Teensy 3.1 temperature rating

[flipflop]

Hello all, reading this thread, Paul say that the crystal is the limiting part, with a minimum spec at -10C, my question is if there exist a possibility of reemplace this crystal for get a lower minimum spec, and what other parts are limiting? I would get to -20Cº in 100 units,

regards!

 

[GremlinWrangler]

Are you after a working USB interface at those temperatures, or is this a device that will log data/do stuff and only be connected to a PC in less hostile conditions?

If so it's perfectly possible that your code will still happily tick away running a couple of PPM slow at those temperatures. My understanding is that you are pretty much stuck with frequency shifts with temperature, and instead you start either sliding your clock correction values around on the fly based on ambient temperature (Fun with registers!), or more simply modify any critical (external interfacing) delay loops to have a temperature correction divisor in there working from the CPU internal temp sensor (or a more accurate external one).

Without knowing more about the planed application hard to tell exactly what could go wrong but my understanding is that the time sensitive part is the USB clock.

 

[Constantin]

I think you're better off thinking about how to mitigate the conditions. The CPU does a nice job of heating itself so if you case the teensy in a small box with 1/2" or thicker XPS) or similar removable rigid foam), the teensy should be ok.

If not, simply add a 200mW heater to the VUSB / GND pins and place it over the crystal. Ideally that heater would be self regulating. I've seen them used in refrigerator mullion strips, for example.

FWIW, I have successfully used a teensy 3 to -44*C and beyond with dry ice. That said, the teensy started at room temperature or was already on when it was operating at those temperatures.

The error of the RTC can be compensated as long as you have a good idea re the ambient temperatures and have characterized the crystal ppm error vs temperature response. I recommend using a ds18b20 or similar digital temperature sensor.

For inspiration, search for my temperature experiments here to see what I have posted about. On iPhone right now so finding and inserting the links is a bit tedious.