基于STM32的hc-sr04超声波测距模块的代码

以下是基于STM32的hc-sr04超声波测距模块的代码示例：

#include "stm32f10x.h"

#define Trig_Pin GPIO_Pin_0
#define Echo_Pin GPIO_Pin_1
#define Trig_Port GPIOC
#define Echo_Port GPIOC

void TIM2_Configuration(void);
float ultrasonic_measure(void);

int main(void)
{
    float distance;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC, ENABLE);
    GPIO_InitTypeDef GPIO_InitStruct;
    GPIO_InitStruct.GPIO_Pin = Trig_Pin;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(Trig_Port, &GPIO_InitStruct);

    GPIO_InitStruct.GPIO_Pin = Echo_Pin;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(Echo_Port, &GPIO_InitStruct);

    TIM2_Configuration();

    while(1)
    {
        distance = ultrasonic_measure();
    }
}

void TIM2_Configuration(void)
{
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;
    TIM_TimeBaseInitStruct.TIM_Prescaler = 72 - 1;
    TIM_TimeBaseInitStruct.TIM_Period = 0xFFFF;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = TIM_CKD_DIV1;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseInitStruct);

    TIM_OCInitTypeDef TIM_OCInitStruct;
    TIM_OCInitStruct.TIM_OCMode = TIM_OCMode_PWM1;
    TIM_OCInitStruct.TIM_OutputState = TIM_OutputState_Enable;
    TIM_OCInitStruct.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OCInitStruct.TIM_Pulse = 0;
    TIM_OC1Init(TIM2, &TIM_OCInitStruct);

    TIM_Cmd(TIM2, ENABLE);
}

float ultrasonic_measure(void)
{
    uint16_t TIM2_CountStart, TIM2_CountEnd;
    float Distance;

    GPIO_ResetBits(Trig_Port, Trig_Pin);
    TIM_SetCounter(TIM2, 0);
    while(TIM_GetCounter(TIM2) < 10); // delay 10us
    GPIO_SetBits(Trig_Port, Trig_Pin);

    while(GPIO_ReadInputDataBit(Echo_Port, Echo_Pin) == RESET);

    TIM_Cmd(TIM2, ENABLE);
    while(GPIO_ReadInputDataBit(Echo_Port, Echo_Pin) == SET);
    TIM_Cmd(TIM2, DISABLE);

    TIM2_CountStart = TIM2->CCR1;
    TIM2_CountEnd = TIM_GetCapture1(TIM2);

    Distance = (float)(TIM2_CountEnd - TIM2_CountStart) * 0.01715f; // Distance = (High level time * sound velocity (340M/S) / 2)

    return Distance;
}

代码中使用了STM32的定时器TIM2进行计时，测量距离的原理是通过发送一个10us的高电平脉冲触发hc-sr04模块，然后接收返回的超声波信号并测量高电平持续时间，最后通过公式计算出距离。需要注意的是，本示例中使用的是72MHz的系统时钟，如果系统时钟不同，需要相应地修改计时器的预分频值。