[GreenKeys] Lorenz Lo15 - advice request!

[John Nagle]

> From: Mattis Lind<mattislind at gmail.com>
> Subject: [GreenKeys] Lorenz Lo15 - advice request!
> So I have been working with a Lorenz Lo15 teleprinter for some time.
> ...
> I designed a small circuit. Still in prototype. It is a step-up converter
> that creates up to 120 V DC line voltage. Then I made a small hysteresis
> switching current source that could generate up to 60 mA line current.
> 
> https://i.imgur.com/Jok5QL8.jpg?1
> 
> There is a small STM32 micro controller controlling desired output line
> voltage and line current. It also can generate some simple test patterns.
> 
> The idea is to integrate RS-232, USB, and current-loop (yes for interfacing
> an old PDP-11) to this circuit.

    That's useful.

    A few years ago I designed and built a board to connect
60mA Teletypes to a USB port.  It provides 120V 60mA and is
powered entirely from the USB port. Several others have built
this board with good results.

https://github.com/John-Nagle/ttyloopdriver

    The problem is that I designed it as modern electronics.
It's all surface mount with some fine pitch parts.  It
had to be; all the good parts for switching power supplies are
surface mount.

    So it's beyond the building abilities of most US hobbyists.
If someone needed a hundred units, this would be the way to go,
but as a one-off, it's just too much trouble to build.

			John Nagle