LED Strips and Digispark (no sp)

[jonwa]

I was looking forward to controlling my adafruit WS2081 led strips with the new digispark chip. They are so small, just about the same width as the led strip itself.
However, the adafruit WS2801 library a dependency on SP, which appears to be missing from the digispark.
There's comments out there in the blog world about removing references to SP and letting it rely on "bitbanging", whatever that means.

I can code in processing, but C? not so much. What's bitbanging and/or what might it take to end up with a version of the WS2801 that can work with digispark?

Thanks

[pburgess]

"Bitbanging" refers to doing in software something that's normally handled by an on-chip peripheral function. SPI (Serial Peripheral Interface) is one such feature that's present on ATmega chips but not the ATtiny used on the Digispark.

The Adafruit_WS2801 library can operate in either mode (bitbang or hardware SPI)...but as written, still requires hardware support in order to compile, even if it's not used.

The shortest route to getting something working on the Digispark would be to make a fork of the library and strip out all the hardware SPI-specific functions and logic, so only the bitbang cases remain. Adapting the existing code to compile for either case is non-trivial (it might eventually happen, like when Gemma ships, but at this moment there's been no use case and it isn't really a priority).

[jonwa]

Gemma?

[pburgess]

It's a small ATtiny-based wearable board from Adafruit (like Flora, but dinkier). Currently a work-in-progress with no release date set...which is why simply tearing out the SPI-specific logic in the library might be a quicker and easier approach.

[MauiMaker]

We found a digispark compatible library on GitHub
https://github.com/nsthorat/LPD8806-bitbang-only
Just tested it and it worked well for 10-20 LED strips
More than that and the digispark gets hot.