Thursday, 18 December 2014
This fire detection alarm circuit is based on thermistor. A thermistor is nothing but a variable resistor whose resistance changes with temperature.
Components required: Power supply, Resistors (1kΩ), Potentiometer (10KΩ), Capacitor (10µF, 16V), BC548 transistor, High resistance thermistor (NTC), Diode (1N4001), 6/9V Buzzer
Description: In this fire alarm circuit project, a thermistor works as the heat sensor. At normal temperature, the resistance of the thermistor is
approximately kilo-ohms, which reduces to a few ohms as the
temperature increases which turns ON the transistor. When the transistor is turned ON, the current from Vcc starts to flow via buzzer which produces a beep sound. Diode is used for enabling unidirectional conduction and the capacitor removes sudden transients from the thermistor.
Note: As a heat sensor one can also used tube light starter in place of thermistor. In a starter there is a metal plate and a pin with small gap.
When starter gets heated then metal plate of starter expands and get in
contact with the pin and circuit is completed.
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