Eight LEDs on a 74HC595 (pins 12, 9 and 11), on an Arduino Uno

// Eight LEDs from three pins, through a 74HC595 shift register.
//
//   74HC595 DS (pin 14)    -> Uno pin 12   (data)
//   74HC595 SHCP (pin 11)  -> Uno pin 9    (clock)
//   74HC595 STCP (pin 12)  -> Uno pin 11   (latch)
//   74HC595 VCC and MR -> 5V      GND and OE -> GND
//   Q0 to Q7 -> eight LEDs, each through 220 ohm to GND
//
// The chip has eight outputs but takes its data one bit at a time. shiftOut()
// clocks the eight bits of a byte in over DS and SHCP; nothing changes on the
// outputs until the latch pin goes from LOW to HIGH, and then all eight change
// at once. So three Uno pins drive eight LEDs, and two chips chained together
// would drive sixteen.
//
// The sketch lights the LEDs one more at a time, then clears them all.

const int DATA_PIN = 12;
const int CLOCK_PIN = 9;
const int LATCH_PIN = 11;

byte leds = 0;

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

void setup() {
  pinMode(DATA_PIN, OUTPUT);
  pinMode(CLOCK_PIN, OUTPUT);
  pinMode(LATCH_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: 74HC595 on pins 12 (data), 9 (clock) and 11 (latch)");
}

void loop() {
  leds = 0;
  show(leds);
  delay(300);
  for (int i = 0; i < 8; i++) {
    bitSet(leds, i);
    show(leds);
    Serial.print("LEDs lit: ");
    Serial.println(i + 1);
    delay(300);
  }
}