Getting Started With the HC-SR04

The HC-SR04 is a great sensor to detect objects or movement for an Arduino project. We can use it to detect objects in robotic projects, detect movement for light projects or even to measure distances. This tutorial will show you how to setup the HC-SR04 using the New Ping library and we will demonstrate some of its downsides and offer solutions to overcome these.

The benefits of using a HC-SR04 are;

• Cheap
• Easy to use
• Accurate (under good conditions)
• Fairly small
• Can be configured to use either 1 or 2 digital IO pins
• Lots of code examples on the internet
• Good introduction to using sensors
• Range of up to 4 meters

The disadvantages of using a HC-SR04 are;

• Blocks your code when taking a measurement; not good for real time systems
• Accuracy is decreased as the reflection angles increases
• Accuracy decreases with soft absorbent objects

This sensor uses ultrasonic sound of around 40Khz to detect objects, due to the high frequency this is highly directional in nature and the beamwidth is quite narrow. A downside to this is that if the angle of the detected object to too big the ultrasound will be scattered and measurement accuracy decreased. If your using these sensors for a robotics project I would recommend you make the robot turn at least 15 degrees before taking another measurement after an object is detected.

Creating the Circuit

I have connected the echo and trig pin together in the above picture with a short piece of wire, you can barely see it.

Installing the NewPing Library

To install the NewPing library go to;

Scroll down to the download section and download the latest version of the library. This will be in Zip format. Go into Arduino IDE and use the menu selections;

Sketch -> Include Library -> Add .Zip Library

Select the zip file that you just downloaded. The NewPing library will now install and you will be able to use it in any Arduno project by importing it into the project.

Uploading Code

Copy and paste the below code into Arduino IDE and upload to the micro-controller by pressing the upload button within Arduino IDE.

#include <NewPing.h>  //Download the NewPing library from https://playground.arduino.cc/Code/NewPing/



#define SONAR_PIN 5  //We will use D5 for both the trig and echo pin.

#define MAX_DISTANCE 200 //Max distance set to 200cm can be up to 400cm



NewPing sonar(SONAR_PIN, SONAR_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.



int startTime = 0; //Use to monitor the execution time of the main loop

int loopTime = 0; //Use to monitor the execution time of the main loop

int elapsedTime = 0;



int _distance = 0;

    

void setup() {

    // put your setup code here, to run once:

    Serial.begin(115200); // Allows us to get results via the Serial Monitor in Arduino IDE

}



void loop() {

    // put your main code here, to run repeatedly:

    startTime = millis();



    delay(1); //Add a 1mS delay otherwise the program will execute too quickly

    if (elapsedTime > 50) //If 50mS has elapsed since last measurement

    {

        _distance = sonar.ping_cm();  //Get the distance measurement

        loopTime = millis() - startTime; //Calculate how long it took to get the measurement

        Serial.print(_distance); //Print the distance out

        Serial.print(",");

        Serial.println(loopTime); //Print the loop time out

        elapsedTime = 0; //Reset elapased time

    }



    loopTime = millis() - startTime; //Calculate the looptime when a measurement is not being taken

    elapsedTime = elapsedTime + loopTime; //Count the elapsed time from when the last measurement was taken

}

Code Explanation

The above code takes a new measurement every 50mS and prints it via the serial port. I have included a timing loop in the code so we can see how long it takes for each measurement. You will notice that it can take up to 14mS per measurement, this means that your code can’t do anything for that 14mS as it is blocked. If you were to use multiple sensors this problem will be exacerbated causing your project to respond in sub-optimal ways.

To avoid this I would recommend limiting the time between measurements; so for instance instead of taking a measurement every code iteration you should take a measurement every 100mS or so giving the project a refresh rate of 10hz. If you are to use multiple sensors I would suggest taking measurements every 250mS to keep the code responsive or to use another micro-controller to interface with the HC-SR04 sensors.

These senors can be configured to use 2 pins (one for echo and one for trig) or one pin. The above example uses one pin as this does not affect performance and frees up an extra pin on your Arduino.

You can buy these sensors with a mounting bracket from our E-Bay shop.