The FRC Radio can accept “Passive Power Over Ethernet”, 12-24vdc applied to the two unused pairs of Cat-5 cable wired for 100-base-T data.
After hand-crafting some PoE injector cables, we wanted to test them before putting them on the robot and radio. So we built a simple tester.
Prototype
This prototype is hacked onto a scrap of a breakout board for an 8p8c jack. It consists of two LEDs and two resistors.
One LED lights if the brown and blue wires are recieving the correct polarity of DC power. The other LED lights if the white/brown and white/blue wires are OK. Using two independent basic LED circuits allows us to test that all four wires are actually connected properly. Since the two wires of each pair carry the same power, if one were broken the radio might still work - but there would be extra resistance and no redundancy in the defective cable.
Schematic
