Schematic For PCF8574 I2C LCD Keypad Shield Using LiquidCrystal_I2C.h Library

By using PCF8574 I2C port extender, the LCD Keypad Shield can be released 6 digital I/O ports used to control HD44780 compatible LCD by using only SDA and SCL (Arduino A4 and A5). Part of the following schematic is implemented on breadboard to show result on LCD module, run the example sketch of LiquidCrystal_I2C.h library by changing the address to 0x20, the result is showed on the following photo.


Schematic

Photo

Sketch

#include <Wire.h> 
#include <LiquidCrystal_I2C.h>

#define BACKLIGHT_PIN     13

LiquidCrystal_I2C lcd(0x20);  // Set the LCD I2C address

//LiquidCrystal_I2C lcd(0x38, BACKLIGHT_PIN, POSITIVE);  // Set the LCD I2C address

// Creat a set of new characters
const uint8_t charBitmap[][8] = {
   { 0xc, 0x12, 0x12, 0xc, 0, 0, 0, 0 },
   { 0x6, 0x9, 0x9, 0x6, 0, 0, 0, 0 },
   { 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0, 0x0 },
   { 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0, 0x0 },
   { 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0, 0x0 },
   { 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0, 0x0 },
   { 0x0, 0x0, 0x0, 0x6, 0x9, 0x9, 0x6, 0x0 },
   { 0x0, 0x0, 0x0, 0xc, 0x12, 0x12, 0xc, 0x0 }  
};

void setup()
{
   int charBitmapSize = (sizeof(charBitmap ) / sizeof (charBitmap[0]));

  // Switch on the backlight
  pinMode ( BACKLIGHT_PIN, OUTPUT );
  digitalWrite ( BACKLIGHT_PIN, HIGH );
  
  lcd.begin(16,2);               // initialize the lcd 

   for ( int i = 0; i < charBitmapSize; i++ )
   {
      lcd.createChar ( i, (uint8_t *)charBitmap[i] );
   }

  lcd.home ();                   // go home
  lcd.print("Hello, ARDUINO ");  
  lcd.setCursor ( 0, 1 );        // go to the next line
  lcd.print (" FORUM - fm   ");
  delay ( 1000 );
}

void loop()
{
   lcd.home ();
   // Do a little animation by writing to the same location
   for ( int i = 0; i < 2; i++ )
   {
      for ( int j = 0; j < 16; j++ )
      {
         lcd.print (char(random(7)));
      }
      lcd.setCursor ( 0, 1 );
   }
   delay (200);
}

Notes About PCF8574 I2C LCD Using LiquidCrystal_I2C.h

IC Manufacturer
NXP - PCF8574P, PCF8574AP
TI - PCF8574N

Library
LiquidCrystal_I2C.h by Francisco Malpartida download from BitBucket Repository

Address
I2C address of PC8574 (all three address inputs grounded) = 0x20
I2C address of PC8574A (all three address inputs grounded) = 0x38

Pins Mapping (16 Pins 8574) (Schematic)
PCF8574.Pin1 -> GND
PCF8574.Pin2 -> GND
PCF8574.Pin3 -> GND
PCF8574.Pin4 (Port0) -> LCD.Pin11 (DB4)
PCF8574.Pin5 (Port1) -> LCD.Pin12 (DB5)
PCF8574.Pin6 (Port2) -> LCD.Pin13 (DB6)
PCF8574.Pin7 (Port3) -> LCD.Pin14 (DB7)
PCF8574.Pin9 (Port4) -> LCD.Pin4 (RS)
PCF8574.Pin10 (Port5) -> LCD.Pin5 (WR)
PCF8574.Pin11 (Port6) -> LCD.Pin6 (EN)
PCF8574.Pin14 (SCL) -> UNO.A5
PCF8574.Pin15 (SDA) -> UNO.A4
PCF8574.Pin16 (VDD) -> UNO.5V
PCF8574.Pin8 (VSS) -> UNO.GND

LCD Initialization
#include <Wire.h> // comes with Arduino IDE
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x20)
lcd.begin(16,2) // in Setup()

Variations (Yourduino)
   Marked "YwRobot Arduino LCM1602 IIC V1" -> lcd.begin(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE) // also SainSmart LCD2004, DFRobot (DZRMO)
   Marked "Arduino-IIC-LCD GY-LCD-V1" -> lcd.begin(0x20, 4, 5, 6, 0, 1, 2, 3, 7, NEGATIVE)
   Marked "LCD1602 IIC A0 A1 A2" -> lcd.begin(0x20, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE)

Example Code (Yourduino)
/* YourDuino.com Example Software Sketch
 16 character 2 line I2C Display
 Backpack Interface labelled "YwRobot Arduino LCM1602 IIC V1"
 terry@yourduino.com */

/*-----( Import needed libraries )-----*/
#include <Wire.h>  // Comes with Arduino IDE
// Get the LCD I2C Library here: 
// https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads
// Move any other LCD libraries to another folder or delete them
// See Library "Docs" folder for possible commands etc.
#include <LiquidCrystal_I2C.h>

/*-----( Declare Constants )-----*/
/*-----( Declare objects )-----*/
// set the LCD address to 0x27 for a 20 chars 4 line display
// Set the pins on the I2C chip used for LCD connections:
//                    addr, en,rw,rs,d4,d5,d6,d7,bl,blpol
LiquidCrystal_I2C lcd(0x20);  // Set the LCD I2C address

/*-----( Declare Variables )-----*/
//NONE

void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  Serial.begin(9600);  // Used to type in characters

  lcd.begin(16,2);   // initialize the lcd for 16 chars 2 lines, turn on backlight

// ------- Quick 3 blinks of backlight  -------------
  for(int i = 0; i< 3; i++)
  {
    lcd.backlight();
    delay(250);
    lcd.noBacklight();
    delay(250);
  }
  lcd.backlight(); // finish with backlight on  

//-------- Write characters on the display ------------------
// NOTE: Cursor Position: (CHAR, LINE) start at 0  
  lcd.setCursor(0,0); //Start at character 4 on line 0
  lcd.print("Hello, world!");
  delay(1000);
  lcd.setCursor(0,1);
  lcd.print("HI!YourDuino.com");
  delay(8000);  

// Wait and then tell user they can start the Serial Monitor and type in characters to
// Display. (Set Serial Monitor option to "No Line Ending")
  lcd.clear();
  lcd.setCursor(0,0); //Start at character 0 on line 0
  lcd.print("Use Serial Mon");
  lcd.setCursor(0,1);
  lcd.print("Type to display");  


}/*--(end setup )---*/


void loop()   /*----( LOOP: RUNS CONSTANTLY )----*/
{
  {
    // when characters arrive over the serial port...
    if (Serial.available()) {
      // wait a bit for the entire message to arrive
      delay(100);
      // clear the screen
      lcd.clear();
      // read all the available characters
      while (Serial.available() > 0) {
        // display each character to the LCD
        lcd.write(Serial.read());
      }
    }
  }

}/* --(end main loop )-- */


/* ( THE END ) */