Security & Saftey

Doorbell with Security Feature Schematic Circuit Diagram

This doorbell Security system works such that when someone presses your calling bell switch during the night, not only does the bell ring but the bulb connected to it also glows. In order to turn the bulb off, just press the reset pushbutton switch provided in the circuit. Place the bulb near the calling bell switch so that you can see the person pressing the calling bell before opening the door. So you can choose not to open the door to doubtful persons. During day time, the bulb doesn’t glow and only the calling bell sounds.

When the calling bell switch S1 is closed, the bell rings and simultaneously transformer X gets an AC supply. The output of this 6V-0V-6V/500mA step-down transformer is rectified by diodes D1 and D2. The rectified output is filtered by 1000µF, 25V capacitor C1, and fed to the collector of transistor BC547 (T1) via 2.2k resistor R1. A light-dependent resistor (LDR) is connected to the base of this transistor.

Doorbell with Security Feature Schematic Circuit Diagram

During the day, the LDR has very low resistance as it receives continuous light. So when the calling bell switch is pressed, the transistor conducts and its collector is pulled to the ground. Thus the next section of the circuit remains inactive and we hear the calling bell only.

The next section consisting of IC 7408 (IC1) and IC 7473 (IC2) gets a separate supply voltage of 5V from regulator IC 7805 (IC3) as shown in the figure.

A capacitor is a device that stores electrical energy in an electric field. It is a passive electronic component with two terminals. The effect of a capacitor is known as capacitance.
capacitor, a device for storing electrical energy, consisting of two conductors in close proximity and insulated from each other. A simple example of such a storage device is the parallel-plate capacitor.
Capacitors are crucial components in most electronic devices. They are widely used in electronic circuits, power circuits, power supply units, etc. Capacitors are considered as one of the Big Three Passive Components, along with resistors and inductors, which form the basic electronic circuits.18-Mar-2020

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