How to code LED lights on Arduino?

Here are the most common ways to “code LED lights” on Arduino, with working examples. (Assuming Arduino Nano/Uno.)

1) Blink one LED (basic)

Wiring: LED anode → D13 (or any digital pin) through 220–330Ω resistor, LED cathode → GND
(Or use the built-in LED on D13.)

const int LED_PIN = 13;

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

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

2) LED controlled by a button

Wiring: Button from D2 to GND (use internal pull-up)

const int LED_PIN = 13;
const int BTN_PIN = 2;

void setup() {
  pinMode(LED_PIN, OUTPUT);
  pinMode(BTN_PIN, INPUT_PULLUP);   // button to GND
}

void loop() {
  bool pressed = (digitalRead(BTN_PIN) == LOW);

digitalWrite(LED_PIN, pressed ? HIGH : LOW);
}

3) Fade an LED (PWM “dimming”)

Use a PWM pin (Nano/Uno: 3,5,6,9,10,11).

const int LED_PIN = 9;

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

void loop() {
  for (int v = 0; v <= 255; v++) {   // fade up
    analogWrite(LED_PIN, v);
    delay(5);
  }
  for (int v = 255; v >= 0; v--) {   // fade down
    analogWrite(LED_PIN, v);
    delay(5);
  }
}

4) Blink without delay() (non-blocking)

Best if you want to do other things at the same time (read sensors, buttons, etc.).

const int LED_PIN = 13;
unsigned long lastToggle = 0;
const unsigned long intervalMs = 500;
bool ledState = false;

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

void loop() {
  unsigned long now = millis();
  if (now - lastToggle >= intervalMs) {
    lastToggle = now;
    ledState = !ledState;
    digitalWrite(LED_PIN, ledState);
  }

  // Do other work here without being blocked by delay()
}

5) Addressable LED strip (WS2812 / NeoPixel)

If you mean “LED lights” like RGB strips (WS2812B), code is different.

Wiring (important):

• Strip DIN → Arduino D6 (example)
• 5V → external 5V supply (not from Arduino for more than a few LEDs)
• GND of supply ↔ Arduino GND (must share ground)
• Add 330Ω resistor in series with DIN
• Add 1000µF capacitor across 5V/GND near the strip

Code (Adafruit NeoPixel library):

#include <Adafruit_NeoPixel.h>

const int LED_PIN = 6;
const int LED_COUNT = 30;

Adafruit_NeoPixel strip(LED_COUNT, LED_PIN, NEO_GRB + NEO_KHZ800);

void setup() {
  strip.begin();
  strip.show();            // turn off all
  strip.setBrightness(80); // 0-255
}

void loop() {
  // Red wipe
  for (int i = 0; i < LED_COUNT; i++) {
    strip.setPixelColor(i, strip.Color(255, 0, 0));
    strip.show();
    delay(30);
  }

  // Clear
  strip.clear();
  strip.show();
  delay(300);
}