MAX7219 LED Matrix with Arduino: Wiring and Library Guide
Let’s find out how to use the MAX7219 to drive an LED matrix. Wiring, Arduino libraries and sketches will guide us through building custom graphic and numeric displays.
An LED matrix display is one of the most fascinating components for anyone starting to experiment with Arduino: with a small square module we can bring to life numbers, letters, symbols and animations that immediately catch the eye. The problem? An 8×8 matrix means no fewer than 64 LEDs to control individually: an almost impossible task without dedicated support. That is where the MAX7219 chip comes in, an IC designed specifically to simplify the management of matrix and 7-segment displays, reducing the connection to the Arduino board to just a few pins. In this article we will see how to connect the MAX7219 to an 8×8 matrix, how to use the ready-made modules available on the market and how to program everything with the LedControl library.
The MAX7219
The MAX7219 chip has 24 pins. The 8×8 display (Fig. 1) is connected so that the rows are linked to the DIG pins and the columns to the SEG pins of the MAX7219.
Brightness is varied in software after setting the maximum current with an external resistor connected to the Iset pin. Three pins are dedicated to communication with the control board: DIN (to transfer data from the board to the chip), CS (for device selection) and CLK (for the data clock). A further pin, DOUT, is used to connect the DIN of the next chip, in case you want to chain several LED matrices together (for example to build scrolling text).
The complete schematic of the connection between the chip and the display is shown in Fig. 2, with particular emphasis on the links to the Arduino board and to a second chip. Using the MAX7219 is made even simpler by the availability on the market of modules (such as those in Fig. 3) that integrate both the chip and the LED matrix, along with the relevant wiring.
Using a module reduces the wiring to just the connections between the module and the Arduino board, and between modules possibly arranged in a chain. Each module has 5 input pins (VCC, GND, DIN, CS/LOAD and CLK, to be connected to a board such as the Arduino UNO R3) and 5 output pins (VCC, GND, DOUT, CS and CLK, for any subsequent modules in the chain). The Arduino UNO R3 board can be replaced by the more recent Arduino UNO R4 versions, available in the Minima and WIFI models, both fully compatible electrically and in software with the previous R3. Both versions keep the same pin layout and are compatible with most shields and libraries already developed for the R3.
Programming with Arduino
Several libraries make programming the MAX7219 easier; among them, in particular, the LedControl library, which is very widespread and simple to use.
The basic commands are as follows:
#include “LedControl.h” LedControl LC=LedControl (DIN, CLK, CS, number_of_modules)
An object of the LedControl class is created, to which an identifying name is assigned (for example, LC). The DIN, CLK and CS parameters will be replaced with the numbers of the Arduino pins (for example: 2, 4, 3) to which the respective signals are connected.
LC.SHUT (module_number, 0/1)
Enables or disables the chip. The value 0 makes it operational, while 1 puts it in standby. On power-up, the chip is in standby mode by default. The module_number parameter identifies the module in a serial chain, numbered starting from 0.
lc.setIntensity (module_number, intensity)
Adjusts the brightness of the LEDs, with a value between 0 (minimum) and 15 (maximum). The value 0 does not turn the LEDs completely off; to do that, you need to use LC.Shutdown(module_number, 1).
lc.clearDisplay (module_number)
Turns off all the LEDs of the specified module, clearing the displayed content.
lc.setLed (module_number, row_number, column_number, state)
Turns a single LED on or off. row_number and column_number indicate the position of the LED (numbered from 0 to 7). state = true (or 1) turns the LED on, false (or 0) turns it off. Rows are numbered from 0 (top) to 7 (bottom), columns from 0 (left) to 7 (right). For example, the top-left LED occupies position (0, 0), the bottom-right one (7, 7).
lc.setRow (module_number, row_number, byte)
Lets you turn all the LEDs of a row on or off, specifying their state with a binary byte. For example, to turn on the first four LEDs of a row you use: B11110000.
lc.setColumn (module_number, column_number, byte)
Works in a similar way to setRow, but acts on a column. The byte defines which LEDs to turn on or off in the specified column. Let’s now look at some practical examples of use.
Example 1
The first sketch, shown in Listing 1, is meant to display the 8 rows in sequence, one at a time, starting from the top; then the 8 columns, one at a time, starting from the left; then the 8 rows starting from the bottom; then the 8 columns starting from the right. Finally, all the LEDs are turned on gradually in pairs of rows, starting from the two middle rows and following the order: 4-5, 3-6, 2-7, 1-8. In this last phase, the lighting happens at low intensity, with brightness varying progressively from 10 to 2.
Example 2
The purpose of this sketch (Listing 2) is to gradually light up the LEDs of the matrix rows starting from the bottom, as a consequence of a voltage varying between 0 V and 5 V set by a potentiometer connected to pin A5; the comments inside the sketch describe how the gradual lighting works.
Using arrays
The goals of the two previous examples can be achieved in a similar way using arrays. One approach is to define the row structure inside an array of bytes (for example in binary): with 8 elements of 8 bits you describe the LED states of the whole display. The first cell of the array corresponds to the state of the eight LEDs of row 0 (from left to right), the second to that of row 1, and so on up to row 7.
If, for example, you want to turn off all the LEDs of the first four rows and turn on those of the last four, you can use the following array:
byte array [8]={B00000000,B00000000,B00000000,B00000000,B11111111,B11111111,B11111111,B11111111};
To display it on the screen you can proceed using the following code:
for (row=0; row<8; row++) {lc.setRow(0,row,array[row]);}delay (3000);
An editor that lets you obtain the binary codes of the most commonly used symbols more quickly is available at the following link: https://xantorohara.github.io/led-matrix-editor
Example 3
The purpose of this sketch (Listing 3) is to display in sequence all the numbers between 0 and 9 using 10 arrays that define the numbers and 10 for loops that call them up.
Example 4
The purpose of this sketch (Listing 4) is to show when certain temperature and humidity thresholds (set in the program) are exceeded, as shown in Fig. 4. In the left half of the display (columns 0-1-2) the temperature data is shown, while in the right half (columns 5-6-7) the humidity data is shown. In the upper part of the display (rows 0-1-2) the letters T and U appear; in the lower part (rows 4-5-6-7) the lighting of the LEDs indicates that a given temperature or humidity threshold has been reached.
Four thresholds are defined in the code: as the value increases, the corresponding rows light up progressively, starting from row 7. Temperature and humidity are measured with the HTS221 sensor, integrated into the STMicroelectronics IKS01A3 expansion board (Fig. 5), mounted on the Arduino UNO board. Those who do not have this board can use other sensors, such as the DHT11 or DHT22, adapting the data acquisition part of the software accordingly.
Conclusion
The MAX7219 makes LED matrix management accessible to everyone, turning a complex task into a fun, stimulating and creative experience. Once you understand the basic commands, the possibilities become practically endless: custom scrolling text, small animations, graphic indicators, simple light games and real-time data visualisations. All that is left is to experiment, adapt the sketches provided and let yourself be inspired: with a simple LED matrix your Arduino project can finally “speak with light” in a clear, dynamic and original way.
Related products
The post MAX7219 LED Matrix with Arduino: Wiring and Library Guide appeared first on Open Electronics.
Each Pixie module is designed to host two gorgeous little 
In this case, you’ll be losing all of your nickels to an Arduino Pro Mini. The handle is an upgrade to an earlier slot machine project that uses three 8×8 matrices and a custom driver board. When the spring-loaded handle is pulled, it strikes a micro switch to spins the reels and then snaps back into place. Between each pull, the current score is displayed across the matrix. There’s even a piezo buzzer for victory squawks. We only wish the button under the handle were of the clickier variety, just for the feels. Check out the short demo video after the break.
