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MAX31865 multiplexing with TCA9548
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MAX31865 multiplexing with TCA9548

by AdaPhil on Mon Jul 29, 2019 3:25 am

MAX31865 + PT1000 working very fine on my UNO.
Need now to query 4 MAX31865 with a TCA9548 and experienced issues staring with bus scan > no MAX detected: MAX/TCA wiring ?, library ?
Could not find such MAX31865/TCA9548 project example on the forum
Thanks

AdaPhil
 
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Re: MAX31865 multiplexing with TCA9548

by adafruit_support_carter on Mon Jul 29, 2019 7:07 pm

There is no TCA library for Arduino. All that is really needed is the TCA select method shown in the guide:
https://learn.adafruit.com/adafruit-tca ... g-and-test
to switch output channels. See the guide example which shows using two HMC5883 breakouts. Wiring is similar - share power and GND and then use the numbered SCL/SDA outputs to route one pair to each MAX breakout.

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Re: MAX31865 multiplexing with TCA9548

by AdaPhil on Sat Aug 10, 2019 1:19 pm

Thank for your swift reply

- MAX31865 working perfectly, on first shot following Adafruit instructions, congratulation to Adafruit team
- A quite important point : the code given as example in the library has been tested with a PT100. To get the right temperature with a PT100 (3-WIRE) you must use RREF 4300 but RNOMINAL 100.0 and not 1000.0 as indicated (giving temperature output < 120 C).
- The UNO/MAX31865 wiring uses SDI & SDO pins
- I have tested the MAX31865 without SDI pin: does not work. Same of course without SDO one

The example given in the Adafruit TCA9548 manual use HMC5883 breakouts
But there is only one SDA pin on HMC5883

So I am still wondering how it is possible to multiplex MAX31865 breakouts with a TC9548 where only 2 pins are available for each input SCn & SDn as the MAX31865 wiring requires SCL, SDI & SDO ?
Hope my question not too stupid....

AdaPhil
 
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Re: MAX31865 multiplexing with TCA9548

by adafruit_support_bill on Sat Aug 10, 2019 1:32 pm

The MAX31865 uses the SPI bus - not the i2c bus. So an i2c multiplexer is not what you need to use.

Multiple SPI devices can share the same SCK, SDO and SDI pins. But each device needs a unique CS pin. In your code, specify the CS pins you are using for each device in the constructor:
https://learn.adafruit.com/adafruit-max ... rence-5-14

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Please be positive and constructive with your questions and comments.