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Self-Contained Laser Trip (All in one unit) Answered

Hey y’all, I have been searching for a way to create a laser trip wire that doesn’t involve two units that line up to have the beam broken. Is there a way to emit a laser that triggers LEDs or buzzers just when the laser is broken, all coming from one unit? I’ve read about the LED/IR type projections and that’s the closest I’ve found. Any help is welcome. Thanks!


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1 year ago

In the industry laser distance systems are widely used.
Usually in the range of just cm but the principle is the same:
Almost all surfaces reflect visible laser light to some extent.
That means the laser is activated with a pulse or as a continious supply.
A well aligned photo diode or transistor is then able to detect the reflected light.
Usually the incoming signal is amplified and both laser and detector are pulse activated at the same time.
For added security even modulated signals are possible here.
Have a look how a optical mouse works.
For the optics that is.
A laser is directed onto the surface and a close by detector "sees" the reflection.
In your case it could as simple as dead parallel for both units.
If doubt a filter of the same color as the laser keeps stray light out and a good szed lens can focus mor light onto the detecting element.
On the output you just add a transistor or similar to activate whatever you need.
If in doubt inverted so the stuff goes on when the beam is interrupted.

Jack A Lopez
Jack A Lopez

1 year ago

Have you seen, heard, or read about, PIR (passive infrared) sensors?


Those are cheap and ubiquitous, especially the ones that come with a outdoor light fixture attached. The intended application is for spooking prowlers, or friends, or yourself, who walk too close the outside of your house at night.

Those PIR sensors work particularly well for sensing people, although, you did not mention who, or what you are trying to detect.

If you really want to do it with frickin' laser beams, there exist "LiDaR" (Light Detection and Ranging) gizmos, also called "laser range finder" gizmo, and these exist in module form. So if you can figure out how to connect it to your Arduino, or other microprocessor, then you can query that little module, and ask it if is sensing a reflected beam from some object in its expected range, and how far away is it?

Keep in mind, the usual geometry these modules expect, is a reflection from a big flat target several meters away, like a wall on the other side of the room, or the ground as seen from a several meters below the sensor, with the sensor attached to a flying drone.

Here is a link to a typical eBay listing for one of these sensors. I don't know this seller.


I can only guess such a LiDaR sensor might also work, in a room or a hallway, as a people sensor, basically waiting for a person to wander into the beam and reflect a large part back to the sensor...

But why do that when a cheaper PIR sensor would work just as well or better?