ECN Forum Forums Technical Discussion Re: Computers and the Internet Where Does the Time Come From?

FYI / BTW

Just in case anyone is wondering what the Acronym "RTC" means
(NJwirenut mentions in previous message),
it stands for "Real-Time Clock"

Scott35

And here all these long years I've been asking the opposite question..."where does all the time go?"

Now I'm wondering if it's recycled starting with evaporation when my eyes are closed as I sleep or worse, before my very eyes while I surf the 'net or something. Then it probably seeps into the ground and becomes mixed with the mineral deposits and over time begins to dry or solidify thus kicking off the crystaling process...

.... I know, I'm a litte odd when I think too much...

Bren;

LOL!!!

Nearly fell off the chair when the irony clicked in.

Thanks for the post and the laughs!

Scott35

Whatever you guys have, I want some.......

Email me a sample PLEASE.


LOL


Dnk...

I would say that I was 'dropped on my head as a child' but in all honesty, I jumped. True story. Out of the 2nd story balcony and down into the concrete basement incinerator stairwell and landed on my (14 month old) head - hence, I have a reason for warped thinking. Lack of sleep & having 3 small children who are also warped also probably contributes to my oddity.

As an aside, as I was driving I realized that the word I was struggling with was "crystallization" - doh!



[This message has been edited by BuggabooBren (edited 04-15-2005).]

I like electromechanical pendulum clocks, ( masterclocks FAVAG & Bürk ) which I use at home and have a 24 Volts 1 minute alternating polarity system set up which drives about 30 slaves in my house. accuracy is within ± 6 seconds / month. For the seconds I use a tacho generator which does 1 minute in 58.66 seconds, to keep them in step with the master.

As accurate reference clock I use an 4,194,304 Hz crystal oscillator, 22 divider to provide a very accurate time reference of 1 second, (drift less than 2 secs a month). A stable temperature of the crystal is helpful and a good quality trimming capacitor / reference cap.

I'm still working on an automatic synchronising system which opts for the highest accuracy, OK I admit my hobby is a little out of control and there are not always enough hours in a day to get it all sorted out yet, but I prefer brass gears instead of plastic fantastic.

Scott35, I guess I'm a little confused about what you want to do with your 555 crossbuck ckt. One thing that I tend to do with my 555 ckts,(that I don't believe they show in the data sheets), is put a 1N914 or equiv. in parallel with my discharge resistor(2,6 cathode,7 anode) so that my effective charging resistance can be <= my discharge R for a <= 50% duty cycle. The stability is largely dependent on external components but I never really put 555 and accurate in the same sentence. Of course, this one in my pacemaker is arrrrrrgh.......

Trying to answer iwire’s question “How does this cheaply made device 'know' how long 1 second is?” I want to say something previous to inventing of timer ICs (like the 555 you are talking about) more electrical than electronics (maybe not all the electricians in this forum know about flip-flops and comparators, but I’m sure they are more familiarized with resistors and capacitors):

The “time constant” of an R-C circuit (resistor and capacitor) is the time, in seconds, needed to charge that capacitor through that resistor at a value approximately equal to the 63% of the voltage applied to the circuit. So, for a circuit “to know” how long is 1 second (or any time period) is just a mater of doing the proper calculations at design time; no magic on it. Charging and discharging the capacitor is the way of doing an electrical pendulum (asymmetrical, by the way).

There is a nice little article that may help at http://www.tpub.com/neets/book2/3d.htm; it even has some graphs.


Joe.-

Just looking through the thread again...
You will tend to see a lot of R/C & L/C stuff at lower freqs and Crystal oscillators at the high end. Don't forget the ceramic resonators that are very typical in the low-high KHz. range. They often look like little yellow to orange monolithic caps or like small tubular caps. Any remote control in your house is likely to have them.

If you folks want to play with a versatile timing chip, check into LSI/CSI devices LS7210/11/12. Radio Shack at least used to sell the 7210. I designed a 150Y Device calibrator around one, allowing me to step between 12mS to 372mS in 12mS steps. They have quite a few timer,lock, & PIR chips that would be fun to play with.

As for keeping accurate time, my watch cheats. This Wave Ceptor locks into WWVB at 1AM local time to sync. The bummer is when it hasn't captured the signal for 3 days and displays 12 Noon on Mar.1.
Joe

so what do you do if the clock on your computer gains 3 min. every day?


get some ntp software like automachron for windows or ntpd for linux and just
have your computer's clock sync off of a government or university time server...
It will bypass the bios clock and keep your computer within milliseconds of the
atomic clock in colorado..Windows has its own native time service as well but I have never managed to get it working and assume it is of the same low quality as most of MS's other software