This document describes a low cost fire alarm circuit project. It includes an introduction to fire alarms and their importance. The circuit uses transistors as heat sensors to detect a fire and trigger a relay connected to alarms. When the temperature rises, the leakage current of one transistor increases, biasing a second one on and activating the relay. The circuit provides fire detection at low cost with simple components and circuitry. It has advantages of low price, ease of use and portability but cannot detect extremely high temperatures. The summary aims to capture the key purpose, components, working and benefits of the circuit in 3 sentences or less.

1. AECD PROJECT
LOW COST FIRE ALARM CIRCUIT

2. TABLE OF CONTENTS:
 INTRODUCTION
 COMPONENTS REQUIRED
 CIRCUIT DIAGRAM
 HOW IT WORKS
 ADVANTAGES AND DISADVANTAGES
 APPLICATIONS
 CONCLUSION

3. INTRODUCTION
 Fire alarms are prime necessities in
modern buildings and architectures,
especially in banks, data centers and gas
stations. They detects the fire in
ambiance at very early stage by sensing
smoke or/and heat and raise an alarm
which warns people about the fire and
furnish sufficient time to take preventive
measures. It not only prevents a big losses
caused by deadly fire but sometimes
proves to be life savers.

4. Components required:
 9V DC power supply
 9V SPDT Relay
 TRANSISTORS: BC177, BC108, AC128
 DIODE: IN4007
 CAPACITANCES: 2.2µF, 100µF
 RESISTORS: 470KΩ, 100KΩ, 1KΩ

5. CIRCUIT DIAGRAM:

6. WORKING:
 In this project transistor BC177 (Q1) is used as the
fire sensor. When the temperature increases the
leakage current of this transistor also increases.
The circuit is designed so that when there is an
increase in the leakage current of Q1, transistor
Q2 will get biased. As a result when there is a fire
breakout the transistor Q2 will be on. The emitter
of Q2 (BC 108) is connected to the base of Q3(AC
128). So when Q2 is ON Q3 will be also ON. The
transistor Q3 drives the relay which is used to
drive the load i.e, light, bell, horn etc as an
indication of the fire. The diode D1 is used as a
free wheeling diode to protect it from back EMF
generated when relay is switched.

7. ADVANTAGES AND DISADVANTAGES
 ADVANTAGES:
 Low cost
 Less complex circuitry
 Portable
 Simple and efficient
 DISADVANTAGES:
 Very high temperatures
are not applicable

8. APPLICATIONS:
 Home security
 Museums
 Theatres
 All electric departments
 Industries etc

9. CONCLUSION:
 A fire alarm is a device that detects the presence
of fire and atmospheric changes relating to smoke.
The fire alarm operates to alert people to
evacuate a location in which a fire or smoke
accumulation is present. When functioning
properly, a fire alarm will sound to notify people
of an immediate fire emergency. This distinct
sound exists to allow the notification to be
heard The fire alarm constructed by this
project work is reliable at low cost.