/*
 * Index Fan PWM
 * Controls Noctua fan speed via PWM output @25kHz using a
 * Digispark https://content.instructables.com/ORIG/F75/EOPS/JEST5ZTO/F75EOPSJEST5ZTO.jpg
 * Step through PWM speeds in 10% increments with momentary pushbutton.
 * Derived from https://www.arduino.cc/en/tutorial/pushbutton
 * https://digistump.com/wiki/digispark/tricks#how_to_increase_hardware_pwm_frequency
 * https://www.electroschematics.com/attiny85-pwm-primer-tutorial-using-arduino/
 * Noctua PWM white paper https://noctua.at/pub/media/wysiwyg/Noctua_PWM_specifications_white_paper.pdf
 */
#include <Arduino.h>

int speed = 2; //Default starting fan speed to 50%
unsigned long previousMillis = 0; // will store last time button registered
long OnTime = 250;           // milliseconds of on-time
long OffTime = 750;          // milliseconds of off-time

// Maybe Add temp based speed changes?
// int get_temp() {
//   analogReference(INTERNAL1V1);
//   int raw = analogRead(A0+15);
//   /* Original code used a 13 deg adjustment. But based on my results, I didn't seem to need it. */
//   // raw -= 13; // raw adjust = kelvin //this value is used to calibrate to your chip
//   int in_c = raw - 273; // celcius
//   analogReference(DEFAULT);
//   return in_c;
// }

void setup() {
    //P0, P1, and P4 are capable of hardware PWM (analogWrite).
    pinMode(0, OUTPUT); //0 is P0, 1 is P1, 4 is P4 - unlike the analog inputs,
                        //for analog (PWM) outputs the pin number matches the port number.
    pinMode(5, INPUT); //5 is P5
    analogWrite(0,128); //Set the PWM pin to 50%
}

// Loop for button press to increment PWM speed by 10% up to 255
void loop() {
  // check to see if it's time to change the PWM percentage
  unsigned long currentMillis = millis();

  if((digitalRead(5) == HIGH) && (currentMillis - previousMillis >= OnTime))
  {
    previousMillis = currentMillis;  // Remember the time
  }
  else if ((digitalRead(5) == LOW) && (currentMillis - previousMillis >= OffTime))
  {
    previousMillis = currentMillis;   // Remember the time
    // Adjust PWM speed based on current speed.
    switch (speed)
    {
      case 4:
        analogWrite(0,64); //Set the PWM pin to 25%
        speed = 1;
        break;
      case 3:
        analogWrite(0,255); ////Set the PWM pin to 100%
        speed = 4;
        break;
      case 2:
        analogWrite(0,192); ////Set the PWM pin to 75%
        speed = 3;
        break;
      case 1:
        analogWrite(0,128); ////Set the PWM pin to 50%
        speed = 2;
        break;
    }
  }
}