[GreenKeys] Regenerative Loop Driver for Model 15 Teletype

[Harold Hallikainen]

I also thought about the selector magnet and keyboard in series. However,
the selector magnet flyback voltage comes from the top of the keying
transistor, and it would not be there if the loop is interrupted by a
series keyboard, instead.

Here, I'm using the typical high voltage DC supply with series resistor to
drive the loop. I use TRS connectors so the shell can be grounded. The
jacks also have shorting switches so the loop remains closed when
equipment is unplugged.

The boost circuit is clever!

Harold


On Wed, December 8, 2021 2:30 pm, Mike Douglas wrote:
>  Jim,
>
> One of my main goals with this project is to use the Model 15 as an
> operator console with my vintage computers (e.g., Altair 8800, IMSAI 8080,
> etc.) in the same manner as I use my Model 33. This requires full duplex
> operation, and therefore, separate send and receive loops. But I'm a child
> of the computer age, so Irv Hoff and I have different goals for the
> equipment :)
>
> Mike
>
>      On Wednesday, December 8, 2021, 03:10:48 PM CST, Jim Haynes
> <jhhaynes at earthlink.net> wrote:
>
>  That's very interesting - using such modern technology to drive an
> ancient
> Teletype.
>
> "Back in the day" Irv Hoff was always insistent that the Teletype keyboard
> and printer should always be simply in series, and his "Mainline" stuff
> always worked that way, so there was a single 2-conductor cord between the
> machine and the electronics.  I was not particularly taken to that point
> of view, and in fact my designs at the time worked around converting the
> Teletype external interface to something related to RS-232.
>
> But I did fiddle around with, never built, a "leg combiner" circuit that
> allowed the keyboard and printer to be simply in series in a loop but
> provided separate receive and transmit legs.  The trick is to detect
> whether a spacing signal came from the keyboard or from the receive leg,
> which involves setting a latch.  If anybody wants to look at this circuit
> just ask.
>
> Jim W6JVE
>
>  Â Â Â  ---
>
>  Â Â Â  "Ya can argue all ya wanna, but it's dif'rent than it was."
>      "No it ain't! No it ain't!  But ya gotta know the territory."
>  Â Â Â  Â Â Â  Meredith Willson, The Music Man
>


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