This document describes the components and working of a simple fire alarm circuit project. The circuit uses a thermistor to detect changes in temperature, which then triggers a transistor and sounds a buzzer. Key components are a thermistor, transistor, diode, capacitor, resistors and a 6V buzzer. As temperature rises, the thermistor's resistance decreases, increasing the voltage across a resistor to turn on the transistor and activate the buzzer. The circuit aims to detect fires and prevent damage through a simple, low-cost design.

2. FIRE ALARM
PROJECT

3. • Fire Alarm Circuit is a simple circuit that detects the fire and
activates the Siren Sound or Buzzer. Fire Alarm Circuits are
very important devices to detect fire in the right time and
prevent any damage to people or property.
Introduction

4. REQUIRED COMPONENTS
• Power supply
• Capacitor (10μF)
• BC548 transistor
• High resistance thermistor
• Diode (1N4001)
• 6V Buzzer
• Resistors (33kΩ,470 Ω)

5.  Thermistor:
Thermistors are Temperature Dependent Resistors i.e. the
resistance of a Thermistor varies according to the ambient
temperature. In this project we have used a 10 KΩ Thermistor
with NTC. At 250C, the resistance of the 10 KΩ Thermistor is 10
KΩ. The following image shows the 10K Thermistor used in this
project
COMPONENTS DETAIL

6. COMPONENTS DETAIL
 Power supply/Battery:
A well regulated power supply/battery is essential for this
circuit because even slight variations in the supply voltage
could alter the biasing of the transistor used in the fire
sensing section and this could seriously affect the circuit’s
performance

7. COMPONENTS DETAIL
 Transistor:
Transistor is a semiconductor device used for
switching and amplification of weak signals. In this
project transistor 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. When the transistor is turned ON, the
current from Vcc starts to flow via 6V buzzer which
produces a beep sound.

8. COMPONENTS DETAIL
 Diode:
A diode is a two-terminal electronic
component that conducts current primarily in
one direction. In this project diode is used for
enabling unidirectional conduction and the
capacitor removes sudden transients from the
thermistor.

9. Components Detail
 Capacitor:
A device used to store an electric charge, consisting of
one or more pairs of conductors separated by an insulator. In
this project when the current flow in the circuit capacitor will
be charged and when the circuit is broken or removed the
charged capacitor left which will cause to delay the buzzer
sound.

10. CIRCUIT DIAGRAM

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

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

13. ADDVANTAGES & DISADVANTAGES
 No longer use
 Senses near by the
 Fire(Heat)only
 Uses continuous Power Supply
Disadvantages:
Advantages:
 Sensing of fire(Heat) easily
 Simple Circuit
 Low Power Consumption
 Low cost

14. 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
and Audio alert signal

15. PRACTICAL CIRCUIT