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 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: [email protected] <[email protected]> on behalf of Tim McNerney <[email protected]>
Sent: Thursday, May 8, 2025 9:52 AM
To: [email protected] <[email protected]>
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

______________________________________________________________
GreenKeys mailing list
Home: http://mailman.qth.net/mailman/listinfo/greenkeys
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]

Jordan Spencer Cunningham's GreenKeys Search Tool: https://teletype.net/gksearch

2002-to-present greenkeys archive: http://mailman.qth.net/pipermail/greenkeys/

1998-to-2001 greenkeys archive: http://mailman.qth.net/archive/greenkeys/greenkeys.html

Randy Guttery's 2001-to-2009 GreenKeys Search Tool: http://comcents.com/tty/greenkeyssearch.html

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]