Arduino uart serial communication with external power supply

Hi Everyone. I build something and I want to use external power supply for my arduino nano through Vin, but in that way I can't use my uart for serial communication with PC through Rx/Tx. The uart work perfectly with own power if I connected that to arduino, but I want to use external power supply to arduino separately from usb power, but with serial comunnication through an uart (cp2102).

Do you have any idea or solution?

Connect the grounds.

It works :slight_smile: I never thought this solution is so simple. Thank you very much.