Voltage on 5v pin of arduino + Aref

Hi Guys,

I have arduino UNO which has 2 (5v) pins on it. I am giving 5V exactly on one (5V) pin and measuring on the second (5V) pin with the help of multimeter, it is showing 4.76V. Why??? I cant measure on the second 5V pin if i am giving power 5V to the first 5V pin ????

I thougt if i give directly 5V to 5V pin , it must appear 5V. Actually i want to know the Aref and i have read wharever would appear on 5V pin it would be called operating voltage and that operatinmg volatge becomes the Aref volatge exactly.

Is there a way to measure the Aref or 5V pin voltage with DMM ?

Thank you

Post a photo, and mark on it where you are measuring.

Thank you for support :slight_smile: @missdrew

With no power, measure the resistance beween the two 5V points, and with power, measure the voltage between the left 5V and GND, the right 5V and GND and between the two 5V.

Hopefully we can find the issue.

PS - that is NOT an Arduino UNO!


  1. With out power resistance bw two 5v pins = 0 ohm and with power = 8 ohm
  2. Voltgage bw left 5V pin and gnd is 4.76V and same goes with the right 5V pin

Its is clone of arduino UNO , a company in German AZ-Delivery sells it

Do not measure resistance on a powered circuit. The measurement is meaningless and you could damage the DMM or the circuit.

@groundFungus Thank you very much! Could you help me please

What is providing the power and are you sure it's 5V?

Yes I am sure , i have measured it with DMM and osciloscope then i gave it to Arduino Uno. One thing what i am thinking is , may be its not possible to measure the voltage on the same pin where you are providing the power (beacuse of sinking phenomenon). Is it true?

Sounds like there is a voltage drop in the wire you connected to the 5V pin. Is it particularly long or thin?

Even before pluging into the 5V pin, I measured the voltage it was 5V. So there is no voltage drop in the wire.
Wire is 8 cm , a normal jumper

The board is not an arduino so you dont know the exact circuit configuration.
My bet is there is a protection diode.

I had a similar issue as described here

which also describes ways you can measure Vcc.

Also if its important to get an accurate measurement why not use a decent reference?

(this is a different link)

Can you post a good quality photo of the bottom of the board, please?

0 Ohms between the 2 5V pins means there should be no difference in voltage.

What voltage do you read between the 2 5V pins whan power is applied?

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