Ultrasonic distance meter based on 51 single chip microcomputer

  The project is based on HC-SR04 Range finder of ultrasonic sensor , Use digital tube to display distance . The ranging range is 2cm-400cm, Use timer 0 Interrupt setting the sensor measurement frequency , Every time 200ms Refresh the data once .
 HC-SR04 It is a common ultrasonic sensor , It is often used in the ranging of smart cars , Avoiding obstacles , Blind crutches and other fields ; This module directly integrates the ultrasonic transmitter 、 Receiver and control circuit , You can work directly by plugging it in , There is no need to connect the drive circuit .
 HC-SR04 How it works ：

1、 Use a pin of the MCU to send at least 10us High level TTL Pulse signal to module Trig Pin , Used to trigger the operation of the module （ The code is embodied as the start ranging function ）.

2、 After the module detects the trigger signal , Will automatically send 8 individual 40khz The square wave , Then automatically switch to monitoring mode , Monitor whether there is signal return .

3、 If a signal returns , By module Echo The pin will output a high level , The duration of the high level is the time from the ultrasonic wave is emitted to the time it returns （ The code is embodied in the function of getting distance ）.

  This design does not use a simple delay function , Instead, the timer interrupt is used to control the frequency of ranging , This ensures that the sensor has enough time to receive data 、 Processing data .

  The simulation diagram of the system is as follows ：

  It's still drawn PCB Territory , This drawing is for in-line devices PCB, The patch device version will be added later , In this way, it can be made into a small range finder .


  Part of the code is shown below , Code according to HC-SR04 Instructions for writing

int getdistance(void)
{
    
	start();
	while(!ECHO);
	TR1=1;
	while(ECHO);
	TR1=0;
	
	time=TH1*256+TL1;
	TH1=0;
	TL1=0;
	
	s=(time*1.7)/100+1;         // Measured cm
	if(flag==1||(s>700))
	{
    
		flag=0;
		s=0;
		return s;
	}
	return s;
}

void main()
{
    
	init();
	while(1)
	{
    
		display(distance);
	}
}

** Resources include ：keilC The language code +Proteus Simulation schematic +ad Schematic diagram PCB+ Product specification **