Why my arduino uno 3.3v pin draw very small current

Projects General Guidance
21

Yep.
Never put a DMM in current mode across a supply.
That will short-circuit the supply, and could blow the fuse inside the DMM.
A DMM in current mode only goes in series with a load.

There is a 500mA auto-reset fuse (polyfuse) in series with 5volt USB supply that might have saved the Arduino and/or PC from releasing the magic smoke.
If you still have 5volt and 3.3volt on the respective power pins, then all is well.

The 3.3volt pin can supply up to 150mA, not 50mA as stated in the Uno manual.
Leo..

22

Hi,
I would say @maple004 has not moved the positive probe from the voltage reading positon.

Tom.... :smiley: :+1: :coffee: :coffee: :australia:
ps.......................1....2
Deep breaths...

23

@TomGeorge @Wawa @b707
Thank you for the suggestions, finally, I get the right readings. But get another problem:
I have 5v from the uno, connect with three 1k resistor in series. Then I use DMM test the votlage of each resistor, is about 1.7v, the current is 2.6 mA.

24

Why is this a problem?

5/3=1.6 and you measure 1.7. Things are just rounding.

25

What is your problem?
If you connect three resistors with the same value in series, the overall voltage equally divided between it:
5.1v / 3 = 1.7v

26

current should be I = V/R= 5/3k = 1.67 mA. I have 2.6mA.
the voltage of each resistor is equal because is in series, so to averge 5 v in 3, it's about 1.7 v. So, it's right for voltage,

27

it seems that you do not measured the current correctly.... again

28

Then you did it wrongly. Current calculates out to be 0.0016666667.

29

I for one would like to see a picture showing the sockets being used on the meter, the range that it is set to, how it is connected into the circuit of 3 series resistors and the value shown on the screen

30

Sorry for the cofusion, I know what is wrong, 2.6mA is the current through two resistor. That 2.6*2 =5.2 v. Sounds right.
Give me some time to check from the orgional question again (Why my arduino uno 3.3v pin draw very small current). Maybe I will post a new topic.

31

You multiply milliampers and get volts??
What kind of nonsense is this?

32

You can do that if you want a crosspost to be reported. Keep it in this topic.

33

2.6mA * 2k ohms =5.2v

34

The thingies attached to the Uno draw current from the Uno. The Uno is a well of available current. The Uno only has so much to give. The devices attached to the Uno draw the current from the Uno, those devices draw what they need. You are trying to troubleshoot a non-problem.

35

3.3volt on the 3.3volt pin of an Uno comes from a separate voltage regulator.
That regulator gets it's input from the 5volt rail.
The 3.3volt is there for the user only. The Uno does not use 3.3volt itself.

Don't know why you mention current draw of the 3.3volt pin. There is none.
Apart from a few uA that the 3.3volt regulator itself draws, to work.
Leo..