Instructables user [sketchsk3tch] was looking to make a fun toy for his kids using things he had around the house and came up with the Ping Organ. The organ is played by standing in front of the Parallax Ping range sensor, and moving around any which way you please. He interfaced the range sensor with an Arduino, scavenging a small speaker from an old toy for audio output.
The code for the project is fairly straightforward, borrowing most of it from the demo software that shipped with the Ping and the Arduino. He made a few small tweaks in order to get the organ to play frequencies of actual notes, as well as to allow for some flexibility when calculating the specific note to play.
While not the most complex project we have ever featured, [sketchsk3tch] reports that his kids love to spend time flailing around wildly in front of the organ, which is exactly what he intended.
Video of the organ being tested after the break.