//Var declaration
int usI0 = 0; //Unscaled value of Analog Input O
float sI0 = 0; //Scaled value of Analog Input O
int y0 = 0; //Minimum scaled value, intercept
int y1 = 10; //Maximum scaled value
float m; //gradient

void setup() {
  Serial.begin(9600);
  m = y1 - y0;
  m = m / 1023;

  //Timer1 configuration
  //Adapted from: https://www.instructables.com/Arduino-Timer-Interrupts/
  cli();//stop interrupts
  //set timer1 interrupt at 20 Hz
  TCCR1A = 0;// set entire TCCR1A register to 0
  TCCR1B = 0;// same for TCCR1B
  TCNT1  = 0;//initialize counter value to 0
  // set compare match register for 10hz increments
  OCR1A = 781;// = (16*10^6) / (20*1024) - 1 (must be <65536)
  // turn on CTC mode
  TCCR1B |= (1 << WGM12);
  // Set CS10 and CS12 bits for 1024 prescaler
  TCCR1B |= (1 << CS12) | (1 << CS10);  
  // enable timer compare interrupt
  TIMSK1 |= (1 << OCIE1A);
  sei();//allow interrupts

}//end setup

ISR(TIMER1_COMPA_vect){//timer1 interrupt with frecuency = 20 Hz
  usI0 = analogRead(A0); //Read from Analog Input O
  sI0 = m*usI0;
  sI0 = sI0+y0;

}

void loop() {
  Serial.println(sI0);
}