Imagine I have a 4-position selector switch. At each position one set of dry contacts is made.
But I have only two AVR inputs, so I want the four positions 1-of-4 to be turned into binary 00-01-10-11. (Actually, I only have two fully-protected and conditioned "channels" on my board into two AVR inputs.)
There has to be some way to use diodes and jumpers and such to achieve this. But my head hurts after a while thinking about it...
If it helps, the contacts can be NO or NC or a mix.