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 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.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 ");
   case btnLEFT:
     lcd.print("LEFT   ");
   case btnUP:
     lcd.print("UP    ");
   case btnDOWN:
     lcd.print("DOWN  ");
   case btnSELECT:
     case btnNONE:
     lcd.print("NONE  ");

0 thoughts on “LCD / Keypad Shield”

  1. I want to build one of these to run a small air conditioner. Could it be modified to read 2 or 3 temperature sensors and display the readings in f.
    Turn on the device when sensor 1 (room temperature) is above the set point and turn off the device when sensor 2 (the coils on the AC) drop below a certain point.
    Sensor 3 would just be informational, like outside temp.

  2. Thanks for the reply. I found the other post "after" I submitted my question. Nice that the temp sensors are addressable. Ordered everything "I think I need" last night. Ordered a 4 line LCD so I can list set point, TS1, TS2 & TS3 all at the same time. Please don't tell me that can all be done with the 2 line LCD you used above as the LDC Shield would be easier to use and already has buttons.

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