const int strobe = 7;
const int clock = 9;
const int data = 8;

void sendCommand(uint8_t value)
{
  digitalWrite(strobe, LOW);
  shiftOut(data, clock, LSBFIRST, value);
  digitalWrite(strobe, HIGH);
}

void reset()
{
  sendCommand(0x40); // set auto increment mode
  digitalWrite(strobe, LOW);
  shiftOut(data, clock, LSBFIRST, 0xc0);   // set starting address to 0
  for(uint8_t i = 0; i < 16; i++)
  {
    shiftOut(data, clock, LSBFIRST, 0x00);
  }
  digitalWrite(strobe, HIGH);
}

void setup()
{
  pinMode(strobe, OUTPUT);
  pinMode(clock, OUTPUT);
  pinMode(data, OUTPUT);

  sendCommand(0x8f);  // activate
  reset();
}

uint8_t readButtons(void)
{
  uint8_t buttons = 0;
  digitalWrite(strobe, LOW);
  shiftOut(data, clock, LSBFIRST, 0x42);

  pinMode(data, INPUT);

  for (uint8_t i = 0; i < 4; i++)
  {
    uint8_t v = shiftIn(data, clock, LSBFIRST) << i;
    buttons |= v;
  }

  pinMode(data, OUTPUT);
  digitalWrite(strobe, HIGH);
  return buttons;
}

void setLed(uint8_t value, uint8_t position)
{
  pinMode(data, OUTPUT);

  sendCommand(0x44);
  digitalWrite(strobe, LOW);
  shiftOut(data, clock, LSBFIRST, 0xC1 + (position << 1));
  shiftOut(data, clock, LSBFIRST, value);
  digitalWrite(strobe, HIGH);
}

void loop()
{
  uint8_t buttons = readButtons();

  for(uint8_t position = 0; position < 8; position++)
  {
    uint8_t mask = 0x1 << position;

    setLed(buttons & mask ? 1 : 0, position);
  }
}