[Al Skierkiewicz]

In the past on our crab modules, we have used standard LED/photo transistor devices from Digikey. We manufactured a stamped plate that mounted to the side of the wheel. The plate was a sandwich of two pieces of aluminum with black construction paper between. The Digikey sensor then illuminated the plate and produced an output when it reflected from the shiny surface but not when facing the black paper. If you look through the catalog you can find these in a single housing with four leads. I think they were about $1. Put two on and you get quadrature outputs. We stamped 8 openings as I remember to give us a count. Retro-reflective not needed.