Blink Led Onboard Of Esp8266 Lolin, a ESP32 project

This project demonstrates the fundamentals of embedded programming by blinking the built-in LED on an ESP8266 LOLIN board. The onboard LED toggles on and off at a regular interval, providing immediate visual feedback that the microcontroller is running and responding to code.

The guide includes a complete parts list (just the LOLIN board and USB cable), a wiring diagram showing the simple USB connection, and ready-to-upload firmware written in Arduino. Builders will learn how to configure GPIO pins, use timing functions to create non-blocking delays, and work with active-LOW logic—essential concepts for any microcontroller project.

Wiring diagram

Assemble it in 2 steps

1. Use the built-in light

No extra LED or wires are needed. The small blue LED already fitted to the LOLIN D1 mini is connected inside the board, so leave the board on a non-conductive surface while you test it.

The built-in LED is normally marked near D4 or the board’s blue indicator light.
Do not rest the powered board on loose metal parts or a metal table, because they can touch its pins and damage it.

2. Connect the board by USB

Plug a USB data cable into the LOLIN D1 mini and your computer. The USB cable powers the board and lets Schematik install the blink program.

The LED should blink about once per second: half a second on, then half a second off.
Use a USB data cable, not a charge-only cable, or the computer cannot communicate with the board.

Deploy the firmware

main.cppOpen in Schematik

#include <Arduino.h>

// On the LOLIN D1 mini the built-in LED is active LOW.
constexpr uint8_t LED_PIN = 2;
constexpr unsigned long BLINK_INTERVAL_MS = 100;

bool ledOn = false;
unsigned long lastToggleMs = 0;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, HIGH);  // LED off
}

void loop() {
  const unsigned long now = millis();
  if (now - lastToggleMs >= BLINK_INTERVAL_MS) {
    lastToggleMs = now;
    ledOn = !ledOn;
    digitalWrite(LED_PIN, ledOn ? LOW : HIGH);
  }
}