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How do I measure AC current (0 - 7 Amps) using a microcontroller? Answered

 I know how to design microcontroller circuits using PIC/ATMega processors but my analog experience is lacking. I understand I can use a transformer to transduce the current going through  a cable, or use a Hall-Effect based transducer in a similar fashion. How do I scale the output voltage of the transducer (DC in the Hall effect, and AC in the simple coil) to match the -VRef to +VRef swing of the A/D converter built into the microcontroller?  The only thing I know about analog circuits is "ground" is the place you grow roses...

David, Melbourne, Florida


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Best Answer 10 years ago

If you're measuring non-mains voltages, you can also measure with a simple resistor in series with the load. Voltage across the resistor is directly proportional to current.

Unless you want to know instantaneous current to calculate true RMS or such like, you need to rectify  that voltage signal to a DC level for measurement, so the final answer is unipolar and not bipolar. To do THAT ideally you need to use a "perfect rectifier", which is made with an op amp, a diode and a couple of resistors.