[GreenKeys] Loop supplies or selector magnet drivers

[Hugh Pyle]

To add my own experience on this (great) thread...

I have a 33 and built a loop supply, and a USB-driver that uses a Teensy
microcontroller.  The whole thing works really well, but it's definitely in
the "homebrew" category and not "shovel-ready".

Project notes:
https://github.com/hughpyle/ASR33/blob/master/tty-usb.pdf

The 20mA loop supply that I built is easier than a 60mA heavy-metal supply,
since it doesn't need to drive the large inductances (or any reverse
kickback).  But I think with 60mA too, you should be able to use a lower
voltage power supply than 120v by regulating the current in a similar way.

Here's the sort of thing I mean.  Spice model says it should work ;)

The one drawback of this circuit is that the load isn't referenced to
ground.  It should be possible to build a PNP equivalent if that's
important.



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