BMP280 + example

altitude.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

import requests
from bmp280 import *

geo = "" #coordin sea
d_api = "" #api darksky


def internet_on():
    url = 'http://www.google.com/'
    for timeout in [1, 2, 5, 10]:
        try:
            requests.get(url, timeout=timeout)
            return True
        except requests.ConnectionError:
            pass
    return False


if __name__ == "__main__":
    if internet_on():
        forecast = requests.get(
            "https://api.darksky.net/forecast/{0}/{1}?exclude=minutely,hourly,daily,alerts,flags".format(d_api, geo))
        forecast = forecast.json()
        press_sea = forecast['currently']['pressure']
        sensor = BMP280()
        d = sensor.read_temp_press()
        altitude = 44330 * (1.0 - pow(d["p"] / press_sea, 0.1903))
        print(altitude)
    else:
        print("Lost Connection...")

bmp280.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

import smbus, time

class BMP280:
    c_temp = []
    c_press = []

    def __init__(self, bus=0, add=0x76):
        self.N_ADD = add
        # Get I2C bus
        self.bus = smbus.SMBus(bus)
        b1 = self.read_cf()
        self.con_cf_temp(b1)
        self.con_cf_press(b1)
        self.select_register()

    def read_cf(self):
        # BMP280 address, 0x76(118)
        # Read data back from 0x88(136), 24 bytes
        r = 0
        try:
            r = self.bus.read_i2c_block_data(self.N_ADD, 0x88, 24)
        except Exception as e:
            print('Error reading serial port {0}: {1}.'.format(type(e).__name__, e))
        return r

    def con_cf_temp(self, b1):

        # Temp coefficents
        dig_T1 = b1[1] * 256 + b1[0]
        dig_T2 = b1[3] * 256 + b1[2]
        if dig_T2 > 32767:
            dig_T2 -= 65536
        dig_T3 = b1[5] * 256 + b1[4]
        if dig_T3 > 32767:
            dig_T3 -= 65536
        self.c_temp = [dig_T1, dig_T2, dig_T3]

    def con_cf_press(self, b1):

        # Pressure coefficents
        dig_P1 = b1[7] * 256 + b1[6]
        dig_P2 = b1[9] * 256 + b1[8]
        if dig_P2 > 32767:
            dig_P2 -= 65536
        dig_P3 = b1[11] * 256 + b1[10]
        if dig_P3 > 32767:
            dig_P3 -= 65536
        dig_P4 = b1[13] * 256 + b1[12]
        if dig_P4 > 32767:
            dig_P4 -= 65536
        dig_P5 = b1[15] * 256 + b1[14]
        if dig_P5 > 32767:
            dig_P5 -= 65536
        dig_P6 = b1[17] * 256 + b1[16]
        if dig_P6 > 32767:
            dig_P6 -= 65536
        dig_P7 = b1[19] * 256 + b1[18]
        if dig_P7 > 32767:
            dig_P7 -= 65536
        dig_P8 = b1[21] * 256 + b1[20]
        if dig_P8 > 32767:
            dig_P8 -= 65536
        dig_P9 = b1[23] * 256 + b1[22]
        if dig_P9 > 32767:
            dig_P9 -= 65536
        self.c_press = [dig_P1, dig_P2, dig_P3, dig_P4,
                        dig_P5, dig_P6, dig_P7, dig_P8, dig_P9]

    def set_rate(self):
        # Select Control measurement register, 0xF4(244)
        # 0x27(39)	Pressure and Temperature Oversampling rate = 1
        # Normal mode
        self.bus.write_byte_data(self.N_ADD, 0xF4, 0x27)

    def select_register(self):
        # Select Configuration register, 0xF5(245)
        # 0xA0(00) Stand_by time = 1000 ms
        self.bus.write_byte_data(self.N_ADD, 0xF5, 0xA0)

    def read_raw_data(self):
        self.set_rate()
        time.sleep(0.25)
        # Read data back from 0xF7(247), 8 bytes
        # Pressure MSB, Pressure LSB, Pressure xLSB, Temperature MSB, Temperature LSB
        # Temperature xLSB, Humidity MSB, Humidity LSB
        r = 0
        try:
            r = self.bus.read_i2c_block_data(self.N_ADD, 0xF7, 8)
        except Exception as e:
            print('Error reading serial port {0}: {1}.'.format(type(e).__name__, e))
        return r

    def to_19bits(self, data):
        # Convert temperature[0] and pressure[1] data to 19-bits
        return [((data[3] * 65536) + (data[4] * 256) + (data[5] & 0xF0)) / 16,
                ((data[0] * 65536) + (data[1] * 256) + (data[2] & 0xF0)) / 16]

    def read_temp_press(self):
        data = self.read_raw_data()
        adc = self.to_19bits(data)
        temp = self.t_calibration(adc, self.c_temp)                
        press = self.p_calibration(adc, self.c_press, temp)
        temp = temp / 5120.0
        return {"t": temp, "p": press}

    def t_calibration(self, adc, cf):
        # Temperature offset calculations
        return ((((adc[0]) / 16384.0 - (cf[0]) / 1024.0) * (cf[1])) + (
                (((adc[0]) / 131072.0 - (cf[0]) / 8192.0) * ((adc[0]) / 131072.0 - (cf[0]) / 8192.0)) * (cf[2])))

    def p_calibration(self, adc, cf, t_fine):
        # Pressure offset calculations
        var1 = (t_fine / 2.0) - 64000.0
        var2 = var1 * var1 * (cf[5]) / 32768.0
        var2 = var2 + var1 * (cf[4]) * 2.0
        var2 = (var2 / 4.0) + ((cf[3]) * 65536.0)
        var1 = ((cf[2]) * var1 * var1 / 524288.0 + (cf[1]) * var1) / 524288.0
        var1 = (1.0 + var1 / 32768.0) * (cf[0])
        p = 1048576.0 - adc[1]
        p = (p - (var2 / 4096.0)) * 6250.0 / var1
        var1 = (cf[8]) * p * p / 2147483648.0
        var2 = p * (cf[7]) / 32768.0
        return (p + (var1 + var2 + (cf[6])) / 16.0) / 100

main.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

import time
from bmp280 import*

def main():
    sensor = BMP280()
    while True:
        d = sensor.read_temp_press()
        # Output data to screen
        print("Temperature : {0:.3f} °C | Pressure : {1:.3f} hPa".format(d["t"], d["p"]))
        time.sleep(1)


if __name__ == "__main__":
    main()

press_sea.py

#!/usr/bin/python3
# -*- coding: utf-8 -*-

from bmp280 import *

alt_m = 10  # altitude

if __name__ == "__main__":
    sensor = BMP280()
    d = sensor.read_temp_press()
    p0 = d["p"] / pow(1.0 - alt_m / 44330.0, 5.255)
    print(p0)