Regarding Projector Programming using QT

[Prath]

I am writing a code in QT to send the command to the projector to switch it on-off. I tried to send the command but the serial port didn't respond to the command. Following is the basic code written.
Can anyone help me to decipher what is wrong?

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QDebug>
#include<QSerialPort>
#include<string>
using namespace std;
QSerialPort *serial;

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
SetupPort();

}

MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::SetupPort()
{
serial = new QSerialPort(this);
serial->setPortName("COM3");
serial->setBaudRate(QSerialPort::Baud115200,QSerialPort::AllDirections);
serial->setDataBits(QSerialPort::Data8);
serial->setFlowControl(QSerialPort::NoFlowControl);
serial->setStopBits(QSerialPort::OneStop);
serial->setParity(QSerialPort::NoParity);

if(!serial->open(QIODevice::ReadWrite))
{
    qDebug()<<"error: can't open com port";
}

for(int i=1;i<100;i++)

{ //serial->write("57542b4c4544453d31");
serial->write("WT+LEDE=1");
QByteArray data = serial->readAll();

qDebug() << data;

}
}

[Prath]

This post is deleted!

[JonB]

@Prath
Assuming your command works, you cannot expect the readAll() immediately after the write() to read the response. It will only read whatever happens to be available when it is called. You really need a signal/slot here. So you keep sending that command, I don't know if that matters.

[Pablo J. Rogina]

@Prath said in Regarding Projector Programming using QT:

what is wrong?

Not using signal & slots, as @JonB suggested already.
Have you taken a look at Serial Terminal example?

[Prath]

I have used the Qserial port program from Git. The program can connect to the serial port. However, I still could not switch off the projector using the command "WT+LEDE=0".
Any help in this regards? Our entire project is stuck because of this command being not sent to the projector.

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** Copyright (C) 2012 Laszlo Papp lpapp@kde.org
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#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "console.h"
#include "settingsdialog.h"

#include <QMessageBox>
#include <QtSerialPort/QSerialPort>
#include <QDebug>
#include <QLabel>
#include <QPixmap>
#include <QFile>
#include <QTextStream>

//! [0]
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
//! [0]
ui->setupUi(this);
console = new Console;
console->setEnabled(false);
setCentralWidget(console);
//! [1]
serial = new QSerialPort(this);
//! [1]
settings = new SettingsDialog;

ui->actionConnect->setEnabled(true);
ui->actionDisconnect->setEnabled(false);
ui->actionQuit->setEnabled(true);
ui->actionConfigure->setEnabled(true);

initActionsConnections();

connect(serial, SIGNAL(error(QSerialPort::SerialPortError)), this,
        SLOT(handleError(QSerialPort::SerialPortError)));

//! [2]
connect(serial, SIGNAL(readyRead()), this, SLOT(readData()));
//! [2]
connect(console, SIGNAL(getData(QByteArray)), this, SLOT(writeData(QByteArray)));
//! [3]
}
//! [3]

MainWindow::~MainWindow()
{
delete settings;
delete ui;
}

//! [4]
void MainWindow::openSerialPort()
{
SettingsDialog::Settings p = settings->settings();
serial->setPortName(p.name);
if (serial->open(QIODevice::ReadWrite)) {
if (serial->setBaudRate(p.baudRate)
&& serial->setDataBits(p.dataBits)
&& serial->setParity(p.parity)
&& serial->setStopBits(p.stopBits)
&& serial->setFlowControl(p.flowControl)) {

        console->setEnabled(true);
        console->setLocalEchoEnabled(p.localEchoEnabled);
        ui->actionConnect->setEnabled(false);
        ui->actionDisconnect->setEnabled(true);
        ui->actionConfigure->setEnabled(false);
        ui->statusBar->showMessage(tr("Connected to %1 : %2, %3, %4, %5, %6")
                                   .arg(p.name).arg(p.stringBaudRate).arg(p.stringDataBits)
                                   .arg(p.stringParity).arg(p.stringStopBits).arg(p.stringFlowControl));

    } else {
        serial->close();
        QMessageBox::critical(this, tr("Error"), serial->errorString());

        ui->statusBar->showMessage(tr("Open error"));
    }
} else {
    QMessageBox::critical(this, tr("Error"), serial->errorString());

    ui->statusBar->showMessage(tr("Configure error"));
}

}
//! [4]

//! [5]
void MainWindow::closeSerialPort()
{
serial->close();
console->setEnabled(false);
ui->actionConnect->setEnabled(true);
ui->actionDisconnect->setEnabled(false);
ui->actionConfigure->setEnabled(true);
ui->statusBar->showMessage(tr("Disconnected"));
}
//! [5]

void MainWindow::about()
{
QMessageBox::about(this, tr("About Simple Terminal"),
tr("The <b>Simple Terminal</b> example demonstrates how to "
"use the Qt Serial Port module in modern GUI applications "
"using Qt, with a menu bar, toolbars, and a status bar."));
}

//! [6]
void MainWindow::writeData(const QByteArray &data)
{
serial->write(data);
}
//! [6]

//! [7]
void MainWindow::readData()
{
QByteArray data = serial->readAll();
console->putData(data);
}
//! [7]

//! [8]
void MainWindow::handleError(QSerialPort::SerialPortError error)
{
if (error == QSerialPort::ResourceError) {
QMessageBox::critical(this, tr("Critical Error"), serial->errorString());
closeSerialPort();
}
}
//! [8]

void MainWindow::initActionsConnections()
{
connect(ui->actionConnect, SIGNAL(triggered()), this, SLOT(openSerialPort()));
connect(ui->actionDisconnect, SIGNAL(triggered()), this, SLOT(closeSerialPort()));
connect(ui->actionQuit, SIGNAL(triggered()), this, SLOT(close()));
connect(ui->actionConfigure, SIGNAL(triggered()), settings, SLOT(show()));
connect(ui->actionClear, SIGNAL(triggered()), console, SLOT(clear()));
connect(ui->actionAbout, SIGNAL(triggered()), this, SLOT(about()));
connect(ui->actionAboutQt, SIGNAL(triggered()), qApp, SLOT(aboutQt()));
}

[JonB]

@Prath said in Regarding Projector Programming using QT:

connect(console, SIGNAL(getData(QByteArray)), this, SLOT(writeData(QByteArray)));

I would at least verify that whatever console getData() is it does return the exact right string to send on to the port. E.g. I don't know if waits till you type a newline or sends characters immediately, and/or whether it sends that newline and that matters.

At this point, how have you been able to verify your command works in principle outside of anything Qt?

[Prath]

We are using a projector application to send command to the projector.

[Prath]

However, I am not able to write anythinh in the window created after running the Qt programme

[SGaist]

Hi,

Write what ?
Write where ?
In what window ?

[Prath]

Hey @SGaist , after running the above programme , a GUI pops out. We have to send a command to the projector using the GUI. However, I couldn't send any commnad as nothing could be written on the GUI window.

[Pablo J. Rogina]

@Prath said in Regarding Projector Programming using QT:

after running the above programme

which program?
The Serial Terminal example I suggested before?

Have you tested managing the projector using any other terminal application? Just to validate it works fine...

[Prath]

Yes. @Pablo-J-Rogina . I am connecting the projector to Quectel QCOM application. Now I want to skip that application and create my customised application to control the projector.

I wrote a programme based on the guidelines of Quectel to switch off the projector. Following is the code. Even I used the QSerialPort code. But the projector couldn't switch off. However using the command prompt of the Quectel QCOM application, I could control the projector.

main.cpp

#include "mainwindow.h"

#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include<QSerialPort>
#include<string>
#include<QtGui>
#include <QMessageBox>

using namespace std;
QSerialPort *serial;
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
}

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

void MainWindow::on_pushButton_clicked()
{
QMessageBox::information(this,"Title here","Hello World");
serial = new QSerialPort(this);
serial->setPortName("COM3");
serial->setBaudRate(QSerialPort::Baud115200,QSerialPort::AllDirections);
serial->setDataBits(QSerialPort::Data8);
serial->setFlowControl(QSerialPort::NoFlowControl);
serial->setStopBits(QSerialPort::OneStop);
serial->setParity(QSerialPort::NoParity);

if(!serial->open(QIODevice::ReadWrite))
{
    qDebug()<<"error: can't open com port";
}

QString command = "WT+LEDE=0\n";
QByteArray x = command.toLocal8Bit();
serial->write(x);

}

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
MainWindow(QWidget *parent = nullptr);
~MainWindow();

private slots:
void on_pushButton_clicked();

private:
Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

#-------------------------------------------------

Project created by QtCreator 2019-11-02T10:55:21

#-------------------------------------------------

QT += core gui serialport

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = GUISerialPort
TEMPLATE = app

SOURCES += main.cpp
mainwindow.cpp

HEADERS += mainwindow.h

FORMS += mainwindow.ui

[jsulm]

@Prath said in Regarding Projector Programming using QT:

if(!serial->open(QIODevice::ReadWrite))

Does open() succeed?

[Prath]

@jsulm Yes. Open succeeded. But still, the projector could not read the commands which I am sending through serial port.

[jsulm]

@Prath You should check what write() returns and connect a slot to https://doc.qt.io/qt-5/qserialport.html#errorOccurred to see whether you get any errors.

[Prath]

@jsulm Could you please help me with the syntax for checking the error. I am completely new in using this.

[jsulm]

@Prath You know how to connect a slot to a signal?
https://doc.qt.io/qt-5/signalsandslots.html

[Prath]

Yeah @jsulm . We have to connect this signal [signal]void QSerialPort::errorOccurred(QSerialPort::SerialPortError error) to the slot right?

Is this correct?
void MainWindow::errorReport(QSerialPort::SerialPortError error)
{
if(error!=0)
qDebug()<<"ERROR:"<<endl<<error; // nothing printed
}

connect(this->Serial,SIGNAL(error(QSerialPort::SerialPortError)),this,SLOT(errorReport(QSerialPort::SerialPortError)));

[jsulm]

@Prath said in Regarding Projector Programming using QT:

Is this correct?

Signal is https://doc.qt.io/qt-5/qserialport.html#errorOccurred not error. Just check the documentation.

[Prath]

I think it is correct @jsulm. We are catching the signal using the slot and then displaying the signal.

[JonB]

@Prath
You wrote

connect(this->Serial,SIGNAL(error(QSerialPort::SerialPortError)),this,SLOT(errorReport(QSerialPort::SerialPortError)));

Where you have SIGNAL(error(QSerialPort::SerialPortError)) @jsulm is expecting SIGNAL(errorOccurred(QSerialPort::SerialPortError)). If what you have works, we do not understand how.

If you are writing new code and would change over to the new signal/slot syntax you would presumably receive a compile-time error.