//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
boolean toggle_timer1 = 0; //storage variable

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 10 Hz toggles a boolean variable
//generates pulse wave of frequency 20Hz/2 = 10 kHz (takes two cycles for full wave- toggle high then toggle low)
  if (toggle_timer1){
    usI0 = analogRead(A0); //Read from Analog Input O
    sI0 = m*usI0;
    sI0 = sI0 + y0;
    toggle_timer1 = 0;
  }
  else{
    toggle_timer1 = 1;
  }
}

void loop() {

  //Serial.println();
  Serial.println(sI0);
  //delay(2000);
}