[GreenKeys] Low voltage set, was Trepac 538-A Telegraph Relay

[Jim Haynes]

> FWIW, Here’s the 60ma selector magnet driver used for military low level
> +/-6v signaling. 
> http://www.navy-radio.com/manuals/tty/wd/323810WD-SMD.pdf
> 
> It has two ORed inputs, one of which can be tied to the keyboard in a KSR. 
> 
That's an awfully complicated circuit.  Attached is the one I was using
circa 1970.  The + and - 9 volt power supplies come from a 6.3V
transformer and rectifiers.  The 120 volt supply is standard Teletype,
and is used for the keyboard contacts to insure burning off any oil films
on the contacts (and because it's there).  This uses RS-232 input voltages
where - is mark and + is space.  You can use all the diode OR gates you
want to allow multiple inputs.
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