kopia lustrzana https://github.com/micropython/micropython-lib
49 wiersze
1.4 KiB
Python
49 wiersze
1.4 KiB
Python
# MH-Z19 CO2 sensor driver for MicroPython.
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# MIT license; Copyright (c) 2018 Fredrik Strupe
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import machine
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import utime
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class TimeoutError(Exception):
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pass
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class MHZ19:
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"""MH-Z19 CO2 sensor driver"""
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def __init__(self, pin, max_value=5000):
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"""
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Args:
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pin: the pin that the PWM pin on the MH-Z19 is connected to.
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max_value: upper bound of measuring range. usually 2000 or 5000.
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"""
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self.pin = pin
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self.max_value = max_value
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def _wait_on_condition(self, cond, timeout=5000):
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start = utime.ticks_ms()
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while not cond():
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if utime.ticks_diff(utime.ticks_ms(), start) > timeout:
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raise TimeoutError
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def pwm_read(self):
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"""Read CO2 value via PWM pin.
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Reading usually takes 1-2 seconds.
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Returns:
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CO2 value in ppm (parts per million), with an accuracy of
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±(50 + result * 0.05) ppm.
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Raises:
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TimeoutError: if the reading takes more than 5 seconds.
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"""
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# Wait until a new cycle starts
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self._wait_on_condition(lambda: self.pin.value() == 0)
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# Measure high and low duration during cycle
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t_h = machine.time_pulse_us(self.pin, 1, 1500000)
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t_l = machine.time_pulse_us(self.pin, 0, 1500000)
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return self.max_value * (t_h - 2000) / (t_h + t_l - 4000)
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