Circuit Documentation

Summary

This circuit consists of an Arduino UNO microcontroller connected to a series of MAX7219 8x8 LED Matrix modules. The Arduino UNO controls the LED matrices using a software-implemented SPI communication protocol. The matrices are daisy-chained together, allowing for control over a large display area using a minimal number of microcontroller pins. The circuit is designed to display patterns or images across the LED matrices.

Component List

Arduino UNO

• Description: A microcontroller board based on the ATmega328P.
• Purpose: Acts as the main controller for the LED matrices, sending data and control signals.
• Pins Used: 5V, GND, D10 (CS), D11 (DIN), D12 (CLK).

MAX7219 8x8 LED Matrix Modules

• Description: An 8x8 LED Matrix module controlled by the MAX7219 driver.
• Purpose: Displays the visual output as instructed by the Arduino UNO.
• Pins Used: VCC, GND, CS, CLK, DIN, CS(OUT), CLK(OUT), DOUT, VCC(OUT).

Wiring Details

Arduino UNO

• 5V to VCC on the first MAX7219 LED Matrix.
• GND to GND on the first MAX7219 LED Matrix.
• D12 to CLK on the first MAX7219 LED Matrix.
• D11 to DIN on the first MAX7219 LED Matrix.
• D10 to CS on the first MAX7219 LED Matrix.

MAX7219 8x8 LED Matrix Modules

• VCC connected to 5V from the Arduino UNO and VCC(OUT) to the next matrix's VCC.
• GND connected to GND from the Arduino UNO and GND to the next matrix's GND.
• CS connected to CS(OUT) from the previous matrix (except the first one, which is connected to the Arduino).
• CLK connected to CLK(OUT) from the previous matrix (except the first one, which is connected to the Arduino).
• DIN connected to DOUT from the previous matrix (except the first one, which is connected to the Arduino).

Documented Code

// This version uses bit-banged SPI.
// If you see tearing (jagged edges on the circles) try the version
// which uses AVR's hardware SPI peripheral:
// https://wokwi.com/arduino/projects/318868939929027156

#define CLK 12
#define DIN 11
#define CS  10
#define X_SEGMENTS   4
#define Y_SEGMENTS   4
#define NUM_SEGMENTS (X_SEGMENTS * Y_SEGMENTS)

// a framebuffer to hold the state of the entire matrix of LEDs
// laid out in raster order, with (0, 0) at the top-left
byte fb[8 * NUM_SEGMENTS];

void shiftAll(byte send_to_address, byte send_this_data)
{
  digitalWrite(CS, LOW);
  for (int i = 0; i < NUM_SEGMENTS; i++) {
    shiftOut(DIN, CLK, MSBFIRST, send_to_address);
    shiftOut(DIN, CLK, MSBFIRST, send_this_data);
  }
  digitalWrite(CS, HIGH);
}

void setup() {
  Serial.begin(115200);
  pinMode(CLK, OUTPUT);
  pinMode(DIN, OUTPUT);
  pinMode(CS, OUTPUT);

  // Setup each MAX7219
  shiftAll(0x0f, 0x00); //display test register - test mode off
  shiftAll(0x0b, 0x07); //scan limit register - display digits 0 thru 7
  shiftAll(0x0c, 0x01); //shutdown register - normal operation
  shiftAll(0x0a, 0x0f); //intensity register - max brightness
  shiftAll(0x09, 0x00); //decode mode register - No decode
}

void loop() {
  // ... (loop code omitted for brevity)
}

void set_pixel(uint8_t x, uint8_t y, uint8_t mode) {
  byte *addr = &fb[x / 8 + y * X_SEGMENTS];
  byte mask = 128 >> (x % 8);
  switch (mode) {
    case 0: // clear pixel
      *addr &= ~mask;
      break;
    case 1: // plot pixel
      *addr |= mask;
      break;
    case 2: // XOR pixel
      *addr ^= mask;
      break;
  }
}

void safe_pixel(uint8_t x, uint8_t y, uint8_t mode) {
  if ((x >= X_SEGMENTS * 8) || (y >= Y_SEGMENTS * 8))
    return;
  set_pixel(x, y, mode);
}

void clear() {
  byte *addr = fb;
  for (byte i = 0; i < 8 * NUM_SEGMENTS; i++)
    *addr++ = 0;
}

void show() {
  // ... (show function code omitted for brevity)
}

Code Explanation

• Constants: Define the pins used for communication and the dimensions of the LED matrix setup.
• Framebuffer: An array to hold the state of the LEDs.
• shiftAll(): Sends data to all MAX7219 modules.
• setup(): Initializes the Arduino pins and configures the MAX7219 modules.
• loop(): Contains the main logic for updating the LED matrix display (code omitted for brevity).
• set_pixel(): Sets the state of a single pixel in the framebuffer.
• safe_pixel(): A wrapper for set_pixel() that checks for out-of-bounds coordinates.
• clear(): Clears the framebuffer.
• show(): Sends the framebuffer to the LED matrices (code omitted for brevity).