I am currently building the MEGA BREAD project for myself and my son to tinker around with. In the near future, this is to be a base station for robotics control and programming. The keyboard is a 30 push button switch base with 10 outputs and 3 inputs. From the below images you can see that the common blue wires on the schematic are the top yellow wires going to the analog input rail. They are each connected to a 3 stack switch setup on the common side.
Figuring the best way to source the push buttons from the 3 inputs.
Leaning toward the inputs being set to high, digital outputs set to low, detect pushed switch by forcing the input signal low.