How to use serial port on Qt 5.5.1

[nistar]

I use Ubuntu 14.04 and Qt 5.5.1.
I want to do a GUI, for write the command to serial port.
Before I did a program of Qt 5.5.0, but now it don't function.

When it run, there is a error "QIODevice::write (QSerialPort): device not open"
I don't know why?
When I use Qt 5.5.0, there isn't error.

//  .pro
QT       += serialport

// controlget.h
#ifndef CONTROLGET_H
#define CONTROLGET_H

#include <QWidget>
#include <QtSerialPort/QSerialPort>
#include <QtSerialPort/QSerialPortInfo>
#include <QDebug>
#include <QString>

namespace Ui {

class controlget;
}

class controlget : public QWidget
{
    Q_OBJECT

public:
    explicit controlget(QWidget *parent = 0);
    ~controlget();

private slots:
    void writeCom();
    void setTarget(unsigned char channelNumber, unsigned short target );

private:
    Ui::controlget *ui;
    unsigned short target;
    unsigned char channelNumber;
    QSerialPort *myCom;
    QByteArray command;
};

#endif // CONTROLGET_H

// controlget.cpp
#include "controlget.h"
#include "ui_controlget.h"
#include "iostream"

controlget::controlget(QWidget *parent) :
    QWidget(parent),
    ui(new Ui::controlget)
{
    ui->setupUi(this);
    ui->slider->setMinimum(1000);
    ui->slider->setMaximum(2000);
    ui->slider->setValue(1500);
    ui->lineEdit->setText("1500");


    myCom= new QSerialPort();
    myCom->setPortName("/dev/ttyACM0");
    myCom->open(QIODevice::WriteOnly);
    myCom->setBaudRate(9600);
    myCom->setDataBits(QSerialPort::Data8);
    myCom->setParity(QSerialPort::NoParity);
    myCom->setStopBits(QSerialPort::OneStop);
    myCom->setFlowControl(QSerialPort::NoFlowControl);


    unsigned short targetInit=6000;
    setTarget(0x01, targetInit);

    targetInit=8000;    // model of Speed(4000) or Position(8000)
    setTarget(0x00, targetInit);

    connect(ui->slider, SIGNAL(valueChanged(int)), this, SLOT(writeCom()));
}

controlget::~controlget()
{
    delete ui;
}

void controlget::writeCom(){
    int pos = ui->slider->value();
    QString str = QString("%1").arg(pos);
    ui->lineEdit->setText(str);
    target=pos*4;

    setTarget(0x01, target );
}

void controlget::setTarget(unsigned char channelNumber, unsigned short target )
{
    if (target<4000){
        target=4000;
    }
    if(target>8000){
        target=8000;
    }

    command.resize(4);
    command[0]=0x84;
    command[1]=channelNumber;
    command[2]=(char)(target & 0x7F);
    command[3]=(char)((target >> 7) & 0x7F);

    myCom->write(command);

    QString string = QString(command.toHex());
    qDebug()<<string;
}

//main.cpp
#include "controlget.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    controlget w;
    w.show();

    return a.exec();
}

[SGaist]

Hi,

Please check that open returns true.

Most likely, you don't have the permissions to access the serial port.

Add yourself to a group that has access to it if it's the case.

[nistar]

@SGaist How to have the the permissions to access the serial port on Ubuntu?

[nistar]

@SGaist

ls -al /dev/ttyACM0

crw-rw---- 1 root dialout 166, 0 ene 6 18:53 /dev/ttyACM0

[SGaist]

Add your user to the dialout group. Don't forget to logout/login before re-running your application.

[SweetOrange]

Because I am doing something similar I have a few beginners questions.
Under public: in class definition there is the constructor explicit controlget(QWidget *parent = 0);
So what does this statement do? You set a pointer to Qwidget equal to 0. What does this mean?
Also under private: in class definition the statement Ui::controlget *ui is a bit unclear to me. Does this set a pointer ui to the class controlget?
In implementation file also is unclear the statement of constructor
controlget::controlget(QWidget *parent) : QWidget(parent), ui(new Ui::controlget)

thanks

[mrjj]

@SweetOrange
--Under public: in class definition there is the constructor explicit controlget(QWidget *parent = 0);
Its the constructor. the QWidget *parent = 0 is a default value. So if you dont give it one , it will
use NULL for parent. Mena have no aprent.

--Ui::controlget *ui is a bit unclear to me.
Its gives access to the objects you put in the UI in the designer.
The Designer creates a UI class that has all these objects and this is
the variable to acces it.

-In implementation file also is unclear the statement of constructor
controlget::controlget(QWidget *parent) << this is our constructor
: QWidget(parent), << here we give the parent variable to our baseClass. (base class is QWidget)
ui(new Ui::controlget) << this NEWs (creates) a UI class for us and assign to -Ui::controlget *ui variable.

thanks