Mastering Ultrasonic Sensor Readings: A Comprehensive Guide

Ultrasonic sensors, like the HC-SR04, are widely used for distance measurement in various applications due to their non-contact measurement capability and relatively high accuracy. The HC-SR04 sensor operates by sending an ultrasonic wave and measuring the time it takes for the wave to bounce back after hitting an object. This time measurement can then be converted into a distance measurement using the speed of sound.

Understanding the Key Factors of Ultrasonic Sensor Readings

When it comes to measurable and quantifiable data on ultrasonic sensor readings, there are several key factors to consider:

Distance Range

The HC-SR04 sensor can measure distances ranging from 2 cm to 400 cm, with a minimum distance of 2 cm to avoid errors caused by the sensor’s own dead zone. This wide range of measurement capabilities makes the HC-SR04 suitable for a variety of applications, from small-scale robotics to large-scale industrial automation.

Accuracy

The accuracy of the sensor depends on various factors, including temperature and the angle of incidence. According to tests conducted by users, the HC-SR04 sensor has an accuracy of ±3 mm at a distance of 10 cm and ±10 mm at a distance of 100 cm. This level of accuracy is suitable for many applications, but it’s important to consider the specific requirements of your project.

Resolution

The resolution of the sensor refers to the smallest change in distance that can be detected. The HC-SR04 sensor has a resolution of approximately 0.1 cm, which means it can detect changes in distance as small as 1 millimeter. This high resolution allows for precise measurements and control in applications that require fine-grained distance data.

Angular Field of View (VFOV)

The VFOV of the sensor is the angle at which it can detect objects. The HC-SR04 sensor has a VFOV of approximately 15 degrees, which means it can detect objects within a 15-degree cone in front of the sensor. This relatively narrow field of view can be a limitation in some applications, but it also helps to reduce interference from nearby objects.

Temperature Correction

The speed of sound varies with temperature, which can affect the accuracy of distance measurements. Therefore, it is important to correct for temperature variations. The formula for sound speed correction is: soundSpeed = 331.3 + (0.606 * tempAir), where tempAir is the temperature in Celsius. By applying this correction, you can improve the accuracy of your distance measurements, especially in environments with significant temperature fluctuations.

Implementing an Ultrasonic Sensor Project

To demonstrate the use of the HC-SR04 sensor for distance measurement, let’s look at an example project that involves measuring the distance to an object and displaying it on an LCD screen.

Components Required

HC-SR04 ultrasonic sensor
Arduino board
LCD display
Jumper wires

Circuit Connections

Connect the VCC of the sensor to the 5V of the Arduino.
Connect the GND of the sensor to the GND of the Arduino.
Connect the TRIG of the sensor to pin 9 of the Arduino.
Connect the ECHO of the sensor to pin 10 of the Arduino.
Connect the VSS of the LCD to the GND of the Arduino.
Connect the VDD of the LCD to the 5V of the Arduino.
Connect the Vo of the LCD to pin A5 of the Arduino.
Connect the RS of the LCD to pin 12 of the Arduino.
Connect the RW of the LCD to the GND of the Arduino.
Connect the EN of the LCD to pin 11 of the Arduino.
Connect the D4 of the LCD to pin 5 of the Arduino.
Connect the D5 of the LCD to pin 4 of the Arduino.
Connect the D6 of the LCD to pin 3 of the Arduino.
Connect the D7 of the LCD to pin 2 of the Arduino.

Arduino Code

#include <LiquidCrystal.h>

// initialize the library with the numbers of the interface pins
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

const int trigPin = 9;
const int echoPin = 10;

void setup() {
  lcd.begin(16, 2);
  lcd.print("Distance:");
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
}

void loop() {
  // Send a short pulse on the trigger pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  // Measure the time it takes for the pulse to return
  long duration = pulseIn(echoPin, HIGH);

  // Convert the time measurement into a distance measurement
  float distance = duration * 0.034 / 2;

  // Display the distance on the LCD screen
  lcd.setCursor(11, 0);
  lcd.print(distance);
  lcd.print(" cm");

  // Wait for a short period before taking the next measurement
  delay(500);
}

In this code, the pulseIn() function is used to measure the time it takes for the ultrasonic wave to travel to an object and back. This time measurement is then converted into a distance measurement using the formula: distance = (duration * 0.034 / 2), where duration is the time measurement in microseconds, 0.034 is the speed of sound in centimeters per microsecond, and 2 is used to account for the round trip of the wave.

To improve the accuracy of the distance measurement, it is recommended to correct for temperature variations using the formula: soundSpeed = 331.3 + (0.606 * tempAir), where tempAir is the temperature in Celsius.

Conclusion

Ultrasonic sensors like the HC-SR04 provide a reliable and accurate method for distance measurement in various applications. By understanding the key factors that affect the sensor’s performance, such as distance range, accuracy, resolution, angular field of view, and temperature correction, engineers and hobbyists can design and implement projects that take full advantage of the sensor’s capabilities.

References

DISTANCE MEASUREMENT USING ULTRASONIC SENSOR & ARDUINO, ResearchGate, 2024-04-23, https://www.researchgate.net/publication/367162982_DISTANCE_MEASUREMENT_USING_ULTRASONIC_SENSOR_ARDUINO
Simple Virtual World Using Ultrasonic Sensor | Technology Tutorials, Top Tech Boy, 2014-07-21, https://toptechboy.com/python-with-ardiuno-3-example-using-ultrasonic-sensor/
HC-SR04: tests on accuracy, precision and resolution of ultrasonic distance measurement, Arduino Forum, 2014-05-27, https://forum.arduino.cc/t/hc-sr04-tests-on-accuracy-precision-and-resolution-of-ultrasonic-distance-measurement/236505
Ultrasonic Sensor HC-SR04 and Arduino – Complete Guide, How To Mechatronics, https://howtomechatronics.com/tutorials/arduino/ultrasonic-sensor-hc-sr04/
measuring within a range ultrasonic sensors, Arduino Forum, 2020-05-28, https://forum.arduino.cc/t/measuring-within-a-range-ultrasonic-sensors/657501

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