Lets examine more closely the actual layout of a LED matrix.

 

 

Here we see  that each row connects to that rows cathode or negative leg of the LED's. Correspondingly, each column connects the anode or positive leg together. Please not that a LED matrix can also be the other way around.

 

To control a LED matrix, we have two options:

It is not possible to control the LED matrix all at once, as all the individual LED's share both their inputs. The way around this is to use Persistance of Vision. By cycling through each row or column quite fast (~50Hz and above) you should not see any flicker, and instead see the whole LED matrix display as if it was all working at once.

 

If we were to choose the first of the two options, we would first ground the first row connection (connection ROW1) and leave the remaining ROWX connections floating or high.

 

 

 

Then, we would pull each column connection high if we wanted that LED to turn on, or leave it floating or low to keep it off. For example if we wanted to turn on LED3 and LED5, then with the ROW1 connection pulled low, we would leave COL1, COL2 and COL4 floating or low, and pull COL3 and COL5 high.

Then after leaving ROW1's displayed LED's on for a set period of time, we would pull ROW1 high or floating and pull ROW2 low. At the same time, we would pull the corresponding column connections high to turn on the individual LED's in that row.

 

But how do we control the switching off and on of these connections? The easiest way is with the use of a microcontroller or microprocessor, as well as some additional circuitry.