BG344213471 You want to look up the datasheet for "WS2812 5050". The LEDs used are WS2812 5050. The 5050 refers to the size of the LED (5.0mm × 5.0mm). There are also 2020 models (2.0mm × 2.0mm) and the newer B-model, WS2812B. The different models seem to have different timings, but they have a fair amount of timing tolerance and the protocol is the same. Some small adjustments should make your code work on all these models. Just note that some timings are in the 300 ns range. That's 4 clock cycles on a 16MHz AVR (like the ATmega328P found on Arduino Nano). Probably wise to disable interrupts during data transfer. Check the assembly output and count clock cycles or use a logic analyser (the cheap LA 1001 is a must have unless you already have a better one). In your bit pushing loop you either don't need any delays or a few no-op's (1 cycle doing nothing = 62.5 ns delay) for the longer delays.

BG344213471 Depends on what you mean by "users manual". The datasheet for the MAX7219 controller is excellent and all you need to know to program these things. If you want plug and play there are multiple libraries to choose from.

BG344213471 Yes. Remember, there are already 4 of these ICs chained together. The PCB comes with connections for further chaining, but as mentioned you probably need to inject some extra power.

BG344213471 @BG495298131 look it up in the MAX7219 datasheet. Another cool thing about these ICs is the need for just one resistor to limit the current for all segments x digits (64 per IC) to retain the same brightness whether only one LED is on or all 64. IIRC there's a chart there with recommended resistor values depending on number of LEDs. I could probably lift one of the 8x8 matrices off and see what resistor value they've used, but the datasheet should give you an idea. Assume you need an external power supply though. They're not super bright but it's still 256 LEDs.

BG344213471 I just looked at that library very briefly a while back after writing my own, and if I remember correctly there where some comments regarding timing that might needed to be adjusted. Have you tried the Adafruit library? Follow their guide. Add the 1000uF capacitor and don't try to reduce brightness by putting a series resistor on the power line. They recommend a resistor on the data line, but I've forgotten why. Those things aside, are you sure it's getting enough power? Too low voltage or current (these can pull a lot) can result in weird behavior. Each LED cleans up the signal before passing it on to the next LED in the chain, so if a few LEDs work fine you might want to check the power levels and that you're sending data fast enough. The library should do this though, but IIRC the library you mentioned is pushing the limits and if waiting too long between writes to the input it will consider it to be a reset condition and start over, writing to the first LED again. TL;DR check Adafruit Neopixel tutorial and library. Make sure you use a separate power source (e.g. don't use the 5V or VIN pin on the Arduino.

BG344213471 It's basically just nuts and bolts so you can unscrew them and move them to the other side of the PCB. Not tried so no promises but I don't see a reason why that would not work.

BG344213471 I've not tested these outside so this is pure guesswork, but based on how bright they are inside in a normally lit room I'd be surprised if they'd not be visible in daylight. Probably not in direct sunlight though. Buy one and give it a try, see if it suits your needs.

BG344213471 There are multiple Arduino libraries for this item. The Adafruit AHTX0 was committed to GitHub over 2 years ago, and I think that one replaces their AHT10 library with support for more AHT devices, so yes there are definitely libraries available for this item, contrary to what that other guy here claims.