Key 128 is a USB Keyboard controller compatible with the Commodore 128. It allows users to convert an old Commodore 128 into a USB-compatible keyboard for any modern machine.

I started by setting up the basic functionality. Reading vintage Commodore manuals, I found a test program for RS232 Serial communication I was able to build off of in BASIC. Next, I wired the RS232 Serial out of the Userport into the Serial connection of an Arduino Leonardo. From there, the Arduino Leonardo communicates with a PC over USB using its standard HID library.

Once I finished the basic functionality, I designed a PCB in KiCad to connect the RX and TX pins of the Arduino and Commodore 128. Lastly, I designed an enclosure in Autodesk Inventor. I added a handle to make inserting and removing the device easier, as shown below.