Using the Doepfer’s modwheel assembly and an Arduino I built this midi controller for a client that needed a standalone box with a center detented, spring loaded pitch bend control and a free moving volume control. There is a switched that puts the device into calibration mode to learn the min and max values of each wheel. The code is pretty simple (though messy and uncommented for the time being) and basically just reads in the analog values of the wheels, scales them to the appropriate midi controller values and has some smoothing applied to take care of jitter. You can download the Arduino source here. It requires the MIDILibrary. Check out the most recent code at my GitHub Project.