I need to make a test nail bed for a board that has an Ethernet interface:

  • in the bottom of the board there is access to the socket ethernet pins
  • i could place test nails under the ethernet socket to access these pins
  • i would like to connect this pins to another board , ex raspberry & test conectivity.

The problem: there seems to be a transformer embedded in the socket , so if i connect my testpoints BEFORE the socket , i would be missing the transformator and impedance adaptation.

Are there similar transformer like this but Without socket that i can add to my nailbed board???

any ideas on how doing this in a clean way ???

  • \$\begingroup\$ What transformer do you refer to? \$\endgroup\$
    – Andy aka
    Dec 16 '15 at 10:36
  • 1
    \$\begingroup\$ Yes, there are discrete transformers available. Hit google and search for ethernet transformer. Whether you can do what you want to is another question since if the jack is populated you will the have two transformers attached to the PHY chip - and it very likely won't like that situation. \$\endgroup\$
    – JRE
    Dec 16 '15 at 10:43

You're not really testing the complete board if you don't stick an RJ-45 in the socket because there is significant circuitry inside the magnetic jack. For example:

enter image description here

As @JRE says, it may not work with two transformers in parallel, or it might. One approach would be to simply use a duplicate jack (as used on the PCB) in parallel and plug your test computer into that. But it may not work reliably.

For some reason I guess you have better than even odds for 10/100 but that's just a wild guess. Worst case you have to plug an RJ45 jumper into each board, which isn't the end of the world.


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