/*
 * 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%


// constants won't change. They're used here to set pin numbers:
const int buttonPin = 5;    // the number of the pushbutton pin
const int pwmPin = 0;      // the number of the LED pin

int buttonState;             // the current reading from the input pin
int lastButtonState = HIGH;   // the previous reading from the input pin

// the following variables are unsigned longs because the time, measured in
// milliseconds, will quickly become a bigger number than can be stored in an int.
unsigned long lastDebounceTime = 0;  // the last time the output pin was toggled
unsigned long debounceDelay = 50;    // the debounce time; increase if the output flickers

void setup() {
    //P0, P1, and P4 are capable of hardware PWM (analogWrite).
    pinMode(pwmPin, 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(buttonPin, INPUT_PULLUP); //5 is P5

    analogWrite(pwmPin,64); //Set the PWM pin to 25%
}

// Loop for button press to increment PWM speed by 10% up to 255
void loop() {
  // read the state of the switch into a local variable:
  int reading = digitalRead(buttonPin);

  // check to see if you just pressed the button
  // (i.e. the input went from LOW to HIGH), and you've waited long enough
  // since the last press to ignore any noise:

  // If the switch changed, due to noise or pressing:
  if (reading != lastButtonState) {
    // reset the debouncing timer
    lastDebounceTime = millis();
  }

  if ((millis() - lastDebounceTime) > debounceDelay) {
    // whatever the reading is at, it's been there for longer than the debounce
    // delay, so take it as the actual current state:

    // if the button state has changed:
    if (reading != buttonState) {
      buttonState = reading;

      // only toggle the LED if the new button state is HIGH
      if (buttonState == HIGH) {
        // Adjust PWM speed based on current speed.
        switch (speed)
        {
          case 5:
            analogWrite(pwmPin,64); //Set the PWM pin to 25%
            speed = 1;
            break;
          case 4:
            analogWrite(pwmPin,0); //Set the PWM pin to 0%
            speed = 5;
            break;
          case 3:
            analogWrite(pwmPin,255); ////Set the PWM pin to 100%
            speed = 4;
            break;
          case 2:
            analogWrite(pwmPin,192); ////Set the PWM pin to 75%
            speed = 3;
            break;
          case 1:
            analogWrite(pwmPin,128); ////Set the PWM pin to 50%
            speed = 2;
            break;
        }
      }
    }
  }
  // save the reading. Next time through the loop, it'll be the lastButtonState:
  lastButtonState = reading;
}