The example code you are showing here and the example code you showed here: SainSmart LCD1602 Module Display [how do i use this?] - #34 by multimedia - Displays - Arduino Forum
are different and are for different libraries.
While the "libraries" may have the same name, and provide a LiquidCrystal_I2C.h header file, different LiquidCrystal_I2C classes are initialized differently, have different functionality and have different API functions.
It appears that you may have installed multiple libraries with a LiquidCrystal_I2C.h header and LiquidCrystal_I2C class.
If you have done this, then things can get very strange since the IDE can end up picking up portions of both libraries or portions of more than one at different points during the compilation/link process.
I would recommend using my hd44780 library package instead.
It is available in the IDE library manager so it can quickly and easily be installed from the IDE gui using the library manager.
With other i2c LCD libraries you must specify the i2c address. Most libraries are also hard coded to work with backpacks that use a specific pin mapping between the PCF8574 and the hd44780 LCD display and if your backpack doesn't use that pin mapping, it won't work.
A few libraries allow the sketch to configure the PCF8574 pin mappings and backlight control.
If the pin mappings are not specified correctly, it will not work.
The hd44780 library can auto detect everything, the i2c address, the pin mappings, and the backlight control.
You can read more about it here: GitHub - duinoWitchery/hd44780: Extensible hd44780 LCD library
The hd44780 github page contains information about the library including installation instructions.
Use the IDE library manager to install it as it is easier and faster than trying to do it manually or using the zip install.
Also, by using the IDE library manager it ensures that the library is installed properly not to mention that you will also get the latest tested version of the library.
The library package includes support for several different h/w i/o interfaces used to communicate with the LCD module.
Each i/o interface has its own i/o class and its own set of examples.
The examples for each i/o class are grouped together in a directory by the name of the i/o class.
While all the examples are always available regardless of which h/w you actually have, using an example for an i/o class that is for different h/w will not work.
It will compile but obviously will not work.
The i/o class you will want to use for a PCF8574 i2c backpack which contains an i2c i/o expander chip is hd44780_I2Cexp
That i/o class includes a diagnostic sketch (I2CexpDiag) which will test the i2c signals and internal RAM of the LCD module to verify that the the library is properly communicating with the LCD module.
It is useful to first run this sketch to verify that the library is properly talking to your backpack and LCD module.
Read the instructions in the sketch for how to run it and what to expect on the serial monitor.
After running the diagnostic sketch, you can run and look at other sketches for the hd44780_I2Cexp i/o class like the HelloWorld sketch to see what header files need to be included and how to declare the lcd object.
The hd44780 library contains additional capabilities not available in other libraries like
- return status to tell if API functions are not working correctly (usually do to i2c communication issues)
- ability to enable automatic line wrapping
- ability to read the display RAM or LCD status
- faster than other libraries as Arduino can run in parallel with LCD commands/instructions
I would recommend first running the diagnostic skech I2CexpDiag to verify that everything is working, then you can run and look at the other examples included in the hd44780_I2Cexp i/o class (like HelloWorld) to see the what header files need to be included and how to declare the lcd object.
--- bill