The AirHarp is an ultrasonic digital autoharp created by Peter Alaric DeSimone. The musician selects chords by pressing buttons with one hand, and strums them in the air (like an invisible harp) with the other. As an open source project, all hardware, software and support documentation is published free at: http://www.airharp.com
Several AirHarp models currently exist. The two currently supported models are:
AirHarp USB: Built around a standard Arduino Uno r2, the AirHarp USB receives power from the USB port and sends class compliant USB MIDI control messages out via the same means. It can control software synthesizers in all major operating systems and some mobile devices, such as the Apple iPad.
AirHarp Lira: Designed around the Lira microcontroller (our own Arduino variant), the AirHarp Lira is more economical and also avoids some flaws inherent to the Arduino itself (such as a wiggly USB jack). The AirHarp Lira features traditional MIDI output and runs off a single AA battery (stepped up to 5 volts via a SparkFun voltage stepup circuit).
Both versions have published electrical schematics, PCB layouts, firmware source code and 3-D printed polymer case designs. Lyratron sells PCBs, kits and completed instruments, but it is possible to build an AirHarp without paying us anything. I fact, building AirHarps for personal use is encouraged!
Both AirHarp enclosures are 2-piece designs composed of a bottom "bathtub" and a top cover piece. We've had excellent results printing them on a 3D Systems Cube. The case halves are held together by standard #4-40x1.25" machine screws. In our experience, they fit snugly in the .1" holes and do not require nuts or washers. Thinner screws could probably be used if desired.
More stuff about the AirHarp project can be found at: