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

// A four-digit display on one 74HC595: every digit shows the same symbol.
//
//   74HC595 DS -> pin 8    SHCP -> pin 10    STCP -> pin 9
//   74HC595 VCC and MR -> 5V      GND and OE -> GND
//   Q0 to Q7 -> segments a to g and the decimal point
//   each digit's common cathode (DIG1 to DIG4) -> its own 220 ohm -> GND
//
// The four digits share their segment lines: segment a of every digit is one
// wire. Each digit lights only while its common pin is grounded. Here all four
// are grounded all the time, so all four show the same symbol. To show four
// different symbols a sketch switches the digits on one after another, faster
// than the eye can follow; the stopwatch circuits do exactly that.
//
// The sketch steps through the sixteen hexadecimal digits, 0 to F, twice a
// second.

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

//                   gfedcba
const byte HEX_DIGITS[16] = {
    0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07,
    0x7F, 0x6F, 0x77, 0x7C, 0x39, 0x5E, 0x79, 0x71,
};
const char SYMBOLS[] = "0123456789ABCDEF";

void show(byte pattern) {
  digitalWrite(LATCH_PIN, LOW);
  shiftOut(DATA_PIN, CLOCK_PIN, MSBFIRST, pattern);
  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: four digits on a 74HC595 (pins 8, 10 and 9)");
}

void loop() {
  for (int i = 0; i < 16; i++) {
    show(HEX_DIGITS[i]);
    Serial.println(SYMBOLS[i]);
    delay(500);
  }
}