Regarding Projector Programming using QT

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.

Prath

Sorry for the delay guys. I tried again with the code and couldn't retrieve anything from the serial port regarding the errror.
I got the attached error:-

SGaist

Your MainWindow class does not have such a signal, it's one from the QSerialPort.

Prath

Didnt get you @SGaist .
Could you please help me with the syntax

Prath

When I click on the push button the function on_pushButton_clicked is called and then I call the Qserialport to check the error. I think the code is written correctly.

What's your take?

jsulm

@Prath said in Regarding Projector Programming using QT:

What's your take?

Your connect is wrong: MainWindow does NOT have signal error(QSerialPort::QSerialPort), this signal is in QSerialPort, so not in "this" but in "serial".

And please do not post screen-shots, copy paste your code...

JonB

@jsulm , @Prath

this signal is in QSerialPort, so not in "this" but in "serial".

Is this a case where changing to new-style signal/slot syntax would generate an error for the wrong "context" variable? Or, would testing the return result from the connect() or from https://doc.qt.io/qt-5/qmetaobject-connection.html#operator-bool in code tell the user if the connection has failed because of the wrong context?