树莓派系列教程12：I2C总线控制BMP180

本章主要讲解python程序，使大家熟悉python编程。关于bcm2835,wiringpi程序具体可参看Pioneer600示例程序。

驱动文件bmp180.py

import time
import smbus

# BMP085 default address.
BMP180_I2CADDR           = 0x77

# Operating Modes
BMP180_ULTRALOWPOWER     = 0
BMP180_STANDARD          = 1
BMP180_HIGHRES           = 2
BMP180_ULTRAHIGHRES      = 3

# BMP085 Registers
BMP180_CAL_AC1           = 0xAA  # R   Calibration data (16 bits)
BMP180_CAL_AC2           = 0xAC  # R   Calibration data (16 bits)
BMP180_CAL_AC3           = 0xAE  # R   Calibration data (16 bits)
BMP180_CAL_AC4           = 0xB0  # R   Calibration data (16 bits)
BMP180_CAL_AC5           = 0xB2  # R   Calibration data (16 bits)
BMP180_CAL_AC6           = 0xB4  # R   Calibration data (16 bits)
BMP180_CAL_B1            = 0xB6  # R   Calibration data (16 bits)
BMP180_CAL_B2            = 0xB8  # R   Calibration data (16 bits)
BMP180_CAL_MB            = 0xBA  # R   Calibration data (16 bits)
BMP180_CAL_MC            = 0xBC  # R   Calibration data (16 bits)
BMP180_CAL_MD            = 0xBE  # R   Calibration data (16 bits)
BMP180_CONTROL           = 0xF4
BMP180_TEMPDATA          = 0xF6
BMP180_PRESSUREDATA      = 0xF6

# Commands
BMP180_READTEMPCMD       = 0x2E
BMP180_READPRESSURECMD   = 0x34


class BMP180(object):
    def __init__(self, address=BMP180_I2CADDR, mode=BMP180_STANDARD):
        self._mode = mode
        self._address = address
        self._bus = smbus.SMBus(1)
        # Load calibration values.
        self._load_calibration()
    def _read_byte(self,cmd):
        return self._bus.read_byte_data(self._address,cmd)

    def _read_u16(self,cmd):
        MSB = self._bus.read_byte_data(self._address,cmd)
        LSB = self._bus.read_byte_data(self._address,cmd+1)
        return (MSB << 8) + LSB

    def _read_s16(self,cmd):
        result = self._read_u16(cmd)
        if result > 32767:result -= 65536
        return result

    def _write_byte(self,cmd,val):
        self._bus.write_byte_data(self._address,cmd,val)

    def _load_calibration(self):
        "load calibration"
        self.cal_AC1 = self._read_s16(BMP180_CAL_AC1)   # INT16
        self.cal_AC2 = self._read_s16(BMP180_CAL_AC2)   # INT16
        self.cal_AC3 = self._read_s16(BMP180_CAL_AC3)   # INT16
        self.cal_AC4 = self._read_u16(BMP180_CAL_AC4)   # UINT16
        self.cal_AC5 = self._read_u16(BMP180_CAL_AC5)   # UINT16
        self.cal_AC6 = self._read_u16(BMP180_CAL_AC6)   # UINT16
        self.cal_B1  = self._read_s16(BMP180_CAL_B1)     # INT16
        self.cal_B2  = self._read_s16(BMP180_CAL_B2)     # INT16
        self.cal_MB  = self._read_s16(BMP180_CAL_MB)     # INT16
        self.cal_MC  = self._read_s16(BMP180_CAL_MC)     # INT16
        self.cal_MD  = self._read_s16(BMP180_CAL_MD)     # INT16

    def read_raw_temp(self):
        """Reads the raw (uncompensated) temperature from the sensor."""
        self._write_byte(BMP180_CONTROL, BMP180_READTEMPCMD)
        time.sleep(0.005)  # Wait 5ms
        MSB = self._read_byte(BMP180_TEMPDATA)
        LSB = self._read_byte(BMP180_TEMPDATA+1)
        raw = (MSB << 8) + LSB
        return raw

    def read_raw_pressure(self):
        """Reads the raw (uncompensated) pressure level from the sensor."""
        self._write_byte(BMP180_CONTROL, BMP180_READPRESSURECMD + (self._mode << 6))
        if self._mode == BMP180_ULTRALOWPOWER:
            time.sleep(0.005)
        elif self._mode == BMP180_HIGHRES:
            time.sleep(0.014)
        elif self._mode == BMP180_ULTRAHIGHRES:
            time.sleep(0.026)
        else:
            time.sleep(0.008)
        MSB = self._read_byte(BMP180_PRESSUREDATA)
        LSB = self._read_byte(BMP180_PRESSUREDATA+1)
        XLSB = self._read_byte(BMP180_PRESSUREDATA+2)
        raw = ((MSB << 16) + (LSB << 8) + XLSB) >> (8 - self._mode)
        return raw

    def read_temperature(self):
        """Gets the compensated temperature in degrees celsius."""
        UT = self.read_raw_temp()

        X1 = ((UT - self.cal_AC6) * self.cal_AC5) >> 15
        X2 = (self.cal_MC << 11) / (X1 + self.cal_MD)
        B5 = X1 + X2
        temp = ((B5 + 8) >> 4) / 10.0
        return temp

    def read_pressure(self):
        """Gets the compensated pressure in Pascals."""
        UT = self.read_raw_temp()
        UP = self.read_raw_pressure()


        X1 = ((UT - self.cal_AC6) * self.cal_AC5) >> 15
        X2 = (self.cal_MC << 11) / (X1 + self.cal_MD)
        B5 = X1 + X2

        # Pressure Calculations
        B6 = B5 - 4000
        X1 = (self.cal_B2 * (B6 * B6) >> 12) >> 11
        X2 = (self.cal_AC2 * B6) >> 11
        X3 = X1 + X2
        B3 = (((self.cal_AC1 * 4 + X3) << self._mode) + 2) / 4

        X1 = (self.cal_AC3 * B6) >> 13
        X2 = (self.cal_B1 * ((B6 * B6) >> 12)) >> 16
        X3 = ((X1 + X2) + 2) >> 2
        B4 = (self.cal_AC4 * (X3 + 32768)) >> 15
        B7 = (UP - B3) * (50000 >> self._mode)

        if B7 < 0x80000000:
            p = (B7 * 2) / B4
        else:
            p = (B7 / B4) * 2
        X1 = (p >> 8) * (p >> 8)
        X1 = (X1 * 3038) >> 16
        X2 = (-7357 * p) >> 16

        p = p + ((X1 + X2 + 3791) >> 4)
        return p

    def read_altitude(self, sealevel_pa=101325.0):
        """Calculates the altitude in meters."""
        # Calculation taken straight from section 3.6 of the datasheet.
        pressure = float(self.read_pressure())
        altitude = 44330.0 * (1.0 - pow(pressure / sealevel_pa, (1.0/5.255)))
        return altitude

    def read_sealevel_pressure(self, altitude_m=0.0):
        """Calculates the pressure at sealevel when given a known altitude in
        meters. Returns a value in Pascals."""
        pressure = float(self.read_pressure())
        p0 = pressure / pow(1.0 - altitude_m/44330.0, 5.255)
        return p0

#!/usr/bin/python

import time
from BMP180 import BMP180

# Initialise the BMP085 and use STANDARD mode (default value)
# bmp = BMP085(0x77, debug=True)
bmp = BMP180()

# To specify a different operating mode, uncomment one of the following:
# bmp = BMP085(0x77, 0)  # ULTRALOWPOWER Mode
# bmp = BMP085(0x77, 1)  # STANDARD Mode
# bmp = BMP085(0x77, 2)  # HIRES Mode
# bmp = BMP085(0x77, 3)  # ULTRAHIRES Mode
while True:
    temp = bmp.read_temperature()

# Read the current barometric pressure level
    pressure = bmp.read_pressure()

# To calculate altitude based on an estimated mean sea level pressure
# (1013.25 hPa) call the function as follows, but this won't be very accurate
    altitude = bmp.read_altitude()

# To specify a more accurate altitude, enter the correct mean sea level
# pressure level.  For example, if the current pressure level is 1023.50 hPa
# enter 102350 since we include two decimal places in the integer value
# altitude = bmp.readAltitude(102350)

    print "Temperature: %.2f C" % temp
    print "Pressure:    %.2f hPa" % (pressure / 100.0)
    print "Altitude:     %.2f\n" % altitude
time.sleep(1)