As I have been prototyping a project using the Adafruit MAX31855 thermocouple amplifier breakout, I have been noticing some varying behavior. Initially, I had and Imp, April and the MAX31855’s laying out flat in a half open enclosure, and my data was very consistent and within the margin of error for K-type thermocouples.
My current prototypes are placing the boards much closer together, and sometimes directly over or under the April/Imp. The circuit also includes an LCD with a serial backpack, and a LiPo charging circuit from Adafruit.
I am noticing these specific behaviors.
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I read the temperature from both boards back to back from SPI189. I am using pins 2, and 8 as CS. Occasionally I will get a temperature reading that is way off the charts. From reading comments on the MAXIM site about the chip, it does seem that some people have experienced RF interference, though it appears that Adafruits board includes all of the recommended components to reduce interference.
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With my new prototype, if I turn on the circuit with all of the boards and the probes settled to room temperature, I initially get an accurate reading. Then over a period of about 15 minutes at the same room temperature, the readings of both probes rise about 8-10 degrees. My initial thinking is that the air inside the enclosure is warming up and changing the reference temperature at the cold junction, though I don’t understand why it can’t compensate for the change in reference temperature.
I certainly don’t expect answers about other companies products, though I’m quite sure the Hugo has some very interesting insight.
I do have this question: Assuming that the occasional random bad reading is caused by the Imp communicating during the SPI reads, is there a way to prevent any any other communication during the SPI read to prevent interference.
Or, is there a position or shielding that I could use around the thermcouple amps to prevent RF interference?
I am reading the chips with the MAX31855 code in the Electric Imp GitHub repo. Thanks!