超聲波測距原理見：超聲波測距原理
超聲波測距模組：HC-SR04
採用定時器及外部中斷方式

/*******************************************************************************
    Driver for HC-SR04 
  測試平臺：STM32F103ZET6最小系統
  引腳連線：TRIG--PC0   ECHO--PC1
*******************************************************************************/
#include "sonar_hcsr04.h"
 

#include "systime.h"

#define SONAR_PORT  GPIOC
#define TRIG_PIN    GPIO_Pin_0
#define ECHO_PIN    GPIO_Pin_1

static volatile uint32_t measurement;


void hcsr04Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;    
    EXTI_InitTypeDef EXTI_InitStructure;
    TIM_TimeBaseInitTypeDef  TIM_TimeBaseInitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC , ENABLE);

    GPIO_InitStructure.GPIO_Pin = TRIG_PIN;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_Init(SONAR_PORT, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin = ECHO_PIN;                   
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;         
    GPIO_Init(SONAR_PORT, &GPIO_InitStructure); 
    GPIO_ResetBits(SONAR_PORT, ECHO_PIN);

    GPIO_EXTILineConfig(GPIO_PortSourceGPIOC, GPIO_PinSource1);  // 中斷線以及中斷初始化配置
 


    EXTI_ClearITPendingBit(EXTI_Line1);

    EXTI_InitStructure.EXTI_Line = EXTI_Line1;
    EXTI_InitStructure.EXTI_Mode = EXTI_Mode_Interrupt; 
    EXTI_InitStructure.EXTI_Trigger = EXTI_Trigger_Rising_Falling;
    EXTI_InitStructure.EXTI_LineCmd = ENABLE;
    EXTI_Init(&EXTI_InitStructure);     

    /* Enable TIM5 clock */
 

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM5, ENABLE);

    /* TIME5 base configuration */
    TIM_TimeBaseInitStructure.TIM_Period = 0xFFFF;                   //  
    TIM_TimeBaseInitStructure.TIM_Prescaler = 72-1;                  // 設定預分頻,F=72MHz/72=1MHz,T=1us
    TIM_TimeBaseInitStructure.TIM_ClockDivision = 0;                 // 設定時鐘分頻係數,不分頻
    TIM_TimeBaseInitStructure.TIM_CounterMode = TIM_CounterMode_Up;  // 向上計數模式
    TIM_TimeBaseInit(TIM5, &TIM_TimeBaseInitStructure);              // 初始化TIME5

    TIM_Cmd(TIM5, DISABLE); 
}

/**
 * 發出測試訊號
 */
void hcsr04StartRanging(void)
{
    GPIO_SetBits(SONAR_PORT, TRIG_PIN);
    delay_us(20);   //  The width of trig signal must be greater than 10us
    GPIO_ResetBits(SONAR_PORT, TRIG_PIN);
}

/**
 * 根據公式計算距離 
 * @return distance units:cm 
 */
float hcsr04GetDistance(void)
{
    // distance = measurement/2/1000*340 = measurement/59 (cm)  measurement-units:us
    float distance = measurement / 58.8;   // measurement-units:us

    return distance;
}

static void ECHO_EXTI_IRQHandler(void)
{
    if (EXTI_GetITStatus(EXTI_Line1) != RESET) {
        if (GPIO_ReadInputDataBit(SONAR_PORT, ECHO_PIN) != 0) {  // 等待高電平回波
            TIM_Cmd(TIM5, ENABLE);  
        } else {
            TIM_Cmd(TIM5, DISABLE);  
            measurement = TIM_GetCounter(TIM5);
            TIM_SetCounter(TIM5, 0); 
        }
    }
    EXTI_ClearITPendingBit(EXTI_Line1);
}

void EXTI1_IRQHandler(void)
{
    ECHO_EXTI_IRQHandler();
}