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. new.cpp new.h

TinyWireM

Open file TinyWire.h.

On line 57 replace

void send(uint8_t); 
by 
void write(uint8_t);

On line 60 replace

void receive(uint8_t); 
by 
void read(uint8_t);

Open file TinyWire.cpp

On line 49 replace

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

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

On line 83 replace

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

#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

#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()  
{ 
}