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PICList Thread
'[EE]: PC mouse optical detectors.'
2003\04\29@055826 by erholm (QAC)

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Hi.
I just scraped an old mouse (a Logitech wheel mouse)
to see what optical components they used.
I noticed that the wheel had one LED (IR?) and one
3 pin "receiver" mounted. Now, the wheel just have a row
of spokes, but someway, the unit must not only detect
spoke/nospoke, but also the direction the wheel is turning.
Anyone know how these receivers work ?

Maybe I'll de-solder a pair and setup a testbed...

No marking on the components, of course...

Jan-Erik.

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2003\04\29@060840 by Guillermo Rodriguez Garcia

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At 11:49 29/04/2003 +0200, Jan-erik Soderholm (QAC) wrote:
>Hi.
>I just scraped an old mouse (a Logitech wheel mouse)
>to see what optical components they used.
>I noticed that the wheel had one LED (IR?) and one
>3 pin "receiver" mounted. Now, the wheel just have a row
>of spokes, but someway, the unit must not only detect
>spoke/nospoke, but also the direction the wheel is turning.
>Anyone know how these receivers work ?

There are actually two sensors on each of those receivers.
These will receive the same signal but with a phase shift.
e.g.:

"Forward" movement:

sensor 1 - 1111000011110000111100001111
sensor 2 - 0011110000111100001111000011

"Backwards" movement:

sensor 1 - 0011110000111100001111000011
sensor 2 - 1111000011110000111100001111

By looking at the phase shift you can find out the direction
the wheel is turning.

G.

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2003\04\29@061246 by Jason Dini

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I've often wondered about this myself. If you say that the receiver has 3
pins, it could just be that they have 2 photo-diodes in one receiver package
and simply see which gets ir light first.

Jason

{Original Message removed}

2003\04\29@061902 by Richard Stevens

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Jan-Erik,
       In response to your posting, 2 mice in my office have been
spontaneously dismantled by their owners! If this is repeated across the
piclist, you could have a serious impact on productivity internationally!


{Original Message removed}

2003\04\29@075521 by hael Rigby-Jones

picon face
> -----Original Message-----
> From: Jason Dini [SMTP:spam_OUTjason.diniTakeThisOuTspamORCHID-SA.CO.ZA]
> Sent: Tuesday, April 29, 2003 11:03 AM
> To:   .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Subject:      Re: [EE]: PC mouse optical detectors.
>
> I've often wondered about this myself. If you say that the receiver has 3
> pins, it could just be that they have 2 photo-diodes in one receiver
> package
> and simply see which gets ir light first.
>
> Jason
>
Correct.  They are more likely to be a pair of photo transistors, but
whatever they are there is two of them.

Regards

Mike



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2003\04\29@082530 by Jinx

face picon face
The phase detection is explained here very clearly (page 3)

http://computer.howstuffworks.com/mouse2.htm

I understand that PICs have been used as the uC

If there's anything that gets thrown away in big numbers it's
mice. They're great for microswitches, leads, IR and other
components

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2003\04\29@095755 by

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OK. I can understand that, and if they had 4 pins, I would
have been even clearer. But with 3 pins (1 look as power and 1 as
gnd), do they code/multiplex the two detectors in 1 signal on 1 pin ?
Jan-Erik.


Guillermo Rodriguez Garcia wrote :
> There are actually two sensors on each of those receivers.
> These will receive the same signal but with a phase shift.

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2003\04\29@101250 by Guillermo Rodriguez Garcia

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At 15:56 29/04/2003 +0200, QAC wrote:
>OK. I can understand that, and if they had 4 pins, I would
>have been even clearer. But with 3 pins (1 look as power and 1 as
>gnd), do they code/multiplex the two detectors in 1 signal on 1 pin ?

You don't apply "power" to a sensor. An IR sensor is just
a photodiode whose response will vary depending on how much
light it receives within the IR band of the spectrum.

G.

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2003\04\29@102700 by

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That sounds logical of course, *but*...

There are three sensors with three pins each.
Each has one pin to GND, one pin via a common
inductor ("W1" ?) to power, and *ONE* pin each
connected to the IC. So, in some way, they
talk to IC via one pin for each sensor. And there
os one sensor for the wheel and one for each
"direction" of movement.

So my bet is that this are some kind of sensors
with some builtin logic.

Well, maybe better to breadboard a sensor and take
out the scope...

Jan-Erik.


Guillermo Rodriguez Garcia :
>You don't apply "power" to a sensor. An IR sensor is just
>a photodiode whose response will vary depending on how much
>light it receives within the IR band of the spectrum.

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2003\04\29@104054 by

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Jinx wrote:
> The phase detection is explained here very clearly (page 3)
> http://computer.howstuffworks.com/mouse2.htm

That uses two pairs of LED/sensors for each "function"
in the mouse. My mouse use one pair.
Jan-Erik.

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2003\04\29@104340 by

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Sorry about that !
If they can't get them together correctly again,
you can always send them to me :-)
(See my plan now ?)

Jan-Erik.

Richard Stevens wrote:

> Jan-Erik,
> In response to your posting, 2 mice in my office have been
> spontaneously dismantled by their owners! If this is repeated across the
> piclist, you could have a serious impact on productivity internationally!

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2003\04\29@105154 by Guillermo Rodriguez Garcia

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At 16:25 29/04/2003 +0200, QAC wrote:
>That sounds logical of course, *but*...
>
>There are three sensors with three pins each.
>Each has one pin to GND, one pin via a common
>inductor ("W1" ?) to power, and *ONE* pin each
>connected to the IC. So, in some way, they
>talk to IC via one pin for each sensor. And there
>os one sensor for the wheel and one for each
>"direction" of movement.

As I said you need two sensors per wheel to determine
direction. These two sensors can be physically closer
or far apart depending on which mouse you're looking
at. From your description I assume that what you have
is 2 leds + 2 sensors per wheel (can't see how it can
be three sensors). The IR sensors will be biased
appropriately and the current flow through them
measured (ADC in the microcontroller) to determine
the direction and rate of movement.



>So my bet is that this are some kind of sensors
>with some builtin logic.

Don't think so :)

G.


{Quote hidden}

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2003\04\29@105816 by

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*ONE* (2 pin) LED and *ONE* (3 pin) sensor per wheel.
Jan-Erik.

Guillermo Rodriguez Garcia wrote:
> From your description I assume that what you have
> is 2 leds + 2 sensors per wheel

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2003\04\29@110233 by Guillermo Rodriguez Garcia

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At 16:57 29/04/2003 +0200, QAC wrote:
>*ONE* (2 pin) LED and *ONE* (3 pin) sensor per wheel.
>Jan-Erik.
>
>Guillermo Rodriguez Garcia wrote:
> > From your description I assume that what you have
> > is 2 leds + 2 sensors per wheel

Then it is as I described at the beginning, one led and
*TWO* sensors (mounted in a single receiver) per wheel.

G.

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2003\04\29@110646 by

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(Well, I'm going to stop this thread soon...)

Yes, but you described a 3 pin sensor with *two*
signal pins. I have a 3 pin sensor with :

One pin to GND
One pin (via a inductor) to power
One pin to the IC

Jan-Erik.

Guillermo Rodriguez Garcia wrote:

> Then it is as I described at the beginning, one led and
> *TWO* sensors (mounted in a single receiver) per wheel.

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2003\04\29@110647 by Olin Lathrop

face picon face
> OK. I can understand that, and if they had 4 pins, I would
> have been even clearer. But with 3 pins (1 look as power and 1 as
> gnd), do they code/multiplex the two detectors in 1 signal on 1 pin ?

Very unlikely.  One pin is either power or ground.  One end of both
photodectors are tied to this pin.  The other two pins are the other ends
of each photodetector.  I seriously doubt you have both a power and ground
rail in the three pins.


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2003\04\29@111316 by

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Yes, but then I'd expect *two* pins beeing
connected to the IC , not ?

As I said :
one pin to GND (black lead in the cable)
one pin to power (read lead in the cable, via an (common) inductor)
one pin to the IC

And the two first pins from each of the three sensors are
tied together (directly, via the PCB). The third pin from
each sensor is connected to three different pins on the IC.

Jan-Erik.

Olin Lathrop wrote:
>One pin is either power or ground.  One end of both
>photodectors are tied to this pin.  The other two pins are the other ends
>of each photodetector.  I seriously doubt you have both a power and ground
>rail in the three pins.

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2003\04\29@111445 by Guillermo Rodriguez Garcia

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At 17:04 29/04/2003 +0200, QAC wrote:
>(Well, I'm going to stop this thread soon...)
>
>Yes, but you described a 3 pin sensor with *two*

I know.

>signal pins. I have a 3 pin sensor with :
>
>One pin to GND
>One pin (via a inductor) to power
>One pin to the IC

I sincerely doubt this is the case. More likely you may have
made a mistake somewhere and you'll actually have one pin to
either GND or power, but not both, and 2 signal pins, no
matter how they are connected. But just play around with it,
you'll find out yourself.

G.

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2003\04\29@112502 by hael Rigby-Jones

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> -----Original Message-----
> From: Jan-erik Söderholm (QAC) [SMTP:.....Jan-erik.SoderholmKILLspamspam.....PAC.ERICSSON.SE]
> Sent: Tuesday, April 29, 2003 4:12 PM
> To:   EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject:      Re: [EE]: PC mouse optical detectors.
>
> Yes, but then I'd expect *two* pins beeing
> connected to the IC , not ?
>
> As I said :
> one pin to GND (black lead in the cable)
> one pin to power (read lead in the cable, via an (common) inductor)
> one pin to the IC
>
> And the two first pins from each of the three sensors are
> tied together (directly, via the PCB). The third pin from
> each sensor is connected to three different pins on the IC.
>
> Jan-Erik.
> If this is correct then there must be some decoding logic built into the
detectors as you suggested.  Do you have a scope to check the third pin
with?  My guess would be some kind of pulse width encoding: i.e. short pulse
= one step forward, long pulse = one step back.

Regards

Mike


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2003\04\29@113116 by

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Well, I'll take a sensor away and setup a testbed.

I just made a last quick check with my ohm-meter, and,
yes, pin 1 from each sensor are tied together (and to
GND), the same for pin 2 (and to power). Pin 3 goes
to the IC.

Anyway, I'll be back after some evening testing !

Jan-Erik.



Guillermo Rodriguez Garcia wrote:

>> I have a 3 pin sensor with :
>>
>>One pin to GND
>>One pin (via a inductor) to power
>>One pin to the IC
>
>I sincerely doubt this is the case. More likely you may have
>made a mistake somewhere and you'll actually have one pin to
>either GND or power, but not both, and 2 signal pins,

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2003\04\29@113321 by Alan B. Pearce

face picon face
>One pin to GND
>One pin (via a inductor) to power
>One pin to the IC

I suspect your sensor may not be two photo diodes, but rather two
photoresistors in series across the supply, and the input on the chip is
actually an analogue one measuring the voltage of the divider. This way it
would be easy for the micro to see the "black stripe" of the spoke in the
wheel move past and trigger an interrupt at midpoint, and then figure out
which way the bar is moving by determining if the voltage moves up or down.

It may not be CDS type sensors, but that was what I had in mind, but I don't
think they are fast enough response for this. Anyone remember the dance arm
sensors on reel to reel tape drives ????

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2003\04\29@114129 by hael Rigby-Jones

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> -----Original Message-----
> From: Alan B. Pearce [SMTP:@spam@A.B.PearceKILLspamspamRL.AC.UK]
> Sent: Tuesday, April 29, 2003 4:34 PM
> To:   KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: PC mouse optical detectors.
>
> >One pin to GND
> >One pin (via a inductor) to power
> >One pin to the IC
>
> I suspect your sensor may not be two photo diodes, but rather two
> photoresistors in series across the supply, and the input on the chip is
> actually an analogue one measuring the voltage of the divider. This way it
> would be easy for the micro to see the "black stripe" of the spoke in the
> wheel move past and trigger an interrupt at midpoint, and then figure out
> which way the bar is moving by determining if the voltage moves up or
> down.
>
Not convinced about this.  The output would have the same mark/space
irrespective of direction.  With no reference to compare this signal to, how
would the direction be decoded?  In fact, you'd get the same output with
just one sensor AFAICT.

Mike


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2003\04\29@115203 by Alan B. Pearce

face picon face
>Not convinced about this.  The output would have the same
>mark/space irrespective of direction.  With no reference
>to compare this signal to, how would the direction be
>decoded?  In fact, you'd get the same output with just
>one sensor AFAICT.

Forget mark/space, think analogue voltage. As the spoke moves clockwise
(say) the spoke will shield a portion of the sensor so the voltage on the
output pin will go (say) high for a midpoint voltage. This could be enough
to put the trigger point outside the window of the chip, thereby generating
an interrupt, or whatever is used to sense the position. As the spoke keeps
moving the voltage will go towards midrail again as the spoke shields both
parts equally, and then as the other half of the sensor gets shielded the
voltage goes low, and again outside the window, generating another
interrupt.

I believe doing this with a 16F630/676/627/628 or any others with
comparators would allow you to sense the mouse mickeys quite successfully.

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2003\04\29@115628 by Olin Lathrop

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> One pin to GND
> One pin (via a inductor) to power
> One pin to the IC
One pin to rule them all, and in the darkness bind them.


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2003\04\29@120254 by Tal

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There are two sensors in a slight angular shift. They are designed such
that there is overlap between there pulses. When you rotate the wheel in
one direction you get

A B
0 0
0 1
1 1
1 0
0 0

And when in the other direction you get this sequence reversed. A simple
finite state machine is used to extract from these sequences Increment
and Decrement pulses. The finite state machine is designed such that
even if the wheels changes direction arbitrarily, you don't accomulate
any error.

Tal

> {Original Message removed}

2003\04\29@120709 by

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Yes, I understand that, questiton is, how do
you represent that using a single pin ?
Jan-Erik.

PS.
And I think you should have read the rest of the thread before replying...
DS.

Tal wrote:

There are two sensors in a slight angular shift. They are designed such
that there is overlap between there pulses. When you rotate the wheel in
one direction you get

A B
0 0
0 1
1 1
1 0
0 0

And when in the other direction you get this sequence reversed. A simple
finite state machine is used to extract from these sequences Increment
and Decrement pulses. The finite state machine is designed such that
even if the wheels changes direction arbitrarily, you don't accomulate
any error.

Tal

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2003\04\29@135753 by

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So, now I'v had my scope connected to the "third" pin of
the sensor.

In the Idle state (wheel standing still) it outputs
two "1" pulses, 2.5 us and 3.5 us long and with a
15.5 us delay between them. This is repeated each
190 us (or with 5.3 kHz).
It doesn't matter if there is a spoke or not in between.

When the spokes moves in one direction, the second (3.5 us)
pulse becomes longer (aprox 13-14 us) and delay between
the pulses shorter with the same amount so the total
time for both pulses stays the same (21.5 us).

When the spokes moves in the other direction, I had problem
with the triggering of the scope, but it looked like the
first puls gets longer instead, so that most of the
170 us delay becomes a long pulse (part of the "first" pulse).

Anyway, one would realy need a data sheet on these, I suspect.

While soldering tiny "probes" on the PCB, I happend to
burn the sensor for the "wheel". I tried to replace it
with one of the sensors for the "movement" detector, but
obviously they are a little different. They detect movement
(spokes moving by) in two different directions (of by 90 deg).

There are a picture of this actual mouse on this page :
www.saitosite.com/pc/0007/pachimouse.html.
Let the page load and search for "SAT48a". There are
two pictures (the page is in Japanes, I think...).


Now, how do one find any datasheet on these ?

Thanks for your time !
Jan-Erik.

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2003\04\29@150308 by Dwayne Reid

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At 07:55 PM 4/29/03 +0200, QAC wrote:

>In the Idle state (wheel standing still) it outputs
>two "1" pulses, 2.5 us and 3.5 us long and with a
>15.5 us delay between them. This is repeated each
>190 us (or with 5.3 kHz).
>It doesn't matter if there is a spoke or not in between.
>
>When the spokes moves in one direction, the second (3.5 us)
>pulse becomes longer (aprox 13-14 us) and delay between
>the pulses shorter with the same amount so the total
>time for both pulses stays the same (21.5 us).
>
>When the spokes moves in the other direction, I had problem
>with the triggering of the scope, but it looked like the
>first puls gets longer instead, so that most of the
>170 us delay becomes a long pulse (part of the "first" pulse).

Is there a capacitor connected from that signal pin to ground (or Vdd?)  If
you disconnect the signal lead from the processor, are there pulses on the
sensor line or the processor line?

I'm thinking that the processor is outputting pulses and the sensor is
modulating them in some way.  An RCtime type measurement comes to mind.

dwayne

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2003\04\29@152729 by

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Nothing between the "output" pin of the sensor
and the IC. Could be a pull up inside the IC, don't know.
Nice sharp pulses.
Jan-Erik.

Dwayne Reid wrote:
>Is there a capacitor connected from that signal pin to ground (or Vdd?)  If
>you disconnect the signal lead from the processor, are there pulses on the
>sensor line or the processor line?
>
>I'm thinking that the processor is outputting pulses and the sensor is
>modulating them in some way.  An RCtime type measurement comes to mind.

dwayne

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2003\04\30@064602 by Guillermo Rodriguez Garcia

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Hi,

>So, now I'v had my scope connected to the "third" pin of
>the sensor.
>
>In the Idle state (wheel standing still) it outputs
>two "1" pulses, 2.5 us and 3.5 us long and with a
>15.5 us delay between them. This is repeated each
>190 us (or with 5.3 kHz).
>It doesn't matter if there is a spoke or not in between.

Maybe the receiver has variable-R sensors or something?
As someone already pointed out, it would be interesting
to know whether the receiver is just modulating pulses
generated by the IC. It seems strange that the receiver
itself will generate the pulses on its own...

[...]
>Anyway, one would realy need a data sheet on these, I suspect.

Yes :)

G.

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2003\04\30@070052 by erholm (QAC)

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Well, after a second thought (an a second test on the
mouse electronics) I'v found out that the pulses are there
even when the sensor is de-soldered. So they must come from
the IC then. Still, I'd like to know how the sensor modulates
the puls train and how it detects which way the spoke is
moving. Well, this was just a late-night-thing, and I'm not
going to take it any longer than this...

Nice component, anyway...

Regards and a happy celebration of Walpurgis night
("Valborgsmassoafton" in Swedish...).

Jan-Erik.



Guillermo Rodriguez Garcia wrote:

>Maybe the receiver has variable-R sensors or something?
>As someone already pointed out, it would be interesting
>to know whether the receiver is just modulating pulses
>generated by the IC. It seems strange that the receiver
>itself will generate the pulses on its own...

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