Debounced switch using pin and timer IRQs on MicroPython

debounce.py

#
# 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)

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

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

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

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 😉