I've tested the whole idea on display which consist of 8 LED Modules in horizontal and 3 in vertical position. This gives us 24 modules that contain 1536 LEDs (88 * 38).
Hardware
First, let's start with the controller, actually, any Arduino will work, I've used Mega due to the large number of digital output pins. You could also use Nano with a shift register and alter the way of addressing Select Slave lines in Display::send(...).You will need an extra power supply for driving LEDs - assuming that you will use more than one LED Matrix.
Driving single LED Matrix Module
I've used the MAX7219 and 788BS LED Matrix, this is the one with a common anode. The schematic below illustrates the wiring of LEDs, MAX and Arduino:
This one is equivalent, but instead of single LEDs we have PIN layout of LED Module:
Connecting all LED Matrix together
In the previous chapter, we've seen how to connect a single LED Module with an MAX chip. Now we will connect multiple LED Modules together into one large display. Below is the physical display that I've used for testing and examples. Each LED Module has label indicating its position and Select Slave line.
Each 3-PIN connector on the schematic above symbolizes one module described in the previous chapter (LED Matrix + MAX72xx), now we've connected all those modules together.
All MAX722xx chips share common MOSI and SCK lines, MISO is not used, and each chip occupies a separate Slave Select line.
The position of LED Matrix on the schematic above directly corresponds to their location on the physical display that I've used for testing. Additionally, each module has a description indicating its position and Select Slave line, so for example: (2,1) SS: 35 gives us a second module on the third row (counting from zero) and PIN:35 on Arduino for the Select Slave line.
Software
Compiling
We are using standard Arduino libraries, which are already available, the only exception is ArdLog. You have to import this LIB into your IDE. This basically means that you have to download the right release: https://github.com/maciejmiklas/ArdLog/releases/tag/v1.0.0 and unzip it into a folder, where you usually place external libraries. In the case of standard Arduino IDE on Mac, it's ~/Documents/Arduino/libraries. In the end you should have the following structure:$ pwd ~/Documents/Arduino/libraries/ArdLog $ ls ArdLog.cpp ArdLog.h LICENSE README.md
Communication with MAX72xxx
We are using the standard SPI library and Select Slave line on the MAX chip for addressing. MAX is configured in LED Matrix mode - so there is nothing special. The setup method can be found in Display::setup()Setting things up
The main class of our interest will be the Display - it's responsible for the setup of MAX chips and provides API for painting.Before we start painting, it's necessary to set things up. The code below creates a 2D array containing Select Slave lines and initializes the display. The display consists of 3 rows, each with 8 LED Modules. You can choose any responsible size, but I will stick to this one.
The layout of the mentioned 2D array corresponds to the physical display: each LED Module has a dedicated MAX chip, and each chip has a dedicated Select Slave line. The first dimension of our array indicates the physical row on display, the second dimension indicates LED Module within this row, and the value itself contains the PIN number for the Select Slave line.
#include <Display.h> Display *disp; /** * Orientation of LED Kits (8x8 LED matrix) on display that I've used for testing. * The numbers are indicating Select Slave line of MAX7219. * 48, 46, 49, 47, 45, 43, 41, 39 * 36, 34, 32, 30, 28, 26, 24, 22 * 37, 35, 33, 31, 29, 27, 25, 23 */ ss_t **ss; ss_t** createSS() { ss_t **ss = alloc2DArray8(3, 8); // first row ss[0][0] = 48; ss[0][1] = 46; ss[0][2] = 49; ss[0][3] = 47; ss[0][4] = 45; ss[0][5] = 43; ss[0][6] = 41; ss[0][7] = 39; // second row ss[1][0] = 36; ss[1][1] = 34; ss[1][2] = 32; ss[1][3] = 30; ss[1][4] = 28; ss[1][5] = 26; ss[1][6] = 24; ss[1][7] = 22; // third row ss[2][0] = 37; ss[2][1] = 35; ss[2][2] = 33; ss[2][3] = 31; ss[2][4] = 29; ss[2][5] = 27; ss[2][6] = 25; ss[2][7] = 23; return ss; } void setup() { util_setup(); log_setup(); ss = createSS(); // Test display consist of 8x3 LED Modules (3 rows, each one 8 Modules) disp = new Display(8, 3, ss); disp->setup(); }
There is one more method worth mentioning: log_setup(). The whole project has quite a precise logger - so that you can see what is actually happening. By default, it's disabled, in order to enable it to check out its documentation: https://github.com/maciejmiklas/ArdLog
Painting on the display
The display consists of a few LED Modules, but from an API perspective, they are connected together into one continuous canvas. You can place on this canvas bitmap any position given by such coordinates: (0,0) -----------------------------> (x)
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The paint method has the following syntax: paint(pixel_t x, pixel_t y, pixel_t width, pixel_t height, uint8_t data).
It allows you to paint a bitmap on given coordinates with limited width and height. So you can, for example, paint a bitmap on (3,4) that has 25x3 pixels. It might be larger than the actual display size - in this case, it will get trimmed.
This is obvious and simple, but there is one catch - you must provide the right data. This is a 2D array, where the first dimension indicates the vertical and the second horizontal position on the display. Technically speaking, data is a flat array of pointers, and each pointer points to an array that represents one horizontal line on the display.
Moving over the first dimension of data traverses over lines of the display. The second data dimension represents horizontal pixels within a single line; each byte represents 8 pixels. Since our display consists of simple LEDs, they can be either on or off, so each pixel is not represented by one byte but by one bit. In order to cover 16 pixels in a horizontal position, we need two bytes, 24 pixels require 3 bytes, and so on.
For example, to fully cover a display consisting of 8x3 LED kits (one used in our examples), we would need data[3][8]. Usually, you will take an array small enough to fit your bitmap and not one that will cover up the whole display.
The paint(...) method updates the internal buffer, in order to send the content of this buffer to MAX chips, you have to call flush(). The idea behind this is to allow you to shift a few bitmaps into the display and then paint the result. You can program a few independent routines that will update different display parts and flush all changes at once.
Communication with MAX chips is not very fast, and sending the content of the whole display with every flush() is time-consuming. You can speed up this process by enabling double buffering (set DEOUBLE_BUFFER in Display.h to true). In this case, flush() method will send only bytes that have changed, so you can call flush() with every loop and not worry about losing performance. The only drawback is increased usage of RAM: we are creating 2D array that allocates 8 bytes per each LED Kit plus a few pointers that are usually required to maintain arrays.
2D arrays in this project have reduced memory footprint because to create a dynamic 2D array, we are creating a single continuous array with a calculated offset (see: alloc2DArray8(....) in DisplayUtil.h).
Examples
Requires Libs
Examples use ArdLog, so you must import this lib into Arduino IDE. Here are the instructions: https://github.com/maciejmiklas/ArdLogSimple Bitmap
In this example, we will display a simple static bitmap with 8x8 pixels:
First, we have to initialize the display, as we have done in the above chapter Setting things up. Next, we have to create data that can hold our bitmap - it will have 8x2 bytes. This gives us up to 8 lines and 16 horizontal pixels. But the size of our bitmap is 9x8 pixels (width x height), which will also be the size of the painted rectangle. It should be as small as possible so you can place another bitmap next to it.
The display will obviously only paint the rectangle given by width/height and not the whole data array. This is normal that a data array can hold more pixels than the accrual size of our bitmap because size of the data is a multiplication o 8, and the bitmap is not necessary.
void setup() { util_setup(); log_setup(); ss = createSS(); disp = new Display(8, 3, ss); disp->setup(); data = alloc2DArray8(8, 2); data[0][0] = B01100001; data[0][1] = B10000000; data[1][0] = B01100001; data[1][1] = B10000000; data[2][0] = B01100001; data[2][1] = B10000000; data[3][0] = B01100001; data[3][1] = B10000000; data[4][0] = B01100001; data[4][1] = B10000000; data[5][0] = B00110011; data[5][1] = B00000000; data[6][0] = B00011110; data[6][1] = B00000000; data[7][0] = B00001100; data[7][1] = B00000000; disp->paint(27, 9, 9, 8, data); } void loop() { util_cycle(); log_cycle(); // Paint method updates only internal buffer, in order to send data to // MAX chips you have to flush display. disp->flush(); delay(100000); }
Static Text
Now we will display static text, actually those are going to be two independent lines.
Here you can find an Arduino sketch containing the whole example: StaticText.
Your sketch needs a setup method, as we've already seen above (chapter: Setting things up), so we will not discuss it again.
In order to display text, you should use StaticText8x8.
The font is defined in Font8x8, each character has 8x8 pixels.
Your code could look like this one (plus initialization stuff from Setting things up):
StaticText8x8 *sta1; StaticText8x8 *sta2; void setup() { util_setup(); log_setup(); ss = createSS(); disp = new Display(8, 3, ss); disp->setup(); sta1 = new StaticText8x8(disp, 64); sta1->box(14, 2, "Hello"); sta2 = new StaticText8x8(disp, 64); sta2->box(5, 15, "World !"); } void loop() { util_cycle(); log_cycle(); disp->flush(); delay(100000); }
We have created two text areas, each one containing different text and being displayed under another.
Single Scrolling Text
This time we will display an area containing text that will scroll from left to right (the link below contains a youtube video).Display *disp; ScrollingText8x8 *message; const char *textMessage; void setup() { util_setup(); log_setup(); ss = createSS(); disp = new Display(8, 3, ss); disp->setup(); message = new ScrollingText8x8(disp, 48, 50, 5); message->init(); textMessage = "This is an example of multiple scorlling areas ;)"; message->scroll(8, 8, ScrollingText8x8::LOOP, textMessage); } void loop() { util_cycle(); log_cycle(); message->cycle(); disp->flush(); }
The initialization of the display is the same as in the examples above, so it's omitted here.
In order to display scrolling text, we are using ScrollingText8x8. In setup(), we are creating an instance of this class and calling method scroll(...). This part only initializes scrolling but does not play the animation itself. In order to play the animation, you have to call cycle() and flush() in the main loop, and you must not have any additional delays there, otherwise, you might get jagged animation.
During the creation of ScrollingText8x8 we have provided the speed of animation - actually, it's a delay of 50ms per frame. Now calling cycle() in the main loop will produce animation frames according to provided delay. When the time comes, the method cycle() will update the display, and finally, method flush() will send updated content to MAX chips.
The whole implementation of ScrollingText8x8 is nonblocking and consumes CPU only when something is to be done. Internally it's using a simple State Machine.
There is one last thing: you must keep the text used for animation in the global variable to avoid deletion. It's not being copied in the scroll() to avoid memory fragmentation.
Scrolling Text Mixed
This example is similar to the one above, but this time we will display several scrolling areas:Here is the sketch.
This code is similar to one with one scrolling area, but this time we have a few:
void setup() { util_setup(); log_setup(); ss = createSS(); disp = new Display(8, 3, ss); disp->setup(); uint8_t borderSpeed = 20; textUpDown = "* * * * * "; up = new ScrollingText8x8(disp, 64, borderSpeed, 1); up->init(); up->scroll(0, 0, ScrollingText8x8::CONTINOUS_LOOP, textUpDown); down = new ScrollingText8x8(disp, 64, borderSpeed, 2); down->init(); down->scroll(0, 16, ScrollingText8x8::CONTINOUS_LOOP, textUpDown); textLeftRight = "* "; left = new ScrollingText8x8(disp, 8, borderSpeed, 3); left->init(); left->scroll(0, 8, ScrollingText8x8::CONTINOUS_LOOP, textLeftRight); right = new ScrollingText8x8(disp, 8, borderSpeed, 4); right->init(); right->scroll(56, 8, ScrollingText8x8::CONTINOUS_LOOP, textLeftRight); message = new ScrollingText8x8(disp, 48, 50, 5); message->init(); textMessage = "This is an example of multiple scrolling areas ;)"; message->scroll(8, 8, ScrollingText8x8::LOOP, textMessage); } void loop() { util_cycle(); log_cycle(); up->cycle(); down->cycle(); right->cycle(); message->cycle(); left->cycle(); disp->flush(); }
We have created a few instances of ScrollingText8x8, each containing different text and positions on the display. In order to play an animation, you have to call cycle() on each instance, but you have to call only once flush(). Each call on cycle() will update its part of the display, and flush will send the changed display to MAX chips.
HELLO. if i want to use 8 led module with dis article , how power do i need?
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