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Debounced switch using pin and timer IRQs on MicroPython
#
# inspired by: https://forum.micropython.org/viewtopic.php?t=1938#p10931
#
import micropython
try:
from machine import Timer
timer_init = lambda t, p, cb: t.init(period=p, callback=cb)
except ImportError:
from pyb import Timer
timer_init = lambda t, p, cb: t.init(freq=1000 // p, callback=cb)
# uncomment when debugging callback problems
#micropython.alloc_emergency_exception_buf(100)
class DebouncedSwitch:
def __init__(self, sw, cb, arg=None, delay=50, tid=4):
self.sw = sw
# Create references to bound methods beforehand
# http://docs.micropython.org/en/latest/pyboard/library/micropython.html#micropython.schedule
self._sw_cb = self.sw_cb
self._tim_cb = self.tim_cb
self._set_cb = getattr(self.sw, 'callback', None) or self.sw.irq
self.delay = delay
self.tim = Timer(tid)
self.callback(cb, arg)
def sw_cb(self, pin=None):
self._set_cb(None)
timer_init(self.tim, self.delay, self._tim_cb)
def tim_cb(self, tim):
tim.deinit()
if self.sw():
micropython.schedule(self.cb, self.arg)
self._set_cb(self._sw_cb if self.cb else None)
def callback(self, cb, arg=None):
self.tim.deinit()
self.cb = cb
self.arg = arg
self._set_cb(self._sw_cb if cb else None)
def test_pyb(ledno=1):
import pyb
sw = pyb.Switch()
led = pyb.LED(ledno)
return DebouncedSwitch(sw, lambda l: l.toggle(), led)
def test_machine(swpin=2, ledpin=16):
from machine import Pin
sw = Pin(swpin, Pin.IN)
led = Pin(ledpin, Pin.OUT)
return DebouncedSwitch(sw, lambda l: l.value(not l.value()), led)
@adamoell
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Hi Christopher,

I would like to use this code pretty much as-is in a small GPLv3 licensed project I'm working on (a free Laser Tag system). There doesn't seem to be a copyright notice; could you confirm that you're OK with me using your code in this way?

Thanks so much!
Adam

@SpotlightKid
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Author

Yes, sure, go ahead. I hereby declare this code to be licensed under the MIT License, Copyright 2017, Christopher Arndt.

@adamoell
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adamoell commented Oct 2, 2021

Ah, that's fantastic Christopher. I'll copy & paste that into the header :-)

@edwinm
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edwinm commented Aug 8, 2022

This is the best Micropython debounce code I could find. Others are using delays inside IRQ’s (wrong) or calling the callbacks directly, without using schedule (wrong). Thank for sharing! Maybe, one day, it will have its own repo with documentation and demo code 😉

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