// Example of multiple software I2C buses with shared SCL.
//
// This is a proof of concept.
// The library files had to be changed to hold a pointer to a SoftwareWire object.
// There is no conflict with the Arduino hardware Wire library.
// It is still possible to connect sensors to the hardware I2C bus.
//
// A better version by arcostasi is here:
//   https://wokwi.com/arduino/projects/307853926099583552
//
//
// Very nice big font:
//   https://www.instructables.com/Custom-Large-Font-For-16x2-LCDs/
//


#include <SoftwareWire.h>

// Create three software I2C buses
SoftwareWire wire1( 10, SCL);
SoftwareWire wire2( 9, SCL);
SoftwareWire wire3( 8, SCL);


#include "LiquidCrystal_I2C_soft.h"

// Create an object for each LCD display
LiquidCrystal_I2C lcd1a( &wire1, 0x27, 20, 4);
LiquidCrystal_I2C lcd1b( &wire1, 0x3F, 20, 4);
LiquidCrystal_I2C lcd2a( &wire2, 0x27, 20, 4);
LiquidCrystal_I2C lcd2b( &wire2, 0x3F, 20, 4);
LiquidCrystal_I2C lcd3a( &wire3, 0x27, 20, 4);
LiquidCrystal_I2C lcd3b( &wire3, 0x3F, 20, 4);


void setup()
{
  lcd1a.init();
  lcd1a.backlight();
  lcd1a.setCursor(0,0);
  lcd1a.print("Hello Display 1a");
  lcd1a.setCursor(0,1);
  lcd1a.print("0x27, I2C bus 1");

  lcd1b.init();
  lcd1b.backlight();
  lcd1b.setCursor(0,0);
  lcd1b.print("Hello Display 1b");
  lcd1b.setCursor(0,1);
  lcd1b.print("0x3F, I2C bus 1");

  lcd2a.init();
  lcd2a.backlight();
  lcd2a.setCursor(0,0);
  lcd2a.print("Hello Display 2a");
  lcd2a.setCursor(0,1);
  lcd2a.print("0x27, I2C bus 2");

  lcd2b.init();
  lcd2b.backlight();
  lcd2b.setCursor(0,0);
  lcd2b.print("Hello Display 2b");
  lcd2b.setCursor(0,1);
  lcd2b.print("0x3F, I2C bus 2");

  lcd3a.init();
  lcd3a.backlight();
  lcd3a.setCursor(0,0);
  lcd3a.print("Hello Display 3a");
  lcd3a.setCursor(0,1);
  lcd3a.print("0x27, I2C bus 3");

  lcd3b.init();
  lcd3b.backlight();
  lcd3b.setCursor(0,0);
  lcd3b.print("Hello Display 3b");
  lcd3b.setCursor(0,1);
  lcd3b.print("0x3F, I2C bus 3");
}

void loop() { }

sharedSCL.ino

diagram.json

// LiquidCrystal_I2C library from:
//   https://github.com/johnrickman/LiquidCrystal_I2C
//   Source code adapted for using SoftwareWire


// Based on the work by DFRobot

#include "LiquidCrystal_I2C_soft.h"

inline size_t LiquidCrystal_I2C::write(uint8_t value) {
	send(value, Rs);
	return 1;
}



// 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(SoftwareWire * softwire, uint8_t lcd_Addr,uint8_t lcd_cols,uint8_t lcd_rows)
{
  _Addr = lcd_Addr;
  _cols = lcd_cols;
  _rows = lcd_rows;
  _backlightval = LCD_NOBACKLIGHT;
  _swire = softwire;
}

void LiquidCrystal_I2C::oled_init(){
  _oled = true;
	init_priv();
}

void LiquidCrystal_I2C::init(){
	init_priv();
}

void LiquidCrystal_I2C::init_priv()
{
	_swire->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(100);      // 1000 changed into 100

  	//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!
  if (_oled) setCursor(0,0);
}

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]);
	}
}

//createChar with PROGMEM input
void LiquidCrystal_I2C::createChar(uint8_t location, const char *charmap) {
	location &= 0x7; // we only have 8 locations 0-7
	command(LCD_SETCGRAMADDR | (location << 3));
	for (int i=0; i<8; i++) {
	    	write(pgm_read_byte_near(charmap++));
	}
}

// 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);
}


/************ 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){                                        
	_swire->beginTransmission(_Addr);
	_swire->write((int)(_data) | _backlightval);
	_swire->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
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wunused-parameter"
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){}
#pragma GCC diagnostic pop
	

LiquidCrystal_I2C_soft.cpp

// LiquidCrystal_I2C library from:
//   https://github.com/johnrickman/LiquidCrystal_I2C
//   Source code adapted for using SoftwareWire



//YWROBOT
#ifndef LiquidCrystal_I2C_h
#define LiquidCrystal_I2C_h

#include <Arduino.h>
#include <inttypes.h>
#include "Print.h" 

#include <SoftwareWire.h>


// 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(SoftwareWire * softwire, 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 createChar(uint8_t location, const char *charmap);
  // Example: 	const char bell[8] PROGMEM = {B00100,B01110,B01110,B01110,B11111,B00000,B00100,B00000};
  
  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();
  void oled_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;
  bool _oled = false;
  uint8_t _cols;
  uint8_t _rows;
  uint8_t _backlightval;
  SoftwareWire * _swire;
};

#endif