Thermostat RTC I2C V5.1

/*Thermostat with Real Time Clock Module and web support using second Arduino with ethernet shield.
This sketch takes temp readings from three temp sensors and a door sensor and decides when to turn the heat on or off.
steve.a.mccluskey@gmail.com

Revisions:
V2.2: Web support using second arduino with ethernet shield. Master sends single char commands over serial and thermostat responds accordingly.
V2.3: Added door and heater state to web page.
V2.4: Added EEPROM functionality to save settings to resume on startup.
V2.5: Added code to handle if one of the sensors is unplugged on the web page, 02/18/14.
V2.6: Rewrote button polling, bottom line display and ReadTimeDate() with switch/cases; consolidated door logic, rewrote average functions. 02/19/14.
V2.7: Added functionality to display negative temps down to -40. 02/20/14.
V2.8: Removed averageC(), removed unneccesary lcd.setCursor()'s, fixed average() to correctly return negative temps, changed tempAvgC calculation,
  sensorInterval variable added, C/F mode saved to EEPROM, tempHold limited to 12F minimum, getTemp() analog reading to tempC now uses floating point math and rounding. 03/02/14.
  Changed average() to use floating point math as well. 03/03/14.
V2.9: Changed how often ReadTimeDate() is called. 03/05/14.
V3.0: Added daylight savings time option menu and functionality. 02/23/15.
V3.1: Added doorState variable and only reads door once per loop instead of several times. 02/25/15.
V3.2: Changed ReadTimeDate() to only initialize one string instead of three. Added heaterDelay variable. 02/27/15.

V4.0: Added One-Wire Temp sensor support for outdoor temps and getOneWireTemp(). Changed temp variables to temp1, temp2, temp3 from tempNear/Far/Out.
Fixed closing parenthesis typo in getTemp(). Changed const uint8_t's to #define in pin declarations. Limited data[] to two slots in getOneWireTemp(). 03/02/14.
Version 4.0 which uses analog TMP36 temp sensors can be found here: http://pastebin.com/YxKFUr2y

V5.0: Rewrote entire sketch to use I2C temp sensors and I2C clock module. 03/04/14.
V5.1: TempHold is now changeable on M8 (temp Out) screen. Added RTC_Interval and changed sensorInterval. Added lastClockCheck2 variable. 03/09/14.

Pin layout as follows:
0  : Hardware serial RX.
1  : Hardware serial TX.
2  :
3 ~: Green LED.
4  :
5 ~: Yellow LED.
6 ~: Red LED.
7  : Door sensor.
8  : Heater relay.
9 ~:
10~: OneWire bus.
11~:
12 :
13 :
A0 :
A1 :
A2 :
A3 :
A4 : I2C SDA.
A5 : I2C CLK.

Sketch outline:
Libraries.
Pin Declarations.
Global Variables.
setup().
loop() {
  Static variables.
  Poll door.
  Poll buttons.
  Poll sensors.
  Print avg/hold to first line.
  Print menu to second line.
  Door closed: switch/case for second line.
  Door open: door open.
  Heater on/off logic.
}
cToF().
getOneWireTemp().
heaterOn().
heaterOff().
clearLine().
average().
serialEvent().
*/

#include <Wire.h>
#include "RTClib.h"
#include <RTC_DS1307.h>
#include "Adafruit_MCP9808.h"
#include <Adafruit_MCP23017.h>
#include <Adafruit_RGBLCDShield.h>
#include <EEPROM.h>
#include <OneWire.h>
#include <SPI.h>

#define RTC_Interval 150 //delay between RTC updates.
#define sensorInterval 1000 //delay between sensor readings.
#define heaterDelay 120000 //heater on/off delay.

//pin declarations:
#define greenLed 3
#define yellowLed 5
#define redLed 6
#define door 7
#define relay 8
#define oneWireBus 10

OneWire oneWire(oneWireBus);
byte addr[8]; //array to store OneWire device's address.

Adafruit_RGBLCDShield lcd = Adafruit_RGBLCDShield();
RTC_DS1307 rtc;
Adafruit_MCP9808 tempSensor1 = Adafruit_MCP9808();
Adafruit_MCP9808 tempSensor2 = Adafruit_MCP9808();
Adafruit_MCP9808 tempSensor3 = Adafruit_MCP9808();

//global variables:
boolean celsius = EEPROM.read(5);
boolean doorLineCleared = false;
boolean daylightSavings = EEPROM.read(6);

uint8_t tempHold = EEPROM.read(0); // read saved tempHold value from EEPROM.
int8_t tempReduction = EEPROM.read(1);
uint8_t menu = EEPROM.read(4);
int8_t temp1, temp2, temp3, tempOneWire, tempAvg; // variables to store temps.
unsigned long heaterOnTime = 0, heaterOffTime = 0, currentTime = 0, lastReadingTime = 0, lastClockCheck = 0, lastClockCheck2 = 0;
uint8_t heaterState = 0, doorState = 0;

DateTime now;
uint8_t hour;
uint8_t eveningHour = EEPROM.read(3);
uint8_t morningHour = EEPROM.read(2);

void setup() {
  pinMode(redLed, OUTPUT);
  pinMode(greenLed, OUTPUT);
  pinMode(yellowLed, OUTPUT);
  pinMode(door, INPUT_PULLUP); //door pin is pulled to ground while door is closed.
  pinMode(relay, OUTPUT);
  Serial.begin(19200);
  Wire.begin();
  lcd.begin(16, 2);
  lcd.setCursor(0, 0);
  lcd.print(F("RTC Thermostat"));
  lcd.setCursor(0, 1);
  lcd.print(F("V 5.1"));
  delay(1000);
  tempSensor1.begin(0x18); //I2C address.
  tempSensor2.begin(0x19);
  tempSensor3.begin(0x1A);
  oneWire.search(addr); //get connected OneWire device address.
  rtc.begin();
  //rtc.adjust(DateTime(__DATE__, __TIME__)); //set RTC to time of compile, will revert to that time every time arduino is reset. run once and then comment out and reload.
  lcd.clear();
} //end setup().

void loop() {
   uint8_t buttons = lcd.readButtons(); //MUST be in main loop. will not work if global.

  if (digitalRead(door) == HIGH) { //only read once per loop.
    doorState = 1;
  } //end if.
  else {
    doorState = 0;
  } //end else.

  currentTime = millis();

  int8_t tempAvgC, temp1C, temp2C, temp3C, tempOneWireC;
  float convF = (5.0 * (tempHold - 32)) / 9.0;
  int8_t tempHoldC = round(convF);
  int8_t tempReductionC = tempReduction / 4;

  if (buttons) { //poll the buttons.
    if (buttons & BUTTON_SELECT) {
      celsius = !celsius;
      EEPROM.write(5, celsius); //only write to EEPROM when something is changed to reduce write cycles.
    } //end if.

    else if (buttons & BUTTON_UP) {
      switch (menu) { //update variables depending on which menu is selected.
        case 1:
          tempHold += 2;
          if (tempHold > 80) {
            tempHold = 80;
          } //end if.
          EEPROM.write(0, tempHold);
        break; //end case 1.

        case 2:
          tempReduction += 2;
          if (tempReduction > 12) {
            tempReduction = 12;
          } //end if.
          EEPROM.write(1, tempReduction);
        break; //end case 2.

        case 3:
          eveningHour ++;
          if (eveningHour > 24) {
            eveningHour = 24;
          } //end if.
          EEPROM.write(3, eveningHour);
        break; //end case 3.

        case 4:
          morningHour ++;
          if (morningHour > 11) {
            morningHour = 11;
          } //end if.
          EEPROM.write(2, morningHour);
        break; //end case 4.

        case 5:
        break; //end case 5.

        case 6:
        break; //end case 6.

        case 7:
          daylightSavings = !daylightSavings;
          EEPROM.write(6, daylightSavings);
        break; //end case 7.

        case 8:
          tempHold += 2;
          if (tempHold > 80) {
            tempHold = 80;
          } //end if.
          EEPROM.write(0, tempHold);
        break; //end case 8.

        default:
        break;
      } //end switch.
    } //end if button_up.

    else if (buttons & BUTTON_DOWN) {
      switch (menu) {
        case 1:
          tempHold -= 2;
          if (tempHold < 12) {
            tempHold = 12;
          } //end if.
          EEPROM.write(0, tempHold);
        break; //end case 1.

        case 2:
          tempReduction -= 2;
          if (tempReduction <= 0) {
            tempReduction = 0;
          } //end if.
          EEPROM.write(1, tempReduction);
        break; //end case 2.

        case 3:
          eveningHour --;
          if (eveningHour < 16) {
            eveningHour = 16;
          } //end if.
          EEPROM.write(3, eveningHour);
        break; //end case 3.

        case 4:
          morningHour --;
          if (morningHour < 3) {
            morningHour = 3;
          } //end if.
          EEPROM.write(2, morningHour);
        break; //end case 4.

        case 5:
        break; //end case 5.

        case 6:
        break; //end case 6.

        case 7:
          daylightSavings = !daylightSavings;
          EEPROM.write(6, daylightSavings);
        break; //end case 7.

        case 8:
          tempHold -= 2;
          if (tempHold < 12) {
            tempHold = 12;
          } //end if.
          EEPROM.write(0, tempHold);
        break;

        default:
        break;
      } //end switch
    } //end if button_down.

    else if (buttons & BUTTON_RIGHT) {
      menu ++;
      clearLine(); //clears 2nd line only when menu number is changed.
      if (menu > 8) {
        menu = 1;
      } //end if.
      EEPROM.write(4, menu);
    } //end if.

    else if (buttons & BUTTON_LEFT) {
      menu --;
      clearLine();
      if (menu < 1) {
        menu = 8;
      } //end if.
      EEPROM.write(4, menu);
    } //end if.
  } // end if buttons.

  if (currentTime - lastClockCheck2 > RTC_Interval) { //get hour of day from RTC.
    now = rtc.now();
    hour = now.hour();
    if (daylightSavings) {
      hour += 1;
    } //end if.
    lastClockCheck2 = currentTime;
  } //end if.

  if (currentTime - lastReadingTime > sensorInterval) { //only poll sensors every interval
    if (!celsius) {
      temp1 = cToF(tempSensor1.readTempC()); //poll the sensors.
      temp2 = cToF(tempSensor2.readTempC());
      temp3 = cToF(tempSensor3.readTempC());
      tempAvg = average(temp1, temp2, temp3);
      tempOneWire = getOneWireTemp();
    } //end if.
    else {
      temp1C = tempSensor1.readTempC();
      temp2C = tempSensor2.readTempC();
      temp3C = tempSensor3.readTempC();
      tempAvgC = average(temp1C, temp2C, temp3C);
      tempOneWireC = getOneWireTemp();
    } //end else.

    lastReadingTime = currentTime;
  } //end if.

   //print avg to screen:
  lcd.setCursor(0, 0);
  lcd.print(F("Avg:"));
  if (!celsius) {
    if (tempAvg >= -40 && tempAvg < 0) { //displays negative temps.
      lcd.print(tempAvg);
      lcd.print(F("F"));
    } //end if.
    else if (tempAvg >= 0) { //displays positive temps and clears last digit.
      lcd.print(tempAvg);
      lcd.print(F("F "));
    } //end else if.
    else {
      lcd.print(F("--F ")); //displays "--" if all 3 sensors are unplugged.
    } //end else.
  } //end if !celsius.

  else {
    if (tempAvgC >= -40 && tempAvgC < 0) {
      lcd.print(tempAvgC);
      lcd.print(F("C"));
    } //end if.
    else if (tempAvgC >= 0) {
      lcd.print(tempAvgC);
      lcd.print(F("C "));
    } //end else if.
    else {
      lcd.print(F("--C "));
    } //end else.
  } //end else.

  //print hold temp to screen:
  lcd.setCursor(8, 0);
  lcd.print(F("Hold:"));
  lcd.setCursor(13, 0);
  if (hour < morningHour || hour >= eveningHour) { //displays night temp hold at night.
    if (!celsius) {
      lcd.print(tempHold - tempReduction);
      lcd.print(F("*")); //star indicates night time temp reduction.
    } //end if.
    else {
      lcd.print(tempHoldC - tempReductionC);
      lcd.print(F("*"));
    } //end else.
  } //end if.

  else if (hour >= morningHour && hour < eveningHour) { //displays regular temp hold during day.
    if (!celsius) {
      lcd.print(tempHold);
      lcd.print(F("F"));
    } //end if.
    else {
      lcd.print(tempHoldC);
      lcd.print(F("C"));
    } //end else.
  } //end else if.

  lcd.setCursor(0, 1);
  lcd.print(F("M")); //displays menu number.
  lcd.print(menu);

  //bottom line display:
  if (doorState == 0) {
    analogWrite(redLed, 0);
    digitalWrite(greenLed, HIGH); //green led indicates system normal.
    if (!doorLineCleared) { //only clears line once when door is shut.
      clearLine();
      doorLineCleared = true;
    } //end if.

    switch (menu) {
      case 1: //displays sensors to screen and allows changing of temp hold.
        lcd.setCursor(2, 1);
        if (!celsius) { //sensor one:
          if (temp1 < -40) { //displays "--" if tempNear returns null and clears leading minus sign.
            lcd.print(F(" --"));
          } //end if.
          else if (temp1 >= -40 && temp1 < 0) { //negative temps.
            lcd.print(temp1);
          } //end else if.
          else {
            lcd.print(F(" ")); //positive temps and clears minus sign.
            lcd.print(temp1);
          } //end else.
          lcd.print(F("F "));
        } //end if.
        else {
          if (temp1C < -40) {
            lcd.print(F(" --"));
          } //end if.
          else if (temp1C >= 40 && temp1C < 0) {
            lcd.print(temp1C);
          } //end else if.
          else {
            lcd.print(F(" "));
            lcd.print(temp1C);
          } // end else.
          lcd.print(F("C "));
        } //end else.

        lcd.setCursor(7, 1);
        if (!celsius) { //sensor 2:
          if (temp2 < -40) {
            lcd.print(F(" --"));
          } //end if.
          else if (temp2 >= -40 && temp2 < 0) {
            lcd.print(temp2);
          } //end else if.
          else {
            lcd.print(F(" "));
            lcd.print(temp2);
          } //end else.
          lcd.print(F("F "));
        } //end if.
        else {
          if (temp2C < -40) {
            lcd.print(F(" --"));
          } //end if.
          else if (temp2C >= 40 && temp2C < 0) {
            lcd.print(temp2C);
          } //end else if.
          else {
            lcd.print(F(" "));
            lcd.print(temp2C);
          } // end else.
          lcd.print(F("C "));
        } //end else.

        lcd.setCursor(12, 1);
        if (!celsius) { //sensor 3:
          if (temp3 < -40) {
            lcd.print(F(" --"));
          } //end if.
          else if (temp3 >= -40 && temp3 < 0) {
            lcd.print(temp3);
          } //end else if.
          else {
            lcd.print(F(" "));
            lcd.print(temp3);
          } //end else.
          lcd.print(F("F "));
        } //end if.
        else {
          if (temp3C < -40) {
            lcd.print(F(" --"));
          } //end if.
          else if (temp3C >= 40 && temp3C < 0) {
            lcd.print(temp3C);
          } //end else if.
          else {
            lcd.print(F(" "));
            lcd.print(temp3C);
          } // end else.
          lcd.print(F("C "));
        } //end else.
      break; //end menu 1.

      case 2: //displays temp drop amount.
        lcd.setCursor(3, 1);
        lcd.print(F("Drop Temp:"));
        if (!celsius) {
          if (tempReduction < 10) {
            lcd.print(F(" "));
          } //end if.
          lcd.print(tempReduction);
          lcd.print(F("F"));
        } //end if.
        else {
          if (tempReductionC < 10) {
            lcd.print(F(" "));
          } //end if.
          lcd.print(tempReductionC);
          lcd.print(F("C"));
        } //end else.
      break; //end menu 2.

      case 3: //displays PM time to drop temp:
        lcd.setCursor(3, 1);
        lcd.print(F("Heat Dn: "));
        if (eveningHour < 22) {
          lcd.print(F(" "));
        } //end if.
        lcd.print(eveningHour - 12);
        lcd.print(F("pm"));
      break; //end menu 3.

      case 4: //displays AM time to raise temp:
        lcd.setCursor(3, 1);
        lcd.print(F("Heat Up: "));
        if (morningHour < 10) {
          lcd.print(F(" "));
        } //end if.
        lcd.print(morningHour);
        lcd.print(F("am"));
      break; //end menu 4.

      case 5: //display time to 2nd row:
        lcd.setCursor(4, 1);
        lcd.print(F("Tm: "));
        if (currentTime - lastClockCheck > RTC_Interval) {
          now = rtc.now();
          if (hour < 10) {
            lcd.print(F(" "));
          } //end if.
          lcd.print(now.hour());
          lcd.print(F(":"));
          if (now.minute() < 10) {
            lcd.print(F("0"));
          } //end if.
          lcd.print(now.minute());
          lcd.print(F(":"));
          if (now.second() < 10) {
            lcd.print(F("0"));
          } //end if.
          lcd.print(now.second());
          lastClockCheck = currentTime;
        } //end if.
      break; //end menu 5.

      case 6: //display date to 2nd row:
        lcd.setCursor(4, 1);
        lcd.print(F("Dt: "));
        if (currentTime - lastClockCheck > RTC_Interval) {
          now = rtc.now();
          if (now.month() < 10) {
            lcd.print(F(" "));
          } //end if.
          lcd.print(now.month());
          lcd.print(F("/"));
          if (now.day() < 10) {
            lcd.print(F("0"));
          } //end if.
          lcd.print(now.day());
          lcd.print(F("/"));
          lcd.print(now.year() - 2000);
          lastClockCheck = currentTime;
        } //end if.
      break; //end menu 6.

      case 7: //daylight savings time enable/disable:
        lcd.setCursor(4, 1);
        lcd.print(F("DST:"));
        if (daylightSavings) {
          lcd.print(F("Active  "));
        } //end if.

        else {
          lcd.print(F("Inactive"));
        } //end else.
      break;  //end menu 7.

      case 8: //prints outside temp to screen.
        lcd.setCursor(4, 1);
        lcd.print(F("Out: "));
        if (!celsius) {
          if (tempOneWire > -51) {
            lcd.print(tempOneWire);
         } //end if.
          else {
            lcd.print("--");
          } //end else.
          lcd.print(F("F   "));
        } //end if celsius.
        else {
          if (tempOneWireC > -51) {
            lcd.print(tempOneWireC);
          } //end if.
          else {
            lcd.print("--");
          } //end else.
          lcd.print(F("C   "));
        } // else.
      break; //end case 8.
    } //end switch menu.
  } //end if door closed.

  else {
    doorLineCleared = false;
    lcd.setCursor(2, 1);
    lcd.print(F(" Door open!   "));
    digitalWrite(greenLed, LOW);
    digitalWrite(yellowLed, LOW);
    digitalWrite(relay, LOW);
    heaterState = 0;
    analogWrite(redLed, 180);
    heaterOffTime = currentTime;
  } //end else if.

  //decide when to turn heater on or off:
  if (hour >= morningHour && hour < eveningHour) { //day time
    if (((!celsius && tempAvg > -41 && tempAvg < tempHold) ||
    (celsius && tempAvgC > -41 && tempAvgC < tempHoldC)) && doorState == 0) {
      heaterOn();
    } //end if.
    else {
      heaterOff();
    } //end else.
  } //end if day time.

  else if (hour < morningHour || hour >= eveningHour) { //night time
    if (((!celsius && tempAvg > -41 && tempAvg < (tempHold - tempReduction)) ||
    (celsius && tempAvgC > -41 && tempAvgC < (tempHoldC - tempReductionC))) && doorState == 0) {
      heaterOn();
    } //end if.
    else {
      heaterOff();
    } //end else.
  } //end if night time.

} //end loop().

int8_t cToF(float c) { //convert float C to int F.
  return round((1.8 * c) + 32.0);
} //end cToF().

int8_t getOneWireTemp() { //get OneWire temp.
  byte data[2]; //array to store data retrieved from sensor.
  oneWire.reset();
  oneWire.select(addr);
  oneWire.write(0x44, 1); //start conversion.
  oneWire.reset();
  oneWire.select(addr);
  oneWire.write(0xBE); //read scratchpad.

  for (byte i = 0; i < 2; i ++) {
    data[i] = oneWire.read(); //collect data.
  } //end for.

  int16_t raw = (data[1] << 8) | data[0]; //convert raw data to C.

  if (celsius) {
    return round((float)raw / 16.0);
  } //end if.
  else {
    return round(((float)raw / 16.0) * 1.8 + 32.0);
  } //end else.
} //end getOneWireTemp().

void heaterOn() {
  if (currentTime - heaterOffTime > heaterDelay) { //check to see if heater has been off for at least 2 min.
    digitalWrite(relay, HIGH);
    analogWrite(yellowLed, 180);
    heaterOnTime = currentTime;
    heaterState = 1;
  } //end if.
} //end heaterOn().

void heaterOff() {
  if (currentTime - heaterOnTime > heaterDelay) { //check to see if heater has been on for at least 2 min.
    digitalWrite(relay, LOW);
    digitalWrite(yellowLed, LOW);
    heaterOffTime = currentTime;
    heaterState = 0;
  } //end if.
} //end heaterOff().

void clearLine() { //clears 2nd line past M#.
  lcd.setCursor(2, 1);
  lcd.print(F("              "));
} //end clearLine().

int8_t average(int8_t temp_1, int8_t temp_2, int8_t temp_3) { //averages 3 temps and knows how depending on which sensors are plugged in.
  uint8_t count = 0;
  float avg = 0.0;
  if (temp_1 > -41) { //sensor connected.
   count ++;
   avg += temp_1;
  } //end if.
  if (temp_2 > -41) {
    count ++;
    avg += temp_2;
  } //end if.
  if (temp_3 > -41) {
    count ++;
    avg += temp_3;
  } //end if.
  if (count != 0) {
    return round(avg / count);
  } //end if.
  else {
    return -41; //all three sensors unplugged.
  } //end else.
} //end average().

void serialEvent() { //called any time serial data is available.
  char c = Serial.read();
  switch (c) {
    case '*': //all values requested. sends string of data to be served by other arduino. IE " 64h63a17j9e7m8t0d1f61x62y65z58w* "
      Serial.print(tempHold);
      Serial.print(F("h")); //indicates end of tempHold.

      if (tempAvg > -41) {
        Serial.print(tempAvg);
      } //end if.
      else {
        Serial.print(F("--"));
      } //end else.

      Serial.print(F("a"));
      Serial.print(hour);
      Serial.print(F("j"));
      Serial.print(eveningHour);
      Serial.print(F("e"));
      Serial.print(morningHour);
      Serial.print(F("m"));
      Serial.print(tempReduction);
      Serial.print(F("t"));
      Serial.print(doorState);
      Serial.print(F("d"));
      Serial.print(heaterState);
      Serial.print(F("f"));

      if (temp1 > -41) {
        Serial.print(temp1);
      } //end if.
      else {
        Serial.print(F("--"));
      } //end else.
      Serial.print(F("x"));

      if (temp2 > -41) {
        Serial.print(temp2);
      } //end if.
      else {
        Serial.print(F("--"));
      } //end else.
      Serial.print(F("y"));

      if (temp3 > -41) {
        Serial.print(temp3);
      } //end if.
      else {
        Serial.print(F("--"));
      } //end else.
      Serial.print(F("z"));

      if (tempOneWire > -51) {
        Serial.print(tempOneWire);
      }
      else {
        Serial.print(F("--"));
      }
      Serial.print(F("w"));

      Serial.println(F("*")); //end of data character.
    break; //end case '*'.

    case 'h': //increase hold temp.
      tempHold += 2;
      if (tempHold > 80) {
        tempHold = 80;
      } //end if.
      EEPROM.write(0, tempHold);
    break; //end case 'h'.

    case 'n': //decrease hold temp.
      tempHold -= 2;
      if (tempHold < 12) {
        tempHold = 12;
      } //end if.
      EEPROM.write(0, tempHold);
    break; //end case 'n'.

    case 'e': //heat off later.
      eveningHour ++;
      if (eveningHour > 24) {
        eveningHour = 24;
      } //end if.
      EEPROM.write(3, eveningHour);
    break; //end case 'e'.

    case 'd': //heat off earlier.
      eveningHour --;
      if (eveningHour < 16) {
        eveningHour = 16;
      } //end if.
      EEPROM.write(3, eveningHour);
    break; //end case 'd'.

    case 'm': //heat on later.
      morningHour ++;
      if (morningHour > 11) {
        morningHour = 11;
      } //end if.
      EEPROM.write(2, morningHour);
    break; //end case 'm'.

    case 'j': //heat on earlier.
      morningHour --;
      if (morningHour < 3) {
        morningHour = 3;
      } //end if.
      EEPROM.write(2, morningHour);
    break; //end case 'j'.

    case 't': //reduce temp more.
      tempReduction += 2;
      if (tempReduction > 12) {
        tempReduction = 12;
      } //end if.
      EEPROM.write(1, tempReduction);
    break; //end case 't'.

    case 'g': //reduce temp less.
      tempReduction -= 2;
      if (tempReduction < 0) {
        tempReduction = 0;
      } //end if.
      EEPROM.write(1, tempReduction);
    break; //end case 'g'.
  } //end switch.
} //end serialEvent().