Hi Olin,

The one I used was a Grayhill 61C11-01-08-02. I just looked it up and
indeed it is 1 "count" (1/4 cycle) per detent. I had remembered a bit
incorrectly, though: it has 32 detents per rev and not 128. That means
that it is only an 8 "line" per rev encoder. Also, it is actually
optical, not mechanical.

The datasheet can be found here:

http://lgrws01.grayhill.com/web1/images/ProductImages/I-21-22.pdf

Sean


On Sun, Sep 6, 2009 at 9:15 AM, Olin Lathrop<olin_piclist@embedinc.com> wro=
te:
> Sean Breheny wrote:
>> Does your encoder have explicit detents? If so, I think that each
>> detent is usually one count, not 4.
>
> Hmm. =A0The ones I have seen have been one full quadrature cycle per dete=
nt.
> That means 4 state transitions per detent, but one "count" or "position" =
as
> described in the datasheet.
>
> There is good reason for this scheme, so I'm a little surprised you really
> found a encoder with one detent per individual state. =A0 The reason is t=
hat
> the length of each state is going to vary from the ideal of 1/4 cycle. =
=A0You
> can get some additional position information from the state, but the
> accuracy is usually not guaranteed. =A0So the states within a cycle may b=
e a
> bit irregular, but since whole cycles repeat, those can be counted on to =
the
> accuracy stated in the datasheet.
>
> Another way to think about this is that a quadrature encoder is intended =
for
> measuring position in whole cycles, which is where the detents are for th=
ose
> that have detents. =A0The 4 states/cycle are only to provide the signals =
to
> robustly decode whole cycles while tolerating irregularity and bouncing
> between adjacent states.
>
>
> ********************************************************************
> Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
> (978) 742-9014. =A0Gold level PIC consultants since 2000.
> --
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>

-- =

http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist