#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 period;
unsigned long time_passed_min;
unsigned long pulse_freq;
unsigned long oldTime;

float velocity;


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

void setup()
   {
    pinMode(sensor, INPUT);
   
    Serial.begin(9600);
   
    attachInterrupt(digitalPinToInterrupt(sensor), pulse, RISING);         // Setup Interrupt
   
    lcd.begin();        // initialize the lcd
    lcd.backlight();
    lcd.setCursor(0,0);
    lcd.print("Anemometer");
       
    delay(3000);
    
    lcd.setCursor(0,0);
    lcd.print("             ");
    
    lastTime = micros();

    time_passed_min = 10000;    // miniumum time in µsec passed after the last interrupt

    oldTime = 0;
   }


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

void loop ()
   {
    if (millis() - oldTime > 1000)
       {
        lcd.setCursor(0,0);
        lcd.print("f = ");
        lcd.print(pulse_freq);
        lcd.print(" Hz       ");

        if (pulse_freq = 0)
           {
            velocity = 0.0;
           }
        else
           {
            velocity = pulse_freq * 0.2361 + 1,1557;    // conversion of pulse-frequency to wind-velocity
           }
        
        lcd.setCursor(0,1);
        lcd.print("v = ");
        lcd.print(velocity, 1);
        lcd.print(" m/s       ");

        oldTime = oldTime + 1000;

        pulse_freq = 0;
       }
          
   }

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

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

    if (currentTime - lastTime > time_passed_min)
       {
        pulse_freq++;

        lastTime = currentTime;    
       }            
   }