Interfacing 8×8 LED Matrix with Arduino

LED matrix displays can be used to display almost anything. Most modern LED sign boards uses various types of matrix boards with controllers. In this tutorial we are going to interface a single color 8×8 LED matrix with Arduino and display a few characters in it.

8×8 matrix consists of 64 dots or pixels. There is a LED for each pixel and these LEDs are connected to total of 16 pins. You can identify the pin out and circuit diagram of it using the following figure.

C1 – C8 – Column pins

R1 – R8 – Row pins

As you can see all anodes of same row is connected to one pin and all cathodes of same column are connected to another pin.We have 8 row pins and 8 column pins. If a positive voltage is  applied to R1 pin and negative to C1, we can see that the first pixel turns on. If we apply negative to C2 then the second pixel turns on. Like this we can turn each pixel by hanging the supply pins. However we have 64 supply combinations, and doing it manually is practically impossible. This is why Arduino is interfaced with the 8×8 matrix.

Circuit Diagram

As you can see in the diagram every column pin is connected to Arduino pin through a 220Ω resistor. All the row pins are connected to one of the output pin of the shift register. The characters are displayed using the multiplexing techniques. Shift register is connected to Arduino as usual by data, latch and clock pins.

Arduino Code

 int latchPin = 4; // pis connected to shift registors
int clockPin = 5;
int dataPin = 3;
int pins [8] = {6, 7, 8, 9, 10, 11, 12, 13}; // common cathode pins
byte A[8] = {   B00000000, // Letters are defined
                B00011000,// you can create your own
                B00100100,
                B01000010,
                B01111110,
                B01000010,
                B01000010,
                B00000000
            };

byte B[8] = {     B00000000,
                  B11111100,
                  B10000010,
                  B10000010,
                  B11111100,
                  B10000010,
                  B10000010,
                  B11111110
            };

byte blank[8] = { B00000000,
                  B00000000,
                  B00000000,
                  B00000000,
                  B00000000,
                  B00000000,
                  B00000000,
                  B00000000
                };
byte R[8] = {  B00000000,
               B01111000,
               B01000100,
               B01000100,
               B01111000,
               B01010000,
               B01001000,
               B01000100
            };


void setup() {
  Serial.begin(9600); // Serial begin
  pinMode(latchPin, OUTPUT); // Pin configuration
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  for (int i = 0; i < 8; i++) { // for loop is used to configure common cathodes
    pinMode(pins[i], OUTPUT);
    digitalWrite(pins[i], HIGH);
  }

}

void loop() {



  for (int k = 0; k < 1000; k++) { // showing each letter for 1 second
    display_char(A);

  }

  for (int k = 0; k < 1000; k++) {
    display_char(B);

  }
  for (int k = 0; k < 1000; k++) {
    display_char(R);

  }

  // add more letters show method here






}
void display_char(byte ch[8]) { // Method do the multiplexing
  for (int j = 0; j < 8; j++) {
    digitalWrite(latchPin, LOW);
    digitalWrite(pins[j], LOW);

    shiftOut(dataPin, clockPin, LSBFIRST, ch[j]);
    digitalWrite(latchPin, HIGH);
    //delay(1);
    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, LSBFIRST, B00000000); // to get rid of flicker when
    digitalWrite(latchPin, HIGH);
    digitalWrite(pins[j], HIGH);

  }


}

Code Explanation

In the code all important lines are commented. The digitalWrite command is used for controlling the column pins and shiftOut command is used to write to shift register. Letters are defined in a byte array when the characters displaying 0 are OFF and 1 is ON. This way you can define your own letters or symbols. In the multiplexing method shiftOut(dataPin, clockPin, LSBFIRST, B00000000);  line is used to reduce the flicker by turning off all the pixels after each step.

Breadboard Configuration

You can see the actual bread board setup in the following figure.