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Just a basic query;
On my understanding of LED Matrix's, The following would light up 4 LEDs.
But what if I only wanted to light up just 3 of those LEDs? The circuit still needs the same inputs, since power will continue across all columns/rows
Thanks
Tom
Multiplexing is the answer.
If you want to, as an example, light up only LEDS 1, 3 and 4, you will:
Do this so that the loop takes less than 10 milliseconds and you are actually refreshing the entire matrix at 100Hz, fast enough to trick the eyes of any human being as if the LEDs 1,3 and 4 are lighted up at the same time: persistence of vision is your friend.
This is very simple. You can turn on each LED one at a time and repeat this over and over again. The easiest way of achieving this is to put this code in the loop section.
Persistence of vision is defined as "the retention of a visual image for a short period of time after the removal of the stimulus that produced it" - dictionary.com
Even though the LED is on for only 1/3 of the time, it is fast enough that the human eye will not be able to tell that each LED turns off. Hence the viewer sees 3 LEDs on at the same time.
This allows any combination of LED patterns in your LED matrix.
7-segment displays also use this technique. You probably have some in a microwave or DVD player that you never realized that they were cycling through each digit, using persistence of vision.
Resources:
http://www.circuitstoday.com/interfacing-8x8-led-matrix-with-arduino (recommended)
http://tronixstuff.com/2013/10/11/tutorial-arduino-max7219-led-display-driver-ic/
https://playground.arduino.cc/Main/LEDMatrix
http://forum.hobbycomponents.com/viewtopic.php?f=43&t=1489
