int motor1pin1 = 2;
int motor1pin2 = 3;

int motor2pin1 = 4;
int motor2pin2 = 5;

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

bool flag = 0;
float duration, distance;

void setup() {
  // put your setup code here, to run once:
  pinMode(motor1pin1, OUTPUT);
  pinMode(motor1pin2, OUTPUT);
  pinMode(motor2pin1, OUTPUT);
  pinMode(motor2pin2, OUTPUT);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);
  Serial.begin(9600);
}

void loop() {
  ultrasonic();
  if (distance < 35 && flag == 0) {
    flag = 1;
    openMotors();
    delay(1000);
    stopMotors();
    delay(500);
  }
  else if (distance > 35) {
    flag = 0;
    closeMotors();
    delay(1000);
    stopMotors();
    delay(500);
  }
}

void openMotors() {
  digitalWrite(motor1pin1, HIGH);
  digitalWrite(motor1pin2, LOW);
  digitalWrite(motor2pin1, LOW);
  digitalWrite(motor2pin2, HIGH);
}

void closeMotors() {
  digitalWrite(motor1pin1, LOW);
  digitalWrite(motor1pin2, HIGH);
  digitalWrite(motor2pin1, HIGH);
  digitalWrite(motor2pin2, LOW);
}

void stopMotors() {
  digitalWrite(motor1pin1, LOW);
  digitalWrite(motor1pin2, LOW);
  digitalWrite(motor2pin1, LOW);
  digitalWrite(motor2pin2, LOW);
}

void ultrasonic() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = (duration * .0343) / 2;
  Serial.print("Distance: ");
  Serial.println(distance);
  delay(100);
}