[GreenKeys] A note of thanks!

[Jim Haynes]

On Wed, 14 Oct 2020, Harold Hallikainen wrote:

> My notes for model 15 are at https://w6iwi.org/rtty/
>
A great thing about the Model 15 is that it is pretty easy to understand
and explain to people.  For basic TTY theory there is the AT&T book
Principles of Electricity Applied to Telephone and Telegraph Work.  At
least one edition is available online.

Once you have the basics it's pretty clear how the thing works.  Selector
magnet, cams, swords, etc. are explained in the AT&T book.  That shows
how you get started and stopped every character and deserialize the bits
of each character into five positions of parts.  Five of the vanes
make that information available across the width of the typing unit.
Bellcranks transfer the information from the vanes to the code bars,
and that's where the decoding takes place.  Then the cam that powers
the printing bail to fling a type bar at the paper.

Behind the vanes, the function bars that decode the functions: LTRS, FIGS, 
etc.  The sixth vane that allows functions to be limited to either LTRS 
or FIGS case.  Underneath the machine the function bar ends push up bars 
to engage a cam-operated bail to do things like shift the carriage up or 
down, ring the bell, suppress spacing, etc.  The spacing mechanism that 
drives the carriage across the width of the machine.  What is a little bit 
tricky is the mechanism that prevents it from moving more than one space 
at a time.  As our old machine shop instructor would say, "That's all they 
are to it."

The keyboard code bars that move right or left according to which key is
pressed.  They engage cam followers that allow or disallow the contacts
to close as the transmitting shaft rotates.  A little tricky mechanism
to insure that only one character gets generated per key press.