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1. Voltage dividing network to reduce the peak to peak amplitude of 5 V
2. Add a DC offset of 2.5 VDC
3. The voltage swing will be from 0 V ( -220 V) to + 5V ( + 220 V)
4. Sample 2048 samples at Nyquist frequency (double the maximum frequency of the measured signal)
5. Use a RMS algorithm to calculate the RMS value
OR
use and RMS chip ( Analog Devices) and measure the DC output with the A2D
woudnt be easier if you rectify and filter ?A diode and a capacitor will give a DC proportional to the peak value. If the AC is a sine wave you will get the rms value just by multipliying by 0.7. Which can be taken into account in the resistive divider without having to multiply by software.
If not a sine wave I agree with klystron.
yes albert
i think also in ur solution but i think it will be special case (the sine wave input).
but also if we use the solution of klyston i think the reading should be refreshed every specific time the time will vary according to the nature of the input voltage.
If dani wants a simple voltmter for the AC mains (220v is mains voltage in some countries). I think that the simple solution is enough. Afer all the cheap digital multimeters dont have a true rms IC inside but just an ICL7107.
The error can be high for very distorted sine waves. With a square wave you will have an error of 30%.
You have to balance: Presicion, Cost and Microcontroller resources
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