#include "FlexiTimer2.h"

const long Tp = 500;
const int led_pin = 3;
const double Vref = 5.0;
const int m = 101;
const int nd = 255;
volatile double duty = 1.0;

void setup() {
  Serial.begin(9600);

  pinMode(led_pin, OUTPUT);

  FlexiTimer2::set(Tp, 1.0/1000, LEDBrightness);
  FlexiTimer2::start();
}

void loop() {

}

void LEDBrightness() {
  int level = nd*duty;
  analogWrite(led_pin, level);
  duty -= (Vref/(m-1));
  Serial.print("Duty value: ");
  Serial.print(duty);
  Serial.print("; PWM value: ");
  Serial.print(duty*Vref);
  Serial.println();
  if (duty < 0.0) {
    duty = 1.0;
  }
}