Jonathan Hayes wrote:
>
> I've been asked to work with an Optical Encoder and a display with the
> capability of updating the readings relatively fast.
>
> Since I've never worked with an optical encoder, my 1st thought was to
> use a PIC.  I was told that the logic may be too intense.  Is this
> true?  Is there an interface to these things?  All I know is that I've
> got two square waves that I have to count and determine which leads the
> other.  My thought is that the speed may be the issue.
>
> Any help would be greatly appreciated!  (assembly code would be
> wonderful)
>
> Any good links for sources of info available?  I don't want to re-invent
> the wheel if I don't have to.
>
> Jon

What's 'relatively fast'?

How fast is the wheel turning?  If you have a 400 slot optical encoder
on a turbine shaft, a PIC won't cut it. If it's on a knob being turned
by somebody, it will.

An optical encoder typically puts out "quadrature" -two 10101010101 streams that
are 90 degrees out of phase. By checking which is leading, you know which way th
e
wheel moved.

What the signal looks like, wheel turning ccw:

LR
00
01
11
10
00
01
11
10
00
01
11
10
00
01
11
10


What the signal looks like, wheel turning cw:

LR
00
10
11
01
00
10
11
01
00
10
11
01
00
10
11
01

--
Anniepoo
Need loco motors?
http://www.idiom.com/~anniepoo/depot/motors.html