注意：定义GPIOB2为超声输出；GPIOB10为输入，定时器用tim2

///////////////////////////////////////////////////.CPP文件/////////////////////////////////////////////////////

#include "HCSR04.h"

#include "delay.h"
#include "sys.h"
int overcount;
float length=0;
void HCSR04_init()
 {
 GPIO_InitTypeDef GPIO_InitStructure;
 TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStructer;
 NVIC_InitTypeDef NVIC_InitStructure;
 RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB , ENABLE);
 RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
 
 
 
 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
 GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
 GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
 GPIO_Init(GPIOB, &GPIO_InitStructure);
 
 
 GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
  GPIO_Init(GPIOB, &GPIO_InitStructure);
 
TIM_DeInit(TIM2);
 TIM_TimeBaseInitStructer.TIM_Period=4999;
 TIM_TimeBaseInitStructer.TIM_Prescaler=7199; 
 TIM_TimeBaseInitStructer.TIM_ClockDivision=TIM_CKD_DIV1;
 TIM_TimeBaseInitStructer.TIM_CounterMode=TIM_CounterMode_Up; 
  TIM_TimeBaseInit(TIM2,&TIM_TimeBaseInitStructer);
  TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE);
  TIM_ITConfig(  
TIM2, 
TIM_IT_Update  |  
TIM_IT_Trigger,   
ENABLE 
);


  TIM_ClearFlag(TIM2,TIM_FLAG_Update);
  NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQChannel;  
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;  
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;  
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; 
  NVIC_Init(&NVIC_InitStructure);
  TIM_Cmd(TIM2,DISABLE);

  
 }
 
 float HCSR04_Read()
 {
 float sum=0,length1=0;
u8 i=0,j=0;
 u16 tim;
{
//  while(i!=5)
 for(i=0;i<5;i++)
{
PBout(2)=1;
delay_us(20);
PBout(2)=0;
while(GPIO_ReadInputDataBit(GPIOB,GPIO_Pin_10)==RESET);
TIM_SetCounter(TIM2,0);
TIM_Cmd(TIM2,ENABLE);


while(GPIO_ReadInputDataBit(GPIOB,GPIO_Pin_10)==SET); 
TIM_Cmd(TIM2,DISABLE);
tim=TIM2->CNT;
length1=tim/58.0*100;
TIM2->CNT=0;
sum+=length1;
} 

}
length=sum/5;
        sum=0;
return length;

 

 }

///////////////////////////////////////////////////.h文件//////////////////////////////////////////////////////////////////

#include "stm32f10x_lib.h"


#define PBout(n)   BIT_ADDR(GPIOB_ODR_Addr,n)  //Êä³ö 
#define PBin(n)    BIT_ADDR(GPIOB_IDR_Addr,n)  //ÊäÈë 
extern  float HCSR04_Read();
extern  void HCSR04_init();
//extern  void HC_RS04_Init();