Using LCD (ST7066U Controller) with PCF8574T Backpack

Using Arduino Displays
#1

I can’t seem to make this 16x4 LCD (https://tinyurl.com/yax5sb49) work with the PCF8574T backpack (I2C module). Just a blank screen but the backlight works.

Based on this tutorial: https://tinyurl.com/kukgb5k, I assumed it will work. The pinouts of my LCD and the tutorial is the same. But I am not so sure with the code… Am I doing something wrong?

The pinout of the trouble LCD:

Here’s the I2C backpack:

/* Demonstration sketch for PCF8574T I2C LCD Backpack 
Uses library from https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads GNU General Public License, version 3 (GPL-3.0) */
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>

LiquidCrystal_I2C lcd(0x27,2,1,0,4,5,6,7); // 0x27 is the I2C bus address for an unmodified backpack

void setup()
{
  // activate LCD module
  lcd.begin (16,2); // for 16 x 2 LCD module
  lcd.setBacklightPin(3,POSITIVE);
  lcd.setBacklight(HIGH);
}

void loop()
{
  lcd.home (); // set cursor to 0,0
  lcd.print(" tronixlabs.com"); 
  lcd.setCursor (0,1);        // go to start of 2nd line
  lcd.print(millis());
  delay(1000);
  lcd.setBacklight(LOW);      // Backlight off
  delay(250);
  lcd.setBacklight(HIGH);     // Backlight on
  delay(1000);
}
#2

Using a backpack with a ST7066 will be exactly the same as a HD44780 LCD. The backpack should be properly soldered.

Install hd44780 library via the Library Manager. Read the instructions. Run the diagnostic sketches. Run the examples.

David.

#3

Thanks, David. I’ll try your suggestion.

So to clarify, apart from these three libraries:
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>

I should install and include the HD44780 library?

#4

Wire.h comes with the Arduino.
You must install hd44780.h with the Library Manager.

There are so many “bad” LiquidCrystal_I2C versions that it is better to avoid them.
In fact your particular fmalpartida version should work ok when you diagnose the correct constructor (with the hd44780.h sketch).

David.

#5