System Description (L)

The LEDs are the output of the program. The system is used to display a letter/word/sentence and roll it across the 24 sets of LEDs right to left.

The anodes of the 6 LEDs in each column are connected in parallel, and to a corresponding parallel output pin from the shift registers. The cathodes of the 24 LEDs in each row are connected in parallel, and to the collector side of a transistor.

The shift registers will provide a high to all the LEDs in the selected columns. The decoder will provide a low to only one row at a time, by means of turning on a transistor and opening a pathway to ground. This is so all the selected columns of LEDs will turn on in the single selected row.