Martin,

> Might I suggest a google of "data diode", the functionality
> that you appear to be seeking sounds close to their usage.

Alas, no. That "data diode" is a one-way communication solution, while I aim
at a solution in which /no/ direct communication between the two groups is
possible (neither side can poke around the other subnets 'puters and ports
thereon).

> There are a number of designs in the public domain most
> of them centered around USB to serial links

I already tried a standard DB9 serial connection, but those are, nowerdays,
simply too slow to send much of anything over.   But yes, I've been taking a
peek in that direction too.

https://www.sjoerdlangkemper.nl/2019/03/20/usb-to-serial-uart/

The 12 Mbit one looks good.  Even its half-speed sibbling would not be too
bad.   On the other hand, seeing talk about "... have drivers that reliably
crash the operating system" doesn't spark much confidence. :-\

I also found some "USB Bridge" references that looked interesting, but there
is very little actual info about them (like what kind of USB device do they
represent on both sides). And that they seem to be supported by the Windows
OS itself could mean they have all the drawbacks of a LAN connection. :-(

Regards,
Rudy Wieser

--- SoupGate-Win32 v1.05