Filtering noise from a wire


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  1. #1
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    Default Filtering noise from a wire

    I have install pushbuttons on the flip side of these (5V circuit), and the button state is sent via a 3rd wire to another board along with the VDD and VSS wires:




    What is the proper technique to filter noise picked up by the wires before the signal is processed by a MCP23017 I/O Expander?


    I searched here and google for "decouple wire lines", but it's too vague of a question. And I don't know how I can state it better, or differently.


    I've read about ferrite beads, but I'm not sure if capacitors could do the job as well. I remember hacking a keyboard many moons ago, and it had aluminium foil along the back cover.


    EDIT: I have to consider that someone might have speakers, cell phones or other "noisy" devices placed right beside the unit.
    Last edited by Demon; - 19th January 2024 at 07:26.
    My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.

    Not as dumb as yesterday, but stupider than tomorrow!

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    Default Re: Filtering noise from a wire

    This lady recommends "This is one of the two ways to control EMI—eliminate the source or eliminate the antenna."

    https://resources.altium.com/p/every...-ferrite-beads


    I can't eliminate the source for the simple reason that I have no idea what a user might put within proximity of the device.

    As for the antenna, I assume she means protecting the wire. I will have a LOT of unshielded small gauge wires, ranging from 1 to 8 inches (I'm up to nearly 100 switches). I could wind them up in aluminium foil like I see on network cables (I haven't done any research on this subject yet).
    Last edited by Demon; - 19th January 2024 at 07:28.
    My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.

    Not as dumb as yesterday, but stupider than tomorrow!

  3. #3
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    Default Re: Filtering noise from a wire

    Maybe it is simpler to put all these stuff in a metal box and earth it?

    Ioannis

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    Default Re: Filtering noise from a wire

    Weight is an issue.
    My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.

    Not as dumb as yesterday, but stupider than tomorrow!

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    Default Re: Filtering noise from a wire

    Then using shielded cables or wraping with copper foils like these may help on this: https://nl.aliexpress.com/item/10050...&mall_affr=pr3

    But why bother with all this stuff? Did you have any reliability problems?

    Ioannis

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    Default Re: Filtering noise from a wire

    Quote Originally Posted by Ioannis View Post
    ...But why bother with all this stuff? Did you have any reliability problems?

    Ioannis

    Nothing so far. I just like to be prepared for the worst case scenario if I can. But I'm not going to drive costs up 500% to protect from 0.0001% insane user conditions either.

    My old scopes are acting up; switches and buttons causing noise on the screen; image is jumping like an old CRT. I'm not going to spend time figuring out if seemingly bad signals are real, or the result of faulty ancient equipment.

    I'm waiting for a small scope that had a good review for testing switch debounce. I don't do any advanced scoping routines; I only need it to check 5V lines for noise and switch bounces.
    Right now, I just don't know just how sensitive or hardy 5V circuits can really be.

    What ordinary household items that a gamer might have on his desk that you would consider as the biggest causes of noise on circuits?

    Electric kettle?
    Large speaker?
    Cell phone playing a movie?

    I'm planning on setting up some tests to see just how much noise my circuit can pick up.
    My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.

    Not as dumb as yesterday, but stupider than tomorrow!

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    Default Re: Filtering noise from a wire

    Quote Originally Posted by Ioannis View Post
    Then using shielded cables or wraping with copper foils like these may help on this...

    I already have a lot of manual tasks required to assemble a single unit. I would probably get shielded wire; something like this.

    Name:  Shielded wire.png
Views: 261
Size:  194.1 KB


    I haven't searched for prices. I just took a pic of the first one I found.

    But first I want to test to see exactly what I'm facing.
    My Creality Ender 3 S1 Plus is a giant paperweight that can't even be used as a boat anchor, cause I'd be fined for polluting our waterways with electronic devices.

    Not as dumb as yesterday, but stupider than tomorrow!

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