Re: [NTLK] rhetorical question: ipod touch - einstein capable?

From: Robert Dylan Stewart <>
Date: Fri Sep 07 2007 - 14:10:52 EDT

Actually, it's not resistance. It's capacitance. There's a grid of
wires in iPhone's screen that detects conductive masses that can act
as capacitors. This method detects anything conductive, including
metal, but you can tune it to only detect the water in the human
body, for example. This is an oversimplification, but it's similar
to how trackpads on laptops work. If there is a stylus that works on
a trackpad, it should work on either iPhone or iPod Touch.

Most tablet PCs I've seen use Wacom digitizers. Those don't really
involve anything magnetic. Instead, there is an induction-powered
circuit in the stylus. The screen actually sends power to it and it
broadcasts back a signal that helps the tablet locate it as well as
the state of its buttons. They work extremely well, but aren't
actually touch-sensitive either.

As for whether a stylus could be designed that would look like a
finger to iPhone, the answer is probably, but there is a problem.
Think of the touch sensor like a camera. Normally, everything it
sees is black. A stylus produces a single, very bright point with a
very sharp rolloff. A finger produces a much larger point with a
much more diffuse rolloff towards the edges. iPhone's touchscreen
sensor may be tuned to ignore sharper points because they're
obviously metal and Apple want it to only work with fingers.

  Robert D. Stewart	AC5ZH
On Sep 6, 2007, at 12:59, Steven Frank wrote:
> But the iPhone and iPod touch are not stylus operated, and require the
> electric resistance of something like human skin, as I understand it.
> I don't think doing handwriting with your finger would be a very good
> experience.  Unless you made a little stylus with a little finger on
> the end.
> I just grossed myself out a little bit.
> Steven
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Received on Fri Sep 7 14:18:30 2007

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