DIY Mini-USB Serial Dongle

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Dec 31, 2018
I recently acquired a Brocade 7250 switch and needed a serial cable for it, but didn't feel like spending $35 or more on a the cable kits I could find on eBay when I knew i could make my own for about $5. Also, all of the kits I found actually required you to go mini-USB to male RJ45 to DB9 female which was just one dongle too many for me.

With this DIY dongle you will not need to butcher any of your USB cables and you can use a standard Cisco Serial RJ45 cable directly. I figure most of us have one or more keystone jacks sitting around. Since the USB data wires are typically such a small gauge and stranded, you will need to do a bit of soldering for them to work properly with your keystone jack. I used a bit of twisted wire from a cat 5 cable, but any 22awg solid wire would work, you really only need about 2 inches at most.

This is the finished product, allowing you to use a normal USB Type A to USB Mini Type B cable along with your standard RJ45 serial cable to make a console connection.

Needed Parts:
Steps to make your own dongle
  1. Cut off the motherboard header from the USB Jack
  2. You can also cut off the red and black wires and shielding as those are not necessary for this dongle to function
  3. Strip the white and green wires about 1/2"
  4. Solder your solid wires onto your USB wires. Be sure to use heat-shrink to prevent shorts between the wires.
  5. Punch down the solid wires into your RJ45 keystone jack. You are punching down to what would be the green pair in a T568B jack, but reversing the wires so that the green/white wire goes onto the solid green pin 6 and the solid green wire goes onto the white/green pin 3.


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Jul 15, 2018
Oh that's clever, nice work!


New Member
Oct 8, 2018
Thank you ! Followed your guide with small changes and I have just finished updating the firmware on my 7250.


New Member
Nov 24, 2020
Thank you ! Followed your guide with small changes and I have just finished updating the firmware on my 7250.
Hi... I did the step by step and mine didn't work, this cable in Brazil is very expensive, what modifications did you make?