That's an update for the older version of the project!
Now you can play the keyboard on the keys from A to J and from Q to U for # notes.
It's set on the fifth scale, but you can set it as you like by editing the code.
I recommend you not to use the Arduino Serial Monitor to play this project, because you would have to hit the "Enter" key after every note to play it.
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So, you should download PuTTY from here and set the connection type as "Serial" in the first window that appear, insert your COM in the serial line (you can verify where Arduino is connected in Windows Device Manager) and then click on "Open".
A terminal windows should appear with the message set in the code.
Now you're free to play it! Hope you have fun :)