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Topic: What to use for a Light Barrier ? (Read 3 times) previous topic - next topic


I dont't think that Ultrasounds are your best bet, I would rather use a laser (any cheap 1$ laser is good) or, simpler, a door magnetic reed switch.


Why not simply use what is used on real alarm systems; that is, a passive IR switch sensor?


3.3V TTL output (so some level conversion would be needed); place it in the corner of the room diagonally opposite that of the door, about 10-15 cm below the level of the ceiling and angled down toward the door. It'll cover the majority of the room, and can be made fairly sensitive. Bonus: You can use it when not in alarm mode to automatically turn on and keep lights on while you are in the room (well, until you stop moving - you need to have a delay to check for motion in the room to reset the time-to-live on the lights going out).
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.


thanks for the answers.
@CharlesDomingue: a laser is a nice idea, however I couldnt find one on ebay, maybe because I don't know what to exactly search for.
@cr0sh: Sounds very good, I want to use what is used in real alarm systems. I have some questions concerning this:
There is no manual nor datasheet attached in the ebay auction and it seems that cables need to be soldered because I couldn't see some pins, so I don't know how to attach it to Arduino.
What does TTL output mean? And did I understand it correctly?: Output is as the following: 3.3V = alarm, 0V = normal state.
And how does this "motion detector" work? I think it recognizes the body heat(?)
And.. Is this a safe system?

Thank you
using Arduino Uno Rev 3


This system just recognizes motion by reflected ir waves on the subject, and for the laser, any cheap laser pointer would do, example: http://www.ebay.com/itm/Mini-LED-Flash-light-Torch-Keychain-Laser-Pen-PURPL-/190732252540?pt=US_Laser_Pointers&hash=item2c6887357c
You just need a laser pointer and a photoresistor hooked up to an Analog Input and +5v, where you can set the threshold for the ambient light in your program. If you need any help for the program I can help you. But your best bet remains the reed switches, if it's not a big deal to put screws on your door frame...


Ah ok, now I understand better.

I already have a photoresistor and tried out some circuits.
And my result is, that it is too sensitive to normal sun light difference over the day.
I was told that there were special photoresistors for different types of lights (distinguished by the wave length, e.g. red laser)
Your link is about a PURPLE laser, is there a PURPLE-sensitive photoresistor?
using Arduino Uno Rev 3

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