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树莓派系列教程12：I2C总线控制BMP180

2016-3-28 13:57:53 6316 I2C

0 本帖最后由 kaloha 于 2017-5-15 17:49 编辑 ---------------------------------------------------------------------------------------- 本文转自：www.waveshare.net/study/article-605-1.html ---------------------------------------------------------------------------------------- 通过上一章，相信各位对树莓派I2C编程有一定的了解了，今天我们继续使用I2C来控制BMP180压强传感器。BMP180压强传感器操作原理比较简单，开机先通过I2C读取出AC1,AC2,AC3,AC4,AC5,AC6,B1,B2,MB,MC,MD等寄存器的值，这些寄存器的值作为校准时使用。如何读取温度寄存器，压强寄存器的值，根据下图公式算出测得的当前温度和压强。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 复制代码主文件bmp180_example.py #!/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: %.2fn" % altitude time.sleep(1) 复制代码 2
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