View source for Lcd through IOexpander

==Goal==
The Goal was to save a lot of pins on the arduino,<br>
I had seen that controlling a LCD through a IOexpander was possible,<br> 
So I thought I'd take the challenge and see if it would work.<br>
And it did, controlling an lcd with only 2 pins!<br>
Now I am gonna share it with the world :)<br>
<br>
And as a plus, When you take the LCD off you've got controlle over 16 IO pins,<br>
To do as you please!<br>

==Hardware==
The Hardware you need:

* 1x Arduino
* 1x MCP23016(or Similar)
* 1x resistor 3K9 Ohm
* 1x resistor 220 ohm 
* 1x pot 5k Ohm
* 1x 33 pF capacitor
* 1x Lcd(In my case 16x2)

==Software==
Arduino Ide

linux or windows or what ever OS you use that supports the Arduino Ide.

(Some programming skill can come in handy)

==Schematic==
[[File:IOlcd schematic.png|border|400px]]

==Explanation==
* R1 is a potentiometer In my case I used a 5K pot meter.
* R2 is 220 ohm (if you lcd doesn't have back lighting you can just forget R2 and the connections to pin 15 and 16.)
* R3 is 3K9 ohm resistor and has to do with how this I/O expander is wired.
* C1 is 33pF and also has to do with how this I/O expander is wired up.
* JP1 3 and 4 go on analog pins 4 and 5 on arduino, and pin 2 on JP1 is voltage +.

Now, if you decide to use a Diffrent type of I/O expander that is pin compatible with this one, you Should look up the value's of R3 and C1.

==Library==
here it is:<br>
https://github.com/Duality4Y/IOlcd<br>
notice: contents of folder IOlcd1_0 contains the source that works with arduino 1.0<br>

there is still a lot to do though, keep that in mind.<br>
only 16x2 is supported yet, other size should be easy to add,<br> 
just don't have the hardware to test so won't even try to code it :)<br>
at the moment these things are available:<br>
<syntaxhighlight lang="c">
* IOlcd lcd;                             // what this does is allow you to run multiple instance's, meening you can controle more lcd's if you want like IOlcd lcd2;
* print();                               // prints any thing you put between the (), put strings in like this "string" and for variables just the name of the variable.
* home();                                // sets cursor first place first line.
* write(data);                           // writes data to lcd example: write(33); would print ! on the lcd.
* setCursor(int x,int y);                // x is columns and y is rows.
* blinkCursor();                         // sets cursor active, blinking square for now.
* noBlinkCursor();                       // sets cursor inactive, no blinking square visible.
* clear();                               // clears the screen.
* createChar();                          // posted an example on how to use it'll clear things up :) remember only place for 8 custom chars..
* scrollDisplayRight();                  // scrolls the contents of the display 1 square to the right every time the function is called.
* scrollDisplayLeft();                   // does the opposite scrolls the contents of the display 1 to the right every time it's called.
* begin(int x, int y);                   // x is the number of columns the display has, and y the number of rows.
* init(address, chip);                   // initializes the IOexpander chipt, address for it's address, and chip for the chip you use 
                                         // mcp23016 mcp23017 mcp23018 are supported but not tested. only mcp23016 is tested, example: init(0x20, MCP23017);
                                         // for now the library only supports 16x2 Liquid Crystal Displays.
</syntaxhighlight>

==Example Sketches==
Can be found in the folder of library Here are a few though:<br>
Hello World:

<syntaxhighlight lang="c">
//include the nesecary header files for this to work.

#include <IOlcd.h>
#include <Wire.h>;

IOlcd lcd;
long count = 1;

void setup(){
  
  lcd.init(0x20, MCP23016);                 //initialize the chip(in this case MCP23016) at address 0x20
  
  lcd.begin(16,2);                          //start the lcd
  
  lcd.home();                               //start at the beginning of the first lcd line.
  
  lcd.print("Hello, World!");               //print hello world to the first line.
}

void loop(){
  
  lcd.setCursor(0,1);                       //set cursor to the second line.
  
  lcd.print(count);                         //number of seconds active, is printed.
  count++;
  delay(1000);
}
</syntaxhighlight>

Serial Display:
<syntaxhighlight lang="c">
/* quick note, more then 16 characters send
the line won't wrap to the line underneath it. */

#include <IOlcd.h>
#include <Wire.h>;

IOlcd lcd;

void setup(){
  
  lcd.init(0x20, MCP23016);                 //initialize the chip(MCP23016) at address 0x20.
  
  lcd.begin(16,2);                          //start the lcd
  
  Serial.begin(9800);                       //start serial connection.
}

void loop(){
  
  if(Serial.available()){                   // check if characters arrive over the serial port.
    
    delay(100);                             //wait a bit.
    
    lcd.clear();                            //clear the screen.
    
    while(Serial.available() > 0){          //read the data.
      
      lcd.write(Serial.read());             //write data to the lcd.
    }
  }
}
</syntaxhighlight>

example on creating custom chars:
<syntaxhighlight lang="c">
#include <IOlcd.h>
#include <Wire.h>

IOlcd lcd;

//here we create an array that contains the actual data that's
//going to display a smiley, you see it even looks like it.
byte smiley[8] = {
  B00000,
  B10001,
  B00000,
  B00000,
  B10001,
  B01110,
  B00000,
};


void setup() {
  //it's important to always first initialize the IO chip.
  lcd.init(0x20, MCP23016);
  //and it's also imporant to create the char before you even 
  //start the lcd.
  lcd.createChar(0, smiley);
  //here we start the lcd like normal
  lcd.begin(16, 2);
  //we set cursor "home", and clearing maybe previous rubish on screen
  lcd.home();
  lcd.clear();
  //we write the costum char. first int in createChar is memory addres.
  //when you write that memory address with lcd.write you'l print it on 
  // the lcd.
  lcd.write(0);
}

void loop() {}

</syntaxhighlight>

==pictures and vids==

[[File:IOlcd screen Cursor.JPG|border|450px]] . [[File:IOlcd board arduino connection.JPG|border|450px]]

<youtube>oBnTo-vmRkU</youtube>