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I need to measure temperatures of -80C, and the circuit needs to be battery-powered. So I thought an RTD probe with the MAX31865 RTD-to-Digital Converter would work well. I am using an nRF52840 for a microcontroller.

I got the circuit working, but unfortunately, the standby current of the MAX31865 is 700uA. This is way to high for my application, I missed this on the datasheet when I purchased it...

My first thought was to use an I/O pin to power on the chip when I needed a reading, then power it off when I am done. The problem presented here is that I have other SPI chips on my board, and this (I believe) damaged the MAX31865 by having the power disconnected while SPI communication was still happening. I can't confirm this, but after reading a bit on this topic it seems likely that this is the culprit.

My next thought is to use a buffer chip to connect/disconnect the power and SPI on the MAX31865, but I feel like there is a simpler solution somewhere here.

Does anyone know how to reduce the standby current of the MAX31865? If not, is there a solution that can safely power down the chip when not in use?

Or potentially a better setup entirely. I read up on thermocouples, but they don't seem to be recommended for very low temperatures, mostly very high temperatures.

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    \$\begingroup\$ thermocouples will work at low temperatures. I have used K-type at -80C. (Dry-ice alcohol mixture) \$\endgroup\$
    – RussellH
    Aug 13, 2023 at 21:32
  • \$\begingroup\$ this site is not a forum ... it is a question and answer site ... please do not ask multiple questions that cannot be answered with one answer \$\endgroup\$
    – jsotola
    Aug 13, 2023 at 21:36
  • \$\begingroup\$ @RussellH what type of accuracy were you getting at -80C ? \$\endgroup\$
    – MattG
    Aug 13, 2023 at 22:11
  • \$\begingroup\$ @jsotola I hope my post bothers you as much as it appears to. \$\endgroup\$
    – MattG
    Aug 13, 2023 at 22:12
  • \$\begingroup\$ @MattG it does not bother me even one bit ... I'm just trying to prevent the question from being closed for not being focused \$\endgroup\$
    – jsotola
    Aug 13, 2023 at 22:39

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