Extremely Simple Laser Alarm Circuit - a Tutorial Using Only Four Components!


Introduction: Extremely Simple Laser Alarm Circuit - a Tutorial Using Only Four Components!

About: Hi there! My name is Patrick, and I am an electronics engineering technician who works full time as a lab tech, and part time as an electronics engineer/salesman. I own an ebay store, and two websites, whic...

Hi Everyone!

Edit: We now have a laser tripwire kickstarter campaign! Check it out here:

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In the past, I've done several laser and light sensor tutorials that were op-amp (Operational amplifier) based. I've always been fond of op-amp based circuits as they are to easy to customize. This circuit is much simpler. All you need is an NPN transistor, a resistor, a light dependent resistor (LDR), and an active 5v buzzer. This video shows you how to build it, and how it works. The video offers a theory lesson, and a lab build. I used a 10k ohm resistor, a 2N2222 NPN transistor, a random LDR (Most will work well with this circuit), and a 5v active buzzer.

I also show you how to employ a 5v regulator at the end of the video. Just in case you want to use a 9v battery to power your circuit. I use a 78L05 5v regulator in the video, but you can just as easily use a 7805.

On another unrelated note, If any of you are Arduino fans, then I'd love for you to have a gander at my most recent Arduino Shield at kickstarter: ICU-Duino Arduino Kickstarter Campaign

I hope that you enjoy the video. Thanks again, everyone! Happy building!



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    3 Discussions

    If I switch places for the 10K resistor and LDR in the voltage divider, will the circuit only activate when the laser shines on it? Thanks.

    Hey, great ible. Simple project, very well explained. I dabble in electronics & was looking for a simple, portable, laser tripwire circuit, et voila.