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Topic: Pin 13 LED always on (Read 34962 times) previous topic - next topic


Ahhh I didn't understand what you meant by floating, but now I see.  Well thanks a lot for your assistance I really appreciate it.  This is going sound weird but I think, I remember looking through the arduino forum (could have been on another page about the same topic maybe, I don't know.) But I think you answered someone else's question, and it had to do with the person putting !!! in a comment or something and you said "time to learn source control".  Was that you?  and I ended up doing a search on the subject and couldn't find any good learning material.  Could you possibly point me in the right direction?  I really want to know what that is and have no idea what that is. lol


Here's something to get you started:


Basically with source control you know what you changed, when. And if you add a whole lot of changes and things get worse rather than better, you can go back or find what, exactly, you changed.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics


Sweet!  And thanks again!!!


I have the same problem...when i connect arduino to pc, Led13 is always on.
When upload scetch, get error "avrdude: stk500_getsync(): not in sync: resp=0x00"
and when i use other programmer and when i use AVRisp mkii   and press shift when uploading gets this-> avrdude: usbdev_open(): did not find any USB device "usb".
I tried reset button, i checked ports(i use com8)boards(those are ok) and still nothing... Maybe it's bootloader but i don't know what to do, i'm new to this

Anyone can help me?

Thank you!


If you wired a say 10k ohm resistor from pin 13 to ground the problem would go away, or set the pin to output mode and output LOW in your setup function
Regarding power consumption, is it still better to set the pin to output mode and output LOW than keep it in input mode and let the LED lit?


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.

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. 


The LED is driven by an analog buffer whose input js connected to D13, see U5B in the top middle of the Uno schematic
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.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


for those with the same problem:

void setup()


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.


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?

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