Hackers in Residence - The ElectricBone
The basic design of the ElectricBone is quite simple. A Redboard controls an ultrasonic distance sensor (HC-RS04), a Sound Detector and a Softpot. The distance sensor uses two digital pins on the microcontroller: one for triggering an ultrasonic pulse and one for receiving the echo. The Sound Detector has three output pins, of which I used two: gate and envelope. The gate pin connects to a digital pin on the Redboard and the envelope connects to an analog pin. The Softpot's output goes on a second analog input. On top of this basic circuit, there are two additional components: a Serial Enabled LCD, using Softserial on a ordinary digital pin, and a MIDI connector attached to the built-in serial ports. Finally there is a button for switching output modes.
The Redboard listens to the gate pin from the Sound Detector to know when the player's lips start to vibrate. If it gets a hit, it starts to track the slide position through the distance sensor and harmonic number with the Softpot, which is operated by the player's left thumb. By combining the two pieces of information (slide position and harmonic), the Redboard can determine which note needs to be played, so it issues a "Note On" message to the MIDI port. After the note start, it begins to track the envelope pin in order to control the intensity of the note. When the gate pin reads low, the Redboard sends out a MIDI "Note Off", and the sound is terminated.