python-bme680/bme680/__init__.py

from .constants import *
import math
import time

class BME680(BME680Data):
    """BOSCH BME680

    Gas, pressure, temperature and humidity sensor.

    :param i2c_addr: One of I2C_ADDR_PRIMARY (0x76) or I2C_ADDR_SECONDARY (0x77)
    :param i2c_device: Optional smbus or compatible instance for facilitating i2c communications.

    """
    def __init__(self, i2c_addr=I2C_ADDR_PRIMARY, i2c_device=None):
        BME680Data.__init__(self)

        self.i2c_addr = i2c_addr
        self._i2c = i2c_device
        if self._i2c is None:
            import smbus
            self._i2c = smbus.SMBus(1)

        self.chip_id = self._get_regs(CHIP_ID_ADDR, 1)
        if self.chip_id != CHIP_ID:
            raise RuntimeError("BME680 Not Found. Invalid CHIP ID: 0x{0:02x}".format(self.chip_id))

        self.soft_reset()
        self.set_power_mode(SLEEP_MODE)

        self._get_calibration_data()

        self.set_humidity_oversample(OS_2X)
        self.set_pressure_oversample(OS_4X)
        self.set_temperature_oversample(OS_8X)
        self.set_filter(FILTER_SIZE_3)
        self.set_gas_status(ENABLE_GAS_MEAS)

        self.get_sensor_data()

    def _get_calibration_data(self):
        """Retrieves the sensor calibration data and stores it in .calibration_data"""
        calibration = self._get_regs(COEFF_ADDR1, COEFF_ADDR1_LEN)
        calibration += self._get_regs(COEFF_ADDR2, COEFF_ADDR2_LEN)

        heat_range = self._get_regs(ADDR_RES_HEAT_RANGE_ADDR, 1)
        heat_value = twos_comp(self._get_regs(ADDR_RES_HEAT_VAL_ADDR, 1), bits=8)
        sw_error = twos_comp(self._get_regs(ADDR_RANGE_SW_ERR_ADDR, 1), bits=8)

        self.calibration_data.set_from_array(calibration)
        self.calibration_data.set_other(heat_range, heat_value, sw_error)

    def soft_reset(self):
        """Initiate a soft reset"""
        self._set_regs(SOFT_RESET_ADDR, SOFT_RESET_CMD) 
        time.sleep(RESET_PERIOD / 1000.0)

    def set_humidity_oversample(self, value):
        """Set humidity oversampling
        
        A higher oversampling value means more stable sensor readings,
        with less noise and jitter.

        However each step of oversampling adds about 2ms to the latency,
        causing a slower response time to fast transients.

        :param value: Oversampling value, one of: OS_NONE, OS_1X, OS_2X, OS_4X, OS_8X, OS_16X

        """
        self.tph_settings.os_hum = value
        self._set_bits(CONF_OS_H_ADDR, OSH_MSK, OSH_POS, value)

    def get_humidity_oversample(self):
        """Get humidity oversampling"""
        return (self._get_regs(CONF_OS_H_ADDR, 1) & OSH_MSK) >> OSH_POS

    def set_pressure_oversample(self, value):
        """Set temperature oversampling
        
        A higher oversampling value means more stable sensor readings,
        with less noise and jitter.

        However each step of oversampling adds about 2ms to the latency,
        causing a slower response time to fast transients.

        :param value: Oversampling value, one of: OS_NONE, OS_1X, OS_2X, OS_4X, OS_8X, OS_16X
        
        """
        self.tph_settings.os_pres = value
        self._set_bits(CONF_T_P_MODE_ADDR, OSP_MSK, OSP_POS, value)

    def get_pressure_oversample(self):
        """Get pressure oversampling"""
        return (self._get_regs(CONF_T_P_MODE_ADDR, 1) & OSP_MSK) >> OSP_POS

    def set_temperature_oversample(self, value):
        """Set pressure oversampling
        
        A higher oversampling value means more stable sensor readings,
        with less noise and jitter.

        However each step of oversampling adds about 2ms to the latency,
        causing a slower response time to fast transients.

        :param value: Oversampling value, one of: OS_NONE, OS_1X, OS_2X, OS_4X, OS_8X, OS_16X
        
        """
        self.tph_settings.os_temp = value
        self._set_bits(CONF_T_P_MODE_ADDR, OST_MSK, OST_POS, value)

    def get_temperature_oversample(self):
        """Get temperature oversampling"""
        return (self._get_regs(CONF_T_P_MODE_ADDR, 1) & OST_MSK) >> OST_POS

    def set_filter(self, value):
        """Set IIR filter size
        
        Optionally remove short term fluctuations from the temperature and pressure readings,
        increasing their resolution but reducing their bandwidth.

        Enabling the IIR filter does not slow down the time a reading takes, but will slow
        down the BME680s response to changes in temperature and pressure.

        When the IIR filter is enabled, the temperature and pressure resolution is effectively 20bit.
        When it is disabled, it is 16bit + oversampling-1 bits.

        """
        self.tph_settings.filter = value
        self._set_bits(CONF_ODR_FILT_ADDR, FILTER_MSK, FILTER_POS, value)

    def get_filter(self):
        """Get filter size"""
        return (self._get_regs(CONF_ODR_FILT_ADDR, 1) & FILTER_MSK) >> FILTER_POS

    def select_gas_heater_profile(self, value):
        """Set current gas sensor conversion profile: 0 to 9
        
        Select one of the 10 configured heating durations/set points.
        
        """
        if value > NBCONV_MAX or value < NBCONV_MIN:
            raise ValueError("Profile '{}' should be between {} and {}".format(value, NBCONV_MIN, NBCONV_MAX))

        self.gas_settings.nb_conv = value
        self._set_bits(CONF_ODR_RUN_GAS_NBC_ADDR, NBCONV_MSK, NBCONV_POS, value)

    def get_gas_heater_profile(self):
        """Get gas sensor conversion profile: 0 to 9"""
        return self._get_regs(CONF_ODR_RUN_GAS_NBC_ADDR, 1) & NBCONV_MSK

    def set_gas_status(self, value):
        """Enable/disable gas sensor"""
        self.gas_settings.run_gas = value
        self._set_bits(CONF_ODR_RUN_GAS_NBC_ADDR, RUN_GAS_MSK, RUN_GAS_POS, value)

    def get_gas_status(self):
        """Get the current gas status"""
        return (self._get_regs(CONF_ODR_RUN_GAS_NBC_ADDR, 1) & RUN_GAS_MSK) >> RUN_GAS_POS

    def set_gas_heater_profile(self, temperature, duration, nb_profile=0):
        """Set temperature and duration of gas sensor heater
        
        :param temperature: Target temperature in degrees celsius, between 200 and 400
        :param durarion: Target duration in milliseconds, between 1 and 4032
        :param nb_profile: Target profile, between 0 and 9

        """
        self.set_gas_heater_temperature(temperature, nb_profile=nb_profile)
        self.set_gas_heater_duration(duration, nb_profile=nb_profile)

    def set_gas_heater_temperature(self, value, nb_profile=0):
        """Set gas sensor heater temperature

        :param value: Target temperature in degrees celsius, between 200 and 400
        
        When setting an nb_profile other than 0,
        make sure to select it with select_gas_heater_profile.

        """
        if nb_profile > NBCONV_MAX or value < NBCONV_MIN:
            raise ValueError("Profile '{}' should be between {} and {}".format(nb_profile, NBCONV_MIN, NBCONV_MAX))

        self.gas_settings.heatr_temp = value
        temp = self._calc_heater_resistance(self.gas_settings.heatr_temp)
        self._set_regs(RES_HEAT0_ADDR + nb_profile, temp)

    def set_gas_heater_duration(self, value, nb_profile=0):
        """Set gas sensor heater duration

        Heating durations between 1 ms and 4032 ms can be configured.
        Approximately 20-30 ms are necessary for the heater to reach the intended target temperature.

        :param value: Heating duration in milliseconds.

        When setting an nb_profile other than 0,
        make sure to select it with select_gas_heater_profile.
        
        """
        if nb_profile > NBCONV_MAX or value < NBCONV_MIN:
            raise ValueError("Profile '{}' should be between {} and {}".format(nb_profile, NBCONV_MIN, NBCONV_MAX))

        self.gas_settings.heatr_dur = value
        temp = self._calc_heater_duration(self.gas_settings.heatr_dur)
        self._set_regs(GAS_WAIT0_ADDR + nb_profile, temp)

    def set_power_mode(self, value, blocking=True):
        """Set power mode"""
        if value not in (SLEEP_MODE, FORCED_MODE):
            print("Power mode should be one of SLEEP_MODE or FORCED_MODE")

        self.power_mode = value

        self._set_bits(CONF_T_P_MODE_ADDR, MODE_MSK, MODE_POS, value)

        while blocking and self.get_power_mode() != self.power_mode:
            time.sleep(POLL_PERIOD_MS / 1000.0)

    def get_power_mode(self):
        """Get power mode"""
        self.power_mode = self._get_regs(CONF_T_P_MODE_ADDR, 1)
        return self.power_mode

    def get_sensor_data(self):
        """Get sensor data.
        
        Stores data in .data and returns True upon success.

        """
        self.set_power_mode(FORCED_MODE)

        for attempt in range(10):
            status = self._get_regs(FIELD0_ADDR, 1)

            if (status & NEW_DATA_MSK) == 0:
                time.sleep(POLL_PERIOD_MS / 1000.0)
                continue

            regs = self._get_regs(FIELD0_ADDR, FIELD_LENGTH)

            self.data.status = regs[0] & NEW_DATA_MSK
            # Contains the nb_profile used to obtain the current measurement
            self.data.gas_index = regs[0] & GAS_INDEX_MSK
            self.data.meas_index = regs[1]

            adc_pres = (regs[2] << 12) | (regs[3] << 4) | (regs[4] >> 4)
            adc_temp = (regs[5] << 12) | (regs[6] << 4) | (regs[7] >> 4)
            adc_hum = (regs[8] << 8) | regs[9]
            adc_gas_res = (regs[13] << 2) | (regs[14] >> 6)
            gas_range = regs[14] & GAS_RANGE_MSK

            self.data.status |= regs[14] & GASM_VALID_MSK
            self.data.status |= regs[14] & HEAT_STAB_MSK

            self.data.heat_stable = (self.data.status & HEAT_STAB_MSK) > 0

            temperature = self._calc_temperature(adc_temp)
            self.data.temperature = temperature / 100.0
            self.ambient_temperature = temperature # Saved for heater calc

            self.data.pressure = self._calc_pressure(adc_pres) / 1000.0
            self.data.humidity = self._calc_humidity(adc_hum) / 1000.0
            self.data.gas_resistance = self._calc_gas_resistance(adc_gas_res, gas_range)
            return True

        return False

    def _set_bits(self, register, mask, position, value):
        """Mask out and set one or more bits in a register"""
        temp = self._get_regs(register, 1)
        temp &= ~mask
        temp |= value << position
        self._set_regs(register, temp)

    def _set_regs(self, register, value):
        """Set one or more registers"""
        if isinstance(value, int):
            self._i2c.write_byte_data(self.i2c_addr, register, value)
        else:
            self._i2c.write_i2c_block_data(self.i2c_addr, register, value)

    def _get_regs(self, register, length):
        """Get one or more registers"""
        if length == 1:
            return self._i2c.read_byte_data(self.i2c_addr, register)
        else:
            return self._i2c.read_i2c_block_data(self.i2c_addr, register, length)
        
    def _calc_temperature(self, temperature_adc):
        var1 = (temperature_adc / 8) - (self.calibration_data.par_t1 * 2)
        var2 = (var1 * self.calibration_data.par_t2) / 2048
        var3 = ((var1 / 2) * (var1 / 2)) / 4096
        var3 = ((var3) * (self.calibration_data.par_t3 * 16)) / 16384

        # Save teperature data for pressure calculations
        self.calibration_data.t_fine = (var2 + var3)
        calc_temp = (((self.calibration_data.t_fine * 5) + 128) / 256)

        return calc_temp

    def _calc_pressure(self, pressure_adc):
        var1 = (self.calibration_data.t_fine / 2) - 64000
        var2 = ((var1 / 4) * (var1 / 4)) / 2048
        var2 = (var2 * self.calibration_data.par_p6) / 4
        var2 = var2 + ((var1 * self.calibration_data.par_p5) * 2)
        var2 = (var2 / 4) + (self.calibration_data.par_p4 * 65536)
        
        var1 = ((var1 / 4) * (var1 / 4)) / 8192
        var1 = ((var1 * (self.calibration_data.par_p3 * 32)) / 8) + ((self.calibration_data.par_p2 * var1) / 2)
        var1 = var1 / 262144
        var1 = ((32768 + var1) * self.calibration_data.par_p1) / 32768
        calc_pres = 1048576 - pressure_adc
        calc_pres = (calc_pres - (var2 / 4096)) * 3125
        calc_pres = (calc_pres / var1) * 2
        var1 = (self.calibration_data.par_p9 * (((calc_pres / 8) * (calc_pres / 8)) / 8192)) / 4096
        var2 = ((calc_pres / 4) * self.calibration_data.par_p8) / 8192
        var3 = ((calc_pres / 256)
                * (calc_pres / 256)
                * (calc_pres / 256)
                * self.calibration_data.par_p10) / 131072
        calc_pres = calc_pres + ((var1 + var2 + var3 + (self.calibration_data.par_p7 * 128)) / 16)

        return calc_pres

    def _calc_humidity(self, humidity_adc):
        temp_scaled = ((self.calibration_data.t_fine * 5) + 128) / 256
        var1 = (humidity_adc - ((self.calibration_data.par_h1 * 16))) \
                - (((temp_scaled * self.calibration_data.par_h3) / (100)) / 2)
        var2 = (self.calibration_data.par_h2
                * (((temp_scaled * self.calibration_data.par_h4) / (100))
                + (((temp_scaled * ((temp_scaled * self.calibration_data.par_h5) / (100))) / 64)
                / (100)) + (1 * 16384))) / 1024
        var3 = var1 * var2
        var4 = self.calibration_data.par_h6 * 128
        var4 = ((var4) + ((temp_scaled * self.calibration_data.par_h7) / (100))) / 16
        var5 = ((var3 / 16384) * (var3 / 16384)) / 1024
        var6 = (var4 * var5) / 2
        calc_hum = (((var3 + var6) / 1024) * (1000)) / 4096

        return min(max(calc_hum,0),100000)

    def _calc_gas_resistance(self, gas_res_adc, gas_range):
        var1 = ((1340 + (5 * self.calibration_data.range_sw_err)) * (lookupTable1[gas_range])) / 65536
        var2 = (((gas_res_adc * 32768) - (16777216)) + var1)
        var3 = ((lookupTable2[gas_range] * var1) / 512)
        calc_gas_res = ((var3 + (var2 / 2)) / var2)

        return calc_gas_res

    def _calc_heater_resistance(self, temperature):
        temperature = min(max(temperature,200),400)

        var1 = ((self.ambient_temperature * self.calibration_data.par_gh3) / 1000) * 256
        var2 = (self.calibration_data.par_gh1 + 784) * (((((self.calibration_data.par_gh2 + 154009) * temperature * 5) / 100) + 3276800) / 10)
        var3 = var1 + (var2 / 2)
        var4 = (var3 / (self.calibration_data.res_heat_range + 4))
        var5 = (131 * self.calibration_data.res_heat_val) + 65536
        heatr_res_x100 = (((var4 / var5) - 250) * 34)
        heatr_res = ((heatr_res_x100 + 50) / 100)

        return heatr_res

    def _calc_heater_duration(self, duration):
        if duration < 0xfc0:
            factor = 0

            while duration > 0x3f:
                duration /= 4
                factor += 1

            return int(duration + (factor * 64))

        return 0xff