[time-nuts] Another "atomic" clock question
lists at rtty.us
Mon Mar 3 07:59:55 EST 2014
The simple approach is to use an op amp, a thermistor, and a couple of resistors. No need for anything digital. You can easily get all the gain possible (before oscillation) out of a very simple circuit.
The net result will be about a 1C stability when you run it over temperature (say 0 to 50 C) in a lab chamber. You can tweak it a bit to get the thermal gain up to a few hundred if you have a chamber to give you feedback on your changes.
On Mar 3, 2014, at 5:18 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
>>> 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
> 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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