narrow beam pir sensor

[bmandl]

Hello there!
I am starting a project for home stairlight. Like this. Now I don't have an idea, how to implement sensor for first and last step. My stairs are not enclosed, so I would need a very narrow beam sensor. Is any PIR sensor apropriate for this job? Or how could I done this any other way?

 

[ard]

The actual PIR element in most PIR sensors is the same. BUT, its the fresnel lens (the while plastic dome) that determines the angle of operation. So, you'd just have to look up the specs of the variuos sensors available from your source. I had also seen ads for just the lenses, to be chosen for the angle yu desire, although unfortunately I cant seem to remember where.

Regards,

 

[bmandl]

**broken link removed** one is supposed to has removable lens. If I remove lens and not put on any others, will sensor still work? Will then suit my needs as narrow beam?

 

[ard]

No, it will NOT work reliably without the lens.

Take a look here; https://electronics.stackexchange.com/questions/30981/reducing-the-sensitivity-of-a-pir-sensor doesnt really reduce the angle of influence, but reduces the sensitivity, which might help.

You could also try putting an IR opaque black insulating tape (2 strips) on the dome with a clear line left open in the center. I dont know whether this will work, but probably worth a try.

Regards.

 

[betwixt]

The tape trick does work but obviously reduces overall sensitivity. Remember that a PIR sensor normally has a flat front surface so without a lens it has extremely wide angle of response, as stated, it's the lens that narrows it down. Also bear in mind that most PIR sensors work by monitoring a differential signal from areas on their surface so in order to work the IR illumination must not fall equally across the whole area.

Brian.