meteostation/meteostation.ino

#define VANE_PIN A0
#define VANE_VOLTAGE 5.0
#define VANE_POWER_PIN 7
#define VANE_REFER 10000
#define VANE_MEASURE_ITERATIONS 3

#define ANEMOMERTER_PIN 2

void setup() {
	Serial.begin(9600);

	pinMode(VANE_PIN, INPUT);
	pinMode(VANE_POWER_PIN, OUTPUT);

	pinMode(ANEMOMERTER_PIN, INPUT_PULLUP);
	attachInterrupt(digitalPinToInterrupt(ANEMOMERTER_PIN), anemometerTick, CHANGE);
}

/*
 * Wind direction (vane)
 *
 * The measurements are made with an R10k as R1 in the voltage divider (VANE_REFER constant).
 *
 * List of corrections as in `documentation => measured value`.
 * 0.32 => 0.37
*/
static const float vaneValue[16] {0.37,0.41,0.45,0.62,0.90,1.19,1.40,1.98,2.25,2.93,3.08,3.43,3.84,4.04,4.33,4.62};
static const float vaneDirection[16] {112.5,67.5,90,157.5,135,202.5,180,22.5,45,247.5,225,337.5,0,292.5,315,270};

float getWindVane()
{
	double vin = 0;

	digitalWrite(VANE_POWER_PIN, HIGH);
	/* Measure voltage several times for greater accuracy */
	for (int i = 0; i < VANE_MEASURE_ITERATIONS; i++) {
		vin = vin + analogRead(A0);
	}
	digitalWrite(VANE_POWER_PIN, LOW);

	vin = vin / VANE_MEASURE_ITERATIONS;
	vin = vin * (VANE_VOLTAGE / 1023.0);

	/* Find the closest value from voltage array */
	for (int i = 0; i < 16; i++) {
		if (vin - vaneValue[i] <= 0) {
			/* Check for the first */
			if (i == 0)
				return vaneDirection[i];

			/*
			 * Check if the new value is in the negative.
			 * This prefers the lower value (4 from 4.5 etc).
			*/
			if (-(vin - vaneValue[i]) < vin - vaneValue[i-1])
				return vaneDirection[i];

			return vaneDirection[i-1];
		}
	}

	/*
	 * In case a negative value is never reached, return the last value in the array.
	 */
	return vaneDirection[15];
}


/* Wind speed */

#define WIND_FACTOR 2.4
#define TEST_PAUSE 60000

volatile unsigned long anem_count = 0;
volatile unsigned long anem_last = 0;
volatile unsigned long anem_min = 0xffffffff;

double getUnitWind()
{
	unsigned long reading = anem_count;
	anem_count = 0;
	return(WIND_FACTOR * reading) / (TEST_PAUSE / 1000);
}

double getGust()
{
	unsigned long reading = anem_min;
	anem_min = 0xffffffff;
	double time = reading / 1000000.0;

	return(1 / (reading / 1000000.0)) * WIND_FACTOR;
}

void anemometerTick()
{
	long thisTime = micros() - anem_last;
	anem_last = micros();

	if (thisTime > 500) {
		anem_count++;
		if (thisTime < anem_min)
			anem_min = thisTime;
	}
}


/* Rain gauge */

#define RAIN_FACTOR 0.2794

volatile unsigned long rain_count = 0;
volatile unsigned long rain_last = 0;

double getUnitRain()
{

	unsigned long reading = rain_count;
	rain_count = 0;
	double unit_rain = reading * RAIN_FACTOR;

	return unit_rain;
}

void rainTick()
{
		long thisTime = micros() - rain_last;
		rain_last = micros();

		if(thisTime > 500)
			rain_count++;
}

void loop() {
	Serial.print(getWindVane());
	Serial.println("°");

	Serial.println(getUnitWind());
	Serial.println(getGust());
	
	delay(1000);
}