This document describes a laser light security system that uses a laser beam, light dependent resistor (LDR), transistor, LED, and buzzer. When the laser beam is interrupted, the resistance of the LDR changes and triggers the transistor to activate the LED and buzzer, alerting of an intrusion. The system provides effective perimeter security for homes inside and out in a discreet and easy to install way. Advancements in technology continue to improve home security systems.

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LASER LIGHT SECURITY
SYSTEM
By
Mehenaz Khan Sorna

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Index:
 Introduction
 Components
 Circuit Diagram
 Experiment Setup
 Working
 Benefits
 Conclusion

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Introduction:
Security is the most important factor today. Technology develops
day by day in the world. The crime gang also improves their
technology to perform their operation.
Therefore, technology of security should modern with time to
protect the crime works. We decided to make a security
We know laser light goes through long distance with out
scattering effect. It is also visible at source and at incident
point, otherwise invisible.
These two properties help us to build up a modern security
system, which may name as “laser light security system”.
When any person or object or cross over the laser line the
security alarm will ring and also the focus light will “on” to focus
the entrance of unauthorized person. We can make a security
boundary of single laser light by using mirror at every corner for
reflection.

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Components:
1.Breadboard-1pc
2.LDR (light depending resistor)-1pc
3.LED (light emitting diode)-1pc
4.BC547 transistor-1pc
5.10kohm resistor-1pc
6.Buzzer-1pc
7.Laser Light-1pc
8.battery with connector-1pc
9.Wires
Circuit diagram:
Experiment setup:
1. Place the bc547 transistor into the breadboard.
2. Now connect LDR to Base and Emitter of the transistor.
3. Connect resistor to Base and blank port of breadboard.

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4. Connect the anode of the LED to the resistor and cathode
to the Collector of the transistor.
5. Now connect the buzzer the same way we have connected
the LED.
6. Connecting the positive side of the breadboard to the
resistor and negative side is with the Emitter of the
transistor.
7. Now connecting the voltage supply.
Working:
1. This circuit is based on LDR (Light Depended Resistor), a
variable resistor in which the resistance varies according to
the light intensity falling on it.
2. The LDR and resistor form a potential divider network,
which is the main part of our security alarm circuit.
3. We know that transistor can acts as a switch, so the same
principle is used here.
4. The voltage drop across the LDR is used to drive the
transistor switch. When the voltage drop is above cut in
voltage (0.7V), the transistor is turned ON.
5. LDR has low resistance (mΩ range) in the presence of light
and high resistance (MΩ range) in the absence of light.
6. In our security alarm, a LASER light is allowed to fall on the
LDR continuously. Light from other sources should not be
allowed to fall on the LDR.

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7. In this situation, the resistance offered by LDR is too low,
since the LASER light is continuously allowed to fall on the
LDR surface. Thus the voltage drop across the LDR is also
low [V=IR (Ohm’s law)] which is insufficient to turn ON the
transistor, so the transistor remains in OFF state.
8. When a person (eg: thief) makes a block to the continuous
flow of LASER beam, then the light falling on the LDR gets
blocked. Thus its resistance increases to a high value in the
order of MΩ range (According to Ohm’s law V=IR).
9. While resistance increases the voltage drop also increases,
when this voltage drop exceeds the cut in voltage of the
silicon NPN transistor (BC547), it will turn ON.
10. Then current from Vcc starts flowing to ground via
the buzzer and transistor, which makes the beep sound. The
beep sound from the security alarm gives the indication of
some security failures.
Benefits:
These are easy to install and work at both within as well as
outside houses. These are very effective perimeter alarm
systems around properties. In indoor system scan, utilize the
normal power outlets and jacks making them inconspicuous.
Conclusion:
Home security is rapidly growing field and there are new &
improved burglar alarms popping up every day.
With rapid advancement of technology, the field is turning out to
be an area full of scope and new changes can be made to make its
more efficient. It has years to come, because security is of prime
importance to all.