8B HC-SR04 Ultrasonic Module Distance Sensor

How Ultrasonic Sensor Works

It all starts when the trigger pin is set HIGH for 10µs. In response, the sensor transmits an ultrasonic burst of eight pulses at 40 kHz. This 8-pulse pattern is specially designed so that the receiver can distinguish the transmitted pulses from ambient ultrasonic noise.

These eight ultrasonic pulses travel through the air away from the transmitter. Meanwhile the echo pin goes HIGH to initiate the echo-back signal.

If those pulses are not reflected back, the echo signal times out and goes low after 38ms (38 milliseconds). Thus a pulse of 38ms indicates no obstruction within the range of the sensor.

If those pulses are reflected back, the echo pin goes low as soon as the signal is received. This generates a pulse on the echo pin whose width varies from 150 µs to 25 ms depending on the time taken to receive the signal.

Pinout

VCC supplies power to the HC-SR04 ultrasonic sensor. You can connect it to the 5V output from your Arduino.

Trig (Trigger) pin is used to trigger ultrasonic sound pulses. By setting this pin to HIGH for 10µs, the sensor initiates an ultrasonic burst.

Echo pin goes high when the ultrasonic burst is transmitted and remains high until the sensor receives an echo, after which it goes low. By measuring the time the Echo pin stays high, the distance can be calculated.

GND is the ground pin. Connect it to the ground of the Arduino.

Wiring

Connecting the HC-SR04 to Arduino is very easy. Start by placing the sensor on your breadboard. Connect the VCC pin to the 5V pin on the Arduino and the GND pin to the ground pin. Now connect the trig and echo pins to digital pins #9 and #10 respectively.

The following table lists the pin connections:

When you are done you should have something that looks similar to the image shown below.

Library Installation

Triggering the ultrasonic sensor and measuring the received signal pulse width manually is a lot of work but luckily there are many libraries available to us. One of the popular libraries is the NewPing library. This is the library we will use in our examples.

The NewPing library is quite advanced. It supports up to 15 ultrasonic sensors at once and can output directly in centimeters, inches, or time periods.

This library is not included in the Arduino IDE, so you will need to install it first.

To install the library navigate to Sketch > Include Libraries > Manage Libraries… Wait for Library Manager to download the library index and update the list of installed libraries.

Filter your search by typing ‘newping’. Click on the first entry and then select Install.

Arduino Example Code

Here is a simple sketch that uses the serial monitor to display a distance measured in centimeters. Give this sketch a try before we start a detailed analysis of it.

// Include NewPing Library
#include "NewPing.h"

// Hook up HC-SR04 with Trig to Arduino Pin 9, Echo to Arduino pin 10
#define TRIGGER_PIN 9
#define ECHO_PIN 10

// Maximum distance we want to ping for (in centimeters).
#define MAX_DISTANCE 400	

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

void setup() {
	Serial.begin(9600);
}

void loop() {
	Serial.print("Distance = ");
	Serial.print(sonar.ping_cm());
	Serial.println(" cm");
	delay(500);
}

Once the sketch is uploaded, open your serial monitor, set the baud rate to 9600 bps. Try pointing the sensor at objects lying around you. You should see the measured distance begin to stream by.

Code Explanation:

The sketch starts by including the newly installed NewPing library.

#include "NewPing.h"

First the Arduino pins are defined to which the Trig and Echo pins of the HC-SR04 are connected. We have also defined a constant called MAX_DISTANCE. It will set a maximum distance where pings beyond that distance are read as no ping “clear”. MAX_DISTANCE is currently set to 400 [default = 500cm].

#define TRIGGER_PIN 9
#define ECHO_PIN 10
#define MAX_DISTANCE 400

After this, an instance of NewPing library named sonar is created.

NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE);

In the setup, we initialize the serial communication with PC.

void setup() {
	Serial.begin(9600);
}

In the loop, we simply call the ping_cm() function and print the result on the serial monitor. This function sends a ping and returns the distance in centimeters.

void loop() {
	Serial.print("Distance = ");
	Serial.print(sonar.ping_cm());
	Serial.println(" cm");
	delay(500);
}