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Controlling RGB LED display on Raspberry Pi GPIO via PixelPusher protocol

Example video

Code is (c) Henner Zeller [email protected], license: GNU General Public License, Version 3.0

For details of the RGB Matrix library used and how to connect, see the github over at Raspberry Pi RGB Matrix.

Compiling

Clone with --recursive to get the RGB matrix submodule when cloning this repository:

git clone --recursive https://github.com/hzeller/rpi-matrix-pixelpusher.git

(If you did a git pull to get the latest state, also make sure to get the latest matrix code: type git submodule update).

Wiring

For wiring, please have a look at the library documentation.

NOTE The wiring changed recently, so if you have some pixel pusher wiring from before September 2015, either compile using the 'classic pinout'

DEFINES+="-DRGB_CLASSIC_PINOUT" make

.. or actually consider changing the wiring, as it reduces potential flickering.

Running

Simply run the program as root (which is needed to access the GPIO pins).

 $ make
 $ sudo ./pixel-push

These are the available options

usage: ./pixel-push <options>
Options:
        -r <rows>     : Display rows. 16 for 16x32, 32 for 32x32. Default: 32
        -c <chained>  : Daisy-chained boards. Default: 1.
        -P <parallel> : For Plus-models or RPi2: parallel chains. 1..3.
        -L            : 'Large' display, composed out of 4 times 32x32
        -p <pwm-bits> : Bits used for PWM. Something between 1..11
        -a <artnet-universe,artnet-channel>: if used with artnet. Default 0,0
        -i <iface>    : network interface, such as eth0, wlan0. Default eth0
        -u <udp-size> : Max UDP data/packet (default 1460)
                        Best use the maximum that works with your network (up to 65507).
        -d            : run as daemon. Use this when starting in /etc/init.d

This will advertise itself as a PixelPusher http://heroicrobotics.boards.net/board/5/pixelpusher device on the network. Number of 'strips' will be number of rows, so 16 or 32 multiplied by the parallel panels (1 .. 3). In the case of the 'Large' (Option -L) display, this is 64. The strip-length is 32 * chained (option -c) (64 for the -L display). For details of -P and -c refer to the library documentation.

Network UDP packet size

The -u parameter specifies the size of the allowed UDP packets. Some network switches don't like this large packets so the default is a conservative 1460 here. But since we have a lot of pixels, using the highest number possible is desirable so ideally we can transmit a full frame-buffer with one packet (use something like 65507 here):

 sudo ./pixel-push -u 65507

Even if the network supports it, sometimes sending devices limit the packet size (e.g. iOS, 8192 seems to be the limit of packets to send) so we have to change:

 sudo ./pixel-push -u 8192

Controlling Software

You can control these for instance with the Processing framework http://processing.org/. The processing framework already has a contrib library section that allows you to select PixelPusher supporting libs.

Another software supporting the PixelPusher support is L.E.D. Lab http://www.ledlabs.co/

Artnet / sACN

If you use the artnet bridge, you can specify the artnet-universe and the artnet-channel with the -a option:

sudo ./pixel-push -a1,1

Large Display

For the 'Large' display (option -L), we are using four boards are daisy-chained 'around the corner', see beginning of the video. This is an example how to compose more complex and larger displays out of smaller ones. See source for details and if you want to modify things.

Chaining multiple displays

If you have a Raspberry Pi 2, consider assembling a display using parallel chains.