🛠 Allumer une LED via le GPIO 40 broches

Objectives

Discover the 40-pin GPIO connector (J8) on the Raspberry Pi 2 Model B and turn on an LED from the command line: first with the legacy sysfs interface, then with libgpiod, the recommended interface on recent systems. By the end, you will know how to export a pin, configure it as an output, and control it without writing a program.

Hardware

• Raspberry Pi 2 Model B running 32-bit Raspberry Pi OS (Bullseye is the practical limit for this ARMv7 model)
• Breadboard and 2 jumper wires
• 1 red LED + 1 330 Ω resistor
• Pins used: GPIO17 (pin 11 on J8) and GND (pin 6)

Full code

# Méthode 1 : sysfs (ancienne interface, dépréciée mais pédagogique)
echo 17 | sudo tee /sys/class/gpio/export
echo out | sudo tee /sys/class/gpio/gpio17/direction
echo 1 | sudo tee /sys/class/gpio/gpio17/value   # LED allumée
sleep 2
echo 0 | sudo tee /sys/class/gpio/gpio17/value   # LED éteinte
echo 17 | sudo tee /sys/class/gpio/unexport

# Méthode 2 : libgpiod (recommandée)
sudo apt install gpiod
sudo gpioset --time 2000 gpiochip0 17=1          # impulsion de 2 s

Expected verification

The LED turns on when the value is 1 and turns off at 0. With gpioset, the --time 2000 option produces a two-second pulse. The controller name may be gpiochip0 or gpiochip1 depending on the kernel: check with gpioinfo before copying the commands.

Common errors

• Forgetting the resistor: the LED burns out or the pin is stressed beyond its capacity (8 mA max per pin).
• Confusing 3.3 V and 5 V: GPIO logic is 3.3 V, never 5 V.
• Permission denied on /sys/class/gpio: use sudo or add the user to the gpio group.
• sysfs missing or unresponsive: the interface is deprecated, switch to libgpiod.