RobertoA wrote:

> How to proceed?

What you're trying to do would traditionally have been done by a
"terminal server" e.g. from DEC or Moxa, but could be done by a Pi.

On a hardware level you'll need a level shifter to convert the PI's
RX/TX pins from 3.3V TTL to +/- 12V e.g.

<https://uk.farnell.com/ftdi/ttl-232r-3v3/cable-usb-to-ttl-level-serial/dp/1329
311>

there are plenty of cheaper ones on ebay/amazon/aliexpress

Then you need to setup something listening on a known IP addr/TCP port,
which invokes the "cu" utility to talk to the /dev/ttyXX port.

not Pi specific, and probably xinetd won't be running by default, but
clues available here ...



Beware where it says there is zero security doing it this way, anyone
who is allowed [by your firewall] to telnet to your Pi, will be directly
connected to the serial port, you'd have to knock up any extra security
yourself ...

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