Arduino LED Blinker

Pan and zoom to explore the wiring. Remix the project to edit it in your own workspace.

1. 01

   Place the LED

   Insert the LED into a breadboard. Identify its long lead as the anode (+) and its short lead, usually beside the flat edge of the LED body, as the cathode (−).

   • Tip: Keep the two LED leads in separate breadboard rows.

   • ⚠ Reversing the LED prevents it from lighting.
2. 02

   Add the current-limiting resistor

   Connect one end of the 220 Ω resistor to the LED anode (long lead). Connect the other resistor end to Arduino Uno digital pin D8.

   • Tip: A 220 Ω resistor commonly has red-red-brown-gold color bands.
   • Tip: The resistor has no polarity, so either end may face D8.

   • ⚠ Do not connect the LED directly to D8 without the resistor; that can overload the LED or Arduino pin.
3. 03

   Connect the LED return

   Connect the LED cathode (short lead/flat side) to any GND pin on the Arduino Uno.

   • Tip: Use a black jumper wire for the ground connection if available.

   • ⚠ All connections should be made with the Uno unplugged from USB.
4. 04

   Power the Uno

   After checking the three connections—D8 → resistor → LED anode and LED cathode → GND—connect the Arduino Uno to your computer with USB. Use Schematik’s Deploy button to compile and flash the project.

   • Tip: The external LED will turn on for one second and off for one second repeatedly.

   • ⚠ If it does not blink, unplug USB and recheck LED orientation and that D8, not D13, is used.

#include <Arduino.h>
// Arduino Uno external LED blink
// LED anode is connected to D8 through a 220 ohm resistor.

constexpr uint8_t LED_PIN = 8;
constexpr unsigned long BLINK_INTERVAL_MS = 1000;

bool ledOn = false;
unsigned long lastToggleMs = 0;

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

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

“Deploy to device” opens this project in Schematik, where you can flash it to your board over USB.