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| 1 | +"""BMP180 Altimeter.""" |
| 2 | + |
| 3 | +import time |
| 4 | +import logging |
| 5 | +import struct |
| 6 | +from pslab.bus import I2CSlave |
| 7 | + |
| 8 | +# BMP180 default address |
| 9 | +_ADDRESS = 0x77 |
| 10 | + |
| 11 | +# Operating Modes |
| 12 | +_ULTRALOWPOWER = 0 |
| 13 | +_STANDARD = 1 |
| 14 | +_HIGHRES = 2 |
| 15 | +_ULTRAHIGHRES = 3 |
| 16 | + |
| 17 | +# BMP180 Registers |
| 18 | +_CAL_AC1 = 0xAA # R Calibration data (16 bits) |
| 19 | +_CAL_AC2 = 0xAC # R Calibration data (16 bits) |
| 20 | +_CAL_AC3 = 0xAE # R Calibration data (16 bits) |
| 21 | +_CAL_AC4 = 0xB0 # R Calibration data (16 bits) |
| 22 | +_CAL_AC5 = 0xB2 # R Calibration data (16 bits) |
| 23 | +_CAL_AC6 = 0xB4 # R Calibration data (16 bits) |
| 24 | +_CAL_B1 = 0xB6 # R Calibration data (16 bits) |
| 25 | +_CAL_B2 = 0xB8 # R Calibration data (16 bits) |
| 26 | +_CAL_MB = 0xBA # R Calibration data (16 bits) |
| 27 | +_CAL_MC = 0xBC # R Calibration data (16 bits) |
| 28 | +_CAL_MD = 0xBE # R Calibration data (16 bits) |
| 29 | +_CONTROL = 0xF4 |
| 30 | +_TEMPDATA = 0xF6 |
| 31 | +_PRESSUREDATA = 0xF6 |
| 32 | + |
| 33 | +# Commands |
| 34 | +_READTEMPCMD = 0x2E |
| 35 | +_READPRESSURECMD = 0x34 |
| 36 | + |
| 37 | +_logger = logging.getLogger(__name__) |
| 38 | + |
| 39 | + |
| 40 | +class BMP180(I2CSlave): |
| 41 | + """Class to interface with the BMP180 Altimeter. |
| 42 | +
|
| 43 | + Parameters |
| 44 | + ---------- |
| 45 | + mode : int, optional |
| 46 | + The mode of operation for the sensor, determining the oversampling setting. |
| 47 | + The default mode is `_HIGHRES`. This parameter affects the precision and speed |
| 48 | + of the temperature and pressure measurements. |
| 49 | +
|
| 50 | + **kwargs : dict, optional |
| 51 | + Additional keyword arguments, such as: |
| 52 | + - address (int): The I2C address of the BMP180 sensor. Default is `_ADDRESS`. |
| 53 | +
|
| 54 | + Attributes |
| 55 | + ---------- |
| 56 | + temperature : float |
| 57 | + The measured temperature in degrees Celsius. |
| 58 | +
|
| 59 | + pressure : float |
| 60 | + The measured pressure in Pa (Pascals). |
| 61 | +
|
| 62 | + altitude : float |
| 63 | + The calculated altitude in meters based on the current pressure reading |
| 64 | + and a reference sea level pressure. |
| 65 | + """ |
| 66 | + |
| 67 | + NUMPLOTS = 3 |
| 68 | + PLOTNAMES = ["Temperature", "Pressure", "Altitude"] |
| 69 | + name = "BMP180 Altimeter" |
| 70 | + |
| 71 | + def __init__(self, mode=_HIGHRES, **kwargs): |
| 72 | + self._ADDRESS = kwargs.get("address", _ADDRESS) |
| 73 | + super().__init__(self._ADDRESS) |
| 74 | + self._mode = mode |
| 75 | + |
| 76 | + # Load calibration values |
| 77 | + self._ac1 = self._read_int16(_CAL_AC1) |
| 78 | + self._ac2 = self._read_int16(_CAL_AC2) |
| 79 | + self._ac3 = self._read_int16(_CAL_AC3) |
| 80 | + self._ac4 = self._read_uint16(_CAL_AC4) |
| 81 | + self._ac5 = self._read_uint16(_CAL_AC5) |
| 82 | + self._ac6 = self._read_uint16(_CAL_AC6) |
| 83 | + self._b1 = self._read_int16(_CAL_B1) |
| 84 | + self._b2 = self._read_int16(_CAL_B2) |
| 85 | + self._mb = self._read_int16(_CAL_MB) |
| 86 | + self._mc = self._read_int16(_CAL_MC) |
| 87 | + self._md = self._read_int16(_CAL_MD) |
| 88 | + |
| 89 | + _logger.debug(f"ac1: {self._ac1}") |
| 90 | + _logger.debug(f"ac2: {self._ac2}") |
| 91 | + _logger.debug(f"ac3: {self._ac3}") |
| 92 | + _logger.debug(f"ac4: {self._ac4}") |
| 93 | + _logger.debug(f"ac5: {self._ac5}") |
| 94 | + _logger.debug(f"ac6: {self._ac6}") |
| 95 | + _logger.debug(f"b1: {self._b1}") |
| 96 | + _logger.debug(f"b2: {self._b2}") |
| 97 | + _logger.debug(f"mb: {self._mb}") |
| 98 | + _logger.debug(f"mc: {self._mc}") |
| 99 | + _logger.debug(f"md: {self._md}") |
| 100 | + |
| 101 | + def _read_int16(self, addr): |
| 102 | + BE_INT16 = struct.Struct(">h") # signed short, big endian |
| 103 | + return BE_INT16.unpack(self.read(2, addr))[0] |
| 104 | + |
| 105 | + def _read_uint16(self, addr): |
| 106 | + BE_UINT16 = struct.Struct(">H") # unsigned short, big endian |
| 107 | + return BE_UINT16.unpack(self.read(2, addr))[0] |
| 108 | + |
| 109 | + def _read_raw_temperature(self): |
| 110 | + """Read the raw temperature from the sensor.""" |
| 111 | + self.write([_READTEMPCMD], _CONTROL) |
| 112 | + time.sleep(0.005) |
| 113 | + raw = self._read_uint16(_TEMPDATA) |
| 114 | + return raw |
| 115 | + |
| 116 | + @property |
| 117 | + def temperature(self): |
| 118 | + """Get the actual temperature in degrees celsius.""" |
| 119 | + ut = self._read_raw_temperature() |
| 120 | + # Calculations from section 3.5 of the datasheet |
| 121 | + x1 = ((ut - self._ac6) * self._ac5) >> 15 |
| 122 | + x2 = (self._mc << 11) // (x1 + self._md) |
| 123 | + b5 = x1 + x2 |
| 124 | + temp = ((b5 + 8) >> 4) / 10.0 |
| 125 | + return temp |
| 126 | + |
| 127 | + @property |
| 128 | + def oversampling(self): |
| 129 | + """oversampling : int |
| 130 | + The oversampling setting used by the sensor. This attribute is settable and |
| 131 | + determines the trade-off between measurement accuracy and speed. Possible values |
| 132 | + include `_ULTRALOWPOWER`, `_STANDARD`, `_HIGHRES`, and `_ULTRAHIGHRES`. |
| 133 | + """ |
| 134 | + return self._mode |
| 135 | + |
| 136 | + @oversampling.setter |
| 137 | + def oversampling(self, value): |
| 138 | + self._mode = value |
| 139 | + |
| 140 | + def _read_raw_pressure(self): |
| 141 | + """Read the raw pressure level from the sensor.""" |
| 142 | + delays = [0.005, 0.008, 0.014, 0.026] |
| 143 | + self.write([_READPRESSURECMD + (self._mode << 6)], _CONTROL) |
| 144 | + time.sleep(delays[self._mode]) |
| 145 | + msb = self.read_byte(_PRESSUREDATA) & 0xFF |
| 146 | + lsb = self.read_byte(_PRESSUREDATA + 1) & 0xFF |
| 147 | + xlsb = self.read_byte(_PRESSUREDATA + 2) & 0xFF |
| 148 | + raw = ((msb << 16) + (lsb << 8) + xlsb) >> (8 - self._mode) |
| 149 | + return raw |
| 150 | + |
| 151 | + @property |
| 152 | + def pressure(self): |
| 153 | + """Get the actual pressure in Pascals.""" |
| 154 | + ut = self._read_raw_temperature() |
| 155 | + up = self._read_raw_pressure() |
| 156 | + # Calculations from section 3.5 of the datasheet |
| 157 | + x1 = ((ut - self._ac6) * self._ac5) >> 15 |
| 158 | + x2 = (self._mc << 11) // (x1 + self._md) |
| 159 | + b5 = x1 + x2 |
| 160 | + # Pressure Calculations |
| 161 | + b6 = b5 - 4000 |
| 162 | + x1 = (self._b2 * (b6 * b6) >> 12) >> 11 |
| 163 | + x2 = (self._ac2 * b6) >> 11 |
| 164 | + x3 = x1 + x2 |
| 165 | + b3 = (((self._ac1 * 4 + x3) << self._mode) + 2) // 4 |
| 166 | + x1 = (self._ac3 * b6) >> 13 |
| 167 | + x2 = (self._b1 * ((b6 * b6) >> 12)) >> 16 |
| 168 | + x3 = ((x1 + x2) + 2) >> 2 |
| 169 | + b4 = (self._ac4 * (x3 + 32768)) >> 15 |
| 170 | + b7 = (up - b3) * (50000 >> self._mode) |
| 171 | + if b7 < 0x80000000: |
| 172 | + p = (b7 * 2) // b4 |
| 173 | + else: |
| 174 | + p = (b7 // b4) * 2 |
| 175 | + x1 = (p >> 8) * (p >> 8) |
| 176 | + x1 = (x1 * 3038) >> 16 |
| 177 | + x2 = (-7357 * p) >> 16 |
| 178 | + pres = p + ((x1 + x2 + 3791) >> 4) |
| 179 | + return pres |
| 180 | + |
| 181 | + @property |
| 182 | + def altitude(self): |
| 183 | + # Calculation from section 3.6 of datasheet |
| 184 | + pressure = float(self.pressure) |
| 185 | + alt = 44330.0 * (1.0 - pow(pressure / 101325.0, (1.0 / 5.255))) |
| 186 | + return alt |
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