I'm building a film-spooling apparatus where two different spools have to have their speeds precisely matched, even as the diameters increase with the film rolling-up.
I plan on using geared DC motors and I need a high-resolution, high reliability way to sense the shaft speed. Maybe DC motors with built-in encoders would be the ticket. I don't see much hardware like this on sparkfun. I have already tried hacking together mechanical mouse optical encoders and stuff, and it's not reliable enough. I want something guaranteed to work in differing lighting conditions and so on.