Sink chaser on an Arduino Uno

// Sink chaser: seven LEDs on an NLSF595, the 595 whose outputs sink current.
//
// Wiring, driver to board:
//   SI   (pin 14, serial data)    -> pin 4
//   SCK  (pin 11, shift clock)    -> pin 5
//   RCK  (pin 12, register clock) -> pin 6
//   SCLR (pin 10) to 5 V, OE (pin 13) to GND
//   each LED from 5 V through 220 ohm, its cathode to QB..QH (QA is free)
//
// The NLSF595's datasheet calls it functionally similar to a 74VHC595, and
// shiftOut() and a latch pulse drive it the same way. The difference is the
// outputs: they are open drain. A stored 0 pulls the output to ground and
// lights the LED wired to it; a stored 1 lets go and the LED goes dark. So
// the sketch sends the inverse of the pattern it wants to see.
//
// This is how the chip drives common-anode RGB LEDs: the anode to 5 V and
// each color's cathode to an output.

const int DATA_PIN = 4;   // SI
const int SHIFT_PIN = 5;  // SCK
const int LATCH_PIN = 6;  // RCK

static void show(uint8_t lit) {
  // Invert: a 0 bit is a lit LED on an open-drain output.
  shiftOut(DATA_PIN, SHIFT_PIN, MSBFIRST, (uint8_t)~lit);
  digitalWrite(LATCH_PIN, HIGH);
  digitalWrite(LATCH_PIN, LOW);
}

void setup() {
  Serial.begin(9600);
  pinMode(DATA_PIN, OUTPUT);
  pinMode(SHIFT_PIN, OUTPUT);
  pinMode(LATCH_PIN, OUTPUT);
  show(0);
  Serial.println("NLSF595 ready");
}

void loop() {
  // Bit n is output Qn: bit 1 is QB, bit 7 is QH.
  for (int i = 1; i < 8; i++) {
    show((uint8_t)(1 << i));
    delay(90);
  }
  for (int i = 6; i > 1; i--) {
    show((uint8_t)(1 << i));
    delay(90);
  }
}