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Touch screen is how to work?


Touchscreens are everywhere.Not just in smartphones, but in supermarkets,ATMs, and even airplane seats.And you may have noticed that not all touchscreensare the same.The old-school touchscreens can be prettytough to use -- sometimes it feels more likea push-really-hard-screen instead of a touchscreen.On the other hand, certain smartphones andcomputer monitors are really responsive tomany different touch patterns.

There are lots of different technologies outthere, but they’re all trying to achievethe same goal: sending precise electricalsignals from specific locations on the screen.One of the most widely used types is the resistivetouchscreen, where you have to physicallypush and bend the screen to make it work.Resistive touchscreens are made of two separatelayers:The top layer is made from a flexible andtransparent material, such as polyethylene,which is a common plastic used to make thingslike soda bottles.And the bottom layer is made of somethingmore rigid, like a sheet of glass.To make the screen work, both of these layersare thinly coated with some sort of metalcompound that conducts electricity, like indiumtin oxide -- which is commonly used becauseit’s transparent.These layers are also separated by tiny insulatingdots, which /don’t/ conduct electricity,called spacers.

They keep the screens apart to make sure therearen’t any false touch signals.When the screen is on, a small voltage isapplied across the screen in both the horizontaland vertical directions.As soon as you push down on the flexible screenwith anything, like your finger or a stylus,it connects the two layers together.This changes the voltage, and a small processorconnected to the screen can calculate exactlywhere you pressed in X and Y coordinates.These resistive touchscreens are pretty affordableand durable.So, they’re useful for things like creditcard readers in grocery stores, where youneed to capture touch data of a messy signature-- over and over again.But they can be a little frustrating to useif you don’t push hard enough.Plus, they normally can’t understand multiple-touchesat the same time – so they’re no goodfor two-finger zoom or more complex tasks.That’s why these days, most smartphonesrely on capacitive touchscreens, where yourfinger 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 containinga grid of hair-thin lines of a conductivemetal, like indium tin oxide.The grid lines in one direction are calledthe driving lines, which provide a constantelectric current.And the lines in the other direction are calledthe sensing lines, which detect this electriccurrent.At every point where the sensing lines andthe driving lines cross, there will be a specificelectrostatic field, which is registered asneutral by the processor in your smartphoneor computer.But that all changes when something conductivecomes along and touches it -- like your finger.

See, the human body has a natural capacitance,which means our bodies can conduct electriccurrent, and can store electric charge.So when your finger touches the screen, thecharge in the screen is drawn around thatpoint, distorting that electrostatic field.The electricity doesn’t actually /flow/through your finger.Basically, the electrostatic field feels theeffects of your electric charge and redistributesitself accordingly.Even really small changes are detected bythe processor, which can then interpret thepatterns you’re making – whether it’sa tap or a slide.Because the lines of the grid are so thin,capacitive touchscreens are super accurate,and some versions can process multiple touchesat a time.But they won’t work if you have gloves on-- because the cloth isn’t conductive, unlessyour gloves have those special fingertipswith metal fibers inside.Plus, something like sweat can affect howelectricity is conducted across the screen,because it’s full of salts.It’s all about the materials that can affectthe electrostatic field generated inside yourscreen.So next time you’re texting on a smartphoneor scrolling through internet forums on atablet, just remember: you’re actually apart of the electronics making it work.Thank you for watching this episode of SciShow,which was brought to you by our patrons onPatreon.If you want to help support our show, youcan go to patreon.com/scishow.And don’t forget to go to youtube.com/scishowand subscribe!

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