Ing. Jorge Raul Casalini+ wrote:

> The switch has got two position, normally Closed (N.C.) and normally
> Open(N.O.) but all the video games use N.O. switch and sense when it
> is closed because (i discover it!) the vibration of the machine make
> that the closed (N.C.) switch will open for a few moment

  Where you have both NO and NC contacts available, the preferred
debounce technique is to implement a R-S latch (which is just as easy
using two PIC inputs) so that a "make" is detected when the NO closes
for a certain minimum period, and a "break" (coin has passed) detected
only when the NC closes for the same period.

  If you have *both* contacts available therefore, (and the common
grounded) *use* both.  Don't forget a 1k (or less) resistor to bias the
contacts to 5V and a 33k in series from this to the PIC input with a
small interference suppression capacitor (47nF?) to ground at that
point, on *each* of the *two* inputs.
--
  Cheers,
        Paul B.