Fahrrad_Drehzahl

volatile float rpm = 0;
unsigned long lastInt = 0; //Letzter Interrupt
unsigned long period = 0; //aktuelle Zeit (Millisekunden)

void setup() {
  Serial.begin(9600);
  attachInterrupt(0, rpm_backwheel, FALLING); //interrupt 0 is on pin 2
}

void loop() {
}

void rpm_backwheel() { /* this code will be executed every time the interrupt 0 (pin2) gets low.*/
  period = millis() - lastInt; //Periodendauer zu letztem Impuls
  lastInt = millis();
  serialOut();
}

void serialOut() {
  rpm = (1000 / period) * 60;
  Serial.print("RPM: ");
  Serial.println(rpm);
  Serial.print("Hz:");
  Serial.println(1000 / period);
}