38 lines
1.2 KiB
ReStructuredText
38 lines
1.2 KiB
ReStructuredText
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Debouncing a pin input
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======================
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A pin used as input from a switch or other mechanical device can have a lot
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of noise on it, rapidly changing from low to high when the switch is first
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pressed or released. This noise can be eliminated using a capacitor (a
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debouncing circuit). It can also be eliminated using a simple function that
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makes sure the value on the pin is stable.
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The following function does just this. It gets the current value of the given
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pin, and then waits for the value to change. The new pin value must be stable
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for a continuous 20ms for it to register the change. You can adjust this time
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(to say 50ms) if you still have noise. ::
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import pyb
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def wait_pin_change(pin):
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# wait for pin to change value
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# it needs to be stable for a continuous 20ms
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cur_value = pin.value()
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active = 0
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while active < 20:
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if pin.value() != cur_value:
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active += 1
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else:
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active = 0
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pyb.delay(1)
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Use it something like this::
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import pyb
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pin_x1 = pyb.Pin('X1', pyb.Pin.IN, pyb.Pin.PULL_DOWN)
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while True:
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wait_pin_change(pin_x1)
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pyb.LED(4).toggle()
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