Why don't they build a watch that measures the temperature and every time you accurately set it, it adds to a small database of time change v temperature and then adjusts itself internally.
Over time it would become quite accurate I would think. Jim On 20 December 2011 11:12, Chuck Harris <cfhar...@erols.com> wrote: > Looking at the datasheet for the DS3232, it doesn't appear > that they mean for it to run off of a small coin cell in a > watch. Its battery operating capability is purely to keep > it running when the main power is turned off. > > I would suspect that the DS3232's power consumption is due > to its being able to drive sizable loads on its various pins. > > There is nothing inherent in temperature correcting a clock > that should take significantly more power than would be used > in a normal watch chip. Measuring the temperature would be > the most power hungry operation, I would suspect... but > fortunately that doesn't have to be done all that often, > perhaps once per minute. > > After the temperature is measured, a lookup table can be used > to find a second by second correction value to be added to > the seconds counter. > > -Chuck Harris > > > Dan Rae wrote: > >> On 12/19/2011 5:34 AM, Chuck Harris wrote: >> >>> >>> >>> It is not clear to me that a 32KHz xtal is any less stable >>> than a 262KHz xtal, though. I would think there would be a lot >>> more to be gained by using a microprocessor/thermistor to >>> measure the temperature within the watch, and provide an >>> adjustment to compensate for the xtal's natural temperature >>> sensitivity. >>> >>> Chuck, I have recently made a couple of Real Time Clocks for my >> homebrew radios using >> the Maxim DS3232 IC which has a built in TCXO at 32+ kHz doing what you >> describe, the >> temperature is checked at intervals and the corrections applied. The >> performance is >> excellent, once set, getting to what I term "Harrison Level", i.e. less >> than a second >> a week error. The downside is that the standby battery demand is pretty >> high and my >> first builds using a Lithium button cell ran for only around a month max, >> so I had to >> go over to NiMH rechargeables. I suspect using this technology in a watch >> one would >> have the same problem. >> >> The best crystals for room temperature use are around 4 MHz with >> temperature >> inflections around 20C, and this is what was used in an early Braun alarm >> clock I had >> which also had this kind of performance. Long gone, alas. >> >> Dan >> >> >> >> ______________________________**_________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/** >> mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> >> and follow the instructions there. >> >> > ______________________________**_________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/** > mailman/listinfo/time-nuts<https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> > and follow the instructions there. > _______________________________________________ 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.