# Wind speed measuring using Hall sensor Hi! I require your help regarding a problem I’m encountering. I am trying to measure wind speed using Hall sensor, Neodymium magnet & below mentioned code. But I only get “0” value for both RPM & KPH values. Can you help me to solve this?

``````volatile byte revolutions;

unsigned int rpmilli;
float speed;

unsigned long timeold=0 ;

void setup()
{
Serial.begin(9600);
attachInterrupt(digitalPinToInterrupt(2), rpm_fun, RISING);

revolutions = 0;
rpmilli = 0;
timeold = 0;
}

void loop()
{
if (revolutions >= 1) {
//Update RPM every 20 counts, increase this for better RPM resolution,
//decrease for faster update

// calculate the revolutions per milli(second)
rpmilli = revolutions/(millis()-timeold);

timeold = millis();
revolutions = 0;
// WHEELCIRC = 2 * PI * radius (in meters)
// speed = rpmilli * WHEELCIRC * “milliseconds per hour” / “meters per kilometer”

// simplify the equation to reduce the number of floating point operations
// speed = rpmilli * WHEELCIRC * 3600000 / 1000
// speed = rpmilli * WHEELCIRC * 3600

speed = rpmilli 1.288053600;

Serial.print(“RPM:”);
Serial.print(rpmilli * 60000 ,DEC);
Serial.print(" Speed:");
Serial.print(speed,DEC);
Serial.println(" kph");
}
}

void rpm_fun()
{
revolutions++;
}

``````

``````rpmilli = revolutions/(millis()-timeold);
All variables in this line are of type `int`, so this is an integer division. When the time delta in ms is larger than the number of revolutions it counted, this always returns 0. You need to change this to:
``````rpmilli = ((float)revolutions)/(millis()-timeold);
and change `rpmilli` to float.