This document describes a fire alarm circuit created by two students, Ram Kumar J K and Ratul Vijh, for their Electronics Devices Lab mini project. The fire alarm uses a thermo couple to sense heat and create a voltage drop, which is compared to a reference voltage using an operational amplifier. If the input voltage is greater, the output is triggered and amplified using a BJT, which then triggers an IC555 timer to generate a square wave that powers an LED and buzzer to signal the alarm. Both students contributed equally to the successful completion of the project as an integral team.

1. Electron Devices Lab (EC1009)
Mini Project - Fire Alarm
2014 - 2015 III Semester
Technical Abstract
Group members:
Ram Kumar J K 1041310288
Ratul Vijh 1041310299
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2. Fire Alarm
EC1009 Mini Project
This is a typical Fire alarm circuit. This is a mini
project assignment for Electron Devices Lab (EC1009).
I would like to emphasis on the fact that both
members of the group was an integral part of the
whole process and had our fair share of learning
experience. We worked as a unified, cohesive team,
where our contribution has been accounted for the
successful completion.The Fire alarm is constructed
on a PCB fabrication board.
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3. The Working: The heat is sensed using a Thremo
couple; therefore a voltage drop is created. The
voltage drop is divided into two using a Potential
Divider. The current is then passed into IC2
(operational Amplifier). In that IC, the reference
voltage is set as Vref. Its function is to compare the
input voltage and the reference voltage. If the input
voltage is lesser than the reference voltage, the
output is not drawn. But if the input voltage is greater
than the reference voltage, the IC conducts and the
output is obtained. After that, the output voltage
passes through a Bipolar Junction Transistor (BJT)
which amplifies the output (Amplification action). The
amplification is required to trigger the buzzer. Then it
passes into 8-Pin IC555 Timer. The input enters the IC
by input terminal 2 (trigger). The input analogous
signal is converted in a digital square wave signal.
Then we get an output from terminal 3. The voltage
then divides into two, one to the BJT and another to
the LED. The function of BJT is to perform switch
action. Then the buzzer gives an alternating ‘BEEP’
sound. This circuit works in 9V DC supply, which is
given by a standard 9V battery.
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4. Circuit (rough) :
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5. Teacher Remarks / Comments:
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