I have made a simple tachometer using old roller ball mouse parts. I
record the output using a soundcard. Works well.

What I want to do now is print a ribbon, attach it to the rim of a
disk, and point a laser mouse at the vertical lines running around the
rim.

Basically I hope to sample the speed of the disk as often as
practical.

I have been thus far stymied in finding out about the data stream of
the mouse - both inside the mouse (DSP chip), and external to the
mouse (USB).

Anybody got any ideas?