Controlling a 8x32 LED Matrix with a Uno335

This short tutorial shows how to control a 8x32 RGB LED Matrix with the BlueberryE Uno335. To illustrate the capabilities of the LED Matrix, we will display some digits of Euler's number (the E in BlueberryE) e = 2.71828 18284 59045 23536 02874 71352 66249 77572 47093 69995...


  • The 8x32 RGB LED Matrix
  • Example Circuit
  • Example sketch

The 8x32 RGB LED Matrix

The LED matrix consists of 256 LEDs arranged in 8 rows and 32 columns. Each LED has a WS2811 IC chip built inside. Only one data line is connected to the LED matrix. Every LED can be addressed individually with this single data line. Thus, the LED Matrix needs only three connections: 5V, GND, DataIn. Libraries for programming sketches in the Arduino IDE are available for downloaded.

Example Circuit

The following illustration shows the connections between an Uno335 and the LED matrix. In this example we use the Uno335 pins 5V and GND pins for power supply. As we are utilizingthe Serial SRAM of the Uno335 for this example, we also have to use special jumper settings.

Connecting the LED matrix to a Uno335

Example sketch

In this example, we display some digits of Euler's number (the E in BlueberryE) on the LED matrix.

Euler's number e = 2.71828 18284 59045 23536 02874 71352 66249 77572 47093 69995... is calculated once in the setup(). The Spigot algorithm of A. H. J. Sale is used to calculate 4096 digits after the decimal point. The values are stored in the Serial SRAM of the Uno335. We use the BB_SramStack library ( download here) to address the SRAM. If you need further information about the Serial SRAM and the BB_SramStack library, refer to the tutorials:
Introduction to the SRAM on the BlueberryE Uno335
Using the BB_SramStack library to access the Serial SRAM of the blueberrye uno335

In each iteration of the loop(), 5 digits of e are shown on the LED matrix. In each cycle the digits are shifted to the left and the next digit is read from the SRAM. The Adafruit libraries GFX,NeoMatrix and NeoPixel provide a comfortable way to address the pixels of the LED matrix.

The following video shows the LED matrix in action:

  1. compu is displayed when the 4096 digits are calculated and written to the Serial SRAM. The total time for calculation is 94s. To save some time, we cut out some frames in the beginning sequence of the video.
  2. 4096! indicates the successful completion of the calculations
  3. BLUEBERRYE is just some advertisment
  4. Finally, the digits of e are shown sequentially.

Here is the code: download on GitHub

  Store 4096 digits of Eulers number e in the Uno335 Serial Sram.
  Display the digits sequentially on a 8x32 RGB LED matrix.

  v0.1 created 10 Oct. 2016
  by Engelbert Mittermeier (BlueberryE GmbH)

// Include the library to access the Serial SRAM
#include  <BB_SramStack.h>

// Include libraries for the 8x32 LED matrix
#include <Adafruit_GFX.h>
#include <Adafruit_NeoMatrix.h>
#include <gamma.h>
#include <Adafruit_NeoPixel.h>

// Define the pin which is used as DataIn on the LED matrix
#define MATRIX_PIN 3

// Parameter 1 = width of NeoPixel matrix
// Parameter 2 = height of matrix
// Parameter 3 = pin number (most are valid)
// Parameter 4 = matrix layout flags, add together as needed:
//     Position of the FIRST LED in the matrix; pick two, e.g.
//     NEO_MATRIX_TOP + NEO_MATRIX_LEFT for the top-left corner.
//   NEO_MATRIX_ROWS, NEO_MATRIX_COLUMNS: LEDs are arranged in horizontal
//     rows or in vertical columns, respectively; pick one or the other.
//   NEO_MATRIX_PROGRESSIVE, NEO_MATRIX_ZIGZAG: all rows/columns proceed
//     in the same order, or alternate lines reverse direction; pick one.
//   See example below for these values in action.
// Parameter 5 = pixel type flags, add together as needed:
//   NEO_KHZ800  800 KHz bitstream (most NeoPixel products w/WS2812 LEDs)
//   NEO_KHZ400  400 KHz (classic 'v1' (not v2) FLORA pixels, WS2811 drivers)
//   NEO_GRB     Pixels are wired for GRB bitstream (most NeoPixel products)
//   NEO_RGB     Pixels are wired for RGB bitstream (v1 FLORA pixels, not v2)

Adafruit_NeoMatrix matrix = Adafruit_NeoMatrix(32, 8,  MATRIX_PIN,
  NEO_GRB            + NEO_KHZ800);

// Amount of digits of e
const unsigned long digitsE = 4096;

// Initialize the stack
BB_SramStack stack(0x0000, digitsE);

// Declare a StackIterator variable
BB_StackIterator iter(&stack);

// newSequence is true, if the diplay of the digits of e has to start from
// the beginning
byte newSequence = 1;

// contains the 5 values which are displayed at once 
char values[5];

// define some color codes
#define white 0xFFFF
#define green 0x07E0
#define red 0xF800
#define cyan 0x07FF
#define magenta 0xF81F
#define yellow 0xFFE0
#define blue 0x001F

// contains the colors which are used to display the digits of e
uint16_t colors[] = {yellow, cyan, magenta, blue, red};

void setup() {
    // initialize the LED matrix
    // set the brightness; max = 255
    // as we power the matrix with the Uno335, we will use only 100

    // initialize the SRAM

    // Display "compu" on the LED matrix to indicate the computation of e
    matrix.setCursor(0, 0);

    // Write e to the SRAM

    // Display "4096!" on the LED matrix to show that the computation of e
    // is done
    matrix.setCursor(0, 0);
    matrix.print(String(digitsE) + "!");;


void loop() {

    if (newSequence < 1){
        // some digits have already been displayed before

        // shift out the first digit
        values[0] = values[1];
        values[1] = values[2];
        values[2] = values[3];
        values[3] = values[4];

        if (iter.hasNext()){
            // add the next digit
            values[4] = + '0';   // get the data and convert to char
            // display all 5 digits on the LED matrix
            for (int i = 0; i < sizeof(values); i++) matrix.drawChar(6 * i, 0, values[i], colors[i], 0x0000, 1);
        else {
            // all 4096 digits have been displayed
            // set newSequence = 1 to restart from the beginning
            newSequence = 1;
    } else {      
        // set the StackIterator to the first element of the stack
        iter = stack.iterator();

        // display some advertisment

        for (int i = matrix.width(); i >= -59; i--){

        // show the first digits of e
        values[0] = 'e';
        values[1] = '=';
        values[2] = '2';
        values[3] = '.';

        if (iter.hasNext()){
            values[4] = + '0';          // get the data and convert to char
            newSequence = 0;
        else values[4] = '_';
        for (int i = 0; i < sizeof(values); i++) matrix.drawChar(6 * i, 0, values[i], colors[i], 0x0000, 1);



// n digits of e are written to the Serial SRAM of the Uno335.
// To do this efficiently with the 8-bit Atmega328P with only 2KB SRAM internal memory, we use the 
// Spigot algorithm of A. Sale.
// see: A. H. J. Sale: The calculation of e to many significant digits. The Computer Journal, Vol. 11 (2), 1968. S. 229–230

void writeEulerDigits(unsigned long n){

    int m;

    switch (n){
        case 64:
            m = 49;
        case 128:
            m = 84;
        case 256:
            m = 146;
        case 512:
            m = 257;
        case 1024:
            m = 458;
        case 2048:
            m = 823;
        case 4096:
            m = 1493;

    byte coef[m + 1];
    for (int j = 2; j <= m; j++) coef[j] = 1;

    int carry;
    int temp;
    for (int i = 1; i <= n; i++){
        carry = 0;
        for (int j = m; j >= 2; j--){
            temp = coef[j] * 10 + carry;
            carry = temp / j;
            coef[j] = temp - carry * j;
        stack.push((byte) carry);  //  write the value to the sram