A doorbell, here described, is activated as soon as a door knock is heard on the door. It is simple, sensitive, and has a low-cost sensor-based circuit. This doorbell circuit is such that Piezo Electric sensor will detect even a small knock on the door and a relay switch help activate the circuit.
Hardware Components
The following components are required to make Door Knock Sensing Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Transistor | 2N4401 | 2 |
| 2. | Relay | 12V | 1 |
| 3. | Battery | 6V-12V | 1 |
| 4. | Electrolytic Capacitor | 2.2µF | 1 |
| 5. | Variable Resistor | 1MΩ | 1 |
| 6. | Piezo Electric Sensor | – | 1 |
| 7. | Diode | 1N4007 | 1 |
| 8. | Resistor | 1KΩ, 10KΩ, 1MΩ | 1, 1, 1 |
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
Door Knock Sensing Circuit
Working Explanation
A Piezo Electric sensor is a low-cost component that uses the piezoelectric effect to measure changes in pressure, acceleration, force, or temperature and converts them to an electrical signal. Thus, in this circuit Piezo placed on the door senses the vibration of the door knock. 1M Ω Potentiometer adjusts the sensitivity of Piezo. Furthermore, the output of the Piezo is a low voltage signal, hence, is unsuitable for the direct input to the relay. Hence, two transistors of 2N4401 are placed in the circuit to amplify the weak signal of Piezo. Moreover, a relay switch connects the circuit with an amplified Piezo signal to any of the doorbells.
The whole circuit is small enough to be placed inside a doorbell box. In addition to this, any AC or DC doorbell is feasible with this circuit. The circuit operates from 6V to 12V. Just make sure to select the relay switch such that the voltage of the relay switch is the same as that of the battery connected.
Application
- Used as doorbells for homes, small offices, hospitals, etc.
- It is also applicable as a protective shield to a locker to protect it from robbery.
