A volume unit (VU) meter is a device displaying a representation of the signal level in audio equipment. They are used in telephone installation and radio broadcast stations. Consumer audio equipment often features VU meters, both for utility purposes (e.g. in recording equipment) and for aesthetics (in playback devices). Audio level VU meter can easily be built by using only some discrete components, transistors, and LEDs.
Hardware Components
The following components are required to make Audio Level VU Meter Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Battery | 12V | 1 |
| 2. | Transistors | 2N4401 | 12 |
| 3. | Transistor | BD140 | 1 |
| 4. | Diodes | 1N4148 | 13 |
| 5. | LEDs | 25mA | 36 |
| 6. | Capacitor | 10µF | 1 |
| 7. | Resistors | 75Ω, 5.1K, 100K | 12, 12, 1 |
2N4401 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N4401
BD140 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of BD140
Audio Level VU Meter Circuit
Working Explanation
The circuit will not require an amplified audio signal at the audio input. It will require a very small audio signal equal to the audio output from the headphone jack of any audio device. The input audio signal to the circuit is filtered by capacitor C1, which is then rectified by diodes D1 and D2. This signal is then amplified by the Q1 transistor BD140. The circuit uses 36 LEDs off 25mA; every three LEDs are connected with a separate transistor. Whenever there is any DC signal at transistor Q1, the LEDs turn on.
The operating voltage of the circuit is 12V DC. But it can also be operated with 9V DC or below from it. If you want to operate the circuit with 9V or below then remove one LED from each three that are connected with a separate transistor and leave the two remaining and use 180 Ohms current limiting resistors from R2 to R13.
Applications and uses:
This circuit can be used to display the variation of an audio signal in a group of 12 LEDs. They are used in telephone installation, sound systems, and radio broadcast stations. Consumer audio equipment often features VU meters, both for utility purposes (e.g. in recording equipment) and for aesthetics (in playback devices)
