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I'm building a system based on one of the old Raspberry Pi model B's (yes, first series) into a very small enclosure. I need to run an Ethernet cable from the POE splitter I have in this enclosure to the RJ-45 connector on the Pi's board, but I find I don't have enough room to do it (at least, not without creating a very small -- three inch -- cable.) I'm wondering if I can simply desolder the RJ45 jack and solder the Ethernet cable directly to the board itself, but I find that there's a lot going on in that jack:

Pi B Ethernet

Given all this "stuff" in there, would soldering the wires directly to the board even work?

blamblambunny
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Given all this "stuff" in there, would soldering the wires directly to the board even work?

Highly unlikely.

The transformers in the jack serve to provide isolation, but they also serve as part of the signal conditioning circuitry, providing a path for bias currents in the transmitter and setting up the correct common mode voltages for the receiver.

Peter Green
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As you've guessed yourself, no, this woun't work.

The plug integrates what network guys call "magnetics", which, in fact, means the transformers that you see in the picture.

Also, if all the problem is building a 10cm cable: That's quite obviously the easier, more stable, and quicker method.

(By the way, if you have the time, take apart a network cable. You don't want to solder these.)

Marcus Müller
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  • Ah yes, magnetics. If I remember right, the early Pi's had a problem where a batch was sent without them and they all had to be fixed. I'll get on making that cable... – blamblambunny Mar 11 '18 at 14:23
  • Ask someone who has a crimp tool. It's really easy if you've got one, and have done this before. – Marcus Müller Mar 11 '18 at 15:06
  • Actually, I already have one! I was hoping to get rid of the connector entirely and save more space. – blamblambunny Mar 12 '18 at 13:55