Interfacing LED matrix displays with the MAX7219 driver [PDF datasheet] in Python using hardware SPI on the Raspberry Pi. The particular kit I bought can be acquired for a few pounds from http://www.banggood.com/MAX7219-Dot-Matrix-Module-DIY-Kit-SCM-Control-Module-For-Arduino-p-72178.html?currency=GBP
Ensure that the SPI kernel driver is enabled:
$ dmesg | grep spi
[ 3.769841] bcm2708_spi bcm2708_spi.0: master is unqueued, this is deprecated
[ 3.793364] bcm2708_spi bcm2708_spi.0: SPI Controller at 0x20204000 (irq 80)
And that the devices are successfully installed in /dev:
$ ls -l /dev/spi*
crw------- 1 root root 153, 0 Jan 1 1970 /dev/spidev0.0
crw------- 1 root root 153, 1 Jan 1 1970 /dev/spidev0.1
Follow the advice in the references below if the devices do not appear before proceeding.
The breakout board has an two headers to allow daisy-chaining:
| Board Pin | Name | Remarks | RPi Pin | RPi Function |
|---|---|---|---|---|
| 1 | VCC | +5V Power | 2 | 5V0 |
| 2 | GND | Ground | 6 | GND |
| 3 | DIN | Data In | 19 | GPIO 10 (MOSI) |
| 4 | CS | Chip Select | 24 | GPIO 8 (SPI CS0) |
| 5 | CLK | Clock | 23 | GPIO 11 (SPI CLK) |
The SPI-Py C-extension has already been included in the source directory, so to build and install:
For Raspian:
$ sudo apt-get install python-dev
$ sudo python setup.py install
For Arch Linux:
# pacman -Sy base-devel python2
# python2 setup.py install
Run the example code as follows:
$ sudo python examples/test.py
NOTE: By default, SPI is only accessible by root (hence using sudo above). Follow these
instructions to create an spi group, and adding your user to that group, so you don't have to
run as root: http://quick2wire.com/non-root-access-to-spi-on-the-pi
- http://hackaday.com/2013/01/06/hardware-spi-with-python-on-a-raspberry-pi/
- http://gammon.com.au/forum/?id=11516
- https://github.com/lthiery/SPI-Py
- http://louisthiery.com/spi-python-hardware-spi-for-raspi/
- http://www.brianhensley.net/2012/07/getting-spi-working-on-raspberry-pi.html
- http://raspi.tv/2013/8-x-8-led-array-driven-by-max7219-on-the-raspberry-pi-via-python
- http://quick2wire.com/non-root-access-to-spi-on-the-pi
Portions of this code are derived from https://github.com/lthiery/SPI-Py which includes the following license notice:
COPYRIGHT (C) 2012 Louis Thiery. All rights reserved. Further work by Connor Wolf.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License V2 as published by the Free Software Foundation.
LIABILITY This program is distributed for educational purposes only and is no way suitable for any particular application, especially commercial. There is no implied suitability so use at your own risk!