// Pin Definitions
const int TRIG_PIN = 7;        // Trigger pin for HC-SR04
const int ECHO_PIN = 6;        // Echo pin for HC-SR04
const unsigned int MAX_DIST = 23200; // Maximum pulse duration for 400 cm

// Variables for Ultrasonic Sensor and Potentiometer
unsigned long t1, t2, pulse_width;
float measuredRange, actualRange = 150.0;  // User-defined actual range (e.g., 50 cm)
float error, percentageError;
float frequency;

// Time for Frequency Measurement
unsigned long currentTime, previousTime = 0;
unsigned long period;

// Setup Function
void setup() {
  pinMode(TRIG_PIN, OUTPUT);  // Trigger pin as OUTPUT
  pinMode(ECHO_PIN, INPUT);   // Echo pin as INPUT
  Serial.begin(9600);         // Start serial communication
}

// Main Loop
void loop() {
  // Part 1: Ultrasonic Sensor Measurement
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);        // Send trigger pulse
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);

  // Measure the echo pulse width
  while (digitalRead(ECHO_PIN) == 0);  // Wait for the start of the echo pulse
  t1 = micros();                       // Get start time
  while (digitalRead(ECHO_PIN) == 1);  // Wait for the end of the echo pulse
  t2 = micros();                       // Get end time

  pulse_width = t2 - t1;               // Calculate pulse width

  // Calculate the measured range in centimeters
  measuredRange = pulse_width / 58.0;

  // Ensure measured range doesn't exceed the sensor's limit
  if (pulse_width > MAX_DIST) {
    Serial.println("Out of range");
  } else {
    // Part 2: Calculate Error and Percentage Error
    error = abs(actualRange - measuredRange);   // Always positive error using abs()
    percentageError = (error / actualRange) * 100;  // Percentage error



    // Part 4: Frequency Measurement
    currentTime = millis();  // Get current time
    if (previousTime > 0) {
      period = currentTime - previousTime;         // Calculate the period (in milliseconds)
      frequency = 1000.0 / period;                 // Calculate frequency in Hz

      // Print all results
      Serial.print("Actual Range: ");
      Serial.print(actualRange);
      Serial.print(" cm, Measured Range: ");
      Serial.print(measuredRange);
      Serial.print(" cm, Error: ");
      Serial.print(error);
      Serial.print(" cm, Percentage Error: ");
      Serial.print(" V, Frequency: ");
      Serial.print(frequency);
      Serial.println(" Hz");
    }
    
    previousTime = currentTime;  // Update the previous time
  }

  delay(2500);  // Delay for half a second before the next loop
}