infra red burglar alrm

[imflyingaway]

can anyone of u guys explain me how to make an infra red burglar alarm .i want to do one that is quite simple butone that works could u give me A FEW LINKS OR HINTS OR AN EXPANATON

[mrbatfink]

if you are looking at a motion sensor alarm you need a PIR (passive infra red) sensor. A PIR will switch a transistor or MOSFET when it recieves inra red rays given of by people/ animals. The transistor can then be used to trigger a siren/buzzer. (PIRs are kind of pricey)

If you are looking at an infra red trip line (normally across a doorway) it is pretty much the same thing but you have an IR emmiter and an ir reciever. The emmiter just emmits a constant IR beam the IR reciever will stay on as long as the beam is on it. When someone walks past through the beam it turns off, you can use this switching to control a siren/buzzer.

You will probably want a little timer circuit so you can set the length of time the alarm sounds for. A 555 timer will do.

[mrbatfink]

http://www.ee.washington.edu/conselec/Sp96/projects/mitchrob/proposal/proposal.htm

try this site they have a few types of alarm circuits

[qapmoc]

To be honest, if you don't already understand some basics of them then you would do better to just buy a ready made unit. I do know a bit of electronics and stuff and it is just too much hassle to make something like this and it will cost you a lot more as well.