POUWIEL|COM

//source: @https://www.instructables.com/id/Simple-Motor-Speed-Tester-Tachometer/
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2); // set the LCD address to 0x27 for a 16 chars and 2 line display

const int dataIN = 3; //IR sensor INPUT

unsigned long prevmillis; // To store time
unsigned long duration; // To store time difference
unsigned long lcdrefresh; // To store time for lcd to refresh

int rpm; // RPM value

boolean currentstate; // Current state of IR input scan
boolean prevstate; // State of IR sensor in previous scan

void setup()
{
  pinMode(dataIN,INPUT);
  lcd.init();
  lcd.backlight();
  prevmillis = 0;
  prevstate = LOW;
}

void loop()
{
 // RPM Measurement
 currentstate = digitalRead(dataIN); // Read IR sensor state
 if( prevstate != currentstate) // If there is change in input
   {
     if( currentstate == HIGH ) // If input only changes from LOW to HIGH
       {
         duration = ( micros() - prevmillis ); // Time difference between revolution in microsecond
         rpm = (60000000/duration); // rpm = (1/ time millis)*1000*1000*60;
         prevmillis = micros(); // store time for next revolution calculation
       }
   }
  prevstate = currentstate; // store this scan (prev scan) data for next scan
  
  // LCD Display
  if( ( millis()-lcdrefresh ) >= 100 )
    {
      lcd.setCursor(0,0);
      lcd.print("Speed of Motor");
      lcd.setCursor(0,1);
      lcd.print("RPM = ");
      lcd.print(rpm);
      lcd.print("   ");
      lcdrefresh = millis();   
    }

}