Flame Sensor. Start Up Project 30

8AWhy going for a costly Fire Alarm system? Some of the Fire alarm systems cost more than Rs.2000. You can make an efficient Fire warning system for just Rs.20. It uses only a few components and is a very efficient Flame sensor. The Thermister based commercial Flame sensors have a drawback because, the alarm sounds only when the Thermister turns hot by the nearby flame. That means, the alarm sounds only after the room is full of fire. But this tiny circuit overrides that drawback. It uses a Photodiode as Fire sensor. It sounds the alarm even if the flame is far away . Interestingly, the spark of the first fire burst can activates the alarm. It can be installed in Home, Commercial shops etc. It will not activate in the ambient light of the room like that of Fluorescent light. It sounds the alarm only when it detects a light similar to a flame, sunlight or incandescent bulb. It is battery operated and in the standby state the current consumption is as low as 5 mA. So Simple, Efficient, and Low cost. Build it.

You need the following
1. 1K Resistors – 2
2. 470K Resistor -1
3. Transistor BC 547 -1
4. Transistor BC 557 -1
5. Photodiode – 1
6. Buzzer – 3-12V DC
7. 9V Battery snap
8. 9V Battery
How it works?
A Photodiode is used as the Flame sensor. It is connected in the reverse biased mode with the Cathode to the Positive rail. In the ambient light, it passes only 0.84 V through it to the Emitter of the PNP transistor T1. But when the Photodiode gets light from the Flame, mainly the Infrared light, the Photodiode passes more voltage .
T1 is a PNP transistor, so it conducts only when its base is held low. So here the base of T1 is held low through the 470K resistor. In this state, it can conduct. But the Photodiode is not passing current to the emitter of T1. At this condition, T2 remains off since it is not getting any base current from the collector of T1. So the circuit remains standby.

When the Photodiode gets light from the flame, it passes more voltage as high as that of positive rail. So T2 gets base bias from the collector of T1. T1 then conducts and the buzzer beeps.

After assembling the circuit on a Perf board, place it an area where there is no sunlight or light from incandescent light. Usually, buzzer remains silent. If it beeps, enclose the Photodiode in a black tube. Buzzer will stop beeping. Fluorescent light, LED lights etc will not activate the circuit. Show a lighted match stick or candle flame to the photodiode. Buzzer will beep. Your Fire alarm system is ready. Fix it near the corner of the room .You can also use a 6-9V adapter for powering the circuit.