int DIN = 4;
int LATCH = 7;
int CLOCK = 8;
int VOLUME = 5;

int led[8] = {0x01,0x03,0x07,0x0F,0x1F,0x3F,0x7F,0xFF};

void setup()
{
  pinMode(DIN, OUTPUT);
  pinMode(CLOCK, OUTPUT);
  pinMode(LATCH, OUTPUT);
}

void loop()
{
  int val=analogRead(VOLUME);
  val = map(val,0,1023,0,7);

  digitalWrite(LATCH, LOW);
  shiftOut(DIN,CLOCK,MSBFIRST,~led[val]);
  digitalWrite(LATCH, HIGH);
}