const int dataIN = 2; //IR sensor INPUT unsigned long prevmillis; // To store time unsigned long duration; // To store time difference unsigned long refresh; // To store time for refresh of reading 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); prevmillis = 0; prevstate = LOW; Serial.begin(9600); } 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 nect revolution calculation } } prevstate = currentstate; // store this scan (prev scan) data for next scan // LCD Display if( ( millis()-refresh ) >= 100 ) { Serial.println(rpm); } }