Can the Uno R3 be run on 5v supplied via the 5v V-In pin while it’s also receiving 5v from the USB from the PC ? Reason for the question - it’s a turnkey application running on 5v at V-In pin, but sometimes will need to be reprogrammed via USB.

[image] feraltek: Grounds are common on my Uno and the shield. Does that mean it’s safe to supply voltage via both the barrel jack and USB? It's safe but has nothing to do with common grounds. The Uno is one of the Arduino boards where you do not need to worry about about applying external power and USB power at the same time

Uno R3, 5v in and USB

Official Hardware UNO Family UNO R3

feraltek February 13, 2026, 5:05am 21

Thanks. Found the solution to what I wanted to do that’s slightly different than my original question. The solution is to power 7v to 12v via the barrel jack, which also allows the USB connection to the PC when needed.

Topic		Replies	Views
External power using Vin when USB is used to upload firmware UNO R4 WiFi	23	447	April 22, 2026
UNO Q: what's the final word on powering via VIN and connecting USB devices to USB-C port with a hub UNO Q	23	846	July 27, 2026
Arduino Uno 3.3v instead of 5v General Electronics	16	1193	July 29, 2023
Arduino Uno - what happens: parallel power-supply from USB and from +5V-Pin General Electronics	2	1119	December 27, 2023
Powering Uno R4 WiFi with External 5 volts UNO R4 WiFi	3	551	July 6, 2025

Uno R3, 5v in and USB

Related topics