In this tutorial, we are making a project of a Simple sensitive knock sensor circuit. This circuit will blink three LEDs giving you a visual indication when any knock or vibration is detected at the place where this circuit is placed.
The circuit is super easy to build, the whole circuit is based on two transistors and a few discrete components like resistors, variable resistors, and a capacitor. The knock sensing is done by a piezoelectric sensor. A piezoelectric sensor or PZT is a device that can measure changes in pressure, strain or force, etc, and convert them into electrical signals.
Hardware Components
The following components are required to make a Sensitive Knock Sensor Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Input Supply DC | 9-12V | 1 |
| 2. | PZT Sensor | – | 1 |
| 3. | Transistor | 2N4401 | 2 |
| 4. | Resistors | 10K, 1K, 1M, 470 | 1, 1, 1, 3 |
| 5. | Variable Resistor | 1M | 1 |
| 6. | Electrolyte Capacitor | 2.2µF/35V | 1 |
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
Sensitive Knock Sensor Circuit
Working Explanation
The operating voltage of this circuit is 9 to 12 volts DC. When the vibration of a knock is sensed by the PZT sensor it will convert these vibrations into electrical signals and send them to the transistor Q1. Now the transistor Q1 will activate and sends a signal to the base of the second transistor Q2 to activate it. This transistor will switch on the three LEDs giving a visual indication whenever there is a knock at the surface where the circuit is placed. The sensitivity of this circuit is adjusted by a 1M variable resistor. Make sure to fit the circuit in a small suitable enclose with lithium coin batteries for the best performance.
This circuit can be operated at a lower voltage like 5 or 6V but for that, you have to use a 220 ohms resistor in the place of 470R for brighter LED light.
Applications and Uses
- Doorknock indicator
- On the guitar surface so the LEDs will glow when the guitar is played to give it a cool effect
- At the surface of the loudspeaker, the box blinks the LEDs when music plays.
