Peter L. Peres wrote:

> What range ? I'd like to get hold of a cheap one that covers 0-10 mW
> with 0.1 or better resolution.

  I wonder what the sensor is?  My "gut feeling" is that you could make
it easily and calibrate it from a reference meter, presuming you can
"con" one.

  I would assume a suitable sensor to be a large area photodiode at the
end of a black pipe.  By "suitable", I mean linear response and
beamwidth independent.  An alternative, self-calibrating, might be a
bolometer.

Richard A. Smith wrote:

> First, don't try to move the laser diode.  Aim the beam at 2 small
> mirrors mounted 90 degrees to each other.  Then move the mirrors.

  The mirrors may be at 90¡ if you want to send the beam back over the
laser, or parallel if you want it to return to the original direction.
What they must be is *close*.

  You know, the design is just as complex to do it on your room wall as
to get a 5W laser and go into the laservision business!

> Second, good luck... Drawing text via lasers requires a mechanical
> system with a very fast response time and a resonant frequency in the
> 100's of Hz.

  Like in a hard disk, but they're hard to come by second hand, aren't
they?

> What you are going to find is that unless you have a system with
> really low inertia when you attempt to stop the dot from moving or
> change direction it will resonate and blur your text.

  Back to the PID thread.  Oh dear!

  Hint: Think *round* numbers, *not* square.  Whether you need to gate
(switch on and off) the beam depends on various things, including the
maximum acceleration.

> Try to go for a refresh rate of at least 10 - 15 Hz, preferably much
> greater.

  Depends on various things; one is whether it is going to annoy you if
it flickers.  Dear me, I can't remember whether flicker is more
noticeable in dim light (as a nightlight/ night club) or bright.  For
impressing friends/ patrons, I suspect it is not critical ;-)

  I am assuming it to be patently obvious that if you can settle for
less efficiency, surplus raster displays are legion.
-- 
  Cheers,
        Paul B.