#define sensor_pin 17

int set_pulse=1; //set how many pulses in a round here
int max_rpm = 600; //set how many RPM you want to go to here

//Configuration for the Tachometer variables
volatile unsigned long lastPulseTime;
volatile unsigned long interval = 0;
long rpm=0;

void sensorIsr() {
  unsigned long now = micros();
  interval = now - lastPulseTime;
  if (interval > 5000){
     rpm = 61000000UL/(interval * set_pulse);
     lastPulseTime = now;
  }
}

void setup(){ // put your setup code here, to run once
Serial.begin(115200);
delay(500);
pinMode(sensor_pin, INPUT); 
attachInterrupt(digitalPinToInterrupt(sensor_pin), &sensorIsr, FALLING);
        
lastPulseTime = 0;
}

void loop(){  

if(rpm >= 0){//Remove the error readings of minus values   
//Let's keep this RPM value under control, between 0 and 9999
rpm = constrain (rpm, 0, max_rpm);
//If the engine is not running, print 0
if((micros() - lastPulseTime) < 5e6) {rpm = rpm;}
else{rpm = 0;}
}


Serial.print("RPM:");
Serial.println(rpm);

delay(500);
}