“FIRE ALARM”A Minor Project
Submitted in partial fulfillment of the requirement for the award of Degree of Bachelor of Engineering in Electronics & Communication
Submitted to
RAJIV GANDHI PROUDYOGIKI VISHWAVIDHYALAYA BHOPAL (M.P.)
Submitted By
Under the supervision of
Prof.
Department of Electronics and Communication Engineering
Technocrats Institute of Technology, Bhopal
Technocrats Institute of Technology, Bhopal
Electronics and Communication Engineering
CERTIFICATE
This is to certify that the work embodies in this Minor Project entitled “Fire Alarm” being
submitted by “Varun Shrivastava” (0111EC091113) in partial fulfillment of the requirement
for the award of “Bachelor of Engineering in Electronics & Communication” to Rajiv
Gandhi Proudyogiki Vishwavidyalaya, Bhopal (M.P.) during the academic year 2012 is a record
of bonafide piece of work, carried out by him under my supervision and guidance in the
“Department of Electronics & Communication Engineering”, Technocrats Institute of
Technology, Bhopal.
Approved and supervised by
Prof. Vikas Gupta Prof. Roop Singh
HOD (ECE) Guide Asst. Prof. (ECE)
TIT,Bhopal TIT,Bhopal
Technocrats Institute of Technology, Bhopal
Electronics and Communication Engineering
DECLARATION
This is to certify that the project entitled “Fire Alarm” being submitted by
1 Varun Shrivastava
2 Swapnil Khaparde
3 Vikash Kumar
4 Vikram Jyoti Das
5 Sheetal Garg
In partial fulfillment of the requirement for the award of “Bachelor of Engineering in Electronics & Communication” to Rajiv Gandhi Proudyogiki Vishwavidyalaya, Bhopal (M.P.) during the academic year 2012 is a record of bonafide piece of work, carried out /developed in the institute itself. This is the original work and has not been carried at side the institute and not purchase readymade from other agencies.
Students Name Roll Nos. Signature
1 Varun Shrivastava 0111ec091113
2 Swapnil Khaparde 0111ec091109
3 Vikash Kumar 0111ec091114
4 Vikram Jyoti Das 0111ec091116
5 Sheetal Garg
Above facts verified :
Sign Sign
Prof Ashish Singh Prof Roop Singh
Project Incharge Guide (ECE)
ACKNOWLEDGEMENT
Indeed it is a matter of great felicity and privilege for me to take an opportunity to work under
the guidance of Prof. Roop Singh, Asst. Professor, Electronics & Communication
Engineering, TIT, Bhopal who constantly supported and encouraged at every step of
dissertation.
I would like to express my thanks to Dr. C.L. Saxena, Director TIT, Bhopal, for his highly
supportive attitude.
I would also like to acknowledge Dr. S. C. Shrivastava, Director P.G. Courses, TIT, Bhopal
for his great cooperation and support.
I acknowledge my gratitude and regards to Prof. Vikas Gupta who were kind enough to share
the precious time as well as for the keen interest and continuous support extended.
I am thankful to all the faculty members of Department of Electronics & Communication
Engineering, TIT, Bhopal, who helped me in one or other way during the course of my study.
And finally all glory to my Parents, Brother without their grace this work was merely a dream.
Place: TIT, Bhopal. Varun Shrivastava
Date: 22/04/2012 Enroll. No.0111EC091113
CONTENTS
ABSTRACT i
List of Figure iii
List of Table v
CHAPTER 1-INTRODUCTION 1-10
1.1 Principle of working
CHAPTER 2-Construction and working of project 11-30
2.1 Circuit block diagram
2.2 Circuit diagram
2.3 Component description
CHAPTER 3- Programming/ component description 31-60
3.1 Printed circuit board
3.2 Layout design
3.3 etching process
3.4 component assembly
3.5 soldering
3.6 PCB Layout
3.7 Testing and Verification
CHAPTER 4- Result and conclusion 61-65
4.1 conclusion
4.2 Application
CHAPTER 5- Bibliography
ABSTRACT
Here’s a Fire Alarm that informs you regarding any fire accident in its vicinity.
It has an IC NE555, wired as an astable multivibrator oscillating in audio frequency band.
There is also a thermistor which acts as a sensor, in the fire alarm.
The circuit also has an 8 ohms, 1 watt speaker for the notification of the fire.
CHAPTER -1
Principle of 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 resistors R5 and R6 and capacitor C2.
When thermistor TH1 becomes hot, it provides a low-resistance path to extend positive voltage
to the base of transistor T1 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.
CHAPTER-2
Circuit Block Diagram
Circuit Diagram
Component Description
About NE555 Timer
The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and
multivibrator applications.
The IC was designed by Hans R. Camenzind in 1970 and brought to market in 1971 by
Signetics (later acquired by Philips).
The original name was the SE555 (metal can)/NE555 (plastic DIP) and the part was
described as "The IC Time Machine".
It has been claimed that the 555 gets its name from the three 5 kΩ resistors used in
typical early implementations, but Hans Camenzind has stated that the number was
arbitrary.
The part is still in wide use, thanks to its ease of use, low price and good stability. As of
2003, it is estimated that 1 billion units are manufactured every year.
IC NE555 Operating Modes
Monostable mode- In this mode, the 555 functions as a "one-shot". Applications include timers,
missing pulse detection, bouncefree switches, touch switches, frequency divider, capacitance
measurement, pulse-width modulation (PWM) etc.
Astable – Free running mode: the 555 can operate as an oscillator. Uses include LED and lamp
flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position
modulation, etc.
Bistable mode or Schmitt trigger- The 555 can operate as a flip-flop, if the DIS pin is not
connected and no capacitor is used. Uses include bouncefree latched switches, etc.
Fig 1.
Pin Name Purpose
1 GND Ground, low level (0 V)
2 TRIG OUT rises, and interval starts, when this input falls below 1/3 VCC.
3 OUT This output is driven to + V CC or GND.
4 RESET A timing interval may be interrupted by driving this input to GND.
5 CTRL "Control" access to the internal voltage divider (by default, 2/3 VCC).
6 THR The interval ends when the voltage at THR is greater than at CTRL.
7 DIS Open collector output; may discharge a capacitor between intervals.
8 V+, VCC Positive supply voltage is usually between 3 and 15 V.
IC NE555 in Astable Multivibrator Mode
Thermistor
A thermistor is a type of resistor whose resistance varies significantly with temperature, more so than in standard resistors. The word is aportmanteau of thermal and resistor. Thermistors are widely used as inrush 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, typically −90 °C to 130 °C.[1]
Basic Operation of Thermistor
Assuming, as a first-order approximation, that the relationship between resistance and temperature is linear, then:
Where,
= change in resistance
= change in temperature
= first-order temperature coefficient of resistance
Thermistors can be classified into two types, depending on the sign of . If is positive, the
resistance increases with increasing temperature, and the device is called a positive temperature
coefficient (PTC) thermistor, or posistor. If is negative, the resistance decreases with
increasing temperature, and the device is called a negative temperature coefficient (NTC)
thermistor. Resistors that are not thermistors are designed to have a as close to zero as possible,
so that their resistance remains nearly constant over a wide temperature range.
Thermistor symbol
ABOUT LS1 SPEAKER
A speaker is an electro acoustic transducer that produces sound in response
to an electrical audio signal input.
To adequately reproduce a wide range of frequencies, most loudspeaker systems employ
more than one driver, particularly for higher sound pressure level or maximum accuracy.
A loudspeaker system with n separate frequency bands is described as "n-way speakers":
a two-way system will have a woofer and a tweeter; a three-way system employs a
woofer, a mid-range, and a tweeter.
The most common type of driver uses a light weight diaphragm, or cone, connected to a
rigid basket, or frame, via a flexible suspension that constrains a coil of fine wire to move
axially through a cylindrical magnetic gap.
ABOUT CAPACITORS
Capacitors are components that are used to store an electrical charge and are used in
timer circuits.
A capacitor may be used with a resistor to produce a timer. Sometimes capacitors are
used to smooth a current in a circuit as they can prevent false triggering of other
components such as relays.
When power is supplied to a circuit that includes a capacitor - the capacitor charges up.
When power is turned off the capacitor discharges its electrical charge slowly.
ABOUT RESISTORS
Resistors determine the flow of current in an electrical circuit.
Where there is high resistance in a circuit the flow of current is small, where the
resistance is low the flow of current is large.
Resistors are used for regulating current and they resist the current flow and the extent to
which they do this is measured in ohms (Ω). Resistors are found in almost every
electronic circuit.
The most common type of resistor consists of a small ceramic (clay) tube covered
partially by a conducting carbon film. The composition of the carbon determines how
much current can pass through.
About Transistors
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed 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 higher than the controlling (input) power, a transistor can amplify a signal. Today, some transistors are packaged individually, but many more are found embedded in integrated circuits.
The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its development in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.
Transistor as an amplifier
Amplifier circuit, common-emitter configuration.
The common-emitter amplifier is designed so that a small change in voltage (Vin) changes the small current through the base of the transistor; the transistor's current amplification combined with the properties of the circuit mean that small swings in Vin produce large changes in Vout.
.
CHAPTER-3
ABOUT PCB LAYOUT
The connections on the PCB should be identical to the circuit diagram, but while the
circuit diagram is arranged to be readable, the PCB layout is arranged to be functional, so
there is rarely any visible correlation between the circuit diagram and the layout.
PCB layout can be performed manually (using CAD) or in combination with an
Autorouter. The best results are usually still achieved using atleast some manual routing
- simply because the design engineer has a far better judgement of how to arrange
circuitry.
Different methods of PCB construction-
Conventional
A rigid PCB (usually of thickness 1.6mm), with wire-leaded components mounted on
only one side of the PCB, with all the leads through holes, soldered and clipped.
Conventional circuitry is generally easier to debug and repair than Surface mount.
Surface Mount Technology (SMT) or devices (SMD)
A PCB with tag-leaded components soldered flush to PCB pads. Holes are still needed on
the PCB, but not where the component leads are attached. Surface mount circuitry is
generally smaller than conventional. Surface mount is generally more suited to automated
assembly than conventional.
Surface mount & conventional mix
In practice, most boards are a mix of surface mount and conventional components. This
can have its disadvantages as the two technologies require different methods of insertion
and soldering.
Double sided Laminate
A bare PCB laminate having tracks on both sides, normally with PTH holes connecting
circuitry on the two sides together.
Double sided Component Assembly
Mounting components on both sides of the PCB. Normally only surface mount circuitry
would be mounted on both sides of a PCB, but some conventional components (such as
LEDs) may be mounted on the reverse of a PCB to suit the enclosure design.
Multi-layer
A PCB Laminate may be manufactured with more than two layers of copper tracks by
using a sandwich construction. The cost of the laminate reflects the number of layers. The
extra layers may be used to route more complicated circuitry, and/or distribute the power
supply more effectively.
Gold plated
Certain areas on a PCB may be gold plated for use as contact pads or
as a ROHS-compliant board finish. If a thicker gold plating is
required (for instance a quality 50um contact) an electrolytic process
is needed. Normally this is limited to pads on the edge of a PCB, as an
electrolytic plating bar must be attached to the pads, and then removed part way through
the PCB manufacturing process. Gold plating normally needs a nickel underplate or the
Gold quickly disappears through migration effects into the underlying copper.
Immersion Silver plating
A ROHS-compliant board finish that is a cost effective alternative to Gold
ROHS Compliance
Simple definition: Getting rid of the Lead in PCBs and components which poisons
groundwater when it leaches out of discarded boards put in landfill waste dumps.
Actually, lead is not the only substance covered, but it is the main one. Frankly it would
also help if people stopped throwing away so much electronics, and that would be helped
if boards were made to last.
Flexible PCB
A technique used extensively with membrane keyboards, combination connector/circuit
boards, and circuit boards to fit in awkward shapes - e.g. cameras.
Chip On Board (COB)
Where the IC die is attached direct to a PCB, and bond out wires from the IC connect
directly to PCB lands. The chip is then covered with a black blob of epoxy. A technique
used mostly with very high volume, cost sensitive applications, e.g. musical greeting
cards.
Phenolic PCB
As distinct from Fibreglass, Phenolic is a cheaper PCB laminate material.
Daughterboard
A circuit board mounted to another circuit board - such as a plug in card.
ABOUT PCB DESIGN
Printed circuit board (PCB) is a component made of one or more layers of insulating
material with electrical conductors.
The insulator is typically made on the base of fiber reinforced resins, ceramics, plastic,
or some other dielectric materials. During manufacturing, the portions of conductors that
are not needed are etched off, leaving printed circuits that connect electronic components.
The width of the circuit conductors should be chosen based on maximum temperature
rise at the rated current and an acceptable impedance. The spacing between the PC traces
is determined by peak working voltage, the coating, location of the circuit, and the
product application.
Depending on the application and product end use, other standards may also apply. For
example, for mains-powered or battery-powered information technology equipment, the
creepage and clearance requirements of IEC/UL 60950-1 shall take precedence over IPC.
Auto placement may be done for most parts of control circuits, but power, ground and
high di/dt circuits should be routed by hand.
ABOUT ETCHING PROCESS
Chemical etching is done with ferric chloride, ammonium persulfate, or sometimes
hydrochloric acid. For PTH (plated-through holes), additional steps of electroless
deposition are done after the holes are drilled, then copper is electroplated to build up the
thickness, the boards are screened, and plated with tin/lead. The tin/lead becomes the
resist leaving the bare copper to be etched away.
The simplest method, used for small-scale production and often by hobbyists, is
immersion etching, in which the board is submerged in etching solution such as ferric
chloride. Compared with methods used for mass production, the etching time is long.
Heat and agitation can be applied to the bath to speed the etching rate. In bubble etching,
air is passed through the etchant bath to agitate the solution and speed up etching. Splash
etching uses a motor-driven paddle to splash boards with etchant; the process has become
commercially obsolete since it is not as fast as spray etching. In spray etching, the etchant
solution is distributed over the boards by nozzles, and recirculated by pumps. Adjustment
of the nozzle pattern, flow rate, temperature, and etchant composition gives predictable
control of etching rates and high production rates.
As more copper is consumed from the boards, the etchant becomes saturated and less
effective; different etchants have different capacities for copper, with some as high as 150
grams of copper per litre of solution. In commercial use, etchants can be regenerated to
restore their activity, and the dissolved copper recovered and sold. Small-scale etching
requires attention to disposal of used etchant, which is corrosive and toxic due to its metal
content.
The etchant removes copper on all surfaces exposed by the resist. "Undercut" occurs
when etchant attacks the thin edge of copper under the resist; this can reduce conductor
widths and cause open-circuits. Careful control of etch time is required to prevent
undercut. Where metallic plating is used as a resist, it can "overhang" which can cause
short-circuits between adjacent traces when closely spaced. Overhang can be removed by
wire-brushing the board after etching.
ABOUT SOLDERING TECHNIQUE
Soldering is the only permanent way to ‘fix’ components to a circuit. However, soldering
requires a lot of practice as it is easy to ‘destroy’ many hours preparation and design
work by poor soldering. If you follow the guidelines below you have a good chance of
success.
1. Use a soldering iron in good condition. Inspect the tip to make sure that it is not past good
operation. If it looks in bad condition it will not help you solder a good joint. The shape of the tip
may vary from one soldering iron to the next but generally they should look clean and not burnt.
2. A PCB eraser is used to remove any film from the tracks. This must be done carefully
because the film will prevent good soldering of the components to the PCB. The tracks can be
checked using a magnifying glass. If there are gaps in the tracks, sometimes they can be repaired
using wire but usually a new PCB has to be etched.
3. Place the PCB, with its components in position, in the bull clip. This will steady the PCB
when you try to use the soldering iron.
4. The heated soldering iron should then be placed in contact with the track and the component
and allowed to heat them up. Once they are heated the solder can be applied. The solder should
flow through and around the component and the track
5. Having completed soldering the circuit the extended legs on the components need to be
trimmed using wire clippers. The circuit is now ready for testing.
PCB LAYOUT
Testing and Verification
The Fire alarm has been tested by bringing a flamed matchstick close to the thermistor. The
thermistor detected the heat and lowered its resistance. The current then amplified by the set of
transistors was then applied to the port 4. Then the square wave output of the NE555 timer from
the port 3 is amplified by the transistor SLB100B, and then applied to the speaker, which emits a
sound which acts as a notification for the users of the fire.
Since the fire alarm detected the change in temperature and alarmed the user nearby regarding
the danger, hence the fire alarm has been verified for usage in any kind of surrounding requiring
fire detection.
CHAPTER-4
Conclusion
The fire alarm has been verified and can be suitably used in different locations whether domestic
or commercial. The alarm successfully detects the rise in temperature and creates a sound to
notify the people in its vicinity.
