How to Blink LED Using Raspberry Pi Python - Simple Guide

To blink an LED using Raspberry Pi and Python, use the RPi.GPIO library to control the GPIO pin connected to the LED. Set the pin as output, then turn it on and off in a loop with delays using time.sleep().

Syntax

Here is the basic syntax to blink an LED using the RPi.GPIO library:

• GPIO.setmode(GPIO.BCM): Sets the pin numbering system to BCM (Broadcom chip-specific).
• GPIO.setup(pin_number, GPIO.OUT): Configures the chosen pin as an output.
• GPIO.output(pin_number, GPIO.HIGH): Turns the LED on.
• GPIO.output(pin_number, GPIO.LOW): Turns the LED off.
• time.sleep(seconds): Pauses the program for the given seconds.
• GPIO.cleanup(): Resets the GPIO pins to a safe state.

python

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)  # Use BCM pin numbering
GPIO.setup(18, GPIO.OUT)  # Set GPIO 18 as output

try:
    while True:
        GPIO.output(18, GPIO.HIGH)  # LED on
        time.sleep(1)  # Wait 1 second
        GPIO.output(18, GPIO.LOW)   # LED off
        time.sleep(1)  # Wait 1 second
except KeyboardInterrupt:
    GPIO.cleanup()  # Clean up GPIO on CTRL+C exit

Example

This example blinks an LED connected to GPIO pin 18 on and off every second. It runs until you stop it with CTRL+C.

python

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)  # Use BCM pin numbering
GPIO.setup(18, GPIO.OUT)  # Set GPIO 18 as output

try:
    while True:
        GPIO.output(18, GPIO.HIGH)  # Turn LED on
        print("LED ON")
        time.sleep(1)  # Wait 1 second
        GPIO.output(18, GPIO.LOW)   # Turn LED off
        print("LED OFF")
        time.sleep(1)  # Wait 1 second
except KeyboardInterrupt:
    GPIO.cleanup()  # Reset GPIO settings
    print("Program stopped and GPIO cleaned up")

Output

LED ON
LED OFF
LED ON
LED OFF
... (repeats every second until stopped)
Program stopped and GPIO cleaned up

Common Pitfalls

Common mistakes when blinking an LED on Raspberry Pi include:

• Not setting the GPIO mode with GPIO.setmode() before setup.
• Forgetting to call GPIO.cleanup() which can cause warnings or pin conflicts on next run.
• Using the wrong pin numbering system (BCM vs BOARD) and wiring the LED to the wrong pin.
• Not using a resistor with the LED, which can damage the LED or the Pi.
• Running the script without root permissions (use sudo to run the script).

python

import RPi.GPIO as GPIO
import time

# Wrong: Missing GPIO.setmode()
GPIO.setup(18, GPIO.OUT)

GPIO.output(18, GPIO.HIGH)  # This will cause an error

# Correct way:
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)
GPIO.output(18, GPIO.HIGH)

Quick Reference

Here is a quick cheat sheet for blinking an LED on Raspberry Pi using Python:

Command	Description
GPIO.setmode(GPIO.BCM)	Set pin numbering to BCM mode
GPIO.setup(pin, GPIO.OUT)	Set a pin as output
GPIO.output(pin, GPIO.HIGH)	Turn LED on
GPIO.output(pin, GPIO.LOW)	Turn LED off
time.sleep(seconds)	Pause program for given seconds
GPIO.cleanup()	Reset GPIO pins safely

Key Takeaways

Always set GPIO mode with GPIO.setmode() before configuring pins.

Use GPIO.setup() to set the LED pin as output before controlling it.

Use time.sleep() to create visible delays between LED on and off states.

Call GPIO.cleanup() at the end to reset pins and avoid warnings.

Run your Python script with sudo to access GPIO pins on Raspberry Pi.