bh1750.py

   1 # https://github.com/flrrth/pico-bh1750
   2
   3 import math
   4
   5 from micropython import const
   6 from utime import sleep_ms
   7
   8
   9 class BH1750:
  10     """Class for the BH1750 digital Ambient Light Sensor
  11
  12     The datasheet can be found at https://components101.com/sites/default/files/component_datasheet/BH1750.pdf
  13     """
  14
  15     MEASUREMENT_MODE_CONTINUOUSLY = const(1)
  16     MEASUREMENT_MODE_ONE_TIME = const(2)
  17
  18     RESOLUTION_HIGH = const(0)
  19     RESOLUTION_HIGH_2 = const(1)
  20     RESOLUTION_LOW = const(2)
  21
  22     MEASUREMENT_TIME_DEFAULT = const(69)
  23     MEASUREMENT_TIME_MIN = const(31)
  24     MEASUREMENT_TIME_MAX = const(254)
  25
  26     def __init__(self, address, i2c):
  27         self._address = address
  28         self._i2c = i2c
  29         self._measurement_mode = BH1750.MEASUREMENT_MODE_ONE_TIME
  30         self._resolution = BH1750.RESOLUTION_HIGH
  31         self._measurement_time = BH1750.MEASUREMENT_TIME_DEFAULT
  32
  33         self._write_measurement_time()
  34         self._write_measurement_mode()
  35
  36     def configure(self, measurement_mode: int, resolution: int, measurement_time: int):
  37         """Configures the BH1750.
  38
  39         Keyword arguments:
  40         measurement_mode -- measure either continuously or once
  41         resolution -- return measurements in either high, high2 or low resolution
  42         measurement_time -- the duration of a single measurement
  43         """
  44         if measurement_time not in range(BH1750.MEASUREMENT_TIME_MIN, BH1750.MEASUREMENT_TIME_MAX + 1):
  45             raise ValueError("measurement_time must be between {0} and {1}"
  46                              .format(BH1750.MEASUREMENT_TIME_MIN, BH1750.MEASUREMENT_TIME_MAX))
  47
  48         self._measurement_mode = measurement_mode
  49         self._resolution = resolution
  50         self._measurement_time = measurement_time
  51
  52         self._write_measurement_time()
  53         self._write_measurement_mode()
  54
  55     def _write_measurement_time(self):
  56         buffer = bytearray(1)
  57
  58         high_bit = 1 << 6 | self._measurement_time >> 5
  59         low_bit = 3 << 5 | (self._measurement_time << 3) >> 3
  60
  61         buffer[0] = high_bit
  62         self._i2c.writeto(self._address, buffer)
  63
  64         buffer[0] = low_bit
  65         self._i2c.writeto(self._address, buffer)
  66
  67     def _write_measurement_mode(self):
  68         buffer = bytearray(1)
  69
  70         buffer[0] = self._measurement_mode << 4 | self._resolution
  71         self._i2c.writeto(self._address, buffer)
  72         sleep_ms(24 if self._measurement_time == BH1750.RESOLUTION_LOW else 180)
  73
  74     def reset(self):
  75         """Clear the illuminance data register."""
  76         self._i2c.writeto(self._address, bytearray(b'\x07'))
  77
  78     def power_on(self):
  79         """Powers on the BH1750."""
  80         self._i2c.writeto(self._address, bytearray(b'\x01'))
  81
  82     def power_off(self):
  83         """Powers off the BH1750."""
  84         self._i2c.writeto(self._address, bytearray(b'\x00'))
  85
  86     @property
  87     def measurement(self) -> float:
  88         """Returns the latest measurement."""
  89         if self._measurement_mode == BH1750.MEASUREMENT_MODE_ONE_TIME:
  90             self._write_measurement_mode()
  91
  92         buffer = bytearray(2)
  93         self._i2c.readfrom_into(self._address, buffer)
  94         lux = (buffer[0] << 8 | buffer[1]) / (1.2 * (BH1750.MEASUREMENT_TIME_DEFAULT / self._measurement_time))
  95
  96         if self._resolution == BH1750.RESOLUTION_HIGH_2:
  97             return lux / 2
  98         else:
  99             return lux
 100
 101     def measurements(self) -> float:
 102         """This is a generator function that continues to provide the latest measurement. Because the measurement time
 103         is greatly affected by resolution and the configured measurement time, this function attemts to calculate the
 104         appropriate sleep time between measurements.
 105
 106         Example usage:
 107
 108         for measurement in bh1750.measurements():  # bh1750 is an instance of this class
 109             print(measurement)
 110         """
 111         while True:
 112             yield self.measurement
 113
 114             if self._measurement_mode == BH1750.MEASUREMENT_MODE_CONTINUOUSLY:
 115                 base_measurement_time = 16 if self._measurement_time == BH1750.RESOLUTION_LOW else 120
 116                 sleep_ms(math.ceil(base_measurement_time * self._measurement_time / BH1750.MEASUREMENT_TIME_DEFAULT))