I am using an arduino mega clone called the Funduino.

I am developing a python based, tkinter application that will receive the serial data that arduino sends.

However, i am witnessing some behavior that i cannot explain and i am trying to debug. I won't say anything more, because this is an arduino forum, not a python forum.

But, in the arduino, there are some leds. One of them is power, which is constantly ON, when the arduino is powered.

There is another led that is named 'L'. When i open a serial connection this is lighted up and it stays ON.

However sometimes, when i send a string to the arduino, in order to trigger some data exchange, this button is switched off.

So what does this 'L' led is, and what it means when it is turned off?

  • "L" is the user LED that is connected to pin 13. It's controlled by your software installed in the Arduino, whatever that might be.
    – Majenko
    Apr 19 at 13:44

This buildin LED is connected to an IO pin of the microcontroller on the Mega (most commonly pin 13, but might be different depending on the board). So the meaning depends on what the code on the Mega does with it.

When the board is reset (which happens on opening of serial connection), first the bootloader will run. It gives you a short blink on the buildin LED. After the bootloader finishes, your own code is in charge. Whatever you do in your code with pin 13 will be reflected on the LED. Here the meaning depends on you.

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