Question: I have so far only worked with WS2812 strips and understood, that the WS2813 have a backup data line. But how do I connect the first LED to my Arduino (acts as a controller)? 

Many tutorials said I should just wire the BI to V0, but doesn't this eliminate the backup functionality? So I thought about wiring both data pins to my data source? Is this a good idea?

Answer: 
This is based on a few sources including the (poor) [datasheet](https://www.elecrow.com/download/WS2813_LED_Datasheet.pdf).

My interpretation is that BIN should be connected to the *previous LED's* DIN. Then if the one LED fails, the next one will not receive any data on DIN, but it will receive data on BIN. It will switch to backup mode, where it uses the data from BIN, and ignores the data intended for the previous LED. This allows the rest of the chain to continue functioning with only one dead pixel, instead of letting the dead pixel break the chain completely. The chain will still be broken if two pixels next to each other are dead.
The WS28xx series of LED drivers are (were?) made by [Worldsemi](http://www.world-semi.com/), but there does not appear to be a datasheet for the WS2813 available on the site (yet). It seems that another company, [Shenzen Normand Electronic Co](http://www.normandled.com/) may be the manufacturer. Maybe it is a copy or a clone... The [datasheet can be found here](http://www.normandled.com/upload/201605/WS2813%20LED%20Datasheet.pdf).

In any case, page 2 states that data at `BIN` and `DIN` are compared. `BIN` is used in the event `DIN` does not receive valid data. It is not well-written; here is the relevant section:

> 
> The BIN receives the data signal, and then compare the data with the DIN side after phagocytosis of 24bit data, if DIN do NOT receive the signal, then switching to BIN for receiving the input signal, which ensure that any the IC's damage does not affect the signal cascade transmission and make the BIN in state of receiving signal until restart after power-off.
> 
> 
> 

I'm amused by the inclusion of *phagocytosis*, a biological process whereby cells can "eat" large particles by engulfing them. I presume this is a bad translation that refers to the process of receiving and checking the 24-bit data packet common to the WS28xx family of LED drivers.

The main purpose of this is not to operate a second LED strip, but rather to allow a single contiguous strip to tolerate failed pixels.

[![WS2812 vs WS2813](https://i.stack.imgur.com/Vflcw.jpg)](https://i.stack.imgur.com/Vflcw.jpg)

*[Image from Elecrow.com](https://www.elecrow.com/blog/ws2813-vs-ws2812/)*

Essentially DIN is a primary data input and `BIN` is a backup, just as you described. The datasheet does not specify how `BIN` should be connected (or left disconnected) if the backup data function is not wanted.

Based on what I was able to find, it appears that you could easily connect data to both `DIN` and `BIN`, and if one of the driver ICs fails, it appears that `DO` will still pass whatever data was received at `BIN`.

If you prefer to not use this pin, you could connect it to ground as some suggest. You may want to test whether connecting `BIN` to ground causes any additional current to flow, should that be a concern in your project. It could be that it is best left floating (not connected) instead. Measure to be sure.