This is an ISA-bus card that you can breadboard yourself in an afternoon or two. This circuit is good for building an encoder for motor speed measurement. The emitter works much like a TV remote, just point it at the detector. Visual Basic allows you to develop Win95 programs. This tutorial provides a basic generator and decoder that you can build your applications upon.
Construction is straight-forward and can be done in an afternoon or two.
Commerical incremental encoders can be both expensive and overkill for your rotation measurement needs. Perhaps you have a mobot and want a cheap solution for wheel positioning reading. Maybe you'd like to read telescope angles. Future Tutorials Projects that Boondog is working on.