One-digit countdown on a 74HC595 (pins 8, 10 and 9), on an Arduino Uno

// One seven-segment digit through a 74HC595, counting down from D to 0.
//
//   74HC595 DS (pin 14)    -> Uno pin 8    (data)
//   74HC595 STCP (pin 12)  -> Uno pin 9    (latch)
//   74HC595 SHCP (pin 11)  -> Uno pin 10   (clock)
//   74HC595 VCC and MR -> 5V      GND and OE -> GND
//   Q0 to Q6 -> segments a to g, Q7 -> the decimal point
//   the display's common cathode -> GND
//
// A seven-segment display is eight LEDs in one package: segments a to g and
// the dot. Each symbol is a pattern of lit segments, one bit per segment, so
// a whole symbol fits in one byte and goes out with a single shiftOut().
//
// The count runs in hexadecimal, D, C, B, A, then 9 down to 0, one a second,
// and rests for five seconds at 0 before it starts again.

const int DATA_PIN = 8;
const int LATCH_PIN = 9;
const int CLOCK_PIN = 10;

//                     gfedcba, segment a in bit 0
const byte SYMBOLS[14] = {
    0b00111111,  // 0
    0b00000110,  // 1
    0b01011011,  // 2
    0b01001111,  // 3
    0b01100110,  // 4
    0b01101101,  // 5
    0b01111101,  // 6
    0b00000111,  // 7
    0b01111111,  // 8
    0b01101111,  // 9
    0b01110111,  // A
    0b01111100,  // b
    0b00111001,  // C
    0b01011110,  // d
};
const char NAMES[] = "0123456789ABCD";

void show(byte pattern) {
  digitalWrite(LATCH_PIN, LOW);
  shiftOut(DATA_PIN, CLOCK_PIN, MSBFIRST, pattern);  // bit 0 lands on Q0
  digitalWrite(LATCH_PIN, HIGH);
}

void setup() {
  pinMode(DATA_PIN, OUTPUT);
  pinMode(LATCH_PIN, OUTPUT);
  pinMode(CLOCK_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: one digit on a 74HC595 (data 8, latch 9, clock 10)");
}

void loop() {
  for (int i = 13; i >= 0; i--) {
    show(SYMBOLS[i]);
    Serial.println(NAMES[i]);
    delay(1000);
  }
  delay(5000);
}