These days many verities of alarm systems are available in the market. Some of them get triggered through touch and some type where a wire needs to broken to get triggered. Both of these types of alarms have some limitations and problems. Wire based alarms are easily avoidable, noticeable and need some regular maintenance. Touch type alarms often pickup RF waves and get activated (because of that it need some controlled environment to function properly).

In this project we design and develop LASER based burglar alarm system. Instead of wire(s) this system use LASER light wave and it can effective for more than 50m. Core features of this alarm system are:

  • High audio output power (Max. 3W PMPO)
  • Master light override switch
  • Inbuilt alarm test functionality
  • Memorized power state
  • Quick response time (aprox. 10ms ~ 30ms)
  • Support for wide input voltage range (15V – 25V DC)
  • Easy to build and calibrate
  • Compact size (aprox. 130 x 200 x 60mm)
This alarm system is specifically design for outdoor use and it is recommended for garages, warehouses, to cover wide range of landscapes, etc.

LASER Based Gate Keeper - final assembly

The core part of this system is ATmega8 MCU and it handles all the functionality of this system. TDA7267A is a power amplifier and NE555 is used as a secondary audio oscillator. TLC393 is used as a sensor driver and it handle both "master LDR" and "environmental sensor LDR".

This system use high voltage and handle it with extreme care. Do not touch U1’s (BTA12-600) heatsink or associated parts when the power is ON. Make sure to use proper heatsinks for U1 (BTA12-600), IC1 (L7805) and IC2 (L7812) and for IC6 (TDA7267A). The circuit board should be placed in a suitable container and it does not need any maintenance.

This system is distributed as an open hardware project. This project is covered under the terms of Creative Commons Attribution 3.0 Unported License and firmware source code is release under the terms of GNU GPL 3.0 License.

Project Related Downloads

Complete schematic, PCB diagrams and firmware files of LASER Based Gate Keeper project


ATmega8/L - Low-power CMOS 8-bit Microcontroller
NE555 - Single Timer
TDA7267A - 3W Mono Amplifier
TLC393 - Dual Micropower LinCMOS Voltage Comparator
MOC3041 - 6-Pin DIP Zero-Cross Optoisolator Triac Driver Output
BTA12-600 - Silicon Bidirectional Thyristor
L7805 - 3-Terminal 1A 5V Positive Voltage Regulator
L7812 - 3-Terminal 1A 12V Positive Voltage Regulator
2SC945 - NPN Silicon Transistor