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'[PIC]:Measuring AC with a DC offset'
2001\12\12@120359 by

If some recall, I was looking for a current measureing device, and I found a
relativly inexpensive unit, that is a hall effect device. Basically you
connect up 5VDC, ground and the device under test, and you get a AC waveform
riding on a 2.5VDC signal.  The amplitude of the DC referenced AC signal is
supposed to vary according to the amount of current but I still need to run
some tests since I was using a dimmer switch to vary the current, but it
simply chops it to lower the voltage and thus the current.  Need to buy some
various voltage light bulbs.

Anyway, has anyone ever measured the AC voltage relative to the DC offset?

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if the DC offset is constant I don't see any problem except you need
probably a zero crossing detection, the easyest way is maybe to
extract the AC voltage with a capacitor and to compare with gnd, but
may be any other solution ( compare directly with the offset ).

Vasile

On Wed, 12 Dec 2001, Micro Eng wrote:

{Quote hidden}

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Why not take advantage of the offset?  If you're a/d range is 0-5, 2.5 would
be perfect if you want to look at the whole wave.  Just subtract half of the
range if you want to compare with ground.  Keep in mind if you're sample
rate is high, and your system has a little noise, zero crossings can be
fuzzy at transitions.

{Original Message removed}

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