Thermometer for measuring -80C temperatures

I am working on a project in which I need to measure a freezer. A very cold freezer. It stays at -80 degrees Celsius all the time. Does anyone know what I should use to measure this? I've thought of a K type thermocouple, but the amplifier board is a little expensive and I was wondering if there was a cheaper alternative.

Thanks in advance!

K-type is one of the best options for this. You really need the converter board. A MAX31855K chip is very easy to interface with. Sparkfun sells them mounted on a board for $15. For $4 more you can buy the special K-type connector to plug in standard thermocouple plugs. (These connectors are actually pretty rare parts. You don't find them in most electronics stores, even very big ones.)

Also look at a PT-100 RTD sensor. Use a MAX31865 for this. They are really easy to buy although finding ones with a specification below -55C is a little rare. The textbook says that the platinum sensors are good to -190C but the ones you can actually buy have a plastic case or some other limitation on the coldest temperature.

I would stay away from any analog amplifier. The process of amplifying the signal from either sensor up to the levels that the Arduino can read is actually more difficult and subject to more errors than buying the proper chip in the first place.

J-type thermocouples are slightly better than K at low temperatures but the prices rapidly get into the hundreds of dollars because they are so much rarer.

Like Morgan, I can recommend the MAX31856. I am using it with a K-type thermocouple, to measure superconducting transition at around -100C. It has been working very well for me.

8bit-Dude, do you have a link to where you purchased it? All the K-type thermocouples I see on amazon say they don't go below 0C.

The thermocouple itself can't possibly be damaged by exposures to temperatures below 0 C, so I can't imagine why Amazon sellers would make such a ridiculous claim. But then, Amazon can be as bad as any when it comes to selling junk.

This setup will work down to about -250 C:

Master_Aar:
8bit-Dude, do you have a link to where you purchased it? All the K-type thermocouples I see on amazon say they don't go below 0C.

I use this very common item: https://www.amazon.co.jp/gp/product/B00JO9WTKM/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Ok thanks! I think I'll go the Adafruit route and get the AD8495.