Battery operated Bells, connecting a buzzer through a simple pushbutton switch also has a couple of disadvantage. For instance, the bell sound is irritates and the visitor has hold the push button for a few seconds. The circuit has a dirt-cheap piezobuzzer into a pleasant sounding door bell. A 555 (IC1) timer is configured as an as table multi vibrator with low time of 7 milliseconds and high time of 235 milliseconds. IC1 provide the output is low, Ti conducts to activate the buzzer and charge capacitor C3 and the output goes to high, the amplitude of the bell tone decays continuously.
The timer circuit operates as follows: Momentarily pushing of switch S1 charges capacitor C1 rapidly via resistor R1. When the voltage on capacitor C1 exceeds the threshold voltage at the gate of transistor T1, it started conducting and remains conducting as long as the charge in the capacitor is greater than the threshold value. The component values given the buzzer sounds for around 15 seconds, which is sufficient to alert the house owner. Assemble the circuit on a general-purpose PCB and enclose in a box, and connect the switch at the gate and the piezobuzzer inside your house.
