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I have a MAX7219 dot matrix module (this one) that I'm trying to run on my Raspberry Pi 4 with the Luma.LED library. Its documentation suggests the following GPIOs/pins be used:

Board Pin Name Remarks RPi Pin RPi Function
1 VCC +5V Power 2 5V
2 GND Ground 6 GND
3 DIN Data In 19 GPIO 10 (MOSI)
4 CS Chip Select 24 GPIO 8 (SPI CE0)
5 CLK Clock 23 GPIO 11 (SPI CLK)

However, mine is connected as follows, because I'm also running an epaper on the Raspberry Pi that needs some of the pins:

Board Pin Name Remarks RPi Pin RPi Functions
1 VCC +5V Power 4 5V
2 GND Ground 14 GND
3 DIN Data In 38 GPIO 20 (DIN/MOSI6/MOSI1/GPCLK0)
4 CS Chip Select 12 GPIO 18 (CLK/CE0N6/CE0N1/PWM0)
5 CLK Clock 40 GPIO 21 (SCLK6/SCLK1/GPCLK1)

I had the dot matrix module working in this configuration before but after a reinstall, I can't get it to work anymore. I have a vague memory I needed to change a config file somewhere to make the module work with the different pin, but cannot remember which one or how. Possibly something in /boot/config.txt?

What I've tried:

  • Made sure SPI is enabled via sudo raspi-config > 3-Interface options > I4-SPI.

1 Answer 1

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After all of this, I finally figured it out thanks to this page: https://pinout.xyz/pinout/spi#

Just needed to add the following line to /boot/config.txt:

dtoverlay=spi1-3cs

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