rpi_ws281x-sys

Bindings to rpi_ws281x

Sources from 1ba8e385708fb7802b09c0177a7ea4293948e25c

GPIO Usage:

The GPIOs that can be used are limited by the hardware of the Pi and will vary based on the method used to drive them (PWM, PCM or SPI). Beware that the GPIO numbers are not the same as the physical pin numbers on the header.

PWM:

        PWM0, which can be set to use GPIOs 12, 18, 40, and 52.
        Only 12 (pin 32) and 18 (pin 12) are available on the B+/2B/3B

        PWM1 which can be set to use GPIOs 13, 19, 41, 45 and 53.
        Only 13 is available on the B+/2B/PiZero/3B, on pin 33

PCM:

        PCM_DOUT, which can be set to use GPIOs 21 and 31.
        Only 21 is available on the B+/2B/PiZero/3B, on pin 40.

SPI:

        SPI0-MOSI is available on GPIOs 10 and 38.
        Only GPIO 10 is available on all models.
        See also note for RPi 3 below.

Power and voltage requirements

WS281X LEDs are generally driven at 5V. Depending on your actual LED model and data line length you might be able to successfully drive the data input with 3.3V. However in the general case you probably want to use a level shifter to convert from the Raspberry Pi GPIO/PWM to 5V.

It is also possible to run the LEDs from a 3.3V - 3.6V power source, and connect the GPIO directly at a cost of brightness, but this isn't recommended.

Know what you're doing with the hardware and electricity. I take no responsibility for damage, harm, or mistakes.

Important warning about DMA channels

You must make sure that the DMA channel you choose to use for the LEDs is not already in use by the operating system.

For example, using DMA channel 5 will cause filesystem corruption on the Raspberry Pi 3 Model B.

The default DMA channel (10) should be safe for the Raspberry Pi 3 Model B, but this may change in future software releases.

Limitations:

PWM

Since this library and the onboard Raspberry Pi audio both use the PWM, they cannot be used together. You will need to blacklist the Broadcom audio kernel module by creating a file /etc/modprobe.d/snd-blacklist.conf with

blacklist snd_bcm2835

If the audio device is still loading after blacklisting, you may also need to comment it out in the /etc/modules file.

On headless systems you may also need to force audio through hdmi Edit config.txt and add:

hdmi_force_hotplug=1
hdmi_force_edid_audio=1

A reboot is required for this change to take effect

Some distributions use audio by default, even if nothing is being played. If audio is needed, you can use a USB audio device instead.

PCM

When using PCM you cannot use digital audio devices which use I2S since I2S uses the PCM hardware, but you can use analog audio.

SPI

When using SPI the led string is the only device which can be connected to the SPI bus. Both digital (I2S/PCM) and analog (PWM) audio can be used.

Many distributions have a maximum SPI transfer of 4096 bytes. This can be changed in /boot/cmdline.txt by appending

    spidev.bufsiz=32768

On an RPi 3 you have to change the GPU core frequency to 250 MHz, otherwise the SPI clock has the wrong frequency.

Do this by adding the following line to /boot/config.txt and reboot:

    core_freq=250

On an RPi 4 you must set a fixed frequency to avoid the idle CPU scaling changing the SPI frequency and breaking the ws281x timings:

Do this by adding the following lines to /boot/config.txt and reboot:

    core_freq=500
    core_freq_min=500

SPI requires you to be in the gpio group if you wish to control your LEDs without root.