Rewiring all the keys seems a bit overkill to me. ADB, just like USB, uses 5V, is fairly well-documented (<a href="https://developer.apple.com/legacy/library/technotes/hw/hw_01.html" rel="nofollow">https://developer.apple.com/legacy/library/technotes/hw/hw_0...</a>), and <i>"A common implementation platform for the protocol is a simple microcontroller: a 2-MHz Motorola 68HC11 has been used with success, although any number of microcontrollers would do a more than adequate job."</i><p>Wouldn't it be easier to write a ADB-to-USB converter for the particular hardware, and put that between the USB cable and the keyboard?