PWM RGB LED

Overview

This is a sample app which drives an RGB LED using the PWM API.

There are three single-color component LEDs in an RGB LED. Each component LED is driven by a PWM port where the pulse width is changed from zero to the period indicated in Devicetree. Such period should be fast enough to be above the flicker fusion threshold (the minimum flicker rate where the LED is perceived as being steady). The sample causes each LED component to step from dark to max brightness. Three for loops (one for each component LED) generate a gradual range of color changes from the RGB LED, and the sample repeats forever.

Requirements

The board must have red, green, and blue LEDs connected via PWM output channels.

The LED PWM channels must be configured using the following devicetree aliases, usually in the BOARD.dts file:

red-pwm-led
green-pwm-led
blue-pwm-led

You will see at least one of these errors if you try to build this sample for an unsupported board:

Unsupported board: red-pwm-led devicetree alias is not defined
Unsupported board: green-pwm-led devicetree alias is not defined
Unsupported board: blue-pwm-led devicetree alias is not defined

See boards/arm/hexiwear_k64/hexiwear_k64.dts for an example BOARD.dts file which supports this sample.

Wiring

No additional wiring is necessary if the required devicetree aliases refer to hardware that is already connected to LEDs on the board.

Otherwise, LEDs should be connected to the appropriate PWM channels.

Building and Running

For example, to build and flash this board for Hexiwear:

west build -b hexiwear_k64 samples/basic/rgb_led
west flash

Change hexiwear_k64 appropriately for other supported boards.