PARIS — In a joint project from Carnegie Mellon University HCI Institute and Disney Research, researchers have demonstrated the use of cheap 3D printed plastic parts in place of complex analogue electronic circuitry to build smartphone plug-in accessories such as docking stations and other playful extensions.

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 dollars 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

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.

This gives plenty of scope for cheap plastic electronic-free app toys delivering rich, tangible interactive functionalities. Experiments have shown that the Acoustruments could achieve 99% accuracy with minimal training while being very robust to noise.