I am using a "LiquidCrystal_I2C" library for a 1602 LCD display in combination with a PCF8574T "backpack" adapter. This on an Attiny85 (Spence Konde AttinyCore 2.0.0) and this works just fine,....but.
The library requires to create an object, before the main function of my code starts. This object holds the I2C address of the display adapter. These adapters however come with a variety of I2C addresses (0x27, 0x3f, ....) and have solderbridges to change the address.
Section of my code where the object is created, just before the main function starts:
#include <LiquidCrystal_I2C.h> //
#define GPIO_ADDR 0x3f // (PCA8574A A0-A2 @5V) typ. A0-A3 Gnd 0x20 / 0x38 for A - 0x27 is the address of the Digispark LCD modules.
LiquidCrystal_I2C lcd(GPIO_ADDR, 16, 2); // set address & 16 chars / 2 lines
int main(void) {
// local variables:
...............
To make it more plug-and-play, I would like to first add a I2C scanner routine in my code, to detect the address and then use that for the starting of the display. But since the creation of the object happens, before my code starts, I am in a catch-22 situation.
The library I use:
(LiquidCrystal_I2C.h)
#ifndef LiquidCrystal_I2C_h
#define LiquidCrystal_I2C_h
#include <inttypes.h>
#include "Print.h"
#include <Wire.h> // original lib include
// commands
#define LCD_CLEARDISPLAY 0x01
#define LCD_RETURNHOME 0x02
#define LCD_ENTRYMODESET 0x04
#define LCD_DISPLAYCONTROL 0x08
#define LCD_CURSORSHIFT 0x10
#define LCD_FUNCTIONSET 0x20
#define LCD_SETCGRAMADDR 0x40
#define LCD_SETDDRAMADDR 0x80
// flags for display entry mode
#define LCD_ENTRYRIGHT 0x00
#define LCD_ENTRYLEFT 0x02
#define LCD_ENTRYSHIFTINCREMENT 0x01
#define LCD_ENTRYSHIFTDECREMENT 0x00
// flags for display on/off control
#define LCD_DISPLAYON 0x04
#define LCD_DISPLAYOFF 0x00
#define LCD_CURSORON 0x02
#define LCD_CURSOROFF 0x00
#define LCD_BLINKON 0x01
#define LCD_BLINKOFF 0x00
// flags for display/cursor shift
#define LCD_DISPLAYMOVE 0x08
#define LCD_CURSORMOVE 0x00
#define LCD_MOVERIGHT 0x04
#define LCD_MOVELEFT 0x00
// flags for function set
#define LCD_8BITMODE 0x10
#define LCD_4BITMODE 0x00
#define LCD_2LINE 0x08
#define LCD_1LINE 0x00
#define LCD_5x10DOTS 0x04
#define LCD_5x8DOTS 0x00
// flags for backlight control
#define LCD_BACKLIGHT 0x08
#define LCD_NOBACKLIGHT 0x00
#define En B00000100 // Enable bit
#define Rw B00000010 // Read/Write bit
#define Rs B00000001 // Register select bit
class LiquidCrystal_I2C : public Print {
public:
LiquidCrystal_I2C(uint8_t lcd_Addr,uint8_t lcd_cols,uint8_t lcd_rows);
void begin(uint8_t cols, uint8_t rows, uint8_t charsize = LCD_5x8DOTS );
void clear();
void home();
void noDisplay();
void display();
void noBlink();
void blink();
void noCursor();
void cursor();
void scrollDisplayLeft();
void scrollDisplayRight();
void printLeft();
void printRight();
void leftToRight();
void rightToLeft();
void shiftIncrement();
void shiftDecrement();
void noBacklight();
void backlight();
void autoscroll();
void noAutoscroll();
void createChar(uint8_t, uint8_t[]);
void setCursor(uint8_t, uint8_t);
#if defined(ARDUINO) && ARDUINO >= 100
virtual size_t write(uint8_t);
#else
virtual void write(uint8_t);
#endif
void command(uint8_t);
void init();
////compatibility API function aliases
void blink_on(); // alias for blink()
void blink_off(); // alias for noBlink()
void cursor_on(); // alias for cursor()
void cursor_off(); // alias for noCursor()
void setBacklight(uint8_t new_val); // alias for backlight() and nobacklight()
void load_custom_character(uint8_t char_num, uint8_t *rows); // alias for createChar()
void printstr(const char[]);
////Unsupported API functions (not implemented in this library)
uint8_t status();
void setContrast(uint8_t new_val);
uint8_t keypad();
void setDelay(int,int);
void on();
void off();
uint8_t init_bargraph(uint8_t graphtype);
void draw_horizontal_graph(uint8_t row, uint8_t column, uint8_t len, uint8_t pixel_col_end);
void draw_vertical_graph(uint8_t row, uint8_t column, uint8_t len, uint8_t pixel_col_end);
private:
void init_priv();
void send(uint8_t, uint8_t);
void write4bits(uint8_t);
void expanderWrite(uint8_t);
void pulseEnable(uint8_t);
uint8_t _Addr;
uint8_t _displayfunction;
uint8_t _displaycontrol;
uint8_t _displaymode;
uint8_t _numlines;
uint8_t _cols;
uint8_t _rows;
uint8_t _backlightval;
};
#endif
(LiquidCrystal_I2C.cpp)
// LiquidCrystal_I2C V2.0
#include "LiquidCrystal_I2C.h"
#include <inttypes.h>
#include <Wire.h> // original lib include
#include "Arduino.h"
// When the display powers up, it is configured as follows:
//
// 1. Display clear
// 2. Function set:
// DL = 1; 8-bit interface data
// N = 0; 1-line display
// F = 0; 5x8 dot character font
// 3. Display on/off control:
// D = 0; Display off
// C = 0; Cursor off
// B = 0; Blinking off
// 4. Entry mode set:
// I/D = 1; Increment by 1
// S = 0; No shift
//
// Note, however, that resetting the Arduino doesn't reset the LCD, so we
// can't assume that its in that state when a sketch starts (and the
// LiquidCrystal constructor is called).
LiquidCrystal_I2C::LiquidCrystal_I2C(uint8_t lcd_Addr,uint8_t lcd_cols,uint8_t lcd_rows)
{
_Addr = lcd_Addr;
_cols = lcd_cols;
_rows = lcd_rows;
_backlightval = LCD_NOBACKLIGHT;
}
void LiquidCrystal_I2C::init(){
init_priv();
}
void LiquidCrystal_I2C::init_priv()
{
Wire.begin();
_displayfunction = LCD_4BITMODE | LCD_1LINE | LCD_5x8DOTS;
begin(_cols, _rows);
}
void LiquidCrystal_I2C::begin(uint8_t cols, uint8_t lines, uint8_t dotsize) {
if (lines > 1) {
_displayfunction |= LCD_2LINE;
}
_numlines = lines;
// for some 1 line displays you can select a 10 pixel high font
if ((dotsize != 0) && (lines == 1)) {
_displayfunction |= LCD_5x10DOTS;
}
// SEE PAGE 45/46 FOR INITIALIZATION SPECIFICATION!
// according to datasheet, we need at least 40ms after power rises above 2.7V
// before sending commands. Arduino can turn on way befer 4.5V so we'll wait 50
delay(50);
// Now we pull both RS and R/W low to begin commands
expanderWrite(_backlightval); // reset expanderand turn backlight off (Bit 8 =1)
delay(1000);
//put the LCD into 4 bit mode
// this is according to the hitachi HD44780 datasheet
// figure 24, pg 46
// we start in 8bit mode, try to set 4 bit mode
write4bits(0x03 << 4);
delayMicroseconds(4500); // wait min 4.1ms
// second try
write4bits(0x03 << 4);
delayMicroseconds(4500); // wait min 4.1ms
// third go!
write4bits(0x03 << 4);
delayMicroseconds(150);
// finally, set to 4-bit interface
write4bits(0x02 << 4);
// set # lines, font size, etc.
command(LCD_FUNCTIONSET | _displayfunction);
// turn the display on with no cursor or blinking default
_displaycontrol = LCD_DISPLAYON | LCD_CURSOROFF | LCD_BLINKOFF;
display();
// clear it off
clear();
// Initialize to default text direction (for roman languages)
_displaymode = LCD_ENTRYLEFT | LCD_ENTRYSHIFTDECREMENT;
// set the entry mode
command(LCD_ENTRYMODESET | _displaymode);
home();
}
/********** high level commands, for the user! */
void LiquidCrystal_I2C::clear(){
command(LCD_CLEARDISPLAY);// clear display, set cursor position to zero
delayMicroseconds(2000); // this command takes a long time!
}
void LiquidCrystal_I2C::home(){
command(LCD_RETURNHOME); // set cursor position to zero
delayMicroseconds(2000); // this command takes a long time!
}
void LiquidCrystal_I2C::setCursor(uint8_t col, uint8_t row){
int row_offsets[] = { 0x00, 0x40, 0x14, 0x54 };
if ( row > _numlines ) {
row = _numlines-1; // we count rows starting w/0
}
command(LCD_SETDDRAMADDR | (col + row_offsets[row]));
}
// Turn the display on/off (quickly)
void LiquidCrystal_I2C::noDisplay() {
_displaycontrol &= ~LCD_DISPLAYON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
void LiquidCrystal_I2C::display() {
_displaycontrol |= LCD_DISPLAYON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
// Turns the underline cursor on/off
void LiquidCrystal_I2C::noCursor() {
_displaycontrol &= ~LCD_CURSORON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
void LiquidCrystal_I2C::cursor() {
_displaycontrol |= LCD_CURSORON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
// Turn on and off the blinking cursor
void LiquidCrystal_I2C::noBlink() {
_displaycontrol &= ~LCD_BLINKON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
void LiquidCrystal_I2C::blink() {
_displaycontrol |= LCD_BLINKON;
command(LCD_DISPLAYCONTROL | _displaycontrol);
}
// These commands scroll the display without changing the RAM
void LiquidCrystal_I2C::scrollDisplayLeft(void) {
command(LCD_CURSORSHIFT | LCD_DISPLAYMOVE | LCD_MOVELEFT);
}
void LiquidCrystal_I2C::scrollDisplayRight(void) {
command(LCD_CURSORSHIFT | LCD_DISPLAYMOVE | LCD_MOVERIGHT);
}
// This is for text that flows Left to Right
void LiquidCrystal_I2C::leftToRight(void) {
_displaymode |= LCD_ENTRYLEFT;
command(LCD_ENTRYMODESET | _displaymode);
}
// This is for text that flows Right to Left
void LiquidCrystal_I2C::rightToLeft(void) {
_displaymode &= ~LCD_ENTRYLEFT;
command(LCD_ENTRYMODESET | _displaymode);
}
// This will 'right justify' text from the cursor
void LiquidCrystal_I2C::autoscroll(void) {
_displaymode |= LCD_ENTRYSHIFTINCREMENT;
command(LCD_ENTRYMODESET | _displaymode);
}
// This will 'left justify' text from the cursor
void LiquidCrystal_I2C::noAutoscroll(void) {
_displaymode &= ~LCD_ENTRYSHIFTINCREMENT;
command(LCD_ENTRYMODESET | _displaymode);
}
// Allows us to fill the first 8 CGRAM locations
// with custom characters
void LiquidCrystal_I2C::createChar(uint8_t location, uint8_t charmap[]) {
location &= 0x7; // we only have 8 locations 0-7
command(LCD_SETCGRAMADDR | (location << 3));
for (int i=0; i<8; i++) {
write(charmap[i]);
}
}
// Turn the (optional) backlight off/on
void LiquidCrystal_I2C::noBacklight(void) {
_backlightval=LCD_NOBACKLIGHT;
expanderWrite(0);
}
void LiquidCrystal_I2C::backlight(void) {
_backlightval=LCD_BACKLIGHT;
expanderWrite(0);
}
/*********** mid level commands, for sending data/cmds */
inline void LiquidCrystal_I2C::command(uint8_t value) {
send(value, 0);
}
inline size_t LiquidCrystal_I2C::write(uint8_t value) {
send(value, Rs);
return 0;
}
/************ low level data pushing commands **********/
// write either command or data
void LiquidCrystal_I2C::send(uint8_t value, uint8_t mode) {
uint8_t highnib=value&0xf0;
uint8_t lownib=(value<<4)&0xf0;
write4bits((highnib)|mode);
write4bits((lownib)|mode);
}
void LiquidCrystal_I2C::write4bits(uint8_t value) {
expanderWrite(value);
pulseEnable(value);
}
void LiquidCrystal_I2C::expanderWrite(uint8_t _data){
Wire.beginTransmission(_Addr);
Wire.write((int)(_data) | _backlightval);
Wire.endTransmission();
}
void LiquidCrystal_I2C::pulseEnable(uint8_t _data){
expanderWrite(_data | En); // En high
delayMicroseconds(1); // enable pulse must be >450ns
expanderWrite(_data & ~En); // En low
delayMicroseconds(50); // commands need > 37us to settle
}
// Alias functions
void LiquidCrystal_I2C::cursor_on(){
cursor();
}
void LiquidCrystal_I2C::cursor_off(){
noCursor();
}
void LiquidCrystal_I2C::blink_on(){
blink();
}
void LiquidCrystal_I2C::blink_off(){
noBlink();
}
void LiquidCrystal_I2C::load_custom_character(uint8_t char_num, uint8_t *rows){
createChar(char_num, rows);
}
void LiquidCrystal_I2C::setBacklight(uint8_t new_val){
if(new_val){
backlight(); // turn backlight on
}else{
noBacklight(); // turn backlight off
}
}
void LiquidCrystal_I2C::printstr(const char c[]){
//This function is not identical to the function used for "real" I2C displays
//it's here so the user sketch doesn't have to be changed
print(c);
}
// unsupported API functions
void LiquidCrystal_I2C::off(){}
void LiquidCrystal_I2C::on(){}
void LiquidCrystal_I2C::setDelay (int cmdDelay,int charDelay) {}
uint8_t LiquidCrystal_I2C::status(){return 0;}
uint8_t LiquidCrystal_I2C::keypad (){return 0;}
uint8_t LiquidCrystal_I2C::init_bargraph(uint8_t graphtype){return 0;}
void LiquidCrystal_I2C::draw_horizontal_graph(uint8_t row, uint8_t column, uint8_t len, uint8_t pixel_col_end){}
void LiquidCrystal_I2C::draw_vertical_graph(uint8_t row, uint8_t column, uint8_t len, uint8_t pixel_row_end){}
void LiquidCrystal_I2C::setContrast(uint8_t new_val){}
Any tips or tricks on how to use or change this library to enable me to either change the LCD display address on the fly, or create the Display object later in my code, after I have scanned for the I2C address?
I was thinking about making a change in the "LiquidCrystal_I2C.h" file and change the private definition of these variables into public, and then change "_Addr" into my scanned I2C address, but do not have enough knowledge about the use of libraries, to determine if that makes sense or has some unforeseen consequences.
private:
void init_priv();
void send(uint8_t, uint8_t);
void write4bits(uint8_t);
void expanderWrite(uint8_t);
void pulseEnable(uint8_t);
uint8_t _Addr;
.............
.