arduino weather shield and wind speed

Question

I have Arduino Mega and Weather Shield. I want to calculate wind speed.

float get_wind_speed()
{

float deltaTime = millis() - lastWindCheck; //750ms 

deltaTime /= 1000.0; 

  float windSpeed = (float)windClicks / deltaTime; //3 / 0.750s = 4

  windClicks = 0; //Sıfırla ve yeni oluşan rüzgarı izle
  lastWindCheck = millis();

  windSpeed *= 1.492; //4 * 1.492 = 5.968MPH

 Serial.println();
 Serial.print("Windspeed :");
 Serial.println(windSpeed);

 return(windSpeed);
}

But when I run my code I see two windspeed value. First one is windspeed=0.0 or any value. Second one is windspeed=nan.

How can I make it better?

Community · Accepted Answer · 2017-05-23 12:37:43Z

When debugging a problem like this one, print out values of the variables that the calculation depends on.

In this case, you may find that both windClicks and deltaTime are 0 or 0.0. The IEEE 754 floating-point-operations specification dictates a result of NaN (not-a-number) for various zero over zero calculations. It dictates a result of +Inf or -Inf for calculations like 7/0.0 or -13/0.0. [See, for example, the stackoverflow question, Why does division by zero with floating point (or double precision) numbers not throw an exception.]

If arithmetic generates a NaN or +Inf result, subsequent arithmetic using that result will also produce NaN or +Inf results.

To deal with the problem, you could use deltaTime > 0 as a required pre-condition for calculation of windSpeed. That is, have an if-statement protecting the calculation block.

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