A while back I saw a video of a guy playing a CRT like a guitar. I wanted to know more but the explanation on their website wasn't very detailed. So I sought to try and make and understand it myself.
What's happening is that the Arduino is sending pitches to the video port of the CRT. This creates the lines on the TV. For example, if you were to code an Arduino to play A4 (440Hz) and send that tone to the video port of a CRT then that should display about 7 white lines on the TV because each white line should be about 60hz (440 / 60 = 7.333... ). The strings on the neck are actually soft potentiometers. These potentiometers are used her as position sensors that track the placement of your finger. I coded them so that one is mapped to C4 to C5 and the other is mapped to E4 to E5.