'1 out of 128 switches'
No-one has mentioned it so far, so here are two ideas. Totally untested, but
1) all switches in parallel, each switch with a specific, know resistor in
series. The PIC embedded control handbook shows an application for resistance
measurement. Is is likely that more than one switch will be closed at the
same time? You will then have to calculate the possible options, as keeping a
file of 128! would be a problem :)
2) all switches in parallel, with a capacitor per switch. Drive with a know
frequency, and measure where the cutoff frequency is.
If either option works, you need TWO pins only.
Hope this helps,
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