How to use NO_KEY ?

Projects Programming
1

Hi I'm studying some keypad functions and I encounter this handy condition but I don't know how it works.
I did a simple test in where word will display if you use NO_KEY and then the lcd will clear and display new set of string.

Here's my code

#include <Keypad.h>
#include <Wire.h>
#include<LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x3F,2,1,0,4,5,6,7,3,POSITIVE); 
const byte ROWS = 4; //four rows
const byte COLS = 4; //four columns
char customkey;
char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

byte rowPins[ROWS] = {8, 7, 6, 5}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {9, 10, 11, 12}; //connect to the column pinouts of the keypad


//initialize an instance of class NewKeypad
Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);



void setup (){
   Serial.begin(9600);
    lcd.begin(16,2);
}

void loop() 
{
customkey = customKeypad.getKey();



while(customkey == NO_KEY )
{ customkey = customKeypad.getKey();
  lcd.print ("HELLLO");} 

if (customkey != NO_KEY)
{
  switch(customkey)
  {
    case '1':
    lcd.clear();
    lcd.setCursor(9,0);
    lcd.print("WELCOME");
    break;
  }
  }
}

My main problem is the word HELLO keeps on displaying even if the condition about NO_KEY is terminated after pressing a KEY

Any help is appreciated,

THANK YOU!

2

Don't forget that the loop() function repeats many times per second so the while loop will be entered many times per second and while a key is not pressed "HELLO" will be printed.

Under what circumstances do you want "HELLO" to be printed ?

3

Generally it's a bad idea to put your sketch in a loop waiting for a key press. Humans are very slow and your sketch can be doing useful stuff other than waiting for a human. You also don't need to check for NO_KEY before you decise what to do with the key value. Just pass every value on to the switch/case statement. If you want something special done when no key was pressed, you can make a 'case NO_KEY:'.

void setup () {
  Serial.begin(9600);
  lcd.begin(16,2);
  lcd.print ("HELLLO");  // Dispay "HELLO" until the '1' key is pressed.
}

void loop() 
{
  customkey = customKeypad.getKey();

  switch(customkey) {
  case '1':
    lcd.clear();
    lcd.setCursor(9,0);
    lcd.print("WELCOME");
    break;
  }
}
1 Like