[GreenKeys] Who made this RS-232 / Current Loop converter? Any docs??

[Chris Elmquist]

On Tuesday (12/02/2014 at 10:08AM -0600), drlegendre . wrote:
> 
> I'm curious about one thing. Were these units ever used in pairs, to extend
> the maximum run for RS-232 devices? RS-232 is only good for distances
> measured in feet, but CL lines should be good for miles, I'd think?

In my experience, this was not typically done.  Instead, RS232 was
extended using "short haul modems".  These were differential line
driver/receiver pairs with a little logic in them that could also convey
the hardware handshake/flow control signaling such as DTR, DCD and
RTS/CTS end to end over a 4-wire circuit.  If you just used a current
loop, you lost the hardware handshake signals and for higher baud rates,
the noise immunity of a current loop wasn't ideal.

I think there was a period where RS232 and 20mA existed together on
lots of data terminal equipment.  For example, my DEC VT220 (c. 1982)
terminals have both an RS232 connection and a 20mA loop connection.
So if the environment was such that they were replacing a 20mA TTY,
they could just drop it in but I don't think they were doing it for the
distance as much as the backward compatibility.

Chris
 
> On Tue, Dec 2, 2014 at 9:09 AM, Chris Elmquist <chrise at pobox.com> wrote:
> 
> > On Monday (12/01/2014 at 08:27PM -0600), drlegendre . wrote:
> > > Any idea who made this, or where I can find a document? Some quick pics
> > are
> > > at:
> > >
> > > https://nerp.net/~legendre/greenkeys/rs232_cl_converter_01.jpg
> > > https://nerp.net/~legendre/greenkeys/rs232_cl_converter_02.jpg
> > >
> > > The only logo on the case looks like "ED&M" which might also be :"EDeM"..
> > > Other sources indicate that it was made by "Camiacs" - and the circuit
> > > board is marked:
> > >
> > > "RS232 / CL MODEL 5"
> > > "CAM 25-116A"
> > >
> > > So perhaps 'CAM' = Camiacs? It has several series of internal jumpers on
> > > the board, so it looks like it can be configured in multiple ways.
> >
> > I concur with that analysis.  If you feed Google, "RS232 / CL MODEL 5",
> > you get lots of links to Camiacs RS232/CL converters, including this one,
> >
> > http://www.ebay.it/itm/Camiacs-RS232-CL-Convereter-Model-V-/180909962801
> >
> > which has their logo in place of the ED&M on yours.
> >
> > > Oh, and FWIW - on the RS-232 side, pins 2,3,5,6,7,8 are in use. The CL
> > side
> > > has pins 1,2,3,4 in use.
> > >
> > > Thanks for any help! I have two of these now, and it would be nice if I
> > > didn't have to reverse-engineer them to put them to use..
> >
> > I didn't find any hints of online documentation.  I'm betting it will
> > be faster to reverse it and make your own schematic.  It shouldn't be
> > a very complicated circuit.
> >
> > Are the AC outlets in parallel with the AC input or are they somehow
> > controlled by the circuit (ie, some kind of auto-power off when line is
> > idle or code controlled maybe?)
> >
> > --
> > Chris Elmquist NØJCF
> >
> >

-- 
Chris Elmquist