[GreenKeys] Signal Line Connection - RS-232 Interface

[Ken Wiebe]

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

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/greenkeys/attachments/20190606/c9b10455/attachment.html>