On Mon, 13 Aug 2001, Scott F. Touchton wrote:

>
> for 60Hz notch... sample at an even harmonic frequency and average the
> result.
>

With the added benefit that you'll notch 30Hz, 15Hz, 7.5Hz, ...
and in general 60/N Hz, including when N -> inifinity. In other words,
you'll filter DC too!

I'm not sure of the application, but you'll probably want to filter
60Hz by integrating over 1/60'th of a second time interval. For
example, if you had a voltage to frequency converter as your A/D then
you can count the pulses it emits for 16.6666 mSec. Or if you have a
successive approximation A2D, then you could synchronously sample say
60*16 times per second and average the last 16 samples (add them
together and then shift right 4) to get a representation of the
signal minus 60Hz. Note that both of these suggestions are really low
pass filters with a notch at 60Hz and not Notch filters per-se.

Scott

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