I believe he said the model 15 one depends on the actual 25 selector coils so it wont work with others except maybe a 14.

The 33 one may work but Its prob hard wired for 110 baud?

A 20ma current loop transmitter may work if you can find a way to feed it data, say from fldigi.

The fastest cheapest easiest test would be the arduino one on Hackaday using a relay. It works!

I think this one: https://hackaday.io/project/2836-arduino-teletype

Jeff



On May 18, 2025, at 8:19 AM, John, W9DDD <[email protected]> wrote:



Actually the M15 adapter would be a better fit.  Same designer, same source.


https://deramp.com/model15_interface.html


Tested on one of my 28s by Mike, don't know whey I didn't think of it when the question was originally posted.


On 5/18/2025 2:20 AM, Erik Grant wrote:
While this one is for the M33, it might be worth while to contact this guy @ https://deramp.com/tty_adapter.html

~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



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---
----
The above comments or recommendations are SWAG. Use at your own risk.

John, W9DDD
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