Whack’ed: Gross touch/gesture recognition

ref: http://homes.cs.washington.edu/~lamarca/pubs/whackgestures.pdf

HCI at CMU and Intel teamed up to solve one of the greatest problems to face modern meeting-holders since doodling was invented: Shutting Up That D*mn Cellphone!

Right now, we have to take our phone out, press some buttons/made slide gestures, and generally make a spectacle of ourselves. I used to short-cut this by yanking out the battery – back when mobile devices had easily accessible batteries. Surely we can do better?

As it turns out, we CAN! Because now in addition to touch sensitive screens, we now have ACCELEROMETERS in ALL THE THINGS. Which lets us finally just smack the darn things to get what we want.

So here’s how it works: The accelerometer looks for spikes in motion above the background noise, using a simple exponential decay average for the recognizer.

Z-axis spikes

Whacks are easily identifiable while sampling 256x a second.

There is also a risk of false positives, which was the major failing of other similar tap-based attempts on phones. They implemented a novel “whack envelope”: whack – whack in a 3-second time-span indicates a deliberate activation. Anything can now go inside the envelope for a more expressive set of actions: a wiggle (movement in x-y plane too), another whack, a flick, tap, twist – a whole gesture alphabet opens up for use. Whack – wiggle – whack through your backpack could be all it takes to turn off that obnoxious ring tone.

Effective and awesome. I can’t wait!

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