John Fields said:

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.

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.

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?

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? I've downloaded the

data sheet 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.