I made this simple piece of code, to make my LED flash.. Which it does when the pin is set low.. But how does that makes sense?

#include "pins_arduino.h"

void setup() {
  // put your setup code here, to run once:

void loop() {
  // put your main code here, to run repeatedly:

I am using the Wemos d1 - http://www.wemos.cc/

  • That depends entirely on how the LED is wired up. How have you wired your LED?
    – Majenko
    Sep 19, 2016 at 18:24
  • I am using a wemos d1 Sep 19, 2016 at 18:29
  • What's a wemos d1?
    – Majenko
    Sep 19, 2016 at 18:29
  • I am using this one wemos.cc/Products/d1_mini.html Sep 19, 2016 at 18:30
  • I see no LED on the schematic. Do you mean the one built in to the ESP-12F module?
    – Majenko
    Sep 19, 2016 at 18:32

1 Answer 1


If the LED is ON when LOW and OFF when HIGH then chances are the LED is connected between +3.3V and the IO pin with a suitable resistor.

When HIGH the IO pin is at +3.3V, so the voltage across the LED is 0V (3.3 - 3.3 = 0) and it is turned off. When LOW the IO pin is at (nearly) 0V and the voltage across the LED (and its resistor) is 3.3V (3.3 - 0 = 3.3), so it lights up.

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