Can signal wires share a ground?
If I run two signal wires, each from a separate pin on an Arduino, I should be able to share a GND wire, correct?
For example, a 3-strand wire connected to pin 8 and 9 and GND on the Arduino, a 50-foot run, and then the pin 8 wire to one LED strip, the pin 9 wire to another strip, and the ground wire spliced the GND on both strips.
That wouldn’t work with twisted pairs obviously – since two’s a pair and three’s a crowd – but, so far, I’ve been fine without twisting.
Yes, they can share the ground.
And you could certainly try twisted pair also. Use two pairs, with data (pin 8) and ground in one pair, and data (pin 9) and ground on another pair. Tie grounds together on ends.
@marmil A great idea! And obvious once someone pointed it out to me. Thank you!
There should only be one point where each ground connects … avoid “loops”
@David_Brenchley “There should only be one point where each ground connects … avoid “loops””
You mean per each strip controlled by a signal wire, correct?
Strip A gets signal wire A and gnd at the beginning of the strip, and strip B gets signal wire B and gnd at the beginning of the strip even though strip B has two halves separated by a 20 foot run of signal wire.
Or maybe better to say connect gnd only at the beginning of each RUN of strips.
Yes … “connect gnd only at the beginning of each RUN of strips”
If grd is terminated at both the beginning and end of a strip, you create a “loop” … which is undesirable for two reasons …
If the two lengths of wire from each end of the strip to the common termination point are of different lengths there is the possibility of a difference of potential which causes current flow not related to signal current which may distort your signalling.
Loops are effective antennas … which could add additional noise to your signalling …
@David_Brenchley Do you have a source for this information? I pretty much ALWAYS have loops in my works and have never seen any kind of issue…I would love to read more on this?
This article is more applicable to to AC main power but the principles are the same … http://www.epanorama.net/documents/groundloop/basics.html
You mean this kind of loops?
Yep … in your situation I would cut the ground and vcc traces midstrip if your powering both ends of the strip because your concerned about current sourcing.
Think of grd distro and vcc distro as spokes of a wheel w/ the power source in the middle …
NOW… if you’ve not been having issues … … this is best practice … don’t want everybody ripping their working rigs apart on my account …
It’s interesting that you are suggesting “no loops”, while many other posts (adafruit, sonic runway project) are actually advocating for the oposite, to deliver power to long strips of LEDs.
It makes sense to power both ends of the strip(s) … just don’t create a loop in the process … cut the traces in the middle or don’t wire power between the middle adjacent strips … believe me my 40+ years in audio/video/instrumentation electronics has taught me loops are bad …
Obviously someone is doing something wrong. Adafruit’s advice is ok with loops: https://learn.adafruit.com/adafruit-neopixel-uberguide?view=all#power
@Jesus_Climent Maybe it’s not a question of “wrong” so much as “works” and “works better”.
I’ve had projects where I didn’t even connect a common ground from the Arduino to the strip and it “worked”… but it wasn’t the best way to do it.
I also suspect having a ground loop over 200 feet of wire up in an attic is an entirely different story than a 2-foot ground loop on a decorative lamp.
true … as I said … if it’s working … don’t “fix” it … but if things start going squirrelly … It’d be a place to look … best practice avoid it in the 1st place …