What is a VU Meter?
A VU meter is an electronic measuring instrument that measures the level of sound intensity for audio equipment. It shows the average moment to moment signal strength from a piece of audio equipment such as an amplifier or a microphone. It is used in several sound recording and reproduction systems, where some method is required for determining audio signal levels in order to avoid discrepancies such as sound overloading, noise, and signal distortion. So, in today’s tutorial, we are going to go over a step by step process on how to make a VU Meter using LM3914 Dot/Bar Driver IC.
LM3915 LED Driver IC
LM3915 is an analog controlled LED driver IC. It eliminates the need for programming a microcontroller and also reduces the hardware required to drive the 10 LEDs. The input voltage for LM3915 can vary from 3V to 18V. The IC has two operating modes DOT mode and BAR mode, also more than one IC can be cascaded to control up to 100 LEDs. Since the LEDs can be controlled without any flickering and perform flawlessly with equal brightness these IC’s are commonly used in visual alarms and other metering or monitoring applications.
Hardware Component
You will need the following parts to build this proejct
| S.No | Component | Value | Qty |
|---|---|---|---|
| 1) | LED Driver IC | LM3915 | 1 |
| 2) | Electret Mic | 5mm | 1 |
| 3) | Potentiometer | 10K | 1 |
| 4) | Resistors | 1K | 2 |
| 5) | LEDs | 5mm, 3.5V | 10 |
| 6) | Capacitor | 1uF | 1 |
| 7) | Toggle Switch | – | 1 |
| 8) | Veroboard | – | 1 |
| 9) | Soldering Iron | 45W – 65W | 1 |
| 10) | Soldering Wire with Flux | – | 1 |
| 11) | DC Battery | 9V | 1 |
| 12) | Battery Clips | – | 1 |
| 13) | Jumper Wires | – | As per need |
LM3915 Pinout
Electret Mic
Useful Steps
1) Solder the +ve terminal of the electret mic with a 1K resistor.
2) After that, solder the -ve terminal of the 1uF capacitor with the electret mic. after that solder the +ve terminal of the capacitor with SIGNAL pin 5 of the IC.
3) Connect a 1K resistor with pin 6 & 7 of the IC. After that solder the fixed ends of the 10K pot between 1K resistor and pin 2 of the IC. Also solder the variable end of the 10K pot with pin 2 of the IC.
4) After that, solder the 10 LEDs with pin 1, 18, 17, 16, 15, 14, 13, 12, and pin 11 of the LM3915 IC.
5) Solder a toggle switch between MODE pin 9 of the IC & GND of the circuit.
6) Power up & test the circuit using a 9V Battery.
Circuit Diagram For VU Meter
Working Explanation
The operation of this circuit is as follows. Any audio playing near the VU meter is received by the electret mic. Here, we are using a 4.7uF coupling capacitor. This capacitor blocks the DC component of the signal allowing only AC to pass through.
The capacitor output then goes to pin 5 (SIGNAL) of the LM3915 comparator. The IC triggers the LEDs to glow in contrast with the strength of the input signal. The reference voltage at Pin 7 is set by a resistor (1K). You can use the 10K pot to tune the sensitivity of the comparator output. The IC output can be taken in two different modes, dot, and bar mode. In Dot mode, the MODE pin (pin 9) is open by using a toggle switch, in this mode, only one LED will turn on depending on the input voltage. In Bar mode, the mode pin (pin 9) connects to the V+ pin and the LED will turn on or turn off sequentially based on the input voltage.
Applications
- Used in music production & Recording, as a Control/ Testing tool.
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