中職擴(kuò)展資源包資料：樹莓派系列教程12：I2C總線控制BMP180

1、通過上一章，相信各位對樹莓派I2C編程有一定的了解了，今天我們繼續(xù)使用I2C來控制 BMP180壓強(qiáng)傳感器。BMP180壓強(qiáng)傳感器操作原理比較簡單，開機(jī)先通過I2C讀取出 AC1,AC2,AC3,AC4,AC5,AC6,B1,B2,MB,MC,MD 等寄存器的值， 這些寄存器的值作為校準(zhǔn) 時(shí)使用。如何讀取溫度寄存器，壓強(qiáng)寄存器的值，根據(jù)下圖公式算出測得的當(dāng)前溫度和壓強(qiáng)。 xw sn 玄” 售 由 2383 327士 sam 23言 聖呂 d -32%I6B NIa6B 5*1 q4 WJS _s uns-JSned 4=ui- LrMIgnrtIZLstiori; LmX2 2i-.5WTA

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3、葦 CUJ云卑呂ue p寵urm t審 g kng 2ned -0n9 unMgnc d 一 2*g Figu 晶護(hù) Acraomhfn fQDC5SUE and 弓 ea5uesmes 程序具體 本章主要講解 python 程序，使大家熟悉python 編程。關(guān)于bcm2835,wiringpi 可參看Pioneer600 示例程序。 驅(qū)動文件 bmp180.py 001 import time 002 import smbus 003 004 # BMP085 default address. 005 BMP180_I2CADDR= 0 x77 006 007 # Operati ng M

4、odes 008 BMP180_ULTRALOWPOWER = 0 BMP180_STANDARD 009 1 010 BMP180_HIGHRES 011 BMP180_ULTRAHIGHRES 012 013 # BMP085 Registers 014 BMP180_CAL_AC1 015 BMP180_CAL_AC2 016 BMP180_CAL_AC3 017 BMP180_CAL_AC4 018 BMP180_CAL_AC5 019 BMP180_CAL_AC6 020 BMP180_CAL_B1 =0 xAA # R Calibration data (16 bits) =0 x

5、AC # R Calibration data (16 bits) =0 xAE # R Calibration data (16 bits) =0 xB0 # R Calibration data (16 bits) =0 xB2 # R Calibration data (16 bits) =0 xB4 # R Calibration data (16 bits) 0 xB6 # R Calibration data (16 bits) 021 BMP180_CAL_B2 =0 xB8 # R Calibration data (16 bits) 022 BMP180_CAL_MB =0

6、xBA # R Calibration data (16 bits) =0 xBC # R Calibration data (16 bits) 024 BMP180_CAL_MD =0 xBE # RCalibratio n data (16 bits) 025 BMP180_CONTROL= 0 xF4 BMP180_TEMPDATA 026 0 xF6 027 BMP180_PRESSUREDATA = 0 xF6 028 029 # Comma nds 030 BMP180_READTEMPCMD= 0 x2E 031 BMP180_READPRESSURECMD = 0 x34 03

7、2 033 034 class BMP180(object): def _ini t_(self, address=BMP180_I2CADDR, 035 036 037 038 039 040 041 042 043 044 045 046 047 048 self._mode = mode self._address = address self._bus = smbus.SMBus(l) # Load calibrati on values. self._load_calibrati on() def _read_byte(self,cmd): return self._bus.read

8、_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 32767:result -= 65536 retur n result 049 050 051 052 053 054 055 056 057 058 059 060 061 def _write_byte(self,cmd,val): self._bus.w

9、rite_byte_data(self._address,cmd,val) def _load_calibrati on( self): load calibrati on # INT16 # INT16 self.cal_AC1 = self._read_s16(BMP180_CAL_AC1) self.cal_AC2 = self._read_s16(BMP180_CAL_AC2) # UINT16 self.cal_AC4 = self._read_u16(BMP180_CAL_AC4) self.cal_AC5 = selfead_u16(BMP180_CAL_AC5)# UINT16

10、 self.cal_AC6 = selfead_u16(BMP180_CAL_AC6)# UINT16 self.cal_B1= selfead_s16(BMP180_CAL_B1)# INT16 self.cal_B2= selfead_s16(BMP180_CAL_B2)# INT16 self.cal_MB= selfead_s16(BMP180_CAL_MB)# INT16 self.cal_MC = selfead_s16(BMP180_CAL_MC)# INT16 self.cal_MD= selfead_s16(BMP180_CAL_MD)# INT16 def read_raw

11、_temp(self): ”Reads the raw (un compe nsated) temperature from the codecs HHII 062 063 064 065 066 067 068 069 070 071 072 073 sen sor. 074 075 076 077 078 079 080 081 082 083 084 085 time.sleep(0.005) # Wait 5ms MSB = selfead_byte(BMP180_TEMPDATA) LSB = selfead_byte(BMP180_TEMPDATA+1) raw = (MSB 8)

12、 + LSB return raw def read_raw_pressure(self): ”Reads the raw (un compe nsated) 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: 086 087 088 089 090 091

13、092 093 094 095 096 097 098 time.sleep(0.014) elif self._mode = BMP180_ULTRAHIGHRES: time.sleep(0.026) else: time.sleep(0.008) MSB = selfead_byte(BMP180_PRESSUREDATA) LSB = selfead_byte(BMP180_PRESSUREDATA+1) XLSB = selfead_byte(BMP180_PRESSUREDATA+2) raw = (MSB 16) + (LSB (8 - self._mode) return ra

14、w def read_temperature(self): ”Gets the compe nsated temperature in degrees celsius.” 099 100 101 102 103 104 105 106 107 108 109 110 111 UT = self.read_raw_temp() X1 = (UT - self.cal_AC6) * self.cal_AC5) 15 X2 = (self.cal_MC 4) / 10.0 return temp def read_pressure(self): ”Gets the compe nsated pres

15、sure in Pascals.” UT = self.read_raw_temp() UP = self.read_raw_pressure() 112 113 114 115 116 117 118 119 120 121 122 123 124 X1 = (UT - self.cal_AC6) * self.cal_AC5) 15 X2 = (self.cal_MC 12) 11 X2 = (self.cal_AC2 * B6) 11 X3 = X1 + X2 B3 = (self.cal_AC1 * 4 + X3) 13 125 126 127 128 129 130 131 132

16、133 134 135 136 137 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 8) * (p 8) X1 = (X1 * 3038) 16 X2 = (-7357 * p) 16 138 139 140 141 142 143 144 145 146 147 148 149 p = p + (X1 + X2 + 3791) 4) return p def re

17、ad_altitude(self, sealevel_pa=101325.0): Calculates the altitude in meters. # Calculatio n take n straight from secti on 3.6 of the datasheet. pressure = float(self.read_pressure() altitude = 44330.0 * (1.0 - pow(pressure / sealevel_pa, (1.0/5.255) retur n altitude def read_sealevel_pressure(self, a

18、ltitude_m=0.0): ”Calculates the pressure at sealevel whe n give n a known altitude in 150 meters. Returns a value in Pascals.” 151 pressure = float(self.read_pressure() 152 p0 = pressure / pow(1.0 - altitude_m/44330.0, 5.255) 153 return p0 主文件 bmp180_example.py 01 #!/usr/bi n/python 02 03 import tim

19、e 04 from BMP180 import BMP180 05 06 # Initialise the BMP085 and use STANDARD mode (default value) 07 # bmp = BMP085(0 x77, debug=True) 08 bmp = BMP180() 09 # To specify a differe nt operati ng mode, un comme nt one of the 10 followi ng: 11 # bmp = BMP085(0 x77, 0) # ULTRALOWPOWER Mode 12 # bmp = BMP085(0 x77, 1) # STANDARD Mode 13 # bmp = BMP085(0 x77, 2) # HIRES Mode 14 # bmp = BMP085(0 x77, 3) # ULTRAHIRES Mode 15 while True: 16 temp = bmp.read_temperature() 17 18 # Read the curre nt b