Extending 8x8 led matrix to 16x16

Using Arduino LEDs and Multiplexing
1

Hi
I have a 8x8 led matrix(max7219) where the individual leds are selected by two potentiometers and two switches.Pot 1 selects up down.pot 2 selects left right and the two switches select or cancel the led at the current position.This is to display the on/off status of some octal switches eventually.
I'm struggling to find some information how to adapt this sketch so I can use more 8x8's to create a 16x16 and 24x24 display.
I have 4 8x8's laid out like............

1....2....
3....4....

obviously at the moment I get the same thing on all them

I'd be grateful if anyone could advise me or point me in the right direction as to what I need to change in the sketch

/* This sketch detects analog signals from the potentiometers
  and sends it to the serial monitor */

//initialize variable for x and y values on the potentiometers and the pushbuttons at digital pin 4 and 7
int UD;
int LR ;
int button_a = 4;
int button_b = 7;


bool stored_state [8][8];

int last_x, last_y;

#include "LedControl.h" //  importing the library
// DIN to 10, CLK to 12, CS to 11
LedControl lc = LedControl(10, 12, 11, 0);

void setup() {
  Serial.begin(9600);
  lc.shutdown(0, false); // turn off power saving, enables display
  lc.setIntensity(0, 8); // sets brightness (0~15 possible values)
  lc.clearDisplay(0);// clear screen
  pinMode(button_a, INPUT); // button is input
  digitalWrite(button_a, HIGH); // initalize button as ON
  pinMode(button_b, INPUT); // button is input
  digitalWrite(button_b, HIGH); // initalize button as ON


}

void loop() {
  UD = analogRead(A1); // read analog value at pin A1 and stores as UD
  LR = analogRead(A0);  // read analog value at pin A0 and stores as LR
  int stateA = digitalRead(button_a); //determines the state of button_a (HIGH or LOW)
  int stateB = digitalRead(button_b); //determines the state of button_b (HIGH or LOW)
  // scales down the value from 0-1023 to 0-7
  char x_translate = map(LR, 0, 1023, 7, 0);
  char y_translate = map(UD, 0, 1023, 0, 7);

  if ( (last_x != x_translate) || (last_y != y_translate) )
  {
    // the position has moved so we need to restore previous state
    lc.setLed(0, last_x, last_y, stored_state [last_x][last_y] );
  }

  last_x = x_translate;
  last_y = y_translate;

  Serial.print ("Button_a=");
  Serial.print(stateA, DEC);
  Serial.print ("Button_b=");
  Serial.print(stateB, DEC);
  Serial.print(", UD = ");
  Serial.print(UD, DEC);
  Serial.print(", LR = ");
  Serial.print(LR, DEC);
  Serial.print(", x = ");
  Serial.print(x_translate, DEC);
  Serial.print(", y = ");
  Serial.println(y_translate, DEC);

  // clears display whenever a new value is updated
  /// --> dont do this!  lc.clearDisplay(0);

  // just set led in new joystick position
  lc.setLed(0, x_translate, y_translate, true);

  // if button_a is pressed, store it
  if (stateA == 1) {
    stored_state [last_x][last_y] = true;
  }

  // if button_b is pressed, delete it
  if (stateB == 1) {
    stored_state [last_x][last_y] = false;
  }

  delay(150); //Mess with delay to tweak accuracy
}
2 
LedControl lc = LedControl(10, 12, 11, 0);

The last parameter of the constructor specifies how many max chips are connected. You seem to be giving it zero, so I'm a little surprised that works... Anyway, for a 16x16 you need to make that 4. The maximum that the library can support is 8 max chips, so for 24x24 matrix, you will have to modify the library or change to another library (or not use a library at all...)

EDIT: It seems that the library assumes 8 chips are attached if you give it a zero:

    if(numDevices<=0 || numDevices>8 )
        numDevices=8;
    maxDevices=numDevices;

So in your sketch, it will be assuming 8 max chips are connected.

3

I have the parameter set to 4 now but I still have 4 identical displays rather than one big display

4

Yes, I gave you the first step. You have a few miles still to go.

5

Yeah.More like a few thousand miles to go :slight_smile:

I think I've worn google and this forum out searching for a similar project.Some are close like scrolling text etc but no cigar

6

Forget "ledcontrol".

You need to be using the "parola" library for these arrays. It is in the IDE library manager, with examples.

7

The MD_MAXPanel library may be an option. It would allow you to address each LED by it's x,y coordinates on the display.

Links to my code repository in the signature block.

8

Thanks guys.That's great info.