> If you focus a video camera on a paper test pattern with regular
> spaced vertical stripes It will generate very accurate pulses when
> that area is scanned.

This reminded me of a technique that can be used for focussing in
automated telescopes with CCD cameras. Because a star is a
point source, you can just look at the peak on a single line and
adjust the focus to get it as narrow as possible. The circuitry to do
that is really simple compared to an image processing approach.

In Russell's case, an image of a flat surface with a laser dot
through a good optical filter is going to be a similar image. Using
the same approach, it is going to be relatively simple to determine
the position by looking for a peak X microseconds accross and Y
lines down in the frame.

However, probably the easiest and cheapest solution if the person
is close to the target would be a narrow beam red and IR LED
combination on the head and IR detectors on a board. Modulate
the IR led at 38kHz and use a standard detector and the red LED
provides some visual feedback to the user. Have both the source
and detector in a bit of tube to make it even more directional.


Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: steveb@tla.co.nz      fax +64 9 820-1929
======================================================

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