🧠 Arduino Ultrasonic Distance Sensor Tutorial: Control an LED Based on Distance

Learn how to use an ultrasonic distance sensor with an Arduino Uno to detect nearby objects and control an LED. This beginner-friendly tutorial includes the circuit diagram and complete code explanation.

📌 Project Overview

This Arduino project demonstrates how to integrate an HC-SR04 ultrasonic distance sensor with an LED using an Arduino Uno. The setup measures the distance to nearby objects and turns on an LED if an object is within a specified range (e.g., 50 cm). It’s a great starting point for learning about Arduino sensors, distance measurement, and real-time feedback systems.

🔧 Components Needed

Arduino Uno
HC-SR04 Ultrasonic Sensor
LED
220Ω Resistor
Breadboard and Jumper Wires
USB Cable for Programming

⚙️ How It Works

The ultrasonic sensor emits a pulse using the trigPin and listens for the echo on the echoPin. The duration of the echo is used to calculate the distance to an object. If the object is within the 50 cm threshold, the LED (connected to ledPin) is turned on.

🧠 Key Concepts Covered

Interfacing ultrasonic sensors with Arduino
Using pulseIn() to measure echo time
Converting echo duration to distance
Controlling outputs based on sensor data
Serial Monitor debugging
Real-world application: basic obstacle detection

🔌 Circuit Diagram

💻 Arduino Code: Ultrasonic Sensor with LED

// Define pin connections
const int trigPin = 9;
const int echoPin = 10;
const int ledPin = 8;

// Distance threshold (in centimeters)
const int movementThreshold = 50;

void setup() {
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(ledPin, OUTPUT);
  
  Serial.begin(9600);
  Serial.println("Starting distance sensor...");
}

void loop() {
  // Send ultrasonic pulse
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Measure echo duration
  long duration = pulseIn(echoPin, HIGH);
  
  // Calculate distance in cm
  int distance = duration * 0.034 / 2;
  
  Serial.print("Distance: ");
  Serial.print(distance);
  Serial.println(" cm");
  
  // LED control logic
  if (distance > 0 && distance <= movementThreshold) {
    Serial.println("Object detected within range. Turning LED on.");
    digitalWrite(ledPin, HIGH);
  } else {
    Serial.println("No object detected or out of range. Turning LED off.");
    digitalWrite(ledPin, LOW);
  }

  delay(200); // Prevent sensor overload
}

🔄 Applications of This Project




DIY home security systems



Proximity alerts



Line-following or obstacle-avoiding robots



Smart automation (lights, alarms)



Educational STEM kits

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