555-based Toy Organ

Figure 1.  Circuit Diagram for a Simple Toy Organ

This is a circuit for a very simple toy organ.  The main component of this circuit is the 555 timer IC, configured as an astable multivibrator.  A 555 configured as such outputs an oscillating signal with a frequency determined by the values of R1, R2, and the capacitor connected between pin 1 and pin 2.

In this circuit, every time one of the switches is pressed, a capacitor of certain value is connected to the 555, causing it to deliver a signal of corresponding frequency to the speaker, thereby producing a tone specific to the switch pressed. By choosing the capacitor values well, the tones produced may mimic those of an organ.  The number of 'keys' in this toy organ may be increased by adding more switches and capacitors.