#include <Servo.h>

volatile long A;

float checkdistance_11_10() {

  digitalWrite(11, LOW);

  delayMicroseconds(2);

  digitalWrite(11, HIGH);

  delayMicroseconds(10);

  digitalWrite(11, LOW);

  float distance = pulseIn(10, HIGH) / 58.00;

  delay(10);

  return distance;
}

Servo servo_3;

Servo servo_6;

Servo servo_9;

void setup()

{

  A = 0;

  pinMode(11, OUTPUT);

  pinMode(10, INPUT);

  pinMode(12, OUTPUT);

  servo_3.attach(3);

  servo_6.attach(6);

  servo_9.attach(9);
}

void loop()

{

  if (checkdistance_11_10() < 20) {

    A = random(0, 4);

    switch (A) {

      case 1:

        tone(12, 131);

        delay(100);

        noTone(12);

        servo_3.write(179);

        delay(1000);

        servo_3.write(90);

        delay(500);

        break;

      case 2:

        tone(12, 131);

        delay(100);

        noTone(12);

        servo_6.write(179);

        delay(1000);

        servo_6.write(90);

        delay(500);

        break;

      case 3:

        tone(12, 131);

        delay(100);

        noTone(12);

        servo_9.write(179);

        delay(1000);

        servo_9.write(90);

        delay(500);

        break;
    }
  }
}