void setup() {
  

  pinMode(8, INPUT);                                         
  cli();                                  
    TCCR2A = 0;                        
    TCCR2B = 0;                        
    TCNT2 = 0;                           
    OCR2A = 99;                          
    TCCR2A |= (1 << WGM21);            
    TCCR2B |= (1 << CS21);            
    TIMSK2 |= (1 << OCIE2A);             
  sei();                                  
}

void loop() {                            
}

ISR(TIMER2_COMPA_vect) {
                
  val = analogRead(analogPin);
  x++;                                      
  i++;
  y++;
  
  if(y==8000) {
    maxi = 0;
    mini = 999;
    maxig = 0;
    minig = 0;
    y = 0;
  }       
  
  for(x=0; x<6; x++) {
    value_array[x] = value_array[x+1];
  }
  value_array[6] = val;
  avg1 = (value_array[0]+value_array[1]+value_array[2]+value_array[3]+value_array[4]+value_array[5])/6;
  avg2 = (value_array[1]+value_array[2]+value_array[3]+value_array[4]+value_array[5]+value_array[6])/6;
  
  if((t_holdoff > 0) && (holdoff_enable == 1)) {
    t_holdoff--;
  }

  if((T_Periode_HIGH_enable == 1) && (T_Periode_HIGH < 2500)) {
    T_Periode_HIGH++;
  }
  if((T_Periode_LOW_enable == 1) && (T_Periode_LOW < 2500)) {
    T_Periode_LOW++;
  }
  
  switch( state ) {
    
    case 0:
    
      if(avg1 < avg2) {                     // signal increases
        state = 1;                          // go to first state
      }
      if(avg2 < avg1) {                     // signal falls
        state = 3;                          // go to third state
      }
  
    case 1:                                 // signal increases 
        
        if (val > maxi) {
          maxi = val;                       
        }
        if (avg2 < maxi) {
          maxig = 1;                       
          holdoff_enable = 1;
          if(t_holdoff == 0) {
            holdoff_enable = 0;
            t_holdoff = 100;
            state = 2;                      
          }
        }
       
      case 2:                               // signal falls
        
        if (val < mini) {
          mini = val;                       
        }
        if (val > avg2) {
          minig = 1;                        
          holdoff_enable = 1;
          if(t_holdoff == 0) {
            holdoff_enable = 0;
            t_holdoff = 100;
            state = 5;                      
          }
        }
       
      case 3:                               // signal falls
        
        if (val < mini) {
          mini = val;                       
        }
        if (avg2 > mini) {
          minig = 1;                        
          holdoff_enable = 1;
          if(t_holdoff == 0) {
            holdoff_enable = 0;
            t_holdoff = 100;
            state = 4;                     
          }
        }
        
      case 4:                               // signal increases
        
        if (val > maxi) {
          maxi = val;                      
        }
        if (val < avg2) {
          maxig = 1;                       
          holdoff_enable = 1;
          if(t_holdoff == 0) {
            holdoff_enable = 0;
            t_holdoff = 100;
            state = 5;                     
          }
        }  
      
      case 5:                               
        
        diff = maxi - mini;                 
        amplitude_on = diff * 0.5;                  
        on_treshold = mini + amplitude_on;                 
        tolerance = diff * 0.2;                  
        tolerance_HIGH = on_treshold + tolerance;                  
        tolerance_LOW = on_treshold - tolerance;                  
        a = diff * 0.08;
        b = maxi - a;
        c = mini + a;
        holdoff_enable = 1;
        if(t_holdoff == 0) {
          holdoff_enable = 0;
          t_holdoff = 100;
          state = 6;
        }
      
      case 6:                               

        if(val > tolerance_HIGH) {           
          digitalWrite(8, HIGH);   
          T_Periode_LOW_enable = 0;
          if((T_Periode_LOW_enable == 0) && (T_Periode_HIGH_enable == 0)){
            T_Periode_ms = ((T_Periode_HIGH * 0.25) + (T_Periode_LOW * 0.25));
            rpm = (60000/T_Periode_ms);
            T_Periode_HIGH = 0;
          }
          T_Periode_HIGH_enable = 1;
          state = 7;
        }
        
      case 7:
        
        if(val < tolerance_LOW) {                             
          digitalWrite(8, LOW);
          T_Periode_HIGH_enable = 0;
          if((T_Periode_HIGH_enable == 0) && (T_Periode_LOW_enable == 0)) {
            T_Periode_ms = ((T_Periode_HIGH * 0.25) + (T_Periode_LOW * 0.25));
            rpm = (60000/T_Periode_ms);
            T_Periode_LOW = 0;
          }
          T_Periode_LOW_enable = 1;
          state = 0;
        }
  }
}