超声波传感器 STM32 测距代码

下面是使用STM32与超声波传感器进行测距的代码示例：

#include "stm32f10x.h"
#include <stdio.h>

void GPIO_Configuration(void);
void TIM_Configuration(void);
void Delay_us(uint32_t nTime);
float get_distance(void);

volatile uint32_t TimingDelay = 0;

int main(void)
{
    GPIO_Configuration();
    TIM_Configuration();

    while(1)
    {
        float distance = get_distance();
        printf("distance: %.2f cm\n", distance);
        Delay_us(50000);
    }
}

void GPIO_Configuration(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    // 初始化GPIOB10
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_Init(GPIOB, &GPIO_InitStructure);

    // 初始化GPIOB11
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB, ENABLE);
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_11;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOB, &GPIO_InitStructure);
}

void TIM_Configuration(void)
{
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    // 初始化TIM2
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);
    TIM_TimeBaseStructure.TIM_Period = 0xFFFF;
    TIM_TimeBaseStructure.TIM_Prescaler = 72 - 1;
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);
    TIM_Cmd(TIM2, ENABLE);

    // 初始化TIM2中断
    TIM_ITConfig(TIM2, TIM_IT_CC1, ENABLE);
    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    // 设置TIM2的CC1
    TIM_OCInitTypeDef  TIM_OCInitStructure;
    TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStructure.TIM_Pulse = 10;
    TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM2, &TIM_OCInitStructure);
}

void Delay_us(uint32_t nTime)
{
    TimingDelay = nTime;
    while(TimingDelay != 0);
}

void TIM2_IRQHandler(void)
{
    if(TIM_GetITStatus(TIM2, TIM_IT_CC1) != RESET)
    {
        TIM_ClearITPendingBit(TIM2, TIM_IT_CC1);
        TimingDelay--;
    }
}

float get_distance(void)
{
    float distance = 0;
    uint32_t time_start, time_stop;
    GPIO_SetBits(GPIOB, GPIO_Pin_10);
    Delay_us(10);
    GPIO_ResetBits(GPIOB, GPIO_Pin_10);
    while(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_11) == RESET);
    time_start = TIM_GetCounter(TIM2);
    while(GPIO_ReadInputDataBit(GPIOB, GPIO_Pin_11) != RESET);
    time_stop = TIM_GetCounter(TIM2);
    distance = (float)(time_stop - time_start) * 0.034 / 2;
    return distance;
}

其中，`GPIO_Configuration()`函数用于配置GPIO，将PB10设置为输出模式，用于控制超声波传感器的Trig引脚，将PB11设置为输入模式，用于读取超声波传感器的Echo引脚；`TIM_Configuration()`函数用于配置TIM2，将它设置为计数器模式，并设置其时钟频率为72MHz，使其能够计算出Echo引脚高电平的时间；`Delay_us()`函数用于延时一定的时间，以等待超声波发射并接收到返回的声波；`get_distance()`函数用于计算出距离，通过计算Echo引脚高电平持续的时间来计算出距离，公式为`distance = (float)(time_stop - time_start) * 0.034 / 2`，其中0.034为声速，除以2是因为声波需要往返传播。

在程序中，我们使用了定时器中断来实现延时，因为单片机在执行循环等待时会浪费大量的时间，因此使用定时器中断能够有效地提高程序效率。

需要注意的是，超声波传感器测距时需要注意避开反射面和避免多个传感器同时工作导致数据干扰。