Ok i dont own one of these but was looking in my jameco catalog and then looked up the datasheet.
"The CD4021BC is an 8-stage parallel input/serial output shift register."
know that you know that do you think its possible to accomplish this?
Connect 8 switches (buttons(tactile)) to each parallel input and then connect another button to the first 2 then another to the next 2 so it end up like when you press button 1 it will send a clock and a 1.
I know you would need quite a few transistors to accomplish this but would it work?
The advantage is no ADC needed! and uses about 2-3 wires to PIC .
I got the idea looking at my remote controls PCB when it fell on the floor. You might not need any transistor but i would have to think more on how to wire it lol