This is a PCB [partial] kit to assemble your own ADB Keyboard to USB adapter. Includes the PCB, a 4.7k resistor, and ADB jack from US supplier. 

To accompany this kit you only need to add a Pro Micro w/headers, which are available widely. 

PCB Layout by Roman Gaillard https://github.com/ronangaillard/adb2usb


I strongly recommend using an elite-c pro micro, unless you are experienced doing DFU flashing / using another arduino to burn a bootloader. An elite-c will take the ADB QMK firmware very easily typically without having to burn a bootloader just using the QMK Toolbox GUI. Full information and instructions either way are contained in the forum thread here:

https://68kmla.org/bb/index.php?threads/cheap-and-simple-adb-to-usb-converter.39402/