How to Use Interrupts on Raspberry Pi Pico: Simple Guide

To use an interrupt on Raspberry Pi Pico, attach an interrupt handler function to a GPIO pin using Pin.irq(). This lets your program respond immediately to events like button presses without constantly checking the pin state.

Syntax

Use the Pin.irq() method to set up an interrupt on a GPIO pin. You provide a handler function and specify the trigger event.

• handler: The function called when the interrupt triggers.
• trigger: The event that triggers the interrupt, e.g., Pin.IRQ_FALLING for button press.
• debounce: Optional, to ignore rapid repeated triggers.

python

pin.irq(handler=callback_function, trigger=Pin.IRQ_FALLING)

Example

This example shows how to use an interrupt to detect a button press on GPIO 15 and toggle an LED on GPIO 25.

python

from machine import Pin
import time

led = Pin(25, Pin.OUT)
button = Pin(15, Pin.IN, Pin.PULL_UP)

# Interrupt handler toggles the LED
interrupt_triggered = False
def button_handler(pin):
    global interrupt_triggered
    interrupt_triggered = True

# Attach interrupt on falling edge (button press)
button.irq(handler=button_handler, trigger=Pin.IRQ_FALLING)

print("Press the button to toggle the LED.")

while True:
    if interrupt_triggered:
        led.toggle()
        interrupt_triggered = False
    time.sleep(0.1)

Output

Press the button to toggle the LED.

Common Pitfalls

Common mistakes when using interrupts on Raspberry Pi Pico include:

• Doing heavy or blocking work inside the interrupt handler, which can cause missed interrupts.
• Not using Pin.PULL_UP or Pin.PULL_DOWN resistors, leading to noisy signals.
• Failing to debounce the button, causing multiple triggers from one press.
• Not declaring variables as global when modified inside the handler.

python

from machine import Pin

# Wrong: heavy work inside handler
# def button_handler(pin):
#     for i in range(1000000):
#         pass  # This blocks and is bad

# Right: just set a flag
interrupt_triggered = False
def button_handler(pin):
    global interrupt_triggered
    interrupt_triggered = True

Quick Reference

Term	Description
Pin.irq()	Attach an interrupt handler to a pin
handler	Function called on interrupt
trigger	Event type: IRQ_FALLING, IRQ_RISING, or both
Pin.PULL_UP / PULL_DOWN	Internal resistor to stabilize input
Debounce	Ignore rapid repeated triggers

Key Takeaways

Use Pin.irq() with a handler function to respond to GPIO events immediately.

Keep interrupt handlers short and avoid heavy processing inside them.

Use internal pull-up or pull-down resistors to prevent noisy signals.

Set a flag in the interrupt handler and handle logic in the main loop.

Debounce buttons to avoid multiple triggers from a single press.