[time-nuts] Has anybody checked this? GPSDO in kit
tshoppa at gmail.com
Sun Oct 23 09:44:59 EDT 2016
I've been very impressed by the LED/VFD car clocks that come built into
cars for the past 20 years. They have to work in temperature extremes from
below zero to way above 120F when parked in the sun on a hot day. And every
six months at DST time when it's time to reset them, I find they are never
off more than a minute. This leads me to believe, they must have some sort
of temperature compensation (I'm guessing a lookup table or maybe just a
simple few-parameter formula to adjust divide-down clock based on cheap
temperature sensor) built in.
On Sat, Oct 22, 2016 at 10:52 PM, Mark Sims <holrum at hotmail.com> wrote:
> Yep, I recently sorted through a bag of 100 crystals from China ($10,
> shipped) looking for a "good" one. They were ALL good... a complete waste
> of time. I was rather amazed at their consistency and performance for a 10
> cent part.
> Last year I bought an alarm clock / game from China (looks like 7 sticks
> of dynamite with an ominous circuit board / LED display strapped to it).
> It uses a 40 pin (AVR?) processor driven by a 16 MHz processor crystal. I
> have not set it in over a year and it is still within a few seconds. I
> suspect they measure the frequency and have a calibration tweak stored in
> EEPROM... but that seems excessive work for a $20 toy. I highly doubt they
> go as far as doing temperature compensation. Maybe they characterized a
> bucket of XTALs and use a generic compensation factor?
> > Yes, you can build gear to do temperature runs on crystals and sort
> bags full of them.
> It’s likely that your whole bag of 5,000 came from the same bar and your
> net result will all look a lot alike…..
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