A Major

Has three pushbutton switches that control the frequency of square wave output from an op amp. The frequency for each switch corresponds to a note in the A major chord (A, C sharp, E).

Connect the op-amp invertign input to the capacitor and the noninverting input to the voltage divider. Then connect the inverting and non-inverting inputs with through the smaller resistors and switches as shown. Run op-amp output to the speaker.