Just relating my own experience here.  In normal use, I find
that the Phase B signal has done all the bouncing that it's
likely to at the point when the Phase A transition happens.
Once I made a routine that took a sample right after the
Phase A transition, then waited a while (200 uSec? or so)
and took another sample, waited again, and took a third
sample.  Then I took the "best 2 out of 3" as the answer.
At the time it sounded elegant, but in reality didn't help
very much.

What electrical components are you using around your
encoder?  For me, a pullup of around 47K ohms to +5
and a bypass of around 680 pF from each contact to
ground works pretty well.

Brian Aase

On 22 Jul 2001, at 19:32, SkinTech wrote:

> Brian,
> You may have a point here, but what about the chattering/bouncing of the
> contact? Maybe I should process the change at the first indication of a
> change, let the thing bounce away with maybe some delay AFTER processing
> BEFORE polling again, what do you think?
>
> Jan Didden
>
> PS This thing has 15 detents and 30 steps over 360 deg. Even turning at 1
> rev/sec (which is pretty fast for a manually operated knob) gives some 33
> msec to leisurely process each change.
>
> ----- Original Message -----
> From: "Brian Aase" <ulcsa@ESKIMO.COM>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Sunday, July 22, 2001 7:09 PM
> Subject: Re: [EE]: Stumped by rotary encoder
>
>
> > 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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