INTERFACE hacks

Experiments in New Interfaces

This is a collection of electronic/sensor/controller hacks I did during my work at CNMAT. Sometimes it's fun to play around and try stuff. Sometimes you learn something in the process!

HEAD TRACKING HEADPHONES

These headphones are augmented with sensors for tracking head motions including a 3-axis accelerometer, gyro, and magnetometer. The sensors are connected to a PIC microcontroller which streams the data back to a computer using the OSC protocol over a USB Serial link.

Calibration and sensor fusion was performed using a servo-powered 3-axis motion rig. The work was sponsored in part by Sennheiser Research.

References

Schmeder, Andrew, and Adrian Freed. "A Low-level Embedded Service Architecture for Rapid DIY Design of Real-time Musical Instruments." NIME. 2009.

Schmeder, Andrew, and Adrian Freed. "uOSC: The Open Sound Control Reference Platform for Embedded Devices." NIME. 2008.

CIRCULAR RANGEFINDER

This is a circular array of infrared range finders that I built to track the movement of people around a spherical loudspeaker. The distance and position measurements were used to drive real-time demonstrations of spatial audio processing algorithms using directional beamforming. For example, maintaining constant loudness and apparent source width as a person walked toward the loudspeaker from any direction, giving the illusion of a virtual acoustic source at a fixed distance.

References

Schmeder, Andrew. "An exploration of design parameters for human-interactive systems with compact spherical loudspeaker arrays." Ambisonics Symposium. 2009.

LED PEAK METER + TOUCH VOLUME CONTROL

I created a prototype of an audio peak meter from a linear array of LEDs driven by a microcontroller that simultaneously operates as a volume display and optical touch detector, enabling the user to see the current song volume and change the volume by sliding a finger along the array.

This hack works by rapidly alternating the LED between light emitting and light detecting. LEDs can be turned into ambient light detectors by reverse-biasing the diode and then measuring the discharge rate from incoming photons (note: doing so may void the manufacturers' warranty!)

The alternation between emitting and detecting modes occurs faster than the flicker fusion frequency. Therefore there is no visible flickering. However, the temporal dynamics of the charge-discharge signal can be observed on an oscilloscope (pictured).

PENDAPHONE THROWABLE POSITION SENSOR

I helped to develop a unique positional interface achieved by modifying a stock controller with absolute 3D position sensing. The controller, sold under the brand GameTrak, consists of a tensioned cord on a spring-loaded pulley passing through the center of a 2-axis joystick, enabling 3D position sensing within a cone. The "pendaphone" is created by inverting the default orientation of the controller into an "upside down" configuration, enabling absolute position tracking within a conical region with the apex on the ceiling.

A further innovation was created by attaching a Nintendo "Wiimote" to the pulley, which had neutral buoyancy with respect to the retracting cable's spring, enabling a user to select a height of the "bob" in space using an intuitive grab-and-place action, while also adding additional control channels for orientation (pointing) and button presses.

A popular interactive auditory demo consisted of throwing the "bob" around a circular arc and following it with a spatially directed acoustic beam, e.g., from a spherical loudspeaker.

I constructed a portable version of the apparatus, pictured in a public demonstration at Maker Faire in 2009.

References

Freed, Adrian, et al. "Musical applications and design techniques for the gametrak tethered spatial position controller." Proceedings of the 6th Sound and Music Computing Conference. 2009.

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