Page 1 of 1
I2C multiplexer library?
Posted: Mon Apr 15, 2019 10:16 am
by asuagar
Hello,
Is there a Micropython library for the TCA9548A or another multiplexer device? There is a library for the TCA9548A in CircuitPython. However, I am afraid that it will not work in MicroPython. Is there other way for multilplexing using MicroPython?
Thanks & regards!
Re: I2C multiplexer library?
Posted: Mon Apr 15, 2019 2:00 pm
by Roberthh
Circuitpython is a Micropython variant. The only thing to adapt is typcially the way it speaks to I2C. There are minor differences in the I2C API. I have sucessfully ported Adafruit libraries, and it was usually easy.
Re: I2C multiplexer library?
Posted: Sun Apr 21, 2019 10:50 am
by doublevee
I have been using this mutliplexer in a product I am building and it is very easy to use. I'm not sure it needs a library at all? You select the I2C address for the mux using 3 external pins (can be IO driven or just hard wired). You then just write a single command to that address to select the output channel of the mux. The mux remains on that channel until either a power cycle or you issue a new channel command.
In brief, once you have your mux setup, it's a very small amount of code to add to select a particular device - almost a single line depending on your use case.
Happy to help further if needs be. I'm no expert at all but happy to try and help if needed.
Re: I2C multiplexer library?
Posted: Thu Oct 17, 2019 2:15 pm
by sequel
I am trying to use a tca9548a to drive 2 temperature/humidity sensors (si7021) on an esp32 board, using the CircuitPython code (
https://github.com/adafruit/Adafruit_Ci ... n_TCA9548A) and, i have no success so far.
Here's what i have been doing so far :
Code: Select all
import machine
import si7021
import tca9548a
scl_pin=22
sda_pin=21
i2c=machine.I2C(-1, machine.Pin(scl_pin), machine.Pin(sda_pin))
tca=tca9548a.TCA9548A(i2c)
As soon as i am trying to reach a sensor like this :
Code: Select all
si7021_obj1=si7021.SI7021(tca[0])
I am getting :
Code: Select all
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/lib/si7021.py", line 46, in __init__
File "/lib/si7021.py", line 50, in init
File "/lib/si7021.py", line 87, in reset
File "/lib/si7021.py", line 66, in _command
File "/lib/tca9548a.py", line 39, in writeto
OSError: [Errno 19] ENODEV
I am not sure how to proceed to debug this further. The sensors are working great without the multiplexer.
@ doublevee
Could you kindly post some code snippets on how you manually use this multiplexer? That would help me troubleshoot further.
Thanks in advance.
Re: I2C multiplexer library?
Posted: Thu Oct 17, 2019 5:35 pm
by sequel
Finally got it working with this simple code, if that can help someone :
tca9548a_test.py
Code: Select all
import machine
import ustruct
scl_pin=22
sda_pin=21
class TCA9548A():
def __init__(self,address):
self.address=address
self.bus=machine.I2C(-1, machine.Pin(scl_pin), machine.Pin(sda_pin))
def switch_channel(self,channel):
self.bus.writeto(self.address,ustruct.pack('B',1 << channel))
and then :
Code: Select all
import tca9548a_test
import si7021
tca=tca9548a_test.TCA9548A(0x70)
for channel in range(0,2):
tca.switch_channel(channel)
sensor=si7021.SI7021(tca.bus)
print('humidity on sensor # {} = {}%'.format(channel, sensor.humidity()))
print('temperature on sensor # {} = {}°C'.format(channel, sensor.temperature()))
will give something like this :
humidity on sensor # 0 = 50.7894%
temperature on sensor # 0 = 19.28095°C
humidity on sensor # 1 = 57.13706%
temperature on sensor # 1 = 19.32385°C
Cheers!