🛠 Premier script Python : faire clignoter la LED

Objectives

Write and run your first Python script on the Raspberry Pi Model B Rev 1 (Python 2 or 3 depending on the legacy image). The script blinks an LED on GPIO17 using the RPi.GPIO library, the historical reference on BCM2835. Skills covered: creating a file, editing it with nano, running it, and interrupting it with Ctrl-C.

Hardware

• Raspberry Pi Model B Rev 1, Raspberry Pi OS legacy 32-bit (Buster)
• LED + 330 Ω resistor on GPIO17 (pin 11) and GND (pin 6), as in the LED tutorial
• Library: sudo apt install -y python-rpi.gpio python3-rpi.gpio
• nano editor provided with the image; Python is preinstalled.

Complete code

#!/usr/bin/env python3
"""Clignotement LED sur GPIO17 - Raspberry Pi Model B Rev 1 (BCM2835)."""
import RPi.GPIO as GPIO   # sudo apt install python3-rpi.gpio
import time

LED = 17                  # numerotation BCM : GPIO17 = broche physique 11
GPIO.setmode(GPIO.BCM)    # numeros Broadcom, pas positions physiques
GPIO.setup(LED, GPIO.OUT)

try:
    while True:
        GPIO.output(LED, GPIO.HIGH)   # LED allumee
        time.sleep(0.5)
        GPIO.output(LED, GPIO.LOW)    # LED eteinte
        time.sleep(0.5)
except KeyboardInterrupt:
    pass                              # Ctrl-C arrete proprement
finally:
    GPIO.cleanup                    # toujours liberer la broche

Expected verification

nano clignote.py     # coller le code, Ctrl-O puis Ctrl-X
python3 clignote.py  # la LED clignote 2 fois par seconde
# Ctrl-C : le script s'arrete, GPIO.cleanup libere la broche

The LED blinks at 1 Hz. On Buster images where python3 is not the default, try python clignote.py (Python 2, adapt the import).

Common errors

• RuntimeError: No access to /dev/mem: run with sudo on older images, or add the user to the gpio group.
• Forgetting GPIO.setmode(GPIO.BCM): RPi.GPIO then refuses GPIO.setup.
• The script crashes without finally: the pin remains claimed and restarting fails.
• ImportError: No module named RPi: wrong package (python vs python3) or missing library.
• On the 700 MHz ARM11, a very short sleep saturates the CPU: stay at 0.1 s minimum.