A remarkably effective rotary encoder is a stepper motor. I haven't
used this in anything serious, but in bench tests it worked very
well.
A typical unipolar stepper with 2 coils produces two quadrature
voltage outputs when rotated. While amplitude is proportional to
speed of rotation (up to a limit) the voltages output are very
adequate to swing a comparator or even a transistor base. If you
don't mind committing two amplifiers or 2 comparators to the task you
can turn this slower than you would ever need to.

Small steppers are available at very reasonable prices surplus (often
new but in vast quantity if desired).




                Russell McMahon







>        I kinda like the use of quadrature encoders with a display.
The
>use of the rotary control has a nice feel to it while the display
gives
>precision in setting.  A quadrature encoder should be less expensive
than
>one with a binary output and takes less pins on the PIC.  Also, you
can