LED-SPI

This repository contains a C library for commanding an array of 8x8 LED Matrices that are each equipped with a MAX7219 display driver. A MAX7219 display driver can be accessed via a SPI bus. This repository includes the library and some example code. The library was developed and tested using a Raspberry Pi Pico.

Using this library you can utilize any of the MAX7219 display dirver functions indicated below.

Feature Chart

MAX7219 Function	Supported?
Set Brightness Level (Intensity)	✔️
Set Decode Mode per Digit (Code B or No)	✔️
Set Digits to Display (Scan Limit)	✔️
Enter/Exit Shutdown Mode	✔️
Enter/Exit Display Test	✔️
Writing to Digit 0-7 Registers	✔️
Writing to the No-Op Register	✔️

This allows for the following high-level features:

• Writing a Single Character to a specified 8x8 LED Matrix in an array
• Writing a String to an array of 8x8 LED Matrices
• Showing a Message via discrete (matrix-by-matrix) scrolling
• Showing a Message via smooth (dot-by-dot) scrolling

Orientation

This code assumes the following MAX7219 8x8 LED Matrix Module orientation:

          DP  A  B  C  D  E  F  G 
         +------------------------+ 
         | 7  6  5  4  3  2  1  0 | D0 
 CLK <---|                      1 | D1 <--- CLK 
  CS <---|                      2 | D2 <--- CS 
DOUT <---|                      3 | D3 <--- DIN 
 GND ----|                   O  4 | D4 ---- GND 
 VCC ----|                O  O  5 | D5 ---- VCC 
         |             O  O  O  6 | D6 
         |          O  O  O  O  7 | D7 
         +------------------------+

Although with the appropriate font bit-pattern adjustments this code should work with other orientations.

Example Project Layout

Example Code Snippet

LedSpiConfig config;
memset(&config, 0, sizeof(config));
config.spi_instance = spi0;
config.baudrate = 10000000;
config.pin_cs = 17;
config.pin_sck = 18;
config.pin_mosi = 19;
config.num_8x8_matrix = 4;
config.smooth_scroll_rate = 300;
config.discrete_scroll_rate = 1000;
init_led_spi(&config);

set_shutdown_mode(&config, SHUTDOWN_YES);
set_display_test_mode(&config, DISPLAY_TEST_NO);
set_scan_limit(&config, DISPLAY_DIGITS_0_7); // use 8 digits
set_decode_mode(&config, 0x00); // no decode mode
set_shutdown_mode(&config, SHUTDOWN_NO);
set_brightness_level(&config, BRIGHTNESS_LVL_4);
clear_display(&config);

show_message(&config, "HELLO WORLD!");
show_message_smooth(&config, "Nice to meet you.");

Additional Information:

• License