[time-nuts] How to properly characterize 32kHz oscillators manually and with a microcontroller?

[Hal Murray]

I assume you are doing this for fun.  That means you get to do whatever you 
think will be fun.

The DS3231 is pretty crappy by time nuts standards.  If you can also measure 
the temperature, you should be able to make neat graphs.  If you watch it as 
the temperature ramps up slowly, you should see a sawtooth pattern.  The 
crystal will track the normal freq/temp curve until the temperature changes 
enough for the correction logic to add in another step.

Have you looked at tvb's PICPET and friends?
  http://www.leapsecond.com/pic/picpet.htm
  http://www.leapsecond.com/pic/picdiv.htm

I think he has one that turns 32KHz into PPS.  You could feed that PPS into a 
picPET running off your Thunderbolt.

If you have a spare counter, you can run that in frequency mode and feed that 
to a PC.


Where are you going to collect the data?

The PPS input on a PC may be be useful.


pete at heypete.com said:
> I'm a little concerned about the speed at which the pulses need to be
> counted. The 32kHz pulses come in every ~30.5 microseconds, and handling an
> interrupt on an ATmega328 running at 16MHz takes about 5.125 microseconds[1]
...

Use one of the counters to divide things down to a rate that is easier to 
handle.



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