[time-nuts] 1pps to 10kHz

Murray Greenman Murray.Greenman at rakon.com
Mon Feb 22 02:27:05 UTC 2010


Ashley,

It should be quite easy with any reasonable micro (PIC included) to
generate 10kHz using a 1pps reference.

My approach would be to operate a software DDS (essentially a numerical
oscillator) with a sine-wave look-up table and 8-bit R-2R ladder on an
output port. Operate it in the micro's main loop and choose the phase
increment value which gets closest to 10kHz.

Then all you do is operate a very short interrupt at 1pps which clears
the phase accumulator (or sets it to some arbitrary value). Since at
10kHz the multiplication ratio is very low, the reference provided to
the micro need not be anything stunning (crystal to 50ppm or cheap
TCXO).

With a good reference you could make the interrupt operate every n
interrupts. I've used this technique successfully for radio transmission
at 181kHz using a 2ppm TCXO and AVR micro. See
www.qsl.net/zl1bpu/MICRO/EXCITER/Index.htm.

Regards,
Murray Greenman




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