IBM 5251 terminal USB conversion (but not what you think)

listofoptions · 02 Oct 2020, 02:13

thats cool, ive found some; let me know if these work, im planning on spinning up my own to do some data-sniffing around a system 32/34/36/38 i have occasional access to.
here are my notes for the 5250 anyway:

connector for panel mount connector Amphenol 082-5590-RFX
cable ends use Amphenol 082-5589-RFX
use Belden 9207 or equivalent

the cable ends and connectors should be 50-ohm (93ohm are hens teeth) and the cable is 100ohm (also a hens tooth, but Ive seen 100, 107, 93, 78, etc.. for twin-ax characteristic impedance ratings, so YMMV apparently)

inmbolmie · 02 Oct 2020, 08:24

listofoptions wrote: ↑
02 Oct 2020, 02:13
thats cool, ive found some; let me know if these work, im planning on spinning up my own to do some data-sniffing around a system 32/34/36/38 i have occasional access to.
here are my notes for the 5250 anyway:

connector for panel mount connector Amphenol 082-5590-RFX
cable ends use Amphenol 082-5589-RFX
use Belden 9207 or equivalent

the cable ends and connectors should be 50-ohm (93ohm are hens teeth) and the cable is 100ohm (also a hens tooth, but Ive seen 100, 107, 93, 78, etc.. for twin-ax characteristic impedance ratings, so YMMV apparently)

Connectors look fine. Cable in theory is 110Ω but yes, for short cables it shoudn't be that important. For some time was operating with a random twisted pair cable and terminators on a prototype board and worked just the same. Obviously if you run long cables with multiple stuff connected that becomes important.

monty11ez · 12 Dec 2020, 04:44

This is so amazing. I was just looking for a nice terminal project for my computer and came across some IBM terminals that looked really nice, but I didn't know how to connect them to a modern computer. Fortunately Google brought me here, so it looks like I might have a new project on my hands.

Pingmeide · 05 Jan 2021, 20:27

Hi, I just want to report that the 5250 adapter I got from Inmbolmie in July still works very well. The IBM 3477 Terminal I obtained works fine with the box and I use the terminal frequently - the picture quality is far more friendly (crisp) for the eyes than the normal computer screen.(In my opinion) Back in mid-2020 inmbolmie was very helpful in creating a "mapping" table for the German keyboard-layout and the money I spent was a good investment - thanks again !

inmbolmie · 26 Jan 2021, 00:23

Pingmeide wrote: ↑
05 Jan 2021, 20:27
Hi, I just want to report that the 5250 adapter I got from Inmbolmie in July still works very well. The IBM 3477 Terminal I obtained works fine with the box and I use the terminal frequently - the picture quality is far more friendly (crisp) for the eyes than the normal computer screen.(In my opinion) Back in mid-2020 inmbolmie was very helpful in creating a "mapping" table for the German keyboard-layout and the money I spent was a good investment - thanks again !

You are welcome, I'm happy that the converter worked well for you.

I have a couple of updates for this project. I recently got a new scope and was finally able to capture the signals over the wire, so here they are to document how the converter works at that level.

First, some frames from the converter. Yellow is Channel-A, blue is Channel-B, and purple is A minus B

Spoiler:

The same capture for frames generated by the 5251 as a comparison

Spoiler:

The captures were made with the line fully terminated. You can see levels are a little higher and transitions a little overshot in the converter signal, but nothing terrible and they are better than I expected. Also maybe the 5251 signal is a little smoothed because it was sampled at the other end of the cable.

Capture showing both, request and response

Spoiler:

The second update is about performance, some time ago the Python script performance was quite improved compared to what was published here, so I include a second video showing some more ASCII action as a comparison. I show Asciiquarium, text scrolling and the very famous ASCII Star Wars movie.

AJM · 28 Jan 2021, 18:44

I haven't seen that Asciiquarium before. It's very soothing.

And well done with the speed improvements. Thanks a lot.

jagtenfoxran · 03 Jun 2021, 23:48

I've just got hold of an IBM InfoWindow II 3486, and came across this thread when looking for ways to interface with it. Would be PCBs posted above be a possible way to interact with it? And if so, would I just be able to connect it from the DB15 connector on the terminal to the DB-15 on the PCB, or is the twin coax required?

inmbolmie · 04 Jun 2021, 00:50

jagtenfoxran wrote: ↑
03 Jun 2021, 23:48
I've just got hold of an IBM InfoWindow II 3486, and came across this thread when looking for ways to interface with it. Would be PCBs posted above be a possible way to interact with it? And if so, would I just be able to connect it from the DB15 connector on the terminal to the DB-15 on the PCB, or is the twin coax required?

There are no users I know currently with a 3486, but there is one user with a working 3477, that is a very similar model, so it should work but is untested.

I'm not terribly familiar with those "modern" terminals but the DB15 is intended to be used with a Twinax T adapter that is autoterminated. So using directly a DB15 to DB15 cable will not work as the terminal doesn't provide termination on its end. Of course you could "hack" some kind of terminators into the cable/connector on the terminal side.

jmaynard · 04 Jun 2021, 02:07

There were baluns available to use these terminals with 4-wire telephone cord. Wonder how those handled termination.

jagtenfoxran · 04 Jun 2021, 14:38

inmbolmie wrote: ↑
04 Jun 2021, 00:50

There are no users I know currently with a 3486, but there is one user with a working 3477, that is a very similar model, so it should work but is untested.

I'm not terribly familiar with those "modern" terminals but the DB15 is intended to be used with a Twinax T adapter that is autoterminated. So using directly a DB15 to DB15 cable will not work as the terminal doesn't provide termination on its end. Of course you could "hack" some kind of terminators into the cable/connector on the terminal side.

Thanks for the information! So I'm just trying to work out how I connect your PCB to the 3486. The only ports on the terminal are one female DB-15 and one female DB-25 (which I guess is used as a printer port). So I'm guessing that I would use the 3-pin twinax header on the PCB, connected to the screen by a cable like this: https://www.ebay.co.uk/itm/324348212725 (although I've just noticed this might not be an autoterminating cable)

Is this correct? Or is there another way to do it?

inmbolmie · 04 Jun 2021, 15:05

jagtenfoxran wrote: ↑
04 Jun 2021, 14:38

inmbolmie wrote: ↑
04 Jun 2021, 00:50

There are no users I know currently with a 3486, but there is one user with a working 3477, that is a very similar model, so it should work but is untested.

I'm not terribly familiar with those "modern" terminals but the DB15 is intended to be used with a Twinax T adapter that is autoterminated. So using directly a DB15 to DB15 cable will not work as the terminal doesn't provide termination on its end. Of course you could "hack" some kind of terminators into the cable/connector on the terminal side.
Thanks for the information! So I'm just trying to work out how I connect your PCB to the 3486. The only ports on the terminal are one female DB-15 and one female DB-25 (which I guess is used as a printer port). So I'm guessing that I would use the 3-pin twinax header on the PCB, connected to the screen by a cable like this: https://www.ebay.co.uk/itm/324348212725 (although I've just noticed this might not be an autoterminating cable)

Is this correct? Or is there another way to do it?

Well, the PCB already has a place to solder a DB15 female connector. So can use that or take the signals from there (pins 7,8 and 14) or from the Twinax header. The signals in any case are exactly the same. I don't directly solder a connector in my converters but that's because I don't have a custom 3D printed case design so I use bigger standard off-the-shelf cases with connectors directly mounted in the box.

The cables you indicate are usually autoterminated, with the termination enabled when no Twinax cable is connected on one side.

jagtenfoxran · 04 Jun 2021, 15:13

inmbolmie wrote: ↑
04 Jun 2021, 15:05

Well, the PCB already has a place to solder a DB15 female connector. So can use that or take the signals from there (pins 7,8 and 14) or from the Twinax header. The signals in any case are exactly the same. I don't directly solder a connector in my converters but that's because I don't have a custom 3D printed case design so I use bigger standard off-the-shelf cases with connectors directly mounted in the box.

The cables you indicate are usually autoterminated, with the termination enabled when no Twinax cable is connected on one side.

OK, great. Are you still selling the boards, or will I need to get one made up?

jgch · 29 Mar 2024, 11:38

Just stumbled upon this great project!

I might have overlooked it, but is there way to change the keyboard settings? Specifically, I would love to use the 'real' 5250 enter key (the one where the right control key normally is).
A bonus would be to use the Field Exit key (located at the classic enter key), as a tab right.

AJM · 11 Apr 2024, 11:35

Hi,
It has become quite quiet here on this forum, but I just wanted to say: I had a 5250 Terminal + keyboard + converter. I've sold them some time ago so my memory is getting a bit fuzzy.
I'm pretty sure, it would not have been a problem to change, what you suggested. It was all a big python script, which you could adjust as you like.

inmbolmie · 18 Apr 2024, 20:27

jgch wrote: ↑
29 Mar 2024, 11:38
Just stumbled upon this great project!

I might have overlooked it, but is there way to change the keyboard settings? Specifically, I would love to use the 'real' 5250 enter key (the one where the right control key normally is).
A bonus would be to use the Field Exit key (located at the classic enter key), as a tab right.

Yes, the keyboard mappings are editable on the Python script, it is not an extremely easy task but some people have made their own custom mappings.