Quote Originally Posted by Joe S.
I have one LAST Idea as to the source of this problem:
As I understand their operation, a hall Effect switch outputs 1/2 of it's supply voltage in the on condition, so 5v in 2.5 v out, That's dangerously close to the logic low threshold of TTL, so any voltage drop in supply or signal and POOF no encodeer operation. Check the logic high voltage out of the Hall effect sensor and see what it is.
JS
Yes, this could be. I've attached the schematics to this thread. As you can see around T2 there is a network made by a transistor. I think that also 2.5V are enough to switch the transistor on/off (really are needed only 0.7V) and is this transistor that drive (by another filter made by zener) the PIC pin RA4. I'm right or I'm missing/misunderstunding something?

Thank you.