MUSICAL DOOR BELL

This circuit generates a sweet melody for two minutes when it is triggered. It uses the ROM IC UM66 to produce the melody. The music stops automatically.

When the push switch is pressed momentarily, NPN transistor T1 conducts and pull the base of T2 and it also conducts. When T2 conducts, C1 charges and provides power to IC UM66. Zener diode ZD is used to regulate the supply voltage to UM66 to 3 volts. When UM 66 gets 3 volts supply, it oscillates and the music tone from it will be amplified by T3 which can be heard through the speaker.

Note

If component removal is required for re assembling, do not bend the excess leads of components before soldering. Cut the excess lead close to the PCB and apply some flux. Apply little solder at the contact point. Do not apply, excess solder or over heat the solder points. PCB tracks will detach. Clean the surface with kerosene, or PCB cleaning fluid to remove flux and dirt.