I am making a temperature logger using the Arduino UNO. I have 5 MAX31855 thermocouple amplifiers installed with K-type thermocouples.
I can get four working properly by powering directly from the 3.3V pin. However, when I add a fifth, I start getting bad results across multiple thermocouples. Moving them to the 5V pin did not change the outcome. Is this possibly an issue with current drop across the thermocouples?
Why would you connect them to 5V? They are rated for 3.3V supply, max 3.6V, absolute maximum 4V.
Perhaps five of these is just too much current for your power supply to handle, along with everything else. The 3.3V regulator will have a limit.
Hang on, those only draw about 1mA each...
Perhaps a lack of bypass caps on the power supplies are an issue.
Would you anticipate any issues with the 'clock' and 'chip select' pins being wired in series for all five thermocouples? I did this to only use 7 of the Arduino digital pins instead of 15.
bin971: Would you anticipate any issues with the 'clock' and 'chip select' pins being wired in series for all five thermocouples? I did this to only use 7 of the Arduino digital pins instead of 15.
All of the chips should share the clock and slave out (or digital out, whatever) pin but each chip needs its own chip select pin.
Chagrin:
bin971: Would you anticipate any issues with the 'clock' and 'chip select' pins being wired in series for all five thermocouples? I did this to only use 7 of the Arduino digital pins instead of 15.
All of the chips should share the clock and slave out (or digital out, whatever) pin but each chip needs its own chip select pin.
Wow, I'm dumb, many thanks! I'll make the switch tomorrow. Already confirmed they all work individually.