Signal Processing (in Java)

Question

I have a sensor that I am reading, currently the code is in Java, but I don’t think the problem is with the language, more suitable for the approach.

The sensor produces a signal with high and low pulses, approximately like a pulse. However, a "high" impulse is not always the same level, as well as a "low" one. I'm interested in the relative difference. However, this is not enough, because during one “session” both high and low values ​​can change (read the curve midpoint)

Ive included an image of 4 "types" of signals that I would like to process. The upper left is “perfect,” I’m sure that I can handle it already, the other three, unfortunately, are more common and less easy to use.

My current approach was to find the average value of the data and see how many times this point intersects, which will tell me how many large and low pulses were there.

I would like to know if there is an easy way to detect high and low pulses without using the averaging method.

Answer 1

When you stated that you wanted to extract the wave frequency, the first thing I thought about was the Fourier transform; this converts the signal from the time domain to the frequency domain. Given the following wave pattern:

This is the sine to which I added noise and trend. The main sine wave has a frequency of 1.5 Hz

You get this fourier transform

0hz, , . 1,5 , . ; , ( ).

Java

Apachi commons , . , ( ) . i i*samplingFrequency/noOfSamples.

java . , 2.

import org.apache.commons.math3.complex.Complex;
import org.apache.commons.math3.transform.DftNormalization;
import org.apache.commons.math3.transform.FastFourierTransformer;
import org.apache.commons.math3.transform.TransformType;

public class FourierTest {

    public static void main(String[] args) {

        double samplingFrequency=10; //hz, You will know this from your data and need to set it here



        double[] frequencyDomain = new double[input.length];

        FastFourierTransformer transformer = new FastFourierTransformer(DftNormalization.STANDARD);
        try {           
            Complex[] complex = transformer.transform(input, TransformType.FORWARD);

            for (int i = 0; i < complex.length; i++) {               
                double real = (complex[i].getReal());
                double imaginary = (complex[i].getImaginary());

                frequencyDomain[i] = Math.sqrt((real * real) + (imaginary * imaginary));
            }

        } catch (IllegalArgumentException e) {
            System.out.println(e);
        }

        //only to frequencyDomain.length/2 since second half is mirror image or first half
        for(int i=0;i<frequencyDomain.length/2;i++){
            double frequency=samplingFrequency*i/frequencyDomain.length;
            System.out.println("Frequency: " + frequency + "\t\tEnergyComponent: " + frequencyDomain[i]);
        }
    }

    static double[]  input = new double[]{
            0.017077407 , //sample at 0 seconds
            1.611895528 , //sample at 0.1 seconds
            2.063967663 , //sample at 0.2 seconds
            1.598492541 , //etc
            0.184678933 ,
            0.02654732  ,
            0.165869218 ,
            1.026139745 ,
            1.914179294 ,
            2.523684208 ,
            1.71795312  ,
            0.932131202 ,
            1.097366772 ,
            1.107912105 ,
            2.843777623 ,
            2.503608192 ,
            2.540595787 ,
            2.048111122 ,
            1.515498608 ,
            1.828077941 ,
            2.400006658 ,
            3.562953532 ,
            3.34333491  ,
            2.620231348 ,
            2.769874641 ,
            2.423059324 ,
            2.11147835  ,
            3.473525478 ,
            4.504105599 ,
            4.325642774 ,
            3.963498242 ,
            2.842688545 ,
            2.573038184 ,
            3.434226007 ,
            4.924115479 ,
            4.876122332 ,
            4.553580015 ,
            3.92554604  ,
            3.804585546 ,
            3.476610932 ,
            4.535171252 ,
            5.398007229 ,
            5.729933758 ,
            5.573444511 ,
            4.487695977 ,
            4.133046459 ,
            4.796637209 ,
            5.091399617 ,
            6.420441446 ,
            6.473462022 ,
            5.663322311 ,
            4.866446009 ,
            4.840966187 ,
            5.329697081 ,
            6.746910181 ,
            6.580067494 ,
            7.140083322 ,
            6.243532245 ,
            4.960520462 ,
            5.100901901 ,
            6.794495306 ,
            6.959324497 ,
            7.194674358 ,
            7.035874424 

        };
}

Answer 2

, . .

, sign(f(x)-f(x-1)) sign(f(x+1)-f(x))

. , , .

Answer 3

, .