🚀 go-pugleaf

In article <1992Sep13.040534.3754@newshub.ariel.yorku.ca> cs911461@ariel.yorku.ca (CHRISTIAN D. ARMOUR) writes:
>This may seem a little weird, but I'm trying to connect an
>old Teletype machine (one of those noisy things you see in
>early seventies cop shows) to my Unix based PC.  The only
>way I can imagine doing this is to get it connected via 
>the RS-232 port.  The problem is, the connector cable on
>the tty has a 6-pin male connection.  Can anyone of a 
>technical nature please tell me how I can cut this thing
>off and replace it with a RS-232 plug.  I'd appreciate any
>kind of response, even if you're not sure.

Genuine Teletype electromechanical printers used "current loop"
interfaces, initially something like 60mA and later 20mA in many
computer applications (early 1970s).  The general idea of the
current loop is that the transmitting (keyboard) and receiving
(type selector) subunits are connected in series with a power
supply and the remote transmitter/receiver, with a constant
current flow in "idle" condition that holds solenoids shut.
When a key is depressed it selects a bunch of levers that set
up an encoding and triggers a clutch that then samples the
encoding and transmits first, a "space" (absence of current),
then a series of either "marks" (normal current flow) or "spaces"
(no current) representing the encoding, then ends with a constant-
"mark" idle current condition.  The receiver's solenoid lets go
when the initial start "space" arrives, triggering a rotating
selection mechanism that in effect periodically samples the
encoding marks/spaces (a solenoid toggles as the current
changes, moving attached levers etc.), setting up a set of type
selector bars.  At the end of the rotation, the stop "marking"
(idle) current relatches the trigger solenoid as the set-up type
selector bars control which type element is positioned under the
print hammer.  (There are also control functions such as carriage
return, line feed, bell, etc. but they're just variations on the
general theme.)

Anyway, "all you need to do" is convert RS-232-C transmit/receive
voltages to 20 (or 60?) mA currents.  These current-loop converters
used to be fairly easy to find, but any decent EE ought to be able
to whip one together for you using spare parts from his junk box.
One thing to watch out for is that the Teletype is a highly
inductive load.  I think low RS-232-C voltages correspond to
"mark" (current flowing) and high voltage to "space" (no current).