On Mon, Mar 3, 2014 at 2:18 AM, Hal Murray <hmur...@megapathdsl.net> wrote: > >>> Junk crystals are good thermometers. Ballpark is 1 ppm/degree-C > > albertson.ch...@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.
There is only one value of "perfect". The goal is to keep the frequency spot-on the marked 10MHz If this system works the crystal never moves off it's design value. We are not using het to push or pull the crystal off it's fundamental design point but maybe we say to "push or pull it back to center. > > 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. That is my goal too. I'm never impressed that people with unlimited budget do good work. But doing the same with recycled junk parts really is impressive. > > 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. Why are you measuring temperature. Just let it be "whatever". You measure the frequent and then adult the current in the heater to keep the frequency constant. I assume that if the crystal really is a good thermometer then frequency is all you need to measure. One can make the control easier by adding some thermal mass. A big chunk of metal would add some stability. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.