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一、基本原理

1.1. 引脚功能

VCC	电源 (需要5V直流电源)
GND	地
Trig	信号触发脉冲 (>10us TTL脉冲)
Echo	输出TTL电平信号, 电平持续时间与距离程正比

1.2. 电气特性

工作电压	5V
工作电流	15mA
工作频率	40kHz
射程范围	0.02 ~ 4m (参考值,不同厂家质量可能也不一样)
测量精度	1mm (理论值,也跟代码实现有关系)
测量角度	15°

1.3. 测距原理

HC-SR04超声波测距模块提供2cm~400cm的测距功能，精度达3mm。

外部通过Trig引脚提供一个持续时间 >10us的TTL脉冲，内部则产生8个40kHz的模拟声波信号输出，并通过Echo引脚输出回响TTL电平，电平在接收到回响信号后无效，通过Echo引脚TTL电平的持续时间，以及声波的传输速度，即可估算出器件与物体间的距离。公式如下：

$Dis = \frac{T_{ttl} * V_{acoustic} }{2}$

其中，Tttl为高电平持续时间，Vacoustic为声波理论速度340m/s 。

1.4. 代码思路

Trig引脚的TTL电平输出：可以使用普通的GPIO口，配合延时函数进行输出。
Echo引脚的回响电平接收：由于需要计算回响电平持续时间，因此使用EXTI中断的边沿触发模式，配合定时器中断计数。在上升沿时获取定时器时间戳t1，在下降沿时再次获取定时器时间戳t2，(t2-t1)*时间戳粒度即为回响电平持续时间，即可得到距离。

二、驱动代码

2.1. IO配置代码

#define HCSR04_TRIG_GPIO_PORT   GPIOA
#define HCSR04_TRIG_GPIO_MODE   GPIO_MODE_OUTPUT_PP
#define HCSR04_TRIG_GPIO_PIN    GPIO_PIN_12
#define HCSR04_TRIG_GPIO_PULL   GPIO_NOPULL
#define HCSR04_TRIG_GPIO_SPEED  GPIO_SPEED_FREQ_HIGH
#define HCSR04_TRIG_HIGH()     HAL_GPIO_WritePin(HCSR04_TRIG_GPIO_PORT, HCSR04_TRIG_GPIO_PIN, GPIO_PIN_SET) 
#define HCSR04_TRIG_LOW()     HAL_GPIO_WritePin(HCSR04_TRIG_GPIO_PORT, HCSR04_TRIG_GPIO_PIN, GPIO_PIN_RESET)#define HCSR04_ECHO_GPIO_PORT   GPIOB
#define HCSR04_ECHO_GPIO_MODE   GPIO_MODE_IT_RISING_FALLING
#define HCSR04_ECHO_GPIO_PIN    GPIO_PIN_1
#define HCSR04_ECHO_GPIO_PULL   GPIO_NOPULL
#define HCSR04_ECHO_GPIO_SPEED  GPIO_SPEED_FREQ_HIGH
#define HCSR04_ECHO_GPIO_READ()     HAL_GPIO_ReadPin(HCSR04_ECHO_GPIO_PORT, HCSR04_ECHO_GPIO_PIN) #include"gpioM.h"void GpioInit(void);void GpioInit(void)
{GPIO_InitTypeDef tGpioInit;/* -1- Enable GPIO Clock (to be able to program the configuration registers) */__HAL_RCC_GPIOA_CLK_ENABLE();__HAL_RCC_GPIOB_CLK_ENABLE();tGpioInit.Mode  =  HCSR04_TRIG_GPIO_MODE;tGpioInit.Pull  =  HCSR04_TRIG_GPIO_PULL;tGpioInit.Speed =  HCSR04_TRIG_GPIO_SPEED;tGpioInit.Pin =  HCSR04_TRIG_GPIO_PIN;HAL_GPIO_Init(HCSR04_TRIG_GPIO_PORT, &tGpioInit);tGpioInit.Mode  =  HCSR04_ECHO_GPIO_MODE;tGpioInit.Pull  =  HCSR04_ECHO_GPIO_PULL;tGpioInit.Speed =  HCSR04_ECHO_GPIO_SPEED;tGpioInit.Pin =  HCSR04_ECHO_GPIO_PIN;HAL_GPIO_Init(HCSR04_ECHO_GPIO_PORT, &tGpioInit);return ;
}

2.2. EXTI中断配置和处理代码

#include "stm32f1xx_hal_cortex.h"#define HCSR04_EXTI_PRIORITY    1u
#define HCSR04_EXTI_SUBPRIORITY    0u
#define HCSR04_EXTI_IRQ         EXTI1_IRQnfloat hcsr40Distance = 0.0f;void ExtiInit(void);
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin);
void Hcsr04_IRQHandle(void);void ExtiInit(void)
{/* 配置 EXTI 中断源 到key1 引脚、配置中断优先级*/HAL_NVIC_SetPriority(HCSR04_EXTI_IRQ, HCSR04_EXTI_PRIORITY, HCSR04_EXTI_SUBPRIORITY);/* 使能中断 */HAL_NVIC_EnableIRQ(HCSR04_EXTI_IRQ);}void EXTI1_IRQHandler(void)
{HAL_GPIO_EXTI_IRQHandler(HCSR04_ECHO_GPIO_PIN);
}/*外部中断回调函数*/
void HAL_GPIO_EXTI_Callback(uint16_t GPIO_Pin)
{  if(GPIO_Pin == HCSR04_ECHO_GPIO_PIN){Hcsr04_IRQHandle();}
}void Hcsr04_IRQHandle(void)
{static unsigned char flag = 0;static unsigned int startTime100Us = 0;static unsigned int endTime100Us = 0;if (0 == flag) // 上升沿{startTime100Us = timer100UsCounter;flag = 1;}else // 下降沿{endTime100Us = timer100UsCounter;if (endTime100Us >= startTime100Us){// 距离 = 高电平时长 * 声波速度 / 2hcsr40Distance = 1.0 * (endTime100Us - startTime100Us) * (ACOUSTIC_VELOCITY >> 1);}else{hcsr40Distance = 1.0 * (0xFFFFFFFF - startTime100Us + endTime100Us) * (ACOUSTIC_VELOCITY >> 1);}flag = 0;}
}

2.3. 定时器中断配置和处理代码

#include "stm32f1xx_hal_dma.h"
#include "stm32f1xx_hal_tim.h"
#include "stm32f1xx_hal_rcc.h"
#include "stm32f1xx_hal_cortex.h"#define HCSR04_TIMER_PRIORITY    2u
#define HCSR04_TIMER_SUBPRIORITY    0u
#define HCSR04_TIMER_IRQ        TIM2_IRQn#define HCSR04_COUNTER_TIMER TIM2
#define HCSR04_COUNTER_TIMER_PRESCALER (64-1)
#define HCSR04_COUNTER_TIMER_PERIOD_VALUE (100-1)
#define HCSR04_COUNTER_TIMER_CLK_ENABLE() __HAL_RCC_TIM2_CLK_ENABLE()volatile unsigned int timer100UsCounter = 0;void HCSR04_Timer_Init(void)
{// Timer2计数中断HAL_NVIC_SetPriority(HCSR04_TIMER_IRQ, HCSR04_TIMER_PRIORITY, HCSR04_TIMER_SUBPRIORITY);HAL_NVIC_EnableIRQ(HCSR04_TIMER_IRQ);HCSR04_COUNTER_TIMER_CLK_ENABLE();hcsr04TimHandle.Instance               = HCSR04_COUNTER_TIMER;hcsr04TimHandle.Init.Prescaler         = HCSR04_COUNTER_TIMER_PRESCALER;hcsr04TimHandle.Init.Period            = HCSR04_COUNTER_TIMER_PERIOD_VALUE;hcsr04TimHandle.Init.ClockDivision     = TIM_CLOCKDIVISION_DIV1;hcsr04TimHandle.Init.CounterMode       = TIM_COUNTERMODE_UP;hcsr04TimHandle.Init.RepetitionCounter = 0;hcsr04TimHandle.Init.AutoReloadPreload = TIM_AUTORELOAD_PRELOAD_DISABLE;if (HAL_TIM_Base_Init(&hcsr04TimHandle) != HAL_OK){/* Initialization Error */Error_Handler("HCSR40 TIM Init Err0.");}// 使能定时器3更新中断并启动定时器HAL_TIM_Base_Start_IT(&hcsr04TimHandle);// 清除定时器初始化过程中的更新中断标志，避免定时器一启动就中断 (这句一定要在Start_IT后面!!!!)__HAL_TIM_CLEAR_IT(&hcsr04TimHandle, TIM_IT_UPDATE);
}void TIM2_IRQHandler(void)
{// HAL_GPIO_TogglePin(LED_GPIO_PORT, LED_GPIO_PIN);HAL_TIM_IRQHandler(&hcsr04TimHandle);
}// 定时器更新中断回调函数
void HAL_TIM_PeriodElapsedCallback(TIM_HandleTypeDef *htim)
{// HAL_GPIO_TogglePin(LED_GPIO_PORT, LED_GPIO_PIN);if(htim->Instance == HCSR04_COUNTER_TIMER){timer100UsCounter++;}
}

2.4. HCSR04功能驱动代码

extern float hcsr40Distance;void Hcsr04_Trig(void);
void Hcsr04_Show(void);
float Hcsr04_GetDistance(void);void Hcsr04_Trig(void)
{HCSR04_TRIG_HIGH();Delay_us(15);HCSR04_TRIG_LOW();
}float Hcsr04_GetDistance(void)
{float totalDistance = 0.0f;unsigned char time = GET_DISTANCE_TIME;// 求均值while (time > 0){Hcsr04_Trig();Delay_ms(65);totalDistance += hcsr40Distance;time--;}totalDistance /= GET_DISTANCE_TIME;return totalDistance;
}void Hcsr04_Show(void)
{char distance[20];float nowDistance = 0.0f;nowDistance = Hcsr04_GetDistance();sprintf(distance,"dis: %.2f mm",nowDistance);SSD1306_WriteStr(distance, strlen(distance));
}