[GreenKeys] Modem with 20mA current loop interface

[Jim Haynes]

On Mon, 15 Dec 2014, drlegendre . wrote:

> What other 20mA 'levels' exist, and what differentiates them?
> Would the 12V / 470-600R loop used with many simple level converters be
> considered low-level 20mA?
> 
Yeah, what I mean is that the M32/33/35 machines use electronic selector
magnet drivers and the input to those is 20 or 60 ma but at low voltage,
like 20 volts.  The older machines, M14/15/28 have the selector magnets
brought out, not run through a solid state driver, so they require 60 or 
20 ma at typically a high voltage like 120V and generate inductive kick
when the circuit is opened.  A very few of them have solid state drivers
incorporated so the input loop can run at low voltage.  And you can use
less than 120V with a more complicated driver circuit, or if you have
perfect signals to begin with.