Building a Laser Alarm Circuit for Security

Want to be your own home security hero?

This post will show you how to build a basic laser alarm circuit like something a real spy might use.

It is a fun project you can do yourself to protect your stuff and it is easier on the wallet than fancy store bought alarms.

What is a Laser Alarm Circuit for Security:

An electronic device which is designed to detect when a laser beam stops working and trigger an alarm or alert is called a laser alarm circuit for security.

This circuit type is commonly used in security applications in which the laser beam works like an artificial barrier which switches on the alarm when it is broken.

A laser diode, a photodiode and related electronics usually become the main parts of the circuit.

The laser pointer circuit which is connected across the region which needs to be protected is required for generating the laser beam.

• Equation 1: Laser Power (P) = (Energy per Photon) x (Number of Photons emitted per second)

The LDR sensor is placed carefully along a path of the laser beam and is protected from other light sources by a light proof container with a tiny opening for the laser beam to pass through.

A 1M resistor is used to link the LDR sensor to the base of a BC557 transistor.

This transistor is essential for functioning of the circuit.

The transistors collector is linked to pin 2 of the IC 555.

This IC 555 is an important part of the alarm triggering mechanism because it functions as a monostable multivibrator.

A relay is attached to pin 3 of the IC 555 and the contacts on the relay are set up to match the alarm.

The circuit has a capacitor and resistors represented by the letters R to control the duration of the alarm activation.

• Equation 2: Time Constant (τ) = R x C
• Equation 3: Output Pulse Width (t) = 1.1 x R x C

Building the Laser Alarm Circuit:

Arrange the laser pointer circuit such that it shines a laser beam over the region you want to keep safe.

Make sure the LDR sensor is protected by a light proof container and position it at an exact spot along the laser beams path.

To let the laser beam in while keeping other light sources out this container should have a tiny opening.

To make the connection use a 1M resistor to connect the LDR sensor to the base of a BC557 transistor.

Connect pin 2 of the IC 555 monostable multivibrator to the transistors collector.

Connect a relay to pin 3 of the IC 555 and wire up the contacts on the relay so that they line up with the alarm.

Set the alarms activation period through combining the resistors and capacitor into the IC 555.

Parts List:

Working Principle

A laser pointer and a light dependent resistor LDR are used in the Simple Laser alert Circuit to detect intrusions and sound an alert acting as a security system.

The LDR which is kept in a light proof container is placed to respond to the laser beam once it has been projected across the protected area.

Advantages and Disadvantages of Laser Alarm Circuit:

Advantages:

• Building a laser alarm circuit is a budget friendly approach to enhancing your security.
• This circuit can be tailored to safeguard various items or spaces such as jewelry boxes, cabinets or rooms.
• Beyond basic security this circuit can be adapted for scientific experiments, educational projects or simply for amusement.

Disadvantages:

• Laser based security systems have a limited range restricting their application in larger areas.
• Obstructions in the laser path can lead to false alarms or reduced effectiveness.
• The circuits performance is be affected by ambient light conditions potentially impacting its reliability.

Conclusion:

The Simple Laser Alarm Circuit emerges as a best yet efficient security solution for safeguarding agricultural areas and open spaces from unauthorized access.

Farmers and landowners can confidently protect their crops and property with this user friendly DIY system.

If you have any queries or require further clarification, please do not hesitate to ask in the comment section.

References:

Introduction to Laser Security System