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Thread: Avoiding a possible ground loop

  1. #1
    Junior Member
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    Avoiding a possible ground loop

    Hello everyone,

    I have a project that I hook up Teensy 4.0 and a RPi together with a USB cable and was wondering if my setup would cause a mishap.
    I have one 24V PSU and two separate 5V buck converters, one going to T4.0 and another to RPi, hence their grounds are connected.(In the future Iíll just make a buck capable of powering both, at this time one canít do it properly). My question is, the T4.0 and RPi communicate via USB and USB has a ground reference. So would that be a problem for my setup? I believe that since the 5V power supplies share a common ground, RPi and T4.0 are referenced to the same ground and Iím basically connecting two grounds with the current setup. Should I cut the USB cables ground.

    *** Iíve already cut the VIN and VUSB trace

  2. #2
    Senior Member Blackaddr's Avatar
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    Quote Originally Posted by BlueTurtle View Post
    Hello everyone,

    I have a project that I hook up Teensy 4.0 and a RPi together with a USB cable and was wondering if my setup would cause a mishap.
    I have one 24V PSU and two separate 5V buck converters, one going to T4.0 and another to RPi, hence their grounds are connected.(In the future Iíll just make a buck capable of powering both, at this time one canít do it properly). My question is, the T4.0 and RPi communicate via USB and USB has a ground reference. So would that be a problem for my setup? I believe that since the 5V power supplies share a common ground, RPi and T4.0 are referenced to the same ground and Iím basically connecting two grounds with the current setup. Should I cut the USB cables ground.

    *** Iíve already cut the VIN and VUSB trace
    You must have a ground between the boards otherwise they won't be able to communicated with each other. Even if you cut the ground in the cable, they'll find a ground between them somehow, but it will take a longer path and be more likely to pickup noise and interference along the way.

    Ground loops are literally ground wires that have a hole in the middle somewhere. Any EM radiation going through that loop (radio, lighting and power line EMI) will induce a proportional current in the loop, which becomes noise/interference on the signals using that ground path as their reference.

    Generally speaking digital circuits are mostly immune to ground loop interference. Analog signals are not.

    - Removing the ground from a balanced analog audio connection between two pieces of equipment is safe and may reduce ground loop noise. This is possible because the balanced nature of the signals means they don't use the ground for reference. Disconnecting the ground on only one end still allows the cable to be shielded without creating a ground loop.
    - single ended analog audio cannot have it's ground removed as that's it's reference.
    - digital cables cannot have their ground removed as that is their reference.

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