I have been looking around and there seems to be no good tutorials on how to make a button matrix (like the one on the Ben Heck Raspi Zero Computer). I understand how the matrix works e.g. rows and columns being high etc but I don't understand how to create a PCB design that will allow me to create one or a way to make the code use a port expander to use the matrix. I would be using a raspberry pi but don't want to use most of the GPIO hence the port expander.
Any help would be greatly appreciated. Thanks