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Design & Implementation of Fire Alarm Circuit
Technical Report · March 2012
DOI: 10.13140/2.1.1126.9440
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DESIGN & IMPLEMENTATION OF FIRE ALARM
CIRCUIT
BY
Asok Bala
ID: ECE-070200074
Md. Najmul Hossain
ID: ECE-070300082
Supervised By
Ashraful Arefin
Senior Lecturer, Department of EEE
This Project submitted in partial fulfillment of the requirements for the Degree of
Bachelor of Science in Electronics and Communication Engineering
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
NORTHERN UNIVERSITY BANGLADESH
March 2012
DESIGN & IMPLEMENTATION OF FIRE ALARM
CIRCUIT
BY
Asok Bala
ID:ECE-070200074
Md. Najmul Hossain
ID:ECE-070300082
Supervised By
Ashraful Arefin
Senior Lecturer, Department of EEE
This Project submitted in partial fulfillment of the requirements for the Degree of
Bachelor of Science in Electronics and Communication Engineering
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
NORTHERN UNIVERSITY BANGLADESH
March 2012
APPROVAL
The project report on “Design and Implementation of Fire Alarm Circuit” submitted by Asok
Bala, ID: ECE-070200074 and Md. Najmul Hossain, ID: ECE-070300082, to the department of
Electronics and Communication Engineering from Northern University Bangladesh has been
accepted as satisfactory for the partial fulfillment of the requirements for the degree of Bachelor
of Science in Electronics and Communication Engineering and approved as to its style and
contents. This project report has been approved by the following members of Project/Thesis
defense committee.
Board of Examiners:
1. Engr. Md. Badiuzzaman
…………………………
(Head of Department EEE&ECE)
2. Ashraful Arefin
(Supervisor)
.…… ………………….
3. Md. Abdul Hamid
…………………………
(Lecturer)
Prof. Dr. Md. Nurul Islam
Dean
Faculty of science & engineering
………………………………
Northern University Bangladesh
(i)
DECLARATION
We hereby declare that the work presented in this project is the outcome of the investigation
performed by us under the supervisor of Ashraful Arefin, Senior Lecturer, Department of
Electrical & Electronics Engineering, Northern University Bangladesh. We clearly declare that
no part of this project has been submitted else-where for the award of any degree or diploma and
is solely edited to us.
Countersigned
Signature
.................................
(Ashraful Arefin)
……………………..
(Asok Bala)
.………………………
(Md. Najmul Hossain)
(ii)
ABSTRACT
Design and Implementation of Fire Alarm Circuit combinational digital circuit which can
perform an alarm by the voice signal. In this project detects smoke using Light Dependent
Resistor & Light Emitting Diode. Normally speaker no alarm but when smoke detect then
alarming. The project is based upon a major approach to control and security home, office, shop,
market and University etc. For fire alarm main circuit design to using (ISIS) software and circuit
finally implemented on bread board.
(iii)
ACKNOWLEGDEMENT
First of all we would like to thank of Creator. Today we are successful in completing our Project
work with such ease because He gives us the ability, chance and co-operating supervisor. We
would like to thank all of our teachers for their help to that made this project successful. After
that we are relay thank to our head of Department Engr. Md. Badiuzzaman and our supervisor
Ashraful Arefin. Our supervisor not only gives us time but also his proper guidance and valuable
advice. He was always with us whenever we faced difficulties. These comments and guidance
helped us a lot to prepare our project report. We are also thankful to all of our teachers who
helped us a lot in a number of ways by providing various resources and moral supports and our
classmates and friends also who supplied a lot of information to make this accomplished. Finally
we are grateful to our family who are always with us in every step of our life.
NUB
Authors
March 2012
(iv)
Table of Contents
APPROVAL……………………………………………………………………………………...(i)
DECLARATION………………………………………………………………………………..(ii)
ABSTRACT…………………………………………………………………………………….(iii)
ACKNOWLEGDEMENT……………………………………………………………………...(iv)
Table of Contents………………………………………………………………………….(v,vi,vii)
List of Figures…………………………………………………………………….......……….(viii)
Chapter-01-Introduction…………………………………………………………………….…….1
1.1 What is smoke detector………………………………………………..…………………2
1.2 Types of Smoke Detector……...………………………………………………..……….2
1.3 Importance of Smoke Detectors…………...................................................…………….2
1.4 How Smoke Detectors Work……………………………………………………….……2
1.5 Organization of the Project………………………………………………………….…...3
Chapter-02-Optical Smoke Detector…………………………………..……….………………….4
2.1 How optical smoke detectors work………………………………..……….…………...5
Chapter-03-Circuit Elements………………………………………………………………….......7
3.1LightDependentResistor………………………….....……………………………………8
3.2 Example of a light sensor circuit…………………..…………………………………..10
(v)
3.3 LM7809 FIXED VOLTAGE REGULATOR (POSITIVE)…………...……………….11
3.4 3-TERMINAL 1A POSITIVE VOLTAGE REGULATORS………………………….12
3.5 FEATURES…………………………………….……………………...……………….12
3.6 Block Diagram……..………………………………………...……….….…………….13
3.7 Instructions of 7809 IC……….…………………………………...…...……………….13
3.8 Transistor BC547……………..…………………………………………………………16
3.9 Pin Diagram………………………………………..…....………………………………17
3.10 Transistor C1815Y…………………..…….……………..…………………………….18
3.11 Description……………………………...….….……………………………………….18
3.12 Applications…………………………………………..……………….……………….18
3.13 Features……………………..……………………………………..…………….……..19
3.14 Basics of measuring resistance……………………………..…………….……………20
3.15 How to measure resistance with an analogue multimeter……..…………...…………..20
3.16 How to measure resistance with an digital multimeter, DMM…………....…………...23
3.17 General precautions when measuring resistance……………………...….……………24
3.18 How Light Emitting Diodes Work…………………………………….……...………..27
3.19 How Speakers Work……...……………………………………………….………….29
3.20 How Capacitors Work……………………………………………………….…………30
Chapter-04-Power Supply & Fire Alarm Circuit …………………………………….………….32
(vi)
4.1 Power supply for the circuit….…………………………………….…...……………….33
4.2 Fire alarm circuit……………...……………………………………..…………………..34
4.3 Figure of Capacitor .01µf,Transformer 230-12V, Transistor BC547……….….……….35
4.4 Figure of Transistor C1815Y, Power supply with fire alarm circuit,7809IC,Capacitor
1000µf…………………………………………………………………………….……………...36
Chapter-05-Conclusion & Future Plan…………………………………………………………..37
5.1 Conclusion…..………………………………………………………………………….38
5.2 Future Plan…..………………………………………………………………………….38
References…………………..……………………………………………………………………39
(vii)
List of Figures
Figure Optical smoke detector work………………………………………………………………5
Figure LDR………………………..……………………………………..…….………………….8
Figure LDR works………………….…………………………………………...….……………10
Figure LM7809 Voltage Regulator……………………………………………………...……….11
Figure 7809 Pins…………………………………………………………………………………14
Figure 7809 Circuit Diagram…………………………………………………………………….15
Figure Transistor BC547…………………………………………………...…………………….16
Figure Transistor C115Y………...………………………………………………………………18
Figure LED………………………………………………………………………………………27
Figure Speakers…………………………………………………………………………………..29
Figure 9v Power Supply………………………………………………………………………….33
Figure Fire Alarm Circuit………………………………………………………………………..34
Figure Capacitor .01µf, Transformer 230-12V, TransistorBC547…..…………………………..35
Figure Transistor C1815Y, Power supply with fire alarm circuit, 7809IC, Capacitor 1000µf…36
(viii)
Chapter -01
Introduction
1
1.1 What is smoke detector:
A smoke detector is a device that detects smoke, typically as an indicator of fire. Commercial,
industrial, and mass residential devices issue a signal to a fire alarm system, while household
detectors, known as smoke alarms, generally issue a local audible or visual alarm from the
detector itself.
1.2 Types of Smoke Detector:
There are two main kinds of smoke detectors. Such as(i)
Photoelectric smoke detectors and
(ii)
Ionization smoke detectors.
1.3 Importance of Smoke Detectors:
A smoke detector's purpose is a simple one, to give you ample notification in case of a fire in
your house. Without a smoke detector, by the time you realize that there is a fire, your house
could be so badly engulfed that you cannot find a safe exit or the smoke can be so overwhelming
that you suffocate trying to get out.
The National Fire Protection Association reports that while 75 percent of homes have at least one
working smoke alarm, between 2003 and 2006, 66 percent of fire deaths happened in homes with
no working smoke alarm.
1.4 How Smoke Detectors Work:
Photoelectric sensors generate a beam of light focused on a light-sensitive cell, enclosed in the
alarm. If the light beam is interrupted from smoke entering the detector, the alarm goes off.
Ionization sensors work by having a small piece of radioactive material create an electric current
between two plates. If smoke or hot air enters the chamber, the reaction is changed and the
current is disrupted, causing the alarm to go off. Photoelectric smoke detectors work best with
slow, smoky fires and ionization detectors work best with quick, hot fires.
2
1.5 Organization of The Project:
In Chapter 02, we have discussed about on Optical Smoke Detector using Photoelectric sensor.In
Chapter-03, we have discussed about on Light Dependent Resistor, LM7809IC Positive Voltage
Regulator, Transistor BC547, C1815Y & its Pin Diagram, Resistance, Light Emitting Diode
(Led), Capacitor, Speaker and their works.
In Chapter-04, we have discussed about on Power Supply and Fire Alarm Circuit and how it
works and
In Chapter-05, we have discussed about on Conclusion and Future Plan.
3
Chapter-02
Optical Smoke Detector
4
2.1 How optical smoke detectors works:
The answer to that question is really two answers, because there are two quite different kinds of
smoke detectors. One is a kind of electronic eye; the other's a sort of electronic nose. The eye
type of detector is more properly called an optical smoke detector (or photocell smoke detector)
and it works a bit like Tom Cruise in Mission Impossible. Remember the scene when Tom
dangles from the ceiling trying to avoid all those light-detecting burglar beams? An optical
smoke detector is just like that inside. Let's take a look.
The detector must be screwed to your ceiling because that's where smoke heads for when
something starts to burn. Fire generates hot gases and because these are less dense (thinner—or
weigh less per unit of volume) than ordinary air they rise upward, swirling tiny smoke particles
up too.
The detector is designed with a large opening in the bottom (1), shown upper right in our top
photo, that leads to the detection chamber up above.
5
An invisible, infrared light beam, similar to the ones that Tom Cruise dodged, shoots across the
chamber from a light-emitting diode or LED (2) to a photocell (3). The photocell is an electronic
light detector that generates electricity for as long as light falls on it. Normally, when there is no
smoke about, the light beam shoots constantly between the LED and the detector. An electronic
circuit (4) detects that all is well and nothing happens. The alarm (5) remains silent.
But if a fire breaks out, smoke enters the chamber (6) and interrupts the beam (7). Because no
light is falling on the photocell, it does not generate an electric current anymore. The circuit spots
this straight away (8), realizes something's amiss, and triggers the shrill and nasty alarm (9) that
wakes you up and saves your life.
6
Chapter-03
Circuit Elements
7
3.1 Light Dependent Resistor:
LDRs or Light Dependent Resistors are very useful especially in light/dark sensor circuits.
Normally the resistance of an LDR is very high, sometimes as high as 1000 000 ohms, but
when they are illuminated with light resistance drops dramatically.
8
The animation opposite shows that when the torch is turned on, the resistance of the LDR
falls, allowing current to pass through it. Circuit Wizard software has been used to display, the
range of values of a ORP12, LDR .
When a light level of 1000 lux (bright light) is directed towards it, the resistance is
400(ohms).
When a light level of 10 lux (very low light level) is directed towards it, the resistance has
risen dramatically to 10.43M (10430000 ohms).
9
3.2 Example of a light sensor circuit:
When the light level is low the resistance of the LDR is high. This prevents current from
flowing to the base of the transistors.Consequently the LED does not light. However, when
light shines onto the LDR its resistance falls and current flows into the base of the first
transistor and then the second transistor. The LED lights.
The preset resistor can be turned up or down to increase or decrease resistance, in this way it
can make the circuit more or less sensitive.
10
3.3 LM78XX (KA78XX, MC78XX) FIXED
VOLTAGE REGULATOR (POSITIVE):
(LM7809 Voltage Regulator)
11
3.4 3-TERMINAL 1A
POSITIVE VOLTAGE
REGULATORS:
The LM78XX series of three-terminal positive regulators are available in the TO-220/D-PAK
package and with several fixed output voltages, making them useful in a wide range of
applications. Each type employs internal current limiting, thermal shut-down and safe area
protection, making it essentially indestructible.
If adequate heat sinking is provided, they can Deliver over 1A output current. Although designed
primarily as fixed voltage regulators, these devices can be used with external components to
obtain adjustable voltages and currents.
3.5 FEATURES:
· Output Current up to 1A
· Output Voltages of 5, 6, 8, 9, 10, 11, 12, 15, 18, 24V
· Thermal Overload Protection
· Short Circuit Protection
· Output Transistor SOA Protection
12
3.6 Block Diagram:
3.7 Instructions of 7809 IC:
7809 is a voltage regulator integrated circuit (IC) which is widely used in electronic circuits.
Voltage regulator circuit can be manually built using parts available in the market but it will take
a lot of time to assemble those parts on a PCB. Secondly, the cost of those parts is almost equal
to the price of 7809 itself so professionals usually prefer to use 7809 IC instead of making a
voltage regulator circuit from scratch. Before you start using 7809, you will need to know about
the pin structure of IC 7809. Apparently, it looks like a transistor. It has three pins. For a better
understanding, I have given an image of 7809 bellow. Please take a look.
You can easily see the V in and V out pins as well as the ground pin. It is really easy to use 7809
for voltage regulation purposes. I have also included a circuit diagram of 7809 so that you may
learn how to use it in a circuit diagram.
13
It is wise to use two .1uF capacitors on both input and output sides to filter any ripple or
distortion in voltage but it is not necessary. In the image, you can see that 12V are being supplied
on the input side of 7809 but the out put side of 7809 is outputting Regulated 9V. As long as the
input voltage remains above 9V, output voltage of 7809 will remain smooth and regulated.
Please note that input voltage of 7809 can be up to 23V but under my experience, it is wise to
avoid input over 15V. 7809 is claimed to output 9V and almost 1.5A Current but again, I have
experienced that we should not put a load over 9V and 1A on it.
Since we are using it in power supply, the transfer of power will result in heat output. We will
need to use a heat sink with 7809 otherwise this heat can damage it. It is advised to use a 1A fuse
on the output side of 7809 and a 1.5A fuse on the input side of 7809 to avoid damage in case of
short circuit.
14
15
3.8 Transistor BC547:
BC547 is an NPN bi-polar junction transistor. A transistor, stands for transfer of resistance, is
commonly used to amplify
current. A small current at its base controls a larger current at collector & emitter terminals.
BC547 is mainly used for amplification and switching purposes. It has a maximum current gain
of 800. Its equivalent transistors are BC548 and BC549.
16
The transistor terminals require a fixed DC voltage to operate in the desired region of its
characteristic curves. This is known as the biasing. For amplification applications, the transistor
is biased such that it is partly on for all input conditions.
The input signal at base is amplified and taken at the emitter. BC547 is used in common emitter
configuration for amplifiers. The voltage divider is the commonly used biasing mode. For
switching applications, transistor is biased so that it remains fully on if there is a signal at its
base. In the absence of base signal, it gets completely off.
3.9 Pin Diagram:
17
3.10 Transistor C1815Y:
3.11 Description:
Enhanced performance, new generation, high-voltage, high-speed switching npn transistor with
an integrated damper diode in a plastic full-pack envelope intended for use in horizontal
deflection circuits of colour television receivers. Features exceptional tolerance to base drive and
collector current load variations resulting in a very low worst case dissipation.
3.12 Applications:
96 Outputs Plasma Display Driver 90V Absolute Maximum Rating Reduced EMI (Electro
Magnetic Interference) 3.3V / 5V Compatible Logic -40 / 30 mA
Source / Sink Output Mos 6 Bit Data Bus (40 MHz) BCD Process Packaging Adapted to
Customer Request (DICE, COB, COF, TAB).
18
3.13 Features:
The C1815Y is assembled using a 0.062" thick laminate board with three sets of connector
interface pads to accommodate analog and digital isolation. Analog Devices recommends using
the FSI-110-03-G-D-AD-K-TR connector from Samtec: The overall card fits a 2.2 " 2.8" PCB
specified from 0C to 70C.
19
3.14 Basics of measuring resistance:
When measuring resistance, all musltimeters use exactly the same principle whether they are
analogue multimeters or digital multimeters. In fact other forms of test equipment that measure
resistance also use the same basic principle.
The basic idea is that the multimeter places a voltage at the two probes and this will cause a
current to flow in the item for which the resistance is being measured. By measuring the
resistance it is possible to determine the resistance between the two probes of the multimeter, or
other item of test equipment.
3.15 How to measure resistance with an analogue
multimeter:
Analogue multimeters are good at measuring resistance, although they are a few points to note
about the way in which it is done. The first point to note is that as the meter itself responds to
current flowing through the component under test, a high resistance which corresponds to a low
current appears on the left hand side of the dial, and a low resistance which corresponds to a
higher current appears on the right hand side of the dial as shown below. It will also be noticed
that the calibrations become much closer together as the resistance becomes higher, i.e. on the
left hand side of the dial.
The calibrations on an analogue meter face
20
Another aspect of using an analogue multimeter for measuring resistance is that the meter needs
to be "zero'ed" before making a measurement. This is done by connecting the two probes
together so that there is a short circuit, and then using the "zero" control to give full scale
deflection on the meter, i.e. zero ohms. Each time the range is changed, the meter needs to be
zero'ed as the position may change from one range to the next.
The meter needs to be zero'ed because the full scale deflection will change according to aspects
such as the state of the battery. There are a few simple steps required to make a resistance
measurement with an analogue multimeter:
1. Select the item to be measured: This may be anything where the resistance needs to be
measured and estimate what the resistance may be.
2. Insert the probes into the required sockets Often a multimeter will have several sockets
for the test probes. Insert these or check they are already in the correct sockets. Typically
these might be labeled COM for common and the other where the ohms sign is visible.
This is normally combined with the voltage measurement socket.
3. Select the required range
The analogue multimeter needs on and the required range
selected. The range selected should be such that the best reading can be obtained.
Normally the multimeter function switch will be labeled with the maximum resistance
reading. Choose the one where the estimated value of resistance will be under but close to
the maximum of the range. In this way the most accurate resistance measurement can be
made.
4. Zero the meter: The meter needs to be zero'ed. This is done by firmly placing the two
probes together to give a short circuit and then adjusting the zero control to give a zero
ohms (full scale deflection) reading. This process needs to be repeated if the range is
changed.
21
5. Make the measurement with the multimeter ready to make the measurement the probes
can be applied to the item that needs to be measured. The range can be adjusted if
necessary.
6. Turn off the multimeter Once the resistance measurement has been made, it is wise to
turn the function switch to a high voltage range. In this way if the multimeter is used to
again for another type of reading then no damage will be caused if it is inadvertently used
without selecting the correct range and function.
Analogue multimeters are ideal pieces of test equipment for measuring resistance. They
are relatively cheap and they offer a reasonably good level of accuracy and general
performance. They normally provide a level of accuracy that is more than sufficient for
most jobs.
22
3.16 How to measure resistance with an digital
multimeter, DMM:
Measuring resistance with a digital multimeter is easier and faster than making a resistance
measurement with an analogue multimeter as there is no need to zero the meter. As the digital
multimeter gives a direct reading of the resistance measurement, there is also no equivalent of
the reverse reading found on the analogue multimeters.
There are a few simple steps required to make a resistance measurement with a digital
multimeter:
1. Select the item to be measured: This may be anything where the resistance needs to be
measured and estimate what the resistance may be.
2. Insert the probes into the required sockets Often a digital multimeter will have several
sockets for the test probes. Insert these or check they are already in the correct sockets.
Typically these might be labelled COM for common and the other where the ohms sign is
visible. This is normally combined with the voltage measurement socket.
3. Turn on the multimeter.
4. Select the required range
The digital multimeter needs on and the required range
selected. The range selected should be such that the best reading can be obtained.
Normally the multimeter function switch will be labelled with the maximum resistance
reading.
23
maximum of the range. In this way the most accurate resistance measurement can be
made. Choose the one where the estimated value of resistance will be under but close to
the
5. Make the measurement With the multimeter ready to make the measurement the probes
can be applied to the item that needs to be measured. The range can be adjusted if
necessary.
6. Turn off the multimeter
Once the resistance measurement has been made, the
multimeter can be turned off to preserve the batteries. It is also wise to turn the function
switch to a high voltage range. In this way if the multimeter is used to again for another
type of reading then no damage will be caused if it is inadvertently used without selecting
the correct range and function.
Digital multimeters are ideal pieces of test equipment for measuring resistance. They are
relatively cheap and they offer a high level of accuracy and general performance.
3.17 General precautions when measuring
resistance:
As with any measurement, when measuring resistance, there are some precautions to observe. In
this way damage to the multimeter can be prevented, and more accurate measurements can be
made.

Measure resistance when components are not connected in a circuit:
It is always
advisable not to measure the resistance of an item that is in a circuit. It is always best to
make the measurement of the component on its own out of the circuit.
24

If a measurement is made in-circuit, then all the other components around it will have an
effect. Any other
paths that will allow current to pass will affect the readings, making them inaccurate to
some degree.

Remember to ensure the circuit under test is not powered on Under some circumstances
it is necessary to measure resistance values actually on a circuit. When doing this it is
very important to ensure the circuit is not powered on. Not only will any current flowing
in the circuit invalidate any readings, but should the voltage be high enough, the current
resulting could damage the multimeter.

Ensure capacitors in a circuit under test are discharged.Again when measuring resistance
values in a circuit, it is necessary to ensure that any capacitors in the circuit are
discharged. Any current that flows as a result of them will cause the meter reading to be
altered. Also any capacitors in the circuit that are discharged may charge up as a result
of the current from the multimeter and as a result it may take a short while for the
reading to settle.

Remember diodes in a circuit will cause different readings in either direction
When
measuring resistance in a circuit that includes diodes the value measured will be
different if the connections are reversed. This is because the diodes only conduct in one
direction.
25

Leakage path through fingers can alter readings in some cases. When making some
resistance measurements it is necessary to hold a resistor or component onto the
multimeter test probes.

If high resistance measurements are being made the leakage path through the fingers can
become noticeable. Under some circumstances the resistance path through fingers can be
measured at just a few megohms, and as a result this can become significant. Fortunately
the levels of voltage used in most multimeters when measuring resistance is low, but
some specialised meters may use much higher voltages. It is wise to check.
Measuring resistance with a multimeter is very easy and convenient. When looking at how to
measure resistance, it is quite straightforward for both analogue and digital multimeters and the
process is virtually the same in both instances, although readings may not be quite as easy to take
if the resistance is high and the measurement needs to be taken where the calibrations are close
together. Nevertheless whatever test equipment is used, resistance is easy to measure.
26
3.18 How Light Emitting Diodes Work:
Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world.
They do dozens of different jobs and are found in all kinds of devices. Among other things, they
form numbers on digital clocks, transmit information from remote controls, light up watches and
tell you when your appliances are turned on. Collected together, they can form images on a
jumbo television screen or illuminate a traffic light.
Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike
ordinary incandescent bulbs, they don't have a filament that will burn out, and they don't get
especially hot. They are illuminated solely by the movement of electrons in a semiconductor
material, and they last just as long as a standard transistor.
27
The lifespan of an LED surpasses the short life of an incandescent bulb by thousands of hours.
Tiny LEDs are already replacing the tubes that light up LCD HDTVs to make dramatically
thinner televisions.
In this article, we'll examine the technology behind these ubiquitous blinkers, illuminating some
cool principles of electricity and light in the process.
28
3.19 How Speakers Work:
In any sound system, ultimate quality depends on the speakers. The best recording, encoded on the
most advanced storage device and played by a top-of-the-line deck and amplifier, will sound awful if the
system is hooked up to poor speakers.
A system's speaker is the component that takes the electronic signal stored on things like CDs,
tapes and DVDs and turns it back into actual sound that we can hear. In this article, we'll find out
exactly how speakers do this.
We'll also look at how speaker designs differ, and see how these differences affect sound quality.
Speakers are amazing pieces of technology that have had a profound impact on our culture. But
at their heart, they are remarkably simple devices.
29
3.20 How Capacitors Work:
In a way, a capacitor is a little like a battery. Although they work in completely different ways,
capacitors and batteries both store electrical energy. If you have read How Batteries Work, then
you know that a battery has two terminals. Inside the battery, chemical reactions produce
electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler
than a battery, as it can't produce new electrons -- it only stores them.
In this article, we'll learn exactly what a capacitor is, what it does and how it's used in
electronics. We'll also look at the history of the capacitor and how several people helped shape
its progress.
30
Inside the capacitor, the terminals connect to two metal plates separated by a non-conducting
substance, or dielectric. You can easily make a capacitor from two pieces of aluminum foil and a
piece of paper. It won't be a particularly good capacitor in terms of its storage capacity, but it will
work.
In theory, the dielectric can be any non-conductive substance. However, for practical
applications, specific materials are used that best suit the capacitor's function. Mica, ceramic,
cellulose, porcelain, Mylar, Teflon and even air are some of the non-conductive materials used.
The dielectric dictates what kind of capacitor it is and for what it is best suited.
Depending on the size and type of dielectric, some capacitors are better for high frequency uses,
while some are better for high voltage applications. Capacitors can be manufactured to serve any
purpose, from the smallest plastic capacitor in your calculator, to an ultra capacitor that can
power a commuter bus. NASA uses glass capacitors to help wake up the space shuttle's circuitry
and help deploy space probes. Here are some of the various types of capacitors and how they are
used.
 Air - Often used in radio tuning circuits

Mylar - Most commonly used for timer circuits like clocks, alarms and counters

Glass - Good for high voltage applications

Ceramic - Used for high frequency purposes like antennas, X-ray and MRI machines

Super capacitor - Powers electric and hybrid cars
31
Chapter-04
Power Supply & Fire Alarm Circuit
32
4.1 Power supply for the circuit:
A well regulated power supply is essential for this circuit because even slight variations in the
supply voltage could alter the biasing of the transistor used in the fire sensing section and this
could seriously affect the circuit’s performance.
A regulated 9V/500mA power supply that can be used for powering the basic fire alarm circuit
and its modified versions is shown above. Transformer T1 is a 230V primary, 12V secondary,
500mA step down transformer. D1 is a 1A bridge which performs the job of rectification.
Capacitor C1 filters the rectifier output and C2 is the AC by-pass capacitor. IC1 (7809) is a 9V
fixed positive voltage regulator. The output of the rectifier+filter section is connected to the input
of 7805 and a regulated steady 9V is obtained at its output. S1 is the ON/OFF switch. F1 is a
500mA safety fuse.
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4.2 Fire alarm circuit:
Normally, led are high lighting & then LDR resistance are very low. Then the transistor Q1 off
& collector current of Q1 flowing to the base of transistor Q2 & it on. Then collector current of
Q1 flowing to the emitter. Then transistor Q3 off. The collector current of Q3 pass to the base of
Q4 transistor & it on. The current are passing from collector to emitter. Then transistor Q5 off &
Speaker no alarm.
But when fire breakout LDR resistance increased & transistor Q1 on, current are flowing
collector to emitter. Then transistor Q2 off. The collector current of Q2 flowing to the base of the
Q3 transistor. This current on transistor Q3 & current flowing collector to emitter. Then
transistor Q4 off. The collector current of Q4 flowing to the base of transistor Q5 & it on. Then
current flowing collector to emitter & speaker alarming.
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4.3 Figure of Capacitor.01µf,Transformer23012V,TransistorBC547:
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4.4 Figure of Transistor C1815Y,Power supply with fire
alarm circuit,7809IC,Capacitor: 1000µf:
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Chapter-05
Conclusion & Future Plan
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5.1 Conclusion:
Smoke detectors are devices created and designed to alarm by voice signals when Lighting
energy reduce safe levels. They are supposed to alert people if there is a danger of fire, and they
are required in public places, especially ones where fire accidents are more likely to happen,
such as kitchens.
5.2 Future plan:
1.We implemented smoke detect, but we want to thief detect before any stolen.
2.To make the circuit complex free and less expensive.
3.To implement the circuit by applying latest version of the renown software.
4.Minimising the transistor.
5.To protect our home, office, University, industry etc. automatically without any person when
fire occurred.
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References:
http://en.wikipedia.org/wiki/Smoke_detector
http://www.ehow.com/info_7983696_introduction-smoke-detectors.html
http://www.explainthatstuff.com/smokedetector.html
htt http://www.technologystudent.com/elec1/ldr1.htm
http://www.123eng.com/projects/microcontroller_based_home_security_project.h
http://www.researchcell.com/general/7809-pin-and-circuit-diagram/
http://www.engineersgarage.com/electronic-components/transistor-bc547-datasheet
http://www.exchangeic.com/Data/C1815Y.html
http://www.howstuffworks.com/led.htm
http://electronics.howstuffworks.com/capacitor.htm
http://www.howstuffworks.com/speaker.htm
http://www.electronics-radio.com/articles/test-methods/meters/multimeter-resistance-measurement.php
http://fpietronics.net/product.php?id_product=291
http://www.circuitstoday.com/fire-alarm-circuit
http://www.ehow.com/how_7845177_write-report-heat-detectors.html#ixzz1ozH96N1G
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