I am running the blinking LED program with stm32duino, and an STM32. By trial and error, and a bit of debugging, I have worked out the following:

  • pin C13 blinks as well as the built in LED (except my external LED is on the built-in LED is off)
  • the constant LED_BUILTIN equals 17

I found this pinout: https://stm32duinoforum.com/forum/wordpress/wp-content/uploads/2016/07/The-Generic-STM32F103-Pinout-Diagram.pdf

enter image description here

But it says nothing about C13 being pin 17.

Does anybody know where to look to find out where the arduino pins line up to the codes on the board?

  • In the source code. Look around for the variants in the source code (on github?) and find where the pinouts are. I can't tell you what file to look in, because all cores are different.
    – Majenko
    Jul 17, 2020 at 14:35
  • regarding your external LED ... read the notice about the pins with the warning symbol (yellow triangle with an exclamation mark)
    – jsotola
    Jul 17, 2020 at 15:42

1 Answer 1


OK if this helps anybody, they give you constants for every pin that look like PC14 for the one that says C14, so you don't need to worry about the integers that they assign to the pins.

I mean there are constants named for the yellow boxes on the above diagram.

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