[GreenKeys] Signal Line Connection - RS-232 Interface

[Clay Archer]

On my 33ASR's it's necessary to supply the loop current externally.    If
you loop it back to itself without a power source it will continue to run
open-loop.    However, on my 35 ASR I can loop it back to itself (jumper 6
to 7, and 5 to 8) it will run looped and echo typed characters like in local
mode.    My 35 has had several modifications (probably like most 33 & 35's
out there), so I don't know if providing a loop current source is standard
on the 35.

Clay

 

 

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Ken Wiebe
Sent: Thursday, June 06, 2019 9:41 AM
To: Thomas Tillson via GreenKeys
Subject: Re: [GreenKeys] Signal Line Connection - RS-232 Interface

 

Thanks.  The next goal for my 35 project is to interface it with an RS-232
device via the converter circuit.

 

As I prepare to do that, I am wondering about the signal line itself.
Setting RS-232 aside for the moment, in a real world scenario from
yesteryear, where does the loop current come from (power source)?

 

Remember I'm a newbie.  So, if I connected my tester to the 35 transmit
terminals and typed, would I expect to see anything happening?

 

I guess I'm looking ahead to what I would do next if my RS-232 experiment
doesn't work first try.  Is there a test or tests I can perform to isolate
the cause of the 35 not transmitting/receiving?

 

Ken

 

 

On Thu, May 30, 2019, at 23:01, Clay Archer wrote:

 

The shorting link is for half duplex operation with I/O on terminals 5 & 8.
Remove the shorting link for full duplex with send loop on terminals 5 & 6,
and receive loop 7 & 8.     When I got my 35 ASR it had been rewired
incorrectly and caused it to be looped in line mode.    A good schematic of
the ASR is available at https://www.blunham.com/Misc/ASR35/   The terminal
block is the one below where the power cord attaches (at least on my 35
ASR).

 

There are several good designs for RS232 to 20ms current loop.    There is
one that uses two opto-isolators and has fewer parts, but the one you show
works well too.

Clay

 

 

 

From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Ken Wiebe
Sent: Thursday, May 30, 2019 6:19 PM
To: Thomas Tillson via GreenKeys
Subject: [GreenKeys] Signal Line Connection - RS-232 Interface

 

As you may know, for the 33 ASR several people have designed and built
circuits to convert current loop to RS-232.  Example, I think Mike Douglas
may be a member of greenkeys and here is a link to his:

 

http://altairclone.com/teletype.htm

 

Question:

 

What about the 35 ASR?

 

I need to do this for the 35.  I couldn't find much online so I turned to
the 35 wiring diagrams in an attempt to find the signal line circuitry
equivalent to the 33.  On the 33, it's four pins on the P2 connector which
equate to the terminal strip pins 3, 4, 6, 7.

 

I think I found the relevant diagram for the 35, please see attached.
Something called "T" power terminal block, pins 5-8.

 

Anyone know where this is?

 

Sidenote:  See the note in the attd pic, "REMOVE LINK".  It looks like that
link sets up a loopback, right?  That may explain why my 35 seems always to
be in Local mode?

 

Anyway, I don't know where that "T" block is, and if you all could give me a
sanity check I'd appreciate.

 

Am I on the right track you think?

 

Thanks!

 

Ken

 

PS  I also attd Mike's schematic for the 33 version of the RS-232 adapter so
you can see what I'm making comparisons to

 

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