Pin 13 LED always on

Development Tools IDE 1.x
21

blablatros:
Hello everybody,

I just received my UNO yesterday. I tried the blink example and it works without any problems. I then tried the fade example - the LED on pin 9 fades as it should, but the on-board LED (pin 13) is always on. It is the same with other examples as well (AnalogReadSerial, even BareMinimum).

Is this normal behavior? Shouldn't the on-board LED be turned off?

I am able to switch it off by adding the DigitalWrite(13, LOW) in the example sketch.

Hi,

Well this happened to me as well. IN my case the PIN 13 was working perfectly. I mean if i wanted to use it as input or output, it worked fine. But it was just, that it would glow to show power on indication. So what i did was

  1. If i wanted to use the PIN 13 for any input or output i would define it in the sketch and it worked finr.

  2. For rest of the times when i don't use the PIN 13, i would set it low by adding 3 lines of code in the sketch.

With the LED at PIN13 glowing, my arduino is still working fine, so don't worry.

22

The LED is driven by an analog buffer whose input js connected to D13, see U5B in the top middle of the Uno schematic
https://forum.arduino.cc/index.php?action=dlattach;topic=444354.0;attach=192334
If D13 is an Output and it's High, the LED is On. And Off when Low.
If D13 is an Input, which is the default if your sketch does nothing with D13, then the pin "floats" and the buffer may see electrical fields in the air (the wires & pins act as a simple antenna) as being high enough to turn on the LED a little, or more. If it really bothers you, connect a 10K resistor from D13 to Gnd on your board to keep the buffer input Low when you are not driving it as an Output.

23

for those with the same problem:

void setup()
{
digitalWrite(LED_BUILTIN,LOW);
}

24

As I understand, my Ethernet card connected to Arduino Nano uses D13 as SCK. Pins D10(CS),D11(SI),D12(SO),D13(SCK) seem to be in use.
I can make LED_BUILTIN blink, if I do not use ethernet library.

25

Hi, I would like to ask if the onboard led is dimmer in its brightness because it seems to appear dimmer than the on led (yellow colour) on the board? Anyone facing the issues?