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DIY Laser Tripwire with Arduino

Submitted By: 

Shalini Verma

We do understand the urge of keeping our house, work, family safe from intrusions. This project by Ben miller, co-founder of Bluelock.com, guides us how to construct a laser tripwire that buzzes an alarm assoon as the laser is disturbed. This tutorial is based on photo resistor that senses the laser beam and usespiezo to play alarm from an Arduino without an amplifier.

This project requires breadboard, Arduino, 5V General purpose USB charger, Laser chess game mirror, Laser, enclosed piezo element, Breadboard hookup wire kit and Laser mounting stand along with same basic tools like Third hand tool, Computer with Arduino IDE for programming etc. The project uses breadboard and the small wire leads of the laser as well as the piezo element are not breadboard friendly, therefore some rearrangements are done.

The wires are soldered into a short hookup wire to make them attach to the breadboard. Both leads from their respective components are matched to the color of the hookup wire with the color of the lead for consistency. This project uses a Class IIIa laser, which can cause damage to an eye, therefore take extra precautions while dealing with it. The breadboard circuit is assembled based on the following diagram.

The Arduino code in the breadboard is uploaded after with the following steps after the Arduino is attached to the computer with the USB cable and both the lasertripwire.ino and pitches.h files are loaded in the sketch. The tripwire circuit must be pointing the laser at the top of the photo-resistor and the built in LED on pin 13 of the Arduino must light when the laser is positioned on the photo-resistor.

Flip the switch while keeping the laser pointed at the photo-resistor and use a finger to break the laser beam. An alarm will start buzzing, which shows that the circuit is operating properly. Next the device is powered off and the laser is assembled in the mounting bracket to hold the laser level when it is self-supporting on horizontal surfaces.
 
After the device is assembled and tested, the tripwire is installed across the doorway to the laboratory. The mirror is used to reflect the laser, which keeps all the wires and power connectors on one side of the door. There are other ways to build this project, so keep exploring.