The project about doorbell circuit is made up of CMOS LSI designed UM3561 IC which consumes less power. It is commonly used in toys and alarm watches because of its low cost. A compact sound module can be constructed using this IC. It includes oscillator and selector circuit and only few components are required to be added externally. It also contains a programmed ROM to produce siren sound.
When the switch S1 or S2 is pressed, the pin1 or pin5 of the IC1 receives the high signal which is used to drive the transistor that is connected to pin3 of IC1. Hence the speaker gets the supply and IC1 produces the sound of siren so as to indicate the presence on the door. A transistor is used for the process of amplification as the output of pin3 is very low.
Many other different sounds can be produced by referring the datasheet of UM3561. Similarly many other ICs are there to produce different sounds i.e. UM3481, UM3484, and UM34811.