I want to detect if an ethernet cable has become disconnected using an Arduino. The Arduino will be plugged into a wall, not battery powered.
Using a LM358 seemed like the correct fit. I hooked up orange & orange stripe to one side of the op amp and green & green stripe to the other side. Looking at the output on my scope, it never goes below ~3.5 volts. If I measure the difference with my volt meter, the difference goes to 0 when the cable is disconnected.
Looking around online, it seems as though I would need some kind of feedback loop. But if I do that, I believe that would tie one of the ethernet wires to the ground or power rail of the Arduino.
Assuming the LM358 would work, what would the circuit look like?
I don't need or want network capabilities on the Arduino itself. I'm looking to build a passive device that can detect the connection state between two other devices.