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Yet Another WS2812/SK6812 Driver — Parallax Forums

Yet Another WS2812/SK6812 Driver

Ding-BattyDing-Batty Posts: 302
in Propeller 1

Just uploaded to the ObEx: Yet Another WS2812/SK6812 driver
https://obex.parallax.com/obex/yet-another-ws2812-sk6812-driver/

This driver manages one or two strings of WS2812-like addressable RGB LEDs. It handles mapping the color layout in memory to the color output order of different type of LEDs; it handles mapping the timing requirements of the LEDs based on the system clock speed; it is fairly flexible in how it is configured and controlled.

Features:

  • Controls one or two strings of LEDs
  • Normal or inverted output (for use with an inverting buffer/isolator/level-shifter).
  • Clock cycle accurate timings in all cases (maximum 1/2 system clock error).
  • Handles either three or four color LED string (with limitations, see below).

  • Flexible configuration:

    • Predefined configurations for:
    • WS2811, WS2812, WS2812B, WS2813, WS2815
    • SK6812RGB, SK6812RGBW
    • SM16703
    • User defined configurations:
    • Should work for all LEDs that use pulse-width encoding of 0/1, with fixed time per bit.
    • Timing specified in nanoseconds.
    • The two strings can be different types (with a few limitations)
    • The two strings can have different lengths
    • The two strings can use different color byte order.
    • The two strings can have normal/inverted output independently
    • Flexible memory layout for colors per LED, and iteration over the memory locations for the individual LEDs in a chain.

  • Should work for all clock speeds from 48 MHz up for a typical RGB LED that uses a 1.25 us bit time.

    • It might work at 40 MHz, which would use a bit time of 1.5 us, which is 20% too long, but might fall within the acceptable tolerance for many LED types.

  • Periodic refresh (e.g. 100 Hz), or on-demand refresh (refresh-and-pause)

Limitations:

  • Typically requires a system clock of 48 MHz or higher.
  • The two strings must have the same overall bit timing (but the zero and one times per bit may be different), e.g. 1.25 us as used by WS2812-type LEDs)
  • The two strings must have the same number of colors, either 3 or 4. Four colors are used for RGBW LEDs.
  • Color values of 8 bits are sent out high order bit first.
  • The two strings use the same update frequency, because they are updated in parallel. The shorter string will not get "extra" channels of output.

  • For the most flexibility, the memory layout of the colors for each LED in the string should be in a single LONG. There is a demonstration of using three bytes for a string of RGB LEDs, but there is little
    flexibility of layout, and the string myst be a multiple of 4 LEDs in length.

  • Currently, the number and types of LEDs in the strings is fixed at initialization. That might change in the future.

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