Sound Operated Music Bell

Sometimes ringing the bell manually becomes difficult, especially when you are holding something in your hands. The sound-operated music bell takes care of the problem

In this circuit, the use of an external relay has been eliminated. The circuit comprises a trigger stage (around BC548B), a timer stage (NE555) and a melody stage (around UM66 and SL100).
Transistor BC548B is biased inn class C operation. Every second sound cause triggering at pin 2 of 555 timer IC.
When VR₁ is at maximum, the hold-on time of NE555 is around 30 seconds. But this time period can be set to a lower value by VR₁, as per requirement, using the relationship.
T = 1.1*VR₁*C₁
Where VR₁ is the actual resistance of the preset in circuit. UM66 IC has  ROM memory of 64 notes which are produced one by one and then over with a sound of a clap, the timer is triggered and the output at pin 3 of IC NE555 goes high which gets applied through diode 1N4001 to pin 2 of musical IC UM66. S UM66 gets the positive supply, it starts giving electrical fluctuations of the music to the base of SL100, and the charming music comes and fed to 4-ohm speaker.

PARTS LIST

Resistors (all ¼-watt, ± 5% Carbon)

R₁ = 10 KΩ

R₂ = 470 KΩ

R₃ = 2.2 KΩ

R₄ = 150 KΩ

R₅ = 100 Ω

VR₁ = 1 MΩ

Capacitors

C₁ = 22 µF/16V

C₂ = 0.1 µF

C₃ = 0.22 µF

C₄ = 220 µF/10V

C₅ = 0.01 µF

Semiconductors

IC₁ = NE555

IC₂ = UM66

T₁ = BC548B

T₂ = SL100

D₁ = 1N4001

Miscellaneous

MIC₁ = Condensers microphone 34 LOD

SW₁ = On/Off switch