IR LED/PIR?

[OldNick]

If I have an IR LED, will a PIR pick it up if I either switch it on or turn it off, while aiming it at the PIR? Does the change act as "movement" for the PIR?

Thanks for any help

Nick

 

[Packhorse]

You want to rob a bank or something?

 

[OldNick]

ummmm...no...last thing I want to do if I rob a bank is set the alarm off surely. Would my idea work?

Nick

 

[Packhorse]

Setting the alarm off could be useful in some situations :naughty:.

What I can tell you is that if I hold a TV remote in front of a PIR it has no effect.

 

[OldNick]

Ok. Yeah. I was looking at more of a 0.5 watt IR LED. I tried with an incandescent torch and it did trigger it, but only when it moved.

The LEDs cost about $3 posted from DX. I might just get one and a $5 PIR and try it.

I actually want as a movement sensor, but using an interrupted beam rather than IR detection as such. If I was using normal light I would probably use a solid state detector.

Nick

 

[Magic Matt]

If I have an IR LED, will a PIR pick it up if I either switch it on or turn it off, while aiming it at the PIR? Does the change act as "movement" for the PIR?

An IR light source (or IR reflected light source) appearing and disappearing is ignored.
An IR light source (or IR reflected light source) which makes a transition from one 'area' of the lens to another will trigger a detection state.
Some PIR detectors require more than one 'detection state' before they will send a signal back to an alarm panel which helps reduce accidental alarm triggering.

Buying a cheap PIR is not that different from buying a cheap flashlight - don't expect it to do the job very well.

 

[OldNick]

AhAh! Thanks for that. That gels with my little experiment with the incandescent torch. I even think the PIR does have the double take before triggering as well, as that was what happened when I moved the torch. Had to move it twice before the trigger.

So. I have found that there are ICs that ar IR sensitive switches, so that is probably the best way to go.

thanks again

Nick