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Researchers Create Touchpads With a Can of Spray Paint (phys.org)
Researchers at Carnegie Mellon University have figured out a way to turn any surface into a touchpad using none other than spray paint. "Walls, furniture, steering wheels, toys and even Jell-O can be turned into touch sensors with the technology, dubbed Electrick," reports Phys.Org. From the report: The "trick" is to apply electrically conductive coatings or materials to objects or surfaces, or to craft objects using conductive materials. By attaching a series of electrodes to the conductive materials, researchers showed they could use a well-known technique called electric field tomography to sense the position of a finger touch. With Electrick, conductive touch surfaces can be created by applying conductive paints, bulk plastics or carbon-loaded films, such as Desco's Velostat, among other materials. Like many touchscreens, Electrick relies on the shunting effect -- when a finger touches the touchpad, it shunts a bit of electric current to ground. By attaching multiple electrodes to the periphery of an object or conductive coating, Zhang and his colleagues showed they could localize where and when such shunting occurs. They did this by using electric field tomography -- sequentially running small amounts of current through the electrodes in pairs and noting any voltage differences. The tradeoff, in comparison to other touch input devices, is accuracy. Even so, Electrick can detect the location of a finger touch to an accuracy of one centimeter, which is sufficient for using the touch surface as a button, slider or other control, Zhang said. You can watch a video about how it works here.
I remember there were a few electronics kits you could buy in the 1980's that did the same trick with pencil "lead". First, you scribbled onto some paper, then you attached a lead and pressed onto the graphite square you drew to make different sounds, etc.
I read an article long ago about how you can't truly understand an engineering design unless you understand the context. One example they used was the dashboard of the Saab automobile. Saab, in those days, had a very clunky looking dashboard with large controls spaced far apart. To Americans it looked ugly. What they pointed out in the article was that the Saab was designed in Sweden, by Swedish engineers. The engineers assumed the driver would be wearing winter gloves most of the year and so designed the controls to accommodate.
Anyway; sometimes a big, fat button makes sense.