It seems surprisingly hard to find that, though this
https://forum.vcfed.org/index.php?threads/rs-232-to-current-loop-interface.47841/
is close.
Conceptually it's really easy. The main tricky part, certainly if you're
driving a mechanical terminal like a Teletype, is the current source. You need
something that can drive 20 mA into an inductive load. The classic answer was
to use a fairly high voltage with a big series resistor so the inductive
impedance is much less than the resistance. A current regulator would be a
modern replacement. Also, for the case of the inductive load, you'd need a
shunt diode across the switch to absorb the voltage spike from the inductor
when the current is switched off, otherwise the switching transistor will be
quickly destroyed.
paul
> On May 2, 2023, at 7:42 AM, Jonathan Katz via cctalk <[email protected]>
> wrote:
>
> Hi everyone!
>
> I'm working on a project where I need to build an RS-232 to Current
> Loop adapter. I've seen some schematics on-line and the parts list
> seems pretty small, but does anyone have a specific set of
> instructions and schematics that they trust? Or does anyone in the UK
> have a spare adapter they'd like to send me? :D
>
> Thanks!
>
> --
> -Jon
> +44 7792 149029
