View source for Use a LCD i2c with attiny84


Using an ATtiny84 to drive an i2c LCD screen.

==Target Hardware==
* ATtiny84 MCU 
* LCD display with i2c adaptor board.

==Libraries installation==

Three libraries are required.
* The tiny core. https://code.google.com/p/arduino-tiny/
* TinyWireM. This one is different from the official one has it support ATtiny84.  http://www.scenelight.nl/?wpfb_dl=22
* LiquidCrystal.  https://bitbucket.org/fmalpartida/new-liquidcrystal/downloads/LiquidCrystal_V1.2.1.zip


==Libraries Modifications==

===Tiny Core===

The tiny core will need to see the new.cpp and new.h from the arduino core. An easy way get this working is to copy files. 
On Linux platform this will be something like

 cp /usr/share/arduino/hardware/arduino/cores/arduino/new.* /home/user/sketchbook/hardware/tiny/cores/tiny/

Note. If using arduino IDE version 1.5 and above you will need to copy the new.h and new.cpp from an older version of the IDE. These are given here. [http://lechacal.com/stepper_pilot/new.cpp new.cpp]  [http://lechacal.com/stepper_pilot/new.h new.h]

===TinyWireM===

Open file '''TinyWire.h'''. 

On line 57 replace<br>
 void send(uint8_t); 
 by 
 '''void write(uint8_t);''' 

On line 60 replace<br>
 void receive(uint8_t); 
 by 
 '''void read(uint8_t);''' 


Open file '''TinyWire.cpp'''

On line 49 replace<br>

 void USI_TWI::send(uint8_t data){ // buffers up data to send 
 by 
 '''void USI_TWI::write(uint8_t data){ // buffers up data to send''' 

On line 76 replace<br>

 if (xferOK) return 0; 
 by 
 '''if (xferOK) return 1;''' 

On line 83 replace<br>

 uint8_t USI_TWI::receive(){ // returns the bytes received one at a time 
 by 
 '''uint8_t USI_TWI::read(){ // returns the bytes received one at a time''' 

Open file '''USI_TWI_Master.cpp'''

On line 23 replace<br>
 #define F_CPU 1000000UL          // Sets up the default speed for delay.h 
 by 
 '''#define F_CPU 8000000UL          // Sets up the default speed for delay.h''' 


Open file '''USI_TWI_Master.h'''

On line 23 replace<br>
 #define SYS_CLK   1000.0  // [kHz]    Default for ATtiny2313 
 by 
 '''#define SYS_CLK   8000.0  // [kHz]    Default for ATtiny2313'''

===LiquidCrystal===

Open file '''I2CIO.cpp'''

After line 34 insert the code below:

 #if defined(__AVR_ATtiny84__) || (__AVR_ATtiny2313__)
 #include "TinyWireM.h"      // include this if ATtiny85 or ATtiny2313
 #define Wire TinyWireM
 #else
 #include <Wire.h>           // original lib include
 #endif

Then delete the line that says:

 #include <../Wire/Wire.h>

==Basic sketch example==

 #include <TinyWireM.h>          
 #include <LiquidCrystal_I2C.h> 
 
 LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  
 
 
 void setup()    
 {
 
 lcd.begin(16,2);   
 
 //3 flash introduction
   for(int i = 0; i< 3; i++)
   {
     lcd.backlight();
     delay(150);
     lcd.noBacklight();
     delay(150);
   }
   lcd.backlight(); 
 
   lcd.setCursor(2,0);
   lcd.print(">lechacal.com<");
   lcd.setCursor(6,1);
   lcd.print("...");
   
 }
 
 void loop()  
 { 
 }

==Related Links==

This article has mainly been inspired by this article here for the ATtiny85.
http://meta-blog.eklablog.com/attiny85-lcd-en-i2c-p977350