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Topic: Measuring voltage on Adruino (Read 842 times) previous topic - next topic


Hi all,

I'm having a problem with my Arduino, I think I broke it when I tried to learn some things about measuring the voltage.

I plugged my Arduino board into a 12V 500 mA DC power adapter as I ussually do, then I tried to measure the voltage. I connected a wire to the 5V and a wire to the Ground in the Power PINs and set my multimeter to 200V in the DCV section. After that, I connected the red probe from multimeter to 5V wire and the black to the Ground and the value showed on the multimeter's LCD was 4.95 or something like that.

I think I've connected the multimeter for about 10-15 seconds and the red and black probe were correctly connected to the multimeter. Also, I am pretty sure that I didn't touched the 5V and GND pins together because I know that would mess up any circuit.

After that operation I think I destroyed the board because every time when I connect it to the PC or power adapter, it heats.

My questions are:

1. When I want to measure my Arduino, it's better to plug in the USB, instead of power adapter?

2. The 200V DCV was too big and that caused a short circuit on my board?

3. In the multimeter manual I read something about the red probe that should be connected to a different terminal if the current exceeds 200 mA (in some manuals the value is 100 mA), could that cause problems given that my power adapter current is 500 mA?
"Plug in connector for red (positive) test lead for all voltage, resistance and current ( up to 200mA ) measurements." (from Manual)

4. Also in the multimeter manual I read that the terminal for 10 mA must be used for a maximum 10 seconds and the interval between measurements must be at least 15 minutes, but I didn't used that terminal, but it's specified that rule is for current only.
"Plug in connector for red (Positive) test lead for current ( between 200mA and 10A ) measurement. There is no fuse for "10A" jack. To use safely, each measurement can not last for more than 10 seconds, and the interval between each measurement must be more than 15 minutes." (from Manual)

Please provide an answer to my problem, I hope I described it in detail. I don't want to ruin another Arduino board  :smiley-roll-sweat:


What you did would not have caused any damage to your arduino.

1) it matters not what you use.
2) the setting on your voltmeter will not affect anything.
3) no you were measuring voltage not current.
4) see above.

Something else must have happened other than what you think.


Thank you for your answer. I forgot to mention that after I measured the Arduino and since then my L led (the one that blinks when the bootloader loads) is always ON.

Can you tell me if that represents a problem, I can't find any info about those LEDs on my board. Also, is there any general reset or something?

Do you know why the ATmega heats very bad when I plug the USB or power adapter and what are the conditions in which the controller behaves like this? I want to know if there is something that I can do to restore the board to it's normal state.


While you have done nothing in what you describe to damage the arduino, the fact that it is heating says there is something wrong.
Try and find out what is overheating, that is what chip it is.
This could be due to a faulty part or a short circuit on the power and ground pins you have connected.

The LED is connected to pin 13. So you should set this pin as an output in the setup and then write a low to this pin to turn it off.


Thanks for your answer, you are very skilled and I apreciate your help.

I can't try anything now, the board is ruinned for good. When I plug it to my laptop I don't get nothing and the COM is not present in the Device Manager. The Arduino gets very hot and even pinches a bit.

I must find out if the short circuit between the 5V and the GND produces a problem like mine, in which conditions my board could broke if I touch those 2 wires (for 1 second to 10 seconds or more) or there is some king of protection that keep the board working. Anyways, I'm pretty sure that I didn't do anything like that, but if I get a new board, I must know how to keep that new one safe.

Last night I even measured the DC power adapter that I've been speaking of and surprise: even if on the box it says 12 V, 500 mA, when I measure the voltage I gent 17.95 V or around this value. Maybe my board started to malfunction after several days and the adapter is the source of that problem. Maybe that adapter just "fried" my board nice and slow without me even suspecting something.

Anybody have an idea? I don't want to pay another board and ruin that one too, I try to investigate all the things that gone wrong in my case to protect from future incidents.


even if on the box it says 12 V, 500 mA, when I measure the voltage I gent 17.95 V or around this value.

That suggests it is an unregulated supply and only gives 12V at the maximum current.
I would ditch it.
It could be that you have a board with only 16V capacitors on and it fryer them. However they are normally 25V capacitors. On the other hand your supply could have a rectifier blown and the peak voltage is much higher than the voltage you measured with a meter, if you can try looking at the supply on a scope.

Yes shorting the suply out will give the same sort of problem but please do not try it as I could damage your computer.
If it is the arduino chip itself that gets hot (you have not mentioned what sort of arduino you have) you could try removing the chip and seeing if the PC will still pick it up. However unfortunately it sounds like a dead parrot. (if you don't know what that means google it along with the word python)


My board it's an Arduino Leonardo, I forgot to metion this in previous posts. And yes, I know what a dead parrot means and seems that Polly doesn't want a cracker no more :) (maybe my english is not so good sometimes, but I can understand or I can google, regarding your advice, an expression).

I spoke with one of my friend and I'll buy another adapter from an electronics store with protection and regulated voltage.

Thanks for your assistance, it was very helpfull.

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