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> I was trying to think of a system for this using a
> pulsing LED in the pen, and phototransistors in the
> bar at the top of the page.  But with uni-directional
> signals, 3 sensors would be needed at the top.  Some
> math would be in order, but nothing a PIC couldn't
> handle.  The system seemed quite doable.

And here I just claimed I would bow out of this conversation.  Oh,
well...

To the best of my knowledge, triangulation requires only angle
sensors (however you work that out) with a fixed distance between
them.  And remember that triangulation is likely to require some
division, which PICs are terrible at doing.

- --Brendan

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