Beginner
10 min
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Translate the complexity of RMS into a clear, constant DC voltage with AD8436 and STM32L073RZ

Turning RMS complexity into DC simplicity – that's our converter promise!

RMS to DC 2 Click with Fusion for STM32 v8

Published Nov 14, 2023

Click board™

RMS to DC 2 Click

Development board

Fusion for STM32 v8

Compiler

NECTO Studio

MCU

STM32L073RZ

With a focus on simplicity and accuracy, our RMS-to-DC converter is the key to translating RMS input signals into a DC voltage, ensuring your measurements are both reliable and easy to interpret.

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Hardware Overview

How does it work?

RMS to DC 2 Click is based on the AD8436, a low-cost, low-power, true RMS-to-DC converter from Analog Devices. It computes a precise DC equivalent of the RMS value of AC waveforms, including complex patterns such as those generated by switch mode power supplies and triacs. The accuracy conversions crest factor spans between 1 and 10. On-board buffer amplifiers enable the widest range of options, while the built-in high-impedance FET buffer provides an interface for external attenuators, frequency compensation, or driving low-impedance loads. A matched pair of internal resistors enables an easily configurable gain of two or more, extending the usable input range even lower. The RMS or Root

Mean Square describes the input signal's power: the current's RMS value equals a DC current value that would produce the same heat dissipation on the resistive load. Therefore, it is often important to know the RMS value of the signal. RMS to DC 2 Click allows measuring of the RMS value of a periodically repetitive signal. The output values of the AD8436 can be read over the analog-to-digital converter of the host MCU or over the MCP3221, a low-power 12-bit ADC from Microchip. The selection can be made over the ADC SEL jumper, where the MCP3221 is set by default. There are two terminals on RMS to DC 2 Click. The VEXT supplies the RMS core of the AD8436 with a voltage of 4.8 to 36V, while the INPUT is the AC signal input

terminal. RMS to DC 2 Click can use the analog AN pin of the mikroBUS™ socket or the I2C interface of the MCP3221 to communicate with the host MCU and read the RMS value. The default choice is the MCP3221, with its standard and fast modes of the I2C interface supporting frequencies of up to 400kHz. 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. Also, this 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.

RMS to DC 2 Click hardware overview image

Features overview

Development board

Fusion for STM32 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 32-bit ARM® Cortex®-M based MCUs from STMicroelectronics, 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, Fusion for STM32 v8 provides a fluid and immersive working experience, allowing

access anywhere and under any circumstances at any time. Each part of the Fusion for STM32 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. Fusion for STM32 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.

Fusion for STM32 v8 horizontal image

Microcontroller Overview

MCU Card / MCU

default

Type

8th Generation

Architecture

ARM Cortex-M0

MCU Memory (KB)

192

Silicon Vendor

STMicroelectronics

Pin count

64

RAM (Bytes)

20480

Used MCU Pins

mikroBUS™ mapper

Analog Output
PA0
AN
NC
NC
RST
NC
NC
CS
NC
NC
SCK
NC
NC
MISO
NC
NC
MOSI
Power Supply
3.3V
3.3V
Ground
GND
GND
NC
NC
PWM
NC
NC
INT
NC
NC
TX
NC
NC
RX
I2C Clock
PB6
SCL
I2C Data
PB7
SDA
Power Supply
5V
5V
Ground
GND
GND
1

Take a closer look

Schematic

RMS to DC 2 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 Fusion for STM32 v8 as your development board.

Fusion for PIC v8 front image hardware assembly
GNSS2 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
v8 SiBRAIN Access 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 RMS to DC 2 Click driver.

Key functions:

  • rmstodc2_set_vref - This function sets the voltage reference for RMS to DC 2 click driver.

  • rmstodc2_read_voltage - This function reads raw ADC value and converts it to proportional voltage level.

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 RMS to DC 2 Click Example.
 *
 * # Description
 * This example demonstrates the use of the RMS to DC 2 click board by measuring
 * the RMS voltage of the input signal.
 *
 * The demo application is composed of two sections :
 *
 * ## Application Init
 * Initializes the driver and logger.
 *
 * ## Application Task
 * Reads the RMS voltage of the input signal and displays the results on the USB UART
 * approximately once per second.
 *
 * @author Stefan Filipovic
 *
 */

#include "board.h"
#include "log.h"
#include "rmstodc2.h"

static rmstodc2_t rmstodc2;   /**< RMS to DC 2 Click driver object. */
static log_t logger;    /**< Logger object. */

void application_init ( void )
{
    log_cfg_t log_cfg;  /**< Logger config object. */
    rmstodc2_cfg_t rmstodc2_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.
    rmstodc2_cfg_setup( &rmstodc2_cfg );
    RMSTODC2_MAP_MIKROBUS( rmstodc2_cfg, MIKROBUS_1 );
    err_t init_flag = rmstodc2_init( &rmstodc2, &rmstodc2_cfg );
    if ( ( ADC_ERROR == init_flag ) || ( I2C_MASTER_ERROR == init_flag ) )
    {
        log_error( &logger, " Communication init." );
        for ( ; ; );
    }
    
    log_info( &logger, " Application Task " );
}

void application_task ( void ) 
{
    float voltage = 0;
    if ( RMSTODC2_OK == rmstodc2_read_voltage ( &rmstodc2, &voltage ) ) 
    {
        log_printf( &logger, " RMS voltage : %.3f[V]\r\n\n", voltage * RMSTODC2_RMS_VOLTAGE_COEF );
        Delay_ms( 1000 );
    }
}

void main ( void ) 
{
    application_init( );

    for ( ; ; ) 
    {
        application_task( );
    }
}

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

Additional Support

Resources