# How does the iPod touch-pad work? **URL:** \ **Category:** Factual Questions\ **Created:** [March 5, 2007, 7:58am UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654 "2007-03-05T07:58:15Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![jackelope](https://avatars.discourse-cdn.com/v4/letter/j/a6a055/32.png) [@jackelope](https://boards.straightdope.com/u/jackelope)\ **Post date:** [March 5, 2007, 7:58am UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/1 "2007-03-05T07:58:15Z")
My wife gave me an iPod Nano a few days ago. While I am absolutely in love with the little gadget, I keep wondering: How does the circular touch-pad work? I.e., how does it know when I’m touching it, sliding my finger around the circle, etc.? I’m not pressing on it hard enough to be a pressure-response; also, trying to manipulate it with a plastic pen is futile. So is it magnetic? Is it electrical? How does it work? And now that I type this, I realize that it’s probably the same device that runs touch-pads on laptops. Is it? And if not, how do those work differently? ---
**Author:** ![Patty\_O\_Furniture](https://avatars.discourse-cdn.com/v4/letter/p/96bed5/32.png) [@Patty\_O\_Furniture](https://boards.straightdope.com/u/Patty_O_Furniture)\ **Post date:** [March 5, 2007, 2:39pm UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/2 "2007-03-05T14:39:25Z")
It’s called [capacitive sensing](http://electronics.howstuffworks.com/ipod4.htm). ---
**Author:** ![jackelope](https://avatars.discourse-cdn.com/v4/letter/j/a6a055/32.png) [@jackelope](https://boards.straightdope.com/u/jackelope)\ **Post date:** [March 5, 2007, 5:27pm UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/3 "2007-03-05T17:27:12Z")
Now why couldn’t I find that? Great link; thanks, **Patty O’Furniture**. ---
**Author:** ![bouv](https://avatars.discourse-cdn.com/v4/letter/b/bc8723/32.png) [@bouv](https://boards.straightdope.com/u/bouv)\ **Post date:** [March 5, 2007, 5:34pm UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/4 "2007-03-05T17:34:53Z")
It’s the same way a touch pad on a laptop works, right? ---
**Author:** ![control-z](https://avatars.discourse-cdn.com/v4/letter/c/eada6e/32.png) [@control-z](https://boards.straightdope.com/u/control-z)\ **Post date:** [March 5, 2007, 7:27pm UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/5 "2007-03-05T19:27:21Z")
And it won’t work when you have leather gloves on, which is sort of annoying on a cold morning. ---
**Author:** ![chaoticbear](https://avatars.discourse-cdn.com/v4/letter/c/f07891/32.png) [@chaoticbear](https://boards.straightdope.com/u/chaoticbear)\ **Post date:** [March 5, 2007, 8:59pm UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/6 "2007-03-05T20:59:21Z")
[QUOTE=control-z] And it won’t work when you have leather gloves on, which is sort of annoying on a cold morning. [/QUOTE] They make gloves that do work, with little metal bits. ---
**Author:** ![Cardinal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cardinal/32/4000_2.png) [@Cardinal](https://boards.straightdope.com/u/Cardinal)\ **Post date:** [March 24, 2007, 10:31pm UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/7 "2007-03-24T22:31:23Z")
I came here to ask this question, and I’ve already read the HSW article. What I don’t understand is 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. But there’s a piece of nonconductive plastic in the way – the Click Wheel cover. 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.” This seems to say that somehow a charge builds up around your finger, but doesn’t flow. Later on, they seem to say that you need something fairly large like a human body to take up the small current the iPod is passing through the wheel. What don’t I get here? ---
**Author:** ![magellan01](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@magellan01](https://boards.straightdope.com/u/magellan01)\ **Post date:** [March 25, 2007, 6:26am UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/8 "2007-03-25T06:26:55Z")
[QUOTE=jackelope] How does the circular touch-pad work? [/QUOTE] iMagic, of course. ---
**Author:** ![CynicalGabe](https://avatars.discourse-cdn.com/v4/letter/c/3e96dc/32.png) [@CynicalGabe](https://boards.straightdope.com/u/CynicalGabe)\ **Post date:** [March 25, 2007, 6:53am UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/9 "2007-03-25T06:53:21Z")
Ever notice how if your hands are really cold, the touch pad won’t work? ---
**Author:** ![Autolycus](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@Autolycus](https://boards.straightdope.com/u/Autolycus)\ **Post date:** [March 25, 2007, 6:56am UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/10 "2007-03-25T06:56:39Z")
[QUOTE=magellan01] iMagic, of course. [/QUOTE] Yeah, but only iWitches can use iMagic 😃 ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [March 25, 2007, 10:39am UTC](https://boards.straightdope.com/t/how-does-the-ipod-touch-pad-work/394654/11 "2007-03-25T10:39:41Z")
[QUOTE=Cardinal] This seems to say that somehow a charge builds up around your finger, but doesn’t flow. Later on, they seem to say that you need something fairly large like a human body to take up the small current the iPod is passing through the wheel. What don’t I get here? [/QUOTE] AC vs. DC is the hole in your understanding. DC would charge the capacitor, and then the current would stop. With AC, current can continue to flow as the capacitor is constantly charged and discharged…the flow is first one direction, then the other, so the time-average flow is zero, but that doesn’t matter as far a detecting the flow.