Key de-bouncing in 4x4 matrix Keypad. I need the output to the 2 7-segment LED.

Question

Key de-bouncing in 4x4 matrix Keypad. I need the output to the 2 7-segment LED. It will show last two number. For example if I press 5, it shows 5 on the right. If I keep press 5 again, it will show 5 on the left, 5 on the right. If I press 8, it will show 5 on the left, 8 on the right.

Please add key de-bouncing to my code to make it work.

void read(void) {
char left_val = 'n';
char right_val = 'n';
char next_val = readKeyPad();

while(1){
  
next_val = readKeyPad();

if (right_val == next_val || next_val == 'n'){
printChar(left_val, Left);
delay(FRAME_PERIOD);
printChar(right_val, Right);
delay(FRAME_PERIOD);
}
  
else {
left_val = right_val;
right_val = next_val;
}

}
}

Explanation / Answer

long lastDebounceTime = 0; // the last time the output led was toggled
long debounceDelay = FRAME_PERIOD;    // the debounce time; increase if the output flickers
void read(void)
{
    char left_val = 'n';
    char right_val = 'n';
    char next_val = readKeyPad();

    char last_val = 'n';

    while(1)
    {
    
        next_val = readKeyPad();

        // If the switch changed, due to noise or pressing:
        if (next_val != last_val)
        {
           // reset the debouncing timer
           lastDebounceTime = millis();
        }

        if ((millis() - lastDebounceTime) > debounceDelay)
        {
        // whatever the reading is at, it's been there for longer than the debounce
        // delay, so take it as the actual current state:
        // if the button state has changed:
           if (next_val != right_val && next_val!='n')
           {
               left_val = right_val;
               right_val = next_val ;
           }
          }
         
          // Frame period is removed from here and added to debounceDelay
          printChar(left_val, Left);
       printChar(right_val, Right);

       last_val = next_val ;
   
   }
}

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