const int trigPin = 2;       // Trigger pin of HC-SR04
const int echoPin = 3;      // Echo pin of HC-SR04
const int motorPin1 = 8;     // Input 1 of L293D
const int motorPin2 = 11;    // Input 2 of L293D
const int enablePin = 12;    // Enable pin of L293D

void setup() {
  // For the ultrasonic sensor
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  // For the gear motor
  pinMode(motorPin1, OUTPUT);
  pinMode(motorPin2, OUTPUT);
  pinMode(enablePin, OUTPUT);
  // Initialize serial communication at 9600
  Serial.begin(9600);
}
 
void loop() {
  // Measure distance
  long duration, distance;
  digitalWrite(trigPin, LOW);
  digitalWrite(trigPin, HIGH);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH); // Read the echo pulse
  distance = duration * 0.034 / 2; // Convert distance to centimeters

  // Print the distance for debugging
  Serial.print("Distance: ");
  Serial.println(distance);

  // If an object is within 20 cm, turn on the motor
  if (distance > 0 && distance <= 20) {
    digitalWrite(motorPin1, HIGH); //  Set motor pin 1 to high
    digitalWrite(motorPin2, LOW); // Set motor pin 2 to low
    analogWrite(enablePin, 155); // Set the speed of the gear motor
    delay(20); // Set how long the gear motor runs before turning off
    analogWrite(enablePin, 0); // Turn off the gear motor
    delay(2); // Set how long until the gear motor turns on again
  }
  // If there is no object within 20 cm from the sensor, turn everything off
    else{ 
    digitalWrite(motorPin1, LOW);
    digitalWrite(motorPin2, LOW);
    analogWrite(enablePin, 0);
  }

  delay(100); // Delay for 100 seconds
}