jackrae:
Note that this system only caters for one switch being operated at any time. If you google R-2R you'll get info on how this is accomplished
Just to avoid any confusion, I'm sure that you intended to say that you can Google R-2R to get info on how to detect multiple simultaneous button presses. (Your original wording seems to imply that R-2R only caters for one switch being operated at a time.)