FIRE ALARM WITH THERMISTOR AND NE555 CIRCUIT SCHEMATIC DIAGRAM

FIRE ALARM WITH THERMISTOR AND NE555 CIRCUIT SCHEMATIC DIAGRAM
The thermistor will have a low resistance at high temperature, while at low temperature, the transistor resistance is high. This characteristic of thermitor is used to build the fire alarm.

The difference value of thermistor will decide the transistor 1 and transistor 2 to switching on or off, while TI and T2 has function to drive the NE555 to generate audio frequency. We can say that the thermistor’s condition (its sensing) will determine the alarm to be on or off.

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