Pinouts, Schematics & Lab Codes

// ============================================================
// EKD GENERAL PROJECT KIT - EXPERIMENT #01
// Title: Ultrasonic Distance Meter & Visual Threshold Alarm
// Microcontroller: Arduino Uno R3 / Arduino Nano
// ============================================================

const int trigPin = 9;
const int echoPin = 10;
const int alertLedPin = 13;

long duration;
int distanceCm;

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(alertLedPin, OUTPUT);
  Serial.println(F("[EKD LAB ENGINE] HC-SR04 Distance Sensor Active."));
}

void loop() {
  // Clear trigger pin
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  
  // Transmit 10 microsecond ultrasonic burst
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  
  // Measure echo pulse width (time taken in microseconds)
  duration = pulseIn(echoPin, HIGH, 30000); // 30ms timeout
  
  // Speed of sound = 343 m/s = 0.0343 cm/µs. Round-trip divided by 2
  distanceCm = duration * 0.034 / 2;
  
  if (distanceCm > 0 && distanceCm <= 400) {
    Serial.print(F("Distance: "));
    Serial.print(distanceCm);
    Serial.println(F(" cm"));
    
    // Proximity trigger (under 20cm)
    if (distanceCm < 20) {
      digitalWrite(alertLedPin, HIGH);
    } else {
      digitalWrite(alertLedPin, LOW);
    }
  } else {
    Serial.println(F("Sensor Out of Range!"));
    digitalWrite(alertLedPin, LOW);
  }
  
  delay(100); // Refresh rate
}