Avian’s Blog

Back when I was a student I designed and built an UTP cable tester. It's a battery operated hand-held device that uses finite state machine (more exactly a Moore automaton implemented with ROM and some logic - no microcontrollers with unreliable software here) to control some simple analogue circuits that check for proper connections and polarity of pairs in a standard Ethernet cable.

It was designed from the start to have two separate parts that need to be connected on the opposite ends of the cable. One part plays an active role and has all the logic and the diagnostic lights, while the other is a simple passive terminator with a diode circuit.

At the start I implemented both in a single case for simplicity, but that meant that you had to be able to bring both ends of the cable into one spot. Since I'm planning to lay some cables in my new apartment in Ljubljana I went on and made a second, separate terminator so I will be able to test cables once they are already fixed on the walls.

I didn't bother to make a circuit board. It's going to be sealed shut and filled with hot resin, so nobody will be able to see the rat's nest anyway.

On the second though it would probably be better if I made a metal box that would provide some shielding. But I had this piece of plywood at hand and no conductive paint. It works this way just as well and it's not something that will be in continuous operation anyway.

Finally I gave it a coat of black paint to match the metal box of the tester.