitch leads, two conductors plus shield Semiconductors 2 4011B quad CMOS NAND gate (IC1,IC2) 1 4093B quad Schmitt NAND gate (IC3) 4 1N4148 diodes (D1,D2,D3,D4) Capacitors 1 470mF 16V PC electrolytic 1 10mF 16V PC electrolytic 4 470nF MKT metallised polyester 4 100nF MKT metallised polyester 3 100nF multilayer monolithic ceramic Resistors (0.25W 1%) 4 1MW 4 100kW 4 22kW its label, which can be photocopied from Fig.5 (or downloaded and printed out from www.siliconchip. com.au). You’ll need to cut four holes for the lid mounting screws. The final step is to fit the small plastic sealing bungs above each screw head (these also hide any oopses in cutting the label!). Receiver assembly The Telltale receiver is assembled in much the same way as the transmitter. As before, we suggest that you assemble the K190 receiver module first. This module again has a small pre64  Silicon Chip Receiver Unit 1 ABS Jiffy box, UB3 size (130 x 68 x 44mm) 1 PC board, 57 x 122mm, code 03101072 1 Oatley Electronics K190 UHF receiver module kit 1 2.5mm DC connector, PC mounting (CON1) 1 PC pin, 1mm diameter 4 25mm M3 tapped spacers 4 6mm M3 countersunk-head machine screws 5 6mm M3 round-head machine screws 4 10mm M3 round-head machine screws 9 M3 nuts Semiconductors 1 4001B quad CMOS NOR gate (IC1) 1 4011B quad CMOS NAND gate (IC2) 1 7809 9V positive regulator (REG1) 3 PN100 NPN transistors (Q1,Q2,Q3) 1 5mm red LED (LED1) 1 5mm orange/yellow LED (LED2) 1 5mm green LED (LED3) 1 1N4004 1A diode (D1) Capacitors 1 470mF 16V PC electrolytic 1 10mF 16V PC electrolytic 1 100nF MKT metallised polyester 2 100nF multilayer monolithic ceramic Resistors (0.25W 1%) 1 100kW 3 10kW 3 680W wired SMD sub-board, which in this case is elongated and mounts ‘on edge’ near the centre of the receiver module board. Its three main connections to the rest of the receiver module are made via the pins of a 3-way 90° SIL connector near one end. The receiver antenna wire does not pass down through the module board, however. You solder it directly to the SMD board’s terminal pad later. The SMD receiver board is mounted on the K190 module board simply by passing its three connection pins down through the matching board holes and then soldering them to the pads underneath. After soldering do not cut off the pins though, because again they will pass down through holes in the main board and be soldered to pads underneath. Of course before this can be done you should fit the rest of the receiver module components. Again, there are only a handful of these: an 18-pin DIL socket for the SM5172 decoder chip, an 8-pin DIL socket for the module’s L4949 voltage regulator, two resistors (which are mounted on end), two small electrolytic capacitors (watch their polarisation), a 22nF polyester capacitor and a LED (provided for ‘valid data received’ indication). Before mounting the completed K190 receiver module onto the Telltale’s receiver board, turn it over and again solder some short lengths of tinned copper wire or resistor lead offcuts to the module’s off-board connection pads. In this case there are five of these at the top of the module board for the A-D outputs and a ground connection, plus two more at the upper left of the module for the +9V supply input and another ground connection. (There are also the three pins from the SMD module, which pass through into the main board as well.) When these off-board wires have all been fitted to the K190 receiver module, it is again fitted with four 10mm-long M3 machine screws, passed through each of the corner mounting holes from the top. Then fit each screw with a single M3 nut as before, to act as the mounting spacers. After tightening the nuts you can then attach the receiver module Resistor Colour Codes o o o o o No. 4 5 4 3 3 Value 1MW 100kW 22kW 10kW 680W 4-Band Code (1%) brown black green brown brown black yellow brown red red orange brown brown black orange brown blue grey brown brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown red red black red brown brown black black red brown blue grey black black brown siliconchip.com.au The receiver (left) mounts on the lid of the receiver box, while the transmitter (below) mounts on pillars inside the box. The transmitter battery is loose inside the box. It is unlikely to short to anything in this area of the box but is placed inside a tiny plastic bag, just in case. to the Telltale’s receiver board, again by passing all of its connection wires and pins down through their matching board holes – and the four mounting screws through their larger holes. Once the module is resting down on the spacer nuts you can then turn the board over and fit the four remaining M3 nuts to fasten it securely, followed by soldering the connection wires and pins to their board pads. With the receiver module fitted, you can fit the rest of the components on the Telltale’s receiver board. This is easiest if you fit them in the following order: first the single PC board terminal pin for TP1, then the single wire link (just below the K190 module), ANTENNA ANTENNA and then the 2.5mm concentric DC power connector at bottom centre. Next fit the seven resistors, the two multilayer monolithic capacitors and the MKT capacitor, the two polarised electrolytic capacitors, the 1N4004 power diode D1, the 7809 regulator REG1 (its tab is attached to the board using a 6mm M3 screw and nut) and the three PN100 transistors (Q1-Q3). Then fit the two ICs or their 14-pin sockets if you’re using them, followed by the three LEDs. All three LEDs are mounted vertically, with their leads soldered to the board pads so that the tops DOOR DOOR of their bodies are about POWER FULLY OPEN FULLY SHUT 30mm above the top of TRANSMITTER the board. RECEIVER To complete the reUPPER LOWER 9 – 12V ceiver board assembly, cut LIMIT LIMIT DC INPUT SWITCH SWITCH another 173mm length of + – NC COM NO NC COM NO solid core hook-up wire for the receiver’s antenna and carefully solder one one end to the antenna Fig.5: suggested front panels for the project. By the way, there is no significance in the fact connection pad on the top that the boxes we used are different colours – you can choose which ones you want! siliconchip.com.au SILICON CHIP SILICON CHIP OOR D GE TE A R GA REMO LE LTA L E T OOR D GE TE A R GA REMO LE LTA L E T January 2007  65 20 A A 18 UPPER END OF BOX UPPER END OF BOX B B BOX MOUNTING HOLE AS REQUIRED B 47 B 47 94 CL CL 18 47 47 18 D D D 19 B B 24.75 B B 24.75 24.75 HOLE SIZES: A: 3mm DIAMETER B: 3mm DIAMETER, COUNTERSUNK C: 8mm DIAMETER D: 5mm DIAMETER OUTER REAR OF BOX 49.5 ALL DIMENSIONS IN MILLIMETRES 24.75 OUTER SURFACE OF LID 49.5 18.5 C 32 5 16 TERMINAL BLOCK ACCESS SLOT LOWER END OF BOX CL TRANSMITTER UNIT 17 LOWER END OF BOX RECEIVER UNIT CL Fig.6: drilling details for both boxes. These are based on a standard UB3 (130 x 68 x 44mm) Zippy box. 66  Silicon Chip siliconchip.com.au 03101072 © 2007 + 03101071 © 2007 NO NC COM NO NC COM end of the SMD receiver sub-board. You’ll find this pad on the top end of the SMD board, down near the top surface of the K190 board. The receiver board fits to the inside lid of its box, attached via four 25mmlong M3 tapped spacers, fastened to the box lid using four 6mm-long countersunk-head M3 screws. The board assembly is then mounted on the spacers using four 6mm long round-head screws, after making sure that the three LEDs pass up through their matching clearance holes. To complete the Telltale receiver, the antenna wire is then passed out through the small hole in the top of the receiver box as the lid and board assembly are lowered into the box. Then the lid is fastened into the box using the four small self-tapping screws provided, and finally the dress bungs pushed in to seal the screw holes. If you wish to use the front panels you will need to cut or drill holes for the four lid screws and bungs in both boxes and also the three LEDs in the receiver box. LED bezels can hide any blemishes around hole edges. Trying it out Now that both the transmitter and receiver units have been completed, you’re almost ready to make sure they’re both working and ‘talking to each other’. Connect the two microswitches (S1 and S2) to the ends of the cables from the transmitter unit. Make sure that the NC terminals on the transmitter board connect through to the NC lugs on the microswitches; the NO and COM terminals likewise. If you followed the wiring instructions earlier, the COM terminals will be connected via the cable shield. Next, connect a 12V battery or some other source of 12V DC to the receiver unit using a suitable power lead terminated in a 2.5mm concentric plug (centre pin positive). The receiver’s power LED3 should light to indicate that the receiver is working but both of the other LEDs should remain off. Now place the transmitter unit a few metres away from the receiver and try pressing the actuator button on microswitch S1, holding it down. You should find that LED1 (the ‘Door Fully Open’ LED) on the receiver should begin glowing, and continue to glow while ever you keep holding the S1 button down. siliconchip.com.au Fig.7: same-size PC board artwork for the transmitter (left) and receiver. When you next let go of the S1 button and allow it to snap out, you should now find that LED1 on the receiver turns off again. Now try pressing in the actuator button on microswitch S2, and again hold it in. This time LED2 (the ‘Door Fully Shut’ LED) on the receiver should light, and stay that way until you release the S2 button again. Only then should it turn off. If your system behaves just as described, everything is working as it should and you’ll be ready for its installation. Installation There is very little involved in installing the Telltale transmitter and receiver. The transmitter unit is simply attached to the inside wall of your garage, near the door to be monitored and fairly high up if possible (for the best UHF transmission range). It’s very small and light in weight, so it can be attached to the wall using a single screw. Once the box is in place, you need to fit the two microswitches to the side frame of the door – so they can be actuated by either the door itself, or a small extension bracket you can screw to the door. S1 needs to be actuated when the door is in its fully open position, while S2 is actuated when it’s fully shut. The cables running from each switch back to the transmitter box will need to be attached to the wall securely so they are protected against accidents. Installing the receiver unit inside your house is even simpler. Here all you need to do is mount the receiver box on the wall in a convenient position, again fairly high up for the most favourable UHF reception. For the most reliable operation, if possible it should be within 10-15 metres of the transmitter unit and the antennas should be aligned in the same plane (eg, both vertical). Then all that’s needed is to provide it with its necessary 12V power, and you’re finished. Your Garage Door Remote Telltale should be fully installed SC and operating. January 2007  67