Eight LEDs on a 74HC595 (pins 2, 5 and 4), on an Arduino Uno

// Eight LEDs on a 74HC595: one light runs along the row.
//
//   74HC595 DS (pin 14)    -> Uno pin 2   (data)
//   74HC595 STCP (pin 12)  -> Uno pin 4   (latch)
//   74HC595 SHCP (pin 11)  -> Uno pin 5   (clock)
//   74HC595 VCC and MR -> 5V      GND and OE -> GND
//   Q0 to Q7 -> eight LEDs, each through 220 ohm to GND
//
// A shift register turns three pins into eight outputs. shiftOut() clocks a
// byte into it one bit at a time, and a pulse on the latch copies all eight
// bits to the outputs at once, so the LEDs never flicker while bits move.
//
// One bit is set in the byte, and it moves up one place every quarter
// second, so one LED lights at a time from Q0 to Q7, then starts again.

const int DATA_PIN = 2;
const int LATCH_PIN = 4;
const int CLOCK_PIN = 5;

int current = 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(LATCH_PIN, OUTPUT);
  pinMode(CLOCK_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: eight LEDs on a 74HC595 (data 2, latch 4, clock 5)");
}

void loop() {
  byte leds = 0;
  bitSet(leds, current);
  show(leds);
  Serial.print("LED ");
  Serial.println(current);
  current = (current + 1) % 8;
  delay(250);
}