How to Implement an Environmental Monitoring System on the STM32MP257 Board

This article is excerpted from the outstanding creator - lugl4313820, who integrated the ongoing Thingy:91X cellular IoT prototype development platform testing project with MYIR's MYD-LD25X development board (MYIR's STM35MP257-based development board) to implement a simple environmental monitoring system.

1. Hardware Platform

1) MYIR MYD-LD25X Development Board

2) Thingy:91X

2. Implementation Steps

1) The MYR-LD25X development board integrates an onboard Wi-Fi module, enabling connection to the internet via Wi-Fi.

2) Enable MQTT communication to connect with a private server and subscribe to specified topics for data transmission.

3) Design and develop a user interface (UI) using the Qt framework.

4) Receive data and display it in the user interface.

3. How to design QT

1) Qt Installation

1.1 Please download the online installer for Qt from the following link: 

Index of /qtproject/official_releases/online_installers/

1.2 After downloading, upload the it to the virtual machine and proceed with the installation. There are several aspects to consider during the installation process. For the rest, just follow the official tutorial to complete the installation.

2) Configuring Cross-Compilation Toolchain in Qt Creator

1.1 In the official example, unlike this version, you only need to select gcc to set GCC first, and then g++ is automatically selected below:

1.2 Select the QT version according to the picture below.

1.3 Then you can cross-compile, as shown below.

3) Creating Desktop Program

Based on the introduction in this article, I created a QT-based desktop program with the following UI:

4) Define Label Values

Define the corresponding label values for the labels that need to be displayed based on the received data:

5) Import QT's QtMqtt/QMqttClient library

#include <qtmqtt qmqttclient="">

Note: The officially released firmware does not include a QTMqtt connection file. When executing a program that uses QtMqtt, an error will be reported.

error while loading shared libraries: libQt5Mqtt.so.5: cannot open shared object file: No such file or directory

Therefore, it needs to be copied from the SDK to the development board directory.

6) Checking the Status of the Connection

At the same time, in order to detect the connection status with the MQTT server, a thread needs to be introduced to detect whether it is connected to the server: 

     void run() override

{

         while (true)

         {

             if (m_client)

             {

                 QString statusText = m_client-&gt;state() == QMqttClient::Connected

                                          ? "Connected to server: Success"

                                          : "Connected to server: Failed";

                 emit updateStatus(statusText);

             }

             msleep(1000); // Check once every second

         }

      }

7) Write the following code within the main function:

MainWindow::MainWindow(QWidget *parent)

    : QMainWindow(parent), ui(new Ui::MainWindow), m_client(new QMqttClient(this)) // Initialize the MQTT client instance

{

    ui-&gt;setupUi(this);

    // Set MQTT client parameters

    m_client-&gt;setHostname("hostname");

    m_client-&gt;setPort(1883); // Default MQTT port

    m_client-&gt;setClientId("client_id");

    m_client-&gt;setUsername("usrename");

    m_client-&gt;setPassword("pwd");

     // Connect signal slot to handle successful connection event

      connect(m_client, &amp;QMqttClient::connected, this, [this]()

              {

          // Connection successful, update label text

          ui-&gt;mqtt_client_state-&gt;setText("Connected to server: Success");

          // Subscribe to topic

          m_client-&gt;subscribe(QMqttTopicFilter("devacademy/publish/topic")); });

       // Connect signal slot to handle message reception event

       connect(m_client, &amp;QMqttClient::messageReceived, this, &amp;MainWindow::onMessageReceived);

       // Start MQTT connection

       m_client-&gt;connectToHost();

        // Create and start connection status checking thread

        MqttConnectionChecker *checker = new MqttConnectionChecker(m_client, ui-&gt;mqtt_client_state, this);

        connect(checker, &amp;MqttConnectionChecker::updateStatus, this, [this](const QString &amp;status)

                { ui-&gt;mqtt_client_state-&gt;setText(status); });

       checker-&gt;start();

}

8) The callback function for receiving subscription messages is as follows:

void MainWindow::onMessageReceived(const QByteArray &amp;message, const QMqttTopicName &amp;topic)

{

    Q_UNUSED(topic);

    // Parse JSON data

    QJsonDocument doc = QJsonDocument::fromJson(message);

    if (!doc.isNull() &amp;&amp; doc.isObject())

    {

        QJsonObject obj = doc.object();

        double temp = obj.value("temp").toDouble();

        double press = obj.value("press").toDouble()/100;

        double humidity = obj.value("humidity").toDouble();

        int iaq = obj.value("iaq").toInt();

        double co2 = obj.value("co2").toDouble();

        double voc = obj.value("voc").toDouble();

        //Update these data to the UI

        ui-&gt;label_temp-&gt;setText(QString::number(temp, 'f', 2));

        ui-&gt;label_press-&gt;setText(QString::number(press, 'f', 2));

        ui-&gt;label_humidity-&gt;setText(QString::number(humidity, 'f', 2));

        ui-&gt;label_iaq-&gt;setText(QString::number(iaq, 'f', 2));

        ui-&gt;label_co2-&gt;setText(QString::number(co2, 'f', 2));

        ui-&gt;label_voc-&gt;setText(QString::number(voc, 'f', 2));

        // You can update the parsed data to the UI or other processing logic here

    }

    Else

    {

        qDebug() &lt;&lt; "Invalid JSON message received";

    }

}

9) Experimental Results 

After compiling the program, upload it to the development board and run it; the results are as follows:

The MYIR MYD-LD25X STM32MP257 development board allows for the design of a user interface with Qt, and with MQTT, it is possible to subscribe to particular topics for real-time environmental monitoring. This solution has significant potential within the Internet of Things (IoT) domain!