I might just add that your initial 10 mS debounce delay should
not be necessary.  If you look at the rotary encoder data sheet,
you will see that when Phase A "fires", Phase B is already at
the 50% point of its (virtual) period.  My experience has been
that adding any additional delay here usually makes things less
reliable. FWIW.
Brian Aase

On 23 Jul 2001, at 2:28, Roman Black wrote:

> 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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