BMP180 luchtdruk + temperatuur sensor (Raspberry Pi)

bmp180.py

#!/usr/bin/python
# BMP180 luchtdruk + temperatuur sensor
# https://www.raspberrytips.nl

import smbus
import time
from ctypes import c_short
 
DEVICE = 0x77
 
bus = smbus.SMBus(1) 
 
def convertToString(data):
  return str((data[1] + (256 * data[0])) / 1.2)

def getShort(data, index):
  return c_short((data[index] << 8) + data[index + 1]).value

def getUshort(data, index):
  return (data[index] << 8) + data[index + 1]

def readBmp180(addr=DEVICE):
  REG_CALIB  = 0xAA
  REG_MEAS   = 0xF4
  REG_MSB    = 0xF6
  REG_LSB    = 0xF7
  CRV_TEMP   = 0x2E
  CRV_PRES   = 0x34 
  OVERSAMPLE = 3  
  
  cal = bus.read_i2c_block_data(addr, REG_CALIB, 22)

  AC1 = getShort(cal, 0)
  AC2 = getShort(cal, 2)
  AC3 = getShort(cal, 4)
  AC4 = getUshort(cal, 6)
  AC5 = getUshort(cal, 8)
  AC6 = getUshort(cal, 10)
  B1  = getShort(cal, 12)
  B2  = getShort(cal, 14)
  MB  = getShort(cal, 16)
  MC  = getShort(cal, 18)
  MD  = getShort(cal, 20)

  # Lees Temperatuur
  bus.write_byte_data(addr, REG_MEAS, CRV_TEMP)
  time.sleep(0.005)
  (msb, lsb) = bus.read_i2c_block_data(addr, REG_MSB, 2)
  UT = (msb << 8) + lsb

  # Lees Luchtdruk
  bus.write_byte_data(addr, REG_MEAS, CRV_PRES + (OVERSAMPLE << 6))
  time.sleep(0.04)
  (msb, lsb, xsb) = bus.read_i2c_block_data(addr, REG_MSB, 3)
  UP = ((msb << 16) + (lsb << 8) + xsb) >> (8 - OVERSAMPLE)

  # Opmaak temperatuur
  X1 = ((UT - AC6) * AC5) >> 15
  X2 = (MC << 11) / (X1 + MD)
  B5 = X1 + X2
  temperature = (B5 + 8) >> 4

  # Opmaak luchtdruk
  B6  = B5 - 4000
  B62 = B6 * B6 >> 12
  X1  = (B2 * B62) >> 11
  X2  = AC2 * B6 >> 11
  X3  = X1 + X2
  B3  = (((AC1 * 4 + X3) << OVERSAMPLE) + 2) >> 2

  X1 = AC3 * B6 >> 13
  X2 = (B1 * B62) >> 16
  X3 = ((X1 + X2) + 2) >> 2
  B4 = (AC4 * (X3 + 32768)) >> 15
  B7 = (UP - B3) * (50000 >> OVERSAMPLE)

  P = (B7 * 2) / B4

  X1 = (P >> 8) * (P >> 8)
  X1 = (X1 * 3038) >> 16
  X2 = (-7357 * P) >> 16
  pressure = P + ((X1 + X2 + 3791) >> 4)

  return (temperature/10.0,pressure/ 100.0)

def main():
    
  deg = u'\xb0'
  (temperature,pressure)=readBmp180()
  print "Temperatuur : ", temperature,deg.encode('utf8'), "C"
  print "Luchtdruk    : ", pressure, "mbar"
  
if __name__=="__main__":
   main()