Thursday, May 9, 2013

OpenPipe and breath control

I have been playing around with the OpenPipe Breakout, the electronic pipe/flute control, for a few weeks now, trying to revive some old and mostly forgottens skills on how to play a flute or Irish tinwhistle.

The pipe is connected through a I2C interface to a Maple clone, the Olimexino STM32 and then with MIDI to Garageband on my iMac. Its a fun instrument but I find it a bit hard to balance, holding it and playing some fast fingering at the same time, using a thumb for note on/off is also a bit unusal.

So I decided to try and make a breath control so that the pipe can be played almost like a real flute.

The breath control sensor is a BMP085 breakout board, this atmospheric pressure sensor
connects to the Maple board over I2C. The mouthpiece is made from two pieces of nylon tubing. A cork from a bottle of good Italian wine holds things in place. The sensor is placed inside the tube and the end is sealed with the cork, a small ventilation hole lets some air pass thrugh the mouthpiece.

The sketch reads the BMP085 and the touch sensor in the OpenPipe Breakout and starts a note if the pressure is more than 50Pa above ambient. Some early tests shows that the basic setup works but theres a lot more to do before the sound can be controlled by breath like in a real flute.

Selecting a pressure sensor

BMP085 is an absolute pressure sensor accessed using the I2C protocol. No extra components are needed. The drawbacks are that the breath only represents a small fraction of the sensors range and the baseline pressure, ambient pressure, must me calibrated for.. Price is ___

The other major type of pressure sensor is a MEMS bridge giving a small voltage representing the difference between measured pressure and ambient. The problem here is that the small sensor output must be amplified before the signal is input to a AD converter. No calibration for changing ambient temperature is needed.