Power crazy

Using Arduino Project Guidance
1

My breadboarded project is growing. The Nano was able to supply a 3.3v Wtv020sd16p voice module ok, but since adding an RTC, OLED and some port expanders, I've needed to use a breadboard power supply, which is also connecting to the Nano Vin pin.

To avoid any possibility of the breadboard and Nano supplies conflicting - perhaps one with a slightly higher voltage trying to drive into the other and causing damage - I have always turned off the breadboard supply before connecting the Nano to USB to for uploading.
But this 'either/or' situation poses it's own problems...

  1. With just the Nano USB, the other modules have no power, so cannot be debugged.
  2. With just the breadboard supply, there is no Nano USB serial available for debugging.

I'd appreciate any advice from others who have got around similar problems.

2

I'm confused, is it VIN or 5V or 3.3V ?

The Arduino Nano 3.3V pin is very weak. It can power a sensor, but that's about it.
Connecting power to the VIN is okay, you can connect and disconnect the usb cable as you like. No problem.

You might even connect a 5V power supply to the 5V pin, even if one is higher than the other. It is dangerous, since current might flow via the usb cable into the computer. I have that very often, but so far nothing is damaged.