How to build fire alarm

Fire Alarm

Fire alarm is a very important device in any house, It protects us from unknown fires and give time to prevent any miss happening.  In this project we are going to make a small fire alarm which can be installed on places like kitchen. It senses fire from close range so it can kept near to the places, which are vulnerable to fire. A smoke alarm is more effective which is generally installed on roof and detects smoke.

The circuit is same as previous one, only we are going to insert a thermistor in the probes which we kept open in above figure and a variable resistance instead of R3 to adjust the sensitivity according to thermistor.

Materials : 1– Thermistor 7-8 kΩ at room temperature (Fire Sensor), R1-100, R4 – 1k, R5 – 10k, 3 Transistors –BC547, 1 IC –UM66,  1 Speaker, Battery – 6volts, 1 LED

Step1 : In the Fire  alarm circuit , just put thermistor between the probes as a heat sensor.

Step2 : Assemble the melody circuit in breadboard, Please refer the previous melody project to make the circuit.

Step3 : As done before, Connect the melody circuit to LED pins , So that melody circuit will also get power when LED will light up.

Step4 : Switch On the circuit and touch thermistor with a hot object, LED should light up with ringing melody. If it doesn’t glow up circuit needs calibration. Rotate the variable resistance knob to increase resistance and touch the hot object again to sensor and see if it works,

Tip : Be patient with this circuit, As it requires calibration.

Warning : Don’t use direct flame/candle with thermistor. You may use ice instead of hot objects to calibrate correct position of  variable resistance knob. –If you are really intending to use candle flame, you should wrap thermistor with aluminum foil, keeping in mind that the two wires of thermistor should not get short because of foil.