----- Original Message ----- > 
> A solution is to use a different oscillator/divider IC that also
> supports a crystal oscillator, the 74HC4060. Using a 5.0688 mhz CPU
> crystal (which is readily available) and the IC's divide by 1024 (2^10)
> output, 4950 hz is obtained for input to the 8-step sine converter, 
> which then has an output of 618.75hz. This method maintains the low power
> provision of the original design. Of course, other crystal frequency
> and divider combos are possible; I think the "74HC" design is good
> to 20 mhz. (THe parts are available from Mouser or Jameco for $0.69
> and $0.65).
> 
> ...

Depends upon your energy budget for the clock and divider.
For an "absolute minimum" (sort of) energy, 
you could use a watch crystal (rumored to be about 32 Khertz)
and a smaller divider.  The major loading of the presumed
CMOS circuits is capacitive - 
      every cycle is a fixed number of electrons
and the lower the frequency the better.      :-)

This may be over-kill in your situation  - but interesting 




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