Hi Javier! Thanks for your help.
On 24/11/2011, at 13:16, Javier Herrero <jherr...@hvsistemas.es> wrote: > El 24/11/2011 13:56, Miguel Gonçalves escribió: >> >> >> Right! That is what I am doing. >> >> The problem is the drift between adjustments. Arduino's clock is slow 25 ms >> every minute and if temperature changes it will surely be different. >> >> > That is more than 400ppm error, that sounds quite high. Is the clock > frequency of the Arduino so drifted? I would try first to check (and correct > a bit) the source of that error. If the crystal frequency is ok, perhaps > there is an error in the programming of the timer that generates the timing > interrupt. I am using an Arduino Uno that presumably is running at 16 MHz. I am using a 16 bit timer with a 256 pre-scaler: 16000000 / 256 = 62500 Hz 1 / 62500 = 16 us 65536 - 62500 = 3036 I am setting the counter to 3036 and let it overflow after 65535. If I check the error every second I see the clock getting behind correct time and after 60 seconds it's 25 ms apart from UTC. Perhaps I should increase the initial value from 3036 to 3036+25E6/(60/16). I will make the second shorter this way. What do you think? Cheers, Miguel > > Regards, > > Javier > > > _______________________________________________ > 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. _______________________________________________ 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.