PressureSensor.ino

/*
  Arduino Pressure sensor based on BMP085

 Contribution: epierre
 
 G      GND
 V      VCC 5V/3.3V
 SCL    A4
 SDA    A5

*/

#include <MySensor.h>  
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_BMP085.h>

float myAltitude = 45;

#define CHILD_ID_PRESSURE 0
#define CHILD_ID_TEMP 1
#define CHILD_ID_FORECAST 2
#define PRESSURE_SENSOR_ANALOG_PIN 0
unsigned long SLEEP_TIME = 60; // Sleep time between reads (in seconds)

Adafruit_BMP085 bmp = Adafruit_BMP085();      // Digital Pressure Sensor 
MySensor gw;
MyMessage pressureMsg(CHILD_ID_PRESSURE, V_PRESSURE);
MyMessage tempMsg(CHILD_ID_TEMP, V_TEMP);
MyMessage forecastMsg(CHILD_ID_FORECAST, V_FORECAST);

float lastPressure = -1;
float lastTemp = -1;
int lastForecast = -1;
char *weather[]={"stable","sunny","cloudy","unstable","thunderstorm","unknown"};
int minutes;
float pressureSamples[180];
int minuteCount = 0;
bool firstRound = true;
float pressureAvg[7];
float dP_dt;
boolean metric; 

void setup() {
  gw.begin();

  // Send the sketch version information to the gateway and Controller
  gw.sendSketchInfo("Pressure Sensor", "1.0");

  if (!bmp.begin(BMP085_ULTRAHIGHRES)) {
    Serial.println("Could not find a valid BMP085 sensor, check wiring!");
    while (1) { }
  }

  // Register sensors to gw (they will be created as child devices)
 
  gw.present(CHILD_ID_PRESSURE, S_BARO);
  gw.present(CHILD_ID_TEMP, S_TEMP);
  metric = gw.getConfig().isMetric;

}


void loop() {

  //BMP085 pressure from adafruit gives you absolute pressure, that is NOT the barometric pressure the meteo forecast shows. You have to recalculate it by the following equation.
  float pressure_raw = bmp.readPressure();
  float pressure = pressure_raw/pow((1.0 - ( myAltitude/44330.0 )), 5.255);
  float temperature = bmp.readTemperature();
  float altitude = bmp.readAltitude();
  
  if (!metric) {
    // Convert to fahrenheit
    temperature = temperature * 9.0 / 5.0 + 32.0;
  }
  
  int forecast = sample(pressure);

  Serial.print("Temperature = ");
  Serial.print(temperature);
  Serial.println(metric?" *C":" *F");
  Serial.print("Pressure = ");
  Serial.print(pressure);
  Serial.println(" hPa");
  Serial.println(weather[forecast]);
  Serial.print("Altitude = ");
  Serial.print(bmp.readAltitude());


  if (temperature != lastTemp) {
    gw.send(tempMsg.set(temperature,1));
    lastTemp = temperature;
  }

  if (pressure != lastPressure) {
    gw.send(pressureMsg.set(pressure,1));
    lastPressure = pressure;
  }

  if (forecast != lastForecast) {
    gw.send(forecastMsg.set(weather[forecast]));
    lastForecast = forecast;
  }
  
  /*
   DP/Dt explanation

   0 = "Stable Weather Pattern"
   1 = "Slowly rising Good Weather", "Clear/Sunny "
   2 = "Slowly falling L-Pressure ", "Cloudy/Rain "
   3 = "Quickly rising H-Press",     "Not Stable"
   4 = "Quickly falling L-Press",    "Thunderstorm"
   5 = "Unknown (More Time needed) 
  */

  // Power down the radio.  Note that the radio will get powered back up
  // on the next write() call.
  delay(1000); //delay to allow serial to fully print before sleep

  gw.sleep(SLEEP_TIME * 1000); // sleep to conserve power
}

int sample(float pressure) {
	// Algorithm found here
	// http://www.freescale.com/files/sensors/doc/app_note/AN3914.pdf
	if (minuteCount > 180)
		minuteCount = 6;

	pressureSamples[minuteCount] = pressure;
	minuteCount++;

	if (minuteCount == 5) {
		// Avg pressure in first 5 min, value averaged from 0 to 5 min.
		pressureAvg[0] = ((pressureSamples[1] + pressureSamples[2]
				+ pressureSamples[3] + pressureSamples[4] + pressureSamples[5])
				/ 5);
	} else if (minuteCount == 35) {
		// Avg pressure in 30 min, value averaged from 0 to 5 min.
		pressureAvg[1] = ((pressureSamples[30] + pressureSamples[31]
				+ pressureSamples[32] + pressureSamples[33]
				+ pressureSamples[34]) / 5);
		float change = (pressureAvg[1] - pressureAvg[0]);
		if (firstRound) // first time initial 3 hour
			dP_dt = ((65.0 / 1023.0) * 2 * change); // note this is for t = 0.5hour
		else
			dP_dt = (((65.0 / 1023.0) * change) / 1.5); // divide by 1.5 as this is the difference in time from 0 value.
	} else if (minuteCount == 60) {
		// Avg pressure at end of the hour, value averaged from 0 to 5 min.
		pressureAvg[2] = ((pressureSamples[55] + pressureSamples[56]
				+ pressureSamples[57] + pressureSamples[58]
				+ pressureSamples[59]) / 5);
		float change = (pressureAvg[2] - pressureAvg[0]);
		if (firstRound) //first time initial 3 hour
			dP_dt = ((65.0 / 1023.0) * change); //note this is for t = 1 hour
		else
			dP_dt = (((65.0 / 1023.0) * change) / 2); //divide by 2 as this is the difference in time from 0 value
	} else if (minuteCount == 95) {
		// Avg pressure at end of the hour, value averaged from 0 to 5 min.
		pressureAvg[3] = ((pressureSamples[90] + pressureSamples[91]
				+ pressureSamples[92] + pressureSamples[93]
				+ pressureSamples[94]) / 5);
		float change = (pressureAvg[3] - pressureAvg[0]);
		if (firstRound) // first time initial 3 hour
			dP_dt = (((65.0 / 1023.0) * change) / 1.5); // note this is for t = 1.5 hour
		else
			dP_dt = (((65.0 / 1023.0) * change) / 2.5); // divide by 2.5 as this is the difference in time from 0 value
	} else if (minuteCount == 120) {
		// Avg pressure at end of the hour, value averaged from 0 to 5 min.
		pressureAvg[4] = ((pressureSamples[115] + pressureSamples[116]
				+ pressureSamples[117] + pressureSamples[118]
				+ pressureSamples[119]) / 5);
		float change = (pressureAvg[4] - pressureAvg[0]);
		if (firstRound) // first time initial 3 hour
			dP_dt = (((65.0 / 1023.0) * change) / 2); // note this is for t = 2 hour
		else
			dP_dt = (((65.0 / 1023.0) * change) / 3); // divide by 3 as this is the difference in time from 0 value
	} else if (minuteCount == 155) {
		// Avg pressure at end of the hour, value averaged from 0 to 5 min.
		pressureAvg[5] = ((pressureSamples[150] + pressureSamples[151]
				+ pressureSamples[152] + pressureSamples[153]
				+ pressureSamples[154]) / 5);
		float change = (pressureAvg[5] - pressureAvg[0]);
		if (firstRound) // first time initial 3 hour
			dP_dt = (((65.0 / 1023.0) * change) / 2.5); // note this is for t = 2.5 hour
		else
			dP_dt = (((65.0 / 1023.0) * change) / 3.5); // divide by 3.5 as this is the difference in time from 0 value
	} else if (minuteCount == 180) {
		// Avg pressure at end of the hour, value averaged from 0 to 5 min.
		pressureAvg[6] = ((pressureSamples[175] + pressureSamples[176]
				+ pressureSamples[177] + pressureSamples[178]
				+ pressureSamples[179]) / 5);
		float change = (pressureAvg[6] - pressureAvg[0]);
		if (firstRound) // first time initial 3 hour
			dP_dt = (((65.0 / 1023.0) * change) / 3); // note this is for t = 3 hour
		else
			dP_dt = (((65.0 / 1023.0) * change) / 4); // divide by 4 as this is the difference in time from 0 value
		pressureAvg[0] = pressureAvg[5]; // Equating the pressure at 0 to the pressure at 2 hour after 3 hours have past.
		firstRound = false; // flag to let you know that this is on the past 3 hour mark. Initialized to 0 outside main loop.
	}

	if (minuteCount < 35 && firstRound) //if time is less than 35 min on the first 3 hour interval.
		return 5; // Unknown, more time needed
	else if (dP_dt < (-0.25))
		return 4; // Quickly falling LP, Thunderstorm, not stable
	else if (dP_dt > 0.25)
		return 3; // Quickly rising HP, not stable weather
	else if ((dP_dt > (-0.25)) && (dP_dt < (-0.05)))
		return 2; // Slowly falling Low Pressure System, stable rainy weather
	else if ((dP_dt > 0.05) && (dP_dt < 0.25))
		return 1; // Slowly rising HP stable good weather
	else if ((dP_dt > (-0.05)) && (dP_dt < 0.05))
		return 0; // Stable weather
	else
		return 5; // Unknown
}