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'[EE]: Optical mouse technology'
2001\10\03@133327 by Pedro Drummond

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How does it work ? It seems to have a laser diode and a photo sensor, but
how is it able to respond to movements in every direction ?

TIA,

Pedro.



{Original Message removed}

2001\10\03@144447 by Douglas Butler

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It takes images, about 16x16 pixels, and correlates them looking for
offset.  The light comes in at a grazing angle so the texture of the
surface shows up.

Sherpa Doug

> {Original Message removed}

2001\10\03@154203 by Barry Gershenfeld

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There's a little camera in it.

Barry

>How does it work ? It seems to have a laser diode and a photo sensor, but
>how is it able to respond to movements in every direction ?
>
>TIA,
>
>Pedro.

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2001\10\03@154209 by Stephen Webb

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> How does it work ? It seems to have a laser diode and a photo sensor, but
> how is it able to respond to movements in every direction ?

I'll speculate that it has a small camera of say 20x20 pixels in it.  It
correlates successive images to find out which direction you moved.  It
could also use physical models to help it search for the next
frame.  Maybe even a Kalman filter thrown in there, eh?

-Steve

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2001\10\03@164831 by Dave Dribin

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On Wed, Oct 03, 2001 at 12:45:40PM -0300, Pedro Drummond wrote:
> How does it work ? It seems to have a laser diode and a photo sensor, but
> how is it able to respond to movements in every direction ?

It's got a small CCD camera that takes pictures at 1,500 times per
second.  It can infer the direction and speed of movement by DSP
software inside the mouse analyzing the pictures:

 http://www.wave-report.com/tutorials/OM.htm

-Dave

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2001\10\03@164841 by Madhu Annapragada

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This months Scientific American has an article on this.
If I remember right, the mouse has a CCD array and an
image processor. The processor compares successive images,
determines the change in position and velocity and transfers
this information to the host...which explains why they work
on my lap as well as on the bench.
Madhu


{Original Message removed}

2001\10\03@183413 by Raymond Choat

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Phase.

----- Original Message -----
From: "Pedro Drummond" <.....digicallKILLspamspam.....IFXBRASIL.COM.BR>
To: <EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU>
Sent: Wednesday, October 03, 2001 7:45 AM
Subject: [EE]: Optical mouse technology


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2001\10\04@202217 by Peter L. Peres

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> How does it work ? It seems to have a laser diode and a photo sensor,
> but how is it able to respond to movements in every direction ?

It makes a speckle pattern on the target with the laser (whose beam
interferes with itself at the irregularities in the surface) and a small
CCD camera looks at the pattern and determines if it moved and in what
direction. There are other ways to sense this, but they all rely on the
speckle pattern afaik.

Peter

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2001\10\04@214338 by Silvio

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Are you right they are laser?
I've seen some people that put blue led's replacing the red ones, and they
work.
Not to mention the nice appearance...



"Peter L. Peres" wrote:

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2001\10\05@062011 by Peter L. Peres

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> Are you right they are laser? I've seen some people that put blue led's
> replacing the red ones, and they work. Not to mention the nice
> appearance...

All the ones I've seen use a laser. This allows them to work an a very
smooth surface. If the surface is rough you get shades from the slanted
light, and thus contrast. If it is smooth you get speckles, and thus
contrast. Maybe someone makes mice with IR lasers and the LED is just for
coolness...

Peter

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2001\10\05@063852 by code

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Greetings,
   I don't think there's a laser in the mouse, it's just a super bright red
LED

cheers,
Tan



{Original Message removed}

2001\10\05@073412 by eddiemurphy

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> Are you right they are laser? I've seen some people that put blue
led's
> replacing the red ones, and they work. Not to mention the nice
> appearance...

>All the ones I've seen use a laser. This allows them to work an a
>>very
>smooth surface. If the surface is rough you get shades from the
>>>>slanted
light, and thus contrast. If it is smooth you get speckles, and thus
contrast. Maybe someone makes mice with IR lasers and the LED is just
for
coolness...

NO!! You cannot buy a mice with laser. All optical mouse based on a
single bright led /red or blue/ and a small CMOS sensor, similar to CMOS
image sensors. The sensor picks up the image of the mouse pad or the
surface, and a small DSP processes the image.
A laser? No, it's still too expensive, and DANGEROUS to use without
proper optical shielding.

I have a .comMouse /made in Germany/ with an optical sensor and WITH A
RED LED for the CMOS sensor, and a lot of blue leds for email
notification and as a backlight for the small LCD screen.

I have an original MS optical mouse too, with separated red leds for the
sensor and one for fun.

Eddie

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2001\10\05@095836 by M. Adam Davis

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Were there a laser in the mouse, the manufacturer would be required (by
the FDA?) to put labels on the mouse itself describing the power of the
laser and the regulations the device falls under.

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.

-Adam

Peter L. Peres wrote:

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2001\10\06@223508 by Richard Malcolm-Smith

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"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.

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