WarhammerBueno designed a keyboard with a replaceable numpad – using a unique rail system.
KBD.news Published June 18, 2022
After months of work I have successfully designed a keyboard that allows you to replace the numpad with a different module using a rail on the right side – WarhammerBueno.
Each module has its own Pro Micro, the link system is essentially a USB that connects the module straight to the PC through an internal USB splitter in the main keyboard unit.
Magnets would work too, the author was initially going to use those, but he didn't have access to pogo pins and wanted the module to stay firmly attached to the main unit.
The method I went with was basically using the metal rails from one of those Nintendo switch joycon holders with the pins removed and replaced with a standard female 2 pin socket. The part I designed fits in the rails and has two male pins to interface with the socket on the switch rails.
Currently, the author has a numpad and a macropad module, but he is thinking of making a spacemouse looking module for CAD, as well as another one with a screen.