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Topic: DCF77 Master Pulse Bracket Clock (Read 9704 times) previous topic - next topic

oliverb



Quote
it transpires we have no LF time transmitter in Australia


What about using a  GPS module instead?
I think it will be my next project.


How about both, so you can compare the results... :-)



I think in the long run they are both 100% . I don't know about GPS but DCF77 only updates once a minute on a perfect signal for the other time your are relying on the Arduino for timing. My clock looses a second around 6 or 7 times a day (it always corrects itself) so I presume using the Arduino for a clock without any external correction is not a good idea.

My voltmeter clock http://home.btconnect.com/brettoliver1/Voltmeter_Clock/Voltmeter_Clock.htm built from a design by Alan-Parekh http://alan-parekh.com/projects/multimeter-clock-simpson-260/ losed many seconds a day until I sync'd it to my original logic master clock every 30 seconds.

I would expect 1 second in 2 weeks on a properly adjusted quartz clock in a reasonably stable temperature. Maybe  I could add a trimmer to the Arduino crystal ?

fungus


I think in the long run they are both 100% . I don't know about GPS but DCF77 only updates once a minute on a perfect signal for the other time your are relying on the Arduino for timing.


Yes, I looked into the DCF77 signal a few months ago because I had an antenna from a broken clock. I decided not to use it because the signal is terrible in this room (I live in a tall building). The signal was almost 100% noise. It was OK out in the street but not in here.

(It's fun to look at the DCF signal on an oscilloscope - you can see the pulses very easily out in the street...indoors it was just garbage, no clear pulses at all)


My clock looses a second around 6 or 7 times a day (it always corrects itself) so I presume using the Arduino for a clock without any external correction is not a good idea.


It would be terrible. If you put two Arduinos running "blink" side by side and simultaneously press reset on both they only take a minute or two to noticeably go out of sync with each other.


I would expect 1 second in 2 weeks on a properly adjusted quartz clock in a reasonably stable temperature. Maybe  I could add a trimmer to the Arduino crystal ?


Maybe better to figure out the time error in software (you have a good reference clock!) and add extra cycles to the calculations to compensate.
Advanced Arduino

oliverb

I think it's the crystal that is the problem quartz clocks use a 32.768Khz crystal. You just divide by 2  15 times to get 1 second. 16mhz on the Arduino divided by 2  24 times gives 0.95 of a second. Maybe there are other value crystals that will work?

fungus


I think it's the crystal that is the problem quartz clocks use a 32.768Khz crystal. You just divide by 2  15 times to get 1 second. 16mhz on the Arduino divided by 2  24 times gives 0.95 of a second. Maybe there are other value crystals that will work?


I think an AVR chip can divide by 16 million ... it won't rely on a simple counter overflow to indicate seconds.

Advanced Arduino

oliverb

I notice there are loads of Real Time Clocks for Arduino they all seem to have  crystals of 32.768kHz. Is this what they do just keep the time in sync?

fungus


I notice there are loads of Real Time Clocks for Arduino they all seem to have  crystals of 32.768kHz. Is this what they do just keep the time in sync?


Most (all?) digital watches use those crystals. I think the RTC manufacturers are just using what's readily available.
Advanced Arduino

oliverb


I have changed my display by adding pulse length and cycle length to the lower row of the LCD.



Latest code can be downloaded here http://home.btconnect.com/brettoliver1/LCD_Master_Clock/DCF77_LCD_Clock.zip

Main site is here http://home.btconnect.com/brettoliver1/LCD_Master_Clock.htm

RH314



Quote
it transpires we have no LF time transmitter in Australia


What about using a  GPS module instead?
I think it will be my next project.


How about both, so you can compare the results... :-)



DCF77 like long wave time signal is regional, but can be received indoors. GPS is global, but will work indoors if signal attenuation is moderate, like 2 story flat. Combining the two would be VERY interesting.

An awesomely cool clock !

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