The Mac Plus (including 128 and 512) mouse is often very hard to find and so a common question is can I convert another mouse for use on the Mac Plus?
The short answer is normally no, or the alternative mouse (a PC Bus mouse) is just as difficult to find.
The reason is the Original Mac mouse has very little circuit decoding done inside of it, instead it is performed by the Mac itself, most modern mice perform a lot of the decoding work internally and normally send clocked data signals indicating what the user is doing straight to the computer, examples are all PC mice (except the bus mouse of course), ADB mice etc. But there is hope in that earlier home computers used the same crude mice decoding like the Mac Plus, an example is the Atari ST or the Commodore Amiga, and using a simple adapter cable detailed below you can use an Atari ST or Amiga mouse on your old Mac.
ST mouse adapter
Mac Plus Atari mouse
9W male 9W male
Amiga mouse adapter
Mac Plus Amiga mouse
9W male 9W male
All mice (with balls that is) use the same technique to determine the ball’s movement, and it involves 2 infrared LED’s and 2 corresponding IR detectors on each axis, (up and down, or left and right). Some mice have combined IR detectors and/or LED’s. and finally a wheel with small holes sits between the LED’s and the detectors and due to the spacing of the detectors it can be calculated which way the mouse is travelling.
Now with crude mice these signals are tidied up electronically and then basically sent direct to the computer to work out which way the mouse is moving, so in theory it should be possible to convert any mouse to work with the Mac Plus, although the amount of effort is probably prohibitive.
Luckily though broken (or working if you wish!) PC mice can often be used as component donors to help fix the more rarer mouse.