Tuesday, May 14, 2019

Backplane "Mapper" (DG Nova, DCC D-116 & Entrex 480/Nixdorf 620)

This is a crazy project that I'm just muddling my way through with sheer ignorance and determination.

I want to test every connection in every slot of the backplane of Dominique's Entrex 480/Nixdorf 620, since it is the only known surviving system of its kind in existence, and then reverse engineer the thing from the center outward.

So, here's the backplane "adapter board" design (version 2)
Click to download the Gerber files version 3 by Alberto Medrano

Order this at 1.2mm thickness, NOT 1.6mm default.  I did my first round at 1.6mm default, and the board was too thick to fit into the backplane card edge connectors.

And here's my concept schematic on how I'm going to use an Arduino (I know...can't I do better??!!!) to test each and every connection in each slot I plug the set into.

Yes, there are so many things wrong with it...I know...

Here's the Gerber files of my latest version by Alberto Medrano

And for the first time, I'm going to try to order these from JLCPBC

This is what I'm comparing against, and these are the only backplane schematics/charts that I have for any Entrex 480/Nixdorf620, DSS-116 or Data General NOVA system.  Can anyone else find more on bitsavers, or elsewhere?

The version below this line is an earlier version, and can be ignored, or reviewed for entertainment...
Click to see full-size schematic

I even asked for help here on Upwork:

And the results were successful (above)!  

Here's the archived job description for reference:

This hand-drawn image of a circuit is a rough draft of what will become an "oversized" Arduino shield.

You will want to right-click and download this, because it is a large image, high resolution, with high detail, and will require a lot of zooming in.


This circuit is intended to use 12 Fairchild ADG732 chips, and 4 Texas Instrument CD54HC251 chips. (Yes, I know that the ADG732 is surface mount and the CD54HC251 is through-hole, we'll keep it that way for now).

This rough-draft version of the circuit makes certain assumptions that you should fill in, such as proper chip grounding pins, chip source voltage "power" connectivity. It may also contain some mistakes or logic errors.

I am fully open to suggestions here.

However, the job is intended to be straightforward. Create production-ready Gerber files from this rough schematic.

I am going to leave the board layout to your imagination, creativity, and "best judgement" (even though I will, of course, be the final judge of how it needs to be...but I want to see your ideas in action).

So, there you go. I've done all of the "thinking" work for design/concept, but I need your refinement, and Gerber building skills.

So, are you up for this challenge?

Datasheets for the chips I chose to use are the


and the


or the similarly equivalent more modern MM74HC251

Thanks, and good luck.

My internal job notes:
April 8 Post
May 22nd Post

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