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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