[GreenKeys] RS232 to current loop dongle

[Jeffrey D Angus]

On 12/8/2014 10:48 PM, drlegendre . wrote:
> I don't see any reason this shouldn't work, but there's something that
> might need to be pointed out.. take a look at this line from the specs:
>
> "Power: Interface powered or external 9V DC/300mA power
> acceptable"
>
> To me, this means that it's a passive interface, and cannot supply
> the loop current for the CL side. So, unless your CL equipment
> has active (powered) interfaces, you're going to have to use some
> kind of external power supply. Otherwise, it's the correct device for
> the job.
It is a passive interface by itself. The suggested source for the 
external loop
is a 9 volt DC source.

If I remember correctly, a Model 15 selector magnet is around 60 ohms,
but it's also a fairly large inductance. Which is also WHY they use a 120
volt supply. So as to act as a current source with high compliance to
overcome the inductance and get the waveform to better approximate a
square wave with minimum distortion.

The only "correct" application for this converter is talking to a matching
converter at the other end and at a distance of under 3200 ft.

If you're looking for a method of safely dealing with vintage Teletype gear,
this <http://www.aetherltd.com/connecting.html> is a "know to be good"
implementation.


-- 
Jeff-1.0
wa6fwi
http://www.foxsmercantile.com

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