Input text into your arduino code using 5 key keyboard`

// Mario's Ideas
// Text input using OLED display an 5 Key Keyboard

#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// Oled display size
#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels

//Potentiometer PIN A1
  int Keyboard=A7;

// Variables capturing current and newly calculated position on the letter board (9x3 - 27 postions)
  int New_X=0;
  int Old_X=0;
  int New_Y=0;
  int Old_Y=0;
  
// Variable capturing output from Keyboard pin (Values 0 1023)
  int Key_read=0;
  int Prev_Key_read=1023;
  boolean Key_pressed=false; 

// String variable holding the text to transmit
  String To_Transmit="";

// Length of the text to transmit
  int To_Transmit_Length=0;


// Declaration for an SSD1306 display connected to I2C (SDA, SCL pins)
  #define OLED_RESET     4 // Reset pin # (or -1 if sharing Arduino reset pin)
  Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);


// Used for displaying Leter board
char Letters[3][9]={"ABCDEFGHI",
                    "JKLMNOPQR",
                    "STUVWXYZ_"};




void setup() {
  Serial.begin(9600);
  
  // SSD1306_SWITCHCAPVCC = generate display voltage from 3.3V internally
  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // Address 0x3D for 128x64
    Serial.println(F("SSD1306 allocation failed"));
    for(;;); // Don't proceed, loop forever
  }

  // Show initial display buffer contents on the screen --
  // the library initializes this with an Adafruit splash screen.
  display.display();
  delay(2000); // Pause for 2 seconds
  
  // Clear the buffer
  display.clearDisplay();
  display.display();
  
  // Display filled in rect in the top section of the display when To_Transfer would be output
  display.fillRect(0, 0, 128, 15, SSD1306_INVERSE);
  display.drawRect(110, 2, 16, 12, SSD1306_BLACK);
  display.setTextSize(1);            
  display.setTextColor(SSD1306_BLACK);  
  display.setCursor(113,4); 
  display.println("OK");
  display.display();
  // Display Letter Board 3 rows 9 character in each row 
  display.setTextSize(2);            
  display.setTextColor(SSD1306_WHITE);       
  for (int j=0; j<3;j++){
    for (int i=0; i<9;i++){
       display.setCursor(i*12+2*i+1,j*16+17);           
       display.println(Letters[j][i]);
       delay(10);
     display.display();
    }
  }

  // Highlight character A by displaying Inverse rect at first position
  display.fillRect(0, 16, 12, 16, SSD1306_INVERSE);
  display.display();
  
}

void Highlight_letter(int X, int X_Old, int Y, int Y_Old){
  // When position changes 
  // Draw the inverse rect in the Old_pos to deactivate  the highlight in the old spot
  // Draw the inverse rect to Highlite the new spot

  // Displaying Inverse rect in a new position to highlight
  display.fillRect(X*12+2*X, Y*16 +16, 12, 16, SSD1306_INVERSE);
  
  // Displaying Inverse rect in the old positon to unhighlight
  display.fillRect(X_Old*12+2*X_Old, Y_Old*16 +16, 12, 16, SSD1306_INVERSE);
  
  display.display();
}


void loop() {
  Key_read =analogRead(Keyboard);
  if (Prev_Key_read>1000 and Key_read<1000){
    Key_pressed=true;
    if (Key_read<10 and Old_X>0) New_X=Old_X-1; 
    if (Key_read>160 and Key_read<170 and Old_X<9) New_X=Old_X+1;
    if (Key_read>25 and Key_read<35 and Old_Y>-1) New_Y=Old_Y-1;
    if (Key_read>80 and Key_read<90 and  Old_Y<2 ) New_Y=Old_Y+1;
    if (Key_read>350 and Key_read<360) {
     if (New_Y!=-1){
       To_Transmit=To_Transmit + Letters[New_Y][New_X];
       To_Transmit_Length++;
       display.setTextSize(1);
       display.setCursor(3,1);
       display.setTextColor(BLACK     );
       display.fillRect(0, 0, 100, 15, SSD1306_WHITE);
       display.println(To_Transmit);
       display.display();
     }
     else{
      for (int i=1;i<9;i++) {
        display.fillRect(0, 0, 128, 15, SSD1306_INVERSE);
        delay(300);
        display.display();
      }
     }
    }     

    if (New_Y==-1 and Old_Y==0){
        display.fillRect(110, 2, 16, 12, SSD1306_INVERSE); 
        display.fillRect(Old_X*12+2*Old_X, Old_Y*16 +16, 12, 16, SSD1306_INVERSE); 
    }
    if (New_Y==0 and Old_Y==-1){
        display.fillRect(110, 2, 16, 12, SSD1306_INVERSE); 
        display.fillRect(New_X*12+2*New_X, New_Y*16 +16, 12, 16, SSD1306_INVERSE);
        Prev_Key_read=Key_read;
        Old_X=New_X;
        Old_Y=New_Y;;
    }
    if ((Old_X!=New_X or Old_Y!=New_Y) and Old_Y!=-1 ){
        if (New_Y!=-1 )Highlight_letter (New_X,Old_X,New_Y,Old_Y);
        Old_X=New_X;
        Old_Y=New_Y;
    }
  }
  
  display.display();
  Prev_Key_read=Key_read; 
      
}