main.ino

#include <Servo.h>

volatile long A;

float checkdistance() {
    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() < 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;
        }

    }
}