一阶低通滤波的C语言实现

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#include <stdio.h>

#include <string.h>



/*************************** 模拟输入数据 ********************************/

float input_data[251] = {

    0.00, 0.86, 1.59, 2.10, 2.35, 2.35, 2.18, 1.94, 1.76, 1.73, 1.90, 2.26, 2.75,

    3.24, 3.63, 3.80, 3.70, 3.30, 2.68, 1.93, 1.18, 0.54, 0.11, -0.10, -0.11,

    0.00, 0.11, 0.10, -0.11, -0.54, -1.18, -1.93, -2.68, -3.30, -3.70, -3.80, 

    -3.63, -3.24, -2.75, -2.26, -1.90, -1.73, -1.76, -1.94, -2.18, -2.35, -2.35,

    -2.10, -1.59, -0.86, 0.00, 0.86, 1.59, 2.10, 2.35, 2.35, 2.18, 1.94, 1.76, 

    1.73, 1.90, 2.26, 2.75, 3.24, 3.63, 3.80, 3.70, 3.30, 2.68, 1.93, 1.18,

    0.54, 0.11, -0.10, -0.11, 0.00, 0.11, 0.10, -0.11, -0.54, -1.18, -1.93, 

    -2.68, -3.30, -3.70, -3.80, -3.63, -3.24, -2.75, -2.26, -1.90, -1.73,

    -1.76, -1.94, -2.18, -2.35, -2.35, -2.10, -1.59, -0.86, 0.00, 0.86, 1.59,

    2.10, 2.35, 2.35, 2.18, 1.94, 1.76, 1.73, 1.90, 2.26, 2.75, 3.24, 3.63, 

    3.80, 3.70, 3.30, 2.68, 1.93, 1.18, 0.54, 0.11, -0.10, -0.11, 0.00, 0.11,

    0.10, -0.11, -0.54, -1.18, -1.93, -2.68, -3.30, -3.70, -3.80, -3.63, -3.24,

    -2.75, -2.26, -1.90, -1.73, -1.76, -1.94, -2.18, -2.35, -2.35, -2.10, -1.59,

    -0.86, 0.00, 0.86, 1.59, 2.10, 2.35, 2.35, 2.18, 1.94, 1.76, 1.73, 1.90, 2.26,

    2.75, 3.24, 3.63, 3.80, 3.70, 3.30, 2.68, 1.93, 1.18, 0.54, 0.11, -0.10, -0.11,

    0.00, 0.11, 0.10, -0.11, -0.54, -1.18, -1.93, -2.68, -3.30, -3.70, -3.80, -3.63, 

    -3.24, -2.75, -2.26, -1.90, -1.73, -1.76, -1.94, -2.18, -2.35, -2.35, -2.10, -1.59,

    -0.86, 0.00, 0.86, 1.59, 2.10, 2.35, 2.35, 2.18, 1.94, 1.76, 1.73, 1.90, 2.26, 2.75, 

    3.24, 3.63, 3.80, 3.70, 3.30, 2.68, 1.93, 1.18, 0.54, 0.11, -0.10, -0.11, 0.00, 0.11,

    0.10, -0.11, -0.54, -1.18, -1.93, -2.68, -3.30, -3.70, -3.80, -3.63, -3.24, -2.75,

    -2.26, -1.90, -1.73, -1.76, -1.94, -2.18, -2.35, -2.35, -2.10, -1.59, -0.86, 0.00};



float get_data(void)

{

  static int i = 0;

  return (input_data[i++]);

  if (i == 251) //轮回

    i = 0;

}



float fc = 2.0f;     //截止频率

float Ts = 0.02f;    //采样周期

float pi = 3.14159f; //π

float alpha = 0;     //滤波系数



/************************ 滤波器初始化 alpha *****************************/

void low_pass_filter_init(void)

{

  float b = 2.0 * pi * fc * Ts;

  alpha = b / (b + 1);

}



float low_pass_filter(float value)

{

  static float out_last = 0; //上一次滤波值

  float out;



  /***************** 如果第一次进入，则给 out_last 赋值 ******************/

  static char fisrt_flag = 1;

  if (fisrt_flag == 1)

  {

    fisrt_flag = 0;

    out_last = value;

  }



  /*************************** 一阶滤波 *********************************/

  out = out_last + alpha * (value - out_last);

  out_last = out;



  return out;

}



void main(void)

{

  float result[251];



  low_pass_filter_init();

  for (int i = 0; i < 251; i++)

  {

    result[i] = low_pass_filter(get_data());

    printf("%f,", result[i]);

  }

}