Interrupt on both edges of a switch

[DracoTomes]

Hello all,

I wanna detect a physical switch being flipped on a pin with mode Pin.OUT.
From what I've researched it's impossible to have multiple Pin.irq() active at the same time, one for Pin.IRQ_FALLING and one for Pin.IRQ_RISING.
In this old Reddit post someone got it working with trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING but I couldn't get it to work on my pi pico with 1.20 thus far.
Should I just run a regular check in an asyncio coroutine?

[rkompass]

This works:

from machine import Pin
from time import sleep_ms

p0 = Pin(0, Pin.OUT)

def p_isr(pin):
    print(f"pin {pin} is now {'high' if pin() else 'low'}")

p0.irq(trigger=Pin.IRQ_RISING | Pin.IRQ_FALLING, handler=p_isr)

p0(1)
sleep_ms(20)
p0(0)
sleep_ms(20)
p0(1)
sleep_ms(20)
p0(0)

Output:

pin Pin(GPIO0, mode=OUT) is now high
pin Pin(GPIO0, mode=OUT) is now low
pin Pin(GPIO0, mode=OUT) is now high
pin Pin(GPIO0, mode=OUT) is now low

And it should work the same if the pin mode is Pin.IN.
In your ISR you might check which flank did the triggering, if you want to treat the flanks differently.

[robert-hh]

@DracoTomes I had just set up a similar test, using Pin.IN and an external source for a square wave signal. Works as expected, triggering at both slopes of the signal. I wonder why you have set the Pin to OUT mode. For detecting the state of an external switch, IN mode would be appropriate. Also, when using a mechanical switch, you must deal with contact bouncing, which will generate a fast burst of on/off states during the transition.

[DracoTomes]

It turns out I've never actually written that part of the interrupt handler but assumed I had in my head.
The reason it's in OUT mode is because the pin switches a relay that is also controlled by a hardware override - if the external switch is pressed I would like to update the internal state to reflect that.
This works flawlessly now that the pico doesn't have to read my thoughts anymore.