Hi, Ioannis

70 pots ... wow, how much hands to drive them ??? two 8 channel low Ron multiplexers could do it ... makes 8 I/O ports

for the keyboard ... 7 port lines can give you 42 buttons ... the trick is just to add a series diodes with each button, and swap the line levels that test the buttons.

Total is 15 I/Os ...

Sorry for Sayzer, but 35 resistors will really be too close a value to each others ( 3% steps ) ... will give a rock'n roll decoding !!! and we do not talk about the POT command !!!

Alain