A DIY TWI LCD Using PCF8574AP For Arduino

A character LCD with a 44780 LCD controller generally controlled by an MCU parallel port. Even the data transfer in-used is 4-bit mode, but it still require up to six MCU pins. 

A character LCD with PCF8574AP

PCF8574AP is an 8-bit general purpose digital I/O expanding. We can read and write digital data between this device and a master MCU, or even controlling a parallel LCD module. However using an I2C IC bridge the master MCU uses only two pins of its digital I/O to interface to the LCD.

In online market the PCF8574AP is built in module the a character LCD that cost a few Dollars. For an electronics hobbyist like me, I only bought a single DIP version of this chip. I can program it to read/write digital data before I decide to put it with a character LCD.

I decided to make my own I2C board module for my Arduino Uno board. This design follows the liquidCrystal_I2C LCD library from an author on GitHub. The overall design is not difference from the original one's but I made my own schematic and PCB design for my personal use.

I use Eagle CAD from Auto Desk software due to its richness of symbols and footprints library. The result yield with a small rectangular PCB module wired with PCF8574AP and a character LCD.

Schematic Diagram

PCB View

This design example is fully worked as I have tested it with Arduino Uno using its library.

A zip file of this design could be download here.

Connection Diagram

 

This Arduino sketch is from the library itself with some of my own modification.

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

// set the LCD address to 0x38 for PCF8574A with A0 A1 A2 wired to GND
LiquidCrystal_I2C lcd(0x38,16,2); 
void setup()
{
  // initialize the lcd
  lcd.init();                     
  lcd.backlight();
  lcd.clear();
  Serial.begin(9600);
  lcd.setCursor(0,0);
  lcd.print("Serial Port LCD");
}

void loop()
{
  // 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());
    }
  }
}

This sketch could be download here, or you can get from the library after the installation.