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HUB75

Example image Example 64x64 image

Library for controlling the cheap RGB matrix displays with the interface colloquially known as hub75 with embedded-graphics & embedded-hal impls in rust.

Main support for panels with a resolution of 64x32 (tested on panel "P3-(2121)64*32-16S-D10").

64x64 support when using features = ["size-64x64"] (tested on panel P3-(2121)64*64)

See rpi-rgb-led-matrix for hookup instructions.

Pinout:

Hub 75 interface

Problem Solving

  • It flickers

    Reduce the bits for the color output, call the output method more often or use a faster micro

  • Some colors aren't displayed correctly/not at all

    If one of the rgb components after gamma correction has less than the provided bits, it isn't shown at all. For example, when using 3 color bits, having a value less than 124 leads to nothing being shown (as it's then gamma corrected to 31, which is less than 1<<5).

Improving performance

There are many ways to further improve performance, even being able to achieve 8 bit color depth, unfortunately it doesn't seem possible with the current embedded-hal abstractions:

  • Use binary code modulation and adjust oe time with a one-shot timer

    See LED dimming using Binary Code Modulation for further explanations on how binary code modulation works.

  • Prerender the data, so shifting the data out is faster

    The idea is that the gpio state is precomputed and then just copied to the gpio output register. To do this, r1, r2, g1, g2, b1, b2 all need to be connected to the same port. Combined with binary code modulation, this will take more ram, but be much faster. The output loop can then be replaced with the dma, which will lead to greatly reduced cpu usage and very high refresh rates.

You might want to take a look at an mcu specific implementation that uses most of these things for inspiration.

License

Licensed under either of

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.