3D-printed plastic smartphone plug-ins replace complex analog circuits
There is a burgeoning market for so called app toys, or smartphone application-driven toy peripherals. In fact, this is one of the fastest growing tech sectors and according to MarketWatch.com, it is expected to generate billions in sales in 2015 and beyond, linking the two multi-billion-dollar toy and mobile app industries together.
Today even the most humble smartphone docking station has built electronics and control knobs to activate circuitry and send the right control signals to the docked phone. But such accessories could be made much more simply and cheaply, according to 2nd year PhD Candidate Gierad Laput, investigating a new type of interface at the Human-Computer Interaction Institute, Carnegie Mellon University.
Like for most of these app toys, Laput relies on the smartphone’s compute capacity and rich display interface to do most of the work, but the actual user interface extensions he has built, in the shape of knobs or sliders or any other linear sensors, bear no electronics whatsoever.
Instead Laput leverages the smartphone’s speaker as an analogue signal source of ultrasounds, and cheap plastic structures that can passively interfere with the sound waves as the user interacts with them.
The phone’s microphone picks up the modulated ultrasounds and interprets these variations as user inputs. Today, the researcher uses 100ms linear sweeps from 16.50 to 22.05kHz, but in a paper titled "Acoustruments: Passive, Acoustically-Driven, Interactive Controls for Handheld Devices", he notes that for increased resolution, both sweep rate and frequency range could be drastically increased as the sampling rate of handheld devices continues to improve.
The name Acoustruments relates to the small instrument extensions that could be built around smartphones, modulating acoustic waves in very much the same way that musical air instruments operate when a musician affects their resonating cavities (pressing a piston or blinding a hole).
In this paper, the researchers describe how they have designed a number of structural elements to be placed along the speaker-microphone pathway to characteristically alter the acoustic output. These take the shape of various physical mechanisms involving small tubes, deformable resonating cavities, knobs offering multiple selectable audio path, and more practically, all this translates into numerous functions such as turn knobs, sliders, proximity and pressure sensors, rotary encoders or even tilt sensors.
This gives plenty of scope for cheap plastic electronic-free app toys delivering rich, tangible interactive functions. Experiments have shown that the Acoustruments could achieve 99% accuracy with minimal training while being very robust to noise.
To prove their point, the researcher created an iPhone case built from soft, squishy tubes that can recognize when it’s on a table, in your hand, or taking a photograph.
They also constructed an alarm clock that you could activate with a switch, and snooze by pressing a large button. In another application, they developed a toy car that attaches to a phone and whose wheels’ motion actually drives a racing game in real-time.
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