Can we have two Serial Monitor windows?

I have a project with an RS485 board. I will obviously need at least two arduino board to see the communication going on between them. My question is, is it possible to open two Serial Monitors, one for each COM port? I can see that I am only able to open one at a time, but this means that if i had two boards connected I would need 2 computers.

Yes. You need to start the Arduino IDE twice. This creates two instances of the Arduino IDE. That is difference from opening two IDE windows of the same instance. When you have two IDE windows of the same instance open, any time you change the port in one instance it changes the port in the other. When you have two instances running, changes made in one instance don't affect the other. That means you can select a port in one instance and a different port in the other instance, and open a Serial Monitor for each of those ports.

Adding to pert's advice

If it's only about serial monitor and not about upload, you can also use another terminal program (e.g. putty, realterm, minicom).

In that case, please be aware that only one PC program at a time can make use of a specific serial port. So trying to upload while e.g. putty has the port in use will result in upload failure.

For serious debugging, I suggest hterm. It has a lot of advanced bells and whistles that are very useful (show modem control pin states - I've used these to monitor pins from terminal - and manually poke dtr/rts, input and output data as ascii, hex, decimal or binary)

Thanks for all your ideas. I actually did open two IDEs twice before I made my posting, but i noticed that even though I’ve opened it twice, I am only able to open one Serial Monitor window. If I click the Serial Monitor on the other IDE, it will switch over to the COM port of that IDE so that’s tricky, but I guess using one Serial Monitor and one putty might be a workaround.

I think with Arduino nano, reopening the serial monitor seems to start the script from the beginning as if I reset the arduino. With ESP-12E it is not the case. It will just continue from where it left off.

hterm also looks interesting. It might be helpful later on once I get deep into the project.

sed003: Thanks for all your ideas. I actually did open two IDEs twice before I made my posting, but i noticed that even though I've opened it twice, I am only able to open one Serial Monitor window. If I click the Serial Monitor on the other IDE, it will switch over to the COM port of that IDE so that's tricky,

Which operating system are you using? I guarantee the trick with two IDE instances works in Windows with every version of the Arduino IDE I've tried (including 1.8.7) but I haven't tried it on other operating systems.

sed003: I think with Arduino nano, reopening the serial monitor seems to start the script from the beginning as if I reset the arduino.

Correct. The reason for this is the board needs to be reset before uploading a sketch to activate the bootloader. So there is an auto-reset circuit that resets the board when a serial connection is opened. There is a solder jumper on the Nano you can cut to disable the auto-reset but then you'll need to do a manual reset of the board at just the right time during the upload. You can also attach a separate USB to TTL serial adapter to your Nano's 0 and 1 pins to permit opening a serial connection without the auto reset.

Hi Pert,
Actually you’re right. I just didn’t change the port before opening the serial monitor. I just assumed opening the serial monitor would open a separate session, but it doesn’t and thinking about it now I understand why. I am using Windows 7 (the last good operating system Microsoft made)

I'm glad to hear it's working for you now!

I agree about Windows 7. I'm now using Windows 10 and I hate it. Once it's time to upgrade my OS I'm switching to Linux because Microsoft clearly doesn't target their OS to users like me any more.