I still dont get what I have to do. I know that I am goin to use the optical encoding disk, but how do I interface it with a computer. Do I simply plug the mouse in and download some software, and thats it or do I have cut out the the rest of the mouse or what.What do I do? The link you showed me showed how to replace the tiny mouse ball with a larger version . Thats not what I need I want to discard the ball, use the disk with the IR Led and Ir sensor to read how pulses and turn that into rpm.