CHAPTER 1

INTRODUCTION

1.1 AIM OF THE PROJECT:

A alarm is a type of security equipment that can be used to safeguard homes and

property. If we love our home then buying burglar alarm should be our first priority when

moving to a new home. Burglar crimes are continually rising with each passing day. Many have

lost their homes and families through violent burglaries in many countries today. Some have lost

what they considered precious and valuable to them. Things such as jewelry, vehicles, and

clothes are huge investments to many.

During the olden days a watchman would be hired to take care of property and offer needed

security in the home. Some homes also had fierce dogs that would be let out only at night. The

two were supposed to provide security to our belongings even in the absence of the owner.

However, hiring a watchman was not an effective method since most of them would be killed in

the line of duty. Sometimes dogs would attack even visitors while some watchmen looted

property. This led to the development of alarm equipments.

1.2 ABOUT THE CICUIT:

The circuit is divided into two parts i.e. the transmitter and the receiver part

Transmitter point:

The tranmitter circuit is othing but a laser diode driven by a battery connected to the

diode through a series resistance R1. In order to ensure that the current through the diode

remains constant irrespective of drop in battery voltage, a 3-terminal voltage regulator VR-1 has

bee used. This regulator produces a constant 5V output as long as input remains equal to or more

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than 7.5V thus ensuring a constant drive current for the laser diode. The drive current in this case

would be(3500/47) mA.

The laser diode here can be the one typically used in laser pointers emitting in red. This would be

more economical than buying one. If the experiment so desires, we can use the laser pointer itself

as a complete transmitter circuit. The pointer has in-built suitable series resistance and an

ON/OFF switch and a battery. The given circuit would help when we want to go a step further

and want to use infrared laser diode so as to get an invisible laser beam, which would be a

requirement in any intruder alarm system, I recommend the use of laser pointer for the purpose

of learning and demonstration.

Receiver part:

The receiver part basically comprises of a current to voltage converter section

configured around IC1(OP AMP 356) feeding a positive edge triggered monoshot configuration

buit around IC2(555 timer). The output of the monoshot feeds a buzzer that gives an audio beep

during the time it get a high input from the timer IC 555. The receiver section operates from +5V

DC generated from another 9V battery and 3 terminal regulator VR2. The battery can be

connected to the circuit through switch SW2

The current-to-voltage converter section converts the photocurrent produced by the photodiode

PD1 as a result of laser light falling on it into an equivalent vltage across resistor R2. This

voltage gets amplified bya factor of 23 in the non-inverting amplifier provided by an OP-AMP

and resistors R3,R4. So, when the laser light is falling on the photodiode, the opamp output is

same DC voltage, The component values have been so chosen as to produce about 5V DC for a

laser power of 0.5mW, typical of a laser pointer. Otherwise the amplifier gain can be adjusted to

produce 5VDC.

1.3 ADVANTAGES OVER COMMERCIAL SECURITY SYSTEMS:

There are dozens of different security systems on the market that utilize lasers and

can effectively protect everything from small apartments and businesses to large areas of

property. Most home laser security systems consist of two parts: a basic alarm unit and an

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infrared motion detector. Laser security systems of the past used to rely on connections wired to

a keypad, requiring the customer to use special codes to arm and disarm the system. Since the

majority of laser security systems are now wireless, the units can be turned on or off with a

wireless remote or, in some models, by touch tone phone from anywhere in the world.

The basic sensing component of a modern laser security system is an infrared motion detector.

An infrared motion detector works by using beams of infrared light to detect changes in heat

which is absent in most of the commercial security systems. Laser alarm systems provides the

state of the art features and benefits of a conventional monitored alarm system. Laser alarm

systems is an advanced and effective security system that does the job right. Laser alarm systems

can be activated in seconds without programming, installation, in-home sales people and

technicians; and with no hassle, mess, or waiting. There are no hidden costs, no on-going service

calls and costs, and Rapid Response Monitoring Service provides the most technologically

advanced monitoring service available. All at a fraction of the cost of other major brands. Laser

alarm systems is perfect for homes, condos, apartments, small offices, and retail stores.

Laser security systems have many advantages. They are simple to install and can be used

effectively inside or outside a home. The systems can be used as a highly effective perimeter

alarm for property boundaries or even for pools, where customers can have the lasers set to

detect when small children come within a set number of feet from the edge of the water. Indoors,

the sensors utilize normal power outlets and telephone jacks; outdoors, the sensors can be hidden

beneath plants and bushes and will not harm lawns or other vegetation. However, laser security

systems can be prohibitively expensive. While some security system plans allow for customers to

target one room, plans that protect large amounts of land or an entire house will cost much more

and can be difficult for many customers to afford .

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CHAPTER 2

BLOCK DIAGRAM AND EXPLANATION

2.1 BLOCK DIAGRAM:

Block diagram

2.2 BLOCK DIAGRAM EXPLANATION

2.2.1 Laser Diode/Pointer:

The laser diode is a laser where the active medium is a semiconductor similar to

that found in a light-emitting diode. The most common type of laser diode is formed from a p-n

junction and powered by injected electric current. In this we are using 593 nm – Yellow-Orange

laser pointers, DPSS. The common wavelengths used are:

375 nm – excitation of Hoechst stain, Calcium Blue, and other fluorescent

dyes in fluorescence microscopy

405 nm – InGaN blue-violet laser, in Blu-ray Disc and HD DVD drives

445 nm – InGaN Deep blue laser multimode diode recently introduced (2010) for use in

mercury free high brightness data projectors

473 nm – Bright blue laser pointers, still very expensive, output of DPSS systems

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485 nm – excitation of GFP and other fluorescent dyes

510 nm - Green diodes recently (2010) developed by Nichia for laser projectors.

532 nm – AlGaAs-pumped bright green laser pointers, frequency doubled 1064 nm Nd:YAG

laser or (more commonly in laser pointers) Nd:YVO4 IR lasers (SHG)

593 nm – Yellow-Orange laser pointers, DPSS

635 nm – AlGaInP better red laser pointers, same power subjectively 5 times as bright as

670 nm one

640 nm – High brightness red DPSS laser pointers

657 nm – AlGaInP DVD drives, laser pointers

670 nm – AlGaInP cheap red laser pointers

760 nm – AlGaInP gas sensing: O2

785 nm – GaAlAs Compact Disc drives

808 nm – GaAlAs pumps in DPSS Nd:YAG lasers (e.g. in green laser pointers or as arrays

in higher-powered lasers)

848 nm – laser mice

980 nm – InGaAs pump for optical amplifiers, for Yb:YAG DPSS lasers

1064 nm – AlGaAs fiber-optic communication

1310 nm – InGaAsP, InGaAsN fiber-optic communication

1480 nm – InGaAsP pump for optical amplifiers

1512 nm – InGaAsP gas sensing: NH3

1550 nm – InGaAsP, InGaAsNSb fiber-optic communication

1625 nm – InGaAsP fiber-optic communication, service channel

1654 nm – InGaAsP gas sensing: CH4

1877 nm – GaSbAs gas sensing: H2O

2004 nm – GaSbAs gas sensing: CO2

2330 nm – GaSbAs gas sensing: CO 2680 nm – GaSbAs gas sensing: CO2

2.2.2 Photo Transistor:

A photodiode is a type of photodetector capable of converting light into

either current or voltage, depending upon the mode of operation.[1] The common, traditional solar

cell used to generate electric solar power is a large area photodiode.

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Photodiodes are similar to regular semiconductor diodes except that they may be either exposed

(to detect vacuum UV or X-rays) or packaged with a window or optical fiber connection to allow

light to reach the sensitive part of the device. Many diodes designed for use specifically as a

photodiode will also use a PIN junction rather than the typical p-n junction.

Materials commonly used to produce photodiodes

2.2.3 Op-Amp LM 356:

The LM356 is a power amplifier designed for use in low voltage consumer

applications. The gain is internally set to 20 to keep external part count low, but the addition of

an external resistor and a capacitor between 1 and 8 will increase the gain to any value up tp 200.

The inputs are grounded referenced while the output is automatically biased to one half the

supply voltage. The quiescent power drain is only 24mW when operating from a 6V supply,

making the LM356 ideal for battery operation.

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MaterialElectromagnetic spectrum

wavelength range (nm)

Silicon 190–1100

Germanium 400–1700

Indium gallium arsenide 800–2600

Lead(II) sulfide <1000 – 3500

Connection Diagram

Applications of LM 356 are Am-FM radio amplifiers, Portable tape player amplifiers,

Intercoms, TV sound system, Line drivers, Ultrasonic drivers, Small servo drivers, Power

converters.

2.2.4 Monostable 555 timer:

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse

generation and oscillator applications. Depending on the manufacturer, the standard 555 package

includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini

dual-in-line package. In the monostable mode, the 555 timer acts as a “one-shot” pulse generator.

The pulse begins when the 555 timer receives a signal at the trigger input that falls below a third

of the voltage supply. The width of the output pulse is determined by the time constant of an RC

network, which consists of a capacitor (C) and a resistor (R).  Applications include timers,

missing pulse detection, bouncefree switches, touch switches, frequency divider, capacitance

measurement, pulse-width modulation (PWM) and so on.

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Pin diagram

Graph

2.2.5 Piezo Buzzer:

The piezo buzzer produces sound based on reverse of the piezoelectric effect. The

generation of pressure variation or strain by the application of electric potential across a

piezoelectric material is the underlying principle. These buzzers can be used alert a user of an

event corresponding to a switching action, counter signal or sensor input. They are also used in

alarm circuits. 

The buzzer produces a same noisy sound irrespective of the voltage variation applied to it. It

consists of piezo crystals between two conductors. When a potential is applied across these

crystals, they push on one conductor and pull on the other. This, push and pull action, results in a

sound wave. Most buzzers produce sound in the range of 2 to 4 kHz.

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The Red lead is connected to the Input and the Black lead is connected to Ground.

2.2.6 Capacitor:

A capacitor is a passive electronic component consisting of a pair

of conductors separated by a dielectric (insulator). When there is a potential difference (voltage)

across the conductors, a static electric field develops across the dielectric, causing positive

charge to collect on one plate and negative charge on the other plate. Energy is stored in the

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

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

difference between them.

Capacitors are widely used in electronic circuits for blocking direct current while

allowing alternating current to pass, in filter networks, for smoothing the output of power

supplies, in the resonant circuits that tune radios to particular frequencies and for many other

purposes.

2.2.7 Resistor:

A linear resistor is a two-terminal, linear, passive electronic component that

implements electrical resistance as a circuit element. The current flowing through a resistor is in

a direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage

applied across resistor's terminals to the intensity of current flowing through the resistor is called

resistance. This relation is represented with a well-known Ohm's law:

2.2.8 Diode:

A p–n junction is formed by joining P-type and N-type semiconductors together in very

close contact. The term junction refers to the boundary interface where the two regions of the

semiconductor meet. If they were constructed of two separate pieces this would introduce a  grain

boundary, so p–n junctions are created in a single crystal of semiconductor by doping, for

example by ion implantation, diffusion of dopants, or by epitaxy

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2.2.9 Switch:  

A switch is an electrical component that can break an electrical circuit, interrupting

the current or diverting it from one conductor to another.

2.2.10 Battery:

An electrical battery is one or more electrochemical cells that convert stored

chemical energy into electrical energy.In this we are using a 9V battery.

2.2.11 Relay:

A relay is an electrically operated switch. Many relays use an electromagnet to operate

a switching mechanism mechanically, but other operating principles are also used. Relays are

used where it is necessary to control a circuit by a low-power signal (with complete electrical

isolation between control and controlled circuits), or where several circuits must be controlled by

one signal. The first relays were used in long distance telegraph circuits, repeating the signal

coming in from one circuit and re-transmitting it to another. Relays were used extensively in

telephone exchanges and early computers to perform logical operations.

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CHAPTER 3

CIRCUIT DIAGRAM AND OPERATION OF CIRCUIT

3.1 Circuit diagram:

3.2 Operation of the circuit:

The transmitter circuit is nothing but a laser diode (LD1) driven by a 9V PP3

battery. The output of IC1 is regulated 5V as long as its input remains equal to or more than

7.5V, thus ensuring a constant drive current for the laser diode. The battery (Batt1) is connected

to the circuit through switch S1. The laser diode (LD1) can be replaced with a laser pointer

(torch) emitting red laser beam. The laser pointer itself can be used as a transmitter. The pointer

has in-built series resistance, on/off switch and battery. The receiver circuit is basically a current-

to-voltage converter built around IC LM356 (IC3). The output of IC3 is fed to the monostable

built around 555 timer (IC4). The high output of the monostable drives the piezobuzzer to sound

an audio alarm. The receiver section operates off 5V DC generated from another 9V battery and

voltage regulator IC 7805 (IC2). The battery (Batt.2) is connected to the circuit through switch

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S2. When the laser light transmitted through LD1 falls on phototransistor T1, the output of the

op-amp (IC3) at its pin 6 remains high. In this condition, the output of IC4 remains low and the

buzzer does not sound. When the laser beam falling on phototransistor T1 is interrupted by

someone, the output of op-amp IC3 goes low and IC3 produces a pulse. This pulse triggers

monostable IC4 and its output goes high to sound the alarm for a time period of about R8xC8.

Assemble the transmitter and receiver circuits on separate generalpurpose PCBs and enclose in

suitable cabinets. Mount the transmitter and receiver units on opposite pillars of the entrance,

aligning the two such that the laser beam from the transmitter directly falls on the

phototransistor. Block the laser beam with your hand and measure the op-amp output. It should

not be low. At pin 3 of IC4, we should get a positive-going pulse of one-second duration

beginning with high-to-low edge of the trigger pulse appearing at pin 2 of IC4 or collector of

transistor T2.

CHAPTER 4

CONSTRUCTION AND TESTING

4.1 Parts List:

R2, R3 1K,1/4W

R4 22K,1/4W

R5, R7 10K,1/4W

R6 47K,1/4W

R8 1M,1/4W

C3 10uF, 25V

C4, C5, C7 0.1uF

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C6 0.01uF

C8 10uF, 16V

D1 IN4007

Battery 9V

Switches ON/OFF,SPST type

IC 555 Timer

IC OPAMP LM 356

Relay 6V

Buzzer Piezo buzzer

Transistor BC548

Photodiode(PD-1) BPX-65

Laser Diode(LD-1) Laser pointer

4.2 Construction steps:

Connect a phototransistor(T1) to the resistor R2 in series and connect it to the 3rd

pin of the IC LM 356. Connect the resistor R3 to the 2nd pin of IC LM 356. Connect the 4th pin

to the ground. Connect the resistor R4 to the 6th pin in series with the resistor R2. From the 6th

pin connect the capacitor C6, resistor R5, R6, diode D1 to the base of the transistor T2. the

resistor R5 is connected in parallel to diode D1. the collector is connected to the resistor R7. the

capacitor C5 is connected to the pin 7 and 8 of the IC 356 and 555 timer. the collector of T2 is

connected to the pin 2 of 555 timer. The pins 6,7 are connected to resistor R8 and capacitor C8.

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the pin 3 is connected to the piezo buzzer. The pins 4,6,7,8 of 555 timer and pin 7 of LM356 are

connected to the collector of the T1. The pin 1 of 555 timer is connected to the ground and pin 5

is connected to C7 which in turn connected to the ground. The relay is connected to the 555

timer.

4.3 Testing:

Switch on the transistor circuit. Align the transmitter and receiver circuit so that the laser

beam falls on the photodiode. We can use a small transmitter receiver distance, even a

few feet, for the purpose.

If necessary, change the value of one or more resistors(R5,R6,R7) to get a signal peak

magnitude of 2 to 3 V at opamp output.

Block the laser radiation with our hand and again measure the opamp output. It should be

near zero volt.

If we have the services of an oscilloscope, observe the pulse waveforms appearning at

pin-8 of IC-1 and pin-6 of IC-3. At pin-8 of IC-4, we would see a HIGH-to-LOW

transition every time we block the laser beam.

We can observe change in the pitch of the audio beep by changing the frequency of the

signal on the transmitter card.

CHAPTER 5

SPECIFICATION AND APPLICATION

5.1 Specification:

PCB 4x4

593 nm – Yellow-Red laser pointers

Battery 9V

Photodiode BPX-65 or equivalent

PiezoBuzzer

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5.2 Advantages:

Simplicity of installation.

The effective ability to be used indoors and outdoors. 

It could be used as an effective alarm for the house/company boundaries. 

It uses the normal power outlets and telephone jacks in case it used indoors. 

It could be expensive and could be difficult for many customers to afford it. 

5.3 Disadvantages:

The disadvantage of laser beamsystem is that it may get activated by a cat walking on

the wall or a large bird sitting on the wall.

They are more expensive compared to simple security alarm systems.

5.4 Applications:

Can be used as home security system

Can be used in Museums, Banks, Offices for safe guard many valuable things.

CHAPTER 6

CONCLUSION

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The Laser Based Intruder Alarm was built to our satisfaction. This project is about

how to prevent theft in homes, offices, banks, museums etc, This project can be implemented by

both wired and wireless technologies. Another application of this instrument is as an "ANTI-

THEFT SYSTEM", that means to protect vehicles from kidnapping. In short I am sure that this

device is highly useful to mankind especially present scenario.

References:

http://www.ieee.org/searchresults/index.html?

cx=006539740418318249752%3Af2h38l7gvis&cof=FORID%3A11&qp=&ie=UTF-8&oe=UTF-

8&q=laser+alarm+systems&siteurl=www.ieee.org%252Findex.html

http://en.wikipedia.org/wiki/Main_Page

http://books.google.com/books?

id=Dx3Mdx_oDHsC&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f

=false

http://www.scribd.com

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