How to fix PlatformIO Olimex E407 LED_BUILTIN not working

Problem

You are trying to run a firmware on the Olimex E407 that blinks the builtin green status LED. You code uses LED_BUILTIN similar to this:

#include <Arduino.h>

void setup() {
    pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
    digitalWrite(LED_BUILTIN, LOW);
    delay(500);
    digitalWrite(LED_BUILTIN, HIGH);
    delay(500);
}

but when you upload the code onto the board, the LED does not blink and stays off.

Solution

Instead of LED_BUILTIN, use PC13 - the pin the LED is connected to (which you can see on the Olimex E407 schematic:

#include <Arduino.h>

void setup() {
    pinMode(PC13, OUTPUT);
}

void loop() {
    digitalWrite(PC13, LOW);
    delay(500);
    digitalWrite(PC13, HIGH);
    delay(500);
}