// Create variables at the top
int once = 1;
char kval = 'Z', inChar = ' ';

// Setup is run one time. Define pins and assign starting values here.
void setup()
    {
    // This is for the KEYPAD set up 4 output pins and 4 input pins
    pinMode(13, OUTPUT);
    pinMode(12, OUTPUT);
    pinMode(11, OUTPUT);
    pinMode(10, OUTPUT);
    pinMode(9, INPUT);
    pinMode(8, INPUT);
    pinMode(7, INPUT);
    pinMode(6, INPUT);
    
    // set 4 keypad output pins to 5V 
    digitalWrite(13, HIGH);
    digitalWrite(12, HIGH);
    digitalWrite(11, HIGH);
    digitalWrite(10, HIGH);

    // set 4 pins to connect to the four LEDs
    pinMode(A0, OUTPUT);
    pinMode(A1, OUTPUT);
    pinMode(A2, OUTPUT);
    pinMode(A3, OUTPUT);

    // On Power Up, turn off all the LEDs
    digitalWrite(A0, LOW);
    digitalWrite(A1, LOW);
    digitalWrite(A2, LOW);
    digitalWrite(A3, LOW);

    // Need this for serial commands, set to 9600 Baud.
    Serial.begin(9600);

    }


// The main loop of the code is next.
void loop( )
    {
    
    // If something showed up, it is stored in 'inChar' and
    // it is no longer a blank space. Jump to mail_call.

    if (inChar != ' ')
        {
        mail_call();
        }

    
    // Check the keypad and see if anything is being pressed
    scankeypad( );

    // If the keypad had a button pressed, kval is something other than "Z"
    if (kval != 'Z' )
          {
          // Some code you want to run when a key is pressed.
          Serial.println (kval);
          }

    }

void mail_call( )
    {
    if (inChar == 'A')
        {
        digitalWrite(A0, !digitalRead(A0));
        }
    else if (inChar == 'B')
        {
        digitalWrite(A1, !digitalRead(A1));
        }
    else if (inChar == 'C')
        {
        digitalWrite(A2, !digitalRead(A2));
        }
    else if (inChar == 'D')
        {
        digitalWrite(A3, !digitalRead(A3));
        }
    else if (inChar == 'X')
        {
        digitalWrite(A0, LOW);
        digitalWrite(A1, LOW);
        digitalWrite(A2, LOW);
        digitalWrite(A3, LOW);
        }
    // Blank space means "Nothing received"
    inChar = ' ';
    }



void scankeypad()
    {
    // kval can be anything as long as it is NOT '0' - '9' or 'A' - 'F' (So I just picked 'Z')
    kval = 'Z';
    
    digitalWrite(13, LOW);
      if (digitalRead(9) == LOW) kval = '1';
      if (digitalRead(8) == LOW) kval = '4';
      if (digitalRead(7) == LOW) kval = '7';
      if (digitalRead(6) == LOW) kval = '0';
    digitalWrite(13, HIGH);
    
    digitalWrite(12, LOW);
      if (digitalRead(9) == LOW) kval = '2';
      if (digitalRead(8) == LOW) kval = '5';
      if (digitalRead(7) == LOW) kval = '8';
      if (digitalRead(6) == LOW) kval = 'F';
    digitalWrite(12, HIGH);
    
    digitalWrite(11, LOW);
      if (digitalRead(9) == LOW) kval = '3';
      if (digitalRead(8) == LOW) kval = '6';
      if (digitalRead(7) == LOW) kval = '9';
      if (digitalRead(6) == LOW) kval = 'E';
    digitalWrite(11, HIGH);
    
    digitalWrite(10, LOW);
      if (digitalRead(9) == LOW) kval = 'A';
      if (digitalRead(8) == LOW) kval = 'B';
      if (digitalRead(7) == LOW) kval = 'C';
      if (digitalRead(6) == LOW) kval = 'D';
    digitalWrite(10, HIGH);
    
    // Limits the number of values being sent to 1, no matter how long the key is pressed.
    if (kval != 'Z' && once == 1)
        {  
        once = 0;   
        }
    else if (kval != 'Z' && once == 0)
        {  
        kval = 'Z'; 
        }
    else
        {  
        once = 1;   
        }

    }


// SerialEvent occurs whenever a new data comes in the hardware serial RX. This
// routine is run between each time loop( ) runs, so using delay inside loop can
// delay response. Multiple bytes of data may be available.

void serialEvent()
    {
    while (Serial.available())
        {
        // get the new byte:
        inChar = (char)Serial.read();
        }
    
    }