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Building IR BEAM Break alarm system

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New Member
First off. I know it would be much easier for me to just go and buy all this in a kit but my challenge from this project is actually building it from scratch.

The laser transmitting portion of this circuit I beleive i won't have trouble with this portion. I intend on using a IR LED with about 850nm and a variation of a laser driving circuit i found on the net.......unless somone has a better version i can study.

However, im not sure how to do the recieving part. I intend to build it so that once the light is interupted it sets off a relay. There is actually other parts of the alarm system but im just having problems comming out with a schematic for the beam reciever.

Here's what my plan is. I was going to use a PIN Photo diode since i've read that its sensitivty is the best detector with a peak range at around the same frequency of the laser. I CAN put the reciever in a pvc pipe or something to block out ambient light and external sources however i wan't to build this with some filters in it as well.


when theres a sudden voltage drop from the beam dissapearing it sets of the relay?

Anyone have suggestions on basicly anyhting i have said?


Well-Known Member
Have you seen the date on the post.?:)
Hi Eric!

I think that's some kind of record for dead thread resurrection.

Now, if the OP actually responds--that should *definitely* be a record. :)



New Member
Ok, I'll bring this back from the dead. I want to build a device for my garage so that when the front of the car breaks a beam, it triggers a light on the wall to turn on.

I have one of those devices that connects into my garage door but the LED is SO TINY I cannot see it when it turns on to tell me that the doorway is clear in the rear, hence my need for something bigger.

I can run wire, solder, etc, but only simple circuits. :eek: Any help would be appreciated!


New Member
hi there you obviously seem to know your stuff. im actually looking to do a similar circuit but i am unsure how the interuption of laser beam can trigger the relay. , do i have to use a logic gate to trigger the relay? i would appreciate your feedback.


Well-Known Member
Most Helpful Member


New Member
Any criticism is appreciated..lol...since Im just a fool hobbyist :). I'm a noob here and read in grade 10. So I've some question about this project.

You can laugh at me after looking at this image but I have no problem because Im a LEARNER so Im asking for your assistance.

NB: Another sorry for my bad English skill. I live nearby india.

Here is my questions. Look at the image, I wrote my questions on this image.
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