working library & example

Author: ladyada

adafruit_htu31d.py

@@ -27,7 +27,134 @@
 
 """
 
-# imports
+import time
+import struct
+import adafruit_bus_device.i2c_device as i2c_device
+from micropython import const
 
 __version__ = "0.0.0-auto.0"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_HTU31D.git"
+
+_HTU31D_DEFAULT_ADDR = const(0x40)  # HTU31D default I2C Address
+
+_HTU31D_READSERIAL = const(0x0A)  # Read Out of Serial Register
+_HTU31D_SOFTRESET = const(0x1E)  # Soft Reset
+_HTU31D_HEATERON = const(0x04) # Enable heater
+_HTU31D_HEATEROFF = const(0x02) # Disable heater 
+_HTU31D_CONVERSION = const(0x40) # Start a conversion
+_HTU31D_READTEMPHUM = const(0x00) # Read the conversion values
+
+class HTU31D:
+    """
+    A driver for the HTU31D temperature and humidity sensor.
+
+    :param ~busio.I2C i2c_bus: The `busio.I2C` object to use. This is the only required parameter.
+
+    """
+
+    def __init__(self, i2c_bus):
+        self.i2c_device = i2c_device.I2CDevice(i2c_bus, _HTU31D_DEFAULT_ADDR)
+        self._buffer = bytearray(6)
+        self.reset()
+
+    @property
+    def serial_number(self):
+        """The unique 32-bit serial number"""
+        self._buffer[0] = _HTU31D_READSERIAL
+        with self.i2c_device as i2c:
+            i2c.write_then_readinto(self._buffer, self._buffer, out_end=1, in_end=4)
+        ser = struct.unpack(">I", self._buffer[0:4])
+        return ser
+
+    def reset(self):
+        """Perform a soft reset of the sensor, resetting all settings to their power-on defaults"""
+        self._buffer[0] = _HTU31D_SOFTRESET
+        with self.i2c_device as i2c:
+            i2c.write(self._buffer, end=1)
+        time.sleep(0.015)
+
+    @property
+    def heater(self):
+        """The current sensor heater mode"""
+        return self._heater
+
+    @heater.setter
+    def heater(self, new_mode):
+        # check its a boolean
+        if (new_mode != True) and (new_mode != False):
+            raise AttributeError("Heater mode must be boolean")
+        # cache the mode
+        self._heater = new_mode
+        # decide the command!
+        if new_mode:
+            self._buffer[0] = _HTU31D_HEATERON
+        else:
+            self._buffer[0] = _HTU31D_HEATEROFF
+        with self.i2c_device as i2c:
+            i2c.write(self._buffer, end=1)
+
+    @property
+    def relative_humidity(self):
+        """The current relative humidity in % rH"""
+        return self.measurements[1]
+
+    @property
+    def temperature(self):
+        """The current temperature in degrees celsius"""
+        return self.measurements[0]
+
+    @property
+    def measurements(self):
+        """both `temperature` and `relative_humidity`, read simultaneously"""
+
+        temperature = None
+        humidity = None
+
+        self._buffer[0] = _HTU31D_CONVERSION
+        with self.i2c_device as i2c:
+            i2c.write(self._buffer, end=1)
+
+        # wait conversion time
+        time.sleep(0.02)
+
+        self._buffer[0] = _HTU31D_READTEMPHUM
+        with self.i2c_device as i2c:
+            i2c.write_then_readinto(self._buffer, self._buffer, out_end=1)
+
+        # separate the read data
+        temperature, temp_crc, humidity, humidity_crc = struct.unpack_from(">HBHB", self._buffer)
+
+        # check CRC of bytes
+        if temp_crc != self._crc(temperature) or humidity_crc != self._crc(
+            humidity
+        ):
+            raise RuntimeError("Invalid CRC calculated")
+
+        # decode data into human values:
+        # convert bytes into 16-bit signed integer
+        # convert the LSB value to a human value according to the datasheet
+        temperature = -45.0 + 175.0 * temperature / 65535.0
+
+        # repeat above steps for humidity data
+        humidity = -6.0 + 125.0 * humidity / 65535.0
+        humidity = max(min(humidity, 100), 0)
+
+        return (temperature, humidity)
+
+    @staticmethod
+    def _crc(value):
+        polynom = 0x988000   # x^8 + x^5 + x^4 + 1
+        msb = 0x800000
+        mask = 0xFF8000
+        result = value << 8  # Pad with zeros as specified in spec
+
+        while msb != 0x80:
+            # Check if msb of current value is 1 and apply XOR mask
+            if result & msb:
+                result = ((result ^ polynom) & mask) | (result & ~mask)
+            # Shift by one
+            msb >>= 1
+            mask >>= 1
+            polynom >>= 1
+
+        return result

examples/htu31d_simpletest.py

@@ -1,3 +1,24 @@
-# SPDX-FileCopyrightText: 2017 Scott Shawcroft, written for Adafruit Industries
+# SPDX-FileCopyrightText: Copyright (c) 2020 ladyada for Adafruit Industries
 #
-# SPDX-License-Identifier: Unlicense
+# SPDX-License-Identifier: MIT
+
+import time
+import busio
+import board
+import adafruit_htu31d
+
+i2c = busio.I2C(board.SCL, board.SDA)
+htu = adafruit_htu31d.HTU31D(i2c)
+print("Found HTU31D with serial number", hex(htu.serial_number))
+
+htu.heater = True
+print("Heater is on?", htu.heater)
+htu.heater = False
+print("Heater is on?", htu.heater)
+
+while True:
+    temperature, relative_humidity = htu.measurements
+    print("Temperature: %0.1f C" % temperature)
+    print("Humidity: %0.1f %%" % relative_humidity)
+    print("")
+    time.sleep(1)