General Question

FireMadeFlesh's avatar

How does a laptop mouse pad know what is touching it?

Asked by FireMadeFlesh (14355 points ) March 13th, 2011

Laptop mouse pads don’t seem to work unless used with a naked finger. They don’t work with gloves, plastics, or even fingernails if you use the back of your finger. I think the same may be true of some newer touch screens. How do they distinguish between different surfaces?

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12 Answers

YARNLADY's avatar

It depends entirely on the type of mouse you have. Mine works with gloves, and even when the cat walks over it.

FireMadeFlesh's avatar

@YARNLADY Interesting. I’ve tried this on my Asus, my Dad’s old Compaq, and several Toshibas.

blueiiznh's avatar

mine works with my tongue.

wiki

MissAnthrope's avatar

Some touch screens/pads operate by reacting to electricity, which the body naturally generates. I’m pretty sure this is the case with my iPod, as certain materials appear to conduct my electricity and others don’t.

FireMadeFlesh's avatar

@blueiiznh Just tested that, after cleaning it, and so does mine. Very strange indeed. Thanks for the link, it seems electrical conductivity is the key.

BBSDTfamily's avatar

Maybe yours requires a warm finger. my mother in law has a touch screen phone that requires her naked warm finger, so if her hands are cold she actually has to rub them and warm them to use her phone!

gasman's avatar

Mine works just fine while sometimes wearing rubber gloves at work. The technology in the pads senses your finger’s capacitance using small electric fields generated by the pad. The exact location of your finger is determined either by a grid of closely-spaced wires in the pad or by measuring time delays within the pad’s electronics. Thin insulating coverings such as gloves have little effect on the capacitance of your finger (or @blueiiznh‘s tongue).

@MissAnthrope: It isn’t really electricity generated by the body, but how the body affects the electricity in the pad.

FireMadeFlesh's avatar

Thanks @gasman. My gloves are pseudo-leather sports gloves, so they are probably too thick.

jerv's avatar

Good shot, @gasman; saved me some typing :D

YoBob's avatar

To elaborate a bit on how capacitance works. A capacitor is basically a reservoir that holds electrons. a capacitance switch consists of a conductive plate that will cause a switch to toggle when electrons begin flowing out at a sufficient rate. Humans are basically big bags of mostly water, which makes them a great reservoir for electrons to flow in to. So, when your finger touches the plate it opens the electron flood gate.

Your mouse pad is basically a grid of such “plates”

gasman's avatar

@YoBob GA! Humans are basically big bags of mostly water… Saltwater – lots of ions.

RocketGuy's avatar

A Trekker would call us “ugly bags of mostly water”

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