int b = 33;

void setup() {
  Serial.begin(115200);
  pinMode(b, OUTPUT); // Ensure l4 is set as OUTPUT
}

void loop() {
  for (int i = 0; i <= 20; i++) {
    Serial.print("Iteration: ");
    Serial.println(i);
    if (i >= 1 && i <= 5) {
      tone(b, 1000); 
      Serial.println("Buzzer at 1000 Hz");
    } else if (i >= 6 && i <= 10) {
      tone(b, 5000); 
      Serial.println("Buzzer at 5000 Hz");
    } else if (i >= 11 && i <= 15) {
      noTone(b); 
      Serial.println("Buzzer off");
    } else if (i >= 16 && i <= 20) {
      tone(b, 10000); 
      Serial.println("Buzzer at 10000 Hz");
    }
    delay(1000); 
  }
}