[time-nuts] 32768Hz from 10MHz

Murray Greenman Murray.Greenman at rakon.com
Wed Jul 23 14:35:24 EDT 2008


There is no easy way to divide directly from 10MHz to 32768Hz.

On my web site at www.qsl.net/zl1bpu/MICRO there are several signal
generator projects which would do the job of generating 32768Hz from
10MHz for you.

With any of these (single chip micro approach, using 24-bit Direct
Digital Synthesis) the closest you'd get would be to load 078CBC into
the DDS. The result would be 32767.9846Hz, an error of 0.47ppm (14
sec/year).

By extending the algorithm to 32 bit, as I did in my LF Exciter, the
step resolution improves to 0.23mHz, and by loading 8637BD0 you'd
generate 32767.999917 Hz, or an error of 2.5ppb. To put it into
perspective, that's an error of 8 seconds in 100 years!

Similar maths would apply to any micro-based DDS. I suggest adapting my
design purely because it's simple, and a chip like the ATTiny2313 is
well suited to the job.

Regards,
Murray ZL1BPU




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