Touch Screens

By Georgie Prichard

What are touch screens?

a display device which allows the user to interact with a computer by touching areas on the screen.

Touch screens come in two main variants: capacitive and resistive. A capacitive touch screen features an insulating external material, such as glass or plastic, coated with a transparent conductor such as indium tin oxide. Because the human body is also conductive, touching a finger to this screen changes the distribution of an otherwise homogeneous electrostatic field that is sensed at the edges of the screen as a change in capacitance. Sensors pinpoint the location of the placed fingertip through this change in capacitance, registering touch.

A resistive touch screen features electrically resistive layers that are placed parallel to one another with a slight gap in between. The inner layer of the outside resistive layer and the outer layer of the inside layer are coated with a conducting material. A constant voltage is applied between the two layers. When a finger is depressed against the outer layer it causes the two layers to meet, changing the voltage between the two layers, signifying a touch incident. The advantage of the resistive touch screens over their capacitive counterparts is that the former are inherently pressure sensitive.
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