Never mind synchronizing. Just make sure your receiving leds are in the
analog range, if you want you can modulate a wave and filter it in the
receiving end for better interference rejection. Then tie each receiver to a
differentiator to detect changes. When you get a change higher than a set
level that means the leds are being partially obstructed and thus receiving
less light, so you trigger.

On 6/5/07, alan smith <micro_eng2@yahoo.com> wrote:
>
> HI folks....me again with another one of those...how would you do it
> questions...
>
>   Some time ago, had a short discussion here about getting longer
> distances with IR LEDs, and my thoughts on this was to pulse them at a
> higher current to do this.  So picture this setup.  A square "bin" or hopper
> that gets objects ranging from a several inches square (small toys) to a
> larger item (stuffed animal) and on each side of the hopper is a row of IR
> transmitters and across is a row of receivers...8 pairs.  So the original
> design when I arrived on the scene was just wiring ORing the rx and the tx
> was on all the time.  However, with the angle of radiation from the tx, you
> could  block the tx across from the rx (the pair) but the rx would still get
> IR from one of the adjacent tx.  I think they told me...each tx IR would
> have enough angle of radiation to trigger the one across from it...plus each
> one to the side as well.  So, even tho something might have blocked a
> particular tx beam, the ones next to it would still not allow that one to
> activate it (ie...turn it on
> and pull the signal low).
>
>   OK, so the idea...first pulsing the tx with higher current, and second
> syncronize the tx/rx pairs so that only when the tx.1 was on, rx.1 would
> be looking for a signal.  Works pretty good, each board has a PIC16F818 on
> it, and sending a sync from the transmit to the receiver so they lock up.
> However....as you pull the boards away....the alignment of the beams become
> more difficult.  I didnt increase the power on the LED's yet...told them
> this morning to try that.  But the issue as I see it.....there are now HUGE
> holes in the sensing pattern.  The LEDs are about 1/2" apart and even tho
> the radiation pattern is the same, its no longer looking at the IR from the
> adjacent transmitter.
>
>   So, looking for thoughts on how to get rid of the holes in the sensing
> field. The answer might be obvious, but you know how it goes...after staring
> at the problem for so long, you cant see the forest for the trees.
>
>
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