How to make an automatic fire alarm circuit using a thermistor

 The circuit that detects fire and activates the alarm sound or buzzer is called an automatic fire alarm circuit. 

It is a very important device to detect fire in time and prevent loss of personnel or property. It is part of a security system that protects people and valuable property (such as the accounting records of banks, households, and organizations). Fire alarm circuits are an essential part of today's busy life. There are many expensive fire alarm circuits on the market, but we will make 5 very simple automatic fire alarm circuits in this article.

In this fir-tree alarm system, we use a thermistor as a thermal sensor. When heat reaches the sensor, its resistance increases, and the transistor connected to the sensor turns on the circuit. 

Components of the fire alarm circuit 

1. Thermistor 10k 
2. Variable resistance (POT)
3. Diode in4007 
4. Resistance 220 to 500ohm 
5.BC547 NPN transistor Any speaker 
6. Battery 6v to 9v 

 Circuit diagram Simple fire alarm system


In this circuit, we use a thermistor with a 555 timer ic instead of a transistor to improve sensitivity.
 The circuit consists of two stages. The first stage of the fire alarm circuit is the input stage connected to the thermistor. The second stage of the fire alarm circuit consists of the output stage.


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