Flyback diode mesa 7i95t

Using the 12v rail from your PC negates the protection the optos are used for.

I suggest to forget all the BS you've learnt from the Hipster Maker crowd and read & learn by someone that knows his stuff.

This is a good start, written by the guy that designed the TEC-1 sbc back in '83 or '84:
www.talkingelectronics.com/te_interactive_index.html

The function of an optocoupler is to completely isolate one side of a circuit from another. Hence the large no copper regions under the device.
No amount of filtering, hoping nor thinking will provide this if the same supply is used or if 2 different supplied are used and their grounds connected.
Pickup a book, read & learn.
Eventually your mis advice will end with someone with less knowledge and experience than yourself having a bad time.
Those unseen electrons moving around can bite.

Connecting the wires "far from each other" from the same supply will do nothing.There is no electrical isolation. None whatsoever.

Is it really bickering when correcting so much bad information from langdons ?

This is what I meant in my problem thread.

Apologies to the OP, just didn't want you to do anything that could cause issues.