I want to make a temperature controlling faucet, and I would like to do it with one motor. I need a valve that can go from "cold" to "hot" with a single turn. I have stayed in hotels that had showers with valves like this...all the way counter-clockwise is cold, all the way clockwise is hot. If I had a valve like this, I could mix any water temperature using only one stepper motor. Any ideas where to get such a valve?
You can try the home improvement stores or plumming supplies. Most any single knob faucet has this type of temperature control, although the movement may not be rotary.
So-called "mixer" taps are very common in any hardware store (at least they are here in Oz), if you take the handle off there's normally a standard tap shaft (threaded with two flat sides or just square) so you should be able to control that by rotating the shaft (needs quite a lot of torque though).
This only gets you the hot/cold mixing though, in normal operation the handle is lifted for on/off. Don't know how you'd do that without a seperate solenoid valve.