A touchscreen computer from 1982!

So, you think Touchscreen is a modern technology. However, according to the Wikepedia's article on Touchscreen, touchscreens have been around since the 1970s. The following video shows a touchscreen computer from 1982.

The way it works is by having Photodiodes arranged both vertically and horizontally, transmitting infrared beams, as to form a sort of invisible grid. These infrared beams are received by photoreceptors, placed on the other sides of the Monitor. So, as soon as your finger interesect that invisible grid, the Monitor would know where to put the dot.

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Most modern touchscreens on the other hand work on the principles of resistance or capacitance, as described in this article. However, Infrared touchscreens are still in use, such as in the case of this Sony eBook reader.

The resistive touchscreen is the most basic and common touch screen, which is used for example in ATM machines. It works by having electrically conductive layers separated by a slight air gap, so that when you press the facing side hard enough, it bends to touch the back layer, producing electricity at that point, which is measured by sensors to locate the coordinates on the screen.

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Capacitive touch screens on the other hand, which are used in smartphones for example, depend upon electrical charge on your fingers. That is why, unlike resistive touchscreens, you don't need to press such screens hard to make them work. Like in the case of resistive touch screens, a capactive touchscreen is made up of two conductive layers of glass. Those glasses are separated by an insulator. As you touch your finger on the outer layer, the electric field between the conductive layers would change at that point, which would then be sensed by the sensors to locate the coordinates.

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