measure ac voltage adc
shahrol_hisham,
The most straighforward way is to convert the AC voltage to DC using one of the following:
A) Precision Rectifier followed by a Low Pass filter
B) RMS to DC converter
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A) will result in a DC voltage that is proportional to the average value of the AC input. Google on "Precision Rectifier" for precision rectifier circuits.
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B) will result in a DC voltage that is proportional to the RMS value of the AC Input. There are several IC RMS to DC converters available. Visit Analog Devices' web site.
Regards,
Kral