low power watch (32.768Khz) xtal recommendation? (of topic)

teekaytk · Joined: 14 Jan 2005 Posts: 28

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: 1634 Location: Perth, Australia

10 minutes per year is not accurate. You can get away with a 50 cent crystal to meet this requirement.
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teekaytk · Joined: 14 Jan 2005 Posts: 28

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

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

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

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