A BMP180 Micropython example on an ESP32

In this example we connect a BMP180 barometric pressure sensor to an ESP32 running Micropython

The BMP180 is the new digital barometric pressure sensor of Bosch Sensortec, with a very high performance, which enables applications in advanced mobile devices, such as smartphones, tablet PCs and sports devices. It follows the BMP085 and brings many improvements, like the smaller size and the expansion of digital interfaces.

The ultra-low power consumption down to 3 μA makes the BMP180 the leader in power saving for your mobile devices. BMP180 is also distinguished by its very stable behavior (performance) with regard to the independency of the supply voltage.

Applications

– Indoor navigation

– GPS-enhancement for dead-reckoning, slope detection, etc.

– Sport devices, e.g. altitude profile

– Weather forecast

– Vertical velocity indication (rise/sink speed)

Parts List

Connection

An easy module to connect to an ESP32, SCL is 22 and SDA is 21 on the Wemos board I used, you can see this is the schematic below

esp32 and bmp180

Code

You can use any method to upload files or an IDE for development, I used uPyCraft to u

The following is based on a github library – just search for Micropython bmp180. The first part of this is the library which I upload to my ESP32

This is the library called bmp180.py

[codesyntax lang=”python”]

rom ustruct import unpack as unp
from machine import I2C, Pin
import math
import time

# BMP180 class
class BMP180():
    '''
    Module for the BMP180 pressure sensor.
    '''

    _bmp_addr = 119             # adress of BMP180 is hardcoded on the sensor

    # init
    def __init__(self, i2c_bus):

        # create i2c obect
        _bmp_addr = self._bmp_addr
        self._bmp_i2c = i2c_bus
        self._bmp_i2c.start()
        self.chip_id = self._bmp_i2c.readfrom_mem(_bmp_addr, 0xD0, 2)
        # read calibration data from EEPROM
        self._AC1 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xAA, 2))[0]
        self._AC2 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xAC, 2))[0]
        self._AC3 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xAE, 2))[0]
        self._AC4 = unp('>H', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB0, 2))[0]
        self._AC5 = unp('>H', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB2, 2))[0]
        self._AC6 = unp('>H', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB4, 2))[0]
        self._B1 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB6, 2))[0]
        self._B2 = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xB8, 2))[0]
        self._MB = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xBA, 2))[0]
        self._MC = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xBC, 2))[0]
        self._MD = unp('>h', self._bmp_i2c.readfrom_mem(_bmp_addr, 0xBE, 2))[0]

        # settings to be adjusted by user
        self.oversample_setting = 3
        self.baseline = 101325.0

        # output raw
        self.UT_raw = None
        self.B5_raw = None
        self.MSB_raw = None
        self.LSB_raw = None
        self.XLSB_raw = None
        self.gauge = self.makegauge() # Generator instance
        for _ in range(128):
            next(self.gauge)
            time.sleep_ms(1)

    def compvaldump(self):
        '''
        Returns a list of all compensation values
        '''
        return [self._AC1, self._AC2, self._AC3, self._AC4, self._AC5, self._AC6, 
                self._B1, self._B2, self._MB, self._MC, self._MD, self.oversample_setting]

    # gauge raw
    def makegauge(self):
        '''
        Generator refreshing the raw measurments.
        '''
        delays = (5, 8, 14, 25)
        while True:
            self._bmp_i2c.writeto_mem(self._bmp_addr, 0xF4, bytearray([0x2E]))
            t_start = time.ticks_ms()
            while (time.ticks_ms() - t_start) <= 5: # 5mS delay
                yield None
            try:
                self.UT_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF6, 2)
            except:
                yield None
            self._bmp_i2c.writeto_mem(self._bmp_addr, 0xF4, bytearray([0x34+(self.oversample_setting << 6)]))
            t_pressure_ready = delays[self.oversample_setting]
            t_start = time.ticks_ms()
            while (time.ticks_ms() - t_start) <= t_pressure_ready:
                yield None
            try:
                self.MSB_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF6, 1)
                self.LSB_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF7, 1)
                self.XLSB_raw = self._bmp_i2c.readfrom_mem(self._bmp_addr, 0xF8, 1)
            except:
                yield None
            yield True

    def blocking_read(self):
        if next(self.gauge) is not None: # Discard old data
            pass
        while next(self.gauge) is None:
            pass

    @property
    def oversample_sett(self):
        return self.oversample_setting

    @oversample_sett.setter
    def oversample_sett(self, value):
        if value in range(4):
            self.oversample_setting = value
        else:
            print('oversample_sett can only be 0, 1, 2 or 3, using 3 instead')
            self.oversample_setting = 3

    @property
    def temperature(self):
        '''
        Temperature in degree C.
        '''
        next(self.gauge)
        try:
            UT = unp('>H', self.UT_raw)[0]
        except:
            return 0.0
        X1 = (UT-self._AC6)*self._AC5/2**15
        X2 = self._MC*2**11/(X1+self._MD)
        self.B5_raw = X1+X2
        return (((X1+X2)+8)/2**4)/10

    @property
    def pressure(self):
        '''
        Pressure in mbar.
        '''
        next(self.gauge)
        self.temperature  # Populate self.B5_raw
        try:
            MSB = unp('B', self.MSB_raw)[0]
            LSB = unp('B', self.LSB_raw)[0]
            XLSB = unp('B', self.XLSB_raw)[0]
        except:
            return 0.0
        UP = ((MSB << 16)+(LSB << 8)+XLSB) >> (8-self.oversample_setting)
        B6 = self.B5_raw-4000
        X1 = (self._B2*(B6**2/2**12))/2**11
        X2 = self._AC2*B6/2**11
        X3 = X1+X2
        B3 = ((int((self._AC1*4+X3)) << self.oversample_setting)+2)/4
        X1 = self._AC3*B6/2**13
        X2 = (self._B1*(B6**2/2**12))/2**16
        X3 = ((X1+X2)+2)/2**2
        B4 = abs(self._AC4)*(X3+32768)/2**15
        B7 = (abs(UP)-B3) * (50000 >> self.oversample_setting)
        if B7 < 0x80000000:
            pressure = (B7*2)/B4
        else:
            pressure = (B7/B4)*2
        X1 = (pressure/2**8)**2
        X1 = (X1*3038)/2**16
        X2 = (-7357*pressure)/2**16
        return pressure+(X1+X2+3791)/2**4

    @property
    def altitude(self):
        '''
        Altitude in m.
        '''
        try:
            p = -7990.0*math.log(self.pressure/self.baseline)
        except:
            p = 0.0
        return p

[/codesyntax]

Now you either update main.py or create it with the following code

[codesyntax lang=”python”]

from bmp180 import BMP180
from machine import I2C, Pin                        # create an I2C bus object accordingly to the port you are using
#bus = I2C(1, baudrate=100000)           # on pyboard
bus =  I2C(scl=Pin(22), sda=Pin(21), freq=100000)   # on esp8266
bmp180 = BMP180(bus)
bmp180.oversample_sett = 2
bmp180.baseline = 101325

temp = bmp180.temperature
p = bmp180.pressure
altitude = bmp180.altitude
print("Temperature: ",temp)
print("Pressure: ",p)
print("Altitude: ",altitude)

[/codesyntax]

Testing

Open up the REPL window. Here is what I saw in uPyCraft

Ready to download this file,please wait!
….
download ok
exec(open(‘./main.py’).read(),globals())
Temperature: 19.65517
Pressure: 98344.88
Altitude: 238.5229