Undestanding the pin assignment LCD i2C

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, 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

Ok I think more or less I am understanding now how it works. I think that the main problem here is the documentation of all of these modules but anyway...

Thanks to all of you, Is a great pleasure talk with you

Your welcome

Any please if you will, mark helpful and or Correct answers for people that have helped you as it earns us badges and points

Thanks

Peter

Ok hahaha

Hey, José

Peter is serious. We  all enjoy helping but it is nice to be recognized as helpful.

Bill

Yes, I know but i already have clicked in "i like button" Thanks

Unfortunately it selected as a question....

Sorry, i dont understand, i'm newby in this forum and spanish also and for this reason sometimes i dont understand hahaha.

I clicked in button "like" in all replies. Is it all ok?

Sorry, i dont understand

When you first entered this post, it should have asked if you want to make this a question (and given you a short time to make the choice)

When you mark it as a question, it allows you to mark the answers helpful (3 ... I think) or correct (1)

http://www.element14.com/community/docs/DOC-68325/l/earning-points-for-sharing-your-expertise-on-element14-community

You might be able to go back and change it ...according to this.

http://www.element14.com/community/message/154267/l/re-updatingediting-a-discussion-to-indicate-as-a-clear-question#154267

Mark

Sorry, i dont understand

When you first entered this post, it should have asked if you want to make this a question (and given you a short time to make the choice)

When you mark it as a question, it allows you to mark the answers helpful (3 ... I think) or correct (1)

http://www.element14.com/community/docs/DOC-68325/l/earning-points-for-sharing-your-expertise-on-element14-community

You might be able to go back and change it ...according to this.

http://www.element14.com/community/message/154267/l/re-updatingediting-a-discussion-to-indicate-as-a-clear-question#154267

Mark