From: marc@targon.UUCP (Marc Dierikx)
Newsgroups: comp.sys.atari.st.tech
Subject: Re: help my mouse won't stop
Summary: automatic mouse movement stopped
Keywords: mouse
Date: 20 Nov 92 06:34:56 GMT
Followup-To: comp.sys.atari.st.tech
Organization: Siemens Nixdorf Infosystems


The Dutch magazine 'ST' of July/August 1990 had an article 'Stop
de Genius!' which explains what may be causing the problem of
automatically moving mouse pointers.
I'll try to translate and summarize (in my broken English anyway...)


For each direction the mouse has two light sensitive diodes.
These diodes are lit by some light source. Between the light
source and the diode rotates a disk with holes in it.
Depending on the mouse movement, the light sensitive diodes
see a block wave of light pulses. The block waves for the two
diodes are 90 degrees out of phase; thus the direction can be
estimated from the fase difference of these block waves (see figure).


        Right movement		      Left movement
V
 d1       ____      ____		 ____      ____
     ____|    |____|    |____       ____|    |____|    |__

V       ____      ____      _	    _      ____      ____
 d2  __|    |____|    |____|         |____|    |____|    |


Now the ST reacts to the flipping of one or both of V   and V  .
						     d1      d2
The problem would not have occurred when it would have reacted
only when both of the pulses were flipped, but now it is possible
that due to some distortion on one of the signals the mouse pointer
moves in one direction!
It must even be possible to simulate this distortion manually if
you move the mouse just a very little bit. In mice like the Genius
this distortion may be caused by some 50/60Hz noise on the 5V line.

The Genius mouse has for every diode the following circuit:

      ______________________ 5V
     |                |
   ____               _
 -> /\               | | R6
   /__\ D1           |_| 10K
     |         _______|_____ V
     |       |/               out
     --------|
     |       |\
     _         v
    | | R1     |
    |_| 6K8    |
     |         |
     ----------------------- 0V

The problems occur when V   is about 2.5V.
                         out
You may get rid of the problem if you replace the transistor with
a Schmitt trigger. Then you get something like this:

      ______________________ 5V
     |                |
   ____               _
 -> /\               | | R6
   /__\ D1           |_| 10K
     |      ____      |_____ V
     |     |  __\     |
     ------|_|_| 0----
     |     |____/
     _  
    | | R1 
    |_| 6K8
     |
     ----------------------- 0V

So all you need is a quad Schmitt Trigger and some solder experience.
Ofcourse you do this on your own risk, I take no responsibility
for damage of whatsoever! (But the people of the 'ST' magazine seem to
know what they are talking about). I have not tried it myself
(no thanks, no Genius mouse for me), so I hope this really helps.
Is this something for the hardware FAQ?

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Newsgroups: comp.sys.atari.st.tech