The circuit consists of six 1 kohm resistors connected in series. There are six buttons connected in the circuit. When one button is pressed it produces a tone. Similarly, six buttons produce six different tones. That means, it just works as a toy piano. When the first button from right is pressed it produces high pitch tone. When the last button is pressed it delivers a low tone. This is because of the resistance connected to the buttons. The low thresh hold voltage obtained at the sixth pin slows the charging and discharging of 10 micro farad capacitor at the speaker. As the resistance value increases voltage at the threshold pin decreases and low frequency passes through speaker.