Chris Chronopoulos' Quadrant Is a Four-Sensor Input Board, Doubles as a "Four-Dimensional Theremin"

Maker Chris Chronopoulos has put together a human-computer interface, Quadrant, designed for zero-touch interaction — and it doubles as a "four-dimensional theremin" to boot.

"Quadrant is a human-computer interface based on an array of distance sensors," Chronopoulos explains of the project. "The hardware consists of four time-of-flight sensors and is specifically designed to detect the position, velocity, and orientation of the user’s hand in free space. Signal processing techniques are used to recognize gestures and other events, which can be mapped to a variety of musical parameters in software."

The four distance sensors, which give the compact STMicroelectronics STM32-powered Quadrant board its name, are designed to cover the user's whole hand when positioned over the center point of the board. Move your hand in any way, and the distances reported by the sensors change accordingly — offering an input that could be used to recognize gestures or move an on-screen representation of the user's hand.

"This project developed from an interest in gestural interfaces for music," Chronopoulos explains. "We had some promising early results with arrays of photometric distance sensors, but ultimately the low range, rampant cross-talk, and susceptibility to ambient light conditions motivated us to look beyond these basic sensors."

"Recent advances in time-of-flight technology presented the opportunity to switch to a far more accurate and robust class of sensors. By shrinking the array to just four sensors, we were able to keep the BOM affordable while still offering a broad range of interaction paradigms."

The readings could also be used to make music - and that's Chronopoulos' primary focus. "We can use the average distance measurement to control the pitch of an instrument," he explains, "creating a simple theremin effect. The distance measurements are sent as a stream of four channel values; you can use the scripts I provided to convert this to MIDI data or OSC or you can develop your own mappings in your preferred software."

"I hope you find Quadrant to be a useful controller for your musical explorations, and come up with new applications beyond what I've suggested here."

Both the hardware design files and the firmware source code for the Quadrant are open-source, with the latest version of the board — Quadrant Rev 3.1, at the time of writing — available to download from the Quadrant Hackaday.io project page under the CERN Open Hardware License 2 Strongly Reciprocal and the permissive MIT license respectively. The board is also available to buy pre-assembled on the Interstitial Tindie store at $55.