Arduino LED Blinker, a Arduino project

This project demonstrates the fundamentals of Arduino programming by creating a simple LED blinker circuit. The LED turns on and off at regular intervals, providing a hands-on introduction to digital output control and basic microcontroller programming.

The guide includes a complete parts list, wiring diagram showing how to connect the LED and current-limiting resistor to the Arduino Uno, and ready-to-upload firmware. Follow the assembly steps to breadboard the circuit, load the code onto the board, and watch the LED blink.

Wiring diagram

Gather all the parts

Qty	Component
1	LED 5 mm LED Standard 3mm/5mm through-hole LED. A current-limiting series resistor is added automatically.
1	Resistor 220 Ω, 1/4 W Through-hole resistor (current-limiting in series with an LED)

Qty

Component

LED

5 mm LED

Standard 3mm/5mm through-hole LED. A current-limiting series resistor is added automatically.

Resistor

220 Ω, 1/4 W

Through-hole resistor (current-limiting in series with an LED)

Assemble it in 4 steps

1. 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 (−).

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. 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.

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. 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.

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. Power and deploy

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

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.

Review all connections

1. Connections between "resistor_1" and "Arduino"

Function	resistor_1	Arduino
`digital`	P1	GPIO 8
`digital`	P2 → LED ANODE	EXT

2. Connections between "led_1" and "Arduino"

Function	led_1	Arduino
`ground`	GND	GND

Deploy the firmware

main.cppOpen in Schematik

#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);
}