Blink an LED with Arduino Uno
The classic first project. You'll connect an LED and a 220 Ω resistor to Arduino Uno pin 13, upload the built-in Blink sketch, and watch it flash every second. Confirms your board, cable, IDE and driver are working.
Materials
- Arduino Uno R3
- USB Type-B cable
- Breadboard
- 1 × 5 mm LED (any colour)
- 1 × 220 Ω resistor
- 2 × jumper wires
Tools
- Arduino IDE
- Laptop (Windows / Mac / Linux)
Step-by-step guide
- 1
Wire the LED
Insert the LED into the breadboard. Connect the long leg (anode) through a 220 Ω resistor to Arduino pin 13, and the short leg (cathode) to GND.
- 2
Install Arduino IDE
Download the Arduino IDE from arduino.cc/en/software, install it, and open it.
- 3
Open the Blink sketch
File → Examples → 01.Basics → Blink.
- 4
Select board & port
Tools → Board → Arduino Uno. Tools → Port → the COM/tty port that appears when you plug in your Uno.
- 5
Upload
Click the → arrow. The RX/TX LEDs on the Uno flash, and after 3–5 seconds your LED begins blinking every 1 second.
FAQs
Why do I need a resistor?
The LED forward voltage (~2 V) is lower than 5 V. Without the resistor, current spikes past the LED's 20 mA limit and burns it out.
My LED doesn't blink — what should I check?
1) LED polarity (long leg to +), 2) resistor in series, 3) correct COM port selected, 4) the on-board LED at pin 13 usually also blinks — if it does, the wiring is the issue.
