On Sat, 24 Aug 2002, Bob Blick wrote:

> > 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?

Sensor and emitter one to two meters apart.  Probably multiple pairs
separated by about six inches or so.  Of course I can stagger the pairs to
make that "look" farther apart like this:

E --> S

S <-- E

E --> S

> > 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.

Well, I just looked at what it would REALLY cost to do a 40kHz modulated
pair...  child's play, and cheap.  I thought the Sharp IR receivers were a
lot more expensive than that, but they're really cheap.  And I can use one
PWM output to drive all the emitters.

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

There are a lot of indoor applications for this, but outdoor applications
would significantly expand the possibilities.  Hmm.  Maybe longer
shrouding or something...  I'll have to do some playing around with this,
obviously.  Or it may be as simple as a sun shade over the whole mess,
which is not great but not unworkable.

Thanks for the response, any information I get at this point is a
plus!

Dale

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