Unable to communicate with arduino using QSerialPort if the arduino-ide has not opened the connection before
arduino, arduino-ide, c++, qt, qtserialport
Solution
I do not know how to set fOutX and fIutX using QT.
Please read my answer is in here.
Also be convinced that the Putty (or your arduino-terminal) configuration (parity, flow control, baud rate) are same as QSerialPort configuration. In addition, you can try the Terminal example (from the QtSerialPort examples), e.g. instead of Putty (or your arduino-terminal).
UPD:
You can try to add:
setDataTerminalReady(true);
and
setRequestToSend(true);
after opening of port.
Problem
I am using the following code to open a serial port to communicate with the arduino. ``` const qint32 baud = Global::getInstance().getSettings().value("Hardware/baudRate", 115200).toInt(); const QString portName = Global::getInstance().getSettings().value("Hardware/port", "COM3").toString(); port.setPortName(portName); if(!port.open(QIODevice::ReadWrite)) { qFatal("Unable to open serial port"); exit(1); } if(!port.setParity(QSerialPort::NoParity) || !port.setStopBits(QSerialPort::OneStop) || !port.setDataBits(QSerialPort::Data8) || !port.setFlowControl(QSerialPort::NoFlowControl ) || !port.setBaudRate(baud)) { qFatal("Unable to configure serial port"); exit(1); } if(port.error() != QSerialPort::NoError) { qFatal("some error occurred!"); exit(1); } ``` Afterwards I try to read from the connection using the following code: ``` bool Light::waitForReady() { char data[1]; data[0] = -1; if(port.waitForReadyRead(10000)) { const int numRead = port.read(&data[0], 1); if(numRead == 1) { return data[0] == (char)RDY; } else { qWarning("Read error, read %d bytes", numRead); } } else { qWarning("Read timeout"); return false; } return false; } ``` The read does not work, it times out after waiting for 10 seconds. However when I open and close the serial monitor inside the arduino-ide before running my QT code it works. My guess is that the ardunio-ide does something to the port that I am missing but as far as I can tell I am using the exact same settings as the arduino-ide to open the serial port. This is the code that is running on the arduino: ``` void setup() { Serial.begin(115200); Serial.write(RDY); } ``` This guy has had a similar problem and he compared the serial port settings of putty and QSerialPort. He found that the settings `fDtrControl`, `fOutX` and `fIutX` differed. I tried changing `fDtrControl` but it had no effect. I do not know how to set `fOutX` and `fIutX` using QT. Any ideas what might be causing this bug? edit: Solution: `port.setDataTerminalReady(true)` was missing