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How does a touchscreen work?



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Photo: Astrid Blank

A touchscreen is an electronic display that does the job of a computer mouse. It can detect where a user touches the screen and can process that information to control an input/output device. Three main types of touchscreens exist:
A resistive touchscreen has two layers and uses voltage to recognise a user’s touch. It does this by sensing the electrical resistance caused when the pressure of a finger brings one layer into contact with the other. The technology can detect the resistance at the exact point where it occurs.
Capacitive touchscreens use a layer of glass and a transparent metal oxide. AC voltage is applied to each corner and creates a uniform electric field across the whole screen. When you touch the screen, your finger draws current towards it from all four corners. By measuring how far the point of contact is from each corner, the system’s controller can identify exactly where your finger is.
Inductive touchscreens are often used in graphics tablets. The technology reacts to a special stylus (known as a pen), not to the touch of a hand or finger. When a user draws or writes with the pen, the screen doesn’t just measure and process information on where it is being touched; it can also register the tilt of the pen, how far it is from the surface, and whether or not the user has activated any button functions.

This question was answered by Carsten Kraft, a freelance software developer and blogger: