Angle sensor

There's one in the digikey catalog -- I couldn't tell you the part number or manufacturer, but I _can_ tell you that it's the same idea with a different mechanical layout.

-- Tim Wescott Control systems and communications consulting

Need to learn how to apply control theory in your embedded system? "Applied Control Theory for Embedded Systems" by Tim Wescott Elsevier/Newnes,

I've used these on an arm, in a PID loop.