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 on the breadboard

   Insert the external LED so its two leads occupy different breadboard rows. The longer lead is the anode (+); the shorter lead and the flat edge of the LED body identify the cathode (−).

   • Tip: Place the LED across the breadboard’s center gap if convenient; this helps keep its leads separate.

   • ⚠ Do not reverse the LED: it will not light when connected backwards.
2. 02

   Add the current-limiting resistor

   Insert one lead of the 220 Ω resistor into the same row as the LED’s long anode lead. Put its other lead into an unused row. The resistor has no polarity.

   • Tip: A 220 Ω resistor is commonly marked red-red-brown-gold.

   • ⚠ Do not connect the LED directly to an Arduino output pin; the resistor is required to limit current.
3. 03

   Connect the Arduino Uno

   Connect Arduino Uno digital pin D8 to the free end of the 220 Ω resistor with a jumper wire. Connect an Arduino GND pin to the breadboard row containing the LED’s short cathode lead.

   • Tip: The complete path is D8 → 220 Ω resistor → LED long lead (anode); LED short lead (cathode) → GND.

   • ⚠ Check that the D8 wire goes to the resistor, not directly to the LED.
4. 04

   Power and deploy

   Connect the Uno by USB. In Schematik, press Deploy to compile and flash the blink firmware.

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

   • ⚠ Disconnect USB before rearranging breadboard wiring to avoid accidental shorts.

#include <Arduino.h>

// External LED anode is connected to D8 through a 220 ohm resistor.
const uint8_t LED_PIN = 8;
const unsigned long BLINK_INTERVAL_MS = 1000;

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

void loop() {
  digitalWrite(LED_PIN, HIGH);
  delay(BLINK_INTERVAL_MS);

  digitalWrite(LED_PIN, LOW);
  delay(BLINK_INTERVAL_MS);
}

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