Undestanding the pin assignment LCD i2C

Jose, if I understand you correctly you want to know the connections between the Arduino and the LCD serial module.  There are several versions of the serial modules and they all use different pin configurations.  The best source of information and how to identify the modules that I have found is on "yourduino.com"  There is also some Arduino code for each module type.  I have used the serial or I2C modules with great sucess using the information on the site noted above.

If you need more help please ask.

Bob

I have the same question. Is there a complete list of codes for the display?  Some are used in the sketches such as blank the display, blink the cursor etc.

Thanks Bill

There are two variations of the serial to LCD adapters floating around

The chip on the board linked is a PCF8574 I2C 8 bit port expander  http://www.ti.com/lit/ds/symlink/pcf8574.pdf

and as such does not support SPI even though the ebay add says it does

so this is a standard library driver and it is probably connected in a standard way to what ever LCD display you hock it too providing it follows the 1602 / 2004 standard pin out which is most of them

the codes needed for the display is found in the display documentation, not the I2C to LCD adapter and again is usualy following the Hitachi standard

the standard driver and samples should all work for you

What do you get on the display when you try to run the samples, have you verified your using the library for the PCF8574 ?

Yes, finally I could run one example with succes, the problem is that i dont know how to know where is the docuementation for the values of the constructor

LiquidCrystal_I2C LCD(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE); // Set the LCD I2C address

I know that 0x27 is the address of device but i dont know how to find the correct values of the next parameters, for example 2,1,0....

I know also that 2 is for enable, 1 is for rw and so on... But WHY? hahaha, i found the correct values trying with differents examples

but I always want to understand all that I wrote in my programs because if in the future I need to modify this program how I will do it? hahahah

Thanks

Bill,

        if you look on www.yourduino.com at these modules and the associated Wiki there is a full list of all the functions and some very good explanations.  With reference to Peter's comments the variants available on EBAY do, I believe, differ in the way the PCF8574 pins are connected to the LCD display.  I have two versions at least and I can get both versions to work perfectly by changing the pin list in LiquidCrystal_I2C.  There may also be modules that use a different I2C to parallel converter chip.

Yes I know that the only thing that you need to do in order to work with differents modules (with differents pinouts) is change the constructor but my question and I think that it's the same for other people is what is the way to discover the pinout of the differents modules (all modules with the same controller).

For example, you told that you have two version, okay, what way you followed to discover what values to put in the constructor? (the only way is yourduino.com)

Thanks bob.

So to see more about that I would suggest simply looking at the library CPP file (It will be the same name as the header file (.h) but with a .CPP extention instead, with luck it is commented but at least you will see the signature of the method calls, the header file should also show the signatures and possibly more comments

I have never yet found much actual user guides for these things

Peter

I think the codes relate to the LCD not the expander. As I understand the port expander only translates the serial data to parallel. the actual code would be the same.

Is this correct. Maybe I am looking in the wrong place?

Bill

Bill, Jose,

                    The codes in the constructor reflect the way the I2C to parallel chip (PCF8574) is connected to the LCD.  These devices use the 4 bit data transfer method from the 8574 to the LCD. So in the example lcd(0x27,2,1,0,4,5,6,7,3,POSITIVE).  The numbers refer to En, RW, RS, data pins 4,5,6,7, 3 is the back light control pin and POSITIVE is the back light polarity.  The pins referred to are on the LCD module linked to the 8574 chip.  Thus provided the constructor is correct the data sent to the LCD via the I2C interface will be displayed correctly.  The code written and programmed into the Arduino will work correctly provided the constructor for the particular I2C to LCD module reflects the wiring between the 8574 and the LCD module.  Bill is therefore correct in his understanding.

I do have a PDF file that shows the connections of one LCD backpack module but I don't know how to attach it to this note.  If anyone wants it please email me.

Now the rub!  As Peter has noted there is very little information on these devices apart from that on yourduino.com, so to answer Jose'e question specifically there is no easy way to find the correct constructor for these back packs unless the supplier has the information.  Alternatively a logic analyser could be used.

Again as Peter noted much of the information above can be gleaned from the comments of the library files.

Yep, looks like the most complete data may be on Sparkfun.com. go there and lookup the LCD module their number (LCD-00790) the datasheet seems to be the most complete.

It is difficult to comprehend but the data is there for all the codes for the display.

Thanks guys.

Bill