If a twisted pair is connected to the pins of an arduino, then how to determine that on the other hand it is connected somewhere?

Question

Arduino

And can it be done directly?

Answer 1

As I understand it, you need an idea for an algorithm that determines that the other end of the line is connected or not connected to a network port, so that you can implement it on an arduino.
It's elementary. The check is based on the fact that the line is connected to the network controller through pulse transformers, i.e. windings with a small number of turns of wire. In fact, this is an analogue of "dialing". For a 100-megabit connection:
1. We apply to the pin to which the orange wire is connected, alternately 0 and 1.
2. After a short pause (1 ... white-orange wire, check what is there.
3. If the applied and received signals match, then there is a connection. If the received signal does not change, there is no connection.
4. For a guarantee, we repeat the same on the green pair.
For a gigabit connection, we do the same check on the blue and brown pairs (or you can not do it).
PS: Belatedly, it occurred to me that the described procedure is only suitable if the other end of the line has a regular port, without PoE power. If it is there, then 12 or 48 volts are applied between the pairs, and when both pairs are connected to the arduino, this voltage will go directly to its pins, which is not good. Therefore, it is necessary to check only on one pair, and the second (for confirmation) can be checked only after the first is turned off. This should always be done, since it is not known in advance whether there is PoE at the other end.

Answer 2

Well, yes, we hook Ethernet-Shield to the arduino - and the task is solved.
There is also this one , but this thing does not check for the presence of a link on the other side (it’s still easier to take a shield for this than to reinvent it on transistors)

Answer 3

Basically, no way.

Answer 4

To determine whether it is connected or not, you need to set log 1 on one pin and measure the voltage or current level on other pins (there must be resistors) and repeat this for all other pins. As a result, it will be clear which pins I call with which ones.