0

Neopixel project - PSU causing radio interference?
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Neopixel project - PSU causing radio interference?

by royshearer on Tue Dec 11, 2018 9:58 am

I have a project involving one 6m strip of rgbw neopixel running off Arduino mega, powered by a 150w switching regulated PSU. We have noticed the project causes interference with a digital (dab) radio in the same room, only momentarily as the strip fades between different states, not when it holds in a static lighting state. I have tried a few tests and think that it might be the PSU that is the root of the problem as the project does not cause any interference when powered from usb.
I presumed initially that if the PSU was to cause interference it would be constant, but now wonder if it could cause this momentary behaviour.
Does this sound plausible?

royshearer
 
Posts: 27
Joined: Wed Mar 07, 2007 10:29 pm

Re: Neopixel project - PSU causing radio interference?

by adafruit_support_bill on Tue Dec 11, 2018 10:34 am

Switching mode power supplies generally do have some residual switching noise on the output. It is possible that the output filtering effectiveness changes with the load.

Neopixels also have their own switching noise since they control the LED brightness via PWM. It is possible that there is some interaction between the power supply and pixel noise at certain output levels also.

adafruit_support_bill
 
Posts: 71765
Joined: Sat Feb 07, 2009 10:11 am

Re: Neopixel project - PSU causing radio interference?

by royshearer on Tue Dec 11, 2018 1:19 pm

Thanks for your reply. We will try a different brand of power supply. This is going into a public setting so we would like to be sure that it is not going to cause issues with any other devices people are carrying, or in the building. Do you think the dab interference suggests that that could happen, or am i over reacting?

royshearer
 
Posts: 27
Joined: Wed Mar 07, 2007 10:29 pm

Re: Neopixel project - PSU causing radio interference?

by adafruit_support_bill on Tue Dec 11, 2018 1:45 pm

If the installation will be in a larger space, the potential for interference may be reduced somewhat. EMI follows the 'inverse square' law - meaning that the power of the emitted waves decreases by the square of the distance from the source. So a little distance can result in a substantial decrease in interference.

That said, a public space is also more likely to be saturated with cell-phones, wi-fi hot spots and other devices competing for radio waves. Not to mention lighting, HVAC and other EMI-emitting equipment. Any reduction in interference is probably a good thing.

adafruit_support_bill
 
Posts: 71765
Joined: Sat Feb 07, 2009 10:11 am

Re: Neopixel project - PSU causing radio interference?

by royshearer on Wed Jan 09, 2019 7:33 am

Hi there, we have tried switching out the power supply with a Meanwell branded power supply but still have the exact same interference issue sadly.

Currently the interference is happening over a distance of about 4m and we are not able to specify a 'quiet zone' around the installation (not up to us).

If anyone has any other ideas that would be much appreciated.

royshearer
 
Posts: 27
Joined: Wed Mar 07, 2007 10:29 pm

Re: Neopixel project - PSU causing radio interference?

by adafruit_support_bill on Wed Jan 09, 2019 8:46 am

Meanwell supplies are generally pretty good. But a 6m strip of pixels makes a pretty good broadcast antenna for noise - regardless of the source. You could try adding some clip-on ferrite rings to the power and ground wires.

adafruit_support_bill
 
Posts: 71765
Joined: Sat Feb 07, 2009 10:11 am

Re: Neopixel project - PSU causing radio interference?

by royshearer on Wed Jan 09, 2019 8:52 am

Yes we did try this, but it didn't have any effect. We clipped them seperately over the power and ground wires on the 5v side, everywhere we could access. We did not coil the wires around the ferrite core however, would that make much difference do you think?

royshearer
 
Posts: 27
Joined: Wed Mar 07, 2007 10:29 pm

Re: Neopixel project - PSU causing radio interference?

by adafruit_support_bill on Wed Jan 09, 2019 8:58 am

The effective inductance will be roughly proportional to the number of turns. So if possible, coiling the wire is good. Other possible mitigation strategies would include adding some capacitors at various points along the strip. Ceramic capacitors are generally better at absorbing the higher frequencies.

adafruit_support_bill
 
Posts: 71765
Joined: Sat Feb 07, 2009 10:11 am

Re: Neopixel project - PSU causing radio interference?

by royshearer on Wed Jan 09, 2019 9:05 am

We have a 1000uF electrolytic between 5v and ground as described here:
https://learn.adafruit.com/adafruit-neo ... onnections

Do you mean adding additional ceramic caps between 5v and ground along the strip? Any particular values of capacitor?

royshearer
 
Posts: 27
Joined: Wed Mar 07, 2007 10:29 pm

Re: Neopixel project - PSU causing radio interference?

by adafruit_support_bill on Wed Jan 09, 2019 2:33 pm

Unless you are certain of the nature and source of the noise, mitigation strategies are mostly a matter of 'try it and see if it makes a difference'.

Most of the strips have 0.1uf ceramic bypass caps per pixel. These are generally pretty good at filtering the higher frequencies. Electrolytics are a bit 'slower' but have higher capacitance values. You could try adding something like a 100uF electrolytic in parallel with a 1uF ceramic between 5v and GND every meter or so.

adafruit_support_bill
 
Posts: 71765
Joined: Sat Feb 07, 2009 10:11 am

Re: Neopixel project - PSU causing radio interference?

by jps2000 on Wed Jan 09, 2019 3:19 pm

Suggest to find out the source of the interference.
You can wrap up the neopixel strip to a ball which would reduce the antenna dimension. Then you see i the interference is less or not.
May be you can try to ground the usb connector as you said the supply via usb has not the effect.
Just try first to contact both grounds from plug and socket if it helps
You can try also a car battery as supply etc.
You can reduce neopix clock frequency etc.
Finding causes of EMI is usually cumbersome and takes significant time.

jps2000
 
Posts: 333
Joined: Fri Jun 02, 2017 4:12 pm

Re: Neopixel project - PSU causing radio interference?

by royshearer on Tue Feb 05, 2019 4:08 pm

We tried the suggestion of the capacitors every metre along the length of the strip today but without luck.
However we then tried making a ground plain of alumnium foil underneath the installation and that made a huge difference and has basically solved the EMI problem as far as we can tell (ie. its no longer interfering with the digital radio).

Thanks for all your help!

royshearer
 
Posts: 27
Joined: Wed Mar 07, 2007 10:29 pm

Re: Neopixel project - PSU causing radio interference?

by adafruit_support_bill on Tue Feb 05, 2019 4:10 pm

Good to hear you found a solution. Thanks for the update. :)

adafruit_support_bill
 
Posts: 71765
Joined: Sat Feb 07, 2009 10:11 am

Please be positive and constructive with your questions and comments.