Send a signal when a USB serial cable is unplugged

Question

Is there a way to send a signal, or any other way to tell if a USB serial cable is unplugged, using Qt?

László Papp · Accepted Answer · 2013-09-27T20:46:20.287

8

You could use the error signal of the QSerialPort class in the QtSerialPort add-on. See the details for that in our documentation.

http://qt-project.org/doc/qt-5.1/qtserialport/qserialport.html#error-prop

You will need to write this basically:

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

...

void MyClass::handleError(QSerialPort::SerialPortError error)
{
    if (error == QSerialPort::ResourceError) {
        QMessageBox::critical(this, tr("Critical Error"), serial->errorString());
        closeSerialPort();
    }
}

QtSerialPort can be installed easily with Qt 5.1 < as the packages are distributed. However, we have made sure QtSerialPort works with prior versions, including Qt 4.8.X. Here you can find the instructions for Qt 4 to get this installed for you:

git clone git@gitorious.org:qt/qtserialport.git
cd qtserialport
qmake
make
sudo make install.

Then, you will need the following lines in your qmake project file if you happen to use qmake:

Qt 5: QT += serialport
Qt 4: COMFIG += serialport

edited Sep 27 '13 at 20:46

answered Sep 27 '13 at 20:30

László Papp

51,870
39
111
135

1

Finally got together a solution. I actually ended up using `QSerialPortInfo` to validate a port before using it. – Jared Price Sep 30 '13 at 16:40
1

You pointed me in the right direction. I just needed something to validate that the serial port was actually plugged in before it tried to do anything with an open port. I did something slightly different that worked for what I'm doing. – Jared Price Sep 30 '13 at 17:48
What exactly *is* a `ResourceError`? I'm occasionally seeing it in the middle of some serial-port communication, but I'm still able to send and receive some data on the port. (My communications layer starts behaving badly, but it doesn't seem entirely broken--some valid packets still get through.) – Kyle Strand May 27 '16 at 17:57

score 2 · Answer 2 · edited Sep 30 '13 at 17:12

2

Using QSerialPortInfo will achieve the result:

bool MyClass::checkPort()
{
    QSerialPortInfo *portInfo = new QSerialPortInfo(ui->serialDevice->currentText());
    // ui->serialDevice being a combobox of available serial ports

    if (portInfo->isValid())
    {
        return true;
    }
    else
    {
        return false;
    }
}

edited Sep 30 '13 at 17:12

Bleeding Fingers

6,993
7
46
74

answered Sep 30 '13 at 16:44

Jared Price

5,217
7
44
74

score 1 · Answer 3 · answered Feb 01 '16 at 14:40

isValid() is now obsolete. isBusy() can be used instead as it will return true when you have opened the port and false when the port is no longer there (and you still have it open). This is also the case when availablePorts() keeps returning the non-existent, but opened port, because you are keeping the port in the list by having it opened.

Send a signal when a USB serial cable is unplugged

3 Answers3