Watt, Why & How e-Newsletter

How Do They Do That? Touchscreens


Touchscreens are everywhere, from airport terminals to the smartphone you hold in your hand. They are so fast and easy to use, it begs the question, how does the screen know where you touch?

As it turns out, the technology has been around since the 1960s, and many methods have been tried and tested. Today, resistive and capacitive touchscreens dominate the market. Both use electrically charged touch sensors and hardware that converts voltage changes into a signal that the device can understand.


A resistive touchscreen has a flexible plastic panel on top with a rigid glass layer below. Each is coated with a material that conducts electricity. An electric current flows between the two layers. When the top layer is touched, the two layers connect, creating an electrical circuit. A controller detects the change in the current and calculates the coordinates of the touch point.

Resistive touchscreens can only read one touch point at a time, so they are used in applications that only require simple typing functions, like self-checkout systems in grocery stores.

Source: www.energy.gov
Mobile computer


Capacitive touchscreens give you a charge, literally. They take advantage of the fact that the human body conducts electricity. The screen stores an electrical charge, and when you touch it, a tiny amount of that charge transfers to you. The device measures the difference in charge at each corner of the screen to calculate where the touch took place.

Capacitive touchscreens have no moving parts and can read two or more touch points at a time, allowing for advanced multi-touch capabilities, such as virtual keyboards, swiping and zooming. Capacitive touchscreens are commonly used with tablets, smartphones and laptops.

The gloves are off

The conductive nature of capacitive touchscreens gives them an advantage, but it's also their biggest drawback. Have you ever tried to send a text on a smartphone while wearing gloves and found that the screen didn't respond? Was the battery low? No, the problem was that your glove didn't conduct electricity. Pull the gloves off and, like magic, the screen starts working again!

That's great, but typing on a screen can be a real inconvenience when your fingers are frozen. Fortunately, special touchscreen gloves are now available. These use fibers or finger pads that are coated with a conductive material, such as silver or nickel. Slip on a pair of these and you can stay warm while staying in touch, even when it's cold outside.

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