FIRE ALARM using Op-amp Comparator

This report is submitted to

Bundelkhand Institute of Engineering and Technology
For the partial fulfillment for the award of degree of
Bachelor of Technology
in
Electronics and Communication Engineering

By
Deepak Kumar Sharma (2100430310022)
Deepesh Rajpoot (2100430310023)
Devansh Shukla (2100430310024)
Under the supervision of
Dr. Satish Kumar Singh

Department of Electronics and Communication Engineering

Bundelkhand Institute of Engineering & Technology
Jhansi
(An Autonomous Institute)
 Certificate

This is to certify that the work contained in the thesis entitled “Fire Alarm”
submitted by Deepak Kumar Sharma, Deepesh Rajpoot, Devansh Shukla for the
award of the degree of Bachelor of Technology in Electronics and
Communication Engineering to the Bundelkhand Institute of Engineering and
Technology, Jhansi is a record of bonafide research works carried out by him under
my direct supervision and guidance.

I considered that the thesis has reached the standards and fulfilling the
requirements of the rules and regulations relating to the nature of the degree. The
contents embodied in the thesis have not been submitted for the award of any other
degree or diploma in this or any other university.

Dr. Satish Kumar Singh

Professor
ECE Department
BIET Jhansi
 Declaration

We hereby declare that the project work “Fire Alarm” entitled is an authenticated
work carried out by us under the guidance of Dr. Satish Kumar Singh of Electronics
and Communication Engineering Department at Bundelkhand Institute of
Engineering and Technology, Jhansi. Information derived from the other source has
been quoted in the text and a list of refrences has been given.

Deepak Kumar Sharma (2100430310022)

Deepesh Rajpoot (2100430310023)
Devansh Shukla (2100430310024)
 Acknowledgement

We would like to express our gratitude towards Dr. Satish Kumar Singh for his
guidance and constant supervision as well as for providing us necessary information
regarding the project and this report. We feel thankful and express our kind gratitude
towards our Director, Head of Department and all faculty members. We would also
like to express our special gratitude and thanks to our parents for giving us constant
support that improved our performance significantly.
 ABSTRACT

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.

Fire Alarm Circuits and Smoke Sensors are a part of the security systems which help in
detecting or preventing damage. Installing Fire Alarm Systems and Smoke Sensors in
commercial buildings like offices, movie theatres, shopping malls and other public places is
compulsory.

There are many expensive and sophisticated Fire Alarm Circuit in the form of stand-alone
devices, but we have designed five very simple Fire Alarm Circuits using common
components like Thermistor, LM358, Germanium Diode, LM341 and NE555.

This is a very simple alarm circuit using Thermistor, LM358 Operational – Amplifier and a
Buzzer. The primary purpose of fire alarm system is to provide an early warning of fire so
that people can be. evacuated & immediate action can be taken to stop or eliminate of the fire
effect as soon as possible. Alarm can be. triggered by using detectors or by manual call point
(Remotely).
 INTRODUCTION

A fire alarm system has a number of devices working together to detect and warn people
through visual and audio appliances when smoke, fire, carbon monoxide or
other emergencies are present. These alarms may be activated automatically from smoke
detectors, and heat detectors or may also be activated via manual fire alarm activation devices
such as manual call points or pull stations.
Alarms can be either motorized bells or wall mountable sounders or horns. They can also
be speaker strobes which sound an alarm, followed by a voice evacuation message which
warns people inside the building not to use the elevators. Fire alarm sounders can be set to
certain frequencies and different tones including low, medium and high, depending on the
country and manufacturer of the device. Most fire alarm systems in Europe sound like a siren
with alternating frequencies.
Fire alarm electronic devices are known as horns in the United States and Canada, and can be
either continuous or set to different codes. Fire alarm warning devices can also be set to
different volume levels. Manually actuated devices; also known as fire alarm boxes, manual
pull stations, or simply pull stations, break glass stations, and (in Europe) call points. Devices
for manual fire alarm activation are installed to be readily located (near the exits), identified,
and operated.
They are usually actuated by means of physical interaction, such as pulling a lever or
breaking glass. Automatically actuated devices can take many forms intended to respond to
any number of detectable physical changes associated with fire: convicted thermal energy;
heat detector, products of combustion; smoke detector, radiant energy; flame detector,
combustion gases; fire gas detector, and release of extinguishing agents; water-flow detector.
The newest innovations can use cameras and computer algorithms to analyse the visible
effects of fire and movement in applications inappropriate for or hostile to other detection
methods.

COMPONENTS REQUIRED
1. 10k Thermistor 1
2. LM358 Operational Amplifier (Op-Amp) 1
3. 4.7k ohm resistor (1/4 watt) 1
4. 10k ohm potentiometer 1
5. Small Buzzer (5v buzzer) 1
6. Connecting wires
7. Mini bread board
8. 5v power supply
 COMPONENT DISCRIPTION

10K THERMISTOR
An NTC thermistor is a thermally sensitive resistor whose resistance exhibits a large, precise
and predictable decrease as the core temperature of the resistor increases over the operating
temperature range.
The enclosed negative temperature coefficient (NTC) thermistor, p/n 1600-10K, works by
translating temperature into resistance, with resistance decreasing as temperature increases
(hence the 'negative coefficient'). As can be seen be the graph, the resistance of
the thermistor drops very quickly.
Testing a PTC thermistor follows all the same steps as a NTC thermistor. First check, with an
ohmmeter, the thermistor without any heat applied. With a PTC thermistor at room
temperature or below, the thermistor should measure a very low resistance.
Usually, thermistor failure is caused by an open circuit due to mechanical separation between
the resistor element and lead material. This can happen as a result of improper handling,
thermal mismatch, or heat damage. Another common reason thermistors fail is simply aging.
A thermistor is an inexpensive and easily obtainable temperature sensitive resistor, thermistor
working principle is, it's resistance depends upon the temperature. When temperature
changes, the resistance of the thermistor changes in a predictable way. The benefits
of using a thermistor is accuracy and stability.
A thermistor is a resistance thermometer, or a resistor whose resistance is dependent on
temperature. ... This type of thermistor is used the most. A PTC thermistor works a little
differently. When temperature increases, the resistance increases, and when temperature
decreases, resistance decreases. Thermistors do not have continuity, they show resistance.
You should read around 10k Ohms at room temperature. If the igniter is getting 120 volts, but
not glowing, then you have a bad igniter WP33002789.
 LM358 OPERATIONAL AMPLIFIER

LM358 is a dual op-amp IC integrated with two op-amps powered by a common power
supply. The differential input voltage range can be equal to that of power supply voltage. The
LM358 IC is a great, low power and easy to use dual channel op-amp IC.
It is designed and introduced by national semiconductor. It consists of two internally
frequency compensated, high gain, independent op-amps. This IC is designed for specially to
operate from a single power supply over a wide range of voltages. LM358 consists of two
independent, high gain operational amplifiers in one package. Important feature of this IC is
that we do not require independent power supply for working of each comparator for
wide range of power supply.
LM358 can be used as transducer amplifier, DC gain block etc. Ideal Operational
Amplifier or Ideal Op Amp. So, an ideal op amp is defined as, a differential amplifier with
infinite open loop gain, infinite input resistance and zero output resistance. The ideal op
amp has zero input current. An operational amplifier, or op amp, generally comprises a
differential-input stage with high input impedance, an intermediate-gain stage, and a push-
pull output stage with a low output impedance (no greater than 100 Ω).
That is, the output gets fed back to the inverting input through some impedance. An
Operational Amplifier or op-amp is a voltage amplifying device designed to be used with
external feedback components such as resistors and capacitors between its output and input
terminals. It is a high-gain electronic voltage amplifier with a differential input and usually a
single-ended output.

Gain of an inverted op amp = -Rf/Ri

Gain of a non-inverted op amp = 1+(Rf/Ri)
4.7k ohm RESISTOR (1/4 watt)

Every 1,000,000 Ohms is known as a Megohm (Mega = one million), abbreviated to the
capital letter "M". As a couple of examples; a 4,700 Ohm resistor would be written as
either 4.7K or 4K7, and 5,600,000 Ohms would be written as 5.6M or 5M6.

Formula for color coding

R= (AB x 10^C) + D
From the figure
A=4
B=7
C=2
D=5
R = (47 x 10^2) +5%tolerance
R = 4.7x10^3
R = 4.7k = 4k7 ohm with 5% tolerance added to it
10k ohm POTENTIOMETER

A potentiometer is a manually adjustable variable resistor with 3 terminals. Two terminals are
connected to both ends of a resistive element, and the third terminal connects to a sliding
contact, called a wiper, moving over the resistive element. A potentiometer is a manually
adjustable variable resistor with 3 terminals.
Two terminals are connected to both ends of a resistive element, and the third terminal
connects to a sliding contact, called a wiper, moving over the resistive element. The only
difference is the load of the +5V supply, which will be a bit lower with a 10K pot vice a
5K... but it's tiny in either case. A 3 terminal pot used with 3 terminals, is basically just a
voltage divider. As you move the wiper, you increase one resistor in the voltage divider,
while decreasing the resistance in the other So long as the wiper is connected to one leg of
the potentiometer, it
will behave a variable resistor.
The difference between high and low ends of a range—called the span of the circuit—has not
changed, though: a range of 10 kΩ to 20 kΩ has the same 10,000 Ω span as a range of 0 Ω to
10 kΩ. If we wish to shift the span of this rheostat circuit as well, we must change the range
of the potentiometer itself. Potentiometers, trimmers, and rheostats are all variable
resistors. Potentiometers and trimmers are used to create a variable voltage by varying
the voltage between their wiper terminal and two ends. Rheostats are used to vary the amount
of current. Without ground, there is no complete circuit. Without a complete circuit, three
Arduino can't read from the pot. But can't the A0 pin be the (-ve) part of the circuit? Voltage
inputs are what's called high-impedance, meaning they don't sink or source (much) current so
as not to affect the circuit you're measuring.
SMALL BUZZER (5V)

The buzzer consists of an outside case with two pins to attach it to power and ground. When
current is applied to the buzzer it causes the ceramic disk to contract or expand. Changing the
This then causes the surrounding disc to vibrate. That's the sound that you hear. PUI has the
AI-3035, a piezoelectric buzzer rated for 2-5 Volt operation, nominal 3 Volts, and with a
maximum current requirement of 9 mA.
The dimensions are 30 mm diameter, 20.5 mm height excluding leads. To reduce the sound
of the buzzer, measure the resistance of the buzzer, then place a resistor the same value
as the buzzer in series with it, see how much this drops the volume. The more resistance to
quieter the buzzer should be. If the buzzer does not work with half the value try a value lower
in resistance. The purpose of the buzzer test is to test functions of the buzzers installed in a
computer.
Typically, the buzzer test is done by controlling the buzzer to sound a continuous buzzing
sound while a test engineer listens to the buzzer with ears to determine if the buzzer is in
working condition. Sensor-Buzzer is a passive buzzer. Like a magnetic speaker, it needs
voltage with different frequency so that it can make sound accordingly. The pitch becomes
louder when the frequency gets higher. All buzzers with internal oscillators have
polarity because they have small circuit built into them while the buzzers with only Piezo
disks can be operated both ways.
 CONNECTING WIRES
These are used to connect the components in the circuit.
These are used to allow current through them.
These are made up of copper, since copper is a good conductor of electricity.

MINI BREAD BOARD

Breadboards are designed to work with through-hole electronic components. These
components have long metal leads that are designed to be inserted through holes in a printed
circuit board (PCB) that are plated with a thin copper coating, which allows the components'
leads to be soldered to the board.
This board is divided into 4 parts, the 1 st and 4th part slots are connected horizontally whereas
2nd and 3rd part slots are connected vertically.
The mini breadboard has 400 slots.

5V POWER SUPPLY
For this we use a 5v battery
 CIRCUIT DIAGRAM

The circuit diagram of this simple Fire Alarm Project is shown in the following image.

CIRCUIT DESIGN

The design of the Fire Alarm Circuit with Siren Sound is very simple. First, connect the 10
KΩ Potentiometer to the inverting terminal of the LM358 Op - Amp. One end of the POT is
connected to +5V, another end is connected to GND and the wiper terminal is connected to
Pin 2 of Op - Amp.

We will now make a potential divider using 10 K Thermistor and 10 KΩ Resistor. The output
of this potential divider i.e. the junction point is connected to the non – inverting input of the
LM358 Operational Amplifier.

We have chosen a small, 5V buzzer in this project to make the alarm or siren sound. So,
connect the output of the LM358 Op - amp to the 5V Buzzer directly.

Pins 8 and 4 of the LM358 IC i.e. V+ and GND are connected to +5V and GND respectively.
WORKING

We will now see the working of the simple Fire Alarm Circuit. First thing to know is that the
main component in detecting the fire is the 10 K Thermistor. As we mentioned in the
component description, the 10 K Thermistor used here is a NTC type Thermistor. If the
temperature increases, the resistance of the Thermistor decreases.

In case of fire, the temperature increases. This increase in temperature will reduce the resistance
of the 10 K Thermistor. As the resistance decreases, the output of the voltage divider will
increase. Since the output of the voltage divider is given to the non – inverting input of the
LM358 Op – Amp, its value will become more than that of the inverting input. As a result, the
output of the Op – Amp becomes high and it activates the buzzer.

ADVANTAGES

 Low cost
 Reliable
 Fast response
 Circuit can be easily constructed
 High level security
 Easy to design
 Easy to modify
 Low power consumption
 Early warning benefits
 Can easily be installed anywhere in commercial buildings
 Early warning is essential to effective fire safety because fires can occur at any time
any place
 Detection distance
 Speed of response
 Sensitivity
 Range of applications
 Portable

DISADVANTAGES
 False alarm
 Blinded by thick smoke
 Senses near range heat(fire) only
 Uses continuous power supply

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 APPLICATIONS
 Fire alarm in office
 Remote LCD Annunciator
 Fire alarm in hotel rooms
 Fire alarm in schools
 Fire alarm projects

CONCLUTION

Thus, we conclude from this fire alarm is used for safety and emergency
purpose. This is not only use in houses but also in any type of buildings.

REFERENCES
1. https://www.electronicshub.org/simple-fire-alarm-circuit/#Circuit_Design

2. https://www.youtube.com/watch?v=cgsB6VmNGXo

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