[GreenKeys] Affordable current loop adapter

[Erik Grant]

While this one is for the M33, it might be worth while to contact this guy @ https://deramp.com/tty_adapter.html
Teletype RS-232 Adapter - DeRamp.com<https://deramp.com/tty_adapter.html>
The Teletype RS-232 adapter comes fully assembled and tested as shown in the pictures on this page. A telephone cord and modular DB-25 connector are not included.Version "B" of the board is now shipping.
deramp.com

~KF7WAI

________________________________
From: greenkeys-bounces at mailman.qth.net <greenkeys-bounces at mailman.qth.net> on behalf of Tim McNerney <mc at media.mit.edu>
Sent: Thursday, May 8, 2025 9:52 AM
To: greenkeys at mailman.qth.net <greenkeys at mailman.qth.net>
Subject: [GreenKeys] Affordable current loop adapter

I need to test my 28RO.
Most of the RS-232 to 20 mA current-loop adapters are "wicked expensive."
Plus nowadays, RS-232 is not exactly easy to find as an interface.
So I'll be up to $200 before I finally connect to a computer via USB.
And of course USB to current-loop... good luck finding that adapter...

Can anyone recommend a circuit for a simple 20 mA current loop transmitter?
I have EE and soldering chops.  Happy to build my own prototype.

BTW, I've noticed lots of affordable 4-20 mA current loop transmitters
for remote industrial sensors.
Can these be adapted to serve as a 20 mA digital transmitter?
Intuition makes me think yes, but I want to double-check.
Maybe 4 mA does not equal "0".

Thanks.
--Tim McNerney

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20250518/4de33dc3/attachment.html>