Ulam Spirals Using Arduino and LED Displays

Here's an animated gif of my Arduino-powered 32x16 LED screen. I wired this up using the Adafruit tutorial at https://learn.adafruit.com/32x16-32x32-rgb-led-matrix/wiring-the-16x32-matrix

The code to generate the spiral. Note this is unoptimized. You can probably do it better. The basic nugget to get the spiral is this line: round( sqrt( pow(pNumber, 2 ))*_piCounter*PI)%2==0).

void loop()

{

   initSpiral();

  _piCounter += .001;

  delay(200);

  _globalCounter += 1;

}

void initSpiral()

{

  int posX = 15;

  int posY = 7;

  int numberCounter = 1;

  int _spacer = 1;

  int legLength = 0;

  //establish the first dot

  //matrix.drawPixel(x, y, matrix.Color333(r, g, b));

  matrix.drawPixel(posX, posY, matrix.Color333(3, 4, 5));

  for (int i=1;i<17 font="" i="">

  {

    for (int k=0;k<=legLength;k++)

    {

      numberCounter += 1;

      posX += _spacer;

      testNumber(numberCounter, posX, posY);

    }

    for (int k=0;k<=legLength;k++)

    {

      numberCounter += 1;

      posY -= _spacer;

      testNumber(numberCounter, posX, posY);

    }    

    legLength += 1;

    for (int k=0;k<=legLength;k++)

    {

      numberCounter += 1;

      posX -= _spacer;

      testNumber(numberCounter, posX, posY);

    }

    for (int k=0;k<=legLength;k++)

    {

      numberCounter += 1;

      posY += _spacer;

      testNumber(numberCounter, posX, posY);

    }

    legLength += 1;

  }

}

String _bigNumber = "01234567012345670123456701234567012345670123456701234567012345670123456701234567012345670123456701234567012345670123456701234567";

void testNumber(int pNumber, int pX, int pY)

{

  if (round( sqrt( pow(pNumber, 2 ))*_piCounter*PI)%2==0)

  {

    matrix.drawPixel(pX, pY, matrix.Color333(_bigNumber.charAt(pX), _bigNumber.charAt(pY), _bigNumber.charAt(_globalCounter)));

  }

  else

  {

    matrix.drawPixel(pX, pY, matrix.Color333(3, 0, 2));

  }

}

Interesting note: these 32x16 panels are so incredibly bright they are painful to look at. So I'm using two sheets of paper to stop down the light, which also has a nice diffusion effect.