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# Digitizing AC sine wave by voltage measurament

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#### Miguel Gonzalez

##### New Member
Hi!, I need help to digitize an AC sine wave by voltage measurament of a half cycle in a 60 Hz AC wave form. My project consist in operating while I have a sine waveform in my AC power line and to stop if any other type of waveform is detected. Any suggestions or ideas. thank you... This is not an easy task. I have tried the PIC 16F876 by converting the voltage to DC. not fast enough for what I need. In conclusion I need to detect the sine wave. Thank you in advance...

Detecting signal other than sine wave??? :shock:

This is going to be difficult because after capturing the signal, you need to characterize it and on basis of that detect if it is sine or not.

For digitizing the signal, first of all you require an ADC which can support sampling rate of atleast 60*2 = 120 Samples per second. This is according to sampling theorem. But for characterizing sine wave, this is very less. You need atleaset 10-20 data points per cycle. That comes out to be 60*20 = 1200 samples per second. This is not considered as very high sampling rate. Most cheap and common ADCs can do it very well. Remember more the sampling rate, more will be your detection accuracy.

For characterizing sine wave, I have a trick. Check it out if it works.
First of all, convert the incoming signal to unity amplitude i.e. 1V(peak to peak) using scaling. In your code make a lookup table consisting of sine values of 1V(p-p) signal sampled at same interval as incoming signal. Compare the incoming signal values to that with the look-up table values. These may not be exactly same so you need to do some math stuff over here. If values matches by a percentage say 85% (or whatever you desire), then the wave is a sine wave.
How does it sound?

Thanks for your help! We are going to do 8 sampling in 4.133ms. Same as your technique peak to peak but at a different voltage.

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