On Tue, 13 Dec 2005 06:30:29 +1100 you wrote: >What would you recommend then if you wanted the accuracy of a normal >digital watch? A standard 32KHz xtal with CKOPT set should be fine. I've used one with an AVR without problems in the async timer of a mega32. I'd guess the problem is using a surplus xtal. The one I used is part #332417 from www.distrelec.at Alternatively, if the xtal gives a consistent 3 seconds an hour error then one could just drop a second every 1200 in firmware. >Chad O'Neill > >Ralph Hilton wrote: > >>On Mon, 12 Dec 2005 15:12:52 +1030 you wrote: >> >> >> >>>Hi All, >>> >>>I'm trying to get a RTC going on a Mega 8 using a 32 kc watch crystal >>>as per Atmel app note AVR134. >>> >>>The code works well except that the time gains about 3 seconds per hour. >>> >>>The crystal is a surplus watch crystal that I had and I have no idea of >>>the capacitance >>>load that it requires. >>> >>>Anyone on the list used a watch crystal on an avr and how accurate can >>>you make them for >>>time keeping ? >>> >>>Do I need a 6pf or 10pf crystal? >>> >>>Do I need any extra caps to gnd, not using any at the moment, would a >>>small trimmer help? >>> >>> >> >>I would enable the CKOPT fuse which makes added capacitors unnecessary. >>I would expect a few seconds a day error from a new crystal. >>If you want something more accurate maxim give away free samples of the DS32KHz oscillator >>which is good to about a second a week. >>-- >>Ralph Hilton >>http://www.ralphhilton.org >>C-Meter: http://www.cmeter.org >>FZAOINT http://www.fzaoint.net >> >> >> >> >>Yahoo! Groups Links >> >> >> >> >> >> >> >> >> >> >> >> -- Ralph Hilton http://www.ralphhilton.org C-Meter: http://www.cmeter.org FZAOINT http://www.fzaoint.net
Message
Re: [AVR-Chat] RTC on Mega 8
2005-12-12 by Ralph Hilton