[PLEASE HELP] how to make a barcode receiver?

[SGaist]

Hi,

It's QSerialPortInfo.

[A Former User]

i dosn't do any thing it always execute "else"
QSerialPort::SerialPortError(DeviceNotFoundError)

[SGaist]

And what is the error ?

[kuzulis]

@raven-worx said in [PLEASE HELP] how to make a barcode receiver?:

thats not true. Of course QtSerialPort works with USB.
USB = Universal Serial Bus

What? QtSerialPort works only with serial ports. It has nothing common with USB... Please don't confuse peoples. ;)

[JKSH]

@davidlabib said in [PLEASE HELP] how to make a barcode receiver?:

QSerialPort::SerialPortError(DeviceNotFoundError)

Well, that means your program can't find a port called COM4. Read the comments in @raven-worx's code and think about what they are asking you to do.

What is the name of the port that your scanner is connected to? https://www.cyberciti.biz/faq/find-out-linux-serial-ports-with-setserial/

@raven-worx said in [PLEASE HELP] how to make a barcode receiver?:

The code above i've posted definitively works with a USB Barcode scanner and i used it myself already.

My apologies; I didn't read the codes or think of the scenario that @mrjj highlighted in his last post.

If the barcode scanner implements RS232-over-USB, then you're right -- Qt Serial Port can indeed work with the scanner via the USB port.

QtSerialPort works with USB.
USB = Universal Serial Bus

Even though they both have "serial" in their names, Universal Serial Bus is completely unrelated to old-school serial ports. The term "serial port" usually refers to an RS-232 port: https://en.wikipedia.org/wiki/Serial_port

A USB device can be programmed to emulate serial port comms, but these are the minority. You cannot, for example, use Qt Serial Port to read your USB keyboard.

[A Former User]

@JKSH i didn't worked
i tried form com 1 to com 18
non of them worked

[JKSH]

@davidlabib said in [PLEASE HELP] how to make a barcode receiver?:

@JKSH i didn't worked
i tried form com 1 to com 18
non of them worked

What is the name of the port that your scanner is connected to? COMX is a Windows name. Linux names are different.

Read https://www.cyberciti.biz/faq/find-out-linux-serial-ports-with-setserial/ to find the name on your Ubuntu machine.

[A Former User]

same error
i tried from ttyS0 to ttyS5 didn't work

[JKSH]

@davidlabib said in [PLEASE HELP] how to make a barcode receiver?:

same error
i tried from ttyS0 to ttyS5 didn't work

You didn't answer my question. What is the name of the port that your scanner is connected to?

Also, what does QSerialPortInfo::availablePorts() give you? http://doc.qt.io/qt-5/qserialportinfo.html#availablePorts

[A Former User]

@JKSH ok i could find the right port and passed from

if( port->open(QSerialPort::ReadOnly) )

now I'm stuck on

if( !port->bytesAvailable() )
                  return;

it always return
witch mean no bytes is available

[JKSH]

@davidlabib said in [PLEASE HELP] how to make a barcode receiver?:

now I'm stuck on

if( !port->bytesAvailable() )
                  return;

it always return
witch mean no bytes is available

Did you choose the correct settings? How is your scanner configured for the following?

• Baud rate
• Parity
• Data bits
• Stop bits
• Flow control

[A Former User]

@JKSH
Baud rate 115200

[aha_1980]

@davidlabib

I guess you don't have permission to use the serial port.

Please type: ls -l /dev/<your-serial-port-name> in a terminal and post the output here.

[A Former User]

@aha_1980 yes i don't have
but i use sudo

[SGaist]

Don't develop as super-user.

The command @aha_1980 will show the user and group affected to the device. Add your own user to that group, then log out and log in again and you will have access to the device.

[aha_1980]

@davidlabib Better add your user to the group dialout and reboot your computer.

Of course sudo works, but may give new problems.

As @JKSH wrote, not only baudrate is important.

I'd suggest to use a terminal program first to verify your scanner works correctly. Then use the same parameters for your code.

[A Former User]

solved PermissionError
now iam stuck in this

   QSerialPort* port = new QSerialPort( this );
   QSerialPortInfo::availablePorts();
   port->setBaudRate( QSerialPort::Baud115200 ); // possible something else, also check the manual
   port->setPort( QSerialPortInfo("ttyACM0") ); // COM port - check Device Manager for connected port
   QSerialPortInfo::availablePorts();
   if( port->open(QSerialPort::ReadOnly) )
   {
       ui->label->setText("port opended sucssefully");
           connect(port, &QSerialPort::readyRead, this, [port]() {
                 if( !port->bytesAvailable() )
                     qDebug() << port->error(); ////////// I'm stuck here it seems that there is no data
                      return;
                 const QByteArray scannedData = port->readAll();
                 // ...
           });
   }
   else
   {
       ui->label->setText("Error");
       qDebug() << port->error();
       QSerialPortInfo::availablePorts();
   }
}

also it will execute this if i clicked a button what if the user didn't click

[jsulm]

@davidlabib said in [PLEASE HELP] how to make a barcode receiver?:

qDebug() << port->error(); ////////// I'm stuck here it seems that there is no data

Do you mean the slot is called but bytesAvailable() returns 0? If so what does

qDebug() << port->error();

print out?

"also it will execute this if i clicked a button what if the user didn't click" - yes, if user does not click the button it will not be executed.

[A Former User]

@jsulm said in [PLEASE HELP] how to make a barcode receiver?:

Do you mean the slot is called but bytesAvailable() returns 0? If so what does

qDebug() << port->error();

print out?

nothing

[jsulm]

@davidlabib Looks like the slot isn't called.
This code is broken:

if( !port->bytesAvailable() )
    qDebug() << port->error(); ////////// I'm stuck here it seems that there is no data
    return;
const QByteArray scannedData = port->readAll();

It shoud be

if( !port->bytesAvailable() ) {
    qDebug() << port->error(); ////////// I'm stuck here it seems that there is no data
    return;
}
const QByteArray scannedData = port->readAll();