Still Thinking (and a Little Building)
I wasn't quite sure where the project was heading, but I needed to experiment with something physical. I was considering an interface that would scrub audio at human scale; in order words, I could perform a piece of audio (or video for that matter), by attaching myself to a simulated tape reel. In this way, I could walk or run through the linear media, with the motion of my body driving the playback. My building focused on how to detect this linear motion.
I started out with a motor, thinking I could detect the positive and negative voltages it would generate as it was turned.. Arduino takes 0-5 volts on its analog inputs, though, and I wasn't sure how to convert the positive and negative voltages from the motor.
The Physical Computing book had an example of using a potentiometer to detect motion, so I tried to prototype that system.
Ultimately, what I discovered is that the modified potentiometer didn't work reliably. The "stop" I removed left a dead space in the resistance range that fluctuated as I turned through it. There seemed to be a pattern, but I felt that the code to smooth out this abnormal behavior would be prone to breaking. I needed some other way to detect rotation.