User:Rluhar/iPod Click Wheel

The iPod click-wheel is the navigation component of the device that uses both touch technology and traditional buttons to let a user find their music, videos, and photos. The wheel lies flat on the face of the iPod, directly underneath the screen.

The science behind the touch-sensitive technology is known as capacitive sensing, which stores the energy created between users' fingers and the wheel itself. This technology dates back to 1919.

How it works:

The click-wheel detects a user’s input via its touch sensitive ring, and because of the four mechanical buttons that lie beneath it, the ring is able to perform multiple commands. For example, if you are scrolling through your music, and you happen to select a particular song, the click-wheel’s function will now be to adjust the volume. Press the select button once again, and now you can skip to a specific part in the song.

Capacitive Sensing

History

The primary technology that the click-wheel demonstrates is that of Capacitive Sensing. This technology actually dates back to 1919, where it was first utilized in a musical instrument called a Theremin. It allowed the pitch and volume of the instrument to be controlled by the distance from the musician’s hands to two antennae. This happens by placing two metal plates very close to one another, while avoiding touching each other. After running a current through the plates, energy is stored, but once the current is taken away, the stored energy creates a current on its own. This is how a capacitor gathers and stores energy.

Capacitance in the iPod

This same principle is applied to the iPod classic and iPod nano.

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 (in this case your finger), tries to send a current through your finger, but is 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 your 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.

Controversy behind the technology:

It is a little known fact that Apple was not behind the development of the click wheel, but it was actually a company name Synaptics that came up with the design for the device. , but there have nevertheless been a few lawsuits concerning its capacitance-sensing technology. In January of 2007, a U.K Based company named Quantum Research made public a lawsuit against Apple claiming that its own patents on this technology suffered from copyright infringement by Apple. Legal action regarding this lawsuit had been going on since 2005, but was not made public until two years after.