[Ladyada] and [pt] had an old keyboard from NeXT, but since it used a custom protocol it wasn’t usable with modern hardware. So they built a custom device to convert the NeXT protocol to USB.
The device uses a Arduino Micro to read data from the keyboard and communicate as a HID device over USB. It connects to the keyboard using the original mini-DIN connector, and is housed in the classic Altoids tin enclosure.
Since the protocol used by NeXT isn’t standard, they had to figure it out and write some code to interpret it. The keyboard communicates bidirectionally with the computer, so they needed to send the correct frames to key data back.
The final product is an adapter for NeXT to USB, which allows for the old keyboards to be used on any computer with USB. It’s a good way to bring back life to some otherwise unusable antique hardware.