[GreenKeys] 18 volt Internal Loop Supply

[Jeffrey Golas]

Someone recently posted that Teletype had an rs-232 adapter or two. I think the thing about the current loop is that it was so prevalent that it was less risky and more flexible to design around it than do something natively new.

The polarity thing on the 32 had to do with the switching gear; it was still current loop from the carrier, so a temp reversal I think meant an ended call (or answered I forget). A reversed current from idle indicated an incoming call. The 32/33 manual describes the call control states, which was via telegraph lines/loop yet.

Meanwhile the 33 CCU (UCC3?) was intended for a POTs line so its completely different from the 32.

At least thats what I learned so far. 

Jeff




> On Jul 8, 2022, at 10:46 PM, Jim Haynes <jhhaynes at earthlink.net> wrote:
> 
> On Fri, 8 Jul 2022, Tom Hunter wrote:
> 
>> That is why the 32 is polarity sensitive.
> And why it was smart of the designers of MITE to throw a bridge rectifier
> in front of the thing to make it polarity insensitive.  What I still don't
> understand is why the Bell Labs people designing the 101 Data Set chose
> to have it drive the Teletype selector magnet driver with a current rather
> than with a voltage.  And why Teletype didn't develop a selector magnet
> driver with RS-232 input rather than current input.
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