使用STM32F103ZET6和HC-SR04开发超声波测距

步骤如下：

1.连接硬件：将HC-SR04的VCC接到STM32F103ZET6的5V，GND接到GND，Trig接到STM32F103ZET6的PB10，Echo接到STM32F103ZET6的PB11。

2.配置STM32F103ZET6的GPIO：将PB10配置为输出模式，PB11配置为输入模式。

3.编写程序：使用定时器来生成10us的高电平，然后将Trig引脚拉高，等待10us后拉低。然后等待Echo引脚变高，开始计时，直到Echo引脚变低，停止计时。根据计时器的值计算距离并输出到串口。

下面是代码示例：

#include "stm32f10x.h"
#include "stdio.h"

#define TRIG_PIN GPIO_Pin_10
#define ECHO_PIN GPIO_Pin_11
#define TRIG_PORT GPIOB
#define ECHO_PORT GPIOB

void TIM3_init(void)
{
    TIM_TimeBaseInitTypeDef TIM_TimeBaseInitStruct;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

    TIM_TimeBaseInitStruct.TIM_Prescaler = (SystemCoreClock/1000000) - 1; //1us per tick
    TIM_TimeBaseInitStruct.TIM_Period = 0xFFFF;
    TIM_TimeBaseInitStruct.TIM_ClockDivision = 0;
    TIM_TimeBaseInitStruct.TIM_CounterMode = TIM_CounterMode_Up;

    TIM_TimeBaseInit(TIM3, &TIM_TimeBaseInitStruct);
    TIM_Cmd(TIM3, ENABLE);
}

void delay_us(uint32_t us)
{
    TIM_SetCounter(TIM3, 0);
    while(TIM_GetCounter(TIM3) < us);
}

float get_distance(void)
{
    uint32_t time_start, time_end;
    float distance;

    GPIO_ResetBits(TRIG_PORT, TRIG_PIN);
    delay_us(2);

    GPIO_SetBits(TRIG_PORT, TRIG_PIN);
    delay_us(10);
    GPIO_ResetBits(TRIG_PORT, TRIG_PIN);

    while(GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN) == RESET);
    time_start = TIM_GetCounter(TIM3);
    while(GPIO_ReadInputDataBit(ECHO_PORT, ECHO_PIN) == SET);
    time_end = TIM_GetCounter(TIM3);

    if(time_end > time_start)
    {
        distance = (float)(time_end - time_start) * 0.017; //calculate distance in cm
    }
    else
    {
        distance = 0;
    }

    return distance;
}

int main(void)
{
    USART_InitTypeDef USART_InitStruct;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB | RCC_APB2Periph_AFIO | RCC_APB2Periph_USART1, 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_IPU;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(ECHO_PORT, &GPIO_InitStruct);

    USART_InitStruct.USART_BaudRate = 115200;
    USART_InitStruct.USART_WordLength = USART_WordLength_8b;
    USART_InitStruct.USART_StopBits = USART_StopBits_1;
    USART_InitStruct.USART_Parity = USART_Parity_No;
    USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStruct.USART_Mode = USART_Mode_Tx;
    USART_Init(USART1, &USART_InitStruct);
    USART_Cmd(USART1, ENABLE);

    TIM3_init();

    while(1)
    {
        float distance = get_distance();
        printf("Distance: %.2f cm\n", distance);
        delay_us(500000);
    }
}