Patric Anvegard wrote:

> Am I right or.....

  Yes, you're quite right.  You have clarified that you are looking at
*both* edges of the "clock" (interrupt) phase.  The problem comes when
this is not understood and someone attempts to simplify it by using only
*one* edge.

  The whole system (*any* quadrature encoder) depends on the ability of
the firmware to respond to a transition on one phase (and that includes
bounces) before any transition occurs on the other.

  Also, any encoder in which the bounce of one phase can ever extend to
the subsequent transition on the other would be essentially useless in
consequence.

  "Mechanical" encoders (contacts) are thus limited to non-critical uses
such as manual adjustment knobs.  All my mice with PCB encoder discs are
now in the "curiousity" box (I can't bring myself to throw anything
out...).

  The chief limitation of "count" and "direction" encoding is that it
halves the resolution, i.e., you can only respond to transitions on the
"count" phase.  Better is to XOR the two inputs and feed that to the
IRQ input (which still must detect both transitions).

  I like John Payson's suggestion which is a two-phase debounce.
--
  Cheers,
        Paul B.