Re: scavenging opto-isolators

On 26 Dec 2007 13:41:12 -0500, Allan Adler
<ara@xxxxxxxxxxxxxxxxxxxx> wrote:

John Fields <jfields@xxxxxxxxxxxxxxxxxxxxx> writes:

On 25 Dec 2007 07:03:51 -0500, Allan Adler
<ara@xxxxxxxxxxxxxxxxxxxx> wrote:
I've uploaded digital photos of the mouse PCB. That might make it easier
for people to figure what I'm talking about or identify components.

WRT your comments:
The resistors are identified by a numerical code where the first two
digits are significant figures and the third digit denotes how many
zeros follow the first two digits. So the resistors marked "330" would
be 33 ohm resistors since the trailing zero indicates zero zeros follow.
The resistor marked "513" would be interpreted as 51 followed by
three zeros, or 51300 ohms (51.3k ohms)

Thanks for the explanations. That would be 51000 ohms.

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LOL, yup! :-)
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The optoisolators with pins tied together are more than likely the
emitters (IRLEDs).

I'll have to take another look at the PCB, but I recall being confused
by the fact that the manner in which pins were tied together was different
on the two opto-isolator pairs.

While you've gone to the trouble to generate your matrix and all,
much more useful documentation would be a schematic which you could
easily generate by just examining the wiring and tracing all its
connections to the various components.

Actually, I didn't generate the matrix. I just made sure that every pin
had another pin somewhere that it was connected to and recorded the connection.
I considered just looking at the connected components of the wiring and
enumerating the pins on each component, but I was afraid of missing one,
since the components move around so much. On the other hand, my method
is also flawed, since it is possible that I could wind up generating a
partition of the equivalence class represented by the connected component,
unlikely as that seems (given a set S of 2 element subsets of an n element
set X such the union of S is X, what is the probability, with fixed X and
variable S, that the graph whose set of vertices is X and set of edges is S
is connected?). From this anecdotal information about pin connections, it
would be possible to generate the 95x95 matrix and all that follows from it,
but I didn't actually do so.

Like this guy did:
http://colinfahey.com/oldpages/2002june5_ps2mouse/index.htm

Thanks for bringing this website to my attention. It is pretty
impressive! I had been searching for mouse printed circuit boards
in Google but didn't come up with this. What was your search string?

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microsoft mouse schematics.
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It's amazing the lengths this guy went to, replacing himself in the
circuit by a bowl of water and some wires, before he finally figured out
what's going on.

How likely do you think it is that the unidentified 16 pin IC on my mouse
is a clone of the 16 pin IC on Colin Fahey's mouse?

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Dunno, but if you'll draw a schematic of what you have and compare
the pinouts of your chip with his,you can get a pretty good idea of
whether it is or not.
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I've downloaded the
data *** of his IC and will take a look at it later.

His page shows that the Microsoft PS/2 mouse is a very sophisticated
device. I had expected the HP mouse to be basically simple, which is one
reason I thought that observation without measurement might suffice to
make sense of it, but now I expect otherwise. On the other hand, even if
I had the equipment, I doubt that I would ever have figured out what Colin
Fahey did. I'm going to study his page very carefully.

The page he links to at the end of his page, regarding a similar approach
to PS/2 keyboards, doesn't seem to exist anymore.

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Here's a good PS-2 link:

http://www.computer-engineering.org/ps2protocol/



--
JF
.

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