Subject:
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Gutting an optical mouse - Part I
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Newsgroups:
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lugnet.robotics
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Date:
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Fri, 12 Jul 2002 05:28:00 GMT
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Original-From:
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Rob Limbaugh <rlimbaugh@greenfieldgroup.com#IHateSpam#>
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Viewed:
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931 times
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Based on recent discussions of using a mouse as a positioning device and
sheer curiousity in exploiting the potential of a PS/2 device in general, I
bought one. I couldn't wait to void the warranty! The following is
lengthy, just to warn you. Also, if you tear apart your mouse, you void the
warranty and could damage the mouse.
The hope was to find the Agilent ADNS-2030 chip, which is the new low-power
optical chip. It is designed primarily for RF wireless mice, so I didn't
expect to find it in this one. A likely candidate will be an RF optical
mouse that doesn't have a charging cradle. My suspicion is the charging
cradles were necessary to compensate for the power guzzling chips as a way
to spice up the product. (After all, who wants to spend $60-$100 on an RF
wireless mouse if it eats $5-10 in batteries every few weeks?)
And now, on to the gruesome details...
Device:
Memorex Optical ScrollPro Mouse ($14.99 US) purchased from CompUSA:
http://www.compusa.com/products/product_info.asp?product_code=290122
General Description:
PS/2 with three buttons and a scroll wheel. Because it has the scroll wheel
and extra button, it is assumed to use the extended PS/2 protocol. (For
more information about mouse protocols, see
http://panda.cs.ndsu.nodak.edu/~achapwes/PICmicro/mouse/mouse.html)
Exploratory surgery:
Opening the critter was pretty easy, just remember to have it unplugged.
There are 3 screws, one is obvious. The other two are located underneath
the pads near the cable. Gently pry them up with a precision screwdriver or
razorblade. (Don't lose the pads!). Remove the three screws and lift the
head (end opposite the buttons) of the mouse away from the bottom. When
reassembling, the end with the buttons may not align properly--just screw it
back together and it will snap the halves into place.
Internals:
Optical chip: Agilent ADNS-2051 (marked A2051 on chip)
http://literature.agilent.com/litweb/pdf/5988-4289EN.pdf
Controller chip: Holtek 3D PS/2 Controller (marked HT82M39A on chip)
http://www.holtek.com/docum/computer/82m39a.htm
Buttons:
Three 1Amp 125VAC push-button switches (Can be used as Normally Open or
Closed... in circuit as NO)
Two red LED's (one provides illumination for optical sensor, the other is
used to make scroll wheel glow red).
Rotation sensor:
Used for scroll wheel - this part is of major interest (see #5 below)
Remaining electronic parts:
A few resistors, a few capacitors, one ZTA18.43 clock Xtal
Non electronic parts:
Scroll wheel, Lense assembly, and black LED/optical chip cover
What I found out:
1) The mouse works fine over carpets (thick and thin). However, the design
of the bottom plate and lense assembly has a recessed area and could allow
carpet fibers to be trapped over time.
2) This particular mouse does not have to be in perfect contact with the
floor or carpet. However, spacing the mouse above a flat wood surface using
several 2x2 flat plates was too far away for the mouse to sense movement.
(The $60 Microsoft Intellipoint 5 button + scroll mouse I use at work could
sense movement from approximately 2/3 a brick height above the table top.)
3) The lense for the optic sensor must be used. All attempts using a
magnifying glass (including the Lego one) failed, even when used in
conjunction with the lense the mouse came with.
4) The circuit board would fit inside a frame built with 1x12 and 1x8
beams.
5) I removed the rotational sensor because it appeared to be a 360 degree
potentiometer. It wasn't... it's an encoder. It has 24 detents. There are
3 pins. Looking from the side where the scroll wheel is inserted, there are
3 pins: 1 (left), 2 (center), and 3 (right). +V is hooked to pin 2. Bits
0 and 1 are pins 1 and 3, respectively.
Each detent position is either 00 or 11. So, starting from a 00 position,
the next detent would be 11, the next 00, and so on. The half-step between
detents alternates a pattern as well: 00 and 01. Starting from a 00
detented position and turning gives the following output patterns:
Clockwise
Detent? Bit 0 Bit 1
Y 0 0
N 0 0
Y 1 1
N 0 1
(pattern repeats 11 more times)
Counter-Clockwise
Detent? Bit 0 Bit 1
Y 0 0
N 0 1
Y 1 1
N 0 0
(pattern repeats 11 more times)
6) By removing the metal shroud/holder, the detent plate can be removed so
the rotation sensor can "freewheel" with little friction. With two
resistors, this device can become a 15-degree-per-step non-powered rotation
sensor (as it functions like a touch sensor without any internal resistance
value). The patterns 01 and 11 are 7.5 degrees from each other. Angle
between 01 and next 01 is 30 degrees. Accuracy could be increased to 7.5
degress per step by using two of these sensors 30 degrees out of phase with
each other. The resultant patterns would be:
Clockwise
Sensor 1 Sensor 2
Detent? Bit 0 Bit 1 Detent? Bit 0 Bit 1
Y 0 0 Y 1
1
N 0 0 N 0
1
Y 1 1 Y 0
0
N 0 1 N 0
0
(pattern repeats 11 more times)
Counter-Clockwise
Sensor 1 Sensor 2
Detent? Bit 0 Bit 1 Detent? Bit 0 Bit 1
Y 0 0 Y 1
1
N 0 1 N 0
0
Y 1 1 Y 0
1
N 0 0 N 1
1
(pattern repeats 11 more times)
7) The switches are small enough to be mounted on a 2x4 brick.
8) The 3 switches and rotation sensor can all be removed and the optical
sensing of the mouse will still function.
9) The circuit board is very simple in trace design. It is only one layer
(solder side) and there are no surface mount components. This board would
be very easy to re-design in a more compact space without losing
functionality.
Keith O'Hara has already used a mouse as a positioning device, but it is
connected to a computer. The wireless version of the Memorex mouse is
around $30. Check out Keith's site:
http://elvis.rowan.edu/~ohara (Click on the "RowBotics" link or go to
http://elvis.rowan.edu/~ohara/mps/)
I'll post this information along with pictures on the web later this
weekend.
Also, if anyone else has optical mice at their disposal and not afraid to
open them up, could you please do so and email me some particulars so I may
post them? Desired info: Make, Model, chip information, RF or not RF,
approximate cost, number of buttons, type of interface (PS/2, USB, or both),
and pictures of the top and bottom of the circuit boards if possible.
Sorry for the long post!
Rob
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