555, LM324, 74HC191, 74HC4028
In this project, you're going to build a player organ that sounds four tones cyclically. You have a scale available of doh, ray, me, fah, soh, lah, ti, doh.
You can use four of the eight pitches to play a piece of music or part of it. Let the organ play on a four-pitch scale.
When you finish wiring, turn power ON. Set the connecting points "1" - "4" to four different pitches. You'll hear the four pitches of your choice played repeatedly.
Then, rotate the control volume and see how the sound changed. The play speed should have shifted.
Change the connecting points and try another musical number.
U2 is an astable multivibrator that determines pitches of the organ. The output of U2 is sent to the up/down counter U3 where it is counted up. The outputs Q0 and Q1 of U3 are decoded by U4, which thus selects the four connecting points "1" - "4" one after another.
On the other hand, U1A is a musical oscillator, which outputs sound to the voltage follower U1B, Q1 and Q2, and the speaker. Suppose the connecting point "1" is connected to "don." When "doh" is grounded, U1A oscillates at a frequency of "doh," so you hear a "doh" sound from the speaker.