Otáčkomer na platforme Arduino Uno s modulom IR senzora prekážok KY-032

Otáčkomer.ino

//Martin Chlebovec (martinius96@gmail.com)
//Schéma zapojenia: http://arduino.clanweb.eu/otackomer.php
//Základná implementácia pre otáčkomer na platforme Arduino Uno / Nano (ATmega328P)
//Neobsahuje ošetrenie zákmitov, volatile premenné v interrupt rutine (negarantované obslúženie premennej)
//Verzia zdarma pre orientačné meranie, chybovost meraní do: 30%
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x3F, 20, 4);     //alebo 0x27 (najpouzivanejsie I2C komunikacne adresy)
int rev = 0;
int rpm;
unsigned long oldtime = 0;
unsigned long time;

void isr() {
  rev++;
}

void setup() {
  lcd.begin(); //100 kHz I2C speed - Standard Mode
  lcd.backlight();
  lcd.setCursor(0, 0);
  lcd.print("-----ZETOR 4011-----");
  attachInterrupt(digitalPinToInterrupt (2), isr, RISING); //interrupt pin
}

void loop() {
  delay(1000);
  detachInterrupt(digitalPinToInterrupt(2));      
  time = millis() - oldtime;    //rozdiel casov
  rpm = (rev / time) * 60000;   //vyrataj otacky/min
  oldtime = millis();           //uloz aktualny cas
  rev = 0;
  lcd.setCursor(0, 1);
  lcd.print(rpm);
  lcd.print(" ot/min   ");
  attachInterrupt(digitalPinToInterrupt (2), isr, RISING);
}