🛠 Lire un bouton et afficher les appuis dans la console

Objectives

Complete the first project by adding an input: wire a push button to GPIO27, enable the internal pull-up resistor, and display each press in the console using gpiomon, without writing any code.

Hardware

• Raspberry Pi Model B+ running Raspberry Pi OS legacy 32-bit, connected via Ethernet
• 1 push button (4-pin "push" switches), Dupont wires
• Optional: 10 kΩ resistor if the internal pull-up is not available

Complete code

# 1) Activer le pull-up interne de GPIO27 au démarrage
#    (ligne firmware récente ; sinon câbler 10 kΩ entre GPIO27 et 3,3 V)
echo "gpio=27=pup" | sudo tee -a /boot/config.txt
sudo reboot
# 2) Écouter les 5 prochains appuis : passage 1 -> 0 (bord descendant)
sudo gpiomon --num-events=5 --falling-edge gpiochip0 27
# 3) Variante « compteur » : état instantané de la broche
while true; do sudo gpioget gpiochip0 27; sleep 0.2; done

Wiring: one leg of the button to pin 13 (GPIO27), the other to pin 20 (GND). Without a press, the pull-up keeps the pin at 1; pressing it connects it to 0.

Expected verification

After rebooting, gpioinfo gpiochip0 shows line 27 with the pull-up active. gpiomon displays one event line per press ("event: edge: falling edge") and exits after 5 presses. gpioget returns 1 at rest, 0 when held.

Common errors

• Pull-up forgotten: the pin "floats", gpiomon triggers constantly or never.
• Button wired between GPIO and 3.3 V without a pull-down: inverted logic, you look for the rising edge instead.
• Mechanical bouncing: multiple events for a single press — normal, we will filter this in the script.
• Wrong GND pin: the circuit does not close, no press detected.