The "brain" behind the click-wheel is the conductive membrane behind the plastic covering. This membrane has "channels" that when connected, create a set of coordinates. These channels are conductors, which when connected to another conductor (a finger in this case), try to send a current through the user's finger, but are blocked by the plastic covering the click-wheel. So instead of passing through the plastic, the current creates a charge at the closest location to the finger, which is also known as capacitance. The component that detects this change in capacitance is the controller. Whenever the controller senses a change, it sends a signal to the microprocessor, which performs the desired action. The faster a finger moves around the wheel, the more concentrated the stream of signals it sends out. The moment the finger leaves the wheel, however, is when the controller stops detecting change in capacitance, therefore stopping the current process.
