LED - Lens - Lens - Photocell Question

[benitosuave]

Hi, everybody, first post so I hope I'm in the right place.

I'm working on a project where I need to make a specialized proximity sensor (well, I suppose a proximity switch).

It will work about like the failsafe on a garage door opener. There is going to be a beam (probably infrared) that is pointed at a photocell. When someone stands in front of it, the beam won't hit the photocell and from there I can condition the signal so that it operates like a switch. Proximity switch should be able to work at around 3 feet.

I'm wondering if anyone know how to select lenses or other parts in order to make an IR LED into a beam.

This should be pretty cheap and nothing too fancy.

Anyone have any thoughts?
Thanks

 

[bychon]

I have several remote controls for my TV's, and they all work at 3 feet without a lens. I think that qualifies as pretty cheap and not too fancy. Try it.

Measuring the behavior of parts and circuits is often a good substitute for trying to "math out" every aspect of the design.

 

[crutschow]

Be sure to limit ambient light to the sensor, so that doesn't swamp the IR signal since standard silicon IR sensors are also sensitive to visible light. Mount the sensor in a tube to limit the light it gets. Also may need a dark red filter the minimizes visible light transmission, but allows IR to pass.

 

[cowana]

... may need a dark red filter the minimizes visible light transmission, but allows IR to pass.

I'm sure you can buy better, but I've found bin-bag material, or old camera film to be excellent for this.

Andrew