dhenry:
R-2R networks only work with SPDT switches, not SPST push buttons.
Are you sure about that?
With a r2r type button, you can read multiple buttons from one pin, and you can detect simultaneous presses as well.
Thank you for pointing me t R/2R networks.
I'm no expert (in fact i learned about it today) but from the wikipedia article it would seem they would work also with momentary pushbuttons.
The problem of the low separation of voltages still remains as the resolution, for 12 pins is:
5/2^12 = 0.00122V