Here's the CircuitPython code that uses the multiple TCA9548As:
# SPDX-FileCopyrightText: 2022 Carter Nelson for Adafruit Industries
#
# SPDX-License-Identifier: MIT
import time
import board
import adafruit_tca9548a
from adafruit_bme280 import basic as adafruit_bme280
# Create I2C bus as normal
i2c = board.I2C() # uses board.SCL and board.SDA
# i2c = board.STEMMA_I2C() # For using the built-in STEMMA QT connector on a microcontroller
#--------------------------------------------------------------------
# NOTE!!! This is the "special" part of the code
#
# For each TCA9548A, create a separate instance and give each
# the *same* I2C bus but with specific address for each
tca1 = adafruit_tca9548a.TCA9548A(i2c, 0x70) # TCA with address 0x70
tca2 = adafruit_tca9548a.TCA9548A(i2c, 0x71) # TCA with address 0x71
# Create each BME280 using the TCA9548A channel instead of the I2C object
# Be sure to use the TCA instance each BME280 is attached to
bme1 = adafruit_bme280.Adafruit_BME280_I2C(tca1[0]) # TCA 1 Channel 0
bme2 = adafruit_bme280.Adafruit_BME280_I2C(tca1[1]) # TCA 1 Channel 1
bme3 = adafruit_bme280.Adafruit_BME280_I2C(tca2[0]) # TCA 2 Channel 0
#--------------------------------------------------------------------
print("Multiple BME280 / Multiple TCA9548A Example")
while True:
# Access each sensor via its instance
pressure1 = bme1.pressure
pressure2 = bme2.pressure
pressure3 = bme3.pressure
print("-"*20)
print("BME280 #1 Pressure =", pressure1)
print("BME280 #2 Pressure =", pressure2)
print("BME280 #3 Pressure =", pressure3)
time.sleep(1)
With that code running on the CircuitPython board, the output will look like this:
Auto-reload is on. Simply save files over USB to run them or enter REPL to disable. code.py output: Multiple BME280 / Multiple TCA9548A Example -------------------- BME280 #1 Pressure = 994.355 BME280 #2 Pressure = 994.413 BME280 #3 Pressure = 994.165 -------------------- BME280 #1 Pressure = 994.39 BME280 #2 Pressure = 994.425 BME280 #3 Pressure = 994.159
The CircuitPython library already disables all channel outputs (when context manager exits) on the TCA9548As. Therefore, the only extra work needed is in the initial setup. For each TCA9548A, a separate instance is created:
# For each TCA9548A, create a separate instance and give each # the *same* I2C bus but with specific address for each tca1 = adafruit_tca9548a.TCA9548A(i2c, 0x70) # TCA with address 0x70 tca2 = adafruit_tca9548a.TCA9548A(i2c, 0x71) # TCA with address 0x71
Then, just like before, the TCA channel is passed in when creating each BME280 instance:
# Create each BME280 using the TCA9548A channel instead of the I2C object # Be sure to use the TCA instance each BME280 is attached to bme1 = adafruit_bme280.Adafruit_BME280_I2C(tca1[0]) # TCA 1 Channel 0 bme2 = adafruit_bme280.Adafruit_BME280_I2C(tca1[1]) # TCA 1 Channel 1 bme3 = adafruit_bme280.Adafruit_BME280_I2C(tca2[0]) # TCA 2 Channel 0
NOTE - be careful on the specific instance variable used. Note how tca1 is used for bme1 and bme2, while tca2 is used for bme3.
After the initial setup, nothing special needs to be done. Simply use the properties of each instance:
# Access each sensor via its instance pressure1 = bme1.pressure pressure2 = bme2.pressure pressure3 = bme3.pressure
Page last edited January 22, 2025
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