19.[STM32]HC_ SR04 ultrasonic ranging_ Timer mode (OLED display)

Author's brief introduction ： Hello, everyone , My name is DW, Share some of my new knowledge every day , Look forward to making progress with you
   
 
  Series column ：STM32
   
 

  Small experimental target ： stay OLED Displayed on the HC_SR04 Ranging value
  If there is anything that is not well written, you are welcome to correct

  Development board ：STM32F103ret6
Creation time ：2022 year 6 month 11 Japan

Catalog

HCSR_04 characteristic

Ultrasonic ranging principle  

Physical diagram connection diagram

HC_SR04 Programming  

To configure IO mouth

  Ultrasonic ranging function

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HCSR_04 characteristic

        HC_SR04 Ultrasonic ranging module can provide 2cm~400cm Non contact distance sensing function of , The ranging accuracy can reach 3mm; The module includes an ultrasonic transmitter 、 Receiver and control circuit .

Ultrasonic ranging principle  

         The principle of ultrasonic distance measurement is to send out ultrasonic waves in the ultrasonic transmitting device , Its basis is The time difference when the receiver receives the ultrasonic wave , Similar to the principle of radar ranging . An ultrasonic transmitter emits ultrasonic waves in a certain direction , The launch Start timing at the same time , Ultrasonic waves travel through the air , Come back immediately when you come across obstacles , When the ultrasonic receiver receives the reflected wave, it immediately stops timing .

Ultrasonic waves in the air Speed of propagation by 340m/s, according to timer Recorded time t( second ), You can calculate the distance between the starting point and the obstacle (s), namely :s=340t/2.

Physical diagram connection diagram

​

VCC for 5V Power Supply

GND Ground wire

Trig  touch Hair control system Letter Number Input , And STM32 MCU connection PA6 Connect

Echo()  Echo signal , And STM32 MCU connection PA7 Connect

HC_SR04 Programming  

To configure IO mouth

initialization Trig and Echo Two pins , And configure timer interrupt . 

u32 msCount = 0;

void HC_SR04_UserConfig(void){

	GPIO_InitTypeDef GPIO_InitStructure;
	TIM_TimeBaseInitTypeDef TIM_InitStructure;
	NVIC_InitTypeDef NVIC_InitStructure;
	
	 
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);	// Can make USART1,GPIOA The clock 
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM6,ENABLE);		// Enable timer 6 The clock 
	


	GPIO_InitStructure.GPIO_Pin = Trig; // Trigger the ranging pin 
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;	// Push pull output 
	GPIO_Init(HC_PROT, &GPIO_InitStructure);
	
	GPIO_InitStructure.GPIO_Pin = Echo; // Signal echo pin 
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPD;	// The drop-down 
	GPIO_Init(HC_PROT, &GPIO_InitStructure);
	
	TIM_DeInit(TIM6);
	TIM_InitStructure.TIM_Period = 1000-1;//1MS
	TIM_InitStructure.TIM_Prescaler = 72-1;// Pre distribution coefficient 
	TIM_InitStructure.TIM_ClockDivision = TIM_CKD_DIV1;// Regardless of the frequency 
	TIM_InitStructure.TIM_CounterMode = TIM_CounterMode_Up;// Count up 
	TIM_InitStructure.TIM_RepetitionCounter = DISABLE;// Do not turn on repeat counting 
	TIM_TimeBaseInit(TIM6,&TIM_InitStructure);// Timer initialization 
	
	TIM_ClearFlag(TIM6,TIM_FLAG_Update);
	TIM_ITConfig(TIM6,TIM_IT_Update|TIM_IT_Trigger,ENABLE);// Enable interrupt source and interrupt trigger 
	TIM_Cmd(TIM6,DISABLE);// off timer 
	
	NVIC_PriorityGroupConfig(NVIC_PriorityGroup_0);
	NVIC_InitStructure.NVIC_IRQChannel = TIM6_IRQn;// choice TIM6 interrupt 
	NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;// preemption 
	NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;// Child priority 
	NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;// Interrupt enable 
	NVIC_Init(&NVIC_InitStructure);// Initialization interrupt 
	

}
void TIM6_IRQHandler(void){

	if(TIM_GetITStatus(TIM6,TIM_IT_Update) != RESET){// Judge whether the interrupt is generated   1MS
	
		TIM_ClearITPendingBit(TIM6,TIM_IT_Update);// Clear the interrupt flag bit 
		msCount++;
	}
}

  Why configure Echo Pin for Drop down mode Well ？ Because it can be seen from the sequence diagram , When no echo signal is detected ,Echo Always at low level , If the mode is set to floating, it is unstable .

         When a signal is detected, the pin is pulled high , When no signal is detected, the pin Automatic lowering , So it is configured as a drop-down mode .

         The above sequence diagram shows that you only need Provide a 10uS The above pulse trigger signal , The module Internal will send 8 individual 40kHz Cycle level and detect echo . once If an echo signal is detected, the echo signal is output . The pulse width of the echo signal is proportional to the distance measured . Thus, the interval between the time when the signal is transmitted and the time when the echo signal is received , You can calculate the distance .

         The formula ：uS/58= centimeter perhaps uS/148= Inch ; or ： distance = High level time * The speed of sound （340M/S）/2; The recommended measurement period is 60ms above , To prevent the influence of the transmitted signal on the echo signal . 

  Ultrasonic ranging function

1. data1 For adoption Centimeter conversion Value ,data2 For adoption Sound velocity conversion Value .

2. We can know from the ultrasonic sequence diagram , When there is 10us When the trigger pulse above ,Echo In signal echo state , At the beginning, we are not sure that the echo signal is output at this time Echo Whether it is in the low-level state , So we must first judge Echo The level state of the pin , This is used to check whether the data conversion was completed last time , Then trigger the signal Trig.

	while(GPIO_ReadInputDataBit(HC_PROT,Echo) == 1);//!1, Then go to the next step 
	
	Trig_High;
	delay_us(20);
	Trig_Low;

3.  If there is a trigger signal Trig, The module will automatically generate 8 individual 40kHz Period level , Then judge Echo Whether there is high-level output ;

	while(GPIO_ReadInputDataBit(HC_PROT,Echo) == 0);//!=0
	TIM_SetCounter(TIM6,0);// Clear the counter 
	msCount = 0;// Clear the interrupt counter value 
	TIM_Cmd(TIM6,ENABLE);// Turn on TIM6 interrupt 

 4. When Echo Not for high electricity , Then we record the next reverberation level , We close at this time TIM6.

	while(GPIO_ReadInputDataBit(HC_PROT,Echo) == 1);//!1
	TIM_Cmd(TIM6,DISABLE);

 5. Get high level time , And carry out distance conversion .

	Count = msCount*1000;//us = ms * 1000
	Count = Count + TIM_GetCounter(TIM6);// High level time 
	
	*data1 = Count/58;// us/58
	*data2 = Count*0.017;// 340 00/1000 000=0.034  0.034/2=0.017
    // There are two distances back and forth , So we need /2
	delay_ms(100);

The complete function code is as follows ：

void HC_SR04_Ranging(u16 *data1,u16 *data2){
	
	u32 Count = 0;

	while(GPIO_ReadInputDataBit(HC_PROT,Echo) == 1);//!1, Then go to the next step 
	
	Trig_High;
	delay_us(20);
	Trig_Low;
	
	while(GPIO_ReadInputDataBit(HC_PROT,Echo) == 0);//!=0
	TIM_SetCounter(TIM6,0);// Clear the counter 
	msCount = 0;// Clear the interrupt counter value 
	TIM_Cmd(TIM6,ENABLE);// Turn on TIM6 interrupt 
	
	while(GPIO_ReadInputDataBit(HC_PROT,Echo) == 1);//!1
	TIM_Cmd(TIM6,DISABLE);// off timer 
	
	Count = msCount*1000;//us = ms * 1000
	Count = Count + TIM_GetCounter(TIM6);// High level time 
	
	*data1 = Count/58;// us/58
	*data2 = Count*0.017;// 340 00/1000 000=0.034  0.034/2=0.017
	delay_ms(100);
}

340m/s be equal to ? cm/us

1s=1000 000 us
340 00/1000 000=0.034
340m/s=0.034cm/us 

6. In order to make the obtained data more accurate , We need multiple measurements to get the average .

void HC_SR04_Debolan(u8 mode){

	u16 data1 = 0,data2 = 0; u32 data = 0;
	HC_SR04_Ranging(&data1,&data2);
	
	if(mode){  // Centimeter conversion 
	
		for(u8 i=0;i<5;i++){
		
			data = data + data1;
		}
		OLED_Write_Number(0,40,data/5);
	}
	else{	// Sound velocity conversion 
	
		for(u8 i=0;i<5;i++){
		
			data = data + data2;
		}
		OLED_Write_Number(4,40,data/5);
	}
}

We configured two modes , Pattern 1 The value converted to centimeters , Pattern 0 Is the converted value of sound velocity .

 7.  The main function

#include "sys.h"
#include "delay.h"
#include "usart.h"
#include "oled.h"
#include "HC_SR04.h"


 int main(void)
 {		
	  delay_init();
	  OLED_UserConfig();
	  OLED_Init();
	  OLED_Display_On();
	  HC_SR04_UserConfig();
	 
	  //OLED_Display_Off();
 	while(1){
	
		    //OLED_Write_Number(2,40,131);
			HC_SR04_Debolan(1);// Centimeter conversion 
	}
 }
 

         All the source code has been introduced , We are in the ranging module 3cm Put obstacles out , You can see the number displayed on the LCD screen 3, In mode 1 And pattern 0 Can accurately measure the distance under .

In order to facilitate the next search , Remember to pay a little attention .

This chapter ends , I'll see you in the next chapter

Reference material ：

1.STM32 Firmware library manual

2. The punctual atoms STM32 Incomplete manual _ Library function version

3. Reference video

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