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teekaytk

Joined: 14 Jan 2005
Posts: 28

 low power watch (32.768Khz) xtal recommendation? (of topic) Posted: Thu Dec 22, 2005 4:00 pm Hi all I am looking for the most accurate but very low power watch xtal or oscillator module. need timing accurate to 10 minutes per year, any ideas / help is most appriciated thanks
asmallri

Joined: 12 Aug 2004
Posts: 1626
Location: Perth, Australia

 Posted: Thu Dec 22, 2005 5:06 pm 10 minutes per year is not accurate. You can get away with a 50 cent crystal to meet this requirement._________________Regards, Andrew http://www.brushelectronics.com/software Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!
teekaytk

Joined: 14 Jan 2005
Posts: 28

 Posted: Thu Dec 22, 2005 7:46 pm hi is there a formula to calculate the accuracy in a years time using ppm value? my device is going to be in extremly variable temperatures from -30 to +30 degress centigrades regards
kender

Joined: 09 Aug 2004
Posts: 768
Location: Silicon Valley

 Posted: Thu Dec 22, 2005 8:20 pm As you probably know, PPM means Parts Per Million. For example Xppm means that for one (1) million oscillations the crystal will drift X oscillations. One year is 31 556 926 seconds. During this time 32.786kHz crystal will make 31556926 * 32768 = 1034057351168 oscillations, or 1034057.351168 million oscillations. At a drift rate of X ppm, it will drift X * 1034057.351168 oscillations, or X * 1034057.351168 / 32768 seconds. ////
jecottrell

Joined: 16 Jan 2005
Posts: 559
Location: Tucson, AZ

 Posted: Thu Dec 22, 2005 8:23 pm You may be interested in temperature controlled oscillators. Google: tcxo 32.768 Extremely accurate. Made for your problem. (Why settle for such lousy accuracy when you can have better.... if cost is no object.)
teekaytk

Joined: 14 Jan 2005
Posts: 28

 Posted: Fri Dec 23, 2005 5:19 am thanks for your reply and details, i'll look into the tcxo and xtal i was using turns out to be 25 mins out at -30 deg (50ppm) so thanks for all the info agian, its been very helpful cheers
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