Physical Position of Controller in Strings of WS2811

Hi, I have a simple question: Does it matter where the controller is in the string of LEDs?

I have an installation where putting the controller in a protected location would be an advantage for wiring and durability, but that would put it at a connector at a midpoint between several strings. I understand the need for power application at points along the strings and the code is running with the controller at one end, but am not sure about this one.

Buried in this is the question of how the controller enumerates the WS2811 nodes along strings, but perhaps that’s for another day.

Hi @Thinkerer! Welcome to the forums!

I think most people would choose to use the output expander for a situation like this. It lets you send signal out in multiple directions from the Pixelblaze, and also lets you index them separately. Since index ordering would be left-to-right on one channel branch, and opposite on the other, you may wish to map the overall LED positions in the mapper, or use a small snippet of code to reverse the indices of one of the channels.

You’re intuition is right that you can’t just tap into the middle of a chain of pixels and send signal both directions.

A thing to be mindful of is your distance between PB and output expander, as well as distance from output expander to the first pixel in each string. With WS281Xs, a good rule of thumb is to keep these as short as possible, definitely under 10’ for best results. Search the forums here for lots of good advice on fixing problems you discover experimentally on those longer runs!

Hi Jeff,

Thanks for the info - this mirrors some of my non-Pixelblaze tinkering I’ve done with LED arrays using various flavors of Arduino. I think that for the current (small) application I can arrange the physical wiring to keep it all together (and the short wiring runs are possible in this case) - just a matter of some weather protection. This is just messing around with holiday decorations so less-than-perfect is okay, but the expander seems like a perfect idea for the larger plans I have in mind.

For longer runs, Does the usual EMF/CM/line induction is interfere with the controller signal, and does slowing the controller rate help this or do I have to start thinking about chokes/caps etc.?

For longer runs, assuming you already have power injection well planned, you’ll want to check out threads here about using shielded twisted pair (e.g. Cat6), an inline 100 ohm resistor, and if you really need to extend the length, RS485 differential transceivers.

You can’t reduce the data timing for WS281X pixels - they’re very sensitive to being right at 800 KHz. The SK9822s are more flexible since they’re clocked.