Whenever I've needed significant time / frequency accuracy, I've always used an off-air frequency standard. We have a couple of MF transmitters in the UK with spectacular stability, and these are easily frequency multiplied or divided to whatever you need. However, in MOST instances, a standard rock is accurate enough! Chris ----- Original Message ----- From: "Tauno Siitam" To: Sent: Thursday, November 28, 2002 9:16 AM Subject: Re: [PIC]: Clock accuracy > Note: Don't expect too much accuracy out of your > run-of-the-mill crystal based oscillator. > You will get significant drift over time, > temperature, and I believe supply voltage. How large drift can I expect to be caused by temperature changes? I left my clock running last night and it was ahead 1 second after 3 hours and then stayed behind 4 seconds during next 6 hours. If the room temperature day/night change caused such a drift, what can you expect from extreme conditions in a rally car where temperature can change from -20C in the winter to +60C under the sun in the summer!? I'm starting to believe that using some kind of temperature controlled osc is a must in my case... Tauno -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads