[GreenKeys] TTY word counter

[Jim Haynes]

That's interesting.  I'm sure Teletype had some word counters in the
product line, but they probably counted actual spaces and newlines
rather than just all characters.  But then they counted words from the
keyboard and this thing presumably counts words from incoming traffic.

I see it uses the oscillator-transformer-detector scheme that was more
or less the standard way to get DC isolation of the TTY loop before
we had those wonderful opto-couplers.  In even earlier times there
was an isolator consisting of a gas discharge tube surrounded by an
electromagnet carrying the loop current.  The magnetic field from
loop current would disrupt electron paths so they couldn't get from
cathode to anode of the gas discharge tube.