@RuWex
Please look at the QTimer documentation, and the examples there. This does not work by "inserting a delay" into the code where it is called. Rather, it sets off a timer which keeps running, and you supply a "slot"/"callback" which will be invoked when the timer expires. It is in that function/lambda that you do whatever work you wish to perform each time the repeating or singleshot timer expires, e.g. in your case maybe it sends the next character.

@RuWex Sorry, I mean https://doc.qt.io/qt-6/qserialport.html

@aha_1980 Thank you so much for your ideas. Both problems solved.

After reconfiguring aptitude stuff to use "stable" instead of hard-coded "jessie" and half-a-day-long upgrades and cleaning the mess I really got not only higher version of Qt, but as well QParallelPort working as planned. Definitely worth the effort (even if I did not expect the upgrade to take so much time.)

My mistake. I missed this single character overload to append(). Thank you for pointing me there. Now I got completely rid of that development/release conditionals.

Case closed, thanks to all who assisted.

You're welcome !

Since you have it working now, please mark the thread as solved using the "Topic Tools" button so that other forum users may know a solution has been found :)

yes it should.
you can read about it here
http://manpages.ubuntu.com/manpages/utopic/man1/pumount.1.html

it seems to expect the device to be mounted under /media.

@SGaist
I'm not sure, but I believe solid needs udev. I'm using busybox with mdev.
However, I found a solution with find and grep.
If I know I have to find where, for instance, sda is connected on my 4 ports:

find /sys/bus/usb/devices/usb*/ -name dev -path "*usb1*sd*" | grep -E sda
find /sys/bus/usb/devices/usb*/ -name dev -path "*usb2-1.1*sd*" | grep -E sda
find /sys/bus/usb/devices/usb*/ -name dev -path "*usb2-1.2*sd*" | grep -E sda
find /sys/bus/usb/devices/usb*/ -name dev -path "*usb2-1.4*sd*" | grep -E sda

The return value is 1 if there is no entry matching and 0 if there is.
I wrapped this in a function with sd_ as variable and it works as supposed.

Cheers,
McL

http://api.kde.org/frameworks-api/frameworks5-apidocs/solid/html/index.html

Exact, QSerialPort doesn't call the USB stack directly. Typically for FTDI devices, you would install the FTDI Virtual Com Port driver and then you have a "classic" com port. AFAIK the ARDUINO uses RS232 so it should act also like a serial device.