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BUILD THIS This Smoke Alarm Control Panel will power and monitor up to 10 smoke detectors. It provides a neat solution to the problems of using multiple smoke detectors throughout a house. These days, many homes have smoke detectors and new homes in most Australian states must have them. But what if you have a large house? Individual battery operated smoke detectors are not practical. This Smoke Alarm Monitor is an effective answer for a complicated problem. Control Panel For Multiple Smoke A 24  Silicon Chip D O YOU HAVE a smoke detector in your home? Only one? Then you’re not really protected against fire. If you have a small house with only two bedrooms and all the internal doors are always kept open, then one smoke detector may be enough. But if you have three or four bedrooms and children or teenagers in the house, then one or two smoke detectors is definitely not enough. Picture the scenario. A fire starts in a computer or music system in one of the bedrooms which has its door shut. You’re asleep in your bedroom and your door is shut too. You’ve had a full day and you’re a heavy sleeper as well. And you have one smoke detector in the hallway, say. What chance is there of you being woken up before the house is well alight? Not much. Don’t be lulled into a false sense of security. To effec­tively monitor for fire, you need a smoke detector in every bedroom which is used, particularly if it has any electrical equipment in it – electric blanket, radiator, clock radio, TV, computer or music system. Most of these appliances are perman­ ent­ly plugged in and fires can start in any of them. You also need smoke detectors in your living areas and study or any area where there is electrical equipment. Count in your laundry, workshop or hobby room but leave out your kitchen and garage. You will probably find that you need between six and 10 smoke detectors, or even more if you have a large two or three-storey house. Trouble is, even if you have that many smoke detectors, if they are battery operated and not linked together, you still have the problem of a fire starting in a closed room and you Features • • • • • • • • • • • Based on battery operated smoke detectors Monitors up to 10 smoke detectors Mains power operation (9V batteries not required) 12V battery backup Flashing LED power indicator in each smoke detector All alarms activated when one smoke sensor is triggered Extra alarm output Alarm silencing for two smoke detectors Alarm test on control panel Indication of triggered smoke detector Four-wire connection (telephone wire) between smoke detectors and control panel won’t hear the alarm. And the idea of having 10 battery-operated smoke detectors is not practical – replacing batteries at regular intervals is not cheap or convenient. One answer is to use mains-powered smoke detectors. Typi­cally, up to 11 of these can be linked together and if one de­tects smoke, they all go off. This is a much more effective solution but it is quite expensive. Typically, mains-powered smoke detectors cost about $60 each; $60 x 10 detectors = $600! In addition, they must be installed by an electrician so a typical installation with 10 detectors could easily cost $1500 or more. And you still have the regular cost of replacing the back-up batteries. Add up the cost of replacing the batteries in ten smoke detectors over a period of 10 years and the cost is hundreds of dollars. Furthermore, what if you want to have a birthday party where the kids want to blow out the candles three times? Or a candlelit dinner? Or an open fire in the winter evenings? Or someone likes to have a cigarette after a meal? Having all smoke detectors linked together in those circumstances could be a trifle inconvenient. An effective solution The SILICON CHIP Smoke Alarm Control Panel is designed to power and monitor up to 10 modified smoke detectors. We’re talking about the cheap battery smoke detectors which you can buy everywhere for around $10. They are all linked together with 4-way telephone cable so there is no need to call in a licensed electrician –you can do the installation yourself. The Control Panel is mains powered but also has battery backup to cope with electricity blackouts. As a bonus, two of the 10 smoke detectors can be disabled for periods up to four hours, after which they will Specifications By JOHN CLARKE Alarms • • • • • • • • • Supply to smoke detectors ......................9.0V - 9.75V Current consumption ...............................26mA <at> 9.4V with alarms off Total current with 10 alarms sounding .....1A Standby power .........................................1.2Ah 12V SLA battery Battery trickle charge ..............................22mA Battery charge voltage ............................13.6V Alarm 1 and Alarm 2 silencing time .........15mins, 1hr, 2hrs or 4hrs Power LED flash rate ...............................once every 3 seconds (approx.) External alarm siren rating ......................200mA <at> 9V January 1997  25 Fig.1: block diagram for the Smoke Alarm Control Panel. There is provision for up to 10 smoke detectors to be connected to the unit and these can be wired via 4-way telephone cable. be rearmed automatically or you can rearm them by pushing a button on the Control Panel. So you can have that birthday party with lots of candles after all. There is also provision to connect a piezo siren in the roof. That way, if a fire starts when you’re outside the house or not at home, your neighbours can be alerted. Each smoke detector has its battery removed and a small PC board installed in its place. The board accommodates a diode, two transistors and a LED which flashes every three seconds to in­dicate that the detector is powered – no more need to check each smoke detector. If a detector is disarmed, the LED does not flash. Alternatively, when the alarm is sounding, the LED lights continuously. Control panel The SILICON CHIP Smoke Alarm Control Panel is designed to be mount­ ed vertically on a wall and we assume that normally it will be installed out of view, inside a closet. The control panel has test switches for all 10 smoke detectors plus the 26  Silicon Chip disarm and rearm facility for two detectors. In normal operation, each detector is polled (monitored) for 0.7 seconds and its respective LED lights during that time. If a detector is activated by smoke, its control panel LED remains lit until the smoke has cleared. Block diagram Fig.1 shows the block diagram of the Smoke Alarm Control Panel. Only one smoke detector is shown out of a possible 10 which can be connected. There are four wires to each smoke detec­tor: +9V, 0V, alarm test input and alarm output. The alarm output from the smoke detector indicates the presence of smoke or if the test switch has been pressed. This signal is applied to the alarm selector (IC1, IC2, etc) which monitors each of the smoke detectors in sequence. If the selected smoke detector gives an alarm signal, comparator IC3a will pro­duce an output to power the external alarm siren via transistor Q1. This output is also fed to a deselector (IC5, IC6, etc) via a mixer (D31, D32). The deselector sends an alarm signal to the inputs of all smoke detectors except for the one selected. Thus all smoke detectors will sound the alarm if one alarm is activated. When the smoke clears, all smoke detector alarms will stop. The deselector serves one important func­tion. By sending the alarm signal to all but the smoke detector which originated the alarm, all alarms stop when the smoke clears. Otherwise, if the detector which initiated the alarm also had the alarm signal fed to its input, the alarms would not stop until the power was disconnected. Power for the unit is derived from the mains while an SLA (sealed lead acid) battery provides backup in the event of a blackout. The +9V supply connects to smoke detectors 3-10, while detectors 1 & 2 are supplied via transistors Q2 and Q3. When the disarm switches are pressed for detector 1 or 2, the +9V supply is disconnected for the time set by timer IC7. Detectors 1 & 2 can be independently disarmed or rearmed. However, the disarm time is preset from the time the disarm switch for either detector is pressed. The disarm time can be set at 15 minutes, 1hr, 2hrs or 4hrs and is set by a link on the PC board. The Australian Standard (AS3786-1993) specifies up PARTS LIST 1 PC board, code 03312961, 149 x 251mm 1 PC board, code 03312962, 112 x 151mm 1 Dynamark front panel label, 127 x 144mm 1 label for control panel terminals 1 plastic case, 180 x 260 x 65mm, Jaycar Cat HB-5974 or equival­ ent 1 2155 transformer, 15V at 1A (T1) 1 1.2AH 12V SLA battery 1 250VAC 3-core mains cord and moulded 3-pin plug 1 2AG panel fuse holder and 250mA fuse (F1) 1 DPST mains switch with Neon lamp (S15) 1 solder lug 1 cordgrip grommet for mains cord 12 grey momentary contact snap action PC board switches (S1S11 & S13) 2 green momentary contact snap action PC board switches (S12,S14) 1 mini-U heatsink, 25 x 30 x 16mm 3 10-way PC board terminal strips 1 12-way PC board terminal strip 2 7-way pin header sockets and plugs (can use 8-way) 2 6-way pin header sockets and plugs 1 380mm length of 6-way rainbow cable 1 650mm length of 7-way rainbow cable 1 50mm length of heavy duty green hookup wire (battery connec­tion) 1 50mm length of heavy duty red hookup wire (battery connection) 1 150mm length of medium duty hookup wire 2 spade crimp lugs for SLA battery terminals to 15 minutes of alarm silencing before automatically returning to normal function. We think that up to four hours may be required if the home has an open fire place. Circuit description Fig.2 shows the complete circuit of the Smoke Alarm Control Panel. In 10 small cable ties 10 3mm diameter x 5mm screws to secure main PC board 2 4mm screws and nuts plus star washers for transformer mounting 1 3mm dia x 6mm screw and nut for regulator mounting 4 3mm dia x 10mm screws for front panel PC board mounting 4 6mm untapped spacers for front panel PC board 1 400mm length of 0.8mm tinned copper wire 5 PC stakes 12 3mm LED bezels Semiconductors 2 7555, LMC555CN, TLC555CN CMOS timers (IC1,IC4) 1 4017 decade counter (IC2) 1 LM393 dual comparator (IC3) 2 4049 hex buffers (IC5,IC6) 1 4040 binary counter (IC7) 1 4013 dual D-flipflop (IC8) 3 BC328, BC327 PNP transistors (Q1-Q3) 35 1N914, 1N4148 signal diodes (D1-D35) 7 1N4004 1A diodes (D36-D42) 1 13V 1W zener diode (ZD1) 1 LM317T 1A adjustable regulator (REG1) 10 3mm green LEDs (LED1LED10) 2 3mm red LEDs (LED11,LED12) Capacitors 2 2200µF 25VW PC electrolytic 5 100µF 16VW PC electrolytic 1 33µF 16VW PC electrolytic 7 10µF 16VW PC electrolytic 2 1µF 16VW PC electrolytic 1 .01µF MKT polyester 1 .0015µF MKT polyester Resistors (0.25W 1%) 2 470kΩ 4 1kΩ the top righthand corner of this diagram is a typical circuit of an ionising chamber smoke detector, based on a Motoro­la MC14467P IC. This chip has a high impedance comparator at pin 15 which monitors the ionisation chamber’s output voltage. The ionisation chamber contains a minute quantity of the radioactive el- 10 100kΩ 1 47kΩ 3 33kΩ 25 10kΩ 3 2.2kΩ 1 680Ω 1 180Ω 5W 1 120Ω 1 100Ω Miscellaneous Heatshrink tubing, Blu-Tack® adhesive, solder Smoke Alarm PC board (one per smoke detector) 1 Kambrook SD28 ionisation smoke alarm or equivalent 1 PC board, code 03312963, 46 x 23mm 1 label to indicate terminal connections 1 label “No user serviceable parts inside” 1 self-tapping mounting screw 1 4-way PC mounting terminal strip 1 5mm LED bezel 4 PC stakes 1 crocodile clip Semiconductors 1 BC548 NPN transistor (Q4) 1 BC328 NPN transistor (Q5) 1 1N914 signal diode (D43) 1 5mm red LED (LED13) Capacitors 1 47µF 16VW PC electrolytic capacitor 1 10µF 16VW PC electrolytic capacitor Resistors (0.25W 1%) 1 1MΩ 1 10kΩ 1 100kΩ 1 1kΩ 1 33kΩ Miscellaneous 1 100mm length of yellow hookup wire 1 100mm length of green hookup wire Fig.2 (next page): each smoke detector is polled by decade counter IC2 and its alarm signal (if present) is fed to comparator IC3a which then turns on all the other smoke alarms via IC5f and IC6f. A typical smoke detector circuit is shown at the top righthand corner of the diagram. The additional circuit to the left is the added PC board in each detector. January 1997  27 +9V 47k 28  Silicon Chip January 1997  29 YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 30  Silicon Chip ement Americium 241. As this decays (to Neptunium 237) it emits positively charged Alpha particles and these main­tain a positive charge on the outer metal case of the chamber. When the Alpha particles are blocked by smoke particles, the outer metal case loses its positive charge and this is detected by the high input impedance comparator at pin 15. Note the guard track pins (14 & 16) around pin 15. This is a bootstrap connection to prevent leakage on the PC board from loading the ionisation chamber’s output. When smoke is detected, the piezo transducer is driven from pins 10 & 11 to produce a high sound level. The connection at pin 8 is feedback from a section of the piezo transducer to set the oscillation frequency. The square wave drive signal at pin 10 is monitored by the Smoke Alarm Control Panel. The MC14467P also has a test facility whereby the positive plate of the ionisation chamber is brought to a low voltage via a 1MΩ resistor. This is the normal test button on any smoke detec­tor and it sounds the alarm. We use this feature to set off all alarms if any detector is triggered and also for the alarm test facility. Detector PC board circuit As noted above, each smoke detector has its battery removed and a small PC board installed instead. This circuit of this comprises transistors Q4 & Q5, diode D43 and LED13. When the Alarm Test input at (A) goes high, the 47µF ca­pacitor at the base of Q4 begins to charge via the 100kΩ resistor and D43. When the voltage reaches +0.6V, transistor Q4 switches on to pull the positive side of the ionisation chamber low via a 1MΩ resistor. The Alarm Test input can go high in two separate circum­stances. First, if one of the smoke detectors is triggered by smoke, the Alarm Test inputs on all other smoke detectors will go high to sound their alarms. Second, if an Alarm Test pushbutton is pressed on the Control Panel, the respective input will go high to sound that smoke detector’s alarm. The Alarm Test input is also used to flash the LED each time it is polled by the Control Panel. In this case, the Alarm Test input goes high for 30ms every 3 seconds, to turn on Q5 and LED13. The pulse is too short at 30ms to switch on Q4 due to its delay circuitry. The MC14467P also has provision for a LED flashing circuit which indicates that the power is present. This flashes once every 40 seconds but is not used on most battery-operated detec­ t ors. Mains powered smoke detectors typically use the Motorola MC14468 or an equivalent chip which provides an interconnect facility. The output signal from each smoke detector is applied to inputs 1-10 via diodes D1-D10 to com­ parator IC3a. Note that normally there will be no output from any smoke detector until there is smoke! IC2 is a 4017 decade counter with 10 outputs, each of which go high in turn. Each time one of its outputs goes high, the associated diode (D11-D20) is reverse biased so that it ceases to shunt (ie, short out) its respective alarm input. For example, if pin 3 of IC2 goes high, D11 is reverse biased and the associated alarm signal at input 1 will be fed via diode D1 to pin 6 of IC3a. At the same time, inverter IC5a will turn on LED1 on the Control Panel to indicate that input 1 is being polled (moni­tored). Since only one input is polled at a time, a single 1kΩ resistor is used to feed LEDs 1-10. Note that the output signals from the smoke detectors are high frequency square waves. These are effectively rectified by the relevant input diode (D1-D10) and then filtered by a 10µF capacitor and 100kΩ shunt resistor (adjacent to IC5b on Fig.2). The 10µF capacitor also provides a delay before the voltage reaches the positive threshold of comparator IC3a (next to IC4, bottom of circuit). Normally, the pin 7 output of IC3a is high and pin 5 is at +2.2V. When pin 6 of IC3a goes above +2.2V, pin 7 goes low and pin 5 drops to +2.06V by virtue of the 470kΩ feedback resistor from pin 7. The voltage at pin 6 must now fall below +2.06V before pin 7 will go high again. This hysteresis prevents erratic switching and reduces the effect of noise on the input lines. When IC3a’s output goes low, it causes the outputs of inverters IC5f & IC6f to go high and these drive the Alarm Test signal outputs (1-5) and (6-10) respectively, via 10kΩ resistors. Note that, as each alarm is polled by IC2, its Alarm Test signal is shunted This opened-out view of the Smoke Alarm Control Panel shows the two PC boards and the 12V backup battery. All the smoke detectors are connected to the termination blocks on the main PC board. to ground via diode D21-D30 when its respective LED driver output is low (eg, IC5a in the case of input 1). When IC3a’s output goes low, it also triggers IC4 and switches on Q1. IC4 is a 7555 monostable timer. When triggered, its output at pin 3 goes high to stop IC2 from being clocked. Thus, the selected alarm input remains enabled until the smoke clears. Q1 drives the external alarm when it is switched on by IC3a. Pushbutton switches S1-S10 apply a high signal to their respective Alarm Test outputs via a 10kΩ pull-up resistor. These allow each smoke detector to be tested individually. Note that when the pushbuttons are used to test each smoke detector, the respective LED does not light, unless it happens to be polled at the same time. IC1 is a 7555 astable timer operating at 1.4Hz to provide the clock for counter IC2. Hence, each smoke detector is polled for 0.7 seconds and the full polling cycle takes just over seven seconds (ie, for all 10 smoke detectors to be polled once). IC3b is the LED pulse oscillator and its output is low for 30ms every three seconds. Note that all ten smoke detector LEDs will be flashed simultaneously and that this process has nothing to do with the polling of each smoke detector by IC2. Disarming & rearming IC8a and IC8b are D-type flipflops which provide the disarm and rearm functions for detectors 1 & 2. Normally, their Q-bar outputs are low and so transistors Q2 and Q3 feed +9V to their respective smoke detectors. When the disarm switch for smoke detector 1 (S11) is pressed, the reset (pin 4) of IC8a is pulled high to force the Q output low and Q-bar high. This turns Q2 off and lights LED11. Thus, power to alarm 1 is off. S11 also resets the 4040 counter (IC7) which is clocked by the pin 9 output of IC2 via IC6e. The Q8 output of IC7 goes high after 15 minutes and it applies a positive pulse to the clock input of IC8a and IC8b via link LK1. This causes the Q-bar output to go low and detector 1 is rearmed. Alternatively, to rearm detector 1, push­button S12 can be pressed to pull the set input of IC8a high. A similar sequence of events involving S13, S14 and IC8b applies for the disarming and rearming of detector 2. Longer delay times for IC7 can be set using links LK2, LK3 and LK4. These select one hour, two hours and four hours respec­tively. Power supply D36-D39 rectify the 12.6VAC from transformer T1 and this is filtered using a 2200µF capacitor. REG1, an adjustable 3-terminal regulator, is set to provide a nominal +9V output. The 12V SLA (sealed lead acid) battery is charged via a 180Ω 5W resistor, while 13V zener diode ZD1 and diode D40 restrict the charging voltage to +13.6V to prevent overcharging. Normally the input supply to REG1 is about +17.7V and this is above the +13.6V from the SLA battery so D41 is reverse biased. If the mains supply is off, D41 conducts to supply REG1. Next month, we will give full details of construction and installation of the SC Control Panel. January 1997  31