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General discussion

iPhone Electrical Conductive Touch Screen

Dec 3, 2007 1:06AM PST

I've always wondered why other objects didn't work on the iPhone (gloves, pointing devices, finger nails). I was never able to explain to people, that you need to use your finger tip when operating the iPhone. I thought it was due to the iPhone touch screen needing a larger surface area for input detection. Recently, over the last few weeks... I've began to notice that the fingers I use to interact with the iPhone are beginning to tingle here and there... also.... when I use the iPhone I swear I can feel a small tingling sensation. So I theorized that the screen is conductive or senses heat...

I tested this theory and tried it out on multiple fingers... and I wrote it off as it being in my head. Also... the fact that I placed a membrane to protect the screen caused me to believe that the touch screen can't be conductive.

After some more time... I still feel tingly sensations in my index finger, so I googled for a bit and I haven't been able to find really credible facts, but I did find a post that stated "The iPhone touchscreen works using electrical conductivity, not pressure" (SOURCE: http://www.jasonsantamaria.com/archive/2007/01/14/a_plea_for_the_fatfingered.php). I was unaware of this and would explain why my finger is feeling funny.


My question to the BOL Forum is "How does the iPhone touch screen exactly work?" What are the specifics (current etc), are there any long term effects (tingling, numbness)??? Thanks for any light you all can shed on this for me!!!

Deigratia (Jazzman)

Discussion is locked

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Electric conductive....
Dec 3, 2007 1:14AM PST

I think it's the same type of technology a laptop touchpad or a ipod clickwheel uses you know. Something to do with your finger affecting the capacitance of it.
It's pretty neat that they've got it work on a screen.

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A primer on capacituve touch systems first.
Dec 3, 2007 1:31AM PST

Read http://electronics.howstuffworks.com/ipod4.htm

Ok, what voltages are put on the screen? None. Why? The screen material is glass so your assumption is a bit off.

There can be surface static charges just like any other surface. Those can reach into the many kilovolts and have been around for a few centuries without much effect.

Bob

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Reply
Dec 3, 2007 1:59AM PST

Thanks bob, but your link is for an iPod... and iPhones don't work like iPods Happy Based on your corollary, that leaves the iPhone touch screen with no underlying technical solution... so what do you propose as the underlying tech for the iPhone touch screen... do you think it's pressure sensitive... Also... when I give the iPhone my highly accurate "tap test", it feels like some sort of plastic, but I'm no materials expert. I don't know either way...

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touch-sensitive
Dec 3, 2007 2:03AM PST

Experiment: How About an Apple?
What can you use to control the touch-sensitive Click Wheel? Here's an abbreviated list of what we tested:

* Finger: Yes
* Orange: Yes
* Apple: Yes
* Plastic pen cap: No
* Silly Putty: No
* Paper clip: No
* Tip of Cold Heat soldering tool: No
* Prongs from iPod charger: No

The yesses are easily explainable -- fruit and flesh can conduct electricity. The no's, however, are a bit more mysterious. The pen cap and the Silly Putty are not conductors, end of story. But what about the tip of the soldering tool, the paper clip and the charger prongs? Those are conductors! To solve this riddle, we contacted an expert in the electronics field, who recommended the following action: Wrap your finger in aluminum foil and try to work the Scroll Wheel. Our expert was thinking "surface area." This finger-wrapped-in-foil input worked perfectly.

Can it be that the surface area of the paper clip is not enough to trigger the conductive grid? To investigate this hypothesis, we tried to work the Scroll Wheel using the blunt end of a dinner knife (approx. 0.75 in x 0.5 in). It worked. We concluded that surface area matters.

But there's another factor, too, because holding the dinner knife between two plastic pens and moving it around the Scroll Wheel doesn't work. Same with the apple and the orange. You need to be touching the knife or the orange in order for the Scroll Wheel to detect it. The determining factor, then, is you -- the human body is a very big conductor, providing a very big neutral area for a charge to jump to. The charge difference between your body and the Click Wheel's electrodes provides the voltage -- or electrical "pressure" -- that activates the Click Wheel system.

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Are you aware how a metal detector works?
Dec 3, 2007 2:11AM PST

The click wheel does not use a direct contact system. Your finger does change the "capacitance" in the area in question. So while there is no direct electrical contact you do affect the measurement.

All this is about electronics, physics and more. Sadly too much to put into this small box.

As to the ipod touch it appears to be a "SIX WIRE RESISTIVE" measurement system. The usual is a "FOUR WIRE." Why the extra two wires? It's need to implement multi-touch. I can't find solid documentation on the ipod touch screen but I do know the top surface is glass which is an insulator according to most people.

Bob

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So how do we fake a touch on an iPhone?
Feb 10, 2009 6:25AM PST

I know it's not as simple as hooking up a tip of a hotdog to a large metal weight but I'd be interested in finding a way to artificially click on the iPhone.

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Great explanation
Dec 3, 2007 2:33AM PST
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iPhone and cure for cancer
May 11, 2009 5:05AM PDT

I don't thing the iPhone has an App for that..

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Me too
Dec 12, 2015 11:52PM PST

I searched far and wide to find a mention of this online. Well, I googled for about five minutes before finding your comment. I get the tingling feeling too from touch screens. It's so annoying. I started using different fingers, but it wasn't long before they started feeling it too. Recently I've been using one of those 'pens' so that it's not the tip of my finger touching the screen, but after a week perhaps of using it, I can feel the electricity feeling in my finger or hand where I'm holding the pen.
I'd done some research a while back and found out that it is a very small amount of electricity passing into the finger when you touch the touch screen.
I'm thinking I really need a break from using touch screens, or use it as little as possible. No iPad games for me for a while.
I wonder what makes some people more sensitive to be able to feel it. I've asked a number of people and no-one else, apart from my husband, has said that they can feel it.
I think it's a worry how popular touch screens are, especially even for kids in schools.
So yep, I'll be interested to hear if anyone knows how much electricity is being put out with each tap of the screen, and who else can feel it, and if there are long term impacts.

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The tingly feeling I get
Dec 13, 2015 7:51AM PST

Happens if I tap my finger tip on a desktop too so it's electrical (in my nerves at the tip of my finger!)