Ouput current dropping down

Hello all i did a very simple circuit and try allready with 3 arduino nano and get always same problem, when i drive the pinout HIGH, the tension over the resistance 220 ohms is aroud 25mV and i don't understand why ? I just use the brown and white cable to mesure the tension. The current should be 18mA

Bonjour , j'ai réalisé le simple montage suivant et fait l'essais avec 3 Arduino nano different, et quand je met la sortie à HIGH, j'ai une tension de 25mV au borne de la résistance. Je ne comprend pas pourquoi ?


take a piece of paper, a pencil and a ruler, draw the circuit with your components (with references - is the black IC an optocoupler?) and show us where you performed the measure.

please use only English in the general forum. If you want to post in French, go to the French section - but don't double post. Pick one sub forum and stick to it.

I also moved your question to the General Electronics forum as it's not an installation issue

Please post a schematic showing part numbers, values and pin names/numbers.

OK Thanks as i am new i didn't know all the rules thanks. Where can i find my post easely where you move it ?

Ha ok i understand, so i make a quick drawing and yes it's an optocoupler. For easier understanding i take it out for the moment because the problem is only with the resistor. So the mesurement is done at the both side of the resistor and i have 24mV. What can be the problem ?

On the picture there is an IC which is not in your diagram


How is the Nano powered?

just where you replied :slight_smile:

Yes i took it out as is not part of the problem :wink: The nano is powered by USB laptop

How is the Nano powered? what's your code ?
can you share a picture of how you measure the current and the reading?

The nano is powered by USB laptop, the code is simple :
digitalWrite (10,HIGH);
and for the mesurement is on the picture. Thanks

If you have your code and connections correct, then I think you should check your wires.
Although, pls share an image of your code

not an image of code please... just the Code with code tags (read How to get the best out of this forum and post accordingly).

Hi this is not wire problem, because when i take out the resistor, the voltage come back to 4,6 Volts

Your code (•‿•)

check the resistor value with your tool

if it's broken or super low (and not 220Ω) then you have a short circuit....

Done allready this is 220 ohms

void setup ()
 Serial.begin (9600); 
 Serial.println ("Scenario PV");

void loop()
  digitalWrite (10,HIGH);

measure the current flowing into the circuit


Your pin is not set as an output (so it's a HIGH impedance INPUT by default)... try this

void setup ()
  pinMode(10, OUTPUT);
  digitalWrite (10,HIGH);
void loop() {}
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Declare pin 10 as an output

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