I have an Uno and a Mega, and I decided to measure the voltage on the "3.3V" and "5V" power pins. On both boards, the "3.3V" power pins report 3.3V. But the "5V" power pins give strange readings: on the Uno, the "5V" reports 3.3V (as if it was the "3.3V" power pin), on the Mega I get 3.99V. Should I…

What are you using to power the board? If you feed 5v (e.g., usb) into Vin, it's going to drop on the way to 5v from the linear regulator.

dochawk: If you feed 5v (e.g., usb) into Vin, it's going to drop on the way to 5v from the linear regulator. Thanks, I've just found this out. I had a 5V power adapter going into the power jack. I need minimum 7V into the power jack or 5V directly to the 5V pin. With 7.5V in the power jack, I ge…

A small note on 5V on the 5V pin, DON'T connect the USB cable to a PC when you do. You'll backfeed 5V to the PC. Most modern PC's are smart enough to disable the USB port but it's tempting luck. Does not apply for Pro Mini and Nano as they have a diode in line with the USB power.

element222: Thanks, I've just found this out. I had a 5V power adapter going into the power jack. I need minimum 7V into the power jack or 5V directly to the 5V pin. Important point here - forget the "power jack". Yes, you can power it with 7 - or 9V if you only have a UNO or Mega and nothing el…

I'm not worried about damaging Arduino's, they are dirt cheap. I am however worried about my computer....

Hmm . . . thinking aloud . . . could the user simply short Vin to +5 if using an adequately regulated +5 input? Or does Vin feed anything other than the crummy linear regulator?

Paul__B: If you do, at some stage you will be waning to use more than a few tens of milliamps I plan to power just one servo from the 5V pin. I think Arduino can handle this (with 7V in the power jack). As far as preventing 5V flowing back into the PC, I found this: how to use a diode to prevent…

septillion: I'm not worried about damaging Arduino's, they are dirt cheap Yes, but there are other considerations, like labor and time. At this stage of my project, my Arduino is now buried deep in a tight enclosure, beneath other components. It would cost time and labor to replace it. I'll go w…

I plan to power just one servo from the 5V pin. I think Arduino can handle this No. Servos, being motors, draw lots of (too much) current for that really.

5V voltage on "5V" power pin? (Mega, Uno)

Other Hardware General Electronics

BabyGeezer June 6, 2019, 1:12am 2

have you got anything else connected ?
and i assume you are using a multimeter ?

Topic		Replies	Views
Uno R3, 5v in and USB UNO R3	20	214	February 13, 2026
Arduino mega barrel jack has power coming out when USB is connected Mega 2560	14	108	March 9, 2026
Weird voltage readings General Electronics	34	312	April 13, 2025
Can i connect a 12V 5A power supply to the 2.1x5.5mm power jack in the Arduino board? Motors, Mechanics, Power and CNC	13	240	August 11, 2024
Powering Arduino Uno Interfacing w/ Software on the Computer	20	896	February 2, 2025

5V voltage on "5V" power pin? (Mega, Uno)

Related topics