Arduino + Neopixels on separate switching regulators

[spectral]

Hi,

For my project, I need to run around 360 Neopixels around 20-30 ft away from the Arduino that will be controlling them. Obviously, peaking at 18A, running 5v over this distance is not a real option, so my plan is to run 12v, and use two switching regulators on each side of the length, one for the Arduino, and one for the LEDs.

The regulators I will be using are they typical ones available from ebay: (http://www.ebay.com/itm/DC-DC-Converter ... 1c43766e52) which I believe are basically just Buck converters.

My question is this...
I know (from experience) the arduino and Neopixels need to be connected to the same ground, or behavior will be erratic. These converters always have separate ground lines for input and output. What is the difference between these two ground lines? Is it possible I might get bad results if there is a significant voltage drop between the two regulators? Under high load, the regulators will see possibly a few volt difference at their inputs, is it possible the ground lines will be affected by this and the arduino and Neopixels may fall out of sync?

If the ground lines are in-fact different, what would happen if I bridged them (connected input + output ground on the regulators)? I feel I have actually done this before while prototyping without obvious negative consequences. If that won't work, would it ever be necessary to run a separate ground line across the distance to connect the two output grounds from the different regulators?

Or am I completely misguided here, and all of these grounds are the same, and there is actually no problem at all?

Thanks in advance for any help/advice!!!
- Eric

[adafruit_support_mike]

As long as you connect GND on the Arduino to GND on the NeoPixel strip, things should Just Work.

It's entirely possible for the converters to have electrically isolated input and output GND lines. That's called a 'floating output' or 'offline converter', and there are advantages to doing that. You can connect floating power supplies in series (Vcc of one to GND of the other) to make a split supply, and there are safety benefits to having isolation between the product's supply rails and the upstream supply (you don't want a component failure suddenly connecting your iPod's headphones to the 120v @ 20A circuit breaker in your supply panel).

It's perfectly safe (and usually necessary) to connect the GND lines of two floating supplies though. All voltages are measured between two points, and GND is the common reference point for all voltage measurements in a circuit. Connecting the GNDs of two supplies just means all the components connected to either supply will have a common reference.

If the converter GND-IN and GND-OUT lines are connected, make sure the sources that feed power into them are either floating relative to each other (same idea as above, just moving the floating part upstream of the converter) or have their GNDs at the same level (usually done by connecting them both to a literal Earth GND).