Here is an instrument that fixes the position of a stick hit or finger
tap, based on how long it takes the sound waves to travel to the
sensors.
I started thinking about timing sound waves to control sound at the end
of 2005. I had an idea about using reflected ultrasound for
pitch
detection on a string instrument. I decided that it would be
a
good idea to try something a little simpler first, like measuring the
speed of an audible sound impulse in a solid, and using that as control
data. I learned that this concept had a precedent in the MIT
media lab project "Ping
Pong Plus," so I mined their paper
for ideas.
In April 2007 Sukandar
Kartadinata gave a sensor workshop at
Tesla in Berlin, which I took as an opportunity to work on this
project, as well as an opportunity to absorb some of S.K.'s
formidable experience.
The sensor setup is pretty simple. I have two piezo contact
microphones stuck to a plywood table top with plasti-tak, about a meter
apart. The signal from each piezo goes into a circuit that
returns a digital "high" if the sensor voltage goes above or below a
certain threshold. As soon as one goes high, the
microcontroller
sets a timer which runs until the other goes high. The value
of
this timer represents the distance from the center point between the
sensors. This program
also keeps track of which sensor triggered
first, so we know if we are left or right of center.
Here is another participant trying it out in the workshop: clapboard0.mov
And a year and a half later at DorkbotPDX, still doing the same thing!
