Issue displaying string from Matrix Keypad password to display on lcd screen

Mbed OS
1

Hello,

I am working on a project to type a 6 digit order number on a matrix keypad and this number will be stored in a character string and then this string will be displayed/ updated on an lcd screen as the buttons are pressed. I was previously using a PIC 32 and I had it working as desired (see my original code below). I am now trying to transition to a stm32 Nucleo with a similar code and I am not getting the same results. I am using the lcd and keypad libraries on Mbed and have them working fine, however whenever I press a button, multiple characters appear at a time, and the number of characters does not get capped at 6 like I have it set, it keeps flooding the screen. I have both the serial monitor using sprintf/printf and the lcd print command displaying the information. I have tried messing with the delay but it doesn’t

Screen Shot 2020-11-22 at 4.05.21 PM
Screen Shot 2020-11-22 at 4.05.21 PM532×598 55.4 KB
stop the flooding of button presses it just increases the time between time to accept them. I am assuming I need to implement some sort of button debouncing but im not sure how to do this with the keypad library. Does anyone have any suggestions? A better way to solve this problem ? My current code is also shown below.
Screen Shot 2020-11-22 at 3.41.44 PM
Screen Shot 2020-11-22 at 3.41.44 PM726×623 70.9 KB

2

Hello,

you not linked what a library you exactly use. But it seems like this one

It is correct?

Just for inspiration, you can try something like this

    int i = 0
    char prevKey = 0;
    while(i < 6) {
        char key = keypad.getKey();
        if(key && key != prevKey){
            inpassword[i++] = key;
            // here print out one by one
            lcd.putc(key);
            ThisThread::sleep_for(100ms);
        }
        prevKey = key;
    }
    sprintf(test, "Order Number:\n#%s", inpassword);
    printf("%s\n",test);

You also need to manage the cursor of LCD, when you printing (putc or printf)to the display.
So, when you prints a string again and again to same place, you need to call a cls() method for clear the display, that also relocate the cursor to position 0. Otherwise, the cursor moves forward automatically and the original string will be not override.

    lcd.cls();
    lcd.printf("Somestring\n");
    //or
    lcd.putc(c);

Also if you need print something to a specific place you can use

    lcd.locate(col,row);
    lcd.printf("Some");
    //or
    lcd.putc(c);

BR, Jan

3

Hey Jan, the location function fixes part of my problem so thank you for that. However multiple characters are still appearing for a single button press. I tried to do what you had suggested but the keypad.getkey reads in a character to key, so comparing char with prevkey (int will not work) I tried making prevKey of type char but this lead to more errors.

4

I’m glad something helped.
Yes, you are right, I badly check the .h file of that library. Unfortunately, I don’t have this hardware, so I can’t tune it in real.

BR, Jan