volatile unsigned long REV = 0;
int RPM_VALUE;
unsigned long previous = 0;
unsigned long Time;
#include <AccelStepper.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);
//Define stepper motor connections
#define dirPin 3
#define stepPin 5
#define isrPin 2
//Create stepper object
AccelStepper stepper(1, stepPin, dirPin); //motor interface type must be set to 1 when using a driver.

void INTERRUPT()
{
  REV++;
}
void setup()
{
  lcd.init();
  lcd.init();
  lcd.backlight();
  Serial.begin(9600);
  attachInterrupt(digitalPinToInterrupt(isrPin), INTERRUPT, RISING);
  stepper.setMaxSpeed(1200); //maximum steps per second
  stepper.setSpeed(200); //steps per second
  stepper.runSpeed(); //step the motor with constant speed as set by setSpeed()
  REV = 0;
  lcd.setCursor(0, 0);
  lcd.print(" Tachometer ");
  lcd.setCursor(0, 1);
  lcd.print("REV: ");
  lcd.setCursor(5, 1);
  lcd.print(REV);
  lcd.print(" ");
}
void loop()
{
  stepper.runSpeed();
  Serial.print("REV = ");
  Serial.println(REV);
  lcd.setCursor(5, 1);
  lcd.print(REV);
  lcd.print(" ");
}