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Max7219 (LED Matrix driver)

You can use Max7219.cs in your project to drive a Max7219 based Dot Matrix Module. Write to a 8x8 Dot Matrix Module demonstrates a concrete example using this class.

The following fritzing diagram illustrates one way to wire up the Max7219, with a Raspberry Pi.

Raspberry Pi Breadboard diagram

Usage

You can use .NET Core to drive MAX7219 based Dot Matrix Modules.

These Modules can be cascaded to get a bigger matrix.

Accessing the MAX7219 via SPI

The Raspberry Pi has support for SPI. You need to enable the SPI interface on the Raspberry Pi since it is not enabled by default.

var connectionSettings = new SpiConnectionSettings(0, 0)
{
    ClockFrequency = 10_000_000,
    Mode = SpiMode.Mode0
};
var spi = SpiDevice.Create(connectionSettings);
var devices = new Max7219(spi, cascadedDevices: 4);

The following pin layout:

  • MAX7219 VCC to RPi 5V, Pin 2
  • MAX7219 GND to RPi GND, Pin 6
  • MAX7219 DIN to RPi GPIO 10 (MOSI), Pin 10
  • MAX7219 CS to RPi GPIO 8 (SPI CSO), Pin 8
  • MAX7219 CLK to RPi GPIO11 (SPI CLK), Pin 11

Writing to the Matrix

Write a smiley to devices buffer.

var smiley = new byte[] { 
    0b00111100, 
    0b01000010, 
    0b10100101, 
    0b10000001, 
    0b10100101, 
    0b10011001, 
    0b01000010, 
    0b00111100 
    };
for (var i = 0; i < devices.CascadedDevices; i++)
{
    for (var digit = 0; digit < 8; digit++)
    {
        devices[i, digit] = smiley[digit];
    }
}

Flush the smiley to the devices using a different rotation each iteration.

foreach (RotationType rotation in Enum.GetValues(typeof(RotationType)))
{
    devices.Rotation = rotation;
    devices.Flush();
    Thread.Sleep(1000);
}

Write "Hello World from MAX7219!" to the Matrix using different fonts each iteration.

devices.Init();
devices.Rotation = RotationType.Left;
var writer = new MatrixGraphics(devices, Fonts.CP437);
foreach (var font in new[]{Fonts.CP437, Fonts.LCD, Fonts.Sinclair, Fonts.Tiny, Fonts.CyrillicUkrainian}) {
    writer.Font = font;
    writer.ShowMessage("Hello World from MAX7219!", alwaysScroll: true);
}

How to Cross Compile and Run this sample

This example can also be cross-compiled on another machine and then executed on the Raspberry PI. This can be achieved with enabled SSH access to the RaspPi as follows.

  • Publish project on the development machine
cd ~/Projects/iot/src/devices/Max7219/samples
dotnet publish -c Release -r linux-arm
  • Synchronize published folder to the RaspPi via rsync over ssh
rsync -avz -e 'ssh' bin/Release/netcoreapp3.1/linux-arm/publish/  pi@192.168.1.192:/home/pi/max-sample/
  • Execute the program on the RaspPi or remote via SSH
ssh pi@192.168.1.192
cd /home/pi/max-sample/
./Max7219.sample