Pixel Eye was built for my Rocks and Code installation. It's sole purpose is to provide visitor-reactive waves of ambient simulated Geiger counter sound over the installation.
A slow surge of activity revolves around the room through four loudspeakers hidden in the installation, triggered by an optical device within Pixel Eye, which is placed in an unobtrusive place within the installation, yet exposed to the motion of people in the space. It is not very pretty because it was not intended to be seen, only heard.
It makes a sound vaguely analogous to waves of rain washing over a metal roof, thousands of sharp audible pulses, virtually identical to the sound of the Geiger counter built into the Atomic Number Generator. Based upon Alan Blumlein’s long tailed pair circuit of 1936 (and still a fundamental configuration today) the Pixel Eye can detect faint motion in a room, detecting motion by sensing small changes in ambient light, from reasonably dim to near-sunlight, by “seeing” variations in shadow falling upon a square of white paper. It uses one low-quality cadmium sulphide cell and three transistors. A small computer (Arduino Diecimila) generates surging sinusoidal waves of “Geiger counter” sound – in quadraphonic sound – based upon motion near it.
Pixel Eye is based upon the long tailed pair demonstration lashup/project I made for an independent study with Professor Simon Penny, Fall 2007. It was substantially reworked and packaged, and quadraphonic sound added, for this installation.
Here's a small demonstration video (30 seconds or so).