project file content needed for FIRE ALARM CIRCUIT

Working of fire alarm circuit
Working is based on the switching property of transistor.
The thermistor and R1 forms a potential divider network which drives the transistor.
The heart of this circuit is a thermistor. Thermistors are low-cost, easily-available temperature sensors widely used for uncomplicated temperature measurements.
Thermistors are temperature sensitive resistors. When temperature increases resistance offered by the thermistor decreases and vice versa. At normal temperature, the resistance of the thermistor is around 10kΩ.
All resistors vary with temperature, but the semiconductor materials used for thermistors are especially sensitive to temperature.
The transistor is turned ON by the voltage drop across the resistor R1.
Consider the temperature of the atmosphere is around 25°C, and then the resistance of thermistor is high so the voltage across the thermistor is also high according to the basic ohm’s law V=IR.
The threshold voltage can be set by varying the potentiometer (R1).