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ypu get a lazer and a photo-detector you mount them ontop of eachother (pointing the same way) then you have something reflective in the path of the lazer (pref a bike reflector to scatter the beam a bit) and the photodetector should pick up majority of the refected beam
if some1 breaks the beam phtodetector recieves no light and you can use that signal to trip something
I think that the most sophisticated and reliable (in ability to detect) is a simple video camera with the "empty room" frame stored in memory. If that frame changes, there's obviously an intrustion. It's best for a windowless room, such as a vault so that outside lights such as autos don't trigger the thing.
Shouldn't you have the laser and photodetector opposite eachother? That way, you wouldn't need to "scatter" the lazer - you could have it properly lined up... If the lazer was scattered, would that not increase the likelihood of an error? Sorry if I'm wrong but please explain cos I'm still learning.
It's often far easier to have the transmitter and receiver together (it saves running extra wires), place a small mirror opposite, and bounce the beam back to the receiver - the beam will be broken just as easily by an intruder, but it's easier to do.
is there anyway to make a lazer tripwire that will alarm somewhere else preferably with out a ton of wires. also could someone please explain more how to make it so when the photo detector loses light it completes the circuit to make the alarm go..
From my experience, it's real tough getting the beam lined up with the detector. I used an IR receiver module from an old VCR, and a microcontroller to pulse the laser (pointer) at 37 khz. Mostly just did it to see if a red laser would work, but it was too much trouble getting it aimed right.
This topic has been covered many times here, and on the web, just search a little, maybe you'll find something you can use.
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