Raspberry Pi Program to Blink LED with Python

Use the RPi.GPIO library in Python to blink an LED by setting a GPIO pin as output and toggling it on and off with GPIO.output(pin, GPIO.HIGH) and GPIO.output(pin, GPIO.LOW) inside a loop with delays.

Examples

InputBlink LED on GPIO pin 18 for 5 seconds

OutputLED turns on and off repeatedly every second for 5 seconds

InputBlink LED on GPIO pin 17 for 3 seconds

OutputLED blinks on and off every second for 3 seconds

InputBlink LED on GPIO pin 22 for 0 seconds

OutputNo blinking occurs, program exits immediately

How to Think About It

To blink an LED on a Raspberry Pi, first choose a GPIO pin connected to the LED. Set this pin as an output. Then, repeatedly turn the pin on (power the LED) and off (turn it off) with a pause in between to make the blinking visible. Use a loop to repeat this action for the desired time or number of blinks.

Algorithm

1

Import the GPIO and time libraries.

2

Set the GPIO mode to BCM to use GPIO pin numbers.

3

Set the chosen GPIO pin as an output pin.

4

Create a loop to turn the LED on by setting the pin HIGH.

5

Wait for a short delay (e.g., 1 second).

6

Turn the LED off by setting the pin LOW.

7

Wait for the same delay.

8

Repeat the on/off cycle for the desired number of times or duration.

9

Clean up the GPIO settings after finishing.

Code

python

import RPi.GPIO as GPIO
import time

LED_PIN = 18
GPIO.setmode(GPIO.BCM)
GPIO.setup(LED_PIN, GPIO.OUT)

try:
    for _ in range(5):  # Blink 5 times
        GPIO.output(LED_PIN, GPIO.HIGH)  # LED on
        print("LED ON")
        time.sleep(1)  # Wait 1 second
        GPIO.output(LED_PIN, GPIO.LOW)   # LED off
        print("LED OFF")
        time.sleep(1)  # Wait 1 second
finally:
    GPIO.cleanup()  # Reset GPIO settings
    print("GPIO cleaned up")

Output

LED ON
LED OFF
LED ON
LED OFF
LED ON
LED OFF
LED ON
LED OFF
LED ON
LED OFF
GPIO cleaned up

Dry Run

Let's trace blinking the LED 2 times through the code

1

Setup GPIO

Set GPIO mode to BCM and configure pin 18 as output.

2

First blink ON

Set pin 18 HIGH to turn LED on; print 'LED ON'; wait 1 second.

3

First blink OFF

Set pin 18 LOW to turn LED off; print 'LED OFF'; wait 1 second.

4

Second blink ON

Set pin 18 HIGH again; print 'LED ON'; wait 1 second.

5

Second blink OFF

Set pin 18 LOW; print 'LED OFF'; wait 1 second.

6

Cleanup

Call GPIO.cleanup() to reset pins; print 'GPIO cleaned up'.

Iteration	LED State	Printed Output
1	ON	LED ON
1	OFF	LED OFF
2	ON	LED ON
2	OFF	LED OFF

Why This Works

Step 1: GPIO Setup

We use GPIO.setmode(GPIO.BCM) to refer to pins by their GPIO numbers and GPIO.setup() to set the LED pin as output so we can control it.

Step 2: Blinking Loop

Inside the loop, GPIO.output(pin, GPIO.HIGH) powers the LED on, and GPIO.output(pin, GPIO.LOW) turns it off, with time.sleep() pauses to make the blinking visible.

Step 3: Cleanup

Calling GPIO.cleanup() resets the GPIO pins to a safe state to avoid warnings or conflicts when running other programs.

Alternative Approaches

Using gpiozero library

python

from gpiozero import LED
from time import sleep

led = LED(18)

for _ in range(5):
    led.on()
    print("LED ON")
    sleep(1)
    led.off()
    print("LED OFF")
    sleep(1)

gpiozero is simpler and more beginner-friendly but less flexible than RPi.GPIO.

Blinking with PWM for brightness control

python

import RPi.GPIO as GPIO
import time

LED_PIN = 18
GPIO.setmode(GPIO.BCM)
GPIO.setup(LED_PIN, GPIO.OUT)
pwm = GPIO.PWM(LED_PIN, 1000)  # 1kHz frequency
pwm.start(0)

try:
    for duty_cycle in range(0, 101, 20):
        pwm.ChangeDutyCycle(duty_cycle)
        print(f"LED brightness {duty_cycle}%")
        time.sleep(1)
finally:
    pwm.stop()
    GPIO.cleanup()

PWM allows controlling LED brightness instead of just on/off blinking.

Complexity: O(n) time, O(1) space

Time Complexity

The program runs a loop for n blinks, so time grows linearly with the number of blinks.

Space Complexity

Uses a fixed amount of memory for GPIO setup and variables, so space is constant.

Which Approach is Fastest?

All approaches run in similar time; gpiozero is simpler but adds a small overhead, PWM adds complexity for brightness control.

Approach	Time	Space	Best For
RPi.GPIO basic blink	O(n)	O(1)	Simple on/off blinking
gpiozero library	O(n)	O(1)	Beginner-friendly, easy code
RPi.GPIO with PWM	O(n)	O(1)	Controlling LED brightness