Lots of material out there on on using WS2811/2 LEDS for Christmas lights. A Raspberry Pi is a little overkill; a ESP8266 / NodeMCU running WLED will do you just fine. Reddit's r/led is filled with these projects, or check our DrZzs on YouTube who has a ton of detailed guidance.
On the other hand, if you were, like me, an early adopter of the Raspberry Pi you probably find your old Pi 1 is too slow to use for demanding applications these days. But doing a bit of bit banging and software or hardware SPI to control a strip of LEDs is well within a Pi 1's capability, and the Pi comes for free if you have one gathering dust.
Agreed, ESP8266/ESP32 is totally sufficient. Maybe if you wanted to run Xlights also off the same board it would make sense? I wouldn't bother. Dr. Zzs is selling a couple of pre-flashed boards that make the whole WLED set-up really easy (1).
Doesn't it depend on how many simultaneous strips you want to drive and the no. of leds, for large installations I think an FPGA probably makes more sense?
The signal to drive these LEDs isn't super complex and any simple MCU can bit bang generate it on a digital output. The bigger limitation is usually memory if you're buffering all the color values to animate them, and to a lesser extent raw processing speed to do more and more complex animations and math.
Yeah the ws2811 signal is only around 800kHz or so from what I recall, I was thinking to generate say 8+ simultaneous signals from a framebuffer would be more difficult on an MCU than an FPGA, which can do that trivially. But I think some strips like APA102 can be driven at frequencies in the order of MHz using an SPI type protocol (just saw someone claiming 35MHz on the wire)
No, sadly I stopped really working on the whole thing. I built a neat IDE, a mobile app, firmware, it was really sweet. But it's a hard market to break into. If you're looking for Christmas tree lights for next year (or just for fun) I think Twinkly make a good product
I really like Twinkly lights. You can 3D map lights on the christmas tree with your phone and then play with individually controllable RGBW light points. They are relatively cheap, even non-DIY people can buy and use them. It would be great if they provided some official API, but if you want to hack them, there are ways to do it: https://labs.f-secure.com/blog/twinkly-twinkly-little-star/
And he ran a bunch of viewer-supplied programs on it: https://www.youtube.com/watch?v=v7eHTNm1YtU