TK has already mentioned it in I have created a PCB for the MIDIbox Standard Control Surface (SCS) that does not require any shift registers and connects directly to J10A of the core board. The SCS module integrates nicely into the MIOS framework, check out tutorial #027 if you want to learn how to use this in your own project. Or just use it for a simple user interface in your MIDIBox CV V2.   I have tried to accommodate footprints for a number of different switches: I succeeded with the Mar