Here is a low-cost, invisible laser circuit to protect your house from thieves or trespassers. A laser pointer torch, which is easily available in the market, can be used to operate this device. The block diagram of the unit shown in Fig. depicts the overall arrangement for providing security to a house. A laser torch powered by power-supply is used for generating a laser beam. The laser beam is directed to finally fall on an LDR that forms part of the receiver unit. Any interruption of the beam by a thief/ trespasser will result into energisation of the alarm.   The power-supply circuit is a conventional full wave rectifier-filter circuit. Any alarm unit that operates on 230V AC can be connected at the output. The receiver unit comprises identical step-down transformers LDR, a transistor, and a few other passive components. When the LASER rays cut by the thieves the LDR will get difference and it will activate the Alarm with helm of transistors.

The major features of this project are:

1. Light sensing using LASER and LDR.
2. Alerting regarding thieves through buzzer.

The project provides learning’s on the following advancements:

1. Characteristics of LDR sensor.
2. Conversion of AC supply to DC supply.
3. Transistor working principle.
4. Need for drivers.
5. PCB design.

The major building blocks of this project are:

1. Regulated Power Supply.
2. Receiving circuit.
3. LDR sensor.
4. Buzzer with driver.

     

     

Regulated Power Supply:    

   

     

Block Diagram:    

   

   

   

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