Published November 4, 2021 © GPL3+

HC-SR04 Ultrasonic Sensor with LED feedback

A project utilising the HC-SR04 ultrasonic sensor with an RGB LED that fades from green to red as an object gets closer to the sensor.

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HC-SR04 Ultrasonic Sensor with LED feedback

Things used in this project

Hardware components

Arduino Leonardo

Ultrasonic Sensor - HC-SR04 (Generic)

Story

Introduction

This project uses the HC-SR04 Ultrasonic Sensor with a common anode RGB LED to act as a proximity sensor with visual feedback. The aim is to create a device where the LED fades from green to red as an object is moved towards the device.

Theory

The HC-SR04 Ultrasonic Sensor works by using sound navigation and ranging (SONAR). The sensor emits an ultrasonic sound wave at a frequency of 40kHz. This wave then hits an object and is reflected back to the sensor. The sensor measures the time taken for the wave to be emitted, hit the object, then return to the sensor. Figure 1 shows the timing diagram for the sensor which shows a trigger input to send an ultrasonic sound wave. The echo pulse signal is then returned to the sensor in proportion to its range.

Figure 1: HC-SR04 Timing Diagram (Source: Sparkfun)

The distance the wave travels is equal to twice the distance of the object, as the wave goes to the object and back. Therefore, the equation distance = speed ofsound* time / 2 can be used to calculate the distance of the object.

Methodology

This project uses an Arduino Leonardo clone (ProMicro), however can be recreated using other microcontrollers.

The Trig and Echo pins are to be connected to the digital out pins of the Ardunio, in this case pins D9 and D8 respectively. The RGB LED is connected as shown in the circuit diagram and a more detailed explanation can be found within my guide entitled 'Common Anode RGB LED'.

The Trig pin is set to HIGH for 10µs to send an 8 cycle sonic burst which is reflected off an object and received by the Echo pin. The distance is then calculated using distance = speed ofsound* time / 2 and can be read using the serial monitor using Serial.print. The LED will also visually display the distance by fading from red to green showing a distance of 20cm to 0cm.

Code

HC-SR04 Code

#define echoPin 8 // echo pin connected to pin 8 
#define trigPin 9 // trig pin connected to pin 9 
#define RED 5 // red led connected to pwm pin 5
#define GREEN 6 // green led connected to pwm pin 6 

int time;
int dist; 
const int MAX_DIST = 400; // Anything over 20 cm (120us pulse) is "out of range"
char outputValue; //8bit 0 to 255

void setup() {
  pinMode(trigPin, OUTPUT); // Sets the trigPin as an OUTPUT
  pinMode(echoPin, INPUT); // Sets the echoPin as an INPUT
  pinMode(RED, OUTPUT);
  pinMode(GREEN, OUTPUT);
  Serial.begin(9600);//start serial monitor
}

void loop() {
  // trigger sensor for 10us pulse
  digitalWrite(trigPin, LOW); //reset trig condition 
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH); // set trig HIGH for 10 us
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW); // return to LOW
  
  // read echo pin, output in us
  time = pulseIn(echoPin, HIGH);
  
  // Calculate distance in cm
  dist = time * 0.0343 / 2; // time * speed of sound through air, divided by 2 (pulse is there and back)
  outputValue = map(dist, 0, MAX_DIST, 0, 255); //map int to 8 char 
  
  Serial.print("Distance: ");//Prints distance in serial monitor
  Serial.print(dist);
  Serial.println(" cm");
  
  if (dist < MAX_DIST){
    analogWrite(RED, outputValue); // more red when close
    analogWrite(GREEN, 255 - outputValue); // more green when far away
  }

  else{
    analogWrite(RED, 255);
    analogWrite(GREEN, 255); 
  }

}

Credits

lewiskell

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HC-SR04 Ultrasonic Sensor with LED feedback

Things used in this project

Hardware components

Story

Introduction

Theory

Methodology

Schematics

HC-SR04 wiring diagram

Code

HC-SR04 Code

Credits

lewiskell

Comments

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HC-SR04 Ultrasonic Sensor with LED feedback

HC-SR04 Ultrasonic Sensor with LED feedback

Things used in this project

Hardware components

Story

Introduction

Theory

Methodology

Schematics

HC-SR04 wiring diagram

Code

HC-SR04 Code

Credits

lewiskell

Comments

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