#define OUT 2
#define IN A0

bool tg = false;
int out = 0;
int in  = 0;

unsigned long cont  = 0;
unsigned long timer = 0;

void setup_timer2(){ //set timer2 interrupt at 1kHz
  cli();
  
  TCCR2A = 0;// set entire TCCR2A register to 0
  TCCR2B = 0;// same for TCCR2B
  TCNT2  = 0;//initialize counter value to 0
  // set compare match register for 1khz increments
  //OCR2A = 249;// = (16e6) / (1000*64) - 1 (must be <256)
  OCR2A = 249;// = (16e6) / (250*256) - 1 (must be <256)
  //OCR2A = 155;// = (16e6) / (100*1024) - 1 (must be <256)
  // turn on CTC mode
  TCCR2A |= (1 << WGM21);
  // Prescalers https://microcontrollerslab.com/arduino-timer-interrupts-tutorial/
  // CS = 001 for 1
  // CS = 010 for 8
  // CS = 011 for 32
  // CS = 100 for 64
  // CS = 101 for 128
  // CS = 110 for 256
  // CS = 111 for 1024
  TCCR2B |= (1 << CS22);   
  TCCR2B |= (1 << CS21);  
  // TCCR2B |= (1 << CS20);  
  // enable timer compare interrupt
  TIMSK2 |= (1 << OCIE2A);
  
  sei();//allow interrupts
}

ISR(TIMER2_COMPA_vect){
  timed_loop();
}

void setup() {
  // put your setup code here, to run once:

  setup_timer2();
  pinMode(OUT,OUTPUT);
  
  Serial.begin(115200);
  
}

void timed_loop(){
  timer = micros();  
  cont++ ;
  if(cont >= 250){
    tg = !tg;
    if(tg)  {out = 255;}
    else    {out = 0;}
    cont = 0;
  }
  analogWrite(OUT,out);
  Serial.print(timer);
  Serial.print(",");
  Serial.print(out);
  Serial.print(",");
  Serial.println(in);
}

void loop() {
  
  in = analogRead(IN);
  // put your main code here, to run repeatedly:
  
}