There are two types of doorbells which are called as easy installation doorbells. These type of doorbells are easy to install and so, it gains the name. It doesn’t require any mechanical switches also. Its just enough to be placed in the door itself with a small amount of metal piece or sticking gum.
The working of the circuit is as follows:
The circuit1 completely operates by the Piezoelectric ceramics. The piezoelectric effect causes a crystal to produce an electrical potential when it is subjected to mechanical vibration. In contrast, the reverse piezoelectric effect causes the crystal to produce vibration when it is placed in an electric field.When someone knocks the door, the mechanical vibration arising from the knock reaches the door. So, Piezoelectric ceramic YD. The mechanical vibration is converted into electrical voltage by its piezo electric effect of the ceramic. The small voltage will drive both of the transistors BG1, and BG2, which makes them to conduct.The transistors in turn trigger the musical IC CIC, and the music gets played. Piezo electric ceramic with glue at its center is easily available at markets now.
The Circuit2 is same as that of the circuit1. But, the small difference is that it doesn’t have the Piezoelectric ceramic in it. ie, the voltage which needs to trigger the transistors BG1 and BG2 are taken from the human body itself. When a human touches the switch A, the small voltage from human body, drives both the transistors, and so, the music IC get triggered, and it plays sound. Figure 2 can be called as Touch sensitive doorbell.