Using PCA9548A multiplexer with NI8451 I2C interface device to control multiple sensors

[alicei]

Hi, 

as stated in the subject I have a PCA9548 multiplexer, I am trying to control multiple HTU21D Humidity and temperature sensors, but for now I am just trying to read from 1 channel, 1 temperature reading to figure out how it works.  

Here is the setup for this project : 

The part that I have been unsure of is how do I go from telling the device I want to use the address of 70 for the multiplexer and then from there tell the program that within the multiplexer I need to go into X channel and look for X adress

Here is what I have so far, but I get an error at the write function saying : "NI-845x: The slave did not acknowledge an address+direction byte transmitted by the I2C master..." 

This is a working example for just reading 1 sensor when directly connected to the NI8451 which works ( I simplified it to just read once for simplicity's sake ) 

Thank you for any help or suggestions I can get on this !!! 

[santo_13]

Since all your sensors connected to the MUX are the same address, you need to ensure you configure the MUX (switch actually) to connect to only one channel when you read the sensor.

The order of execution should look as follows,

1. Write to MUX to select only CH0 (write 0x01 to addr 0x70)
2. Read temperature from HTU21D
3. Write to MUX to select only CH1 (write 0x02 to addr 0x70)
4. Read temperature from HTU21D
5. ... so on for the rest of the channels

Here is a simple code to configure the PCA9548 to connect N channels