float value=0;
float rev=0;
int rpm;
unsigned long oldtime,waktu,waktulama;


void isr() 
{
  unsigned long waktu2 = millis();
  if(waktu2 - waktulama >= 50) {
    rev++;
    waktulama= waktu2;
  }

}

void setup()
{
  Serial.begin(115200);
 
 pinMode(21, INPUT);              
  attachInterrupt(digitalPinToInterrupt(21),isr,RISING); 
}

void loop()
{
  unsigned long waktu1 = millis();
 if (waktu1 - oldtime >= 500) {
           
 waktu=millis()-oldtime;        
 rpm=(rev*60)*1;        
 oldtime=waktu1;            
 Serial.print(     rpm);
 Serial.println(" RPM");
 rev=0;
 

// attachInterrupt(digitalPinToInterrupt(21),isr,RISING);

  
 }



}