[GreenKeys] A reliable current-loop-to-RS232 converter
Gabriel Egan
mail at gabrielegan.com
Thu Aug 13 19:15:09 EDT 2015
Dear Gil
It's this converter:
http://uk.rs-online.com/web/p/interface-adapters/6403584/
They don't give a schematic or a manufacturer name/model
number (on the website or with the product).
I'd rather avoid trying to make something myself: I
don't have a good track record.
Regards
Gabriel
On 8/14/2015 12:05 AM, Gil Smith wrote:
> Hi Gabriel:
>
> A couple of questions:
>
> - do you have a schematic of this loop converter, or even a manufacturer
> name/model number?
> - are you handy with a soldering iron?
> - do you have a scope available?
>
> It might not be too tricky to get it running if we know what you have,
> but the wire colors really don't tell us much. And it is really
> difficult to troubleshoot something without a schematic, and even less
> so if you only have a meter available.
>
> If you don't mind a bit of soldering, you could patch together a circuit
> like Jack's and don't even need to worry about a groundplane or anything
> fancy. Just a bunch of air-wired components and connectors that you
> could hot-melt-glue into a toilet-paper tube or whatever.
>
>
> gil smith, AF7EZ
> greenkeys moderator
> gil at baudot.net <mailto:gil at baudot.net>
>
>
> -------- Original Message --------
> Subject: Re: [GreenKeys] A reliable current-loop-to-RS232 converter
> From: Gabriel Egan <mail at gabrielegan.com
<mailto:mail at gabrielegan.com>>
> Date: Thu, August 13, 2015 3:49 pm
> To: Jarratt RMA <robert.jarratt at ntlworld.com
> <mailto:robert.jarratt at ntlworld.com>>
> Cc: Greenkeys <greenkeys at mailman.qth.net
> <mailto:greenkeys at mailman.qth.net>>
>
> Dear Rob
>
> Thanks -- just a found a couple of Westemos in Ebay
> but they're really expensive: hundreds of pounds.
>
> Regards
>
> Gabriel
>
> On 8/13/2015 10:51 PM, Jarratt RMA wrote:
> > I bought a Westermo converter which has worked well for me,
there was
> > one listed on ebay not too long ago, and I seem to remember it
was in
> > the UK. I am not at home now to check how I set it up, and I may
> not get
> > time to look for a while.
> >
> > Regards
> >
> > Rob
> >
> > On 12 August 2015 at 15:32, Gabriel Egan <mail at gabrielegan.com
> <mailto:mail at gabrielegan.com>
> > <mailto:mail at gabrielegan.com>> wrote:
> >
> > I'm trying and failing to get my new ASR-33
> > communicate with my Altair 8800 clone via
> > a current-loop-to-RS232 converter purchased
> > from the usually reliable UK retailer RS
> > Components.
> >
> > The converter has rather a lot options, and
> > it's able to support Active as well as Passive
> > current-loop operation. I've got it set to
> > Active and it's got 5v coming in from a USB
> > cable.
> >
> > On the Teletype end, I have four coloured wires
> > coming from the Teletype:
> >
> > TTY Send: Red (3) and Black (4) wires (not
> > otherwise differentiated)
> >
> > TTY Receive: White (7) (positive) and
> > Blue (6) (negative)
> >
> > (These assignments including the numbers 3, 4, 6, and
> > 7 come from a label on the data cable coming from the
> > Teletype).
> >
> > On the converter I have a terminal block with
> > five screws. If I select Full Duplex operation
> > and select that both Tx (Transmit) and Rx (Receive)
> > are Active then those five terminals have these
> > assignments:
> >
> > TB1: Tx I+ Out / V+
> > TB2: No Connection
> > TB3: Rx I+ Out / V+
> > TB4: No Connection
> > TB5: Tx/Rx I- In / V-
> >
> > (This is exactly how the manual describes them;
> > I assume that "I" means "current", as Andre-Marie
> > Ampere himself decreed.)
> >
> > On the principle that what the converter considers
> > to be the act of 'sending' is what the Teletype
> > considers to be the act of 'receiving' I connected
> > the White wire from the Teletype to TB1 and the Blue
> > wire from the Teletype to TB5. I set the converter
> > to DCE operation and booted the Altair: Success! The
> > MITS BASIC welcome message prints on the Teletype
> > and I'm asked to enter Memory Size, just as
> > expected.
> >
> > So, just the other two wires to connect and all
> > should be well. This is where I get stuck!
> >
> > I connected the Red wire from the Teletype to the
> > TB3 and the White wire from the Teletype to
> > TB5. No luck. I reversed them: White to TB5
> > and Red to TB3. No luck. Then I tried all
> > permutations of the remaining terminals
> > (everything except TB1 and TB5 since these
> > are clearly in use for data going the other
> > way). No luck.
> >
> > Then I did all the above again with the converter
> > set to Active on the Tx side and Passive on the
> > Rx side. (No use setting the Tx side to passive
> > as this just makes the Teletype 'run open'.)
> >
> > What else might I change on the converter? 60ma
> > instead of 20ms? No luck (Teletype just 'runs
> > open'). Half Duplex instead of Full Duplex
> > (No good: seems to be for systems sharing the
> > same pair of wires for both sending and receiving,
> > and we know we're not doing that.)
> >
> > I think I've run out of options with this particular
> > converter. Is a 5v USB supply not enough current?
> > This seems unlikely since they sell this converter
> > for current-loop applications.
> >
> > If anybody on the Greenkeys lists can see my fatal
> > error(s) in the above, I'd be grateful to know.
> >
> > Alternatively, can anybody point me towards the
> > seller of a current-loop-to-RS232 converter that
> > is known to work with Teletypes and for which
> > they can tell me exactly where my four coloured
> > wires go? If anybody is willing to make me such
> > a converter, I'd be happy to pay any reasonable
> > price.
> >
> > Regards
> >
> > Gabriel Egan
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> --
>
________________________________________________________________________
> Professor Gabriel Egan, De Montfort University. www.gabrielegan.com
> <http://www.gabrielegan.com>
> Director of the Centre for Textual Studies http://cts.dmu.ac.uk
> National Teaching Fellow 2014-17 http://www.heacademy.ac.uk/ntfs
> New book: Shakespeare and Ecocritical Theory:
> http://www.bloomsbury.com/uk/9781441145529/
> ______________________________________________________________
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--
________________________________________________________________________
Professor Gabriel Egan, De Montfort University. www.gabrielegan.com
Director of the Centre for Textual Studies http://cts.dmu.ac.uk
National Teaching Fellow 2014-17 http://www.heacademy.ac.uk/ntfs
New book: Shakespeare and Ecocritical Theory:
http://www.bloomsbury.com/uk/9781441145529/
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