理论推导

低通滤波器
见一阶RC低通滤波器的数学模型及算法实现 —— 奔跑的chanchanchan
$Y_n=A?X_n+(1?A)?Y_{n-1}$
$A=\frac{ΔT}{RC+ΔT}=\frac{ΔT}{\frac{1}{2πf}+ΔT}=\frac{1}{1+\frac{1}{2πfΔT}}$
高通滤波器
见一阶RC高通滤波器详解（仿真+matlab+C语言实现）—— 小麦大叔
$Y_n=A?Y_{n-1}+A?(X_n-X_{n-1})$
$A=\frac{RC}{RC+ΔT}=\frac{\frac{1}{2πf}}{\frac{1}{2πf}+ΔT}=\frac{1}{1+2πfΔT}$

产生测试信号

sin_cal.c

#include "sin_cal.h"
#include <math.h>

void sin_Init(sin_Type *Sin, float f, float delta_ms)
{
    Sin->angle = 0;
    Sin->delta = 2 * 3.141592653589793f * f * delta_ms / 1000.f;
    Sin->out = 0;
}

float sin_cal(sin_Type *Sin)
{
    Sin->angle += Sin->delta;
    if (Sin->angle > 6.283185307179586f)
        Sin->angle -= 6.283185307179586f;
    Sin->out = sin(Sin->angle);
    return Sin->out;
}

sin_cal.h

#ifndef __SIN_CAL_H__
#define __SIN_CAL_H__

typedef struct
{
    float angle;
    float delta;
    float out;
} sin_Type;

void sin_Init(sin_Type *Sin, float f, float delta_ms);	//f为设定的频率，delta_ms为时间间隔
float sin_cal(sin_Type *Sin);

#endif

生成波形

初始化

//...
sin_Type Sin_1, Sin_2;
//...
	sin_Init(&Sin_1, 1, 5);		//1  Hz的正弦波
	sin_Init(&Sin_2, 25, 5);	//25 Hz的正弦波
//...

定时器中断周期为1ms，每5ms输出一次数据

extern sin_Type Sin_1, Sin_2;

/********************* Timer0中断函数************************/
void timer0_int (void) interrupt TIMER0_VECTOR
{
	static int count = 0;
	float Data;
	if(++count >= 5)
	{
		count = 0;
		sin_cal(&Sin_1);
		sin_cal(&Sin_2);
		Data = Sin_1.out+Sin_2.out;
		printf("%f\r\n", Data);
	}
}

如图，生成了1Hz和25Hz的混合波形：
在这里插入图片描述

一阶滤波器

FirstOrderFilter.c

#include "FirstOrderFilter.h"

void fof_Init(fof_Type *fof, float f, float delta_ms, char HPForLPF) 
{
	fof->in_old = 0;
    fof->out = 0;
	fof->type = HPForLPF;
	fof->a = 2 * 3.141592653589793f * f * delta_ms / 1000.f;
	if(!HPForLPF)
	{
		fof->a = 1.f / fof->a;
	}
	fof->a = 1.f / (1.f + fof->a);
}

float FirstOrderFilter(fof_Type *fof, float in)
{
	if(fof->type)
	{
		fof->out = fof->a * fof->out + fof->a * (in - fof->in_old);
		fof->in_old = in;
	}
	else
		fof->out = fof->a * in + (1 - fof->a) * fof->out;
    return fof->out;
}

FirstOrderFilter.h

#ifndef __FOF_H__
#define __FOF_H__

typedef struct
{
    float a;
	float in_old;
    float out;
	char type;
} fof_Type;

void fof_Init(fof_Type *fof, float f, float delta_ms, char HPForLPF);	//f为截止频率，delta_ms为时间间隔，HPForLPF为类型选择
float FirstOrderFilter(fof_Type *fof, float in);

#endif

测试

//...
fof_Type fof_1, fof_2;
//...
	fof_Init(&fof_1, 1, 5, 0);	//低通滤波器，截止频率为1Hz
	fof_Init(&fof_2, 25, 5, 1);	//高通滤波器，截止频率为25Hz
//...

extern fof_Type fof_1, fof_2;
extern sin_Type Sin_1, Sin_2;

/********************* Timer0中断函数************************/
void timer0_int (void) interrupt TIMER0_VECTOR
{
	static int count = 0;
	float Data;
	if(++count >= 5)
	{
		count = 0;
		sin_cal(&Sin_1);
		sin_cal(&Sin_2);
		Data = Sin_1.out+Sin_2.out;
		printf("%f, %f, %f\r\n", Data, FirstOrderFilter(&fof_1, Data), FirstOrderFilter(&fof_2, Data));
	}
}