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Device turns your arm into a smartwatch touchpad

SkinTrack can be used as a game controller, to scroll through lists on the smartwatch, to zoom in and out of onscreen maps, and to draw. (Credit: Carnegie Mellon)

New wearable technology turns the entire lower arm into a touchpad, expanding smartwatch interactions beyond the small watch face.

The new system, called SkinTrack, allows for continuous touch tracking on the hands and arms. It also can detect touches at discrete locations on the skin, allowing for functionality similar to buttons or slider controls.

Previous “skin to screen” approaches have used flexible overlays, interactive textiles, and projector/camera combinations that can be cumbersome. SkinTrack requires only that the user wear a special ring, which propagates a low-energy, high-frequency signal through the skin when the finger touches or nears the skin surface.

“The great thing about SkinTrack is that it’s not obtrusive; watches and rings are items that people already wear every day,” says Yang Zhang, a first-year PhD student in the Human-Computer Interaction Institute (HCII) at Carnegie Mellon University.

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“A major problem with smartwatches and other digital jewelry is that their screens are so tiny,” says Gierad Laput, a PhD student at the HCII. “Not only is the interaction area small, but your finger actually blocks much of the screen when you’re using it. Input tends to be pretty basic, confined to a few buttons or some directional swipes.”

“SkinTrack makes it possible to move interactions from the screen onto the arm, providing much larger interface,” says Chris Harrison, assistant professor in the HCII.

Electrodes in the watch strap

The user wears a ring that produces a high-frequency electrical signal. When the finger gets near to the skin or touches the skin, that signal propagates through the skin.

By using electrodes integrated into the watch’s strap, it’s possible to pinpoint the source of those electromagnetic waves because the phase of the waves will vary. Electrodes corresponding to the 12 o’clock and 6 o’clock positions on the watch, for instance, can detect phase differences that can determine the position of the finger along the width of the arm; electrodes at the 3 o’clock and 9 o’clock positions can determine the finger’s position along the length of the arm.

Researchers found that they could determine when the finger was touching the skin with 99 percent accuracy and they could resolve the location of the touches with a mean error of 7.6 millimeters. That compares well with other on-body finger-tracking systems and approaches touchscreen-like accuracy.

Games, maps, and drawings

The researchers demonstrated that SkinTrack can be used as a game controller, to scroll through lists on the smartwatch, to zoom in and out of onscreen maps, and to draw. A number pad application allows users to use the back of the hand as a dial pad for the onscreen number pad; hovering a finger over the hand acts as a cursor, highlighting numbers on the screen to aid in targeting touch points.

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The system has some limitations. Keeping the ring powered up is a challenge. Signals also tend to change as the device is worn for long periods, thanks to factors such as sweat and hydration and the fact the body is in constant motion.

The technology is safe. No evidence suggests that the radio frequency signals used by SkinTrack have any health effects. The body is commonly excited by daily appliances—everything from the tiny amounts of current drawn from the finger by touchscreens to the electromagnetic noise emanating from fluorescent lights—with no ill effects.

Researchers will present a paper on the technology this week at the Association for Computing Machinery’s Conference on Human Factors in Computing.

Source: Carnegie Mellon University