> How about creating your "line" with a pair of spinning lasers?  If they
> spin in opposite directions and are synchronized by a timing belt or
> simillar, a detector would see both lasers simultainously only on a line
> passing between the lasers.  Left or right of that line it would see one
> laser before the other.  You would have to modulate the lasers to tell
> them apart.  I think a PIC would be able to interpret that signal.
>
> Doing anything other than a straight line would require modulating the
> spin rate of the lasers, though but possible.

If you're willing to do all that you could use the same principle as LORAN.
LORAN is a series of radio beacons intended for aircraft navigation.  Each
beacon has a rotating narrow angle constant transmitter and a pulse
transmitter.  The pulse fires once per cycle of the rotating transmitter at
a known angle.  You can determine your angle from the beacon by determining
when you receive the pulse from the rotating transmitter with respect to the
fixed pulses.  You can only tell where you are along a line from each
beacon, but you can tell position from multiple beacons.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, olin@embedinc.com, http://www.embedinc.com

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