A new Firefly

A few months ago I got roped into managing a network installation at a client’s new office. Huge mistake. It was supposed to be a small project but it grew to an unreasonable size, and as usual the client demanded Dom Perignon but only wanted to pay for Prosecco. Plus, in the middle of the installation and after about 2/3 of the cable had been run, they decided to remodel and destroyed a lot of cable.

I was pulled off to work on other projects and things got a little out of hand. In the end we were looking at spending a ridiculous amount of time to figure out which cable went where, and the client was ready to move in. So I ordered a device I’ve always heard referred to as a Firefly. It is a wonderful little device. Pop a small device a little bigger than an RJ45 connector, the firefly remote, into each port on your patch panels. Walk from office to office with the main device. Plug it in and if the connection is good the firefly remote lights up. Fantastic. You can map a thousand ports in a few hours.

But, it only tells you if two of the pins are wired correctly. We found a few ports that weren’t working even though the firefly lit up. One of the firefly remotes had gotten stepped on and broken so I took it apart. The brown and brown-white in a typical 568B configuration are the only ports connected to the LED. Later I wired up a few LEDs to a standard CAT6 connector and verified the power only comes through on those ports. So, the Firefly is fantastic for quickly mapping your ports but it could use a little improvement.

I had to sit through some online training this week, and I typically have to do something with my hands during the boring parts or else I’ll go crazy. I had some CAT6 cable, LEDs and a CR2032 battery within reach so I started playing around with an idea – a 4xLED Firefly. One LED to each pair of pins, 4 LED in all. Each one a different color.

First I crimped a CAT6 connector in a standard 568B config onto a piece of CAT6 cable. I stripped the wires on the other end and twisted them together using a pair of needle nose pliers. I left enough bare cable that it could make contact on CR2032 coin cell battery. The CR2032 is a 3V, 200-250mAh, .12 watt battey. That is a lot less power than you’ll get on a typical POE injector, and only slightly more than the standard Ethernet voltage, so it shouldn’t harm the cable or patch panel.

diyfirefly1 diyfirefly2

I used a little electrical tape to maintain the connection. I took a longer piece of CAT6 and punched down a CAT6 Keystone jack on each end. This is to simulate the patch panel and wall port. I plugged my powered patch cable into one end.


I took another small piece of CAT6 cable and crimped on a CAT6 connector. I stripped about 1cm cable on the other end and plugged it into the Keystone jack. I touched an LED to two of the pins and verified it lit up. I repeated this for each pair.



I took my little creation home and did my usual horrible job of soldering in an attempt to make it look a little more professional.


Maybe it was my horrible solder. Maybe it was my weak attempt at covering up the solder with heatshrink tubing. Or, maybe it was the application of plasti-dip to cover up those two attempts. Regardless, somehow I screwed up two of the LED. But, you get the idea of what I was attempting to accomplish.


So, in theory this device will not only map your network but it will tell you if all of your pins are wired correctly. Use four different colored LED so it is obvious which one is lit – blue for the blue pair, green for green, orange for orange, and maybe purple for the brown. If all of them are lit your connection is wired correctly. If not you should be able to easily tell which pair needs to be looked at.

Now if I can just find someone with a lot more talent than I have with making electronics projects look professional.

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