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You should use opamp (with dual power supply) to amplify signal from currrent transformer (if its small to much).
Then you can make bridge rectifier with schotky diodes (low voltage drop). Then you need ADC (inside mcu or outside), so you need to get samples of current and do some math (to get effective value).
Hi .. Try this circuit from this application note **broken link removed**
I have used it.. Working good with CT and AVR.
Also if you want to get wave sign.. Use Opamp to bring up center of sine to positive so you could measure both side of amplitude in positive voltage. or you could measure only one side of sine by using opamp cut off negative side.(but i don't know is it reading will the same as negative sine or not. You will nees some fast CPU like ATMEGA @ 16M. Take sample and then interpulate reading for error correction and then find out amplitude to get value and must calibrate it to real current value.
OR
if you don't want to add any extra silicon bits.
Use the Mega 8 A/D converter Differential Input Channel with adjustable Gain of 10x or 200x to measure the AC current straight from the current transformer. (may have to add a bias voltage)
For RMS, just square the samples, and sum them. When you have a heap of these summed sqaured values, calculate the mean. RMS = root-mean-square.
Ok I look in analog.com and other solutions in forum , then I found on Linear technologies site IC LTC1966 witch is RMS to DC converter with 5V single supply and it need only two capacitators to work.
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