The authors of this paper sought to create a device that can be powered through the physical effort required to operate it. Their system consists of a small DC motor as a rotary input sensor that can create a temporary 3.3V power supply. The first stage of the circuit determines the direction of the input. The second stage rectifies the output of the motor via a diode bridge. The 3rd stage uses a pair of resistors as a voltage divider, reducing the variable output voltage to a level that can be directly sampled by an analog-to-digital converter in a micro controller. The final stage uses a 3.3 V low drop-out regulator to stabilize the variable voltage to a level that is readily usable by a micro controller.
They created a prototype device and called it the peppermill. When the user turns the knob, the micro controller powers up and samples the inputs from the supply circuit and the states of the 3 buttons. It transmit this as a single wireless packet. They tested with a simple video browsing and playback application. It is used similar to a remote control. They found the users like using the Peppermill. Some users would turn the knob too slowly, but they instinctively knew to turn faster until it works.
Discussion
I think this is a good idea. There are times where physically charging up the battery would be more helpful than an actual battery. However, I doubt there would be much use for this, since it seems only to work for appliances that don't require large amounts of power. Also, I would have liked to see a better user study than the one provided.
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Nicolas Villar and Steve Hodges. The Peppermill: A Human-Powered User Interface Device. TEI 2010.
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