.. zephyr:code-sample:: led-ws2812
:name: WS2812 LED strip
:relevant-api: led_strip_interface
Control an LED strip using a WS2812 (or compatible) driver chip.
Overview
********
This sample application demonstrates basic usage of the WS2812 LED
strip driver, for controlling LED strips using WS2812, WS2812b,
SK6812, Everlight B1414 and compatible driver chips.
Requirements
************
.. _NeoPixel Ring 12 from AdaFruit: https://www.adafruit.com/product/1643
.. _74AHCT125: https://cdn-shop.adafruit.com/datasheets/74AHC125.pdf
- LED strip using WS2812 or compatible, such as the `NeoPixel Ring 12
from AdaFruit`_.
- Note that 5V communications may require a level translator, such as the
`74AHCT125`_.
- LED power strip supply. It's fine to power the LED strip off of your board's
IO voltage level even if that's below 5V; the LEDs will simply be dimmer in
this case.
Wiring
******
#. Ensure your Zephyr board, and the LED strip share a common ground.
#. Connect the LED strip control pin (either I2S SDOUT, SPI MOSI or GPIO) from
your board to the data input pin of the first WS2812 IC in the strip.
#. Power the LED strip at an I/O level compatible with the control pin signals.
Wiring on a thingy52
********************
The thingy52 has integrated NMOS transistors, that can be used instead of a level shifter.
The I2S driver supports inverting the output to suit this scheme, using the ``out-active-low`` dts
property. See the overlay file
:zephyr_file:`samples/drivers/led_ws2812/boards/thingy52_nrf52832.overlay` for more detail.
Building and Running
*********************
.. _blog post on WS2812 timing: https://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/
This sample's source directory is :zephyr_file:`samples/drivers/led_ws2812/`.
To make sure the sample is set up properly for building, you must:
- select the correct WS2812 driver backend for your SoC. This currently should
be :kconfig:option:`CONFIG_WS2812_STRIP_SPI` unless you are using an nRF51 SoC, in
which case it will be :kconfig:option:`CONFIG_WS2812_STRIP_GPIO`.
For the nRF52832, the SPI peripheral might output some garbage at the end of
transmissions, and that might confuse older WS2812 strips. Use the I2S driver
in those cases.
- create a ``led-strip`` :ref:`devicetree alias <dt-alias-chosen>`, which refers
to a node in your :ref:`devicetree <dt-guide>` with a
``worldsemi,ws2812-i2s``, ``worldsemi,ws2812-spi`` or
``worldsemi,ws2812-gpio`` compatible. The node must be properly configured for
the driver backend (I2S, SPI or GPIO) and daisy chain length (number of WS2812
chips).
For example devicetree configurations for each compatible, see
:zephyr_file:`samples/drivers/led_ws2812/boards/thingy52_nrf52832.overlay`,
:zephyr_file:`samples/drivers/led_ws2812/boards/nrf52dk_nrf52832.overlay` and
:zephyr_file:`samples/drivers/led_ws2812/boards/nrf51dk_nrf51422.overlay`.
Some boards are already supported out of the box; see the :file:`boards`
directory for this sample for details.
The sample updates the LED strip periodically. The update frequency can be
modified by changing the :kconfig:option:`CONFIG_SAMPLE_LED_UPDATE_DELAY`.
Then build and flash the application:
.. zephyr-app-commands::
:zephyr-app: samples/drivers/led_ws2812
:board: <board>
:goals: flash
:compact:
When you connect to your board's serial console, you should see the
following output:
.. code-block:: none
***** Booting Zephyr OS build v2.1.0-rc1-191-gd2466cdaf045 *****
[00:00:00.005,920] <inf> main: Found LED strip device WS2812
[00:00:00.005,950] <inf> main: Displaying pattern on strip
Supported drivers
*****************
This sample uses different drivers depending on the selected board:
I2S driver:
- thingy52_nrf52832
- nrf5340dk_nrf5340 (3.3V logic level, a logic level shifter may be required)
- should work for other boards featuring an nRF5340 host processor
SPI driver:
- mimxrt1050_evk
- mimxrt1050_evk_qspi
- nrf52dk_nrf52832
- nucleo_f070rb
- nucleo_g071rb
- nucleo_h743zi
- nucleo_l476rg
GPIO driver (cortex-M0 only):
- bbc_microbit
- nrf51dk_nrf51422
References
**********
- `RGB LED strips: an overview <http://nut-bolt.nl/2012/rgb-led-strips/>`_
- `74AHCT125 datasheet
<https://cdn-shop.adafruit.com/datasheets/74AHC125.pdf>`_
- An excellent `blog post on WS2812 timing`_.
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