In message  <01bd2b18$07724260$083d11ac@heartofgold.satellites.twin.dev>
 PICLIST@MITVMA.MIT.EDU writes:
> >Philip Cowley wrote:
> >
> >> I need to count the pulses coming from a pair
> >> of quadrature incremental encoders.
> >
> >Are these optical encoders, or mechanical?
>
> I have a matched pair of optical encoder disks which I am having mounten on
> to shafts. The disks have 1458 lines, which produces 5832 quadrature
> transitions.
>
> >The latter have _awful_ signals.
>
> I know... but reasonable optical encoders are not actually that difficult to
> build.
>
> >What's the app?
>
> Ahhh there's the rub!
>     I am building a computer control system for a large astronomical optical
> telescope. The telescope weighs about a ton (1000kg) and is driven by a pair
> of synchro motors. These are currently controlled by some analogue
> electronics from a small joystick.
[snips]

Phil,

I would suggest that you don't do the quadrature decoding in the
PIC, but rather use on of the decoder chips from either Texas or
Hewlett Packard.

I have used HPs HCTL2016 successfully in a PIC project. It has 16
pins, maintains 16 bit pulse count which is read using an 8 bit
bus. In my project, I read the 2016 every 1ms adding the difference
of the count into a 32 bit accumulator which is then multiplied by
a 16 bit number for calibration before sending the most significant
32 bits serially to a DSP chip.

Regards,

Mike Watson