The touch wheel, aka Clickwheel, that was the primary way of controlling iPods for many years may seem a little magical. Run your finger around the circle and you'll move things onscreen, even though there are no moving parts. But the touch wheel isn't magic; it's science.
How Does the iPod Touch Wheel Work?
There are two ways in which we use the iPod Clickwheel: for clicking and for scrolling.
The simpler of the two, clicking, simply involves buttons. The touch wheel has icons at its four sides, one each for menu, play/pause, and back and forward. It also has a center button. Beneath each of these icons is a sensor that, when pressed, sends the appropriate signal to the iPod.
Pretty simple, eh? Scrolling's a bit more complicated.
The iPod touch wheel uses a technology similar to that used in touchpad mice on laptops (while Apple now uses a Clickwheel that it developed, the original Clickwheels used on iPods were made by Synaptics, a company that makes touchpads), called capacitive sensing.
When it comes to scrolling, you first need to know that the iPod touch wheel is composed of a couple of layers. On top is the plastic cover used for scrolling and clicking. Beneath that is a membrane that conducts electrical charges. The membrane is attached to a cable that send signals to the iPod.
The membrane has conductors built into it called channels. Each at place where channels overlap, an address point is created.
The iPod is always sending electricity through this membrane. When a conductor--in this case, your finger; remember, the human body conducts and contains electricity--touches the clickwheel, the membrane tries to complete the circuit by sending electricity to your finger. But, since people probably wouldn't like getting shocks from their iPods, the plastic cover of the touch wheel blocks the current from going to your finger. Instead, the channels in the membrane detect what address point the charge is at, which tells the iPod what kind of command you're sending to it via the Clickwheel.
iPod Touch Wheel in Use
While all iPods starting with the iPod mini used the clickwheel for many years, only the iPod Classic still uses it. The 5th-generation iPod nano was the last iPod other than the Classic to use it. With the rise of touchscreens, it seems likely that the iPod touch wheel will eventually become a thing of the past.
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