Hi Jan, I think your problem might be simple, the
standard way to do this is sense ONLY the 0-1 transition
of A, then checking B tells you the direction.
You just ignore the 1-0 transition on A.

I'm sure that will fix it for you. :o)
-Roman


> First I check by polling if there is a change in the 'A' bit. If so, I wait
> some 10mS (debounce) and then look again. If there is still a change, I
> check if it is 1>0 or 0>1. In each case, I then check the 'B' bit to
> determine direction. For debugging I beep once (CW) or twice (CCW) the
> buzzer.
> When turning the encoder I get seemingly random results. Sometimes it beeps
> 3 times, or 4 times, or 1 time, or not at all over half a revolution. Then
> it starts again. I'm pretty sure it has to do with the debounce, but I can't
> get it right. I must add that the beep adds another 10 or 30 mS delay
> between pollings.
> The encoders are spec'd at <5mS chatter.
>
> Has anyone experience with decoding rotary encoders? Any help or ideas would
> be greatly appreciated.
>
> Jan Didden
> SkinTech
>
> ; The encoders output a 2-bit value:
> ; the A-bit signals rotation,
> ; the B-bit signals the direction of rotation.
> ; encoder movement is detected by polling and debouncing in the b-port.
> ;
> ;         --------------------->cw
> ;    channel A     ___       ___       ___  [channel A leads channel B]
> ;                 ___|      |___|      |___|
> ;
> ;       channel B    ___        ___        ___
> ;                  |___|       |___|      |___|

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