How to make the sound of my doorbell circuit louder?

[pmostafa]

I have used one UM66 IC, one BC547 Transistor and one 100 Ohm resistor. The circuits of door bell are as follows but same result. The loudness is extremely poor against both the circuits. How can I increase the loudness? Would you please help me in this regard?

 

[reson8r]

With only a 3.3 V power supply you won't get much power to the speaker, only about a quarter watt by the back of my envelope here. Try a larger supply (but don't blow up your UM66).

It's kind of strange to be driving a speaker with the collector of a transistor, too -- assuming the UM66 switches the transistor on and off that would connect the speaker to ground and then open it, which would result in inductive spikes which might damage the transistor. Looks cheap & cheesy to me!

 

[gleem]

Be careful not to exceed 3V for the input to the UM66. You need a circuit that provides the additional power to the enunciator while keeping the input voltage to the IC less that its maximum permissible.