General • Re: Pi Pico W - DHT11 - wrong number of pulses ONLY after 2 reads

Code:

import arrayimport micropythonimport utimefrom machine import Pinfrom micropython import const class InvalidChecksum(Exception):    pass class InvalidPulseCount(Exception):    pass MAX_UNCHANGED = const(100)MIN_INTERVAL_US = const(200000)HIGH_LEVEL = const(50)EXPECTED_PULSES = const(84) class DHT11:    _temperature: float    _humidity: float     def __init__(self, pin):        self._pin = pin        self._last_measure = utime.ticks_us()        self._temperature = -1        self._humidity = -1     def measure(self):        current_ticks = utime.ticks_us()        if utime.ticks_diff(current_ticks, self._last_measure) < MIN_INTERVAL_US and (            self._temperature > -1 or self._humidity > -1        ):            # Less than a second since last read, which is too soon according            # to the datasheet            return         self._send_init_signal()        pulses = self._capture_pulses()        buffer = self._convert_pulses_to_buffer(pulses)        self._verify_checksum(buffer)         self._humidity = buffer[0] + buffer[1] / 10        self._temperature = buffer[2] + buffer[3] / 10        self._last_measure = utime.ticks_us()     @property    def humidity(self):        self.measure()        return self._humidity     @property    def temperature(self):        self.measure()        return self._temperature     def _send_init_signal(self):        self._pin.init(Pin.OUT, Pin.PULL_DOWN)        self._pin.value(1)        utime.sleep_ms(50)        self._pin.value(0)        utime.sleep_ms(18)     @micropython.native    def _capture_pulses(self):        pin = self._pin        pin.init(Pin.IN, Pin.PULL_UP)         val = 1        idx = 0        transitions = bytearray(EXPECTED_PULSES)        unchanged = 0        timestamp = utime.ticks_us()         while unchanged < MAX_UNCHANGED:            if val != pin.value():                if idx >= EXPECTED_PULSES:                    raise InvalidPulseCount(                        "Got more than {} pulses".format(EXPECTED_PULSES)                    )                now = utime.ticks_us()                transitions[idx] = now - timestamp                timestamp = now                idx += 1                 val = 1 - val                unchanged = 0            else:                unchanged += 1        pin.init(Pin.OUT, Pin.PULL_DOWN)        if idx != EXPECTED_PULSES:            raise InvalidPulseCount(                "Expected {} but got {} pulses".format(EXPECTED_PULSES, idx)            )        return transitions[4:]     def _convert_pulses_to_buffer(self, pulses):        """Convert a list of 80 pulses into a 5 byte buffer        The resulting 5 bytes in the buffer will be:            0: Integral relative humidity data            1: Decimal relative humidity data            2: Integral temperature data            3: Decimal temperature data            4: Checksum        """        # Convert the pulses to 40 bits        binary = 0        for idx in range(0, len(pulses), 2):            binary = binary << 1 | int(pulses[idx] > HIGH_LEVEL)         # Split into 5 bytes        buffer = array.array("B")        for shift in range(4, -1, -1):            buffer.append(binary >> shift * 8 & 0xFF)        return buffer     def _verify_checksum(self, buffer):        # Calculate checksum        checksum = 0        for buf in buffer[0:4]:            checksum += buf        if checksum & 0xFF != buffer[4]:            raise InvalidChecksum()