phase 'a' into D
phase 'b' into CLK

Q has your direction out

Works correctly in 7/8 of the reversals. one case of 8 it will give you one incorrect count, work it out.

Can we once and for good kill this old wives tale, this is the umpteenth time I have stated this in this forum.

HP (Agilent) have some nifty ics
yes

If you want to do it yourself, use a (C)PLD, you need to know current state and previous state and trying to do it in the uC will make you lose since even with the slowest movement you will have occasional vibrations across the borderline. I once measured 1Mhz+ pulses coming out of the encoder on a 36 RPM machine when it stopped at the 'grey zone'..


Been there, done that

Erik