MM74C922N datasheet at http://www.ti.com/lit/ds/symlink/mm54c923.pdf
PCF8574 datasheet at http://www.nxp.com/documents/data_sheet/PCF8574.pdf

Use this library freely.

Hardware connections

#####Keypad to Arduino :

• J1-1 -> D2 or D3
• J1-2 -> +5V
• J1-3 -> A4
• J1-4 -> A5
• J1-5 -> Ground

#####Expansion I2C port :

• J2-1 -> Ground
• J2-2 -> SCL
• J2-3 -> SDA
• J2-4 -> +5V

Installation

To use the Keypad_I2C library:

• Go to https://github.com/F4GOJ/Keypad_I2C, click the Download ZIP button and save the ZIP file to a convenient location on your PC.
• Uncompress the downloaded file. This will result in a folder containing all the files for the library, that has a name that includes the branch name, usually Keypad_I2C-master.
• Rename the folder to Keypad_I2C.
• Copy the renamed folder to the Arduino sketchbook\libraries folder.

Usage notes

You have to instantiate a my_keypad_name object.

Keypad_I2C my_keypad_name(int i2c_addr, int int_pin);

#####Parameters i2c_addr : I2C address of the interface (int)
int_pin : Input pin 2 or 3 to attach the interrupt (int)

#include <Keypad_I2c.h>    //http://github.com/F4GOJ/Keypad_I2C

Keypad_I2C KPD(0x26, 2);

Functions :

###begin() #####Description Initialize and attach interrupt to the input pin, begins the wire connection. #####SyntaxKPD.begin(); #####Parameters None. #####Returns None. #####Example

void setup(){
 KPD.begin();
}

###getKey() #####Description Get key pressed. #####Syntax KPD.getKey(); #####Parameters None. #####Returns The code of the key pressed or 0 if no new key has been pressed. (char) #####Example

ch = KPD.getKey();
if(ch != 0){
 Serial.print(ch);
}

###getKeyNum() #####Description Get only numerical key pressed. #####Syntax KPD.getKeyNum(); #####Parameters None. #####Returns The code of the numerical key pressed or 0 if no new key has been pressed. (char) #####Example

ch = KPD.getKeyNum();
if(ch != 0){
 Serial.print(ch);
}