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Thread: PCB design - grounding tabs on SMD RJ45 jacks?

  1. #11
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    Default Re: PCB design - grounding tabs on SMD RJ45 jacks?

    I'm sticking with the RJ45 jacks. I did some research before beginning the layout, thinking there must be something out there that is economical, flexible, and mostly smaller in size. I actually only need 4 signal lines, maybe one ground. What I found was that IDC is not small and has limited standard configurations, which were either too few or too many conductors - and still larger in size. The only option that looked possibly promising were molex-style connectors - but that would require a crimping tool and 128 robust crimps.

    I also have been concerned about crosstalk between signals in the same cable. While not using the same principal of ethernet signaling (balanced line, common-mode rejection...) using Cat5 cable with signal/ground wire pairs and different twist rates seemed like it may help. So I'm going with the ubiquitous Cat5/RJ45 setup. Good point above about inviting incorrect connections - but in this specific case there aren't any actual ethernet lines running to the controller.

    I've also modified the layout to include the RJ45 jack mounting tabs as part of the ground plane. I will also consider epoxying the jacks to the board to prevent ripping the traces off during disconnection of the plugs from the jacks.

    Thanks for the comments.

  2. #12
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    Default Re: PCB design - grounding tabs on SMD RJ45 jacks?

    If you can, add vias to the mounting pads;; they will help hold the pad to the PCB.

    I did a project where I needed multiple RS485 lines to talk between boards; I too used RJ45 since the cables were off-the-shelf and cheap; each board had 120 RJ45s, so the cost added up quickly (it was a tester used in manufacturing and the entire system tested 4800 units at once)

  3. #13
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    Default Re: PCB design - grounding tabs on SMD RJ45 jacks?

    @n1ist that makes sense and is a good idea. I'm using Oshpark, and I asked previously if they supported vias in pads, and the response was "no". I'm not sure if they will check and reject a design using them or not.

  4. #14
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    Default Re: PCB design - grounding tabs on SMD RJ45 jacks?

    I got 90 feet of TTL ws2811 signaling over cat5 on my controller boards. I need to find time and throw a scope on it so I can see what the signal looks like at different distances. On the video you will see the controller board and at 9:10 the receiver board. The reason for sharing is I used the ground laced pairs of the cat5 cable, so each twisted strand had the ground wire and the signal wire. Each cat5 cable carries 4 SPI lines. Its worked great so far. still refining the project.

    Last edited by crees; 04-15-2018 at 09:24 PM.

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