Weather Shield Hookup Guide

Contributors: Nate

Example Firmware - Weather Station

For the more adventurous, we have the Weather Station example. This code demonstrates all the bells and whistles of the shield. You will need a weather station hooked up to see the wind speed, wind direction and rain values change.

language:c
/*
 Weather Shield Example
 By: Nathan Seidle
 SparkFun Electronics
 Date: November 16th, 2013
 License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).

 Much of this is based on Mike Grusin's USB Weather Board code: https://www.sparkfun.com/products/10586

 This is a more advanced example of how to utilize every aspect of the weather shield. See the basic
 example if you're just getting started.

 This code reads all the various sensors (wind speed, direction, rain gauge, humidty, pressure, light, batt_lvl)
 and reports it over the serial comm port. This can be easily routed to an datalogger (such as OpenLog) or
 a wireless transmitter (such as Electric Imp).

 Measurements are reported once a second but windspeed and rain gauge are tied to interrupts that are
 calcualted at each report.

 This example code assumes the GPS module is not used.

 */

#include <Wire.h> //I2C needed for sensors
#include "SparkFunMPL3115A2.h" //Pressure sensor - Search "SparkFun MPL3115" and install from Library Manager
#include "SparkFunHTU21D.h" //Humidity sensor - Search "SparkFun HTU21D" and install from Library Manager

MPL3115A2 myPressure; //Create an instance of the pressure sensor
HTU21D myHumidity; //Create an instance of the humidity sensor

//Hardware pin definitions
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
// digital I/O pins
const byte WSPEED = 3;
const byte RAIN = 2;
const byte STAT1 = 7;
const byte STAT2 = 8;

// analog I/O pins
const byte REFERENCE_3V3 = A3;
const byte LIGHT = A1;
const byte BATT = A2;
const byte WDIR = A0;
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

//Global Variables
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
long lastSecond; //The millis counter to see when a second rolls by
byte seconds; //When it hits 60, increase the current minute
byte seconds_2m; //Keeps track of the "wind speed/dir avg" over last 2 minutes array of data
byte minutes; //Keeps track of where we are in various arrays of data
byte minutes_10m; //Keeps track of where we are in wind gust/dir over last 10 minutes array of data

long lastWindCheck = 0;
volatile long lastWindIRQ = 0;
volatile byte windClicks = 0;

//We need to keep track of the following variables:
//Wind speed/dir each update (no storage)
//Wind gust/dir over the day (no storage)
//Wind speed/dir, avg over 2 minutes (store 1 per second)
//Wind gust/dir over last 10 minutes (store 1 per minute)
//Rain over the past hour (store 1 per minute)
//Total rain over date (store one per day)

byte windspdavg[120]; //120 bytes to keep track of 2 minute average

#define WIND_DIR_AVG_SIZE 120
int winddiravg[WIND_DIR_AVG_SIZE]; //120 ints to keep track of 2 minute average
float windgust_10m[10]; //10 floats to keep track of 10 minute max
int windgustdirection_10m[10]; //10 ints to keep track of 10 minute max
volatile float rainHour[60]; //60 floating numbers to keep track of 60 minutes of rain

//These are all the weather values that wunderground expects:
int winddir = 0; // [0-360 instantaneous wind direction]
float windspeedmph = 0; // [mph instantaneous wind speed]
float windgustmph = 0; // [mph current wind gust, using software specific time period]
int windgustdir = 0; // [0-360 using software specific time period]
float windspdmph_avg2m = 0; // [mph 2 minute average wind speed mph]
int winddir_avg2m = 0; // [0-360 2 minute average wind direction]
float windgustmph_10m = 0; // [mph past 10 minutes wind gust mph ]
int windgustdir_10m = 0; // [0-360 past 10 minutes wind gust direction]
float humidity = 0; // [%]
float tempf = 0; // [temperature F]
float rainin = 0; // [rain inches over the past hour)] -- the accumulated rainfall in the past 60 min
volatile float dailyrainin = 0; // [rain inches so far today in local time]
//float baromin = 30.03;// [barom in] - It's hard to calculate baromin locally, do this in the agent
float pressure = 0;
//float dewptf; // [dewpoint F] - It's hard to calculate dewpoint locally, do this in the agent

float batt_lvl = 11.8; //[analog value from 0 to 1023]
float light_lvl = 455; //[analog value from 0 to 1023]

// volatiles are subject to modification by IRQs
volatile unsigned long raintime, rainlast, raininterval, rain;

//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

//Interrupt routines (these are called by the hardware interrupts, not by the main code)
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
void rainIRQ()
// Count rain gauge bucket tips as they occur
// Activated by the magnet and reed switch in the rain gauge, attached to input D2
{
    raintime = millis(); // grab current time
    raininterval = raintime - rainlast; // calculate interval between this and last event

    if (raininterval > 10) // ignore switch-bounce glitches less than 10mS after initial edge
    {
        dailyrainin += 0.011; //Each dump is 0.011" of water
        rainHour[minutes] += 0.011; //Increase this minute's amount of rain

        rainlast = raintime; // set up for next event
    }
}

void wspeedIRQ()
// Activated by the magnet in the anemometer (2 ticks per rotation), attached to input D3
{
    if (millis() - lastWindIRQ > 10) // Ignore switch-bounce glitches less than 10ms (142MPH max reading) after the reed switch closes
    {
        lastWindIRQ = millis(); //Grab the current time
        windClicks++; //There is 1.492MPH for each click per second.
    }
}


void setup()
{
    Serial.begin(9600);
    Serial.println("Weather Shield Example");

    pinMode(STAT1, OUTPUT); //Status LED Blue
    pinMode(STAT2, OUTPUT); //Status LED Green

    pinMode(WSPEED, INPUT_PULLUP); // input from wind meters windspeed sensor
    pinMode(RAIN, INPUT_PULLUP); // input from wind meters rain gauge sensor

    pinMode(REFERENCE_3V3, INPUT);
    pinMode(LIGHT, INPUT);

    //Configure the pressure sensor
    myPressure.begin(); // Get sensor online
    myPressure.setModeBarometer(); // Measure pressure in Pascals from 20 to 110 kPa
    myPressure.setOversampleRate(7); // Set Oversample to the recommended 128
    myPressure.enableEventFlags(); // Enable all three pressure and temp event flags

    //Configure the humidity sensor
    myHumidity.begin();

    seconds = 0;
    lastSecond = millis();

    // attach external interrupt pins to IRQ functions
    attachInterrupt(0, rainIRQ, FALLING);
    attachInterrupt(1, wspeedIRQ, FALLING);

    // turn on interrupts
    interrupts();

    Serial.println("Weather Shield online!");

}

void loop()
{
    //Keep track of which minute it is
  if(millis() - lastSecond >= 1000)
    {
        digitalWrite(STAT1, HIGH); //Blink stat LED

    lastSecond += 1000;

        //Take a speed and direction reading every second for 2 minute average
        if(++seconds_2m > 119) seconds_2m = 0;

        //Calc the wind speed and direction every second for 120 second to get 2 minute average
        float currentSpeed = get_wind_speed();
        windspeedmph = currentSpeed; //update global variable for windspeed when using the printWeather() function
        //float currentSpeed = random(5); //For testing
        int currentDirection = get_wind_direction();
        windspdavg[seconds_2m] = (int)currentSpeed;
        winddiravg[seconds_2m] = currentDirection;
        //if(seconds_2m % 10 == 0) displayArrays(); //For testing

        //Check to see if this is a gust for the minute
        if(currentSpeed > windgust_10m[minutes_10m])
        {
            windgust_10m[minutes_10m] = currentSpeed;
            windgustdirection_10m[minutes_10m] = currentDirection;
        }

        //Check to see if this is a gust for the day
        if(currentSpeed > windgustmph)
        {
            windgustmph = currentSpeed;
            windgustdir = currentDirection;
        }

        if(++seconds > 59)
        {
            seconds = 0;

            if(++minutes > 59) minutes = 0;
            if(++minutes_10m > 9) minutes_10m = 0;

            rainHour[minutes] = 0; //Zero out this minute's rainfall amount
            windgust_10m[minutes_10m] = 0; //Zero out this minute's gust
        }

        //Report all readings every second
        printWeather();

        digitalWrite(STAT1, LOW); //Turn off stat LED
    }

  delay(100);
}

//Calculates each of the variables that wunderground is expecting
void calcWeather()
{
    //Calc winddir
    winddir = get_wind_direction();

    //Calc windspeed
    //windspeedmph = get_wind_speed(); //This is calculated in the main loop on line 179

    //Calc windgustmph
    //Calc windgustdir
    //These are calculated in the main loop

    //Calc windspdmph_avg2m
    float temp = 0;
    for(int i = 0 ; i < 120 ; i++)
        temp += windspdavg[i];
    temp /= 120.0;
    windspdmph_avg2m = temp;

    //Calc winddir_avg2m, Wind Direction
    //You can't just take the average. Google "mean of circular quantities" for more info
    //We will use the Mitsuta method because it doesn't require trig functions
    //And because it sounds cool.
    //Based on: http://abelian.org/vlf/bearings.html
    //Based on: http://stackoverflow.com/questions/1813483/averaging-angles-again
    long sum = winddiravg[0];
    int D = winddiravg[0];
    for(int i = 1 ; i < WIND_DIR_AVG_SIZE ; i++)
    {
        int delta = winddiravg[i] - D;

        if(delta < -180)
            D += delta + 360;
        else if(delta > 180)
            D += delta - 360;
        else
            D += delta;

        sum += D;
    }
    winddir_avg2m = sum / WIND_DIR_AVG_SIZE;
    if(winddir_avg2m >= 360) winddir_avg2m -= 360;
    if(winddir_avg2m < 0) winddir_avg2m += 360;

    //Calc windgustmph_10m
    //Calc windgustdir_10m
    //Find the largest windgust in the last 10 minutes
    windgustmph_10m = 0;
    windgustdir_10m = 0;
    //Step through the 10 minutes
    for(int i = 0; i < 10 ; i++)
    {
        if(windgust_10m[i] > windgustmph_10m)
        {
            windgustmph_10m = windgust_10m[i];
            windgustdir_10m = windgustdirection_10m[i];
        }
    }

    //Calc humidity
    humidity = myHumidity.readHumidity();
    //float temp_h = myHumidity.readTemperature();
    //Serial.print(" TempH:");
    //Serial.print(temp_h, 2);

    //Calc tempf from pressure sensor
    tempf = myPressure.readTempF();
    //Serial.print(" TempP:");
    //Serial.print(tempf, 2);

    //Total rainfall for the day is calculated within the interrupt
    //Calculate amount of rainfall for the last 60 minutes
    rainin = 0;
    for(int i = 0 ; i < 60 ; i++)
        rainin += rainHour[i];

    //Calc pressure
    pressure = myPressure.readPressure();

    //Calc dewptf

    //Calc light level
    light_lvl = get_light_level();

    //Calc battery level
    batt_lvl = get_battery_level();
}

//Returns the voltage of the light sensor based on the 3.3V rail
//This allows us to ignore what VCC might be (an Arduino plugged into USB has VCC of 4.5 to 5.2V)
float get_light_level()
{
    float operatingVoltage = analogRead(REFERENCE_3V3);

    float lightSensor = analogRead(LIGHT);

    operatingVoltage = 3.3 / operatingVoltage; //The reference voltage is 3.3V

    lightSensor = operatingVoltage * lightSensor;

    return(lightSensor);
}

//Returns the voltage of the raw pin based on the 3.3V rail
//This allows us to ignore what VCC might be (an Arduino plugged into USB has VCC of 4.5 to 5.2V)
//Battery level is connected to the RAW pin on Arduino and is fed through two 5% resistors:
//3.9K on the high side (R1), and 1K on the low side (R2)
float get_battery_level()
{
    float operatingVoltage = analogRead(REFERENCE_3V3);

    float rawVoltage = analogRead(BATT);

    operatingVoltage = 3.30 / operatingVoltage; //The reference voltage is 3.3V

    rawVoltage = operatingVoltage * rawVoltage; //Convert the 0 to 1023 int to actual voltage on BATT pin

    rawVoltage *= 4.90; //(3.9k+1k)/1k - multiple BATT voltage by the voltage divider to get actual system voltage

    return(rawVoltage);
}

//Returns the instataneous wind speed
float get_wind_speed()
{
    float deltaTime = millis() - lastWindCheck; //750ms

    deltaTime /= 1000.0; //Covert to seconds

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

    windClicks = 0; //Reset and start watching for new wind
    lastWindCheck = millis();

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

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

    return(windSpeed);
}

//Read the wind direction sensor, return heading in degrees
int get_wind_direction()
{
    unsigned int adc;

    adc = analogRead(WDIR); // get the current reading from the sensor

    // The following table is ADC readings for the wind direction sensor output, sorted from low to high.
    // Each threshold is the midpoint between adjacent headings. The output is degrees for that ADC reading.
    // Note that these are not in compass degree order! See Weather Meters datasheet for more information.

    if (adc < 380) return (113);
    if (adc < 393) return (68);
    if (adc < 414) return (90);
    if (adc < 456) return (158);
    if (adc < 508) return (135);
    if (adc < 551) return (203);
    if (adc < 615) return (180);
    if (adc < 680) return (23);
    if (adc < 746) return (45);
    if (adc < 801) return (248);
    if (adc < 833) return (225);
    if (adc < 878) return (338);
    if (adc < 913) return (0);
    if (adc < 940) return (293);
    if (adc < 967) return (315);
    if (adc < 990) return (270);
    return (-1); // error, disconnected?
}


//Prints the various variables directly to the port
//I don't like the way this function is written but Arduino doesn't support floats under sprintf
void printWeather()
{
    calcWeather(); //Go calc all the various sensors

    Serial.println();
    Serial.print("$,winddir=");
    Serial.print(winddir);
    Serial.print(",windspeedmph=");
    Serial.print(windspeedmph, 1);
    Serial.print(",windgustmph=");
    Serial.print(windgustmph, 1);
    Serial.print(",windgustdir=");
    Serial.print(windgustdir);
    Serial.print(",windspdmph_avg2m=");
    Serial.print(windspdmph_avg2m, 1);
    Serial.print(",winddir_avg2m=");
    Serial.print(winddir_avg2m);
    Serial.print(",windgustmph_10m=");
    Serial.print(windgustmph_10m, 1);
    Serial.print(",windgustdir_10m=");
    Serial.print(windgustdir_10m);
    Serial.print(",humidity=");
    Serial.print(humidity, 1);
    Serial.print(",tempf=");
    Serial.print(tempf, 1);
    Serial.print(",rainin=");
    Serial.print(rainin, 2);
    Serial.print(",dailyrainin=");
    Serial.print(dailyrainin, 2);
    Serial.print(",pressure=");
    Serial.print(pressure, 2);
    Serial.print(",batt_lvl=");
    Serial.print(batt_lvl, 2);
    Serial.print(",light_lvl=");
    Serial.print(light_lvl, 2);
    Serial.print(",");
    Serial.println("#");

}

Open the Serial Monitor, and you should see an output string every second containing the current weather information:

$,winddir=0,windspeedmph=0,windspdmph_avg2m=0.0,winddir_avg2m=0,windgustmph_10m=0.0,windgustdir_10m=0,humidity=31.7,tempf=76.3,rainin=0.00,dailyrainin=0.00,pressure=81525.25,batt_lvl=4.32,light_lvl=2.03,#

$,winddir=0,windspeedmph=0,windspdmph_avg2m=0.0,winddir_avg2m=0,windgustmph_10m=0.0,windgustdir_10m=0,humidity=31.7,tempf=76.3,rainin=0.00,dailyrainin=0.00,pressure=81520.75,batt_lvl=4.32,light_lvl=2.02,#

$,winddir=0,windspeedmph=0,windspdmph_avg2m=0.0,winddir_avg2m=0,windgustmph_10m=0.0,windgustdir_10m=0,humidity=31.7,tempf=76.3,rainin=0.00,dailyrainin=0.00,pressure=81517.50,batt_lvl=4.34,light_lvl=2.11,#

$,winddir=0,windspeedmph=0,windspdmph_avg2m=0.0,winddir_avg2m=0,windgustmph_10m=0.0,windgustdir_10m=0,humidity=31.7,tempf=76.3,rainin=0.00,dailyrainin=0.00,pressure=81509.25,batt_lvl=4.31,light_lvl=2.11,#

The $ and # are start and stop characters. These types of bytes are used to make it easy to parse out the data. For example, you could have an Electric Imp listen for a $ and record the data until you see a #. Once you have the string then split on the commas (also known as comma delimited), and start recording the next string.