bmp280.py

'''
    mpy drive for BMP280 Digital Pressure Sensor

    Author: shaoziyang
    Date:   2018.2

    http://www.micropython.org.cn

'''
from machine import I2C

BMP280_I2C_ADDR = const(0x76)

class BMP280():
    def __init__(self, i2c):
        self.i2c = i2c
        self.dig_T1 = self.get2Reg(0x88)
        self.dig_T2 = self.short(self.get2Reg(0x8A))
        self.dig_T3 = self.short(self.get2Reg(0x8C))
        self.dig_P1 = self.get2Reg(0x8E)
        self.dig_P2 = self.short(self.get2Reg(0x90))
        self.dig_P3 = self.short(self.get2Reg(0x92))
        self.dig_P4 = self.short(self.get2Reg(0x94))
        self.dig_P5 = self.short(self.get2Reg(0x96))
        self.dig_P6 = self.short(self.get2Reg(0x98))
        self.dig_P7 = self.short(self.get2Reg(0x9A))
        self.dig_P8 = self.short(self.get2Reg(0x9C))
        self.dig_P9 = self.short(self.get2Reg(0x9E))
        self.mode = 3
        self.osrs_p = 3
        self.osrs_t = 1
        self.setReg(0xF4, 0x2F)
        self.setReg(0xF5, 0x0C)
        self.filter = 3
        self.T = 0
        self.P = 0
        self.version = '1.0'

    def	short(self,	dat):
        if dat > 32767:
            return dat - 65536
        else:
            return dat
	
    # set reg
    def	setReg(self, reg, dat):
        self.i2c.writeto(BMP280_I2C_ADDR, bytearray([reg, dat]))
		
    # get reg
    def	getReg(self, reg):
        self.i2c.writeto(BMP280_I2C_ADDR, bytearray([reg]))
        t =	self.i2c.readfrom(BMP280_I2C_ADDR, 1)
        return t[0]
	
    # get two reg
    def	get2Reg(self, reg):
        self.i2c.writeto(BMP280_I2C_ADDR, bytearray([reg]))
        t =	self.i2c.readfrom(BMP280_I2C_ADDR, 2)
        return t[0] + t[1]*256

    def get(self):
        adc_T = (self.getReg(0xFA)<<12) + (self.getReg(0xFB)<<4) + (self.getReg(0xFC)>>4)
        var1 = (((adc_T>>3)-(self.dig_T1<<1))*self.dig_T2)>>11
        var2 = (((((adc_T>>4)-self.dig_T1)*((adc_T>>4) - self.dig_T1))>>12)*self.dig_T3)>>14
        t = var1+var2
        self.T = ((t * 5 + 128) >> 8)/100
        var1 = (t>>1) - 64000
        var2 = (((var1>>2) * (var1>>2)) >> 11 ) * self.dig_P6
        var2 = var2 + ((var1*self.dig_P5)<<1)
        var2 = (var2>>2)+(self.dig_P4<<16)
        var1 = (((self.dig_P3*((var1>>2)*(var1>>2))>>13)>>3) + (((self.dig_P2) * var1)>>1))>>18
        var1 = ((32768+var1)*self.dig_P1)>>15
        if var1 == 0:
            return  # avoid exception caused by division by zero
        adc_P = (self.getReg(0xF7)<<12) + (self.getReg(0xF8)<<4) + (self.getReg(0xF9)>>4)
        p=((1048576-adc_P)-(var2>>12))*3125
        if p < 0x80000000:
            p = (p << 1) // var1
        else:
            p = (p // var1) * 2
        var1 = (self.dig_P9 * (((p>>3)*(p>>3))>>13))>>12
        var2 = (((p>>2)) * self.dig_P8)>>13
        self.P = p + ((var1 + var2 + self.dig_P7) >> 4)
        return [self.T, self.P]

    # get Temperature in Celsius
    def getTemp(self):
        self.get()
        return self.T

    # get Pressure in Pa
    def getPress(self):
        self.get()
        return self.P

    # Calculating absolute altitude
    def	getAltitude(self):
        return 44330*(1-(self.getPress()/101325)**(1/5.255))

    # sleep mode
    def poweroff(self):
        self.setReg(0xF4, 0)

    # normal mode
    def poweron(self):
        self.setReg(0xF4, 0x2F)