Low-Profile Mod: Part 3 of 5 - Ethernet


2 posts
by peterburk » Mon Feb 04, 2013 1:56 pm
This series of tutorials shows how to make the Raspberry Pi into an even smaller, pocket-sized, PC.

In part 1, I removed the video connector and replaced it with a 3.5mm jack.
http://www.raspberrypi.org/phpBB3/viewtopic.php?f=40&t=32318
In part 2, I removed the audio connector, and joined it into the same 4-core 3.5mm jack.
http://www.raspberrypi.org/phpBB3/viewtopic.php?uid=54716&f=40&t=32322

Now I will show you what I did to flatten the ethernet port!

1. Practice de-soldering on a USB hub.
Seriously, I can't repeat myself enough. Every time you pick up that soldering iron, use a file to grind it down to get a clean connection, and practice desoldering something that doesn't matter.

2. Cover the Raspberry Pi in duct tape.
To protect other components from solder and flux.
Image

3. Use a multimeter to check the pinout on the Ethernet socket.
Wait, why is there no connection between the board-side pins, and the RJ45 ethernet pins?It turns out that the connector is active - there's a magnetic isolating transformer inside.
http://www.raspberrypi.org/archives/781
Now test the sockets on the board. All the ethernet pins seem to be shorted out! Apparently the USB/Ethernet chip downstream of the connector allows a connection to be made. This means that you have no way to test for short-outs. Be careful, and check your connections all along the way!


3. Replace it with a new connector?
I first used an iAudio remote connector, because it had 13 wires - more than the 8 necessary for Ethernet. Unfortunately, it didn't work. Why not? I can't test the wires, because everything appears to be shorted out on the downstream side, and there's no connection to upstream at all. I guessed that it might be an impedance issue - the active connector is too far from the chip to be driven successfully. Keep this in mind when changing Ethernet!
Image

4. Make a stand-off for the ethernet holes.
To bring the connector back, closer to the chip, I needed another plan. I took the stand-off connector from an old PC's video card, stored in a box in my attic, and put that in the Ethernet socket instead.
Image

5. Use a ribbon cable to push the stand-off down evenly.
Each pin of the stand-off has a tendency to be at a different height. This makes them even! But do not use the ribbon cable for a connection! Ribbon cables swap all the the pins around, and you will not be able to plug your Ethernet connector into the other side of the cable. I realised this after a failed test to connect Ethernet, and now my Ethernet port doesn't actually work.
Image

6. Make a female-to-female standoff adaptor to connect the socket.
This allows you to plug in the original Ethernet connector much closer to the chip.
Image

So now the Ethernet connector is gone too! Video, audio, and ethernet are three of the largest connectors on the Raspberry Pi. It's almost thin enough to fit in your pocket!

Peter
Posts: 45
Joined: Tue Jan 29, 2013 12:16 am
by Mixhael » Thu Jun 26, 2014 8:25 pm
Thanx for your guide, it helped me to get some needed confidence to start disassembling the board.

I had trouble getting the network connector to work, similarly to what you describe. I have about 5 cm wire between board and connector now. It did not establish a connection to my network. However measuring the voltage from a generic microusb cable gave me a voltage of 4,7 between tp1 and tp2. What if the power supply was not enough to power the chip and overcome this (small) distance. lo and behold, with a 5,25 V from an external power source my Pi found it's IP address :-)
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Joined: Thu Jun 26, 2014 8:13 pm