![]() The multi-touch screens used by the iPhone rely on a carefully etched matrix of capacitance-sensing wires (rather than relying on changes to the whole capacitance of the screen, this scheme can detect which individual wells are building capacitance). The iPhone introduced an accurate, inexpensive, multi-touch screen. That changed in 2007 with the introduction of the iPhone that you just watched. Resistive screens have a very high accuracy and aren't impacted by dust or water, but pay for those advantages with more cumbersome operation: the screens need significantly more pressure than capacitive (making swipe interactions with fingers impractical) and can't register multiple touch events. The intersection of those lines give you the precise location of the touch event. When an object is pressed against the screen, the lines on the two sheets make contact, and, the voltages provided by both combinations tell you which vertical and horizontal lines have been activated. Both of the sets of lines (horizontal and vertical) can be tested for voltage, and the computer rapidly alternates between feeding current to the horizontal and testing for current in the vertical, and vice-versa. Each line is given a unique voltage, and the computer rapidly alternates between testing the voltage of each sheet. Resistive touchscreens work by using two sheets of flexible, transparent material, conductive lines etched onto both, in opposing directions. ![]() The next major event in touchscreen technology was the invention of the resistive touchscreen in 1977, an innovation made by a company called Elographics. This kind of capacitive touchscreen works, but isn't very accurate, and can't log more than one touch event at a time. By measuring the change in capacitance at each corner of the plate, you can figure out where the touch event is occurring, and report it back to the central computer. When an object like a finger touches the screen, the gap between it and the charged plate forms a capacitor. You use a sheet of a conductive, transparent material, and you run a small current through it (creating a static field) and measure the current at each of the four corners. The technology used in this kind of monotouch capacitive screen is actually pretty simple. The technology proved to be largely impractical, and not much progress was made for almost a decade. The touchscreen was bulky, slow, imprecise, and very expensive, but (to its credit) remained in use until the 1990s). The device was a radar screen, used by the Royal Radar Establishment for air traffic control, and was invented by E. Surprisingly enough, the first touchscreen device was capacitive (like modern phones, rather than the resistive technology of the 1980s and 1990s) and dates back to around 1966.
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