Unexpected low current output

Using Arduino LEDs and Multiplexing
#1

Hi there,

I have multiple chinese copies of the nano board and on each one of them the A0 and A1 pins seem to produce current much lower than expected when measured with a multimeter but the voltage is not changed.

I'm only trying to power LEDs and I'm using the pins as digital outputs.

Is this normal on all arduino nanos? Or are all of my nano copies defective?

Thanks for the help!

#2

Without telling us the expected or measured value? I hope you're not driving LEDs without a current limiting resistor...

Are they 5V or 3.3V Nanos? Do you have a link to what you bought?

1 Like
#3

I'm using 220 ohm res. It's really simple. I'm expecting the LEDs to be the same brightness with all pins, yet A0 and A1 produce a much dimmer light.

Here are the current measurements:

The other pins (including A2 and A3) measure at 77 mA where as A1 and A0 measure at 0.12 mA

I bought the boards from 2 different vendors on Amazon:

#4

It's strange.
Even if the LED Vf is estimated to be 1.2V (quite low), 77mA will not flow.
(5V - 1.2V) / 220Ω ≈ 17.3mA
Also, 77mA from the pin is clearly excess current.

#5

Oh right so I'm measuring the current directly from pin to ground without the led so like there is very minimal resistance. my apologies for not mentioning that.

So with the resistor and led connected:

D10 measures 18.7 mA

A0 measures 0.13 mA

#6

This is one of the easy ways to destroy that PIN. :expressionless:

#7

Good to know. Do you have an answer?

#8

Did you use pinMode() to correctly change the pin to output?
If it is true, they have similar output drivers except A6 and A7, so I think the internal driver for that pin is simply broken.

#9

I did indeed. I'm not sure how the same 2 pins have broken drivers on all 10 boards I have but I guess I got unlucky with a bad batch sold separately or something. Good to hear that the original isn't supposed to exhibit similar behavior.

#10

Like this?

void setup() {
  pinMode(A0, OUTPUT);
  pinMode(A1, OUTPUT);
  digitalWrite(A0, HIGH);
  digitalWrite(A1, HIGH);
}
void loop() {
}
#11

yes except I wrote to the pins in loop(). But I set them up in setup(). But that doesn't matter.

#12

Then, I think it's broken.

#13

If anyone else can confirm, would be appreciated

#14

...which can damage the pin...

Did you solder the pins?

#15

Oh btw can you point me to an article that says that using a multimeter between a pin and ground is bad? I haven't been able to find any info on that doing a quick search. And not to doubt your expertise or anything but I would like to read on the topic more and have a source to refer back to.

#16

No just probes between the two. The pin was damaged before measurements.

#17

one of the arduinos is soldered to LED and resistor. But the rest are not soldered to anything

#18

There are an infinite number of mistakes that you can make in electronics. Do you really expect to find an infinite number of articles warning you about them?

#19

It is correct wiring in the method of measuring voltage.
But don't measure the current with that probing.

The current that can be drawn from the uC pin is specified.

#20

I mean, in the link you provided, the pin headers aren't soldered. Often that is a do it yourself job. Did you do that yourself?