In my early experiments with Arduino, I used Arduino UNO’s, IDE ver 1.8.5, laptop with win10.
Then compiled sketches were uploaded through COM4 succesfully.
For a new project I bought a new Arduino UNO and a new Arduino MEGA 2560. These seem to like uploads through COM 5 or COM7.
The IDE still wants to use COM4 for uploads, as defined in the preferences.txt file.I already tried to modify the preferences file to use COM5 or COM7 resp., however the IDE sticks to use COM4, and so the upload fails.
How to tell the IDE to use the required com 5 or 7 for upload??
Is the COM port to use for the uploades fixed in the bootloader??
Can Arduino’s bought at different times at several shops contain different requirements for the upload port??
Can't you select the COM port from the Tools/Port menu in the Arduino IDE?
...R
I can only select one COM port, and it seems to be fixed for the Arduino UNO board connected.
For the early Arduino UNO's this was COM4, as also set in the preference.txt file.
For newly buyed Arduino's the possible choices are COM5 (for Arduino UNO) and COM7 (for Arduino MEGA), but the IDE sticks to communication through COM4, and so upload fails.
Please help to set the correct COM port as to be used by the IDE to upload to any Arduino.
I use Linux and not Windows and I can certainly choose the appropriate serial port from the Tools/Port menu. But it only lists the serial ports that exist.
It sounds like you need to check what your DeviceManager is doing when you plug in an Arduino board.
Hopefully a Windows expert will come along.
...R
In a later trial, the correct COM ports were recognized for each Arduino board, and I was able to upload the sketches.....
Can anybody explain this? Was it a windows quirk?
wimvanasperen:
Was it a windows quirk?
What else would a Linux user say 
...R
Robin2:
What else would a Linux user say...R
You don't have to be a Linux user to blame Microsoft for what goes wrong on windows systems.I do it on a daily basis 