[time-nuts] Another "atomic" clock question

Richard H McCorkle mccorkle at ptialaska.net
Mon Mar 3 15:04:51 EST 2014


For science-fair level accuracy try a $2 PTC-60 thermistor heater
one component oven for minimal complexity. I tried this with a
small box and insulating foam and it gives surprisingly good
results. Leave it to the ham radio guys to come up with a low
cost solution.



>>> Junk crystals are good thermometers.  Ballpark is 1 ppm/degree-C
> albertson.chris at gmail.com said:
>> So does this mean I can epoxy a sandstone power resister to a junk crystal
>> and keep the frequency exactly perfect by varying the power in the resister?
> Sure, for some values of "perfect" and such.
> I've occasionally thought about building something like this, just for the
> hell of it to see what happens and/or what I learn, and or how good I/we can
> get on a low budget.
> I think there are two problem areas.  One is sensors and control algorithms.
> The other is board layout.
> Where is the sweet spot on complexity vs accuracy?  I'm looking for
> science-fair level of goodness rather than super-expensive to get another 0
> or two.
> What's the best low-cost way to measure temperature?  Many of the obvious
> choices are only good to 0.1 C.  That's great if you are trying to measure
> room temperature or or want to keep your CPU from melting, but it's probably
> leaving a lot on the table if you are interested in the frequency from a
> crystal.
> My straw man would be a thermistor and OP-Amp feeding into the ADC on your
> favorite uProc.  Maybe the other side of a bridge would be adjustable.
> How much power do you need to keep things warm?  I'm assuming something like
> a watt or 2 with something like a PWM from the uProc.
> --
> These are my opinions.  I hate spam.
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