I am making a cryo-cooler and was planning on using the “SparkFun Qwiic Thermocouple Amplifier - MCP9600 (PCC Connector)”, but unfortunately it looks like the module stops making temperature readings below about -153 C. The MCP9600 states that it can go down to -200 C with Type-T thermocouple. ChatGPT seems to think that this is a known issue on the web, but I can’t find any reference. Has anyone had success with this module below -150 C?
More info: There is an I2C register bit that the chip sets to 1 when a reading is completed. This can be written 0, and then polled until it goes to 1 when the next reading is available. This bit never goes to 1 much below -150 C.
pg 3 in the datasheet lists
“Type K: T∆ = -200°C to +1372°C”
for type-K, so if you used this one with this thermocouple and keep the insulation out of the freezer, just the tip should be inside (insulation rated to -72c, probe -270c)…it should work?
If you end up testing this setup report back with your results!
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Did you set the thermocouple type in your code? Wondering if the code assumes type K and thats causing the temp to bottom out.
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Good question. Yes I did. And I confirmed that the register reads T-type after setting it. The K actually goes down to -200 as well, just less linear, more noisy.
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Will do. I only have Type T thermocouples at the moment and the one listed is on back order. I’ll report back if I ever get it working. I’m trying the MAX31856 next. And it’s just the thermocouple tip (small sample 5ml cryocooler).
Thank you. I ordered it. Fingers crossed. Chat-GPT says it is an issue with the measured potential difference being too large for the MCP9600 at that low temperature. Type-K may have better properties…
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