Hi, sorry to miss this thread but my Arduino notifications is broken and I only saw this by chance.
If I'm not back in days, I've probably lost the link and the forum did too, send me a PM!
This new forum software is the worst so far and I know what that means. We get to keep it.
You can find mouse chips if you keep your mice that quit because the button died or you find cheap mice on sale. But you need to find one with a chip that is covered, there are at least four.
Alemane, start with this link to links:
Cutting through dead links on the PS2 mouse reader, it connects to the PS2 connector:
Note this direct to the chip article is old, pre- Arduino IDE 1.0, so some minor changes to the library may need to be made.
If you can find the datasheet for the chip on a mouse, chances are it can be used.
And if you can work a digital caliper into your project:
If your movement is along some kind of rails it should be possible to to make an optical sensor that would read a striped scale and count marks either by reflection off lines on paper or by beam interrupt using lines printed on transparency sheet you can have made in an office store... or at least I have done maybe 5 or 10 years ago.
if you have a rack and pinion gear that could be used, sub-mm is possible down to backlash dimension which is small.
Between mechanical and geometric means, 0.1mm or closer may be possible to be sure of using old machinist techniques.