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I am making a temperature sensor that can go in a freezer and I am trying to figure out what the best method is.

My research has taken me all over the place an I can't seem to find a straight answer. Some sites recommend using LiFePo4, while others say absolutely not, because it needs to be regulated.

One question I have is: could I use more voltage, say 6V from a series of batteries and connect it to the 5V pin since it is regulated, or is it better to go with an external regulator for the 3.3V pin with less voltage?

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  • For battery operation always use an external switching regulator (not an LDO regulator) to 3.3V. It will double your battery life over using the 5V pin. Also: will the whole thing be in the freezer? What temperature freezer?
    – Majenko
    Commented Jan 22, 2021 at 16:00
  • Which ESP32 unit are you considering? Does it have an internal voltage regulator?
    – Duncan C
    Commented Jan 22, 2021 at 16:08
  • @Majenko, yes it is meant to be entirely in the freezer and the temp has been a consideration as well.
    – user71866
    Commented Jan 22, 2021 at 16:39
  • @DuncanC, I am using the ESP32 Dev KitC V4. It has an internal voltage regulator on the 5V pin, not the 3.3V, which is why I was wondering if it would be easier to use the 5V rather than messing with the 3.3V pin and needing a regulator
    – user71866
    Commented Jan 22, 2021 at 16:40
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    Before you get too carried away figuring out how you're going to power it with batteries you might see if you can even get a signal through your freezer walls at all. If you can't, it means your running wires anyway, maybe just a thermocouple wire. So far as I can tell, you are basically asking about putting a wireless device inside of a Faraday cage.
    – timemage
    Commented Jan 22, 2021 at 16:43

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Since it is a freezer (operating temperature unknown) I am assuming it is connected to the mains why not do the same with the electronics. This will save you a lot work and time and when you find out it will not work in a Faraday cage as stated by timemage. Leave the sensor wire long enough to mount the electronics outside just in case. Also consider packaging, it will be cold, possibly below the operating range of some of the components requiring you to keep them warm (above minimum temperature). I would assume your freezer like ours has moisture concerns as ice will form when opened then removed by a defrost cycle. You will also have to protect for that. Then there is the operating temperature range of the batteries, are they capable of operating at your freezer temperatures. I would suggest you redefine your problem before starting the design, this process saves me a lot of grief.

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  • Just wanted to let everyone know that I tested the signal and we had NO issues connecting to the WiFi from inside the freezer! Still looking for advice for a battery solution.....
    – user71866
    Commented Feb 1, 2021 at 20:10
  • I would recommended that the best type of battery for the freezer are the lithium variety. Keep in mind these are 100% disposable. So as much as I normally recommend rechargeable batteries for just about EVERY application, these are better for use in very cold sub zero temperatures.
    – Gil
    Commented Feb 2, 2021 at 2:23

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