30 min

Displays the intensity of an audio signal using LM3914 and TM4C1299KCZAD

Volume Unit Meter

VU Meter Click with UNI-DS v8

Published Mar 12, 2023

Click board™

VU Meter Click

Development board



NECTO Studio



Lighten the bar graph display according to the sound quality



Hardware Overview

How does it work?

VU Meter Click is based on the LM3914, a monolithic integrated circuit that senses analog voltage levels and drives a 10-segment bar graph display from Texas Instruments. This solution is a compact volume unit meter. This analog-controlled driver means it can control display by an analog input voltage and eliminates the need for additional programming. A volume unit meter represents a device that displays the intensity of an audio signal; more specifically, it is used to visualize analog signals. That's why VU Meter Click is suitable as a volume measurement gadget. The LM3914 is configured to work in bar mode, where all parts of the bar graph display below a certain point turn on. This board is manufactured with an onboard sound-detecting device (microphone), the MC33072 Op-Amp, and the LM3914, which gleams the bar graph display according to the sound's quality.

Initially, the microphone captures and transforms the sound into linear voltages to sound amplitude. The capacitor then stops the DC component of the transmission, allowing the AC input from the microphone to enter the MC33072 Op-Amp. One part of the MC33072 represents a variable gain inverting amplifier using the TPL0501, an SPI-configurable digital potentiometer from Texas Instruments, while the second part represents a signal buffer. After filtration and amplification, these filtered and amplified signals are finally provided to LM3914. Considering that this driver is analog controlled, this Click board™ also provides the ability to monitor the analog signal by the MCU via the AN pin of the mikroBUS™ socket. The LM3914 operates in a voltmeter format and lights the XGURUGX10D, a ten-segment bar graph array, according to the strength of the given signal.

The onboard bar graph display segments are bright and uniformly colored, providing pleasant and clean visual feedback. Each segment is composed of green and red-colored LEDs, making it possible to have various essential states marked in a different colors. It can use green, red, and a combination of these two, resulting in amber-colored segments. This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. However, the Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used, as a reference, for further development.

VU Meter Click top side image
VU Meter Click lateral side image
VU Meter Click bottom side image

Features overview

Development board

UNI-DS v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different STM32, Kinetis, TIVA, CEC, MSP, PIC, dsPIC, PIC32, and AVR MCUs regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, UNI-DS v8 provides a fluid and immersive working experience, allowing access anywhere and under any

circumstances at any time. Each part of the UNI-DS v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector. Communication options such as USB-UART, USB

HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. UNI-DS v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

UNI-DS v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M4

MCU Memory (KB)


Silicon Vendor

Texas Instruments

Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Analog Signal
SPI Chip Select
SPI Clock
Power Supply
Power Supply

Take a closer look


VU Meter Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the UNI-DS v8 as your development board.

Fusion for PIC v8 front image hardware assembly
Buck 22 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
v8 SiBRAIN MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
NECTO Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for VU Meter Click driver.

Key functions:

  • vumeter_read_an_pin_voltageThis function reads the results of the AD conversion of the AN pin and converts them to a proportional voltage level.

  • vumeter_set_gain_level This function sets the input signal gain level (the microphone sensitivity).

  • vumeter_calculate_vu_level This function calculates the VU level from the analog voltage input.

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * @file main.c
 * @brief VUMeter Click example
 * # Description
 * This example demonstrates the use of VU Meter click board.
 * The demo application is composed of two sections :
 * ## Application Init
 * Initializes the driver and sets the gain level (the microphone sensitivity) to maximum.
 * ## Application Task
 * Calculates VU level from the analog voltage read from AN pin, and displays the results
 * on the USB UART approximately every 100ms.
 * @author Stefan Filipovic

#include "board.h"
#include "log.h"
#include "vumeter.h"

static vumeter_t vumeter;
static log_t logger;

void application_init ( void )
    log_cfg_t log_cfg;          /**< Logger config object. */
    vumeter_cfg_t vumeter_cfg;  /**< Click config object. */

     * Logger initialization.
     * Default baud rate: 115200
     * Default log level: LOG_LEVEL_DEBUG
     * @note If USB_UART_RX and USB_UART_TX 
     * are defined as HAL_PIN_NC, you will 
     * need to define them manually for log to work. 
     * See @b LOG_MAP_USB_UART macro definition for detailed explanation.
    LOG_MAP_USB_UART( log_cfg );
    log_init( &logger, &log_cfg );
    log_info( &logger, " Application Init " );

    // Click initialization.

    vumeter_cfg_setup( &vumeter_cfg );
    VUMETER_MAP_MIKROBUS( vumeter_cfg, MIKROBUS_1 );
    err_t init_flag  = vumeter_init( &vumeter, &vumeter_cfg );
    if ( SPI_MASTER_ERROR == init_flag )
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... " );

        for ( ; ; );
    vumeter_set_gain_level ( &vumeter, VUMETER_GAIN_LEVEL_MAX );
    log_info( &logger, " Application Task " );

void application_task ( void )
    log_printf( &logger, " VU level: %.3f VU\r\n", vumeter_calculate_vu_level ( &vumeter, 100 ) );

void main ( void )
    application_init( );

    for ( ; ; )
        application_task( );

// ------------------------------------------------------------------------ END

Additional Support