The schematic below shows a very simple and good quality project of mains operated doorbell or door chime circuit. The circuit is using a UM66 CMOS IC, available in TO-92 transistor package. There are many versions of this IC are available, each version has a different melody programmed by the
manufacturer.

Each IC comes with the song code mentioned on it with part number for example UM66T08L contains "Happy birthday song" and UM66T05L contains "Home sweet home" etc. More details can be found in the datasheet. You can select any of your desired IC melody to use in this door bell circuit.

The circuit is simple and using only few parts and can be easily fitted in a small box with the transformer. The transformer steps down the mains voltage, which is rectified by the 1N4007 diode bridge and then filtered by the 220uF electrolytic capacitor. The maximum operating voltage of the IC is 4.5V DC. The 3.3V zener diode steps down 5V to 3.3V to operate the IC smoothly. The 2N3904 transistor is used to amplify the output of UM66 IC.

The transformer used in the circuit is an 110/230V to 5V step down transformer with output current of 200 to 500mA. You can also operate the circuit with any cellphone charger you have in scrap. The figure 2 shows the circuit to use with the cellphone charger.
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Figure 1.
Figure 2.
Mains Operated Doorbell Circuit