"M. Adam Davis" wrote:

> I can gurantee that current optical technology does NOT need a laser to
> sense very smooth surfaces.  It simply focuses on a *very* small area
> (it can see paper fibers), and uses the LED at an angle to show shadows
> (or reflections, if mirror like ) which then goes into a very small
> image sensor.  This sensor images at 10 or more thousand times per
> second, which means that even though it's looking at such a small area,
> you'd still have to move it very quickly in order to change more than
> 50% of the picture it sees before capturing the next frame.
>
> The uC inside the mouse then uses a pretty spiffy algorithm to detect
> edges and compare the current image to the last image.
>
> The senser, being semiconductor, is more sensitive to red light than any
> other color (as red sensitive semiconductor, or where the peak is at
> red, is cheaper and more common to produce) is still sensitive to just
> about any light in and just outside of our visible spectrum.  People who
> replace their LEDs with blue will likely find reduced sensitivity, but
> it won't make a difference unless they use it on a surface that even the
> red LED has a hard time with.

I swapped the LED in my logitech USB wheel mouse for a blue one (Had a
red LED in a blue mouse - ick)

initially it was too bright and only worked on dark surfaces so I put an
additional 100 ohm resistor in series with it. The old red led had 2
brightnesses that it operated at, the blue one doesnt seem to change
ever. I suspect thats why its not so good on bright surfaces. Prob the
different foward voltage drop causes the problems.

Even before changing the LED the old red one would jitter sometimes when
it was on some surfaces.

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.