/* Elegant Keypad extendable to Keyboard
   Details at:
   https://www.instructables.com/An-Elegant-Keypad-Extendable-to-Keyboard/

   Github repository:
   https://github.com/QuteNZ/An-Elegant-Keypad-extendable-to-Keyboard.git

   and Demo Video:
   https://youtu.be/oLSrkSVk7Mg
   ===============================================
   A typical keypad uses matrix configuration for microcontroller.
	 C1 C2 C3
	 |  |  |
   R1 ---1, 2, 3
   R2 ---4, 5, 6
   R3 ---7, 8, 9
   R4 ---*, 0, #
   in which, total IOs taken are number of Rows plus number of Columes.
   
   For a 4X3 matrix keypad, number of IOs can be reduced with 4 diodes as configured below:
	       C1	C2	    C3 	      C4
	      |		 |	     |	       | 
   R1 --- 1/  |    2/    |     3/    | --cDa-- |
   R2 --- 4/  |    5/    |  --cDa--  |    6/   |
   R3 --- 7/  |  --cDa-- |     8/    |    9/   |
   R4 ---cDa--|  star/   |     0/    |    #/   |
   Then the 4x3 matrix was transformed to 4x4 one with diodes between Row & Column.
   
   The software can recongnise a key press by appling a voltage to each row in turn
   while observing the state of the remainning port pin, which are configured as inputs.
*/

//#include <Wire.h>
#include <LiquidCrystal_I2C.h>

//PCF8574 I2C chip,use I2C_Scanner if address is unkown, 0x27 for mine
LiquidCrystal_I2C lcd(0x27, 16, 2);	//0x3F for Simulation
   
const int debounceTime = 160;
const int rowPins[4] = {4, 5, 6, 7};  // Shared row/column pins by diode

char key;
const char keymap[4][4] = {		//D for 1N4048 Diode
	{'1', '2', '3', 'D'} ,
	{'4', '5', 'D', '6'} ,
	{'7', 'D', '8', '9'} ,
	{'D', '*', '0', '#'} 
};

void setup() {
  //Serial.begin(9600);
  lcd.init();	//TinkerCad use init()
  //lcd.begin();
  lcd.print(" Elegant Keypad");
  lcd.setCursor(0,1);
  
  // Initialize all pins as inputs with pull-ups
  for (int i = 0; i < 4; i++) {
    pinMode(rowPins[i], INPUT_PULLUP);
  }
  //Serial.println("ready!");
}

void loop() {
  for (int active = 0; active < 4; active++) {
    // Set one pin as OUTPUT HIGH
    pinMode(rowPins[active], OUTPUT);
    digitalWrite(rowPins[active], LOW);

    // Check other pins for HIGH signal
    for (int i = 0; i < 4; i++) {
      if (i == active) continue;	//Skip the output itself
      pinMode(rowPins[i], INPUT_PULLUP);
      if (digitalRead(rowPins[i]) == LOW) {
	 delay(debounceTime);
	 while (digitalRead(rowPins[i]) == LOW)
	 ;		//Waiting for key release
	 key = keymap[i][3-active];

	 lcd.print(key);
        //Serial.print("Key Pressed: ");
	//Serial.print(key);
        
        delay(debounceTime); // debounce
      }
    }
    pinMode(rowPins[active], INPUT_PULLUP);	// Reset active pin to input
  }
}