[time-nuts] Another "atomic" clock question

[Hal Murray]

>> 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.