Ok well here's an interesting discovery I've made, for anyone who finds this thread in the future: There seems to be an issue with the driver for the off-brand Arduino Nanos possibly not signalling to the OS correctly, or the implementation that Qt uses just really doesn't like the way that the driver responds. I am referring specifically to the nano clone which uses the QinHeng HL-340 serial peripheral. Not sure why this caused a problem, but there it is. Once I used an official Uno the code worked no problem. If I were more patient and had better resources I could possibly trace back the issue, but I do not, so sorry everyone lol. As such I'm marking this as resolved.

@J-Hilk Thanks man, your answer saved my time also, I had Qt 5.13.1 and serial read was not working, I updated to 5.14.0 and now it works.

@aha_1980 Thank you alot Sir your answer was correct and helped to clean up the problem! Regards

I figured out, it was nescessary to set DTR: port.setDataTerminalReady(true); Thanks & br, Clemens

@ftsm Congratulations with the baby ;)

Hi and welcome to devnet, Why the double conversion to stdString and c_str ? You can use something like toLatin1 if you want a QByteArray to write to your serial port.

Yes, i made this program by the terminal example. I solve it. I use QStringList to delete the first response. But, i thank you for for answer.

Workaround: Start an application (QProcess) that pipes the serialport to a localhost socket.

#2 is wasteful way indeed! but in low baud rates it will help, but in this case I don't think this is a low baud rate. EDIT : I said for example 1ms, you really don't need it this fast, it depends on the frequency of getting bytes, for example for 20Hz you will have 20bytes every second which means you need a timer with at least 50ms refresh time and of course you read from serial port in asynchronous way then you can't 100% trust this way to read byte by byte, So as @JKSH said you better don't use this way if you don't have a specific reason.

Hi, Did you check the values that you are sending ? Do you have any code running on the Arduino that your wrote ?

Oh yeah :) ! Finally i have found the bug . The problem was the Load() func. it was before the ,,arduino = new QSerialPort ;" . Thanks for all of the help :) !!!