[GreenKeys] half normal phone jack?

[jhhaynes at earthlink.net]

Thanks for all the explanations.  I was going to mention something much 
more obscure that isn't half-normaling but is definitely half-a**ed.

Western Union got some patents in the 1930s for patching jack systems.
One of the features is a plug with flat conductors rather than round,
so that you can insert it into the jack and not open the normal contacts.
Or you can insert it rotated 180 degrees and open the normal contacts.
And there were dummy plugs which turned the jacks into switches in that
you could rotate the plug to open or not open the normal contacts.
Since these were for telegraph circuits, which are kept closed at all
times, the dummy plug was conducting and would short the tip and sleeve
together as it opened the normal contacts.


jhhaynes at earthlink dot net