Difference between LCD standard and LCD I2C

Please, someone can explain exactly to each of these pins of the display I2C (GND, VCC, SDA, SCL) which corresponds to the pin of old LCD (DB4, DB5, DB6, DB7, E, RW, RS, V0, VDD, VSS )?


There is a big difference. Simply, no one of signals is corresponding (except of VCC, GND and VDD, VSS - power supply, but it is no signal in fact). Standard LCD has an parallel data bus and I2C is serial data bus. You cannot interconnect these directly.

DB4-DB7 ~ four high bidirectional data lines
E ~ enable to read/write
RW ~ read/write mode
RS ~ register selection
VO ~ LCD operating voltage

SCL - clock signal
SDA - serial data

Additional module is needed for non i2C LCD to I2C adaptation e.g. based on old good PCF8574 chip.

thanks for the reply! :slight_smile:
I'll explain my problem: I would like to do this project:
http://www.instructables.com/file/FAZQGW7HOW0HQ7S (or http://www.instructables.com/file/FVBC6TYHOW0HQ7H)
but I have a display with I2C ... how can I do?
Which PIN I have to connect and which are not? Where?
Can you help me? :slight_smile:

You've post wrong URL. Couldn't be found.

If you need to connect standard LCD via I2C you have to use additional module which converts signals as I wrote already.
Try to google and you will obtain lots of results for such module.

... but I have a display with I2C ... how can I do?
Which PIN I have to connect and which are not? Where? ...

Most likely your I2C display is actually a standard parallel device that has a separate I2C adapter board. You could unsolder the adapter board (not a trivial task) and just use the display board by itself but it would be far easier to just buy a new display.


this is working URL

I have a display with I2C ... how can I do?

You have to modify the instructables code to use the i2c display instead of the parallel display with a change of library and constructor. All the lcd.print() and cursor instructions in the code should work with either display.

If currently don't know how to print to the i2c display then you need to begin the learning process of how to do so.

There is a Forum Search box at the top right of this webpage. Some key terms will be "i2c display" "fmalpartida i2c library" and "Bill Perry i2cLCD guesser".

Here's a useful link http://forum.arduino.cc/index.php?topic=260510.msg1839324#msg1839324

You can use also I2C display for this project. Arduino has I2C (SCL, SDA). In this case you can connect display to these pins and in the program you have to modify LCD to I2C version. It uses LiquidCrystal library. So simple modification should work.

EDIT: cattledog was little bit faster. :slight_smile:
I think, fmalpartida's library for LCD is pretty good and complex. I am recommending this.

Thanks! :slight_smile: :slight_smile: The Library had already seen something and how to change
But specifically I would know exactly which pins connect to bradbord and which to discard (like the link that I post) and where connect them.

Discard DB4-7, RW, E, RS and you have to connect SCL from LCD to SCL on Arduino and SDA to SDA.

Thank you all! :slight_smile: :slight_smile: :slight_smile: It seems to work! :slight_smile: