The document describes a simple fire detection circuit using a thermistor. The circuit uses a potential divider configuration with a thermistor and resistor to sense temperature changes. When the temperature and thermistor resistance rises due to heat, the voltage drop across the resistor increases, turning on a transistor and activating a buzzer alert. This simple, low-cost circuit can be used for fire detection in homes, schools, industries, and research facilities.

1. Sri Venkatesa Perumal
College of Engineering & Technology
Gowtham Sana
14G05A0401

3. A simple potential divider
arrangement using thermistor is
capable of sensing the
temperature(presence of fire)
and alerting us with a warning
signal. This is suitable for
your home security systems.

4. Components required
•Power supply
•Potentiometer (10KΩ)
•Capacitor (10µF, 16V)
•BC548 transistor
•High resistance thermistor (NTC)
•Diode (1N4001)
•6V Buzzer
•Resistors (1kΩ)

5. Circuit Diagram

6. 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.

7. As temperature rises,
the resistance of
thermistor decreases
so that the drop
across the resistor
R1 increases which
turns ON the
transistor.

8.  Home Security System
 School/College Labs
 Industries
 R&D Cells

9. • Sensing of fire(Heat) easily
• Simple Circuit
• Low Power Consumption
• Low cost

10. o No longer use
o Senses near by the
Fire(Heat)only
o Uses continuous Power
Supply

11.  To overcome disadvantages and looking
for implementation of Automatic Fire
detection.
 In the place of Thermistor have to use
Sensors…
 Uses the Speakers instead of Thermistor
with Warning message & Audio alert
signal.

12. Practical Circuit