My 2 year old is really into music as well as my instruments, so I decided to make one for him. I took an old Guitar Hero controller bound for the scrap heap and added some simple circuitry and a speaker.
I used a 555 timer circuit for the tone generator and used different resistors for each of the buttons so each one changes the pitch differently and they can be used in various combinations to get many different notes.
PYRAPHONIC 