Andres j Ogayar wrote:

> The idea is having 'something' (read a 555) reading a potentiometer
> position and generating 1 to 2 ms pulses depending on its position
> -1,5 ms will be on the center-.

  Can I suggest you forget the 555s and simplify the thing completely?

  Just connect the joysticks (with a series resistor) to eight PIC
inputs with a parallel capacitor on each.  See the Stamp instructions
for plausible values.  Each capacitor is charged via an output "1" for
the two steps prior to measurement, then the pin is changed to an input
and times the next output pulse until it runs down past the logic "0"
threshold.

  A single-chip PIC implementation of a single-chip R/C encoder, using
the standard sequence.  Just what PICs are for!

  Cheers,
        Paul B.