// Adafruit_SSD1306 - Version: Latest 
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

#define OLED_RESET 4
Adafruit_SSD1306 display(OLED_RESET);

int inpPin = 8;

//Define global variables
volatile uint16_t revTick;    //Ticks per revolution
uint16_t pwm_output  = 0;      //integer for storing PWM value (0-255 value)
int HZ = 0;                  //unsigned 16bit integer for storing HZ input
int ethanol = 0;              //Store ethanol percentage here
float expectedv;              //store expected voltage here - range for typical GM sensors is usually 0.5-4.5v
uint16_t voltage = 0;              //store display millivoltage here (0-5000)
//temperature variables
int duty;                     //Duty cycle (0.0-100.0)
float period;                 //Store period time here (eg.0.0025 s)
float temperature = 0;        //Store fuel temperature here
int fahr = 0;
int cels = 0;
int celstemp = 0;
float fahrtemp = 0;
static long highTime = 0;
static long lowTime = 0;
static long tempPulse;

void setupTimer()	 // setup timer1
{           
	TCCR1A = 0;      // normal mode
	TCCR1B = 132;    // (10000100) Falling edge trigger, Timer = CPU Clock/256, noise cancellation on
	TCCR1C = 0;      // normal mode
	TIMSK1 = 33;     // (00100001) Input capture and overflow interupts enabled
	
	TCNT1 = 0;       // start from 0
}

ISR(TIMER1_CAPT_vect)    // PULSE DETECTED!  (interrupt automatically triggered, not called by main program)
{
	revTick = ICR1;      // save duration of last revolution
	TCNT1 = 0;	     // restart timer for next revolution
}

ISR(TIMER1_OVF_vect)    // counter overflow/timeout
{ revTick = 0; }        // Ticks per second = 0



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

  // by default, we'll generate the high voltage from the 3.3v line internally! (neat!)
  display.begin(SSD1306_SWITCHCAPVCC, 0x3C);  // initialize with the I2C addr 0x3D (for the 128x64)
  // init done
}

void loop() {
  getfueltemp(inpPin); //read fuel temp from input duty cycle
  
  if (revTick > 0) // Avoid dividing by zero, sample in the HZ
  		{HZ = 62200 / revTick;}     // 3456000ticks per minute, 57600 per second 
  		else                        // 62200 calibrated for more accuracy
  		{HZ = 0;}                   
  
    //calculate ethanol percentage
  		if (HZ > 50) // Avoid dividing by zero
  		{ethanol = HZ-50;}
  		else
  		{ethanol = 0;}
  
  if (ethanol > 99) // Avoid overflow in PWM
  {ethanol = 99;}
  
    //Screen calculations
    display.display();
    display.clearDisplay();
    display.setCursor(0,16);
    display.setTextSize(2);
    display.setTextColor(WHITE);
    display.print("Eth:  ");
    display.print(ethanol);
    display.print("%");
    display.setCursor(0,36);
    display.print("Temp: ");
    display.print(cels);
    display.print("C");
    
    delay(250);
}

void getfueltemp(int inpPin){ //read fuel temp from input duty cycle
  highTime = 0;
  lowTime = 0;
  
  tempPulse = pulseIn(inpPin,HIGH);
    if(tempPulse>highTime){
    highTime = tempPulse;
    }
  
  tempPulse = pulseIn(inpPin,LOW);
    if(tempPulse>lowTime){
    lowTime = tempPulse;
    }
  
  duty = ((100*(highTime/(double (lowTime+highTime))))); //Calculate duty cycle (integer extra decimal)
  float T = (float(1.0/float(HZ)));             //Calculate total period time
  float period = float(100-duty)*T;             //Calculate the active period time (100-duty)*T
  float temp2 = float(10) * float(period);      //Convert ms to whole number
  temperature = ((40.25 * temp2)-81.25);        //Calculate temperature for display (1ms = -40, 5ms = 80)
  celstemp = int(temperature);
  cels = celstemp;
  fahrtemp = ((temperature*1.8)+32);
  fahr = fahrtemp;
}