QML : Read data from Serial Port

[RiyG22]

I am working over QT quick kiosk based GUI application and communicating with Arduino to send and receive data over serial port. I've successfully sent and received the data between Arduino and QT Single QML file.

Issue : I've two QML files: main.qml and sample.qml, Sending the data on button press from main.qml and receiving some string data on sample.qml. I am successfully sending the data from main.qml and but not able to read the data from sample.qml. I realized the issue is because of re-initializing serial port in sample.qml file.

If anyone can help me out with this problem, It would be greatly appreciated.Thanks in advance.

Serialport.cpp

#include "serialport.h"
#include <QSerialPort>
#include <QSerialPortInfo>
#include <QDebug>

SerialPort::SerialPort(QObject *parent):QObject(parent)
{

    arduino = new QSerialPort(this);
    connect(arduino, &QSerialPort::readyRead, this, &SerialPort::onReadData);
    openDefault();
}

SerialPort::~SerialPort()
{
    delete arduino;
}

void SerialPort::set_oil_pressure_volt(double newValue)
{
    if (mOil_pressure_volt == newValue)
        return;

    mOil_pressure_volt = newValue;
    emit oil_pressure_volt_Changed(mOil_pressure_volt);
}

void SerialPort::onReadData()
{
    if(arduino->bytesAvailable()>0){

        QByteArray data = arduino->readAll();
        qDebug()<<QString(data).trimmed();
        QString value = QString(data).trimmed();
        bool ok;
        double val = value.toDouble(&ok);
        if(ok)
            set_oil_pressure_volt(val);
    }
}

void SerialPort::onWriteData(const QByteArray &data)
{
    arduino->write(data);
    qDebug() << data;
}


void SerialPort::openDefault()
{
    for(auto info: QSerialPortInfo::availablePorts()){
        qDebug()<<info.portName()<<info.description()<<info.manufacturer();
        if(!info.isBusy() && (info.description().contains("USB Serial Devic") || info.manufacturer().contains("Microsoft"))){
            portInfo = info;
            break;
        }
    }

    if(portInfo.isNull()){
        return;
    }

    arduino->setPortName(portInfo.portName());
    arduino->setBaudRate(QSerialPort::Baud9600);
    arduino->setDataBits(QSerialPort::Data8);
    arduino->setParity(QSerialPort::NoParity);
    arduino->setStopBits(QSerialPort::OneStop);
    arduino->setFlowControl(QSerialPort::NoFlowControl);

    if(arduino->open(QSerialPort::ReadWrite))
        qDebug()<<"Connected to "<< portInfo.manufacturer()<< " on " << portInfo.portName();
    else
        qCritical()<<"Serial Port error: " << arduino->errorString();

}

double SerialPort::get_oil_pressure_volt() const
{
    return mOil_pressure_volt;
}

Serialport.h

#ifndef SERIALPORT_H
#define SERIALPORT_H

#include <QObject>
#include <QSerialPort>
#include <QSerialPortInfo>

class SerialPort : public QObject
{
    Q_OBJECT
    Q_PROPERTY(double oil_pressure_volt READ get_oil_pressure_volt WRITE set_oil_pressure_volt NOTIFY oil_pressure_volt_Changed )

public:
    SerialPort(QObject *parent = 0);
    ~SerialPort();

    double get_oil_pressure_volt() const;
    void set_oil_pressure_volt(double newValue);

public slots:
    void onReadData();
    void onWriteData(const QByteArray &data = QByteArray("r255"));


signals:
    void oil_pressure_volt_Changed(double newValue);

private:
    QSerialPort *arduino;
    static const quint16 arduino_uno_vendor_id = 9025;
    static const quint16 arduino_uno_product_id = 67;

    double mOil_pressure_volt;

    QSerialPortInfo portInfo;

    void openDefault();
};

#endif // SERIALPORT_H

main.qml code snippet:

import QtQuick 2.13
import QtQuick.Window 2.13
import QtQuick.Controls 2.13
import QtMultimedia 5.12

import SerialPortLib 1.0

Window {
    readonly property int appWidth: 1366
    readonly property int appHeight: 768

    id: root
    visible: true
    width: appWidth
    height: appHeight
    title: qsTr("V 2.0")

    SerialPort{
        id: serial
    }
SwipeView{
        id: mainSwipeView
        currentIndex: 1
        anchors.fill: parent
        orientation: Qt.Vertical
        interactive: false
        Page{
            width: appWidth
            height: appHeight
            FlowButton {
                id: flowButton
                x: 760
                y: 76
                width: 373
                height: 717
                imageSrc: "images/A.png"
                area.onClicked: {
                    serial.onWriteData("H")
                }
            }
         }
       }     

Sample.qml

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12
import SerialPortLib 1.0

Item {
    width: 1366
    height: 768 - 80
   // title: qsTr("Test")

    SerialPort{
        id: abc
       onOil_pressure_voltChanged: {
            console.log("122")
            topBar.timerValue = 20
            topBar.timer.start()
            tx.text = "%1".arg(oil_pressure_volt);
        }
    }

    Text {
        id: tx
        anchors.fill: parent
        font.family: "Helvetica"
        font.pointSize: 20
        verticalAlignment: Text.AlignVCenter
        horizontalAlignment: Text.AlignHCenter
    }
}

[SGaist]

Hi,

That's because you instantiate two objects of SerialPort class.

One alternative is to create the instance in your main function and set it as a context property.

[RiyG22]

Hi @SGaist, Thanks for your kind support. Can you share some example for this. I am new to qt ad learning it.

[SGaist]

Please take a look at the documentation.

[RiyG22]

@SGaist Really thank you for pointing me in the right direction. The problem solved with setting context property!