Initial commit

2026-03-19 16:05:34 +01:00
commit 29c698a12a
8 changed files with 309 additions and 0 deletions
@@ -0,0 +1,95 @@
+# dht20.py
+
+from machine import I2C
+from utime import sleep_ms
+
+
+class DHT20:
+    """Class for the DHT20 Temperature and Humidity Sensor."""
+
+    def __init__(self, address: int, i2c: I2C):
+        self._address = address
+        self._i2c = i2c
+        sleep_ms(100)
+
+        if not self.is_ready:
+            self._initialize()
+            sleep_ms(100)
+
+            if not self.is_ready:
+                raise RuntimeError("Could not initialize the DHT20.")
+
+    @property
+    def is_ready(self) -> bool:
+        """Check if the DHT20 is ready."""
+        self._i2c.writeto(self._address, bytearray(b"\x71"))
+        return self._i2c.readfrom(self._address, 1)[0] == 0x18
+
+    def _initialize(self):
+        buffer = bytearray(b"\x00\x00")
+        self._i2c.writeto_mem(self._address, 0x1B, buffer)
+        self._i2c.writeto_mem(self._address, 0x1C, buffer)
+        self._i2c.writeto_mem(self._address, 0x1E, buffer)
+
+    def _trigger_measurements(self):
+        self._i2c.writeto_mem(self._address, 0xAC, bytearray(b"\x33\x00"))
+
+    def _read_measurements(self):
+        buffer = self._i2c.readfrom(self._address, 7)
+        return buffer, buffer[0] & 0x80 == 0
+
+    def _crc_check(self, input_bitstring: str, check_value: str) -> bool:
+        """Calculate the CRC check of a string of bits using a fixed polynomial."""
+
+        polynomial_bitstring = "100110001"
+        len_input = len(input_bitstring)
+        initial_padding = check_value
+        input_padded_array = list(input_bitstring + initial_padding)
+
+        while "1" in input_padded_array[:len_input]:
+            cur_shift = input_padded_array.index("1")
+
+            for i in range(len(polynomial_bitstring)):
+                input_padded_array[cur_shift + i] = str(
+                    int(polynomial_bitstring[i] != input_padded_array[cur_shift + i])
+                )
+
+        return "1" not in "".join(input_padded_array)[len_input:]
+
+    @property
+    def measurements(self) -> dict:
+        """Get the temperature (°C) and relative humidity (%RH).
+
+        Returns a dictionary with the most recent measurements.
+
+        't': temperature (°C),
+        't_adc': the 'raw' temperature as produced by the ADC,
+        'rh': relative humidity (%RH),
+        'rh_adc': the 'raw' relative humidity as produced by the ADC,
+        'crc_ok': indicates if the data was received correctly
+        """
+        self._trigger_measurements()
+        sleep_ms(50)
+
+        data = self._read_measurements()
+        retry = 3
+
+        while not data[1]:
+            if not retry:
+                raise RuntimeError("Could not read measurements from the DHT20.")
+
+            sleep_ms(10)
+            data = self._read_measurements()
+            retry -= 1
+
+        buffer = data[0]
+        s_rh = buffer[1] << 12 | buffer[2] << 4 | buffer[3] >> 4
+        s_t = (buffer[3] << 16 | buffer[4] << 8 | buffer[5]) & 0xFFFFF
+        rh = (s_rh / 2**20) * 100
+        t = ((s_t / 2**20) * 200) - 50
+        crc_ok = self._crc_check(
+            f"{buffer[0] ^ 0xFF:08b}{buffer[1]:08b}{buffer[2]:08b}{buffer[3]:08b}{buffer[4]:08b}{buffer[5]:08b}",
+            f"{buffer[6]:08b}",
+        )
+
+        return {"t": t, "t_adc": s_t, "rh": rh, "rh_adc": s_rh, "crc_ok": crc_ok}