This is an excerpt from a feature article in the latest edition of Cosmos magazine.
The most commonly used touchscreens today – capacitive screens – are almost as old as Baby Boomers: invented in 1966 for air traffic control radar screens at the UK’s Royal Radar Establishment.
This first iteration worked by running a small current through a transparent sheet of material across the screen, which created a static field. The interference of a fingertip pushing on the screen was all it took to charge the plate below, changing the electric charge – capacitance – at the screen’s corners.
Just as each key on a keyboard completes a corresponding circuit when your finger presses down, these early screens relied on the pressure of a finger causing the two layers of material to come into contact with each other, completing a circuit at the point of contact.
As this circuit could be completed with a touch at any location across the screen, the next challenge this early tech overcame was locating that point of contact. The electrical charge at each corner of the screen would vary, depending on the proximity of the circuit closure – so the central computer measured the difference in the charge at each corner of the screen and then calculate the location of the touch.
I can only begin to imagine the excitement that air traffic controllers must have felt when the first radar touchscreen was installed in their workplace. I suspect that excitement may have turned to frustration, however, when they discovered its shortcomings.
It was slow and highly inaccurate, occasionally miscalculating the user’s fingertip location, requiring a second or third prod, or just taking its own sweet time to respond – not ideal features when managing the flow of fast-moving aircraft. It was also bulky. Nevertheless, the principles behind this early touchscreen design form the basis of today’s sleek, smart-device screens.
In 1977 this clunky design was improved upon by the resistive screen. These are the screens that found their way into the interfaces of ATMs. Some may remember mashing their fingertips firmly against these cash-machine screens to make a selection, and while they may have required a bit more pressure than we’re accustomed to now, they were more accurate than their predecessor, which was still being used in radar screens (much to the continued annoyance, I assume, of their users).
A company called Elographics – which is still creating screens today under the name Elo Touch – achieved this feat by incorporating not one but two sheets layered on top of each other, hence the extra pushing needed. Conductive lines were etched into each sheet, horizontally on one and vertically on the other, to create a grid.
Each line gave a unique voltage, and as your fingertip prodded the word “Withdrawal” it would also cause the two sheets to press together and their horizontal and vertical lines to touch at the point of impact. The resulting voltage told the central computer which two lines had touched – a kind of digital Battleship game, more mathematical than magical in reality.
In the 1990s, as mobile phone technology advanced, touchscreen tech also found its way into hand-held devices. In 1993, Apple introduced the Newton, a touchscreen device incorporating a calculator, address book, notebook and calendar all in one.
A few years later a young me was enthusiastically stabbing away at the resistive (a little too resistant to the prod of my tiny fingers perhaps?) screen of a school computer and excitedly showing my awe-inspired (or at least humouring me by pretending to be so) parents the wonders of this miraculous technology.
Read the full article in Issue 87 of Cosmos magazine. You can subscribe here.
Lee Constable hosted the science TV show Scope and recently started a YouTube channel. She was part of the largest all-female expedition to Antarctica in 2018 and is the author of How to Save the Whole Stinkin’ Planet: a garbological adventure.
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