The document describes a simple potential divider circuit utilizing a thermistor for temperature sensing, primarily for fire detection in home security systems. It outlines the necessary components, circuit operation, applications, advantages, and disadvantages, as well as potential future enhancements. The system alerts users when temperatures rise, indicating the presence of fire, but has limitations such as requiring continuous power and only detecting nearby heat.

1.  Introduction
 Components
 Circuit Diagram
 Operation

2. 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.

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

4. Circuit Diagram

5. Operation
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.

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

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

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

9. Dis Advantages
• No longer use
• Senses near by the Fire(Heat)only
• Uses continuous Power Supply

10. Future Scope
 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.