Re: novice question! Optical mouse...

On Mon, 24 Oct 2005 19:11:36 -0400, Impmon wrote:

> The optical imaging sensor (read: tiny digital camera) are attuned to
> red spectrum.

Correct.
But... That does *NOT* mean that it's completely insensitive to other
colours and it *certainly* doesn't mean that anything-other-than-red
will make the sensor go haywire!

The keyword here is: brightness

"high frame rate" + "high contrast requirements" = "bright light
required"
A 3.5cd red LED is relatively cheap *and* meets that requirement, while
still meeting eye safety standards. (And that's why the sensor's
optimised for 639nm)

> If you replace the red LED with blue one, your mouse
> may not track well if at all.

That is, if you purchase you blue LED at 'case modding' or 'spare parts'
outlets.
Those critters barely make it past the 'health and safety' luminous
intensity of 3cd. And that's nowhere near enough to compensate for the
(35-40%) reduced sensitivity for 'blue' light!

Go find a 8cd (=8000mcd) blue LED (so you don't have to worry about the
extra voltage drop that blue LEDs have (saves you from re-adjusting the
LED current)) and please bear in mind that from then on, your mouse will
fall under the same hazard category as lasers pointers (ie, don't let
children play with it!)

> It is possible to get away with color change if you used a white LED.
> Put blue filter around its side so it'd appear blue unless you picked
> the mouse up. And a red filter on the bottom for red light. This
> *may* work but no guarrantee.

#ifdef FLAME
That's some really crazy idea, a clear indication that you don't 'get
it' and it will certainly not work. (Unless you use a 25cd white LED to
compensate for this madness). (And you still have some red light
leaking, keeping the OP's eyesore intact).
#endif


On 25 Oct 2005 07:29:26 -0700, testing_h@xxxxxxxxx wrote:

> I've changed the LED on a Microsoft mouse for a green one before, it
> worked better than the red one. Blue might be too short a wavelength
> though.

At green, the sensitivity will be reduced by merely 15%. With
5.6cd-bright green LEDs being commonplace (equivalent to a 4.7cd red LED
from a mouse sensor's perspective), I've no trouble believing that it
/does/ outperform the original 3.5cd red one.

(And I'm happily mousing along with a 8.5cd white LED on board. Still
tracks true on black cloth!)

.

Relevant Pages

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