next topic »

[on:]

UPDATE: This page on the http://ArduinoInfo.Info WIKI has library information and example code for 3 versions of I2C Backboards:
http://arduino-info.wikispaces.com/LCD-Blue-I2C

This covers display adapter backboards marked:
"YwRobot Arduino LCM1602 IIC V1"
"Arduino-IIC-LCD GY-LCD-V1"
"LCM1602 IIC A0 A1 A2"

That last one was new to me. It's Yet Another variation on the little I2C backpack boards for 16x2 and 20x4 LCD displays.

This one has address 0x20  (The A0, A1, A2 pins are grounded by solder bridges). Here's a Photo:


BUT the internal wiring from the PCF8574T is different and must be handled in Setup.  

Software/Library setup was nicely written up by Gordon Shumway in another post, so I'll steal it here:

Step 1:  Remove all LCD libraries from your Arduino IDE.  Check both the user specific ones, as well as in the Arduino install folder.  Zip them up and save them somewhere else if you think you might need them again, otherwise, delete.

Step 2:  Install the new and improved LCD library by F Malpartida from here:  https://bitbucket.org/fmalpartida/new-liquidcrystal/wiki/Home  This person has done some awesome work for the Arduino community.

And here's the code that works, with the connections fixed in the #defines for the I2C chip to Display connections. Phew!

Code:

/* YourDuino.com Example Software Sketch
 20 character 4 line I2C Display
 ANOTHER NEW TYPE Marked "LCM1602 IIC  A0 A1 A2"
 A0-A1-A2 are grounded so I2C Address is 0x20  
 terry@yourduino.com */
/*-----( Import needed libraries )-----*/
#include <Wire.h>
#include <LCD.h>
#include <LiquidCrystal_I2C.h>  // F Malpartida's NewLiquidCrystal library
//Download: https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads
// Move original LiquidCrystal library elsewhere, copy this in it's place

/*-----( Declare Constants )-----*/
#define I2C_ADDR    0x20  // Define I2C Address for the PCF8574T
//---(Following are the PCF8574 pin assignments to LCD connections )----
// This are different than earlier/different I2C LCD displays
#define BACKLIGHT_PIN  3
#define En_pin  2
#define Rw_pin  1
#define Rs_pin  0
#define D4_pin  4
#define D5_pin  5
#define D6_pin  6
#define D7_pin  7

#define  LED_OFF  1
#define  LED_ON  0

/*-----( Declare objects )-----*/  
LiquidCrystal_I2C  lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin);

void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  lcd.begin (20,4);  // initialize the lcd
// Switch on the backlight
  lcd.setBacklightPin(BACKLIGHT_PIN,POSITIVE);
  lcd.setBacklight(LED_ON);
}// END Setup

void loop()   /*----( LOOP: RUNS OVER AND OVER AGAIN )----*/
{

// Reset the display  
  lcd.clear();
  delay(1000);
  lcd.home();
  
// Print our characters on the LCD
  lcd.backlight();  //Backlight ON if under program control
  lcd.setCursor(3,0); //Start at character 3 on line 0
  lcd.print("Hello, world!");
  delay(1000);
  lcd.setCursor(2,1);
  lcd.print("From YourDuino");
  delay(1000);  
  lcd.setCursor(0,2);
  lcd.print("20 by 4 Line Display");
  lcd.setCursor(0,3);
  delay(2000);  
  lcd.print("http://YourDuino.com");
  delay(8000);
} // END Loop

Thanks to  F Malpartida for saving us all a LOT of work, and to Nick Gammon for his I2C scanner!

[Reply #1 on:]

Terry,
Where is that example/sample code from?
(I'd really like to get it updated)

While setBacklight() works for this device, I would discourage it's use to turn on/off the backlight
as it is used to set an intensity not just for on/off control.
On devices such as this that do not support backlight
dimming, any non zero value will turn the backlight full on, but on devices that support
dimming like when 4bit mode is used, setting the backlight intensity to 1 will be very dim.
If backlight on/off control is desired, then backlight() noBacklight() calls would be the
preferred method as those will work on any device that has backlight control and will
result in full on or full off.

fm's latest library allows setting the backlight bit and polarity in the constructor
as well as turns on the backlight in begin() for all device interfaces.
This can simplify the setup code in the sketch so that it can be the same regardless of the interface
(i2c, SR, 4bit, etc...)
All you have to do is setup the full constructor, then, the begin()
handles everything else regardless of the underlying interface to the LCD.
This allows the actual setup() sketch code to be consistent and the same for all interfaces.
i.e. if you change from i2c to 4bit, all that changes is the constructor.
The sketch code does not have to change.


So for example:

Code:

/*-----( Declare Constants )-----*/
#define I2C_ADDR    0x20  // Define I2C Address for the PCF8574T
//---(Following are the PCF8574 pin assignments to LCD connections )----
// This are different than earlier/different I2C LCD displays
#define BACKLIGHT_PIN  3
#define BACKLIGHT_POL POSITIVE // POSITIVE or NEGATIVE depending board design
#define En_pin  2
#define Rw_pin  1
#define Rs_pin  0
#define D4_pin  4
#define D5_pin  5
#define D6_pin  6
#define D7_pin  7

/*-----( Declare objects )-----*/ 
LiquidCrystal_I2C  lcd(I2C_ADDR,En_pin,Rw_pin,Rs_pin,D4_pin,D5_pin,D6_pin,D7_pin, BACKLIGHT_PIN, BACKLIGHT_POL);

void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  lcd.begin (20,4);  // initialize the lcd, also turns on backlight
}// END Setup

--- bill