Apart from the GPS option, how about getting a 1 second (or whatever) tick signal from the guts of a cheap digital clock? You should be able to pick them up cheaply enough, and the pcbs are generally small and powered from 1.5V or so. RP On 13 January 2011 09:37, Gordon Williams wrote: > > ----- Original Message ----- > From: "Geo" > To: "Microcontroller discussion list - Public." > Sent: Wednesday, January 12, 2011 3:20 PM > Subject: Re: [PIC] Oscillator stability with temperature change > > >> Gordon Williams wrote: >> >> > I'm designing a count down timer to start nordic ski racers at set > intervals >> > over the period of an 8 hour day. =A0I wondering what is the best way = to > get >> > an accurate time over this period with little drift. =A0What I want to= do > is >> > synchronize the device to the rest of the timing system at the beginni= ng > of >> > the day and let it run without having to resync it later. =A0The accur= acy > that >> > I would like to achieve is 0.5 sec over 8 hours or roughly 17 ppm over= a >> > temperature range of -20 C to +40 C. >> > >> Personally, I would use a GPS module with 1 p.p.s output but the initial >> sync might be a problem. >> >> George Smith >> > > The GPS will only be used for testing and calibration - not in the field. > > Regards, > > Gordon Williams > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .