This is a 4x5 matrix sixteen key membrane switch keypad that is simple to use and will look nice in your project. It has four more keys than a 4*4 standard keypad, allowing you to add more features to your project. It has 9 outputs, which you should use. the “Scan Mode” to See which button has been pressed down. It supports Arduino, AVR, PIC, STM, Raspberry Pi

Connecting the Keypad With Arduino:

First, you will need to download the Library and add it to Arduino IDE: for I2C LCD Click Here

       for KeyPad Library Click Here

Navigate to Sketch > Include Library > Add.ZIP Library in the Arduino IDE. Select the option to "Add. ZIP Library" at the top of the drop-down list.

You will be prompted to choose the library to which you want to add it. Open the.zip file by navigating to its location.

Upload the Code:

#include "Wire.h"
#include "LiquidCrystal_I2C.h"
#include "Keypad.h"
LiquidCrystal_I2C lcd (0x27,20,4); // LCD2004
const byte numRows= 5; //number of rows on the keypad
const byte numCols= 4; //number of columns on the keypad
//keymap defines the key pressed according to the row and columns just as appears on the keypad
char keymap[numRows][numCols]=
{
 {'A','B','#','*'},
 {'1','2','3','U'},
 {'4','5','6','D'},
 {'7','8','9','C'},
 {'L','0','R','E'}
};
byte rowPins[numRows] = {10,9,8,7,6};
byte colPins[numCols]= {2,3,4,5};
//initializes an instance of the Keypad class
Keypad myKeypad= Keypad(makeKeymap(keymap), rowPins, colPins, numRows, numCols);
String numstr = "";
void setup()
{
 lcd.init(); // initialize the lcd
 lcd.backlight();
 lcd.print("start LCD2004");
 delay(1000);
 lcd.clear();
}
void loop()
{
 lcd.setCursor(0,0);
 lcd.print("S187:4x5 20 Keypad");
 char keypressed = myKeypad.getKey();
 if (keypressed != NO_KEY)
 {
 // Serial.print(keypressed);
 lcd.setCursor(0,1);
 lcd.print("keypressed=" + (String)keypressed + " ");
 switch (keypressed)
 {
 case '1':
 numstr = "1 ";
 break;
 case '2':
 numstr = "2 ";
 break;
 case '3':
 numstr = "3 ";
 break;
 case '4':
 numstr = "4 ";
 break;
 case '5':
 numstr = "5 ";
 break;
 case '6':
 numstr = "6 ";
 break;
 case '7':
 numstr = "7 ";
 break;
 case '8':
 numstr = "9 ";
 break;
 case '0':
 numstr = "0 ";
 break;
 case 'A':
 numstr = "F1 ";
 break;
 case 'B':
 numstr = "F2 ";
 break;
 case 'C':
 numstr = "ESC ";
 break;
 case 'E':
 numstr = "ENTER";
 break;
 case 'D':
 numstr = "DOWN ";
 break;
 case 'U':
 numstr = "UP ";
 break;
 case 'R':
 numstr = "RIGHT ";
 break;
 case 'L':
 numstr = "LEFT ";
 break;
 case '*':
 numstr = "* ";
 break;
 case '#':
 numstr = "# ";
 break;
 default:
 break;
 }
 if(numstr !="")
 {
 lcd.setCursor(0,2);
 lcd.print("numstr=" + (String)numstr + " ");
 }
 }
}