[GreenKeys] A reliable current-loop-to-RS232 converter
teletypeparts at comcast.net
teletypeparts at comcast.net
Thu Aug 13 20:15:03 EDT 2015
Dear Gabriel and GK's,
I have seen some 33's with only 3 wires on the line cord. They strap one on the Terminal Strip. I don't know what the theory was or how it worked, but I have seen this before.
Jack or anyone on GK's ever see this hook up before?
Wayne
KB1FDW
----- Original Message -----
From: "Gil Smith" <gil at baudot.net>
To: "Gabriel Egan" <mail at gabrielegan.com>, "Jarratt RMA" <robert.jarratt at ntlworld.com>
Cc: "Greenkeys" <greenkeys at mailman.qth.net>
Sent: Thursday, August 13, 2015 7:05:05 PM
Subject: Re: [GreenKeys] A reliable current-loop-to-RS232 converter
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
-------- Original Message --------
Subject: Re: [GreenKeys] A reliable current-loop-to-RS232 converter
From: Gabriel Egan < mail at gabrielegan.com >
Date: Thu, August 13, 2015 3:49 pm
To: Jarratt RMA < robert.jarratt at ntlworld.com >
Cc: Greenkeys < 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 >> 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
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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