Low cost fire alarm circuit.
Description.
When there is a fire breakout in the room the temperature increases.This ultra compact and low cost fire alarm senses fire breakout based on this fact.
Transistor BC177 (Q1) is used as the fire sensor here.When the temperature increases the leakage current of this transistor also increases.The circuit is designed so that when there is an increase in the leakage current of Q1 ,transistor Q2 will get biased.As a result when there is a fire breakout the transistor Q2 will be on.The emitter of Q2 (BC 108)is connected to the base of Q3(AC 128).So when Q2 is ON Q3 will be also ON.The transistor Q3 drives the relay which is used to drive the load ie,light,bell,horn etc as an indication of the fire.The diode D1 is used as a free wheeling diode to protect it from back EMF generated when relay is switched.
Circuit diagram with Parts list.
Notes.
- The Preset R1 can be used to desired temperature level for setting the alarm ON.
- This is not a latching alarm,ie;when the temperature in the vicinity of the sensor decreases below the set point the alarm stops.
- The circuit can be powered using a 9V battery or a 9V battery eliminator.
- All capacitors are electrolytic and must be rated at least 10V.
- The load can be connected through the C,NC,NO points of the relay according to your need.
- The calibration can be done using a soldering iron,and a thermo meter.Switch ON the power supply.Keep the tip of soldering iron near to the Q1.Same time also keep the thermometer close to it.When the temperature reaches your desired value adjust R1 so that relay gets ON.Done!
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hi…we are abeg combne in the fir fiting in sawdi arebia.
we wnt to ask abawt low cost fir alarm braes lik thts model in yor websitik
may ourdr is:500 panel 2zon
500 panel 4zon
300 8zon
200 12 zon
100 18 zon
5000 smok detecotor
2000 hetar detecotor
2000 strop siren
500 alarm beel
hi…we are abeg combne in the fir fiting in k.s.a.
we wnt to ask abawt low cost fir alarm braes lik thts model in yor websitid
may ourdr is:300 panel 2zon
200panel 4zon
100 8zon
50 12 zon
50 18 zon
3000 smok detecotor
1000 hetar detecotor
1000 strop siren
500 alarm beel
we are wating yor bris in thes E MIL:HATIM_ALSAFI@MAKTOOB.COM
fax namber:0096677222277EXT106-105
thnk you….
meneger: hatim al safi
sir the circuit u provide for fire alarm is not working according to the circuit.
actully I am a student and working on this fire alarm project. I joined all the connections according to ur circuit but it is not working plz help me…
at place of Q3(AC128)i used another transister like the same of this.
plz sir help me to complete my project ..
waiting for reply..
thank you.
Hi deepak,
which transistor you used in place of Q3 ?
I think your article very useful for people who want to know about alarm work especially electronic
sir i am from bangladesh.your circuit is very easy to establish.but i face a problem to find transistor Q1(bc177).its unavailable.equivalents of this transistor bc178,bc179 are also unavailable.please help me to find another transistor.
BC 477, BC478 etc can be used in place of BC177
sir i tried your ckt…but after lots of attempts…still the ckt is not responding to the heat.when i connect to the supply the relay gets on (showing that current is flowing through the ckt)..but after that it doesnot respond to heat at all.please help!
This circuit will not work properly as soon as you plug it. You need to calibrate the circuit before using. Calibration can be done by adjusting the POT R1.
I tested this circuit and there is no problem with it.