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HUB75 RGB LED matrix panel library utilizing ESP32 DMA
Table of Content
Introduction
- This is an ESP32 Arduino/IDF library for HUB75 / HUB75E RGB LED panels.
- This library 'out of the box' (mostly) supports HUB75 panels where TWO rows/lines are updated in parallel... referred to as 'two scan' panels within this library's documentation.
- 'Four scan' panels are also supported - but please refer to the Four Scan Panel example.
- The library uses the DMA functionality provided by the ESP32's 'LCD Mode' for faster output.
Features
- Low CPU overhead - Pixel data is sent directly with the use of hardware-backed DMA, no CPU involvement
- Fast - Updating pixel data involves only bit-wise logic over DMA buffer memory, no pins manipulation or blocking IO
- Full screen BCM - Library utilizes binary-code modulation to render pixel color depth / brightness over the entire matrix to give reasonable colour depth
- Variable color depth - Up to TrueColor 24 bits output is possible depending on matrix size/refresh rate required
- CIE 1931 luminance correction (aka natural LED dimming) implemented
- Adafruit GFX API - Library can be built with AdafruitGFX, simplified GFX or without a GFX API at all
ESP32 variants supported
- Original ESP32 - That being the ESP-WROOM-32 module with ESP32‑D0WDQ6 chip from ~2017.
- ESP32-S2; and
- ESP32-S3
RISC-V ESP32's (like the C3) are not supported as they do not have the hardware 'LCD mode' required for this library.
Required memory
"What's the price for those features?" - It's memory, you pay it all by precious MCU's internal memory (SRAM) for the DMA buffer.
A typical 64x32px panel at 24bpp colour uses about 20kB of internal memory.
Please use the 'Memory Calculator' to see what is typically achievable with the typical ESP32. 
For the ESP32-S3 only, you can use SPIRAM/PSRAM to drive the HUB75 DMA buffer when using Octal SPI-RAM (i.e. ESP32 S3 N8R8 variant). However, due to bandwidth limitations, the maximum output frequency is limited to approx. 13Mhz, which will limit the real-world number of panels that can be chained without flicker.
To enable PSRAM support on the ESP32-S3, refer to the build options to enable.
For all other ESP32 variants (like the most popular ‘original’ ESP32), only internal SRAM can be used, so you will be limited to the ~200KB or so of 'free' SRAM (because of the memory used for your sketch amongst other things) regardless of how many megabytes of SPIRAM/PSRAM you may have connected.
Supported panels
Parallel scan lines
-
'Two scan' panels where two rows/lines are updated in parallel.
- 64x32 (width x height) 'Indoor' panels, such as this typical RGB panel available for purchase. Often also referred to as 1/16 'scan panel' as every 16th row is updated in parallel (hence why I refer to it as 'two scan')
- 64x64 pixel 1/32 Scan LED Matrix 'Indoor' Panel
-
'Four scan' panels where four rows/lines are updated in parallel.
- 32x16 pixel 1/4 Scan LED Matrix 'Indoor' Panel using an ingenious workaround as demonstrated in the Four_Scan_Panel example.
- 126x64 SM5266P
Ones interested in internals of such matrices could find this article useful.
Due to the high-speed optimized nature of this library, only specific panels are supported. Please do not raise issues with respect to panels not supported on the list below.
Driver chips known to be working well
- ICND2012
- RUC7258
- FM6126A AKA ICN2038S, FM6124 (Refer to PatternPlasma example on how to use.)
- SM5266P
Unsupported chips
- SM1620B
- RUL5358 / SHIFTREG_ABC_BIN_DE based panels are not supported.
- ICN2053 / FM6353 based panels - Refer to this library, which is a fork of this library ( discussion link).
- Any other panel not listed above.
Please use an alternative library if you bought one of these.
Getting Started
1. Library Installation
- Dependancy: You will need to install Adafruit_GFX from the "Library > Manage Libraries" menu.
- Install this library from the Arduino Library manager.
Library also tested to work fine with PlatformIO, install into your PlatformIO projects' lib/ folder as appropriate. Or just add it into platformio.ini lib_deps section.
2. Wiring the ESP32 to an LED Matrix Panel
Refer to the '*default-pins.hpp' file within the applicable platforms folder.
If you want to change the GPIO mapping at runtime, simply provide the wanted pin mapping as part of the class initialization structure. For example, in your sketch have something like the following:
// Change these to whatever suits
#define R1_PIN 25
#define G1_PIN 26
#define B1_PIN 27
#define R2_PIN 14
#define G2_PIN 12
#define B2_PIN 13
#define A_PIN 23
#define B_PIN 19
#define C_PIN 5
#define D_PIN 17
#define E_PIN -1 // required for 1/32 scan panels, like 64x64px. Any available pin would do, i.e. IO32
#define LAT_PIN 4
#define OE_PIN 15
#define CLK_PIN 16
HUB75_I2S_CFG::i2s_pins _pins={R1_PIN, G1_PIN, B1_PIN, R2_PIN, G2_PIN, B2_PIN, A_PIN, B_PIN, C_PIN, D_PIN, E_PIN, LAT_PIN, OE_PIN, CLK_PIN};
HUB75_I2S_CFG mxconfig(
64, // Module width
32, // Module height
2, // chain length
_pins, // pin mapping
);
dma_display = new MatrixPanel_I2S_DMA(mxconfig);
Various people have created PCBs for which one can simply connect an ESP32 to a PCB, and then the PCB to the HUB75 connector, such as:
- Brian Lough's ESP32 I2S Matrix Shield
- Charles Hallard's WeMos Matrix Shield
- Bogdan Sass's Morph Clock Shield
Please contact or order these products from the respective authors.
Can I use with a larger panel (i.e. 64x64px square panel)?
If you want to use with a 64x64 pixel panel (typically a HUB75E panel) you MUST configure a valid E_PIN to your ESP32 and connect it to the E pin of the HUB75 panel! Hence the 'E' in 'HUB75E'
3. Run a Test Sketch
Below is a bare minimum sketch to draw a single white dot in the top left. You must call begin() before you call ANY pixel-drawing (fonts, lines, colours etc.) function of the MatrixPanel_I2S_DMA class.
Once this is working, refer to the PIO Test Patterns example. This sketch draws simple colors/lines/gradients over the entire matrix and it could help to troubleshoot various issues with ghosting, flickering, etc...
Note: Requires the use of PlatformIO, which you should probably use if you aren't already.
Further information
Can I chain panels?
Yes!
For example: If you want to chain two of these horizontally to make a 128x32 panel you can do so by connecting the panels in series using the HUB75 ribbon cable. Than you must provide proper configuration structure to the class constructor letting it know that you use "one long virtual matrix chain". Refer to Pattern Plasma example for all the details about configuration setup.
Finally, if you wanted to chain 4 x (64x32px) panels to make 128x64px display (essentially a 2x2 grid of 64x32 LED Matrix modules), a little more magic will be required. Refer to the Chained Panels example.
Resolutions beyond 128x64 are more likely to result in crashes due to memory constraints etc. You are on your own after this point - PLEASE do not raise issues about this, the library can't magically defeat the SRAM memory constraints of the ESP32.
Adjusting Panel Brightness
By default you should not need to change / set the brightness value (which is 128 or 50%) as it should be sufficient for most purposes. Brightness can be changed by calling setPanelBrightness(xx) or setBrightness8(xx).
The value to pass must be a number between 0 (for a black screen) and 255 (max brightness).
Example:
void setup() {
Serial.begin(115200);
dma_display->begin(); // setup the LED matrix
dma_display->setBrightness8(192); //0-255
dma_display->clearScreen();
}
Build-time options
Although Arduino IDE does not seem to offer any way of specifying compile-time options for external libs there are other IDE's (like PlatformIO/Eclipse) that could use that. Check Build Options document for reference.
Latch blanking
If you are facing issues with image ghosting when pixels has clones with horizontal offset, than you try to change Latch blanking value. Latch blanking controls for how many clock pulses matrix output is disabled via EO signal before/after toggling LAT signal. It hides row bits transitioning and different panels may require longer times for proper operation. Default value is 1 clock before/after LAT row transition. This could be controlled with MatrixPanel_I2S_DMA::setLatBlanking(uint8_t v). v could be between 1 to 4, default is 1, larger values won't give any benefit other than reducing brightness.
An example:
dma_display->setLatBlanking(2);
Power, Power and Power!
Having a good power supply is CRITICAL, and it is highly recommended, for chains of LED Panels to have a 1000-2000uf capacitor soldered to the back of each LED Panel across the GND and VCC pins, otherwise you WILL run into issues with 'flashy' graphics whereby a large amount of LEDs are turned on and off in succession (due to current/power draw peaks and troughs).
-
Refer to this guide written for the rpi-rgb-led-matrix library for an explanation.
-
Refer to this example issue of what can go wrong with a poor power supply.
-
Refer to this comment in regards to certain panels not playing nice with voltages, and a 3.3volt signal that the ESP32 GPIO can only provide.
Inspiration
This project was inspired by:
- 'SmartMatrix': https://github.com/pixelmatix/SmartMatrix/tree/teensylc
- Sprite_TM's demo implementation here: https://www.esp32.com/viewtopic.php?f=17&t=3188
Cool uses of this library
There are a number of great looking LED graphical display projects which leverage this library, these include:
- 128x64 Morph Clock
- FFT Audio Visualisation
- Clock, GIF Animator and Audio Visualiser
- Aurora Audio Visualiser
- Big Visualisation
- Clockwise
Thank you!
- Brian Lough (youtube link) for providing code contributions, hardware and suggestions
- Vortigont for his game changing code contributions and performance optimisations
- Galaxy Man for donation of 1/16 scan panels to support the implemenation of led matrix panel chaining (virtual display) support
- Pipimaxi for the donation of a ESP32-S2 and Radu for the donation of an ESP32-S3 to enable support for ESP32 S2/S3's to be tested and implemented.
- Mark Donners ('The Electronic Engineer' on youtube) for the donation of a 1/8 scan panel to build and test working support of these led matrix panels!
- PaintYourDragon for the DMA logic for the ESP32-S3.
- And lots of others, let me know if I've missed you.
