[GreenKeys] RS232 to current loop dongle

Tue Dec 9 09:03:11 EST 2014

Gil and other HeavyMetal crew,

Great stuff here. Thanks for the further background. Well, I'm back on 
Greenkeys after a 5 year hiatus. This "new" AN/UGC-129 here has me back 
with the bug. The 28s and other assorted military surplus metal here 
needs some action!

I was thinking RS-232 but frankly USB is better for most nowadays 
(and/or wifi? - wow!). Any way to be able to get PC data to metal would 
be a boon, frankly. Right now I am simply sending text from soundcard 
RTTY software into my Dovetron to make the loop sing locally.

Do you all think there is enough interest to create something that could 
be Kickstarter-ed or offered as a bulk-buy to Greenkeys members?
I'm a hobbyist-fidgeter but not so a designer or engineer. I'm not 
afraid to burn my fingers on a soldering iron, but rely on you smart 
people for the designs.

My Dovetron and ST-6s have been enough for now, but I really want to 
kick it up a notch and send/auto-send from my PCs. Gil, your comments 
and ideas are great. Not sure where we need to go next to make it 
happen, though.

The off-the-shelf dongle I saw online got me excited - and thinking...

http://datainterfaces.com/rs232_female_current_loop_interface_converter.aspx

-"Fibber" AKA: K6FIB/Christopher in Salem, OR
<admin for http://www.drmna.info>

On 12/8/2014 11:09 PM, Gil Smith wrote:
> Hey guys:
>
> Sheesh, this 232 to loop stuff sure gets kicked around a lot.  A lot of
> us have done designs for this:  John Nagle has a board design (and
> awesome restored tty gear);  Jack Hart has done a nice pcb design also;
> I did some designs years ago,  others I'm sure I am forgetting
> (apologies)...
>
> The black-box-etc "low-voltage" loop converters will likely be fine for
> M33 and similar machines, but the M14/15/19/20/28/31/35... high-voltage
> loop equipment is a bit more work.
>
> I am kind of in circuit-board-design mode, so would you folks like
> something new?  There are several aspects which we must consider:
>
> A)  The classic tty loop supply has historically been a 120VDC supply
> with a drop resistor for 60 mA (sometimes 20 mA), and an HV keying
> transistor.  I used a 1:1 isolation transformer on a 120VAC US powerline
> to get about 160VDC, but found it better to wire it in 2:1
> (240VAC:120VAC) configuration so I ended up with a loop supply of about
> 80VDC.  This seemed safer, cooler, and just dandy for me.  Still, it
> needed heat-sinked power resistors.  Jim Haynes had an idea for a
> current-source design, that would minimize power dissipation and just
> need a heat-sinked bjt or mosfet transistor, and no resistors.  Some
> other folks have offered ideas about dynamic switching, to minimize
> non-transmission power consumption.  So the whole loop-supply/keying
> issue is still not optimized.
>
> B)  Once the loop-keying design is chosen, it is probably a good idea to
> opto-isolate the loop keyer from the data source (computer...) for
> safety, if it is simple rs-232.
>
> C)  Is it a hard-wired 232 link, a USB port, or maybe a nice wifi or
> other RF interface (not needing isolation)?
>
> D)  Is the computer going to provide baudot code (eg: Heavymetal, on
> limited serial port/usb-adapters) or is the computer just providing
> ascii text and the interface box needs to do the conversion?
>
> E)  Maybe the interface box needs to provide relay-or-ssr-switched motor
> power when data received, and a bit of buffering so no chars are lost?
>
> F)  Maybe a few pushbuttons to print pre-programmed text (eg: Batcave or
> museum application)?
>
> G)  Maybe a discoverable ethernet IOT device so you can have world-wide
> apps talking to it?
>
> let me know if anyone wants something new.
>
> thx,  gil
>
>
> gil smith, AF7EZ
> greenkeys moderator
> gil at baudot.net <mailto:gil at baudot.net>
>
>
>     -------- Original Message --------
>     Subject: Re: [GreenKeys] RS232 to current loop dongle
>     From: Roy Morgan <k1lky68 at gmail.com <mailto:k1lky68 at gmail.com>>
>     Date: Mon, December 08, 2014 10:50 pm
>     To: digitalham at gmail.com <mailto:digitalham at gmail.com>
>     Cc: greenkeys at mailman.qth.net <mailto:greenkeys at mailman.qth.net>
>
>
>     On Dec 8, 2014, at 9:16 AM, digitalham at gmail.com
>     <mailto:digitalham at gmail.com> wrote:
>
>     > Gents,
>     >
>     > Anyone used this or a similar device to talk to their loop from a PC? This one isn't that expensive. I'm wondering if I should give it a try.
>     >
>     >http://datainterfaces.com/rs232_female_current_loop_interface_converter.aspx
>
>     BEWARE
>
>     It’s been reported recently on this list that some of these gadgets
>     will operate only up to 30 volts or so.
>
>     Roy
>
>     Roy Morgan
>     RoyMorgan at alum.mit.edu <mailto:RoyMorgan at alum.mit.edu>
>     K1LKY Since 1958
>
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