const int trigPin = 6;
const int echoPin = 5;
const int greenLedPin = 8;
const int redLedPin = 9;
const int buzzerPin = 10;

void setup() 
{
  Serial.begin(9600);
  Serial.println("1. Sensor ON");
  Serial.println("2. Sensor OFF");

  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  pinMode(redLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
}

void loop() 
{
  Serial.println("Set your Sensor state:");
  while(Serial.available()==0){}
  int choice = Serial.parseInt();
  do
  {
    switch(choice)
    {
      case 1:
        if(choice == 1)
        {
          Serial.println("Sensor ON");
          long duration, distance;
          digitalWrite(trigPin, LOW);
          delayMicroseconds(2);
          digitalWrite(trigPin, HIGH);
          delayMicroseconds(10);
          digitalWrite(trigPin, LOW);
          duration = pulseIn(echoPin, HIGH);
          distance = (duration / 2) / 29.1;
        
          if (distance >=250) 
          {
            digitalWrite(greenLedPin, LOW);
            digitalWrite(redLedPin, LOW);
            Serial.print("Sensor value : ");
            Serial.println(distance);
          }
          else if (distance <= 250 && distance >=100) 
          {
            digitalWrite(greenLedPin, HIGH);
            digitalWrite(redLedPin, LOW);
            Serial.print("Sensor value : ");
            Serial.println(distance);
            Serial.println("Safe Zone");
          }
          else if (distance < 100)
          {
            digitalWrite(greenLedPin, LOW);
            digitalWrite(redLedPin, HIGH);
            digitalWrite(buzzerPin, HIGH);
            delay(100);
            digitalWrite(buzzerPin, LOW);
            delay(100);
            digitalWrite(buzzerPin, HIGH);
            Serial.print("Sensor value : ");
            Serial.println(distance);
            Serial.println("Danger Zone");
          }
          delay(500);
        }
        break;
      case 2:
        if(choice == 2)
        {
          digitalWrite(trigPin, LOW);
          digitalWrite(greenLedPin, LOW);
          digitalWrite(redLedPin, LOW);
          digitalWrite(buzzerPin, LOW);
          Serial.println("LED OFF");
        }
        break;
      default:
        Serial.println("Want to operate Sensor again!");
    }
  }
  while(choice == 2);
}