home-automation/arduino/Weather_Shield_Basic/Weather_Shield_Basic.ino

/*
  Weather Shield Example
  By: Nathan Seidle
  SparkFun Electronics
  Date: June 10th, 2016
  License: This code is public domain but you buy me a beer if you use this and we meet someday (Beerware license).

  This example prints the current humidity, air pressure, temperature and light levels.

  The weather shield is capable of a lot. Be sure to checkout the other more advanced examples for creating
  your own weather station.

*/

#include <ArduinoJson.h>

#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
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
const byte STAT_BLUE = 7;
const byte STAT_GREEN = 8;

const byte REFERENCE_3V3 = A3;
const byte LIGHT = A1;
const byte BATT = A2;

//Global Variables
//-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
long lastSecond; //The millis counter to see when a second rolls by

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

  pinMode(STAT_BLUE, OUTPUT); //Status LED Blue
  pinMode(STAT_GREEN, OUTPUT); //Status LED Green

  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();

  lastSecond = millis();

  digitalWrite(STAT_GREEN, HIGH); //Signal online / active status
}

void loop()
{
  //Print readings every 10 seconds
  if (millis() - lastSecond >= 10000)
  {
    digitalWrite(STAT_BLUE, HIGH); //Blink stat LED

    lastSecond += 10000;

    //Check Humidity Sensor
    float humidity = myHumidity.readHumidity();

    if (humidity == ERROR_I2C_TIMEOUT) //Humidty sensor failed to respond
    {
      Serial.println("I2C communication to sensors is not working. Check solder connections.");

      //Try re-initializing the I2C comm and the sensors
      myPressure.begin();
      myPressure.setModeBarometer();
      myPressure.setOversampleRate(7);
      myPressure.enableEventFlags();
      myHumidity.begin();
    }
    else
    {
      DynamicJsonDocument jsonBuffer(1024);

      jsonBuffer["humidity_percent"] = humidity; // %

      float temp_h = myHumidity.readTemperature();
      jsonBuffer["temp_c"] = temp_h; // C

      //Check Pressure Sensor
      float pressure = myPressure.readPressure();
      jsonBuffer["pressure_pa"] = pressure; // Pa

      //Check tempf from pressure sensor
      float tempf = myPressure.readTempF();
      jsonBuffer["temp_f"] = tempf; // F

      //Heat Index
      float hi = heatIndex(tempf, humidity);
      jsonBuffer["hi_f"] = hi; // F
      jsonBuffer["hi_c"] = convertFtoC(hi); // C
      
      //Check light sensor
      float light_lvl = get_light_level();
      jsonBuffer["light_lvl_v"] = light_lvl; // V

      //Check batt level
      float batt_lvl = get_battery_level();
      jsonBuffer["batt_lvl_v"] = batt_lvl; // V

      // Print json sensor data
      serializeJson(jsonBuffer, Serial);
      Serial.println();
    }

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

  delay(100);
}

//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);
}

float convertFtoC(float f) {
  return (f - 32) * 0.55555;
}

float heatIndex(float temperature, float percentHumidity)
{
  float hi = 0.5 * (temperature + 61.0 + ((temperature - 68.0) * 1.2) + (percentHumidity * 0.094));

  if (hi > 79) {
    hi = -42.379 +
         2.04901523 * temperature +
         10.14333127 * percentHumidity +
         -0.22475541 * temperature * percentHumidity +
         -0.00683783 * pow(temperature, 2) +
         -0.05481717 * pow(percentHumidity, 2) +
         0.00122874 * pow(temperature, 2) * percentHumidity +
         0.00085282 * temperature * pow(percentHumidity, 2) +
         -0.00000199 * pow(temperature, 2) * pow(percentHumidity, 2);

    if ((percentHumidity < 13) && (temperature >= 80.0) && (temperature <= 112.0))
      hi -= ((13.0 - percentHumidity) * 0.25) * sqrt((17.0 - abs(temperature - 95.0)) * 0.05882);

    else if ((percentHumidity > 85.0) && (temperature >= 80.0) && (temperature <= 87.0))
      hi += ((percentHumidity - 85.0) * 0.1) * ((87.0 - temperature) * 0.2);
  }

  return hi;
}