1、需求

需要采集信号发生器给定正弦波的频率

2、方法

通过求导求符号，找出正弦波的所有波峰，波峰与波峰即为频率

3、问题

ADC时信号可能失真，出现小的信号抖动，影响找到正确的波峰

4、优化方案

在求导求符号前，先对信号进行移动平均，使曲线变得光滑

5、代码

#ifndef QFREQUENCYDETECTOR_H
#define QFREQUENCYDETECTOR_H


class QFrequencyDetector
{
public:
    /********************************************************************
    PURPOSE:
        构造频率探测类
    PARAMETERS:
        nFS              探测信号采样率
        nCount           探测信号持续出现次数
    RETURN VALUE:
        成功返回对应指数控件索引，否则返回-1
    *********************************************************************/
    QFrequencyDetector(int nFS, int nCount);

    /********************************************************************
    PURPOSE:
        计算信号频率
    PARAMETERS:
        dData              探测数据
    RETURN VALUE:
        探测成功返回信号频率，否则返回0
    *********************************************************************/
    double Calc(double dData);

private:
    int         m_nFS;      // 信号采样率
    int         m_nCount;   // 连续出现多少次
    double      m_dLast;    // 上一次的值
    int         m_nLastDiff;
    int         m_nLen;     // 上次顶点到这次顶点的采样数
    int         m_nCurCount;// 已出现多少次
    double      m_dLastFS;  // 上次频率

    double      m_dMean[30]; // 移动平均计算

};

#endif // QFREQUENCYDETECTOR_H


#include "qfrequencydetector.h"
#include <QDebug>
#include <QtMath>

QFrequencyDetector::QFrequencyDetector(int nFS, int nCount)
{
    m_nFS       = nFS;
    m_nCount    = nCount;
    m_dLast     = 0;
    m_nLen      = -1;
    m_dLastFS   = 0;
    m_nCurCount = 0;
    m_nLastDiff = 0;

    for ( int i = 0; i <30; i++ )
        m_dMean[i]  = 0;
}

double QFrequencyDetector::Calc(double dData)
{
    // 移动平均
    double dSum  = dData;
    for ( int i = 0; i < 29; i++ )
    {
        m_dMean[i]  = m_dMean[i+1];
        dSum        +=m_dMean[i+1];
    }

    m_dMean[29]  = dData;
    dData       = dSum/30.0;

    double dFreq    = 0;
    int nDiff       = 0;
    if ( dData > m_dLast )
        nDiff   = 1;
    else if ( dData < m_dLast )
        nDiff   = -1;
    else
        nDiff   = m_nLastDiff;

    if ( -1 != m_nLen )
        m_nLen++;
    // 峰值
    if ( (nDiff - m_nLastDiff < 0) && (0 != nDiff) )
    {
        if ( -1 != m_nLen )
        {
            dFreq       = 1.0*m_nFS/m_nLen;
            if ( qFabs(dFreq - m_dLastFS) < 0.2 )
            {
                m_nCurCount++;
            }
            else
            {
                m_nCurCount = 0;
                m_dLastFS   = dFreq;
            }
            //qDebug("--->%.10lf-%.10lf %d", m_dLastFS, dFreq, m_nLen);
            //qDebug("--->%.10lf-%.10lf %d", m_dLastFS, dFreq, m_nCurCount);
            m_nLen      = -1;
        }
        else
        {
            m_nLen++;
        }
    }

    m_dLast         = dData;
    m_nLastDiff     = nDiff;

    if ( m_nCurCount >= m_nCount )
    {
        m_nCurCount = m_nCount;
        return m_dLastFS;
    }
    else
        return 0;
}