How to make Audio Level Indicator – VU meter using LM3914 IC

An Audio Level Indicator (VU meter) or volume unit meter, are electronic devices that display the intensity of any Input audio signal, usually in musical pieces of equipment (Drum sets, mic, electric guitars, amps, speakers, etc.).  More specifically, it helps to visualize analog signals. So, In this project, we are going to design a simple Audio Level Indicator (VU meter) using the LM3914N dot/bar display driver IC.

LM3914 is an analog-controlled LED driver IC, meaning it can control (turn on or off) 10 LEDs by an analog input voltage. This IC eliminates the need for programming a microcontroller and also reduces the hardware required to control 10 LEDs. For LM3914, the input voltage 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 ICs are commonly used in visual alarms and other metering or monitoring applications.

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5$ PCB Prototype

https://youtu.be/S6vLgSmX3gM

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Hardware Components

The following components are required to make Audio Level Indicator Circuit

S.No	Component	Value	Qty
1.	IC	LM3914	1
2.	LED	–	10
3.	Mic	–	1
4.	Audio jack port (Male)	3.5mm	1
5.	Potentiometer	470K	1
6.	Resistors	1.2K	1
7.	DC Power Supply	12V	1
8.	Connecting Wires	–	1

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LM3914 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of LM3914

Steps

1) Solder IC Base

2) Solder All LEDs

3) Solder Potentiometer & 1.2K Resistor

4) Solder Electret Mic

5) Cut the Signal Wire of the audio cable

6) Solder Audio Cable in Parallel to Mic

7) Solder Power Connector

8) Let’s Powerup the Circuit

Audio Level Indicator Circuit

Working Explanation

The heart of the circuit is an LM3914N-1 LED driver IC. Firstly, the analog input is coming from P1 Audio Input (Mic/Smartphone). The AC input from the Audio IN enters the SIGNAL pin of the IC. These signals go through the LM3914 integrated comparator. The LM3914 comparator glows the LEDs according to the strength of the given signal. The reference voltage at Pin 7 is set by a resistor (1.2K).

The IC can operate in two different modes, one is the dot mode and the other is 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

• It can be reverse-engineered to work as a power level indicator for various energy-storing devices such as batteries and dry cells.
• Also seen in music production & Recording, as a Control/ Testing tool.