Simon,

according to Roman ( and he4s right by the way ) the portpins are not real
oct because of the protection diodes as you found also. Therefore pulling
the base low after a button was pressed would work, but releasing it to high
state ( what means 12V in this case ) would probably not. Also changing the
10M resistors to a significant lower value would result in exessive current
drain while in off state.

Roman, i will decide to use the diodes or not after i finished my
messurements. I took the idea for the simplification out of a MCHIP appnote
about interfacing a pic to the AC powerline via just one resistor. I found
if  thatone worked my should also.

Germain

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