HCSR-04 Introduce

HC-SR04 Ultrasonic ranging module can provide 2cm-400cm Non contact distance sensing function of , measuring
Non contact distance sensing function with high distance accuracy , Ranging accuracy can be as high as 3mm ; The module includes an ultrasonic transmitter 、 Receiver and control circuit .
Online materials say that the accuracy of this module is very high , But I actually feel very general , I use 89C52 and STM32F103C8T6 Have written the procedures of ranging respectively , But the range of accurate measurement is 100cm within , The specific reason is not detailed .

working principle

Use IO Trigger port , First of all Trig Set the high level at least 10us, The module will launch 8 individual 40KHz Pulse square wave , after Trig Set low level , from Echo Receive square wave , Then calculate the distance according to the duration of the reverberation level , The principle is very simple .

Procedural thinking

Just put one IO Mouth configuration Push pull output As Trig, One IO Mouth configuration Drop down input As Echo, Because when Echo The received echo signal will be set from low level to high level , So the default setting Echo Low level . distance = High level time * The speed of sound （340M/S）/2;
First use SysTick Software delay control Trig Send out high level , Then wait for the echo signal , When Echo Receive signal , That is, start the timer , But our program runs in the timer , Use the same timer TIM2, Clear the timer after receiving the signal . Then get the level duration , Calculate the distance and reset the timer again , And turn on the timer , Only when the timer is interrupted next time can it be triggered normally .

Code implementation

#include "HCSR04.h"
#include "stm32f10x.h" // Device header
#include "Usart.h"
#include "Buzzer.h"

int HCSR04_Distance1;
int HCSR04_Distance2;

#define RCC_HCSR04 RCC_APB2Periph_GPIOB

#define GPIO_HCSR04_Trig GPIOB
#define PIN_HCSR04_Trig1 GPIO_Pin_8
#define PIN_HCSR04_Trig2 GPIO_Pin_5
   
#define GPIO_HCSR04_Echo GPIOB
#define PIN_HCSR04_Echo1 GPIO_Pin_9
#define PIN_HCSR04_Echo2 GPIO_Pin_6

void HCSR04_Delay_us(uint32_t xus)
{
    
	SysTick->LOAD = 72 * xus;				// Set the timer reload value 
	SysTick->VAL = 0x00;					// Zero clearing 
	SysTick->CTRL = 0x00000005;				// Set the clock source to HCLK, Start timer 
	while(!(SysTick->CTRL & 0x00010000));	// Wait to count to 0
	SysTick->CTRL = 0x00000004;				// off timer 
}
void HCSR04_Delay_ms(uint32_t xms)
{
    
	while(xms--)
	{
    
		HCSR04_Delay_us(1000);
	}
}

Here because of the need , I set up two ultrasonic sensors .
First, the macro defines the pin , Then define two distance variables , And initialization Systick Software delay function .

void GPIO_HCSR04Init()
{
    
	RCC_APB2PeriphClockCmd(RCC_HCSR04, ENABLE);
	
	GPIO_InitTypeDef GPIO_InitStructure;
	GPIO_InitStructure.GPIO_Pin = PIN_HCSR04_Trig1 | PIN_HCSR04_Trig2;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
	GPIO_Init(GPIO_HCSR04_Trig,&GPIO_InitStructure);
	
	GPIO_InitStructure.GPIO_Pin = PIN_HCSR04_Echo1 | PIN_HCSR04_Echo2;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPD;
	GPIO_Init(GPIO_HCSR04_Echo,&GPIO_InitStructure);
}

Initialize the pins of the two functions respectively , One is push-pull output , One is drop-down input .

void TIM_HCSR04Init()
{
    
	// Universal timer 2 3 4,APB1
	//TIM2 The passage of 1 
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);

	TIM_InternalClockConfig(TIM2);// Select internal clock 
	
	TIM_TimeBaseInitTypeDef timBaseInit;
	TIM_TimeBaseStructInit(&timBaseInit);
	timBaseInit.TIM_ClockDivision = TIM_CKD_DIV1;
	timBaseInit.TIM_CounterMode = TIM_CounterMode_Up;
	timBaseInit.TIM_RepetitionCounter = 0;
	timBaseInit.TIM_Period = 10000 - 1;
	timBaseInit.TIM_Prescaler = 7200 - 1;
	//7200 frequency division , remember 10000 The next is 1 second 
	TIM_TimeBaseInit(TIM2,&timBaseInit);
	
	TIM_ClearFlag(TIM2,TIM_FLAG_Update);// Manually clear the update interrupt flag bit , Avoid entering interrupt automatically after initialization 
	TIM_ITConfig(TIM2,TIM_IT_Update,ENABLE);// Can make TIM2 Update interrupt 
	
	// To configure NVIC
	NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);
	NVIC_InitTypeDef nvic_struct;
	nvic_struct.NVIC_IRQChannel = TIM2_IRQn;
	nvic_struct.NVIC_IRQChannelCmd = ENABLE;
	nvic_struct.NVIC_IRQChannelPreemptionPriority = 1;
	nvic_struct.NVIC_IRQChannelSubPriority = 1;
	
	NVIC_Init(&nvic_struct);
	
	TIM_Cmd(TIM2,ENABLE);
}

First enable the timer , Then configure the time base unit , take 72MHz7200 frequency division , Every time you add one to the counter, you get 1/10000s, remember 10000 Once is a second . After configuration NVIC passageway , Start timer interrupt , Choose the priority randomly .

void StartMode1()
{
    	
	GPIO_ResetBits(GPIO_HCSR04_Trig,PIN_HCSR04_Trig1);// Pre pull down 
	GPIO_SetBits(GPIO_HCSR04_Trig,PIN_HCSR04_Trig1);
	HCSR04_Delay_us(20);
	GPIO_ResetBits(GPIO_HCSR04_Trig,PIN_HCSR04_Trig1);//OK
}
void StartMode2()
{
    	
	GPIO_ResetBits(GPIO_HCSR04_Trig,PIN_HCSR04_Trig2);// Pre pull down 
	GPIO_SetBits(GPIO_HCSR04_Trig,PIN_HCSR04_Trig2);
	HCSR04_Delay_us(20);
	GPIO_ResetBits(GPIO_HCSR04_Trig,PIN_HCSR04_Trig2);//OK
}

Here is Trig Trigger function

void HCSR04Init()
{
    
	GPIO_HCSR04Init();
	TIM_HCSR04Init();
}
// Integrate a function , be used for main For function initialization 
void HCSR04_GetDistance1()
{
    
	unsigned int time = 0;
	
	TIM_SetCounter(TIM2,0x0000);
	
	StartMode1();

	while(GPIO_ReadInputDataBit(GPIO_HCSR04_Echo , PIN_HCSR04_Echo1 ) == 0);
	TIM_Cmd(TIM2,ENABLE);	//Usart_SendStr("TIM2 ON ");
	while(GPIO_ReadInputDataBit(GPIO_HCSR04_Echo , PIN_HCSR04_Echo1 ) == 1);
	TIM_Cmd(TIM2,DISABLE);	//Usart_SendStr("TIM2 OFF ");
	
	// Company cm
	//v = 340m/s = 34000cm/s = 34000cm/10^6us = 0.034cm/us
	//s = vt/2
	time = TIM_GetCounter(TIM2);
	HCSR04_Distance1 = (int)time * 340 / 100 / 2;//cm
	
	TIM_SetCounter(TIM2,0x0000);
}
void HCSR04_GetDistance2()
{
    
	unsigned int time = 0;
	
	TIM_SetCounter(TIM2,0x0000);
	
	StartMode2();

	while(GPIO_ReadInputDataBit(GPIO_HCSR04_Echo , PIN_HCSR04_Echo2 ) == 0);
	TIM_Cmd(TIM2,ENABLE);	//Usart_SendStr("TIM2 ON ");
	while(GPIO_ReadInputDataBit(GPIO_HCSR04_Echo , PIN_HCSR04_Echo2 ) == 1);
	TIM_Cmd(TIM2,DISABLE);	//Usart_SendStr("TIM2 OFF ");
	
	// Company cm
	//v = 340m/s = 34000cm/s = 34000cm/10^6us = 0.034cm/us
	//s = vt/2
	time = TIM_GetCounter(TIM2);
	HCSR04_Distance2 = (int)time * 340 / 100 / 2;//cm
	
	TIM_SetCounter(TIM2,0x0000);
}

Here is the function of distance , Here's a point to Particular attention , Don't mix Software delay time The operation of , For example, serial port printing , This bug I've been looking for it for a long time ,Echo No echo signal has been received , So I try to use serial port printing to find out where the program is stuck , Just like in the program TIM2 ON and TIM2 OFF like that , The result is only TIM2 ON, Can't run OFF It's about . After that, I annotated all the prints at once , Leaving only the printing distance , The result was success ... Because of this bug I searched for hours ...o(╥﹏╥)o

void TIM2_IRQHandler()
{
    
	static int LightADTime = 0;// control LightAD Test interval  
	if(TIM_GetITStatus(TIM2,TIM_IT_Update) == 1)
	{
    
		LightADTime++;
		if(LightADTime == 10)// 
		{
    
			
			// Here is to cooperate with photosensitive sensor AD Conversion and watchdog interrupt program , It will be added later 
			LightADTime = 0;
		}		
		TIM_SetCounter(TIM2,0x0000);
			
		HCSR04_GetDistance1();			
		HCSR04_GetDistance2();
		
		if((HCSR04_Distance1 <= 20 || HCSR04_Distance1 >= 1000) )
		{
    
			BuzzerOn();
		}
		else if((HCSR04_Distance2 <= 80 || HCSR04_Distance2 >= 1000) )
		{
    
			BuzzerOn();
		}
		else BuzzerOff();	
		
		TIM_Cmd(TIM2,ENABLE);
		TIM_ClearITPendingBit(TIM2,TIM_IT_Update);
	}
}

Timer interrupt function , Remember to first judge whether you enter the timer interrupt channel , If it is , After the interrupt function is executed, put The flag bit software is set to zero , Otherwise it will keep cycling , Couldn't go out .
BuzzerOn Is the function of controlling the active buzzer , Buzzer is triggered by low level .

Conclusion

The point to pay attention to is not to perform operations with a certain length of time when calculating the distance , Otherwise, there will be no echo signal , Even waste you hours looking for bug.
There are many blogs that haven't been written ..
If you know why my program accuracy is not high, please tell me in the comment area (*ω*)