“FIRE ALARM USING THERMISTOR”

A PROJECT REPORT SUBMITTED

TO

WALCHAND COLLEGE OF ENGINEERING SANGLI

As a Partial Fulfillment

Of

ELECTRONICS CIRCUIT DESIGN

BY

MISS. DHAVALIKAR DEVIKA C. (ROLL NO. 03, W43450) MISS. GULAVANI POOJA S. (ROLL NO. 04, W43455) MISS. KOLEKAR SUPRIYA S. (ROLL NO. 09, W43468) MISS. PATIL AMRUTA S. (ROLL NO. 15, W43484) MISS. RAJPUT TRUPTI R. (ROLL NO. 16, W43490)

(DEPARTMENT OF ELECTRONICS)

Under the guidance of

MR. DHAYGUDE S.B. MR. HAJARE S.S.

DEPARTMENT OF ELECTRONICS ENGINEERING

WALCHAND COLLEGE OF ENGINEERING SANGLI.

NOVEMBER 2009

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DECLARATION

We, the undersigned, hereby declare that the project report

entitled

“FIRE ALARM USING THERMISTOR”

written and submitted by us to Walchand College Of Engineering Sangli,

as a partial fulfillment for ELECTRONICS CIRCUIT DESIGN under the

guidance of Mr. Dhaygude S.B. & Mr. Hajare S.S. is our original work. The

empirical results in this project report are based on the data collected by us.

We understand that any such copying is liable to be punished as the

authorities deem fit.

Date :

Place : SANGLI.

By:

Miss. Dhavalikar Devika C. Miss. Gulavani Pooja S.

Miss. Kolekar Supriya S. Miss. Patil Amruta S.

Miss. Rajput Trupti R.

Forwarded through:

Head, of Department. Dean Academics Electronics Engineering, W.C.E.

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CERTIFICATE

This is to certify that the project report entitled

“FIRE ALARM USING THERMISTOR”

Submitted by

Miss. KOLEKAR SUPRIYA S. (Roll No. 09, W43468)

As a Partial Fulfillment

of

ELECTRONICS CIRCUIT DESIGN

to

WALCHAND COLLEGE OF ENGINEERING SANGLI,

has been completed under my guidance and supervision.

To the best of my knowledge and belief, the matter presented in this project

report is original and has not been submitted elsewhere for any other

purpose.

Date:

Place: SANGLI.

MR.DHAYGUDE S.B. Dept. of Electronics Engineering

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ACKNOWLEDGEMENT

Gratitude is the hardest emotion to express and often one doesn’t find

adequate words to convey all that one feels.

It is our foremost duty to express our deep sense of gratitude and respect to the

guide Mr. Dhaygude S.B. & Mr. Hajare S.S.for his uplifting tendency and inspiring us

for taking up this project work completely successful.

We are also grateful to Dr. B.V.Pawar, Head of Department of Electronics

Engineering for providing all necessary facilities to carry out the project work and whose

encouraging part has been a perpetual source of inspiration.

We are indebted to the library personnel’s for offering all the help on

completing the project work. Last but not the least we are thankful to our colleagues and

those who helped us directly or indirectly throughout this project work.

By:

Miss. Dhavalikar Devika C. Miss. Gulavani Pooja S.

Miss. Kolekar Supriya S. Miss. Patil Amruta S.

Miss. Rajput Trupti R.

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FIRE ALARM USING THERMISTOR

1. INTRODUCTION

Fire causes tremendous destruction in domestic, industrial fields. It is

necessary to reduce this destructions. We have constructed ‘fire alarm’ as a preventive

measure to detect fire on small scale.

1.1 AIM: To construct a FIRE ALARM using thermistor to detect fire or increased

temperature.

1.2 COMPONENTS: IC 555

Thermistor

Resistors

Capacitors

Transistors

Speaker

Diode

Light Emitting Diode

Power Supply

IC 7806

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2. DETAILS OF COMPONENTS:

IC 555:

The IC 555 Timer is a highly stable device for generating accurate time delay or

oscillations. It is available in two package styles, 8-pin circular style TO-99 can or 8-pin

mini DIP or as 14-pin DIP. The 556 timer contains two 555 timers and is a 14-pin DIP.

A single 555 timer can provide time delay ranging from microseconds to hours. The SE

555 is designed for the operating temperature range from -550C to +1250C, while the NE

555 operates over a temperature range of 00C to 700C.

The 555 timer can be used with supply voltage in the range of +5 V to +18 V and

can drive load up to 200mA (source or sink). It is compatible with both TTL and CMOS

logic circuits.

THERMISTOR:

Symbol

A thermistor is a type of resistor whose resistance varies with temperature. The

word is a portmanteau of thermal and resistor. Thermistors are widely used as inrush

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current limiters, temperature sensors, self-resetting overcurrent protectors, and self-

regulating heating elements.

Thermistors differ from resistance temperature detectors (RTD) in that the

material used in a thermistor is generally a ceramic or polymer, while RTDs use pure

metals. The temperature response is also different; RTDs are useful over larger

temperature ranges, while thermistors typically achieve a higher precision within a

limited temperature range [usually -90C to 130C].

RESISTORS :

Symbol

A resistor is a two-terminal electronic component that produces a voltage across

its terminals that is proportional to the electric current through it in accordance with

Ohm's law:

V = IR

Resistors are elements of electrical networks and electronic circuits and are

ubiquitous in most electronic equipment. Practical resistors can be made of various

compounds and films, as well as resistance wire (wire made of a high-resistivity alloy,

such as nickel/chrome).

The primary characteristics of a resistor are the resistance, the tolerance,

maximum working voltage and the power rating. Resistors can be integrated into hybrid

and printed circuits, as well as integrated circuits. Size, and position of leads (or

terminals) are relevant to equipment designers; resistors must be physically large enough

not to overheat when dissipating their power.

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CAPACITORS:

Symbol

A capacitor or condenser is a passive electronic component consisting of a

pair of conductors separated by a dielectric. When a voltage potential difference exists

between the conductors, an electric field is present in the dielectric. This field stores

energy and produces a mechanical force between the plates. The effect is greatest

between wide, flat, parallel, narrowly separated conductors.

An ideal capacitor is characterized by a single constant value, capacitance,

which is measured in farads. This is the ratio of the electric charge on each conductor to

the potential difference between them. In practice, the dielectric between the plates

passes a small amount of leakage current.

Capacitors are widely used in electronic circuits to block the flow of direct

current while allowing alternating current to pass, to filter out interference, to smooth the

output of power supplies, and for many other purposes.

TRANSISTORS:

Symbol

A transistor is a semiconductor device commonly used to amplify or switch

electronic signals. A transistor is made of a solid piece of a semiconductor material, with

at least three terminals for connection to an external circuit. A voltage or current applied

to one pair of the transistor's terminals changes the current flowing through another pair

of terminals. Because the controlled (output) power can be much more than the

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controlling (input) power, the transistor provides amplification of a signal. Some

transistors are packaged individually but most are found in integrated circuits.

The transistor is the fundamental building block of modern electronic devices,

and its presence is ubiquitous in modern electronic systems.

SPEAKER:

Symbol

A loudspeaker (or "speaker") is an electro-acoustic transducer that converts an

electrical signal into sound. The speaker pulses in accordance with the variations of an

electrical signal and causes sound waves to propagate through a medium such as air or

water.

Loudspeakers (and other electro-acoustic transducers) are the most variable

elements in a modern audio system and are usually responsible for most distortion and

audible differences when comparing sound systems.

DIODE:

Symbol

In electronics a diode is a two-terminal electronic component which

conducts electric current asymmetrically or unidirectionally; that is, it conducts current

more easily in one direction than in the opposite direction. The term usually refers to a

semiconductor diode, the most common type today, which is a two-terminal

semiconductor P-N junction.

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The most common function of a diode is to allow an electric current in one

direction (called the forward direction) while blocking current in the opposite direction

(the reverse direction). Thus, the diode can be thought of as an electronic version of a

check valve. This unidirectional behavior is called rectification, and is used to convert

alternating current to direct current, and remove modulation from radio signals in radio

receivers.

POWER SUPPLY:

Symbol

An electrical battery is a combination of one or more electrochemical cells,

used to convert stored chemical energy into electrical energy. Since the invention of the

first Voltaic pile in 1800 by Alessandro Volta, the battery has become a common power

source for many household and industrial applications,

Batteries may be used once and discarded, or recharged for years as in standby

power applications. Miniature cells are used to power devices such as wristwatches and

portable electronic devices; larger batteries provide standby power for telephone

exchanges or computer data centers

IC 7806:

The LM 78XX series of three terminal regulators are available with several

fixed output voltages. These ICs are designed as fixed voltage regulators and with

adequate heat sinking can deliver output currents excess in 1A. In the series, XX

indicates voltage options. These are available in output voltage range of 5, 6, 8, 12,

15, 18, 24 volts with input voltage in the range of 30-35 volts. These ICs have

internal thermal shutdown and short circuit current limiting.10

3. SPECIFICATIONS:

No. Name of Component Notation Value 1. IC 555 IC1

2. Thermistor TH1 10K

3.

Resistor

R1 R2 R3 R4 R5 R6 R7 R8

470Ω 33KΩ 470Ω 560Ω 47KΩ 2.2KΩ 470Ω 470Ω

4.

Capacitors

C1 C2 C3

10µF 0.04µF 0.01µF

5. Transistors T1 T2 T3

BC548 BC558 SL100B

6. Speaker LS1 8Ω, 1W

7. Diode D1 1N4001

8. Light Emitting Diode LED1

9. Power Supply BAT1 9 Volts

10. IC 7806 IC2 6 Volts

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4. CIRCUIT DIAGRAM:

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5. WORKING:

In this fire alarm circuit, a thermistor works as the heat sensor. When

temperature increases, its resistance decreases and vice versa. At normal temperature,

the resistance of the thermistor (TH1) is approximately 10 kilo-ohms, which reduces to

a few ohms as the temperature increases beyond 100°C. The circuit uses readily

available components and can be easily constructed on any general purpose PCB. Timer

IC NE555 (IC1) is wired as an astable multivibrator oscillating in audio frequency band.

Switching transistors T1 and T2 drive multivibrator NE555 (IC1).The output of IC1 is

connected to npn transistor T3, which drives the loudspeaker(LS1) to generate sound.

The frequency of IC1 depends on the values of resistorsR5 and R6 and

capacitor C2.When thermistor TH1 becomes hot, it provides a low-resistance path to

extend positive voltage to the base of transistorT1 via diode D1 and resistor R2.

Capacitor C1 charges up to the positive voltage and increases the ‘on’ time of alarm. The

higher the value of capacitor C1, the higher the forward voltage applied to the base of

transistor T1 (BC548).Since the collector of transistor T1 is connected to the base of

transistor T2, transistor T2 provides positive voltage to reset pin 4 of IC1

(NE555).Resistor R4 is used such that IC1 remains inactive in the absence of positive

voltage. Diode D1 stops discharging of capacitor C1 when the thermistor connected to

the positive supply cools down and provides a high-resistance(10-kilo-ohm) path. It also

stops the conduction of T1. To prevent the thermistor from melting, wrap it up in mica

tape. The circuit works off a 6V-12V regulated power supply. LED1 is used to indicate

that power to the circuit is switched on.

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6. SUMMARY & CONCLUSION:

Using IC 555 and thermistor, we have constructed ‘fire alarm’. A thermistor

works as the heat sensor. Timer IC NE555 (IC1) is wired as an astable multivibrator

oscillating in audio frequency band. The output of IC1 is connected to npn transistor T3,

which drives the loudspeaker(LS1) to generate sound. By using this circuit, we can

prevent hazardous effects of fire.

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7. COSTING

Sr. No. Name of component Quantity Price(Rs.)

1. IC 555 1 15/-

2. Thermistor 1 10/-

3. Resistors 8 8/-

4. Capacitors 3 6/-

5. Transistors 3 14/-

6. Diode 1 2/-

7. Light Emitting Diode 1 1/-

8. Loudspeaker 1 15/-

9. Power Supply 1 20/-

10. IC 7806 1 15/-

11. Connectors 5/-

Total 21 111/-

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