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I want to run an arduino out in the cold (-40), and use the serial communication - I believe that the crystal is the weakest link (the one for the serial chip) - however I don't see any drop-in (through-hole) replacement crystals that would work in such cold, so would a SMT version work instead? if so, which one would be possible to solder (package?), and do I need to change the caps to match?

P.S. - Yes, I could heat it/insulate it, but that comes at a fairly high power/complexity cost

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    Have you tried it at -40? The crystal may still function but be out of spec, and you might need lower standard baud rates, or to tweak the generated baud rate to match what the reciever would expect.. – Dave X Nov 21 '16 at 15:20
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    If it's the USB to serial you could try connecting to the serial pins directly and have a separate USB to serial breakout, outside of the -40 environment. – Gerben Nov 22 '16 at 8:28
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    What Gerben said--use the hardware serial instead of the 12MB USB2.0 connection, and its lower speeds should be more resistant to mismatched speeds, and should also be tunable if you get far out of spec. – Dave X Nov 28 '16 at 3:10
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    Please give more details about the application. How are you connecting the board? Maybe using a remote oscillating circuit is the best way, or you can make a small board with a compensated oscillator. But... -40° is the limit for the atmega328p, so are you sure that you really need to have a arduino out there? You will need to power it, and batteries are useless at that temperature, so you'll need a power cable. If you have to wire it, then you can wire just the sensor you need to put there... – frarugi87 Dec 2 '16 at 8:49
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    if you insulated it you wouldn't need 10X the power of running it to keep it "warm" – dandavis Feb 19 '17 at 7:29
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There is a solution for just this problem, it's a "crystal oven". It is used to keep a crystal at a constant temperature so that the oscillating ferquency remains very stable.

Crystal ovens are usually expensive as they are quite precise and have good insultaion, but here's a kit that you might adapt for your uses: http://www.minikits.com.au/Oscillator-Heater, or google around to see if you find something that might suit you better.

You could also consider making a heater with a simple temperature regulator of your own to keep the crystal warm (many temperature sensors for Arduino are available on the web).

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