> I'm looking at an object detection problem for which I want to use a
> simple, cheap IR LED/phototransistor pair.  I plan to have each rigidly
> mounted and aimed, say a meter or so apart, and can use a flat black
> tubular shroud say half an inch to an inch in length at each end.

Do you mean that the sensor and the emitter are a meter apart, or
there are two pairs, each pair very close together?

> used outdoors?  I'd hate to have to resort to using a 40kHz modulated
> beam, and I'm not sure that it would make that much difference outdoors.

You really have to modulate, or at least pulse and look for a pulse,
unless you can control the ambient conditions.

Also be aware that a phototransistor will not work beyond a certain
frequency(40khz is too fast). A photodiode is used in the
conventional 40khz modules.

And if you have the emitter and detector a meter apart, it's going to
be very hard to make it work outdoors.

Cheerful regards,

Bob

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