In this tutorial, we are going to make a Doorknock sensing doorbell that activates when someone knocks on your door. This circuit is quite sensitive it can detect even a small knock and it’s super easy to build. We are using a relay switch at the output of this circuit so that you can connect it with any doorbell switch. This circuit is compact so it can be easily placed in a doorbell box along with batteries.
The knocking sound is sensed by a piezoelectric sensor. It is a low-cost sensor and can be easily purchased from your local electronics shop or online. If you have any scrap piezo buzzers, toys, or electronic equipment that use these sensors, you can take this sensor from them as well. This circuit will cost you very less because it is using only a few components.
Hardware Components
The following components are required to make Door Knock Sensing Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | DC Supply | 6V-12V | 1 |
| 2. | Piezo Sensor | – | 1 |
| 3. | Resistors | 1M, 10K, 1K | 2, 1, 1 |
| 4. | Variable Resistor | 1M | 1 |
| 5. | Electrolyte Capacitor | 2.2uF | 1 |
| 6. | Transistor | 2N4401 | 2 |
| 7. | Relay | – | 1 |
| 8. | Door Bell | – | 1 |
| 9. | Diode | 1N4007 | 1 |
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
Door Knock Sensing Circuit
Working
This circuit is operated on a 9-12V battery, we are using a piezo element as a vibration sensor, whenever someone knocks it will sense the vibrations and convert them into electrical signals. These electrical signals are then sent through a capacitor for noise cancellation. These signals are passed through two transistors for the purpose of amplification. We are using a 1M variable resistor to adjust the sensitivity of this circuit.
You will have to place the piezo on the door with thin wire for all the connections with the circuit. There is a relay at the output of this circuit which will enable you to connect your doorbell switch to this circuit. This whole circuit and the batteries can be fixed in a box of a doorbell.
Applications and Uses
Apart from using this circuit as a doorbell sensor, you can use it anywhere you need to be alerted or alarmed on someone’s entrance.
