Other options for time
I have used a DS1307 for keeping track of date and time, but have found that even the SparkFun RTC that uses a 1307 is not very accurate over time. The best I have been able to accomplish is losing about 10 seconds per day. I would like to build a clock but need it to maintain fairly accurate time (so I don't have to reset the thing every few days / weeks). Are there any other options I should be looking at? Can the prop keep accurate time by using cnt, or will I run into the same problems? I have also seen the PropNIC product by uconnect and though that maybe I could use it to connect to a network time server to get the time and periodically update the DS1307 or prop, but don't know where to begin. Anyone have any ideas or places to start looking?
Comments
en.wikipedia.org/wiki/WWV_(radio_station)
http://www.ntp-time-server.com/wwvb-receiver/wwvb-receiver.htm
If you use cnt for your time base, you're only as accurate as your crystal.
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·"I have always wished that my computer would be as easy to use as my telephone.· My wish has come true.· I no longer know how to use my telephone."
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Post Edited (Ken Peterson) : 10/30/2008 3:25:00 PM GMT
I've used WWVB, but I could only synch at night and not at all during periods of bad weather.
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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
I don't see how the DS1307 is losing 10 seconds per day unless the crystal is really, really bad...
There's a version of the DS1307 that has an integrated crystal that is much more precise.· But, it doesn't come in a DIP package...
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4051
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Chris Savage
Parallax Engineering
www.maxim-ic.com/quick_view2.cfm/qv_pk/4627
LIVE DEMO can be seen here:
www.maxim-ic.com/landing.cfm?lp=26
Sure, I have code for the Oncore, plus a DST correction calc. I'm not at home for a few days, but you can remind me at jpeakall AT madlabs DOT info. You can also get an external antenna with enough lead to get you a signal, I'm sure. The other thing that is nice about the Oncore is it has a built in RTC for periods of non reception, and it has a 'keep alive" power input that you can hook a super cap too and keep the time during power outage etc. It also has an accurate 1pps output too.
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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
I see a few of the Oncores listed on ebay and they don't seem to come with an external antenna. Do you use one and are they required for a non-basement setup?
If you see a GT or UT get those. How finicky are your timing needs? One day I am going to change to a UT when I see one cheap. They can have the 1pps adjusted to account for transmission delay errors etc. The only reason I care is I am slowly building a seismicmonitor, and being as closely synched time wise as possible increases the accuracy of origin triangulation and such. For most purposes, any GPS is fine.
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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
For the antenna, did you buy the Motorola active antenna, like this:
http://www.tedss.com/stock/images/1994/1994000169.jpg
or something less expensive? This antenna is more expensive than the GT module.
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www.madlabs.info - Home of the Hydrogen Fuel Cell Robot
best regards
Stefan