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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> >
>
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