Connecting two devices together with the same ethernet cable (some programming required?)

I’m looking to connect two devices together via ethernet, but I’m having trouble with the steps needed. The devices are one PC and one microcontroller. Both devices will have static IP’s, the microcontroller at the very least. I’m running LWIP on the microcontroller. What I’m stuck with is the steps I need to do to get both devices to communicate. Do I need the microcontroller to do an ARP broadcast or something so both devices can see each other and communicate?

E: Auto-negotiate is enabled on the controller

Can I safely connect audio out to audio in with an aux cable?

This question might be really dumb. But can I safely connect the audio output from one pc to the audio/microphone input on another pc, using an aux cable? I want to record audio from one pc on another pc using audacity. What I mean by “safe” is like will it short out or anything crazy? Also can I connect the audio out to the audio in on the same pc without problems? I know sound is just a wave, but I don’t know if that applies here.

Forgive me, if this is the wrong fourm for this question, or if this question is really stupid.

This is just a random image I found online. However, just in case I don’t know the proper names, these are the ports I’m talking about.

Why Thunderbolt Display doesn’t work until unplug/plug power cable?

I have Apple 27 in Thunderbolt Display. But for some reasons I have to unplug power cable for 30 sec or more every time to turn it on!

Why its happens every time, after I detach my MacBookAir 2018/MacBook Pro 2018 Thunderbolt USB-C adapter?

I read some articles for troubleshooting, where this is a step to fix the issue, but why I have to do this constantly?

Is it normal?

Pwr Supply Cable Anomaly 24 pin vs 20 pin

I have a weird scenario. An older computer wolfdale1333-D667. The power supply it came with had a 24 pin power connector. Using a newer but still old enermax liberty 620W power supply, it comes with a 20pin plus separated but in the same cable jacket a four pin jobbie. When I plug both into the 24pin receptacle NOTHING HAPPENS. When I remove the four pin jobbie and only use the main 20 pin connector, the computer turns on lights, beeps fans etc………

There are two other facts that may be pertinent. (1) I should state that a separate 12v connector is connected to the CPU plug in point. (the enermax provided two options (diff plug configs) and thus easy to choose the correct one (and cable for these two states for CPU).

(2) The enermax has a separate pCi-e power supply cable which is attached to the video card.

Can I just ignore the four pins for the MOBO 24 pin connection and leave the 20 pin connector in place?????????????

Is there a lightning cable power splitter / double charger?

A small example use case will make this clearer. I have a really long lightning cable that I use to charge my iPhone on my bedside table at night (there’s no wall socket close). I’m thinking of buying AirPods and naturally I would like to charge them with a cable also on my bedside table next to my iPhone. However, I have no interest in using another USB wall adapter or buying/using another really long cable.

So, is there any small lightning cable power splitter for charging two devices from one cable? What I mean is a small adapter where on one side there is a female lightning port (to connect to the already existing cable) and on the other side the cable splits into two small cables each with a male lightning connector.

I imagine this would be quite easy to do by manually splicing the cables. Since I’m only going to use this for charging (not syncing), it is just a question of splicing two male lightning connectors together by putting power and ground in parallel. But I’d be willing to pay a few bucks for something fabricated. Does anyone know of any product like this?

Note: This is NOT a power/headphone lightning splitter for iPhone7+. I’ve searched the internet with all the search terms I can think of and all I can find are those splitters.