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