At sometime or another you may run out of pins on your Arduino board and need to extend it with shift registers. With this shift out module which is based on74HC595.The datasheet refers to the 74HC595 as an "8-bit serial-in serial or parallel-out shift register with output latches; 3-state." In other words you can use it to control 8 outputs at a time while only taking up a few pins on your microcontroller. You can link multiple registers together to extend your output even more. It canalso be applies to 51 AVR PIC and other microcontroller.

It is ideal to work together with Interface shield.