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####Welcome to the arduino_keypads wiki!

The arduino_keypads libraries add I2C I/O to the Keypad library by using parallel port expander ICs. Different ICs require subtly different versions of the I2C access functions to remain compatible with the Keypad base library. Consequently, several versions of the library have been implemented. The user should just select the one library that supports the IC that is included in the system being developed.

Different devices have more or less elaborate I2C access functions, and thus require different numbers of bytes of code space..as the following table indicates.

####Memory use comparisons for Keypad libraries with I2C I/O

May 29, 2014 - G. D. (Joe) Young [email protected]

Using the HelloKeypad example sketches as being essentially empty of useful code except for bringing in the Keypad libraries, the following code sizes are reported by the arduino 1.05 compilation:

---

|              | HelloKeypad     |                       |
|  library     |     size        | I2C devices supported |
|  :------:    | :-----------:   | :-------------------  |
|Keypad alone  |  4046 bytes     |  none                 |
|Keypad_I2C    |  6530           |PCF8754, PCF8575, PCF8575C(needs pullups)
|Keypad_I2Ca   |  6842           |PCA9554, PCA9555, PCA9534, PCA9539, TCA6408,
|              |                 |TCA6416, others in family (may need pullups)
|Keypad_MCP    |  6626           |MCP23008 (pullups needed)
|Keypad_MC16   |  6774           |MCP23016 (pullups needed)
|Keypad_MC17   |  6858           |MCP23017

---

Adding the I2C I/O adds approx. 2500..2800 bytes to the code space in addition to that already needed for the keypad support.

###HelloKeypad simple example program using PCF8574 I2C port expander

	#include <Keypad_I2C.h>
	#include <Keypad.h>
	#include <Wire.h>
	#define I2CADDR 0x38
	
	const byte ROWS = 4; //four rows
	const byte COLS = 3; //three columns
	char keys[ROWS][COLS] = {
	  {'1','2','3'},
	  {'4','5','6'},
	  {'7','8','9'},
	  {'*','0','#'}
	};
	
	// Digitran keypad, bit numbers of PCF8574 i/o port
	byte rowPins[ROWS] = {0, 1, 2, 3}; //connect to the row pinouts of the keypad
	byte colPins[COLS] = {4, 5, 6}; //connect to the column pinouts of the keypad

	Keypad_I2C kpd( makeKeymap(keys), rowPins, colPins, ROWS, COLS, I2CADDR, PCF8574 );

	void setup(){
	  Serial.begin(9600);
	  while( !Serial ){ /*wait*/ }
	  Wire.begin( );
	  kpd.begin( );
	  Serial.print( "start with pinState = " );
	  Serial.println( kpd.pinState_set( ), HEX );
	}
	void loop(){
	
	  char key = kpd.getKey();
	  
	  if (key){
	  Serial.println(key);
	  }
	}
	

Notes:

-need to include the `Keypad_I2C.h` and `Wire.h` with `Keypad.h`
-The constructor is the same as for Keypad, but has two extra arguments, the I2C
 address, and the device type
-in setup Wire.begin( ) is added

###Constructor arguments, function reference ####Memory use comparisons for Keypad libraries with I2C I/O