#include<ShiftLCD.h>

ShiftLCD lcd(8 ,10 , 9);    // DEFINE LCD PINS

volatile byte REV;       //  VOLATILE DATA TYPE TO STORE REVOLUTIONS

unsigned long int rpm, maxRPM;  //  DEFINE RPM AND MAXIMUM RPM

unsigned long time;         //  DEFINE TIME TAKEN TO COVER ONE REVOLUTION

int ledPin = 12;           //   STATUS LED

int led = 0,RPMlen , prevRPM;  //  INTEGERS TO STORE LED VALUE AND CURRENT RPM AND PREVIOUS RPM

int flag = 0;             //  A VARIABLE TO DETERMINE WHETHER THE LCD NEEDS TO BE CLEARED OR NOT

long prevtime = 0;       //  STORE IDLE TIME TO TOGGLE MENU

 void setup()
 {
     Serial.begin(9600);   // GET VALUES USING SERIAL MONITOR

     lcd.begin(16, 2);     // INITIATE LCD

     attachInterrupt(0, RPMCount, RISING);     //  ADD A HIGH PRIORITY ACTION ( AN INTERRUPT)  WHEN THE SENSOR GOES FROM LOW TO HIGH

     REV = 0;      //  START ALL THE VARIABLES FROM 0

     rpm = 0;

     time = 0;

     pinMode(ledPin, OUTPUT);

     pinMode(3, OUTPUT);

     pinMode(4, OUTPUT);

     digitalWrite(3, HIGH);             //  VCC PIN FOR SENSOR

     digitalWrite(4, LOW);              // GND PIN FOR SENSOR

     lcd.print("TACHOMETER");           //   STARTUP TEXT
     lcd.setCursor(0, 1);
     lcd.print("- ELECTRO18");          //  THAT'S ME
     delay(2000);
     lcd.clear();

 }

 void loop()
 {
  long currtime = millis();                 // GET CURRENT TIME

  long idletime = currtime - prevtime;        //  CALCULATE IDLE TIME

    if(REV >= 5 )                  //  IT WILL UPDATE AFETR EVERY 5 READINGS
   {


     if(flag==0)                     //  CLEAR THE LCD TO AVOID ANY GARBAGE TEXT
     {
       lcd.clear();
       lcd.print("SENSOR MEASURING");
       flag=1;                          //   AFTER FLAG = 1 , THE LOOP WILL NOT EXECUTE AGAIN
     }

     rpm = 30*1000/(millis() - time)*REV;       //  CALCULATE  RPM USING REVOLUTIONS AND ELAPSED TIME

     if(rpm > maxRPM)
     maxRPM = rpm;                             //  GET THE MAX RPM THROUGHOUT THE RUN

     time = millis();

     REV = 0;

     int x= rpm;                                //  CALCULATE NUMBER OF DIGITS IN RPM
     while(x!=0)
     {
       x = x/10;
       RPMlen++;
     }



     if(RPMlen!=prevRPM)                             // IF THE RPM FALLS TO A LOWER NUMBER WITH LESS DIGITS , THE LCD WILL GET CLEARED
     {
       lcd.clear();
       prevRPM = RPMlen;
       flag=0;
       lcd.print("SENSOR MEASURING");
     }

     lcd.setCursor(0, 1);
     lcd.print(rpm,DEC);                        //  PRINT RPM IN DECIMAL SYSTEM

     lcd.setCursor(6,1);
     lcd.print("RPM");
     delay(500);

     prevtime = currtime;                        // RESET IDLETIME

   }

   if(idletime > 5000 )                      //  IF THERE ARE NO READING FOR 5 SEC , THE SCREEN WILL SHOW MAX RPM
   {

     if(flag==1)                            // CLEAR THE LCD
     {
       lcd.clear();
       flag=0;
     }

     lcd.clear();
     lcd.print("MAXIMUM RPM");
     lcd.setCursor(0, 1);
     lcd.print(maxRPM,DEC);                     // DISPLAY MAX RPM
     lcd.print("   RPM");
     delay(2000);
     lcd.clear();
     lcd.print("IDLE STATE");
     lcd.setCursor(0, 1);
     lcd.print("READY TO MEASURE");
     delay(2000);
     prevtime = currtime;
   }

 }

 void RPMCount()                                // EVERYTIME WHEN THE SENSOR GOES FROM LOW TO HIGH , THIS FUNCTION WILL BE INVOKED
 {
   REV++;                                         // INCREASE REVOLUTIONS

   if (led == LOW)
   {

     led = HIGH;                                 //  TOGGLE STATUS LED
   }

   else
   {
     led = LOW;
   }
   digitalWrite(ledPin, led);
 }