Making a 'Backspace key' using 4x4 keypad and oled

Projects General Guidance
1

Hello everyone!
I'm struggling with making a backspace key with 4x4 keypad and display it to oled.
I set 'A' as a backspace. It works when the number input less then3 but when the number input more than 3, it is not working. ex) 123 is working. but 1234 is not. when I input 1234 and push 'A', it displays 1234 with strange pixels.
I'm not making a delete whole things. I just wanna delete the last input.
Here is my code

//INCLUDE LIBRARIES FOR KEYPAD AND OLED SCREEN
#include <SPI.h>
#include <Wire.h>
#include <Keypad.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Arduino.h>
#include <SoftwareSerial.h>

int xpos = 0; //cursor starting point on OLED
int ypos = 0;
int i = 0;
int orders = 1;
int indexCount = 0;
char order[4] = "";
char temp[3] = "";
char allOrders[20] = "";
int cursorx = 0;
int cursory = 0;

const byte numRows= 4; //number of rows on the keypad
const byte numCols= 4; //number of columns on the keypad

char hexaKeys[numRows][numCols]=
{
{'1', '2', '3', 'A'},
{'4', '5', '6', 'B'},
{'7', '8', '9', 'C'},
{'*', '0', '#', 'D'}
};
//DIGITAL PIN LOCATIONS
byte rowPins[numRows] = {5,4,3,2}; //Rows 0 to 4
byte colPins[numCols]= {9,8,7,6}; //Columns 0 to 4

//initializes an instance of the Keypad class
Keypad myKeypad= Keypad(makeKeymap(hexaKeys), rowPins, colPins, numRows, numCols);

const byte address[6] = "00001";
//WIDTH AND HEIGHT OF SCREEN IN PIXELS
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
//declaring SSD1306 object connected to I2C
Adafruit_SSD1306 oled(SCREEN_WIDTH,SCREEN_HEIGHT, &Wire, -1);

void setup() {
  // put your setup code here, to run once:
  oled.begin(SSD1306_SWITCHCAPVCC, 0x3C);
  Serial.begin(9600); //starts serial window for check/error messages
  delay(2000);
  oled.clearDisplay();
  
  oled.setTextSize(2.5);
  oled.setTextColor(WHITE);
  oled.setCursor(0,10);
  oled.println("Welcome to the Deli!"); //Set starting screen to Welcome to Deli!
  oled.display();
}
void loop() {
char customKey = myKeypad.getKey();
  if(customKey){
    if(customKey == 'A'){             // 'A' is the backspace key
      oled.clearDisplay();            // clear the display for the redisplay of text
      oled.setCursor(0,10);           //Set the text position
      oled.display();
      for(int a = 0; a < i; a++){     // Loop to print the char before the backspace
        oled.print(order[a]);
        oled.display();
      }
      i--;                        // Move back one to continue typing
    }
    
    else if(customKey == '*'){    // '*' is the enter key
      if(i != 3){
        Serial.println("Error: Order # Short. ");
        oled.clearDisplay();
        oled.setCursor(0,10);
        oled.print("Error");
        oled.display();
        delay(1500);
        oled.clearDisplay();
        oled.setCursor(0,10);
        oled.print("Retry");
        oled.display();
        i = 0;
      }

      else{
        if(order[1] == 'D' && order[2] == 'D' && order[3] == 'D'){
          
          cursorx = 0;
          cursory = 0;
        }
        else{
          Serial.println();
          Serial.println("Order: ");
          if (indexCount > 18){
             indexCount = 0;
            }
          else{
              allOrders[indexCount] = order[0];
              indexCount++;
              allOrders[indexCount] = order[1];
              indexCount++;
              allOrders[indexCount] = order[2];
              indexCount++;
            }
            for(int c = 1; c < 19; c++){
            Serial.print(allOrders[c]);   // Serial Monitor Test
            if (cursorx >= 63 && cursory == 0){
              cursory = 9;
              cursorx = 0;
              }
            if (cursorx % 21 == 19){
              cursorx += 3;
              Serial.print(" ");
            }
           
            cursorx += 6;
          }
        }
      
      oled.clearDisplay();
      oled.setCursor(0,10);
      oled.print("Order");
      oled.display();
      Serial.println("Order");
      i = 0; 
          }
      }      
    
    
    else{
        if(i == 0){
            *order = '\0';
            oled.clearDisplay(); //To clear the display
            oled.setCursor(0,10); //Set the text position
            oled.print(customKey); //To show the text here
            oled.display(); //To display the text
            Serial.print(customKey);
            i++;
            order[i] = customKey;
            }
            
        else{
          oled.print(customKey); //To show the text here
          oled.display(); //To display the text
          Serial.print(customKey);
          i++;
          order[i] = customKey;
          }
      
      }
    }
}
2

You aren't trying to put 5 characters in there, are you? Like, "xxxxA"?
Also you do realize, the terminating null in a string uses one extra character? So the storage for "hello" is {'h', 'e', 'l', 'l', 'o', \0 } ? Six not five chars.

3

I don't understand.
I'm a beginner.
I'm trying to make is when you input more than 3 numbers and push "*" button it said error.
For the backspace key, I want to make it when I input more than 3 digits, just delete last one and input again.

4

Is it your code? I already read and absorbed your problem description. It's a fairly complicated program, so the discussion will probably be that way too.

My questions, I was hoping it would move you to go back and look at how you made the arrays I mentioned. Reason is, you said it happens on the last digit, that is a red flag of a possible array reference out of bounds.

5

Change the array declaration to the following as @anon57585045 has suggested and check that the Backspace Key works as you have expected (tested).

char order[5] = "";

6

Now I got it thanks

7

It works.
And I understand what you guys talking about.

8

It would be attractive if you can implement the Backspace Key with a blinking cursor.

1 Like
9

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