bike2

 int revolutions = 0;
 unsigned long lasttime = 0;
 float angularVelocity =0, speed = 0;

 void setup(){
 Serial.begin(9600);
 attachInterrupt(0, domeasure, FALLING);
 }
 void loop(){
 if (millis() - lasttime == 1000){ //Uptade every one second, this will be equal to reading frecuency (Hz).
 detachInterrupt(0); //Disable interrupt when calculating
 angularVelocity = float(revolutions * 6.28); // angular velocity = rotation per second (Hz) * 2*Pi
 speed = angularVelocity * 0.12; // speed = angular velocity * 0.12 m (m/s)
 speed = speed * 3.6;// convert m/s to km/h
 Serial.print("Speed =\t");
 Serial.print(speed);
 revolutions = 0; // Restart the rev counter
 lasttime = millis(); // Uptade lasmillis
 attachInterrupt(0, domeasure, FALLING); //enable interrupt
  }
 }
 // this code will be executed every time the interrupt 0 (pin2) gets low.
 void domeasure(){
  revolutions++;
 }