Pi Pico and BME280 Humidity sensor micropython example

Parts Required

I used a Pico sense hat which has 4 sensors on it, it would be possible to wire up a BME280 sensor

In this image you can see a sense hat attached to a Pico

Code

I used Thonny and this example is written in Micropython

The first part is a library for the bme280

You need to upload this to your Raspberry Pi Pico

Go to File > Save as…
Select the Raspberry Pi Pico
Name your file as bme280.py and press the OK button
And that’s it. The library was uploaded to your board. To make sure that it was uploaded successfully, go to File > Save as… and select the Raspberry Pi Pico device. Your file should be listed there:
After uploading the library to your board, you can use the library in your code by importing the library.

Here is the code for the library, it comes from the github link for the sense hat – if you have time then its worth looking at to look at how you can talk to a sensor

[codesyntax lang=”python”]

from machine import I2C
import time

# BME280 default address.
BME280_I2CADDR = 0x76

# Operating Modes
BME280_OSAMPLE_1 = 1
BME280_OSAMPLE_2 = 2
BME280_OSAMPLE_4 = 3
BME280_OSAMPLE_8 = 4
BME280_OSAMPLE_16 = 5

# BME280 Registers

BME280_REGISTER_DIG_T1 = 0x88  # Trimming parameter registers
BME280_REGISTER_DIG_T2 = 0x8A
BME280_REGISTER_DIG_T3 = 0x8C

BME280_REGISTER_DIG_P1 = 0x8E
BME280_REGISTER_DIG_P2 = 0x90
BME280_REGISTER_DIG_P3 = 0x92
BME280_REGISTER_DIG_P4 = 0x94
BME280_REGISTER_DIG_P5 = 0x96
BME280_REGISTER_DIG_P6 = 0x98
BME280_REGISTER_DIG_P7 = 0x9A
BME280_REGISTER_DIG_P8 = 0x9C
BME280_REGISTER_DIG_P9 = 0x9E

BME280_REGISTER_DIG_H1 = 0xA1
BME280_REGISTER_DIG_H2 = 0xE1
BME280_REGISTER_DIG_H3 = 0xE3
BME280_REGISTER_DIG_H4 = 0xE4
BME280_REGISTER_DIG_H5 = 0xE5
BME280_REGISTER_DIG_H6 = 0xE6
BME280_REGISTER_DIG_H7 = 0xE7

BME280_REGISTER_CHIPID = 0xD0
BME280_REGISTER_VERSION = 0xD1
BME280_REGISTER_SOFTRESET = 0xE0

BME280_REGISTER_CONTROL_HUM = 0xF2
BME280_REGISTER_CONTROL = 0xF4
BME280_REGISTER_CONFIG = 0xF5
BME280_REGISTER_PRESSURE_DATA = 0xF7
BME280_REGISTER_TEMP_DATA = 0xFA
BME280_REGISTER_HUMIDITY_DATA = 0xFD


class Device:
  """Class for communicating with an I2C device.

  Allows reading and writing 8-bit, 16-bit, and byte array values to
  registers on the device."""

  def __init__(self, address, i2c):
    """Create an instance of the I2C device at the specified address using
    the specified I2C interface object."""
    self._address = address
    self._i2c = i2c

  def writeRaw8(self, value):
    """Write an 8-bit value on the bus (without register)."""
    value = value & 0xFF
    self._i2c.writeto(self._address, value)

  def write8(self, register, value):
    """Write an 8-bit value to the specified register."""
    b=bytearray(1)
    b[0]=value & 0xFF
    self._i2c.writeto_mem(self._address, register, b)

  def write16(self, register, value):
    """Write a 16-bit value to the specified register."""
    value = value & 0xFFFF
    b=bytearray(2)
    b[0]= value & 0xFF
    b[1]= (value>>8) & 0xFF
    self.i2c.writeto_mem(self._address, register, value)

  def readRaw8(self):
    """Read an 8-bit value on the bus (without register)."""
    return int.from_bytes(self._i2c.readfrom(self._address, 1),'little') & 0xFF

  def readU8(self, register):
    """Read an unsigned byte from the specified register."""
    return int.from_bytes(
        self._i2c.readfrom_mem(self._address, register, 1),'little') & 0xFF

  def readS8(self, register):
    """Read a signed byte from the specified register."""
    result = self.readU8(register)
    if result > 127:
      result -= 256
    return result

  def readU16(self, register, little_endian=True):
    """Read an unsigned 16-bit value from the specified register, with the
    specified endianness (default little endian, or least significant byte
    first)."""
    result = int.from_bytes(
        self._i2c.readfrom_mem(self._address, register, 2),'little') & 0xFFFF
    if not little_endian:
      result = ((result << 8) & 0xFF00) + (result >> 8)
    return result

  def readS16(self, register, little_endian=True):
    """Read a signed 16-bit value from the specified register, with the
    specified endianness (default little endian, or least significant byte
    first)."""
    result = self.readU16(register, little_endian)
    if result > 32767:
      result -= 65536
    return result

  def readU16LE(self, register):
    """Read an unsigned 16-bit value from the specified register, in little
    endian byte order."""
    return self.readU16(register, little_endian=True)

  def readU16BE(self, register):
    """Read an unsigned 16-bit value from the specified register, in big
    endian byte order."""
    return self.readU16(register, little_endian=False)

  def readS16LE(self, register):
    """Read a signed 16-bit value from the specified register, in little
    endian byte order."""
    return self.readS16(register, little_endian=True)

  def readS16BE(self, register):
    """Read a signed 16-bit value from the specified register, in big
    endian byte order."""
    return self.readS16(register, little_endian=False)


class BME280:
  def __init__(self, mode=BME280_OSAMPLE_1, address=BME280_I2CADDR, i2c=None,
               **kwargs):
    # Check that mode is valid.
    if mode not in [BME280_OSAMPLE_1, BME280_OSAMPLE_2, BME280_OSAMPLE_4,
                    BME280_OSAMPLE_8, BME280_OSAMPLE_16]:
        raise ValueError(
            'Unexpected mode value {0}. Set mode to one of '
            'BME280_ULTRALOWPOWER, BME280_STANDARD, BME280_HIGHRES, or '
            'BME280_ULTRAHIGHRES'.format(mode))
    self._mode = mode
    # Create I2C device.
    if i2c is None:
      raise ValueError('An I2C object is required.')
    self._device = Device(address, i2c)
    # Load calibration values.
    self._load_calibration()
    self._device.write8(BME280_REGISTER_CONTROL, 0x3F)
    self.t_fine = 0

  def _load_calibration(self):

    self.dig_T1 = self._device.readU16LE(BME280_REGISTER_DIG_T1)
    self.dig_T2 = self._device.readS16LE(BME280_REGISTER_DIG_T2)
    self.dig_T3 = self._device.readS16LE(BME280_REGISTER_DIG_T3)

    self.dig_P1 = self._device.readU16LE(BME280_REGISTER_DIG_P1)
    self.dig_P2 = self._device.readS16LE(BME280_REGISTER_DIG_P2)
    self.dig_P3 = self._device.readS16LE(BME280_REGISTER_DIG_P3)
    self.dig_P4 = self._device.readS16LE(BME280_REGISTER_DIG_P4)
    self.dig_P5 = self._device.readS16LE(BME280_REGISTER_DIG_P5)
    self.dig_P6 = self._device.readS16LE(BME280_REGISTER_DIG_P6)
    self.dig_P7 = self._device.readS16LE(BME280_REGISTER_DIG_P7)
    self.dig_P8 = self._device.readS16LE(BME280_REGISTER_DIG_P8)
    self.dig_P9 = self._device.readS16LE(BME280_REGISTER_DIG_P9)

    self.dig_H1 = self._device.readU8(BME280_REGISTER_DIG_H1)
    self.dig_H2 = self._device.readS16LE(BME280_REGISTER_DIG_H2)
    self.dig_H3 = self._device.readU8(BME280_REGISTER_DIG_H3)
    self.dig_H6 = self._device.readS8(BME280_REGISTER_DIG_H7)

    h4 = self._device.readS8(BME280_REGISTER_DIG_H4)
    h4 = (h4 << 24) >> 20
    self.dig_H4 = h4 | (self._device.readU8(BME280_REGISTER_DIG_H5) & 0x0F)

    h5 = self._device.readS8(BME280_REGISTER_DIG_H6)
    h5 = (h5 << 24) >> 20
    self.dig_H5 = h5 | (
        self._device.readU8(BME280_REGISTER_DIG_H5) >> 4 & 0x0F)

  def read_raw_temp(self):
    """Reads the raw (uncompensated) temperature from the sensor."""
    meas = self._mode
    self._device.write8(BME280_REGISTER_CONTROL_HUM, meas)
    meas = self._mode << 5 | self._mode << 2 | 1
    self._device.write8(BME280_REGISTER_CONTROL, meas)
    sleep_time = 1250 + 2300 * (1 << self._mode)

    sleep_time = sleep_time + 2300 * (1 << self._mode) + 575
    sleep_time = sleep_time + 2300 * (1 << self._mode) + 575
    time.sleep_us(sleep_time)  # Wait the required time
    msb = self._device.readU8(BME280_REGISTER_TEMP_DATA)
    lsb = self._device.readU8(BME280_REGISTER_TEMP_DATA + 1)
    xlsb = self._device.readU8(BME280_REGISTER_TEMP_DATA + 2)
    raw = ((msb << 16) | (lsb << 8) | xlsb) >> 4
    return raw

  def read_raw_pressure(self):
    """Reads the raw (uncompensated) pressure level from the sensor."""
    """Assumes that the temperature has already been read """
    """i.e. that enough delay has been provided"""
    msb = self._device.readU8(BME280_REGISTER_PRESSURE_DATA)
    lsb = self._device.readU8(BME280_REGISTER_PRESSURE_DATA + 1)
    xlsb = self._device.readU8(BME280_REGISTER_PRESSURE_DATA + 2)
    raw = ((msb << 16) | (lsb << 8) | xlsb) >> 4
    return raw

  def read_raw_humidity(self):
    """Assumes that the temperature has already been read """
    """i.e. that enough delay has been provided"""
    msb = self._device.readU8(BME280_REGISTER_HUMIDITY_DATA)
    lsb = self._device.readU8(BME280_REGISTER_HUMIDITY_DATA + 1)
    raw = (msb << 8) | lsb
    return raw

  def read_temperature(self):
    """Get the compensated temperature in 0.01 of a degree celsius."""
    adc = self.read_raw_temp()
    var1 = ((adc >> 3) - (self.dig_T1 << 1)) * (self.dig_T2 >> 11)
    var2 = ((
        (((adc >> 4) - self.dig_T1) * ((adc >> 4) - self.dig_T1)) >> 12) *
        self.dig_T3) >> 14
    self.t_fine = var1 + var2
    return (self.t_fine * 5 + 128) >> 8

  def read_pressure(self):
    """Gets the compensated pressure in Pascals."""
    adc = self.read_raw_pressure()
    var1 = self.t_fine - 128000
    var2 = var1 * var1 * self.dig_P6
    var2 = var2 + ((var1 * self.dig_P5) << 17)
    var2 = var2 + (self.dig_P4 << 35)
    var1 = (((var1 * var1 * self.dig_P3) >> 8) +
            ((var1 * self.dig_P2) >> 12))
    var1 = (((1 << 47) + var1) * self.dig_P1) >> 33
    if var1 == 0:
      return 0
    p = 1048576 - adc
    p = (((p << 31) - var2) * 3125) // var1
    var1 = (self.dig_P9 * (p >> 13) * (p >> 13)) >> 25
    var2 = (self.dig_P8 * p) >> 19
    return ((p + var1 + var2) >> 8) + (self.dig_P7 << 4)

  def read_humidity(self):
    adc = self.read_raw_humidity()
    # print 'Raw humidity = {0:d}'.format (adc)
    h = self.t_fine - 76800
    h = (((((adc << 14) - (self.dig_H4 << 20) - (self.dig_H5 * h)) +
         16384) >> 15) * (((((((h * self.dig_H6) >> 10) * (((h *
                          self.dig_H3) >> 11) + 32768)) >> 10) + 2097152) *
                          self.dig_H2 + 8192) >> 14))
    h = h - (((((h >> 15) * (h >> 15)) >> 7) * self.dig_H1) >> 4)
    h = 0 if h < 0 else h
    h = 419430400 if h > 419430400 else h
    return h >> 12

  @property
  def temperature(self):
    "Return the temperature in degrees."
    t = self.read_temperature()
    ti = t // 100
    td = t - ti * 100
    return "{}.{:02d}C".format(ti, td)

  @property
  def pressure(self):
    "Return the temperature in hPa."
    p = self.read_pressure() // 256
    pi = p // 100
    pd = p - pi * 100
    return "{}.{:02d}hPa".format(pi, pd)

  @property
  def humidity(self):
    "Return the humidity in percent."
    h = self.read_humidity()
    hi = h // 1024
    hd = h * 100 // 1024 - hi * 100
    return "{}.{:02d}%".format(hi, hd)

[/codesyntax]

You can download from the library from the bottom of this article

After uploading the library to the Raspberry Pi Pico, copy the following code to the main.py.

This will print the temperature, humidity and pressure into the shell every 5 seconds

[codesyntax lang=”python”]

from machine import Pin, I2C
from time import sleep
import bme280

i2c = I2C(1,scl=Pin(7), sda=Pin(6), freq=40000)#all sensor connected through I2C

while True:
  bme = bme280.BME280(i2c=i2c)
  temp = bme.temperature
  hum = bme.humidity
  pres = bme.pressure
  # uncomment for temperature in Fahrenheit
  #temp = (bme.read_temperature()/100) * (9/5) + 32
  #temp = str(round(temp, 2)) + 'F'
  print('Temperature: ', temp)
  print('Humidity: ', hum)
  print('Pressure: ', pres)

  sleep(5)

[/codesyntax]

Link

bme280