A point I missed making in my earlier comments on quadrature decoding is that electrical noise is generally not a serious problem. The leads to the sensors are generally short and generally quite low inpedence. Mechanical noise is for the most part self correcting in the code that I posted. Even the apparent jitter of the edge of a transistion is completely self correcting with the apparent short term error of one count and no system accumulated error. Walter Banks ---------- From: Michael Rigby-Jones The decoder I used (Bournes) had a specified contact bounce time of 5 ms. That was a good reason not to connect it a an interupt pin! Seriously I did think about thihs method and was warned against it by someone else on the list becuase of this. I guess if you are using a super optical encoder with no bounce it would be ok.