An LED matrix is also known as a diode matrix, referring to the LED's one-directional polarity. An LED matrix is a two-dimensional grid with an LED connected to each intersection where a row crosses a column. The columns and rows are isolated from one another in order for the matrix to work. In electronics this is also known as multiplexing.

Figure 3.3 illustrates the entire schematic of all the connections. To the right, you will find the matrix layout. All the negative sides of the LEDs are connected in rows and all the positive sides of the LEDs are connected in columns. When power is applied to one of the columns, and a ground connection is opened up on the negative rows, only one LED will light up. As you might have noticed, we have connected part of the matrix to the analog pins. Since there are not enough digital pins, we will use some of the analog pins instead. The analog pins can be operated as digital pins and their numbering continues on from pin 13. In other...