#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;
unsigned long period;

float pulse_freq;

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

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

    lastTime = micros();
   }


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

void loop ()
   {
    pulse_freq = 1000000.0 / period;

    lcd.setCursor(0,0);
    lcd.print("f = ");
    lcd.print(pulse_freq, 2);
    lcd.print(" Hz       ");

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

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

void pulse () // Interrupt function
   {
    currentTime = micros();

    period = currentTime - lastTime;

    lastTime = currentTime;    
   }