#01 Beginner ⏱ 15 min

ESP32: Blinking LED

The first program on every microcontroller: turn an LED on and off every second. You learn what a digital output is, why you need a resistor and what the endless loop() looks like.

Open it interactively in 3D →

What you learn

pinMode / digitalWrite / delayAnode vs cathodeWhy always a resistor with an LEDHow breadboard columns join components

You need

ESP32 DevKit V1 — microcontroller with WiFi and Bluetooth
Breadboard — wiring without soldering
Jumper wires — M–M, M–F, F–F
LED — light-emitting diode 5 mm
Resistor — 220 Ω, 1 kΩ, 10 kΩ…

How it works

Current flows in a circle: GPIO 2 → LED → resistor → GND. When the program writes digitalWrite(2, HIGH), the pin is internally connected to 3.3 V and current flows — the LED lights. With LOW the pin goes to 0 V, no voltage difference, no current — the LED goes dark.

The setup() function runs once (we say the pin is an output), and loop() repeats forever. delay(1000) "freezes" the processor for 1000 ms — simple, but later we will learn a better way with millis().

Wiring

From	To	Why
ESP32 · D2 (GPIO 2)	LED anode (+), column 20	The pin gives 3.3 V (HIGH) or 0 V (LOW). The long leg of the LED is in column 20, so everything in that column (a–e) is joined to the pin.
LED cathode (−)	column 21	Current leaves the LED through the short leg into column 21.
column 21	Resistor 220 Ω → − rail	The resistor limits the current to (3.3 − 2)/220 ≈ 6 mA. Without it the LED and the pin suffer.
ESP32 · GND	− rail of the breadboard	Closes the loop: current returns into the ESP32. Without GND nothing works.

Step by step

Put the LED into columns 20 (long leg, anode) and 21 (short leg, cathode), row c.
The 220 Ω resistor: one leg in 21a, the other in the − rail above it.
Wire from D2 on the ESP32 to hole 20a.
Wire from GND on the ESP32 to the − rail.
Connect USB, select board "DOIT ESP32 DEVKIT V1" and the port in the Arduino IDE, upload the code.
The LED blinks every second. Change the delay() values and see what happens.

Code (Arduino IDE)

// Project 1: Blinking LED
const int LED_PIN = 2;   // D2 — also the built-in blue LED

void setup() {
  pinMode(LED_PIN, OUTPUT);   // the pin will SUPPLY voltage (output)
}

void loop() {
  digitalWrite(LED_PIN, HIGH); // 3.3 V → LED on
  delay(1000);                 // wait 1000 ms
  digitalWrite(LED_PIN, LOW);  // 0 V → LED off
  delay(1000);
}

Typical problems

LED not lighting? Flip it — reversed polarity is the most common mistake.

Upload stuck at "Connecting…"? Hold the BOOT button until it starts.

The built-in blue LED blinks too — that is because it is also on GPIO 2.

Open it interactively in 3D →

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