Projected Capacitance Touchscreen, confused by how the capacitance is formed.

by eventnick
Tags: capacitance, confused, formed, projected, touchscreen
 P: 2 Hello, I have a question thats really bothering me. So I've been reading about projected capacitance touchscreens (the kind thats in so many cell phones, the iphone etc) and I don't understand what the physical property of my finger is that allows the screen to function. From what I've been reading, which is really hazy incomplete information, I am kind of stumped. I've read that any conductor should be able to work but when I place a penny (copper-plated) on the screen and move it with eraser on the back of a pencil, I get nothing. If I am touching the penny with my finger though it works. The description on wiki does not seem ...complete or seemingly correct in some instances including this specific sentence "Bringing a finger or conductive stylus close to the surface of the sensor changes the local electrostatic field. " ...since I can't seem to make that work. http://en.wikipedia.org/wiki/Touchsc...ed_capacitance I have several questions but I would like to see the response to this before I ask them. So yeah if anyone can explain in a technical manner what property my finger has over the penny that allows the screen to register the input I would appreciate it. I speculate that my finger is holding a charge and thats the difference but I rubbed the penny on the cat haha trying to put some charge on it to get it to work that way and I got nothing. Thank you, E.
 HW Helper Sci Advisor P: 8,962 Your finger is earthed. The penny simply rises to the electric field of the screen - you + the Earth resists changing potential, so a potential difference exists which the screen can sense
P: 2
 Quote by mgb_phys Your finger is earthed. The penny simply rises to the electric field of the screen - you + the Earth resists changing potential, so a potential difference exists which the screen can sense

Interesting...

But my finger is not technically earthed, of course so is it then that my body is just a much larger conductor than the penny relative to the charge on the screen so I can hold a much larger amount of charge without changing my potential?

HW Helper