# Sound Operated Music Bell

In this post we learn how to make a simple sound operated music bell circuit which can be installed in homes for enabling the visitors to ring the door bell by knocking on the door.

A doorbell is sine qua non in every household. Most of the standard types need human intervention to operate. But how about a bell that you don’t need to operate, rather it works as a music bell operated by sound? This article will attempt to explain the idea behind building a simple sound operated music bell.
Following is a circuit diagram of the proposed project:

Above shown is the Circuit Diagram of sound operated music bell
Referring to the circuit, the external relay has not been used. The circuit constitutes a timer stage [NE555], melody stage of around SL100 and UM66, and trigger stage of around NE555. The transistor used in this circuit BC548B is in biased state on Class C operation. The sound generating every second impacts on Pin 2 IC timer 555.
With VR1at its max state, approx., 30 seconds is the hold-on time on NE555. However, as per the requirement we need to set the value lower by VR1and the same is done as per the calculation: T = 1.1*VR1*C1
Here it is important to note that the resistance of the preset in the circuit is VR1. IC UM66 has 64 notes of ROM which produces in series and further with the sound of clap. This leads to the trigger of the timer. The output of IC NE555 at Pin 3 is therefore used via IN4001 diode and further to the Pin 2 of IC UM66. As S UM66 starts receiving supply, it generates electrical fluctuation of music at the base of SL100. The music generated is then heard from the attached 4-ohm speaker.

Following are the list of equipment that you need to build this simple and effective solution:
Resistors Capacitors Semiconductors Others
R1 = 10 KΩ C1 = 22 µF/16V IC1 = NE555 MIC1 = 34 LOD condensers microphone
R2 = 470 KΩ C2 = 0.1 µF IC2 = UM66 SW1 = On/Off switch
R3 = 2.2 KΩ C3 = 0.22 µF T1 = BC548B
R4 = 150 KΩ C4 = 220 µF/10V T2 = SL100
R5 = 100 Ω C5 = 0.01 µF D1 = 1N4001
VR1 = 1 MΩ

NOTE: All resistors should be ¼ watt and ± 5% Carbon.