This is the little 40 Khz ranging sonar head that was developed for the Brain Opera. Click here to examine a much bigger photo. Up to eight of these plug into a MIDI master controller module, using simple RJ-45 cables. These can be individually or collectively pinged using a MIDI control-change (controller #1) command. These devices produce a voltage proportional to the range of the first detected reflection, which is digitized into a 7-bit MIDI value by the master controller. They now can range up to 25 feet or so, with a beamwidth of 40 degrees (set by the transducer width). The units have adjustable TVG, threshold, and transmit power. They are very quiet (unlike the more common Poloroid electrostatic sonars); the ping leaves little audible counterpart. Look here to find a photo of the sonars used to control a large interactive video display, an installation done with the Media Lab's Interactive Cinema Group.
Credits
Joe Paradiso - Circuitry, design, coordination
Joel Rosenberg, Craig Abler - Electronics Production
Josh Strickon - MAX test and installation software
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