piclist 2000\11\08\125259a >
Thread: The tintinnabulation of the noise
www.piclist.com/techref/microchip/devices.htm?key=pic
BY : David VanHorn email (remove spam text)

>> Let's see: 120 hz = 8.33 milliseconds per oscillation.  If I sample at
twice this, that's 4.33 milliseconds.  sampling at exactly twice is cutting
it fine, so say we sample at four times that's ~2 milliseconds.

IF you're exactly locked to the interference waveform, IF it's symmetrical,
and IF it's consistent from one wave to the next, then two samples
equidistant in time will cancel the waveform.  Any two points, 180 degrees
apart on a symmetrical waveform cancel to zero. (that's the inverse
definition of this sort of symmetry)

However. If the waveform is more complex, or varies much, or you're not
exactly synced to it, then more samples will be needed to clean it up.

Since you're trying to read DC, I'd low-pass it as much as you can stand,
and start there.

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