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Control Multipl Last month, we featured the circuit details of this Smoke Alarm Monitor. It will control up to 10 smoke detectors with the ability to disarm and automatically rearm two detectors so you can cater for childrens’ parties, candlelit dinners and open fires in the winter. This month we give the construction and installation details. Based on cheap and readily avail­ able ionisation smoke detectors, this Smoke Alarm Control Panel solves the problems of maintaining contin­ uous monitoring of up to 10 smoke detectors. Why 10? As outlined in last month’s article, if you have only one or two monitors in the typical Australian home, you are not safe against fire. Fire 56  Silicon Chip could start in a room with a closed door and even if a smoke detector is ultimately triggered it may be too late to save your home or your life. As noted last month, you need a smoke detector for every bedroom which has any electrical equipment plus a detector for every other room with electrical gear, apart from the kitchen and garage. For more informa­ tion along these lines and the circuit description, you will need to refer to last month’s issue. In setting out the construction details, we will first discuss the as­ sembly of the Control Panel and then continue with the modification of standard smoke detectors which are available from any hardware store or supermarket. Finally, we will discuss the installation of a typical home system. Control panel assembly The SILICON CHIP Smoke Alarm Control Panel is housed in a plastic case measuring 180 x 260 x 65mm. This would normally be mounted on a wall and so the top cover of the case becomes the control panel. We fitted PART 2: By JOHN CLARKE l Panel For le Smoke Alarms Left: the finished Smoke Alarm Control Panel has 10 LEDs which cycle through as each smoke detector is polled. The smoke detectors are modified battery operated units which are much cheaper to buy than mainspowered detectors. our prototype with a Dynamark label measuring 127 x 144mm. Inside the case, the circuit compo­ nents are mounted on two separate PC boards. The main board measures 149 x 251mm and is coded 03312961. It is installed in the base of the case and has a number of multi-way terminal connectors for all the connections from the smoke detectors. Two large holes at the top of the main board are for cable entry for the smoke detector wiring, although these may not be used if the cables are brought in via one of the side panels. The second board measures 112 x 151mm. It is coded 03312962 and it carries all the LED indicators and pushbutton switches for the smoke detectors. Before you begin assembly of the The finished front panel board with all the LEDs in place. Note that they must be test-fitted in the front panel before they are soldered. PC boards, check each one for shorts between tracks or breaks in the cop­ per pattern. You may need to drill out some holes for mounting the PC boards, the transformer, REG1 and for cable ties to hold down the SLA battery. The component overlay for the main board is shown in Fig.1 while the second board is in Fig.2. Install all the links first and note February 1997  57 Fig.1: this is the parts layout for the main PC board. Take care to ensure that all polarised parts are correctly oriented and note that a heatsink must be fitted to REG1. The 12V SLA battery is secured to the board using two plastic cable ties. 58  Silicon Chip Fig.2: the component overlay for the front panel board. This board mounts face down into the front panel. that you must choose the appropriate link for the preset disarm period you require. Fig.2 shows the link for a 15-minute disarm period although we suggest that most people will want a longer delay – the choice is yours. Next, install the resistors, using the resistor colour code table as a guide to the values. Alternatively, use a digital multimeter to check each resistor be­ fore it is installed. This done, insert the diodes, taking care with their orientation. Note that diodes D1-D20 (see Fig.1) are installed with their cathode bands facing IC2. Similarly, on the second board, diodes D22-D29 are all oriented the same way, with their cathode bands away from the switches. Note that there are two types of diode used on the main PC board: 1A 1N4004s which have a black body and the smaller 1N914s which usually have an orange glass body. The 13V zener diode ZD1 is similar in size to the larger diodes so be careful to install it in its correct place. Five PC stakes are installed on the main PC board. Four of these are for the transformer secondary and the SLA battery terminals. The fifth is mounted at the end of the SLA battery position to stop it from moving along the board and encroaching on adjacent capacitors. Next, insert and solder in the ICs. Take care with the orientation of each and check that the correct type has been installed before soldering. The 3-terminal regulator REG1 is mounted horizontally on a small heatsink using a 3mm screw and nut. Bend its leads so that they insert into the holes pro­ vided. There are three transistors to be mounted on the main board; make sure they are oriented correctly. Take care with the polarity of the electrolytic capacitors when they are installed. Note that the electrolytics on the front panel board are mount­ ed horizontally to allow clearance between the board and front panel. Switches S1-S13 are oriented with the flat side towards the top edge of the board. We used grey switch­es for S1-S11 and S13. Green switches were used for S12 and S14. When installing the terminal strips RESISTOR COLOUR CODES – CONTROL PANEL  No.    2  10    3  25    3    3    1    1    1 Value 470kΩ 100kΩ 33kΩ 10kΩ 2.2kΩ 1kΩ 680Ω 120Ω 100Ω 4-Band Code (1%) yellow violet yellow brown brown black yellow brown orange orange orange brown brown black orange brown red red red brown brown black red brown blue grey brown brown brown red brown brown brown black brown brown 5-Band Code (1%) yellow violet black orange brown brown black black orange brown orange orange black red brown brown black black red brown red red black brown brown brown black black brown brown blue grey black black brown brown red black black brown brown black black black brown February 1997  59 Fig.3: the wiring details inside the case. Apart from the mains wiring, the interconnections are made using rainbow cables terminated to headers. on the main board, orient them with the wire entry side as shown on Fig.1. Also mount the 180Ω 5W resistor and the pin headers for the A, B, C and D connectors. If you use 8-way headers in the 7-way C and D positions, the end pin of each should be cut off. Transformer T1 is mounted on the main board using 3mm screws and nuts. The earth solder lug is secured on the trans­former mounting screw with a star washer and nut. The SLA battery is mounted on its side with the terminals facing the 180Ω 5W resistor. 60  Silicon Chip Secure the battery to the PC board using cable ties as shown. Drilling the case Because it is assumed that the Con­ trol Panel will be mount­ed on a wall, we have used the case unconvention­ ally. The main board is mounted in the case lid (recognised by the brass inserts in the four corner posts), while the front panel is mounted in the base of the case. This has been done so that after installation, the lid can be removed by undoing the four screws. You will need to drill a hole for the cord grip grommet adjacent to where the transformer will be positioned. The main PC board can be attached to the lid of the case using 3mm screws at the mounting standoffs. The front panel section of the case will need to be drilled for the switch­ es, LEDs and fuseholder. S15 and the fuse­holder should be located 17mm in from the lefthand edge of the case to provide clearance for the transformer body. Position the fuse and S15 at 25mm and 55mm respectively up from the bottom edge of the case. The disarm LED11 for alarm 1 is located 22mm in from the righthand edge and 22mm from the top edge of the case. Attach the Dynamark label with LED11 in the above position and drill out holes for the switches and LEDs and insert the 3mm LED bezels. Place the front panel PC board in position under the front panel and secure with 3mm screws and 6mm spacers into the inte­gral standoffs in the case. (The spacers can be held in place over the screw using “Blu-Tack” as an aid in assembly). Push the LEDs into the bezels and solder in place on the board. Then re­ move the front panel PC board which is now ready for wiring. Fig.4: one of these PC boards needs to be fitted inside each smoke detector. The board is designed to fit inside the battery compartment. This is a finished smoke detector PC board, about to be in­stalled in the battery compartment of a Kambrook smoke detector. Wiring All of the wiring details not shown on Fig.1 & Fig.2 are shown in the di­ agram of Fig.3. This should be closely followed, in conjunction with the circuit diagrams published last month. Cut a 220mm length of 6-way and a 160mm length of 6-way rainbow cable. You also need a 400mm length of 7-way and a 250mm length of 7-way rainbow cable. Strip one end of each cable and insert the 220mm 6-way length into the A bus of the front panel PC board. The 160mm length of 6-way cable is inserted into the B bus. The 400mm length of 7-way cable is for the C bus and finally the 250mm length of 7-way is for the D bus. Strip the other ends of each cable of insu­ lation and attach the header pins to each lead. Now slide the pins into the header shell and plug it into the main PC board. Use 250VAC rated hook-up wire for the mains wiring. Alter­natively, strip some wire out of the mains cord. The mains cord should be secured with the cordgrip grommet so that it cannot be pulled out of the case. The green/yellow striped wire should be soldered to the solder lug located on the transformer mounting foot. Use heatshrink tubing over the fuse and mains switch wiring to prevent accidental contact with the live ter­ minals. Similarly, the terminals to the trans­ former primary must be sheathed in heatshrink tubing after wiring. Con­ nect the short lengths of hookup wire from the transformer secondary to the PC stakes on the main PC board. The battery terminal wiring consists of short lengths of hookup wire with spade terminal clips attached to one end. Solder the free end to the PC stake on the board, taking care with the po­ larity when connecting to the battery. Apply power to the circuit and check that there is about 9V between GND and the + terminal on the ter­ minals strips. Initial­ly, LED1 should light and then LEDs 2-10 should light in sequence, taking 7 seconds to cycle through. Press the disarm switches and check that the associated LED11 or LED12 lights. They should extinguish when the associated rearm switch is pressed. If you find that the circuit does not operate as described, check that the rainbow connectors are terminated in the correct positions and with the right polarity. Also check the supply to all ICs. There should be 9V between pins 1 & 8 of IC1, IC4, IC5 & IC6; 9V between pins 16 & 8 of IC2 & IC7; 9V between pins 4 & 8 of IC3; and 9V between pins 14 & 8 of IC8. Smoke detector PC board The small PC boards for the smoke detectors can now be constructed. These measure 46 x 23mm and are RESISTOR COLOUR CODES – DETECTOR PC BOARD  No.   1   1   1   1   1 Value 1MΩ 100kΩ 33kΩ 10kΩ 1kΩ 4-Band Code (1%) brown black green brown brown black yellow brown orange orange orange brown brown black orange brown brown black red brown 5-Band Code (1%) brown black black yellow brown brown black black orange brown orange orange black red brown brown black black red brown brown black black brown brown February 1997  61 This folded-out view of the Control Panel shows the wiring to the two PC boards. Take care to ensure that the mains cord is correctly anchored. coded 03312963. You will need one of these boards for each smoke detector. Install the five resistors and single diode and then the transistors; take care to use the correct type in each place. Insert and solder the four PC stakes on one end of the PC board and the 4-way terminal strip at the other end. The capacitors are mounted as close as possible to the PC board with the polarity as shown. The LED mounts with its leads bent at right angles so that it protrudes above the edge of the board. We used Kambrook SD28 smoke detectors as our prototypes and the PC board is mounted with a self-tapping screw through the battery holder side panel as shown in the photograph. It should be possible to mount the PC board in the battery compartment of the smoke detector but the LED may need to be con­nected to the lid with The front panel board is secured to the lid on 10mm standoffs. It is linked to the main board using rainbow cables terminated in header plugs. 62  Silicon Chip flying leads in some cases. Cut off the battery clip for the smoke detector and solder the supply wires to the + and GND terminals on the PC board. To make a connection to the ionisation chamber, we used an alligator clip soldered to a length of hookup wire. You can’t solder to the ionisation chamber because it is stain­ less steel and you can’t undo one of the screws because they are tamper proof. To make a secure connection, bend out one of the metal slots and attach the alligator clip to this. On other smoke detectors it is pos­ sible to make a connec­tion to a wire which is attached to the ionisation chamber. Finally, attach a length of hookup wire to the piezo termi­nal which has a red wire from the smoke detector circuit already connected. We drilled a hole in the side of the smoke detector case to allow access to the lower screw terminals on the addon PC board. You may have to make a different arrangement for other models of smoke detec­tor. We have produced a label to designate the external con­ nections and a copy of this should be affixed to the terminal block in each detector. Drill a hole in the alarm lid for the LED bezel, taking care to mark the correct place before drilling. Since the smoke detector has now been modified to be pow­ered from an external source, there is no need to access it once it has been installed. We have produced a label which states that the are “No user serviceable parts inside”. Copy as many as you need and affix them to each detector. This is to comply with Australian Standards AS3786-1993. Testing When you have finished modifying all the smoke detectors, they can be temporarily connected to the Control Panel. Make sure that the connections are correct before switching on power. Note that the “in” and “out” terminals on the smoke detectors connect to the “test” and “in” terminals on the con­ trol panel. To avoid confusion, they have also been labelled A and D. The A terminal (in) on the smoke detector should attach to the A terminal (test) on the control panel. Similarly connect the B to B, C to C and D to D. Apply power and check that the LED in each smoke detector flashes about once every three seconds. Press the disarm switches to check that the The modified Kambrook smoke detector. The LED on the PC board protrudes through the lid and flashes every three seconds as an indication that it is powered. Fig.5: this is the full-size etching pattern for the front panel PC board. Once again, check the board carefully before installing any parts. February 1997  63 Fig.6 (left): this is the artwork for the main board, reduced to 70% actual size. It can be reproduced full size on a photocopier set to 1.41x. Fig.7 (above): full size artwork for the smoke detector board. Up to 10 of these boards will be required, one for each smoke detector. 64  Silicon Chip No user serviceable parts inside Fig.8: copy this label on a photostat machine and attach it to the outside of each smoke detector. A B C D Fig.9: attach this label In + Gnd Out to the terminal block in each smoke detector. LEDs for smoke detectors 1 and 2 stop flashing. Press the rearm switches to reapply power. Before proceeding fur­ ther, use some “Blu-Tack” in the top of each smoke detector piezo siren to reduce the sound level. Now press the test switch on the Control Panel for one of the connect­ ed smoke detectors. Its siren should sound after a few seconds and when the LED on the Control Panel lights, it should remain lit for about four seconds. The alarm will then stop and the next LED will light. During this 4-second time interval some of the other sirens may sound. Make this test on all connected smoke detectors. If the test switch on one of the smoke detectors is pressed, then when the associated LED on the Control Panel lights (ie, when the detector is polled, all the other smoke detector alarms will sound. Next, disconnect the mains power and check that the SLA battery con­ tinues to power the circuitry. Do not forget to remove the “Blu-Tack” from the piezo sirens after all the checks have been completed. Installation As noted previously, the Smoke Alarm Control Panel is designed to mount on a wall and preferably in­ side a closet or cupboard. The smoke detectors should be mounted in ac­ cordance with the brochure supplied with each unit. Each detector should be linked back to the Control Panel via its own length of 4-way telephone cable and these cables should all be in the ceiling space. After all, it would be no good if a fire started and burnt out the cables before the alarm went off! Finally, note that the parts list pub­ lished last month should show four 1kΩ resistors (not three), while a 47kΩ resistor should be added to the circuit between pin 11 of IC5f and the +9V supply. In addition, one of the 100µF bypass capacitors should be 10µF. SC We made the connection to the stainless steel ionisation chamber via an alligator clip. Other smoke detectors are easier, as they have a wire connection to the chamber. ALARM TEST REARM DISARM 1 + + + + + 2 + + + + + 3 + + 4 + + 5 + + 6 + + 7 + + 8 + + 9 + + 10 + + SMOKE ALARM CONTROL PANEL Fig.10: this is the full-size front panel artwork for the control panel. February 1997  65