Students in Mr. Graner's class built Capacitor Pianos! The goal was to create four touch sensitive keys out of tin foil that would play different frequencies when pressed. The keys were created from tin foil and mounted on a cardboard backing with glue. Wires were then connected to the keys and plugged into a circuit breadboard. Students used resistors and wires to connect that circuit to an Arduino (tiny computer.) The Ardiuno was pre-programed to measure the capacitance of each “key”. Since the human body is electrically charged when a key is pressed it changes the capacitance of the key and the Arduino picks up that change in electrical capacitance. Then depending on which key is pressed it will send the signal to play a certain tone or frequency through the speaker.
These pianos react very similar to how a touchscreen phone works. If you use your fingers it works great, but if you push it with a pen or anything else that isn’t conductive the screen is unresponsive.