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# AC current measurement

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Hi... I have a simple question, yet for some reason I'm blocked and can't figure out how to do this.

I have a system which generates a variable AC current . What I need to do is measure this AC current and somehow feed it back to a microcontroller (passing through a ADC first). In order to do this, I guess I need to take the AC current and obtain from it a proportional DC voltage level which I cand send back to the microcontroller.

Can anyone help me find the best way to achieve this?

Thank you!

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What you will find is that you already have a circuit. The AC is divided across whatever elements you have and the voltage divided by the resistance is the current. In the case of a single element, you don't have a voltage divider. But you still have the voltage and resistance and thus the current. What you are guessing at is the theoretcal situation in which you have a variable load with an AC source. Maybe a light activated resistor. But I think that even an ammeter uses the voltage over the known resistance to calculate the current.

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I understand, but what I need to know is how to obtain a variable DC voltage level, which is proportional to the variable AC waveform I'm feeding into my system.

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Hi soundboy, I know very little, but maybe you can use a hall effect sensor for measuring the current, then feed the signal from that to a frequency to voltage converter.

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use a coil and opamp circuit, you can convert AC current to DC voltages.

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I understand, but what I need to know is how to obtain a variable DC voltage level, which is proportional to the variable AC waveform I'm feeding into my system.

Hi Soundboy,
You described the function of a rectifier circuit.
It can be a simple, half-wave rectifier using only one diode but will have a 0.7V loss and won't rectify signals below 0.7V peak. It could also be a full-wave "absolute value" rectifier circuit using a couple of opamps, without any loss (can even have gain) and can rectify signals as low as millivolt levels.
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That's just what I needed.

Thank you!

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