OT:
Thanks for the answers, links, tips and for welcoming me! :-)
ONT:
@ripster, since i'm no Keyboard expert, from what i have seen from the link - Was the input of that keyboard already there or did you solder it there?
@Findecanor, Hello there! So in other words you could "just" do a own control chip / solder one into the cable and then solder a USB cable?