Raspberry Pi

You can connect an array to a limited selection of pins on most Raspberry Pi boards. This support is provided by the rpi_ws281x library, see it on GitHub for details.

The LEDs supported by this interface usually run at 5V, but the Pi only outputs a maximum of 3.3V. While this may be enough to drive a small number of LEDs, it is highly recommended that you use some kind of buffer or level shifter when connecting them to GPIO pins.

Don’t forget to install the requirements

pip3 install -r requirements/led-rpi.txt

Paths

Some additional statistics are published when using this output mode.

Path	Description
`{array-id}/gpio`	The GPIO being used will be published here with `retained = True` when the array is started.
`{array-id}/chip`	The LED chip type will be published here with `retained = True` when the array is started.
`{array-id}/frequency`	The transmission frequency will be published here with `retained = True` when the array is started.
`{array-id}/invert`	The invert state will be published here with `retained = True` when the array is started.

Configuration

led:

  array_name:
    rpi:
      gpio:
      #chip: 'WS2812B'
      #frequency: 800
      #invert: false

Array Definition

The following additional options are added to array definitions when using this interface.

Option	Description
`gpio`	GPIO pin number. ONLY BCM/SOC NUMBERING IS SUPPORTED
`chip`	LED type, can be `WS2811`, `WS2812`, `WS2812B`, `SK6812`, or `SK6812W`. Optional, default `WS2812B`.
`frequency`	DO NOT CHANGE THIS UNLESS YOU KNOW WHAT YOU ARE DOING The clock frequency in kHz for transmitting data to the LEDs. Optional, default `800`.
`invert`	Invert the data signal to the LEDs, this is useful if you are using an inverting buffer. Optional, default `false`.

Output Selection

Note

The documentation for rpi_ws281x is not clear on this and I have not tested it, but it may be possible to use multiple interfaces at once.

SPI

The SPI interface is the safest way to control your LEDs using a Pi and the only one available on all models. Connect them to SPI0-MOSI (GPIO10) using a level shifter. When using the SPI interface to control your LEDs you cannot use it for anything else. Using SPI leaves the digital audio (I2S/PCM) and analog/PWM audio available.

To use SPI, the user running MQTTany needs to be a member of the gpio group.

You also need to increase the size of the SPI buffer and change the GPU core frequency. Add the following lines to /boot/config.txt and restart to apply these changes:

spidev.bufsiz=32768
core_freq=250

PWM

The hardware PWM on the Pi is the only interface with 2 outputs. In order to achieve the required timing it uses DMA and requires root privileges.

PWM0 is available on GPIO12 or GPIO18 and MQTTany uses DMA channel 10. It is present on the B+, 2B, 3B, and 3B+.
PWM1 is available on GPIO13 and MQTTany uses DMA channel 11. It is present on the B+, 2B, 3B, 3B+, and Zero.

The on board/analog audio also uses the PWM hardware, so you need to blacklist it by adding the following to /etc/modprobe.d/snd-blacklist.conf:

blacklist snd_bcm2835

On headless systems you may need to force the audio device to be the HDMI out. Add the following to /boot/config.txt and restart:

hdmi_force_hotplug=1
hdmi_force_edid_audio=1

PCM

The hardware PCM can also be used to control a single array of LEDs. It also uses DMA and requires root privileges.

PCM_DOUT is on GPIO21 and MQTTany uses DMA channel 13. It is present on the B+, 2B, 3B, 3B+, and Zero.

When using PCM you will not be able to use any digital/I2S audio devices, analog/PWM audio and the SPI interface are free for use though.