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

LiquidCrystal_I2C lcd(0x27, 16, 2);

const int signalPin = 4;   // Clock connected here
volatile unsigned long pulseCount = 0;

unsigned long previousMillis = 0;
const long interval = 1000;  // 1 second

// Interrupt function
void IRAM_ATTR countPulse() {
  pulseCount++;
}

void setup() {
  lcd.init();
  lcd.backlight();

  pinMode(signalPin, INPUT);

  attachInterrupt(digitalPinToInterrupt(signalPin), countPulse, RISING);

  previousMillis = millis();
}

void loop() {
  unsigned long currentMillis = millis();

  if (currentMillis - previousMillis >= interval) {

    detachInterrupt(digitalPinToInterrupt(signalPin));

unsigned long rpm = pulseCount * 60;

pulseCount = 0;
previousMillis = currentMillis;

attachInterrupt(digitalPinToInterrupt(signalPin), countPulse, RISING);
noInterrupts();
unsigned long pulses = pulseCount;
pulseCount = 0;
interrupts();

unsigned long rpm = pulses * 60;
previousMillis = currentMillis;

    unsigned long rpm = pulseCount * 60;

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("RPM:");
    lcd.setCursor(0, 1);
    lcd.print(rpm);

    pulseCount = 0;
    previousMillis = currentMillis;

    attachInterrupt(digitalPinToInterrupt(signalPin), countPulse, RISING);
  }
}