Infrared photocell

[spinoza]

In a quest to create a light controled "theremin" (in fact a synthstick with a photocell instead of a tape control) that would not go berserk when played on stage (think of all the lights, strobs, etc!) I'm thinking of using an infrared DEL + photocell. Since that infrared is much more constant on stage that the visible light spectrum, I think it would work pretty well.

My question is: do they actually exist? Where do you buy them?

(these guys seem to use the same solution: http://www.frostwave.com/spacebeam/index.html )

Edit: a little forum search showed that it IS doable but I'm not sure if using IR solves the interference problem. Does anyone have an IR theremin that works fine on stage?

[captntasty]

Interesting idea...  I had this feeling that you wouldn't need anything out of the ordinary and lo and behold http://en.wikipedia.org/wiki/Photocell .  Looks like regular old CdS photoresistors would work... They have em at RadioShack so I would guess they can be had from the usual suspects 

Looks like in your situation this article would indicate GeCu (Germanium Copper?  Cupric Germanium?) for infrared detection...  probably expensive?  There was another article talking mostly about CdS but quickly mentioned something about Silicon photoresistors being mostly sensitive to infrared.  Can't imagine these would be too expensive...

I can't speak from any kind of experience and hopefully some of the other Forumites will have ideas, but these are a few avenues of pursuit...  Love to hear/see it if you can put it all together!

[petemoore]

  Questions...
  Are cells available that respond Only to infrared frequencies +/- ...or how much does visible light influence the function.
  Then, how hard would it be to filter all but infrared frequencies being able to strike the cell surface?

[Paul Perry (Frostwave)]

It isn't hard to get filter material to let IR through and block visible light (all the educational science supply places have stuff like this).
But, I doubt that it is true that the IR on stage is any more constant than the visible light. Because, all floodlights put out more IR than visible anyway.
My commercial SpaceBeam works by reflecting its own infrared light (from infrared diodes, modulated at 200KHz or so) that is picked up by a photodiode (specified to be IR sensitive). The idea of the modulation, is that you can filter the signal to discriminate against all the non-modulated hash.

[spinoza]

I guess that the alesis air FX works that way as well.

That's an excellent solution but I wonder if I can find a modulated IR DEL and a LDR that would react only to modulated IR....

[cpm]

necrobump

I dont know if the usual LDR work fine with IR, anyones experiences?

For the stability, i think that some kind of mdulation can be used to filter out the ambience static light, more or less like its done on transmission lines, FM and all that. This would need a fast detector, so LDR would be discarded

[connie_c]

I think roland use an infa red one in their d-beam controls. Its on most of their current keyboards. Dunno if their is info available on they do it but its a lead.