Even if you have a big phone like an iPhone 6 Plus or a tablet, there are times when the screen is just not big enough for the sweeping gestures you might want to make.
The addition of cheap sound sensors could let any nearby desk or table surface extend the apparent size of your touchscreen, say Robert Xiao and his colleagues at Carnegie Mellon University in Pittsburgh, Pennsylvania. They have built a system called Toffee, which uses inexpensive mini microphones attached to each corner of a tablet or smartphone. When you are seated at a table, you launch an app which listens out for the sound of your fingers swiping or tapping the tabletop in certain places around the device. Those will correspond to commands you have chosen in advance, such as scrolling through your pictures right or left, playing a game, or changing the slide in a presentation running on the machine.
The system works out the origin of a sound by measuring how long it takes for sound waves to arrive: the sensors simply triangulate the position of the sound source, says Xiao's colleague Chris Harrison. This technique is known as passive time-difference-of-arrival and is already used in military sonar. "We're just using it in a new way for consumer devices," he says.
It shouldn't cost much for technology firms to upgrade devices to take advantage, either. "The microphones are very cheap today, typically tens of cents," says Harrison. "It would also work on laptops and pretty much any other device that rests on tables."
Toffee was presented at the Mobile HCI conference in Toronto, Canada, last week.
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