#include <LiquidCrystal_I2C.h>
#include <Wire.h>

LiquidCrystal_I2C lcd(0x27,16,2);  // set the LCD address to 0x27 for a 16 chars and 2 line display. ACHTUNG: Adresse kann auch 0x3F sein !!!

// Anschlüsse:
// GND - GND
// VCC - 5V
// SDA - ANALOG Pin 4
// SCL - ANALOG pin 5


int sensor = 2; 
unsigned long currentTime;
unsigned long lastTime;
unsigned long pulse_freq;


// ===========================
// =======   SETUP   =========
// ===========================

void setup()
   {
    pinMode(sensor, INPUT);
   
    Serial.begin(9600);
   
    attachInterrupt(0, pulse, FALLING); // Setup Interrupt
   
    currentTime = millis();
    lastTime = currentTime;

    lcd.begin();        // initialize the lcd
    lcd.backlight();
    lcd.setCursor(0,0);
    lcd.print("Drehzahl-");
    lcd.setCursor(0,1);
    lcd.print("messer");
    
    delay(3000);
    
    lcd.setCursor(0,0);
    lcd.print("             ");
    lcd.setCursor(0,1);
    lcd.print("            ");
   }


// ========================
// =======  LOOP  =========
// ========================

void loop ()
   {
    currentTime = millis();
   
    // Every second, calculate frequency
   
    if(currentTime >= (lastTime + 1000))
       {
        lastTime = currentTime; 
   
        /*
        Serial.print(pulse_freq); 
        Serial.println(" Hz");
        */
        
        lcd.setCursor(0,0);
        lcd.print("f = ");
        lcd.print(pulse_freq);
        lcd.print(" Hz       ");

        lcd.setCursor(0,1);
        lcd.print(pulse_freq * 60);
        lcd.print(" RPM       ");
      
        pulse_freq = 0; // Reset Counter
       }
   }

// =============================
// =======  INTERRUPT  =========
// =============================

void pulse () // Interrupt function
   {
    pulse_freq++;
   }