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#define pingPin 2
#define echoPin 3
long beforeCm = 0;

void setup() {
   Serial.begin(9600);
   pinMode(pingPin,OUTPUT); 
   pinMode(echoPin,INPUT);
   pinMode(12,OUTPUT);
   pinMode(A3,OUTPUT);
}

void loop() {
   long duration, cm, diference;
   digitalWrite(12, LOW);
   
   digitalWrite(pingPin, LOW);
   delayMicroseconds(2);    
   digitalWrite(pingPin, HIGH);
   delayMicroseconds(10);
   digitalWrite(pingPin, LOW);

  
   duration = pulseIn(echoPin, HIGH);
   
   cm = microsecondsToCentimeters(duration);
   
   if (beforeCm != 0) {
     if (beforeCm > cm) {
       //distancia almentou
       diference = beforeCm - cm;
       
       if (diference > 4) {
         for (int i = 0; i < 6; i++) { //repetir o código 5 vezes
           analogWrite(A3,440); 
           delay(300); 
           analogWrite(A3,0); 
           delay(300);
         }
       }
     } else {
       //distancia diminuiu
       diference = cm - beforeCm;
       if (diference > 4) {
         for (int i = 0; i < 6; i++) { //repetir o código 5 vezes
           analogWrite(A3,523);
           delay(100); 
           analogWrite(A3,0); 
           delay(100);
         }
       }
     }
   }
   beforeCm = cm;
   analogWrite(A3,0);
}

long microsecondsToCentimeters(long microseconds) {
   return microseconds / 29 / 2;
}