Quick non-FastLED question for all the electronic experts out there. I’ve been examining two strings of color changing Christmas lights that use a remote control. When you join two strings together, you remove the second remote receiver and connect the two strings with just a 2-pin connector. Assuming that 2-pin connector is for power (no other way to power the second string), how is the signal being sent? Carried over the power line of the string?
It’s probably just an IR controller. I have two Halloween spinning lights that aren’t connected at all but switch to the same colors with the same remote. Try plugging in the strings separately and see if you get the same result.
Each string comes with a combination receiver/stepdown transformer (110V AC to 4V DC), However, when you connect more than one, you remove the receiver/transformer from any and all additional strings and connect the additional strings to the end of the one that still has the receiver. So the one receiver (and it’s remote) are controlling all the strings. Signal has to be getting to the additional strings somehow. I doubt it’s just a transformer and that each bulb has it’s own receiver – which leaves the power wires doing something, somehow… I think. 
In that case, I have absolutely no idea.
I know there’s such a thing as data over AC lines. No idea if there’s similar for DC, or what sort of data rate it might have.
It could be “power line communication” which is accomplished with a couple different methods that you can find by googling that