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  • Touchscreens are everywhere.

  • Not just in smartphones, but in supermarkets, ATMs, and even airplane seats.

  • And you may have noticed that not all touchscreens are the same.

  • The old-school touchscreens can be pretty tough to use -- sometimes it feels more like

  • a push-really-hard-screen instead of a touchscreen.

  • On the other hand, certain smartphones and computer monitors are really responsive to

  • many different touch patterns.

  • There are lots of different technologies out there, but they're all trying to achieve

  • the same goal: sending precise electrical signals from specific locations on the screen.

  • One of the most widely used types is the resistive touchscreen, where you have to physically

  • push and bend the screen to make it work.

  • Resistive touchscreens are made of two separate layers:

  • The top layer is made from a flexible and transparent material, such as polyethylene,

  • which is a common plastic used to make things like soda bottles.

  • And the bottom layer is made of something more rigid, like a sheet of glass.

  • To make the screen work, both of these layers are thinly coated with some sort of metal

  • compound that conducts electricity, like indium tin oxide -- which is commonly used because

  • it's transparent.

  • These layers are also separated by tiny insulating dots, which /don't/ conduct electricity,

  • called spacers.

  • They keep the screens apart to make sure there aren't any false touch signals.

  • When the screen is on, a small voltage is applied across the screen in both the horizontal

  • and vertical directions.

  • As soon as you push down on the flexible screen with anything, like your finger or a stylus,

  • it connects the two layers together.

  • This changes the voltage, and a small processor connected to the screen can calculate exactly

  • where you pressed in X and Y coordinates.

  • These resistive touchscreens are pretty affordable and durable.

  • So, they're useful for things like credit card readers in grocery stores, where you

  • need to capture touch data of a messy signature -- over and over again.

  • But they can be a little frustrating to use if you don't push hard enough.

  • Plus, they normally can't understand multiple-touches at the same timeso they're no good

  • for two-finger zoom or more complex tasks.

  • That's why these days, most smartphones rely on capacitive touchscreens, where your

  • finger becomes a key part of the electronics.

  • There are different kinds of capacitive touchscreens, and they can vary from device to device.

  • But one basic design is a sheet of glass containing a grid of hair-thin lines of a conductive

  • metal, like indium tin oxide.

  • The grid lines in one direction are called the driving lines, which provide a constant

  • electric current.

  • And the lines in the other direction are called the sensing lines, which detect this electric

  • current.

  • At every point where the sensing lines and the driving lines cross, there will be a specific

  • electrostatic field, which is registered as neutral by the processor in your smartphone

  • or computer.

  • But that all changes when something conductive comes along and touches it -- like your finger.

  • See, the human body has a natural capacitance, which means our bodies can conduct electric

  • current, and can store electric charge.

  • So when your finger touches the screen, the charge in the screen is drawn around that

  • point, distorting that electrostatic field.

  • The electricity doesn't actually /flow/ through your finger.

  • Basically, the electrostatic field feels the effects of your electric charge and redistributes

  • itself accordingly.

  • Even really small changes are detected by the processor, which can then interpret the

  • patterns you're makingwhether it's a tap or a slide.

  • Because the lines of the grid are so thin, capacitive touchscreens are super accurate,

  • and some versions can process multiple touches at a time.

  • But they won't work if you have gloves on -- because the cloth isn't conductive, unless

  • your gloves have those special fingertips with metal fibers inside.

  • Plus, something like sweat can affect how electricity is conducted across the screen,

  • because it's full of salts.

  • It's all about the materials that can affect the electrostatic field generated inside your

  • screen.

  • So next time you're texting on a smartphone or scrolling through internet forums on a

  • tablet, just remember: you're actually a part of the electronics making it work.

  • Thank you for watching this episode of SciShow, which was brought to you by our patrons on

  • Patreon.

  • If you want to help support our show, you can go to patreon.com/scishow.

  • And don't forget to go to youtube.com/scishow and subscribe!

Touchscreens are everywhere.

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B1 US screen finger electric electric current conductive electricity

How Do Touchscreens Work?

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    joey joey posted on 2021/05/16
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