#!/usr/bin/env python
import smbus
import time
import math

class bmp180class:
    'Class for working with BMP180 pressure sensor'

    def __init__(self):
        self.bus = smbus.SMBus(1)
        self.BMP180_ADDRESS = 0x77 # sensor address use detect
        # calibration variables 
        self.ac1 = 0
        self.ac2 = 0
        self.ac3 = 0
        self.ac4 = 0
        self.ac5 = 0
        self.ac6 = 0
        self.b1 = 0
        self.b2 = 0
        self.mb = 0
        self.mc = 0
        self.md = 0
        self.oss = 3 # oversampling setting (0..3)
        self.altitude = 48  # 31 # location high in meters
        self.__PressureCompensate = 0
        self.__Temperature = 0

    def bmp180ReadInt(self, addr,reg):
        MSB = self.bus.read_byte_data(addr, reg)
        LSB = self.bus.read_byte_data(addr, reg + 1)
        return int((MSB << 8) + LSB)

    def bmp180ReadTriplet(self, addr,reg):
        MSB = self.bus.read_byte_data(addr, reg)
        LSB = self.bus.read_byte_data(addr, reg + 1)
        XLSB = self.bus.read_byte_data(addr, reg + 2)
        return long((MSB << 16) + (LSB << 8) + XLSB)

    def int2signed_short(self, intvalue):
        # input data is two bytes from sensor stored in integer
        # ouput is signed short from these bytes value between -32767 and 32767
        return (intvalue & 32767) - (intvalue & 32768)

    def bmp180Init(self):
        # load calibration data
        self.ac1 = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xAA))
        self.ac2 = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xAC))
        self.ac3 = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xAE))
        self.ac4 = self.bmp180ReadInt(self.BMP180_ADDRESS,0xB0)
        self.ac5 = self.bmp180ReadInt(self.BMP180_ADDRESS,0xB2)
        self.ac6 = self.bmp180ReadInt(self.BMP180_ADDRESS,0xB4)
        self.b1 = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xB6))
        self.b2 = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xB8))
        self.mb = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xBA))
        self.mc = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xBC))
        self.md = self.int2signed_short(self.bmp180ReadInt(self.BMP180_ADDRESS,0xBE))

    def CalculateSeaLevelPressure(self,local_pressure):
        # Calculate sea level air pressure
        # altitude = 31 # location high in meters
        # float temperature = 283; // K
        temperature_k = self.__Temperature  + 273.15
        sea_level_pressure = local_pressure/math.exp((-9.81 * 0.0289644 * self.altitude)/(8.314 * temperature_k))
        return sea_level_pressure

    def get_temperature(self):
        # perform temperature measurement
        self.bus.write_byte_data(self.BMP180_ADDRESS, 0xF4, 0x2E)
        time.sleep(0.05) #wait 4.5 ms
        # read raw value
        ut = self.bmp180ReadInt(self.BMP180_ADDRESS,0xF6)
        # calculate temperature value
        x1 = ((ut - self.ac6)*self.ac5) >> 15
        x2 = (self.mc << 11)/(x1 + self.md)
        self.__PressureCompensate = x1 + x2 # value used in pressure calculation
        self.__Temperature = ((self.__PressureCompensate + 8)>>4) /10.0
        return self.__Temperature

    def get_pressure(self):
        # before first pressure measurement do one temperature measurement
        count = 0
        # perform pressure measurement
        self.bus.write_byte_data(self.BMP180_ADDRESS, 0xF4, 0x34+(self.oss<<6))
        # time.sleep(0.08) #wait minimum 4.5 - 76.5 ms (see BMP180 data sheet)
        # wait until Sco bit is set to 0 means measuerment completed
        while (count < 1000) and ((self.bus.read_byte_data(self.BMP180_ADDRESS, 0xF4) & 0x20) > 0):
           # print 'The count is:', count
           count = count + 1

        # read raw pressure value
        up = self.bmp180ReadTriplet(self.BMP180_ADDRESS,0xF6)>>(8-self.oss)
        # Calculation
        b6 = self.__PressureCompensate - 4000
        x1 = (self.b2 * (b6 * b6)>>12)>>11
        x2 = (self.ac2 * b6)>>11
        x3 = x1 + x2
        b3 = ((((self.ac1)*4 + x3)<<self.oss) + 2)>>2

        # Calculate B4
        x1 = (self.ac3 * b6)>>13
        x2 = (self.b1 * ((b6 * b6)>>12))>>16
        x3 = ((x1 + x2) + 2)>>2
        b4 = (self.ac4 * (x3 + 32768))>>15

        b7 = ((up - b3) * (50000>>self.oss))
        if (b7 < 0x80000000):
            p = (b7<<1)/b4
        else:
            p = (b7/b4)<<1

        x1 = (p>>8) * (p>>8)
        x1 = (x1 * 3038)>>16
        x2 = (-7357 * p)>>16
        p += (x1 + x2 + 3791)>>4
        p = p / 100 # hPa
        return p


#--------------------------------------------------------
# class usage test
bmp180 = bmp180class() # make class instance

# load calibration data
bmp180.bmp180Init()

# you have to read temperature before geting pressure measurement 
print("Temperature: {0} C").format(round(bmp180.get_temperature(),1))

# get pressure
pressure = bmp180.get_pressure()
print("Local air pressure: {0} hPa").format(round(pressure,1))
print("Sea level pressure: {0} hPa").format(round(bmp180.CalculateSeaLevelPressure(pressure), 1))