I am trying to build a semi-analog timer. Something like those old egg timers that you rotate the face of. I want a knob that I can turn that can be read by a microcontroller, and I also want the microcontroller to be able to position the knob. I'd like to implement "stops" by letting the microcontroller push the knob towards certain positions. As it runs down, the knob should turn. This is my first project of this kind; I've built small robots in the past, but it's been many years.
I've considered hacking a servo motor to read its position, but the small hobby servos I've tried are too hard to turn, very noisy, and pick up too much momentum when turned. They don't act like a good knob.
I'm now considering a rotary encoder connected to a motor, but after hunting at several sites (SparkFun, ServoCity, DigiKey, Trossen, and some others), I haven't been able to find anything that seemed appropriate. I'm not certain how to find a motor that's going to have the right kind of low torque.
This seems like it shouldn't be a really uncommon problem. Is there a fairly normal approach to creating a knob that can be adjusted both by the user and a microcontroller?