Electronics > Beginners
AC measurement circuit question
Tom18991:
Please see the schematic below, which is one of many similar versions on the internet for measuring AC voltage on a microcontroller. If the AC source is independent of the microcontroller's power input (for example, the AC is coming from a sensor that generates its own signal and the microcontroller is powered with a 9v battery), then how can the microcontroller measure the DC voltage on the output of this circuit?
Benta:
Don't do this. You have 230 V live voltage on your MCU and display, it's potentially lethal.
Tom18991:
Thanks and no worries. I don't play with that kind of power. :) I'm borrowing the concept to measure the voltages off a variable reluctance sensor. The volts might climb up to 20-30v, but without the current of a power line. I see there's a ground at the bottom of the circuit, which I presume is tied to the arguido ground, which probably explains my confusion. I'll try it on a (safe) function generator and see how I get on...
Kleinstein:
The circuit is a crude form of a peak detector. It's slow and temperature dependent.
With a decent ADC inside the µC and only mains frequency it is usually better to do direct AC sampling and that do RMS calculation in software. Even a 8 Bit µC with 10 Bit ADC like 8 bit AVR can do that surprisingly well.
Tom18991:
Mains frequency? Meaning the frequency of the 220v? My actual project involves a low-current ac sensor, and the waveform is not a sign wave. I'll play with various circuits, and am looking for something cheap :) without the need to be all that accurate -- +/- 5% is plenty good enough for my purpose. I was just confused how this could even work, but probably just missed the fact that the sensor circuit appears tied to the Arduino ground plane.
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