You might be surprised to learn that most game rules can be prototyped in paper/with physical parts. Paper prototypes are cheap, quick to work with, and very easy to change. However, some concepts like twitchy reaction-based button pressing do not translate very well to paper. Make a list of the mechanics you want in your electronic game, and then see if you can think of a way to represent them in a physical way. For more information about paper prototyping, see the Prototyping in Paper and Limitations of Paper sections of the Design Process Lesson of Ian Schreiber’s Game Design Concepts course.