const int coilPin = 2;
const int buzzerPin = 8;
const int ledPin = 13;

unsigned long pulseCount = 0;

void pulseCounter()
{
 pulseCount++;
}

void setup()
{
 Serial.begin(9600);

 pinMode(coilPin, INPUT);
 pinMode(buzzerPin, OUTPUT);
 pinMode(ledPin, OUTPUT);

 attachInterrupt(
  digitalPinToInterrupt(coilPin),
  pulseCounter,
  RISING
 );
}

void loop()
{
 pulseCount = 0;

 delay(100);

 unsigned long frequency = pulseCount * 10;

 Serial.print("Frequency: ");
 Serial.println(frequency);

 if(frequency > 350)
 {
  digitalWrite(ledPin, HIGH);
  tone(buzzerPin, 1500);
 }
 else
 {
  digitalWrite(ledPin, LOW);
  noTone(buzzerPin);
 }
}