Laser Security System
Here is a simple and cheap Laser Based Security System, which costs below Rs. 100. It is a simple circuit using LM358 OP-AMP and LM555 Timer. This circuit is triggered when the Laser beam falls on the LDR interrupts, which sounds the buzzer connected to it. This can be used to protect your valuable items, money, room etc.. By using different mirror arrangements you can form different security systems. This can also be used to protect more than one objects by suitably arranging mirrors.  One possible arrangement is shown below.
In this arrangement Mirrors B,C,D are arranged such that the reflected beam is making 90° to incident beam and the Mirror A is placed such that the beam form Laser falls on the  Mirror B and the beam from Mirror D falls on the LDR.
Circuit Diagram
Working
In this circuit the IC LM358 ic is working as a comparator and IC LM555 is wired as a bistable multivibrator. The transistor BC548 is wired as a switch to provide the negative trigger at pin 2 of LM555. The 50K pot is used to adjust the sensitivity of the circuit.
When any one interrupts the laser beam, the LDR will go to darkness which increases the resistance across LDR, which in turn increases the voltage across it. When the voltage at Non-Inverting terminal (PIN 3) will greater than Inverting terminal (PIN 2) the output of the comparator goes high. Thus the output of transistor goes low and triggers the 555, which sounds the buzzer.
i have copied your circuit but it is not running what might be the problem
how much time will the buzzer buzz if someone interrupt the laser,and if the circuit will run if the 47k is replaced by 2.2k resistor with 9volts supply plz answer me?
how much time will the buzzer buzz?? and if the 47k resistor is changed by 2.2k will the circuit run!? plz answer me
Sir..
Mein ADC k through leds control krna chahta hn…I am using mikro c
And pic16f877a
Plz help mee
how long is the maximum length between the laser and the LDR?
Adjust the sensitivity using the variable resistor.
I am Doing it with 3v Battery , whenEver i connect battery it starts buzzing continuously , y it is happening?? and one thing is more, i have used 2.2k resistor instead of 47k b/w Op-amp and Npn transistor ….???
my Project is on this coming Monday plz help me out..
can you explain me this circuit of laser light alarm
You can also use without opamp, but the LDR resistance will vary a lot. So if you need to adjust the sensitivity, it is better to use a comparator.
What’s wrong if OP Amp is not used I didnt used OP Amp and took trigger input from emitter
Divide the circuit in to 3 parts and test individually.
1. Comparator
2. Transistor Switch
3. 555
Whats wrong in this one
its not working for me plz help..
Imagine somebody passes through the laser. He/She will cut the laser only for some time, after that the laser re-establishes its line.
So if we are not using 555 timer, it will sound only for the moment laser is cutting and will turn off when it re-establishes.
i would like to know how does it work without using 555timer
It might not work with 3V battery. You try replacing the opamp with a 3V one.
You can provide separate power supply for Laser.
Will it work with 3V battery( or what is the minimum power to make working this circuit)
Sir, where should i connect to if im making the laser with the circuit? if this circuit is 12v, and the laser only using 3v-5v.
555 is wired as BISTABE MULTIVIBRATOR so capacitor not required.
will the buzzer buzz? because i don’t see any capacitors in 555 circuit
It don’t get your question. Do you need a backup battery to power the above circuit ??
how the power supply is give to that circuit
how the power supply is give to that circuit without the power hw its work
how the power supply is give to that circuit
how the power supply is given to this circuit without power how it works please reply to my comment
Yes, it will work.. no change required. .
will this work with 9 volts input? what do i need to change if using 9 volts input?
The 555 is not needed. Simply take the output of the transistor back to the inverting input of the op-amp via a diode and the circuit will latch ON.
mst hai yrrrrrr……..
Good work…..
awesome …bro!! keep it up..
sahi h yaar…..lge rho….
 chaukass hai re ……………….
its very small…in a faction of a second…to decrease this time delay u should set laser beam at lowest intensity,and change the sensitivity of circuit can be set by 50K pot.
What is the time delay, for the alarm to start after the light beam get interrupted??
electronics student please pay attention