Building the Heating / Air Conditioning Thermostat

Our existing thermostat is a White Rogers that currently controls our Air Conditioner and Electric Furnace. We will be replacing this with our Arduino and LCD display. Attached are the photo's, schematic, and documentation of the existing control. We will post the code and schematics of the new system as it develops. More details on how Thermostats work and are wired can be found at http://www.epatest.com/store/resources/images/misc/how-a-thermostat-operates.pdf

LCD / Keypad Shield

We are building a thermostat to control our furnace and A/C. We are using a DFRobot LCD / Keypad shield we received from Hacktronics.com to display the temperature, and to set the temperature ranges for both the heating and cooling modes. The following is a sketch that shows how the lcd and the buttons are utilized. Only one analog input is needed for the 6 buttons, as they are connected to resistors, and the resistance is measured to determine which button is being pushed. We will be customizing this with a Dallas DS18B20 temperature sensor, and MOSFET / SSR control over the Furnace and A/C. A video of how this works has been uploaded to YouTube.

//Sample using LiquidCrystal library

#include "LiquidCrystal.h"

/*******************************************************

This program will test the LCD panel and the buttons

Mark Bramwell, July 2010

********************************************************/

// select the pins used on the LCD panel

LiquidCrystal lcd(8, 9, 4, 5, 6, 7);

// define some values used by the panel and buttons

int lcd_key     = 0;

int adc_key_in  = 0;

#define btnRIGHT  0

#define btnUP     1

#define btnDOWN   2

#define btnLEFT   3

#define btnSELECT 4

#define btnNONE   5

// read the buttons

int read_LCD_buttons()

{

 adc_key_in = analogRead(0);      // read the value from the sensor

 // my buttons when read are centered at these valies: 0, 144, 329, 504, 741

 // we add approx 50 to those values and check to see if we are close

 if (adc_key_in > 1000) return btnNONE; // We make this the 1st option for speed reasons since it will be the most likely result

 if (adc_key_in < 50)   return btnRIGHT; 

 if (adc_key_in < 195)  return btnUP;

 if (adc_key_in < 380)  return btnDOWN;

 if (adc_key_in < 555)  return btnLEFT;

 if (adc_key_in < 790)  return btnSELECT;  

 return btnNONE;  // when all others fail, return this...

}

void setup()

{
 analogWrite(10, 50); // set brightness on pin 10 to 0-255

 lcd.begin(16, 2);              // start the library

 lcd.setCursor(0,0);

 lcd.print("Push the buttons"); // print a simple message

}

  

void loop()

{

 lcd.setCursor(9,1);            // move cursor to second line "1" and 9 spaces over

 lcd.print(millis()/1000);      // display seconds elapsed since power-up

 lcd.setCursor(0,1);            // move to the begining of the second line

 lcd_key = read_LCD_buttons();  // read the buttons

 switch (lcd_key)               // depending on which button was pushed, we perform an action

 {

   case btnRIGHT:

     {

     lcd.print("RIGHT ");

     break;

     }

   case btnLEFT:

     {

     lcd.print("LEFT   ");

     break;

     }

   case btnUP:

     {

     lcd.print("UP    ");

     break;

     }

   case btnDOWN:

     {

     lcd.print("DOWN  ");

     break;

     }

   case btnSELECT:

     {

     lcd.print("SELECT");

     break;

     }

     case btnNONE:

     {

     lcd.print("NONE  ");

     break;

     }

 }

}