The idea of using a touchscreen goes back to the early days of computing in the 1960s. Most systems remained very experimental until the 1990s, when a number of commercial systems became successful.
The first major technology that became successful is resistive touchscreen technology. This uses a panel that consists of several layers, including two thin, electrically charged layers separated by a thin space. By pressing on the panel, these two layers touch and the location of the connection is recorded as the input. Resistive touchscreens are relatively cheap and very resistant to liquids. The major downsides are that you need to actually press down with a certain amount of pressure and they have relatively poor contrast. As a result, resistive touchscreens did not become widely used for computer systems but instead were developed as part as other electronic systems. For example, the display screens used in restaurants to enter orders and control panels in factories are often made of resistive touchscreens.
The second major technology used in touchscreens is capacitive sensing. A capacitive touchscreen uses a layer of insulating material (such as glass) coated with a transparent conductor. The human body is also an electrical conductor, so touching the screen with your finger results in a change in the electrostatic field of the screen. A number of different approaches can be used to record the location of the touch. One of the most common ways is to use a fine grid of capacitors, which record the change in the electrostatic field. These capacitors are organized by rows and columns, and they function independently of each other. This makes it possible to record multiple touches at the same time, known as multi-touch technology.
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