Fortune printer on an Arduino Uno

// Fortune printer: a mini thermal printer and a button.
//
//   pins 5, 6  SoftwareSerial: the printer's TX into 5, its RX from 6
//   pin 2      the button, to ground (INPUT_PULLUP)
//
// The printer runs from its own 9 V supply, sharing ground with the Uno.
// Each press prints a ticket: a bold, centered, double size header, one of
// the fortunes below, and a lucky number as text and as a barcode. The time
// of the press seeds the random numbers, so the tickets differ run to run.

#include <Adafruit_Thermal.h>
#include <SoftwareSerial.h>

const int BUTTON = 2;

SoftwareSerial printerSerial(5, 6);
Adafruit_Thermal printer(&printerSerial);

const char *const FORTUNES[] = {
  "A soldered joint holds fast.",
  "Your next build works first try.",
  "Check the ground wire first.",
  "A blinking light brings joy.",
  "Patience fixes most bugs.",
  "Today, the magic smoke stays in.",
  "An old project wants finishing.",
  "Read the datasheet. It knows.",
};
const int FORTUNE_COUNT = sizeof(FORTUNES) / sizeof(FORTUNES[0]);

int tickets = 0;

void printTicket() {
  randomSeed(micros());
  int lucky = random(10, 100);

  printer.justify('C');
  printer.boldOn();
  printer.setSize('L');
  printer.println("FORTUNE");
  printer.setSize('S');
  printer.boldOff();
  printer.println("--------------------------------");
  printer.justify('L');
  printer.println(FORTUNES[random(FORTUNE_COUNT)]);
  printer.feed(1);
  printer.justify('C');
  printer.print("Lucky number: ");
  printer.println(lucky);

  char code[3];
  code[0] = (char)('0' + lucky / 10);
  code[1] = (char)('0' + lucky % 10);
  code[2] = 0;
  printer.setBarcodeHeight(40);
  printer.printBarcode(code, CODE39);
  printer.justify('L');
  printer.feed(2);

  tickets++;
  Serial.print("Ticket ");
  Serial.print(tickets);
  Serial.print(", lucky number ");
  Serial.println(lucky);
}

void setup() {
  Serial.begin(9600);
  pinMode(BUTTON, INPUT_PULLUP);
  printerSerial.begin(19200);
  printer.begin();
  if (!printer.hasPaper()) Serial.println("Out of paper");
  Serial.println("Press the button for your fortune");
}

void loop() {
  if (digitalRead(BUTTON) == LOW) {
    delay(20);
    if (digitalRead(BUTTON) == LOW) {
      printTicket();
      while (digitalRead(BUTTON) == LOW) delay(10);
      delay(20);
    }
  }
}