Bertho shared his NoLoop galvanic isolator in the project log forum:
I had a problem some time ago with a nasty ground-loop and that cost me the USB port on my old laptop. It took me a while to realize what had happened and it was a generic problem we all run into more often than we think. Time to solve this particular problem once and for all and make generic isolation for Serial and SPI ports.
For more information visit the project’s Tindie site.
Via the forum.