Touchless 3D gestural interface using coded ultrasounds

Touchless human-computer interfaces are possible using wireless position sensors with sufficient positioning accuracy. The proposed locating system is composed of a set of beacons that emit a sequence of ultra-acoustic pulses in the space region containing a number of wireless position sensors. The prototype has four coplanar beacons, placed at the corners of a PC screen, which are forced to emit chirp signals in the 20-48 kHz band. Each battery-supplied sensor is equipped with a wideband miniature microphone, a conditioning circuitry and an infrared transmitter. When impinged by the sequence of acoustic wavefronts, each sensor sends back a signal to a central unit through an infrared optical transmission channel. The central unit preprocesses the received signals using the correlation technique, and obtains the times of arrival of the sensors´ signals. Knowing the position of the acoustic beacons, the central unit computes the coordinates of the sensors, identifying and discarding possible false signals due to echoes and environmental noise. All the computations, including signal filtering, time of arrival detection, localization and results display, are carried out by a notebook PC at 25 Hz.