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HC-SR04 User Guide

Arduino connects ultrasonic sensor for distance measurement 

Ultrasonic sensors are suitable for static distance measurement of large flat surfaces. The range of ordinary ultrasonic sensors is about 2cm-450cm, and the resolution is 3mm (the test environment is not so good, and the personal measurement is relatively stable. The distance is about 10cm-2m. If this distance is exceeded, accidental inaccuracies often occur. Of course not Eliminate technical issues.)

The test object is the SRF-04 ultrasonic sensor, which has four pins: 5v power supply pin (Vcc), trigger control terminal (Trig), receiving terminal (Echo), and ground terminal (GND) 

How to use the module: 
Using this module, occupies two IO ports of the single-chip microcomputer, and one IO port is used as the trigger terminal. One IO port is used as the echo PWM signal capture pin. When writing the program, firstly set the level of 8 40K cycles at the TXD pin, and the program is processed into a PWM signal and output from the RXD pin. Once an echo signal is detected, the echo signal is output for our convenience. When we use it, we only need to read the low level time (T). The echo signal is a distance object proportional to the pulse width. The distance can be calculated from the time interval between the transmitted signal and the received echo signal. Formula: uS/58=cm or uS/148=inch. The formula L=340T/2 can also be propagated in the air by sound waves. You can find L (measured distance). If no reverberation signal is detected, the module’s reverberation signal pin will output a level of about 140uS to prevent the transmitted signal from affecting the reverberation signal. 

The working principle of the module: 

IO trigger ranging to at least 10us high signal;

module automatically sends eight 40kHz square wave, automatically detect whether a signal return;

a signal to return to a high IO output, high duration of the ultrasonic time from launch to return.

Test distance = (time high * speed of sound (340M / S)) / 2;

Circuit connection method: 

Arduino program example: 

const int TrigPin = 2
const int EchoPin = 3
float cm; 
void setup() 

pinMode(TrigPin, OUTPUT); 
pinMode(EchoPin, INPUT); 

void loop() 

digitalWrite(TrigPin, LOW); //Send a short time pulse to TrigPin  
digitalWrite(TrigPin, HIGH); 
digitalWrite(TrigPin, LOW); 

cm = pulseIn(EchoPin, HIGH) / 58.0//Convert the echo time to cm  
cm = (int(cm * 100.0)) / 100.0//Keep two decimal places