#define TIMER     700
#define PIN_U18   7
#define ROWS      5
#define MAX_COLS  4

typedef struct Letter {
  int width;
  boolean data[ROWS][MAX_COLS];
} Letter;

int State = 0;
int lastState = 0;

Letter letters[25];

void setup() {
  for (int pin = 2; pin <= 6; ++pin) {
    pinMode(pin, OUTPUT);
  }
  pinMode(PIN_U18, INPUT);

  // i'm using 'a' as an offset, this way the character 'a' will be stored in position 0
  // character 'a' corresponds to 97 (dec) and it'll be stored in position 97-97
  letters['t' - 'a'] = { // character 't' corresponds to 116-97=19, see: http://web.cs.mun.ca/~michael/c/ascii-table.html
    3,
    {
      {1, 1, 1},
      {0, 1, 0},
      {0, 1, 0},
      {0, 1, 0},
      {0, 1, 0}
    }
  };

  letters['g' - 'a'] = {
    4,
    {
      {1, 1, 1, 1},
      {1, 0, 0, 0},
      {1, 0, 1, 1},
      {1, 0, 0, 1},
      {1, 1, 1, 1}
    }
  };
}

void loop() {
  State = digitalRead(PIN_U18);
  if (State != lastState) {
    if (State == HIGH) {
      WriteString("tttggg");
    }
  }
  lastState = State;
}

void WriteString(const char *text) {
  while (*text != '\0') {
    WriteLetter(letters[*text]);
    ++text;
  }
}

void WriteLetter(Letter letter) {
  int pin;
  for (int col = 0; col < letter.width; ++col) {
    for (int row = 0; row < ROWS; ++row) {
      pin = row + 2; // if you can't use adjacent pins, you can make an array that contains the number of pins like that: a = {1,3,4,5,8} and then pin = a[row]
      digitalWrite(pin, letter.data[col][row]);
    }
    delayMicroseconds(TIMER);
  }
}