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Sending a data to Arduino through serial port using Qt

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  • SGaistS SGaist

    Hi,

    You should take a look at the QtSerialPort examples. You'll find there several possible implementations depending on your application needs.

    brotifyB Offline
    brotifyB Offline
    brotify
    wrote on last edited by
    #4

    @SGaist They seems to me rather complicated and poorly explained.

    1 Reply Last reply
    0
    • A Offline
      A Offline
      asanka424
      wrote on last edited by
      #5

      Hi, I would sugget you to read about how Qt event system works. All Qt IODevice derived classes work asynchronously. You need to use QApplication in order to host its object system. After that you need to change your code so that its not blocking io thread of QSerialPort.

      brotifyB 1 Reply Last reply
      0
      • A asanka424

        Hi, I would sugget you to read about how Qt event system works. All Qt IODevice derived classes work asynchronously. You need to use QApplication in order to host its object system. After that you need to change your code so that its not blocking io thread of QSerialPort.

        brotifyB Offline
        brotifyB Offline
        brotify
        wrote on last edited by
        #6

        @asanka424 Thanks I have solved the problem but this time I have another problem. When I connect the arduino with the usb cable my code works perfectly, but I when I use bluetooth module it does not work correctly. To show what the problem is I will share secreenshot of output with usb cable and bluetooth module.
        With USB cable: http://i.hizliresim.com/MpWPPQ.png
        With bluetooth: http://i.hizliresim.com/Va6gAr.png

        As you can see when working with bluetooth it sometimes get the data wrong.
        Why does it happen?

        My code is here:

        #include <QCoreApplication>
        #include <iostream>
        #include <QSerialPort>
        #include <QDebug>
        #include <Windows.h>
        using namespace std;
        QSerialPort serial;
        int main(int argc, char *argv[])
        {
            QCoreApplication a(argc, argv);
            serial.setPortName("COM21");
            serial.open(QIODevice::ReadWrite);
               serial.setBaudRate(QSerialPort::Baud115200);
               serial.setDataBits(QSerialPort::Data8);
               serial.setParity(QSerialPort::NoParity);
               serial.setStopBits(QSerialPort::OneStop);
               serial.setFlowControl(QSerialPort::NoFlowControl);
                while(!serial.isOpen()) serial.open(QIODevice::ReadWrite);
             
               if (serial.isOpen() && serial.isWritable())
               {
               qDebug() << "Serial is open";
        
               QByteArray output;
               QByteArray input;
        
                 while(true)
                 {
                 output = "a";
                 serial.write(output);
                serial.flush();
        
                 serial.waitForBytesWritten(1000);
                 serial.waitForReadyRead(1000);
        
                 input = serial.readAll();
                 qDebug()<<input;
        
                 }
               }
            return a.exec();
        }
        
        
        1 Reply Last reply
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        • SGaistS Offline
          SGaistS Offline
          SGaist
          Lifetime Qt Champion
          wrote on last edited by
          #7

          The data you receive is not wrong it's just that you don't receive it at the same pace with both devices e.g. the underlying buffer are handled differently. But all in all the data is the same.

          Interested in AI ? www.idiap.ch
          Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

          brotifyB 1 Reply Last reply
          0
          • SGaistS SGaist

            The data you receive is not wrong it's just that you don't receive it at the same pace with both devices e.g. the underlying buffer are handled differently. But all in all the data is the same.

            brotifyB Offline
            brotifyB Offline
            brotify
            wrote on last edited by
            #8

            @SGaist How can I modify my code so that I get the same output?

            1 Reply Last reply
            0
            • M Offline
              M Offline
              michelson
              wrote on last edited by
              #9

              IMO 2 options:

              • QSerialPort::readData() - make your program read data of given length
                http://doc.qt.io/qt-5/qserialport.html#readData
              • QSerialPort::bytesAvailable() - check if there is expected number of bytes available
                http://doc.qt.io/qt-5/qserialport.html#bytesAvailable
              brotifyB 1 Reply Last reply
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              • A Offline
                A Offline
                asanka424
                wrote on last edited by
                #10

                If you know the amount of bytes in a message, don't read it until you have more or same available to read. When you read, only read that number of bytes.

                1 Reply Last reply
                0
                • M michelson

                  IMO 2 options:

                  • QSerialPort::readData() - make your program read data of given length
                    http://doc.qt.io/qt-5/qserialport.html#readData
                  • QSerialPort::bytesAvailable() - check if there is expected number of bytes available
                    http://doc.qt.io/qt-5/qserialport.html#bytesAvailable
                  brotifyB Offline
                  brotifyB Offline
                  brotify
                  wrote on last edited by
                  #11

                  @michelson That works, thanks. I want to share final version of the code

                  #include <QCoreApplication>
                  #include <iostream>
                  #include <QSerialPort>
                  #include <QDebug>
                  #include <Windows.h>
                  #include <QElapsedTimer>
                  using namespace std;
                  QSerialPort serial;
                  QElapsedTimer timer;
                  int main(int argc, char *argv[])
                  {
                      QCoreApplication a(argc, argv);
                      serial.setPortName("COM21");
                      serial.open(QIODevice::ReadWrite);
                         serial.setBaudRate(QSerialPort::Baud115200);
                         serial.setDataBits(QSerialPort::Data8);
                         serial.setParity(QSerialPort::NoParity);
                         serial.setStopBits(QSerialPort::OneStop);
                         serial.setFlowControl(QSerialPort::NoFlowControl);
                          while(!serial.isOpen()) serial.open(QIODevice::ReadWrite);
                  
                         if (serial.isOpen() && serial.isWritable())
                         {
                         qDebug() << "Serial is open";
                  
                         QByteArray output;
                         QByteArray input;
                  
                           while(true)
                           {
                           output = "a";
                           serial.write(output);
                          serial.flush();
                          timer.start();
                         // Sleep(80);
                          qDebug() << timer.elapsed();
                           serial.waitForBytesWritten(100);
                           serial.waitForReadyRead(100);
                          if(serial.bytesAvailable()>=18)
                           input = serial.read(18);
                          qDebug()<<input;
                  
                           }
                         }
                      return a.exec();
                  }
                  
                  
                  sankarapandiyanS 1 Reply Last reply
                  1
                  • SGaistS Offline
                    SGaistS Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on last edited by
                    #12

                    That while on isOpen is just plain wrong. You already opened the serial port and if for any reason if fails to open you'r going to get stuck in that loop.

                    Do the check on the first open and act accordingly.

                    Interested in AI ? www.idiap.ch
                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                    brotifyB 1 Reply Last reply
                    2
                    • SGaistS SGaist

                      That while on isOpen is just plain wrong. You already opened the serial port and if for any reason if fails to open you'r going to get stuck in that loop.

                      Do the check on the first open and act accordingly.

                      brotifyB Offline
                      brotifyB Offline
                      brotify
                      wrote on last edited by
                      #13

                      @SGaist
                      I add this option because sometimes the computer cannot connect to the bluetooth module, therefore if it cannot connect the first time I want my program to try connecting bluetooth module again, but anyway I exluded this option, since I am using GUI in my project.

                      1 Reply Last reply
                      0
                      • SGaistS Offline
                        SGaistS Offline
                        SGaist
                        Lifetime Qt Champion
                        wrote on last edited by
                        #14

                        Then add a "Try Again" button to your GUI. It will be cleaner.

                        Interested in AI ? www.idiap.ch
                        Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                        1 Reply Last reply
                        1
                        • brotifyB brotify

                          @michelson That works, thanks. I want to share final version of the code

                          #include <QCoreApplication>
                          #include <iostream>
                          #include <QSerialPort>
                          #include <QDebug>
                          #include <Windows.h>
                          #include <QElapsedTimer>
                          using namespace std;
                          QSerialPort serial;
                          QElapsedTimer timer;
                          int main(int argc, char *argv[])
                          {
                              QCoreApplication a(argc, argv);
                              serial.setPortName("COM21");
                              serial.open(QIODevice::ReadWrite);
                                 serial.setBaudRate(QSerialPort::Baud115200);
                                 serial.setDataBits(QSerialPort::Data8);
                                 serial.setParity(QSerialPort::NoParity);
                                 serial.setStopBits(QSerialPort::OneStop);
                                 serial.setFlowControl(QSerialPort::NoFlowControl);
                                  while(!serial.isOpen()) serial.open(QIODevice::ReadWrite);
                          
                                 if (serial.isOpen() && serial.isWritable())
                                 {
                                 qDebug() << "Serial is open";
                          
                                 QByteArray output;
                                 QByteArray input;
                          
                                   while(true)
                                   {
                                   output = "a";
                                   serial.write(output);
                                  serial.flush();
                                  timer.start();
                                 // Sleep(80);
                                  qDebug() << timer.elapsed();
                                   serial.waitForBytesWritten(100);
                                   serial.waitForReadyRead(100);
                                  if(serial.bytesAvailable()>=18)
                                   input = serial.read(18);
                                  qDebug()<<input;
                          
                                   }
                                 }
                              return a.exec();
                          }
                          
                          
                          sankarapandiyanS Offline
                          sankarapandiyanS Offline
                          sankarapandiyan
                          wrote on last edited by
                          #15

                          @brotify could you show me the IDE code

                          1 Reply Last reply
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