COM 3 on one board and COM 4 on another?

Hi:
The first UNO that I bought required that I set the port to COM 3. The second UNO that I bought requires that I set the port to COM 4 (I got an error message). I switched ports using the Tools menu and all works. The actual physical location on the master computer (the USB) is the same. Can I make the second computer also look to COM 3? I don't understand and I can't find any help with this. I would appreciate any guidance to understanding.
Bob

Sounds like you're using Windows:

  • Close the Arduino IDE
  • Open Device Manager
  • Find your Arduino's port(COM4) under Ports (COM & LPT) and double click it
  • Port Settings > Advanced... > COM Port Number: > COM3 > OK > OK

On my computer most of the ports show "(in use)" next to them even when they're not in use so Windows gives you a warning dialog that assigning an in use port could cause problems with the application using it but it still works fine for me. Just make sure that COM3 isn't actually being used already by another device on the computer.

Personally I find it more convenient that boards have different port numbers. That way you can develop code for boards that need to communicate and have a serial monitor available for each board.

The computer should still automatically change the port number of one of the boards if you plug multiple in on one computer. This is specifically for making the port name be the same on different computers.

I have multiple non-Arduino devices connected to my computer that also use virtual serial ports so it gets kind of confusing with the Arduino boards that don't show a device name in the Tools > Port menu so it can be helpful to select a specific port that I can easily remember.

I've somewhat eased this situation by creating a dummy hardware package with the VID/PID for the CH340, genuine FT232RL, and counterfeit FT232RL that has been "bricked" by the FTDI driver that labels the chip type(though it still can't differentiate between multiple connected boards with the same chip. In my case FTDIgate did me a favor because the non-Arduino devices have genuine FT232RL and all the FTDI breakout boards I use for my Pro Minis, etc. are counterfeit:

#this file is used to give names to all com ports
##############################################################
tira.name=Tira
tira.vid.0=0x0403
tira.pid.0=0xFA78
tira.build.board=VIDPID_TIRA
##############################################################
FTDI_FT232.name=Authentic FTDI FT232
FTDI_FT232.vid.0=0x0403
FTDI_FT232.pid.0=0x6001
FTDI_FT232.build.board=VIDPID_FTDI_FT232
##############################################################
#FTDI driver update changed PID of counterfeit chips to 0000 but the Smartronics driver makes them work
counterfeitFTDI_FT232.name="Bricked" Counterfeit FTDI FT232
counterfeitFTDI_FT232.vid.0=0x0403
counterfeitFTDI_FT232.pid.0=0x0000
counterfeitFTDI_FT232.build.board=VIDPID_counterfeitFTDI_FT232
##############################################################
CH340.name=CH340
CH340.vid.0=0x1A86
CH340.pid.0=0x7523
CH340.build.board=VIDPID_CH340

Of course you could add CP2102, etc. I just don't happen to have any Arduinos that use the other chips.