In this chapter, we’re going to build a sensor circuit to use with a bow to manipulate the sound of a live instrument, with input given by the gestures of the performer, who will control the instrument’s audio input. This circuit can actually fit any instrument that involves some movement, such as a trombone, for example. The sensor we’ll use is an accelerometer, which in this particular case was chosen for its tilt-sensing capability. means that the sensor is able to orientate itself with respect to the Earth’s surface. This sensor gives values for three axes, which we can use independently. In this project, we’ll give ourselves as much freedom as possible so that we can use any of the three axes at any time (including all three together). We can even receive no input from the sensor, so that the performer can move freely in case he/she doesn’t want to affect the instrument’s sound at certain moments.