calculating wind speed from frequency value - performance

Question

I have NRG #40 wind speed sensor the output frequency is linear with wind speed
output signal range from 0 Hz to 125 Hz
0 Hz mean =0.35 m/s and 125 Hz =96 m/s and transfer function is
m/s = (Hz x 0.765) + 0.35
How can I interface this sensor with a Arduino mega
previously I connect Adafruit (product ID: 1733) which is output voltage not frequency is linear with wind speed
and this code for Adafruit :
//Setup Variables
const int sensorPin = A0; //Defines the pin that the anemometer output is connected to
int sensorValue = 0; //Variable stores the value direct from the analog pin
float sensorVoltage = 0; //Variable that stores the voltage (in Volts) from the anemometer being sent to the analog pin
float windSpeed = 0; // Wind speed in meters per second (m/s)
float voltageConversionConstant = .004882814; //This constant maps the value provided from the analog read function, which ranges from 0 to 1023, to actual voltage, which ranges from 0V to 5V
int sensorDelay = 1000; //Delay between sensor readings, measured in milliseconds (ms)
//Anemometer Technical Variables
//The following variables correspond to the anemometer sold by Adafruit, but could be modified to fit other anemometers.
float voltageMin = .4; // Mininum output voltage from anemometer in mV.
float windSpeedMin = 0; // Wind speed in meters/sec corresponding to minimum voltage
float voltageMax = 2.0; // Maximum output voltage from anemometer in mV.
float windSpeedMax = 32; // Wind speed in meters/sec corresponding to maximum voltage
void setup()
{
Serial.begin(9600); //Start the serial connection
}
void loop()
{
sensorValue = analogRead(sensorPin); //Get a value between 0 and 1023 from the analog pin connected to the anemometer
sensorVoltage = sensorValue * voltageConversionConstant; //Convert sensor value to actual voltage
//Convert voltage value to wind speed using range of max and min voltages and wind speed for the anemometer
if (sensorVoltage <= voltageMin){
windSpeed = 0; //Check if voltage is below minimum value. If so, set wind speed to zero.
}else {
windSpeed = (sensorVoltage - voltageMin)*windSpeedMax/(voltageMax - voltageMin); //For voltages above minimum value, use the linear relationship to calculate wind speed.
}
//Print voltage and windspeed to serial
Serial.print("Voltage: ");
Serial.print(sensorVoltage);
Serial.print("\t");
Serial.print("Wind speed: ");
Serial.println(windSpeed);
delay(sensorDelay);
}

Answer 1

Asuming you use a Arduino UNO or Nano, a easy way is to connect the sensor to pin D2 or D3, witch can be used as Interrupt pins.
You then make a function, or a ISR, that gets called every time the sensor pulses. Then you attach the newly created function to the Interrupt pin.
So it will look something like this.
byte sensorPin = 2;
double pulses = 0;
double wSpeed = 0;
long updateTimer = 0;
int updateDuration = 3000;
void setup() {
Serial.begin(115200);
pinMode(sensorPin, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(sensorPin), sensorISR, FALLING);
}
void loop() {
long now = millis();
if(updateTimer < now) {
updateTimer = now + updateDuration;
wSpeed = ((pulses/(updateDuration/1000)) * 0.765) + 0.35;
pulses = 0;
Serial.println("Windspeed is:" + String(wSpeed));
}
}
void sensorISR() {
pulses++;
}
The ISR functions only job is to increment the pulses variable for every pulse. Then every second you can calculate the frequency and speed. If you wait 3 second instead, like above, you will have a better resolution but will have to account for the extra time in the equation.
I have not testet this code.