[GreenKeys] Estrella Warbirds Museum W6EWM RTTY progress

[Mike Douglas]

Here’s an RS232 to Model 15 solution: https://deramp.com/model15_interface.html

Mike D

> On Oct 14, 2026, at 12:03 PM, Jim Haynes via GreenKeys <greenkeys at mailman.qth.net> wrote:
> 
> Then all you need is a circuit to convert the computer RS-232 to the
> 60 ma 120 volt loop of the Model 15.  preferably a 115:115 volt transformer to isolate your circuit from the power line for safety.
> full wave bridge rectifier and an electrolytic cap to make DC.  1500 or
> some what resistor to limit the current to 60 ma. some kind of keyer
> device.  We used to use a high voltage transistor, but now you can find
> opto-to-FET devices that will do it nicely. Attached is John Nagle's
> circuit and ofcourse you throw away half of it if you are only interested
> in running the printer.  And some suggested loop keyer devices.
> 
> You need something to protect the keyer device from the inductive kick
> when the loop opens.  Could use a Zener diode or an R-C snubber circuit.
>    ---
> 
>    "Ya can argue all ya wanna, but it's dif'rent than it was."
>    "No it ain't! No it ain't!  But ya gotta know the territory."
>        Meredith Willson, The Music Man
> <RS-232-to-loop.png>
> <loop_keyers.pdf>
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