Unfortunately, EC does not yet support sound so you will have to use your imagination.
The array of push buttons across the bottom functions as the keyboard. Each key has a unique value of resistance in series and thus a unique time period when used with the timing capacitor at the timer.
Also, combinations of pressed keys will allow the user to reach pitches outside the range normally mapped by the keyboard, but of course, having a single oscillator means it is not possible to play chords.
The SPST switch above the keyboard facilitates tuning the device by holding A4 while you trim your pot until you reach 440Hz.
The control input can also be used to modulate the pitch. Using a second timer to generate a carefully chosen low frequency square wave, the pitch will alternate rhythmically within two musically complementary notes.
You probably won't be thrilled with the sound quality, but you might be surprised at how much fun these simple circuits can be. They can be most easily constructed around either Schmitt inverters or timers.
