Sample code to operate a combined humidity and pressure sensor: BME280.
The BME280 operation can be done with simple API through its class library.
This code operation is checked with MicroPython v1.22.1 on Raspberry Pi Pico.
Note
CQ出版インターフェース誌2024年3月号(1月25日発売)の記事では，リリース1.0.0がサンプルコードとして使われています．
これよりあとのコードは，より汎用性を高めたものとなっています．記事と同じコードが必要な場合はリリース1.0.0を参照ください．リリース1.0.0 is used as the sample code in the 2024 March issue (Jan 25 release) of CQ-publishing "Interface" magazine. Later code than 1.0.0 is version with better versatility. If you need identical version to the article, plase refer to release 1.0.0.
AE-BME280: A sensor module using BME280
This code had been written to show samples of basic I²C and SPI operation using BME280.
The BME280 supports I²C and SPI interfaces. The interface can be switched by CSB pin setting. When the CSB pin is tied to VDDIO, it is configured for I²C.
For SPI, the CSB is used as a ChipSelect signal input.
For more details, please refer section 6.1 of BME280 datasheet
On addition to the BME280 operation sample, this can perform bit-banging I²C and SPI libralies (bbI2C and bbSPI) demo.
Since the MicroPython has build-in libraris of SoftI2C and SoftSPI, those handmade bit-banging interfaces may not be needed.
However, the libraries were dared by a magazine project.
The magazine article was tried to explain the I²C and SPI protocols from bit-banging Python code.
This BME280.py was made as a test application of the bbI2C and bbSPI.
This BME280.py can be used as a class library which supports both I²C and SPI buses. User don't need to tweak the code for interface changing but just giving an instance of the interface to constructor function.
# An application sample using class library in BME280.py
from machine import Pin, I2C, SPI
if USE_I2C:
intf = I2C( 0, sda = Pin( 0 ), scl = Pin( 1 ), freq = 400_000 )
else:
intf = SPI( 1, 1000000, sck = Pin( 10 ), mosi = Pin( 11 ), miso = Pin( 12 ) )
bme = BME280( intf )
while True:
t, p, h = bme.read()
print( f"{t:5.2f} ℃, {p:7.2f} hPa, {h:5.2f} %RH" )
sleep( 1 )API document is available here
A main function is executed.
In the main function, there are 4 lines to declare the intf instance. One of them should be enabled and others needed to be comment-out.
The I2C and SPI can be enabled and used in default MicroPython environment.
# The main() function in BME280.py
...
..
def main():
intf = I2C( 0, sda = Pin( 0 ), scl = Pin( 1 ) )
#intf = bbI2C( sda = Pin( 0 ), scl = Pin( 1 ) )
#intf = SPI( 1, 1000000, sck = Pin( 10 ), mosi = Pin( 11 ), miso = Pin( 12 ) )
#intf = bbSPI( sck = Pin( 10 ), mosi = Pin( 11 ), miso = Pin( 12 ) )
bme = BME280( intf )
...
..The bbI2C and bbSPI can be enabled if those libraies are installed in executable path. Those libraries are available on bbI2C and bbSPI.
The bbI2C.py and bbSPI.py are needed to be copied in to MicroPython device.
bbI2C and bbSPI libraries installed in in to MicroPython device (Operated in Thonny app)
For I²C and SPI, diferent wirings are required.
Followings are example of hardware connection between a Raspberry Pi Pico and a BME280.
Power supply (3.3V) and GND are common in both cases.
In both cases, the BME280's VDD and VDDIO are connected together. The 3.3V is supplied from pin 36 of Raspberry Pi Pico.
Any one of a GND pin can be used on Raspberry Pi Pico (pin 3, 8, 13, 18, 23, 28, 33 or 38).
GP0 (pin1) and GP1 (pin2) are used for I²C SDA and SCL signals. Both of those signal lines needed to be pulled-up by resisters.
The resister value 1kΩ~10kΩ can be used.
The CSB pin of BME280 is tied to VDDIO pin to select I²C interface.
The SDO is connected to GND to select I²C address: 0b1110110.
BME280 supports to use another I²C address: 0b1110111 by connecting SDO to VDDIO.
Device connection for I2C
BME280.py support to use both I²C addresses. The default is 0b1110110. To specify the 0b1110111, use option parameter of BME280.
A keyword parameter address can be used to use the BME280 which SDO pin is tied to VDDIO.
# When BME280 SDO is connected to GND
from machine import Pin, I2C
intf = I2C( 0, sda = Pin( 0 ), scl = Pin( 1 ) )
bme = BME280( intf ) # to use default address of 0b1110110# When BME280 SDO is connected to VDDIO
from machine import Pin, I2C
intf = I2C( 0, sda = Pin( 0 ), scl = Pin( 1 ) )
bme = BME280( intf, address = 0b1110111 ) # to use address of 0b11101114 wire SPI conection is supported. In next example diagram, GP10 ~ GP13 are used for SPI interface.
Device connection for SPI
If other ChipSelect(CS) pin needed to be specified on the microcontroller, it can be done by giving an option parameter for BME280().
Default setting is GP13 but other pin can be used with keyword parameter cs.
# When BME280 CSB is connected to GP13 (pin 17)
from machine import Pin, SPI
intf = SPI( 1, 1000000, sck = Pin( 10 ), mosi = Pin( 11 ), miso = Pin( 12 ) )
bme = BME280( intf ) # to use GP13 as default ChipSelect pin # When BME280 CSB is connected to GP15 (pin 20)
from machine import Pin, SPI
intf = SPI( 1, 1000000, sck = Pin( 10 ), mosi = Pin( 11 ), miso = Pin( 12 ) )
bme = BME280( intf, cs = Pin( 15 ) ) # to use GP15 as ChipSelect pin instead of GP13 Note
Ifaddressandcsare given for inapprppreate interface, the option will be just ignored.
If both options are given, an invalid option will be ignored.
AE-BME280 (Japanese site) is a module using BME280.
AE-BME280 module
This module has single-inline 6 pins of VDD, GND, CSB, SDI SDO and SCK. This makes easy to wire on bread-board.
Following wiring diagram is a sample for I²C and SPI. Both interface operations can be tried by replacing the module in slots.
For I²C, F25~F30 slot can be used. For SPI, E25~E30 slot can be used.
Bread-board connections between AE-BME280 and Raspberry Pi Pico for both I²C and SPI
AE-BME280 slots for I²C and SPI
When you modify docstring in the code, API document files in doc/ can be updated in following two commands.
sphinx-apidoc -f -o ./docs/docs_gene .
sphinx-build ./docs/docs_gene ./docs