How the iPod click wheel works

By the way I would like to start by saying sorry for not posting for a while. I have been caught up in school work and being Sherando FBLA Vice-Prezzz. It also takes me a while to browse through the tech news and find something worth posting on. I hope you enjoy my posts because I work really hard to find you interesting topics. If you find anything that you think would interest me then feel free to email me at:

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Did you ever wonder how the iPod click wheel worked? Millions use it everyday to browse through and select their favorite songs. But did anyone ever think, “Hey how does it do that, how does it know that I am touching it? I used a stylus and that doesn’t work?” Well yes a stylus does not work on the iPod click wheel. Some people believe that it is caused by the specific pressure of a finger, but what if you tried controlling it through a thick sweatshirt sleeve, nothing happens. Then it couldn’t be the pressure, then could it.

Ok, it’s very complicated to explain, but I will try my best. I am getting all of my information
from the How Stuff Works website.

First under the plastic/rubbery surface of the click wheel, there are four mechanical buttons (Menu, back, forward, play/pause), and one button in the center (select). But what were really interested in is how the scroll wheel works.

Click wheel face

Behind the Click Wheel face (left) and Click Wheel contacts on the motherboard

You’ve got a total of five buttons and five corresponding contacts on the motherboard of the iPod. When you press the skip forward button, the wheel pushes down the forward button. Then under each of the rubber buttons is a metal contact, so pressing it completes the corresponding circuit on the motherboard. The motherboard then tells the processor that circuit is complete, and the processor tells the operating system to fast-forward through the song or skip to the next song (depends on how long you hold it down).

The click wheel’s touch-sensitive function lets you move through lists, adjust volume and fast forward through a song by moving your finger around the stationary wheel. It works a lot like touchpad on your laptop. In fact, sources say that the company that supplied the click wheel for the 4G iPod was Synaptics (the most widely known for making laptop touchpads). For the 5G, Apple went out of the way created its own proprietary click wheel design based on the previous Synaptics-designed click wheel.

Now for how it works:

Under the plastic cover of the click wheel, there is a membrane embedded with metallic channels. Where the channels intersect, a positional address is created, like coordinates on a graph.

At its most basic, a capacitive-sensing system works like this: The system controller supplies an electrical current to the grid. The metal channels that form the grid are conductors (they conduct electricity). When another conductor (say, your finger) gets close to the grid, the current wants to flow to your finger to complete the circuit. Butthere’s a piece of non-conductive plastic in the way. So the charge builds up at the point of the grid that’s closest to your finger. This build-up of an electrical charge between two conductors is called capacitance. The closer the two conductors are without touching, the greater the capacitance.

Back of membrane: Here you can see the Click Wheel controller.

The “sensing” part of the system comes in with the controller. The click wheel controller (see above) is programmed to measure changes in capacitance. The greater the change in capacitance at any given point, the closer your finger must be to that point. When the controller detects a certain change in capacitance, it sends a signal to the microprocessor. As you move your finger around the wheel, the charge build-up moves around the wheel with it. Every time the controller senses capacitance at a given point, it sends a signal. That’s how the Click Wheel can detect speed of motion — the faster you move your finger around the wheel, the more compacted the stream of signals it sends out. And as the microprocessor receives the signals, it performs the corresponding action — increasing the volume, for instance. When your finger stops moving around the wheel, the controller stops detecting changes in capacitance and stops sending signals, and the microprocessor stops increasing the volume.

Now, in discussing the workings of the Click Wheel, a particularly curious HowStuffWorks staffer raised the following question: If your finger controls the Click Wheel because your finger is a conductor, why can’t you control the Click Wheel with a paper clip?

Now will direct you to continue your read on this page to find out their experiments (they are at the bottom of the page). http://electronics.howstuffworks.com/ipod4.htm

Thanks for reading… It may be a while before my next post…getting ready for the end of my senior year and freshman year of college.