• Shaun Ting

How Do Touchscreens Work?

Have you ever wondered about what exactly lies behind your smartphone's screen? We have gotten so accustomed to touchscreens in our everyday lives that we've come to forget about the science behind the screen.

GIF: https://giphy.com/gifs/26BRNiATmtg6s1jC8

The basic idea


I like to think of touchscreens as the modern day keyboard; both are input devices that follow the same concept. When it comes to keyboards, pushing a key down completes an electric circuit and a current flows. That current varies depending on the key that is pressed, helping the computer identify exactly which key was pressed. Touchscreens work similarly, except they use different ways of sensing your touch in order to stay hidden behind the screen!

Resistive Touchscreen


Resistive touchscreen [1]


Resistive touchscreens are the most common touchscreens out there. They're mainly popular because of how cheap they are to make. We find these types of touchscreens on ATMs, kiosks, cameras and more.


The resistive touchscreen is made up of two thin, flexible conductive layers separated by a small gap (typically an insulating membrane). Pressing on the screen causes the two layers to touch, completing the circuit and sending a current – just like a keyboard. The device is able to identify exactly where the contact was made, and carries out the function that corresponds with that spot.


The downsides of resistive touchscreens are that they are less responsive and less clear, as having two layers causes them to reflect more ambient light. They also do not support swiping and multi-touch features, hence why they are typically not found in smartphones.

Capacitive Touchscreen


Capacitive touchscreen [2]


Capacitive touchscreens are easily the second most popular type of touchscreens, and we frequently find these in our smartphones. The capacitive touchscreen is slightly more complex, as it does not rely on the pressure from your finger but rather its electrical charge.


The capacitive touchscreen relies on a transparent electrode film placed on top of a glass panel and below a protective cover. When a finger hits the screen, a tiny electrical charge is transferred to the finger to complete the circuit. The sensors present on all four sides of the screen detects the decrease in current and a controller uses this to determine the coordinates of where the screen was touched. This is also why capacitive touchscreens do not work with gloves.


While there are many upsides to capacitive touchscreens such as greater image clarity and durability, the downsides are still there. Aside from the fact that insulating items like gloves cannot be used to interact with the screen, the screen is also susceptible to electromagnetic interference.

To sum it up...


What I've written here is simply a general idea of the types of touchscreens we commonly know. The touchscreens we find on the latest smartphone flagships are known as projected capacitive touchscreens and are far, far more complex. Smartphone manufacturers have devised ways to deal with all the downsides found in the touchscreens. You won't have to worry about electromagnetic interference and you can even interact with the screens with gloves!


Lastly, I hope you found this short article interesting! I'm looking to write more articles about technology in the coming future so stay tuned for those.

See you around!

References


- https://scienceline.org/2012/01/okay-but-how-do-touch-screens-actually-work/

- https://www.scienceabc.com/eyeopeners/touch-screen-respond-touch.html

[1] https://cdn.mikroe.com/blog/2016/06/resistive_touch.jpg

[2] https://cdn.mikroe.com/blog/2016/06/surface_capacitave.jpg


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