LAN Cable Tester
I acquired a broken old LAN cable tester from work that had been fried by connecting up to a live PoE line.
Rather than letting it go to waste, I designed a much simpler tester out of the components. I removed the IC's and worked out the layout of the PCB where the connection to the pins of the RJ45 terminal are. Added some resistors to bring the 9V power from a battery down to the 2-3V usable for the LED's, I then hooked this up to 4 out of the 8 connections on the RJ45.
On the separate unit, there are 4 LED's connecting between each pair, the LEDs used here are bi-directional ones, meaning in one polarity, they light up green and in the opposite red. I forgot about "this feature" when I was constructing it, and had the un-intended consequence, of when a pair is connected to the opposite, it light up red (see picture of a cross-over cable)
The "0451" serial number is reference to a keypad code in Deus Ex that opens the SatCom door, which is a reference to the first code in the game System Shock, which in turn is a reference to the book Fahrenheit 451.
Note by the amount of stuff I've pulled off the PCB &how simple the schematic is.