East West University
Project
Semester: Spring 2025
Course Title: Electronic Circuits Course Code: CSE251
Sec: 04
Project
Expt Name: A simple fire Alarms
Group No: 05
Group Members:
Student Name Student Id
MD.F.K.Murad 2023-1-60-023
Md Al Fahim Fuyad 2023-1-60-066
Md.Tanvir Shafaf 2023-1-60-072
Toyabur Rhaman 2023-1-60-065
Submitted by-
Md Al Fahim Fuyad
ID: 2023-1-60-066
Submitted to-
Dr. Sarwar Jahan
Associate Professor
Department of Computer Science & Engineering
East West University
Date of Submission: 12th May 2025
Experiment Title: A simple fire Alarms
Objective:
The objective of this experiment is to design and implement a simple fire alarm circuit using a BJT
(BC547), a fire detection sensor (IR LED), and a 5V active buzzer. The goal is to understand how
a transistor can function as a switch in a common emitter configuration to control an output device
(buzzer) based on the input from a fire detection system.
Introduction:
This experiment aims to design and implement a simple fire alarm system using a Bipolar Junction
Transistor (BJT), a fire detector (IR LED), and a buzzer. The system is built on a common emitter
follower configuration to amplify the signal from the fire detector and drive an active buzzer to
alert in case of fire detection. The primary goal is to understand how a BJT can be used as a switch
and signal amplifier in practical applications.
Circuit Diagram:
Design Details:
Working Principle
• The fire detector uses an IR LED and photodiode to detect flame or smoke (which blocks
or reflects IR light).
• When fire is detected, the signal is sent to the base of a BC547 transistor.
• The BC547 operates as a switch in a common emitter configuration.
• When turned ON, it allows current to flow from the collector to emitter, activating a 5V
buzzer.
• A diode is connected across the buzzer to prevent back current damage.
Component List:
• 9V Battery (Power Supply)
• BC547 NPN Transistor
• 5V Active Buzzer
• IR LED & Photodiode (as fire detector)
• 220Ω Resistor (Base resistor)
• LED (Indicator)
• Diode (e.g., 1N4007)
• Breadboard and Jumper Wires
Configuration:
• Transistor Mode: Common emitter
• Input: Fire detector (IR module)
• Output: Buzzer
• Control: BJT base current determines buzzer activation
Voltage & Current Details:
• Transistor base-emitter threshold ≈ 0.7V
• Buzzer current ≈ 30-50mA (well within BC547 collector current capacity)
• Base current ≈ (9V - 0.7V) / 220Ω ≈ 37mA
Simulation Results:
Expected Behavior:
• When no fire is detected, the photodiode receives IR light, and the transistor remains OFF.
• When fire/smoke blocks IR light, the voltage at the transistor base increases.
• The transistor switches ON, and the buzzer sounds.
Conclusion:
This project shows how to make a simple fire alarm using a BJT, IR sensor, and buzzer. When the
sensor detects fire or smoke, the transistor turns on and the buzzer makes a sound. It is a low-cost
and easy way to alert people in case of fire.
