Hi all,
Hoping someone here has had some experience with EMI or other interference with LED strip PWM/data signals.
The data lines I’m running from my Arduino Feather to the the LED strips are about 1-1.5M in length. Each strip has its own data line, and I’m running them parallel to each other, and through a piece of square alloy tube. The data wires have the recommended 470ohm resistors, and the wire itself is a single wire from a cat5 cable twisted pair.
…I’m able to get one LED strip stable, but as soon as I connect a second, the signal goes haywire and it flashes unpredictably. I think I have everything grounded correctly, arduino, level-shifter, and LED strips all connected to the same negative voltage powering the whole project.
Given all that… I feel like it’s an interference problem, having the data lines side by side?
Has anyone else around here needed to shield data signals for multiple LED strips? Is that typical, or am I doing something else wrong?
Many thanks,
Shaun.
Hi Shaun,
You should be able to run a data line to LEDs that distance with no trouble. There is a couple things you could do to reduce interference, but I think the problem might lie somewhere in your wiring. Could you please share a wiring diagram of how everything is put together? Hand drawn would be fine but an exported Fritzing diagram would be better 
Thanks Stephen. Downloading Frizting now, I’ll see what I can do!
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Hi Stephen,
Here’s the diagram. The wire gauges I’m using should be good enough for the large current. I’ve measured the voltage at the points where the LEDs start and I get 5.10V at all the wires (each strip has its own +/- V splitting from some very heavy gauge wire ~2.5mm).
Also… sorry if this diagram is confusing, first go at fritzing.
.
Keen to hear your thoughts!
Cheers,
Shaun.
Hey Shaun,
Everything looks good with how you’ve wired it up. You probably do have emf issues. I would start by replacing the Cat5 cable with something like 22AWG. running your data lines right next to power lines is a sure way to get some EMF interference. For the sake of troubleshooting try wiring your data lines outside of the aluminum channel.
Damn. I was hoping it was some elementary wiring error! I’ll give the 22awg wire ago, though I was using that prior to switching to cat5. Thanks for having a look and the quick reply though.
I wonder if you could answer a general question for me?.. Is the DIN the only signal that suffers from interference? Or can there be cross-talk and interference shared between multiple +/- V wires? Like the power to the LED strips, and the ground or power being supplied to the boards?
Many thanks,
Shaun.
Hi Shaun,
The DIN will be the only signal that suffers from crosstalk. There will be no detectable effect on the V+/-. The relatively high amperage travelling through V+/- generates the EMF that the data line may induct.
HOWEVER, I’ve been giving your problem some more thought and I still think EMF is unlikely to be the cause over such a short distance. If separating your data lines from your power lines doesn’t help, its got to be that Level Shifter. I’ve found some supporting user experiences that suggest that those bidirectional level shifters are not well suited for driving LEDs. Try removing the 470K resistors and see if that helps. Then finally switch to a single direction Level shifter or a bus driver chip like this one:
It may look intimidating with no labelled pins, but wiring it up is easier than the bi-directional.
Let me know how it goes!
Thanks Stephen! Really appreciate it, I’ll give that a go.
One other thing I wouldn’t mind your opinion on… would you expect to see crosstalk between the out of the box JST connections on the LED strips? Say you had 3 of them in close proximity to each other?
Shaun,
I normally wouldn’t expect to see any crosstalk interference on wire lengths of less than 5-10 meters.
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It works, sort of! haha!
The level shifter is doing its job much better than the bi-directional one I had been using. Now… I think I’m having board and code library issues 
i’ll tinker and do some searching before I bug you again 
Thanks so much for the assist, really appreciate it!
Hey Shaun,
Glad to hear it! Happy to help if you get stumped again. We’d love to see your project once its all finished. You can share complete projects in the Projects section of our website!
Hi guys,
A word about EMI, cross-talk and noise from someone who studied comms:
Cross-talk, interference and noise are induced by electrimagnetic radiation. When you want to receive an EM wave you need a sensitive circuit, something with high impedance, because the induced current is usually weak and has very little power (unless you happen to be close to a high powered transmitter of course). The moment you load the induced current up with a low impedance (like a 470ohm resistor) its voltage is dragged down. Conversely, a signal on the line, which don’t forget is driven with an electrical connection, not a pissy little induced current, has plenty of power and dominates. So unwanted induced signals are pretty much never a problem when the line is short, signal power is strong, connections are properly made and/or pull-up / pull-down resistors are employed as they load the line.
I hope that helps a bit.
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