I’m currently finishing (hopefully) our new twisted-pair-(Cat5, ethernet cable)-based intercom/tally system for our tv projects: communication, data and video all over one network cable (more on this soon) – and I stumbled over several CAT5 cables in our bin that were either damaged or wired the wrong way or simply crossover cables that messed up the testing of the system.

So I quickly hacked together this little device to see if the cables are wired ok. Like almost all of my stuff, it’s based on the gnusb (the atmega644 is a little bit overkill for this project, but that’s what I have lying around).

Just plug in a cable and if all 8 leds light up it’s good. If not, you can press the button and see which end of the 8 wires is connected to which other..

It’s dead simple.source code and schematics: rj45Tester