Peter L. Peres wrote:

> The usual way is to connect the metal plate through a high value
> resistor to a diode-protected CMOS input.  With a PIC input and 220V
> mains, 2M2 will work.

  I'd make that two resistors in series.  I am not happy with the
thought or one little resistor 'twixt me and the mains.

> A capacitor is also used in series with the plate and resistor
> sometimes (0.1 uF PMP 400Vdc will be enough).

  More than enough!  Do you mean on its own, as the limiting/ protective
device?  0.1 µF will pass 7.5mA which would be quite a tingle.  I'd have
picked 0.0047 µF or so.

> Since the PIC input was never meant to be used like this, it is good
> to give it an initial DC polarization. I use a 47Meg resistor from the
> PIC input to GND for this.

  The internal diodes will do a better job of controlling teh input
range.  Isn't this just to bias the input and reduce spurious
triggering?
-- 
  Cheers,
        Paul B.