Hi,

I think HP do the optos for this - they're used in motor encoders we use at work.
There are 2 outputs - A & B. For example, if the motor is turning one way, output A switches just before output B, & vice versa.

You can get a similar effect with 2 opto slot detectors (100s on the market!), with one of them offset by a few holes/slots + a fraction more.

Of course, as Babar suggested, if *you* are driving the motor, you should know its direction, so you could get speed control & distance from just 1 channel.

Good luck,
R