[GreenKeys] A reliable current-loop-to-RS232 converter

[Gabriel Egan]

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/