USB monitoring with 3.3volt external power.

[Looplogsend]

Hi. First post here.

I power a ESP32 directly on the 3.3v pin. To avoid conflicting power (5v usb vs 3.3v PSU), I disconnect the 3.3v pin to flash the device and to monitor data on the serial monitor in the arduino IDE.
Now I would like to monitor the data from my device while keeping the 3.3v pin connected. To do this with Arduino UNO (5v device), I strip and physically cut the power line on the USB cable. Doing this, I can monitor the serial output from the arduino and still power the arduino without damaging my laptop USB port.
I tried the same thing with the ESP32 but somehow it don't work. The comport don't show up in the IDE and I can't connect to the ESP.

What can I do about this?
I can use the RX/TX pin but there is 0,1 and 2. I also want to flash the device from time to time. Maybe one serial channel is better at this?
I also use the fucntion Serial.print() / Serial.begin() in my actual program. Is this attach to RX0/TX0 by default or only to the USB serial port?

Thank you

[becorey]

You should clarify which dev board you are using. If you have usb 5v in, it's not just an esp32 mcu.

The usb 5v powers the usb to serial chip, that's what gives you the com port to connect. So you lose it when you remove usb 5v power.

You could supply 5v external to the VBUS / VIN if that's 5v. Then you'll power the usb to serial.

[Looplogsend]

Yes, it is a board with usb connector and 5v to 3.3v regulator but I don't use the later. I have a external 3.3v regulator and I power the board directly with it.
When I connect a usb to monitor the serial port, I send 5v at the same time than my external 3.3v power. Those ''meet'' each other on the board and I end up having dual power source at the same time since the 5v from the usb is then converted to 3.3v with the embedded regulator and I already hace 3.3v from my external regulator. When I remove the power line from the usb cable, serial output don't wotk anymore. Your answer explain why and confirm what I was suspecting.
This week end I was able to monitor the port with RX0 TX0 instead. It work although it require a rs232 to ttl converter. It is more strait forward and user friendly to communicate with the usb cable.
The suggestion of putting 5v on the in pin to power the serial to usb device is a good idea but will also end up with dual power on the board.