[sorry, send at first without tag. therefore resend]

Hi all,

I always try to solve my own problems (I learn from it) but this one has =
me
stumped.
My project has a 16F74, reading the output of a rotary encoder (2 bit), =
see
below.
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

; This is how I think the encoders work:
;The encoders output a 2-bit value:
; the A-bit signals rotation,
; the B-bit signals the direction of rotation. (actually A and B are =
interchangable of course)
; encoder movement is detected by polling PORTB and debouncing.
;
;         --------------------->cw
;    channel A     ___       ___       ___  [channel A leads channel B]
;                 ___|      |___|      |___|
;
;       channel B    ___        ___        ___
;                  |___|       |___|      |___|
;
;
;
; CCW: channel A      ___        ___        ___ [channel A trails =
channel B]
;                          ___|       |___|      |___|
;
;           channel B    ___       ___       ___
;                           _|      |___|     |___|
;
;     A-bit       B-bit      Direction
;     0>1           0           CW
;                       1           CCW
;     1>0           0           CCW
;                        1           CW

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