Cannot output a value using QSerialPort

[mrjj]

Hi
Why not try the same
https://doc.qt.io/qt-5/qtserialport-terminal-example.html
as @Pablo-J-Rogina linked to ?
Its a littel serial comm GUI that can easy open a serial port and
read and write to it.
Very good for testing out if the Arduino responds as expected.

[A Former User]

@mrjj @Pablo-J-Rogina I ran both examples and since this is my first Qt project I'm not exactly sure what I'm looking for. I have attached my results.

I know that my Arduino works already because I have tested it in the Arduino IDE as well as when I am debugging my code. I already know that everything works, my issue is just being able to display it. That second example is similar to what I want to do expect having my own GUI. Many thanks for all the responses thus far!

[mrjj]

Hi
Ok super. so it works.
You are not showing complete code so hard to guess.
QSerialPort::connect(arduino, &QSerialPort::readyRead, this, &Dialog::readSerial);
This looks fine

So in
Dialog::readSerial

you call updateVoltage( yourbuffer )

Or when is that called ?

Im not sure where "too few arguments to function call, expected 1, have 0" comes
but it sounds like you called updateVoltage without its qstring.

[Pablo J. Rogina]

@jude-bato said in Cannot output a value using QSerialPort:

I'm not exactly sure what I'm looking for

If guessing, to write a Qt app that can connect to your Arduino device and display information sent from it via the serial port.

So your next steps would be to use the Simple Terminal example as a reference to check what you need to do in order to open the port, check for errors, how to connect signal and slots, etc.

[A Former User]

@mrjj This is the full code:

#include "dialog.h"
#include "ui_dialog.h"
#include <iostream>
#include <QSerialPort>
#include <QSerialPortInfo>
#include <string>
#include <QDebug>
#include <QMessageBox>

Dialog::Dialog(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Dialog)
{
    ui->setupUi(this);
    ui->voltagelcdNumber->display("0.00");
    arduino = new QSerialPort(this);
    serialBuffer = "";
    parsed_data = "";
    voltage_value = 0.0;

    bool arduino_is_available = false;
    QString arduino_uno_port_name;
    foreach(const QSerialPortInfo &serialPortInfo, QSerialPortInfo::availablePorts()){
        if(serialPortInfo.hasProductIdentifier() && serialPortInfo.hasVendorIdentifier()){
            if((serialPortInfo.productIdentifier() == arduino_uno_product_id) && (serialPortInfo.vendorIdentifier() == arduino_uno_vendor_id)){
                arduino_is_available = true;
                arduino_uno_port_name = serialPortInfo.portName();
            }
        }
    }

    if(arduino_is_available)
    {
        qDebug()<<"Found the port \n";
        arduino->setPortName(arduino_uno_port_name);
        arduino->open(QSerialPort::ReadOnly);
        arduino->setBaudRate(QSerialPort::Baud9600);
        arduino->setDataBits(QSerialPort::Data8);
        arduino->setFlowControl(QSerialPort::NoFlowControl);
        arduino->setParity(QSerialPort::NoParity);
        arduino->setStopBits(QSerialPort::OneStop);
        QSerialPort::connect(arduino, &QSerialPort::readyRead, this, &Dialog::readSerial);
        //ui->voltagelcdNumber->display(sensor_reading); Here is where I'm haveing trouble
    } else {
        qDebug()<<"Could not find the correct port \n";
        QMessageBox::information(this,"Serial Port Error", "Could not open the serial port");
    }
}

Dialog::~Dialog()
{
    if(arduino->isOpen())
    {
        arduino->close();
    }
    delete ui;
}

void Dialog::readSerial()
{
    QStringList buffer_split = serialBuffer.split(",");
    if(buffer_split.length() < 3)
    {
        serialData = arduino->readAll();
        serialBuffer = serialBuffer + QString::fromStdString(serialData.toStdString());
        serialData.clear();
    } else {
        serialBuffer = "";
        qDebug() << buffer_split << "\n";
        parsed_data = buffer_split[1];
        voltage_value = (parsed_data.toDouble()) - 0.1;
        qDebug() << "Voltage: " << voltage_value << "\n";
        parsed_data = QString::number(voltage_value,'g',4);
        Dialog::updateVoltage(parsed_data);
    }
}

void Dialog::updateVoltage(QString sensor_reading)
{
    ui->voltagelcdNumber->display(sensor_reading);
}

sensor_reading is private and initialized in QString

@Pablo-J-Rogina I have tested it in the simple terminal and it works, as well as working in the Arduino IDE

[mrjj]

Hi

Some notes

You call setBaudRate, setDataBits etc AFTER you open port. that is wrong.
must be before open!
All of them. Open goes last. Actually you can :)

You do not check if
arduino->open(QSerialPort::ReadOnly);
fails.
like
if ( ! arduino->open(QSerialPort::ReadOnly) ) {
QMessageBox::information(this,...report error);
return;
}
see @jsulm post !

So does it ever enter into void Dialog::readSerial() ?

[Christian Ehrlicher]

@mrjj said in Cannot output a value using QSerialPort:

You call setBaudRate, setDataBits etc AFTER you open port. that is wrong.

I already said this some days ago: https://forum.qt.io/topic/112346/cannot-output-a-value-using-qserialport/23 but it is simply ignored...

[mrjj]

@Christian-Ehrlicher
Indeed and also @jsulm also noted to check open which seems to be forgotten also.

[kuzulis]

@mrjj said in Cannot output a value using QSerialPort:

You call setBaudRate, setDataBits etc AFTER you open port. that is wrong.
must be before open!

This is not true. You can configure QSP in any time.

[mrjj]

@kuzulis
Ok
thank you for clarifying that.
Over the years I have not had huge success with that without close and reopen the port but its
good to know QSerialPort does support it :)

[Pablo J. Rogina]

@kuzulis said in Cannot output a value using QSerialPort:

This is not true. You can configure QSP in any time.

Are you saying that you can change the settings once a connection has been established?

[mrjj]

@Pablo-J-Rogina

Yes seems so and he should know as he wrote it :)

[kuzulis]

@Pablo-J-Rogina said in Cannot output a value using QSerialPort:

Are you saying that you can change the settings once a connection has been established?

Of course, after open() you can do what you need.

[Pablo J. Rogina]

@kuzulis but changing the settings once you open the port, does impact on the ongoing connection?
I mean, does the other side need to update the settings as well? And if so, won't the connection be interrupted?

[kuzulis]

@Pablo-J-Rogina said in Cannot output a value using QSerialPort:

@kuzulis but changing the settings once you open the port, does impact on the ongoing connection?
I mean, does the other side need to update the settings as well? And if so, won't the connection be interrupted?

The serial communication has no "connection" things. About what "connection" do you speak?

PS: In reality (on a low level), any device configurations always changes after a device has been opened! This belongs to any device.

[Pablo J. Rogina]

@kuzulis said in Cannot output a value using QSerialPort:

About what "connection" do you speak?

An ongoing transmission

[kuzulis]

@Pablo-J-Rogina said in Cannot output a value using QSerialPort:

An ongoing transmission

In this case an ongoing data stream just will be transferred with a new parameters (speed, parity ant etc).