/*
  Use 74hc595 SIPO to extend Output pins 
  By defult, only the left-most and right-most 
  LEDs are ON since they are connected to VCC
*/
#define SRCP 21 // shift register clock 
#define STCP 22 // latch clock
#define DS 23 // serial data out 


void setup() 
{
  pinMode(SRCP, OUTPUT);
  pinMode(STCP, OUTPUT);
  pinMode(DS, OUTPUT);
  
  
}

void loop() 
{

  for(int i=0; i<9; i++){
    int N=pow(2,i)-1; //0,1,3,7..
    digitalWrite(STCP,LOW); //disconnect
    shiftOut(DS,SRCP,LSBFIRST,N);
    digitalWrite(STCP,HIGH); //connect 
    delay(500);
  }

}
74HC595