Electrical noise when using wall outlet

Thread Starter

dashbarkhuss

Joined Jan 20, 2021
2
I'm a newbie, having trouble with some electrical noise when I added a ac adapter to my circuit.

Previously I had my Arduino project powered by my laptop. But I wanted to add a strip of led's to the project and I need the project to be powered over night and connected to my head. For both these reasons I added an ac adapter/wall plug to my project in order to power it.

I'm using a mosfet so my Arduino can control the led strip ala these instructions: : https://www.makeuseof.com/tag/connect-led-light-strips-arduino/

I'm only powering the reds though, if that makes a difference.

My Arduino has a "backyard brains heart and brain spiker shield", which is this Arduino shield that allows you to sense eye movements through electrodes on your face. My eye movements tell the Arduino when to turn the led strip on.

The ac adapter is causing an issue. When I plug it in, the Arduino electrode shield starts picking up electric noise from the adapter. It makes my signals unreadable; the program on my Arduino can no longer detect when my eyes move right or left.

I'm sort of new to electrical circuits. I'm not sure where to turn. How can I approach this problem? Is this something I need to filter? Is it better (or even possible) to switch to battery power? Someone suggested this would be safer too.
 

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SamR

Joined Mar 19, 2019
3,411
Apparently, the wall wart is a switchmode power supply and quite noisy doing it. A linear wall wart would be better. Linears are a bit larger, heavier, older tech, but much quieter since they use a transformer to reduce the voltage instead of "chopping" it up into smaller pieces to obtain a lower voltage. The Arduino does have a regulator that can and should smooth it out. It may also be a defective wall wart that is creating excess noise.
 

MisterBill2

Joined Jan 23, 2018
8,787
Sam is right, cheap switcher supplies are noisy. And in addition there may be line noise passing through even a safe switcher supply. So if you can not use the batteries, an older transformer type of wall supply, followed by additional filtering, followed by a three-terminal 5 volt regulator sould work fairly well. Not really as complicated as it sounds, fortunately
 

Thread Starter

dashbarkhuss

Joined Jan 20, 2021
2
I solved the noise by switching it to battery power. As many of you pointed out its also safer for a device connected to the body.
 

sparky 1

Joined Nov 3, 2018
544
BYB software has been used for but not limited to recording sensed impulse, eye movement muscles ect bio-medical.
The second screen shot shows 2 or three primary waves and the first screen shot shows them plus higher frequency.
If a smartphone function generator app signal is injected the secondary wave's frequency can be identified.
Probably a harmonic from the power supply. I think a low pass filter that allows waves less than 12kHz would have some effect on the harmonics. The advice to go with linear supply might reduce some noise and be easier to filter.

Some impulses in the body can be small. The project might need low electrical noise enviroment especially around sensors.
Using shielding and grounding might help. I think the question of whether the amplitude of the large signal can be distinguished from small might how that threshold is setup might be helpful.
Some noise can be expected sensitivity depends on the application. Possibly op amps configured as filters will enhance the BYB recording.
That would be almost audio analog to digital. Not sure how sophisticated BYB software does filtering.
As you explore the setup you like it may include some analog pre filter.
An interesting experience in bioelectric. I think some of us remember trying out first oscilloscope and seeing signals that have been amplified many times it felt like experiencing close encounters from outer space. Today with switch mode it is more intense. I don't know?
 
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MisterBill2

Joined Jan 23, 2018
8,787
For a safe and quiet power supply try one classed as "medical grade", which will be very well isolated. Digikey has a good selection, and while they are not cheap, you WILL get what you pay for. A friend just lost$36 ordering a thing she saw for sale on facebook. Instead of a puzzle assembly table made in Germany she got a "giveaway class" key fob. Not every seller on line is honest, we know.
 
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