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Thoughts on backplanes and card cages.

Posted: Mon Dec 18, 2017 5:25 am
by ian_krase
If one has a sufficiently complicated or sufficiently multipurpose electronic instrumentation system, one will start accumulating multiple pieces of custom electronics.

I am thinking about the possibility of containing these within a backplane and card cage system, with an individual electronic unit on each card. Something a bit similar to what Thomas Rapp did: http://www.rapp-instruments.de/Elektron ... nframe.htm


However, while it looks like Thomas Rapp used a more or less ad-hoc arrangement, my own thoughts were to abuse an STD bus backplane (of which there are a number of on Ebay, and some pretty compact half-rack ones with built in bipolar power supplies). Data exchange would be using RS-485, probably some kind of quasi-Modbus protocol, and there would be an Arduino or other microcontroller on each board.

(I'm thinking grid drivers, RF drivers, electrometers, etc here. As well as some general purpose gauge and controller I/O boards to tie it all into a nice *uniform* modular setup.)


Proto boards with edge connectors are rather expensive, but in this new era of cheap PCB prototyping, it looks like I can just make custom protoboards for less than 10 dollars a board. Unless some CAM hold guy takes a look and goes "WHAT" at all the holes.

Re: Thoughts on backplanes and card cages.

Posted: Mon Dec 18, 2017 5:54 am
by John Futter
Ian
This has already been done via the NIM standard used extensively in the nuclear physics and optics industry and research labs
There are thousands of funtional modules that let you build from simple to mind boggling challenging solutions to electrical signal conditioning and control problems
modules are relatively cheap on epay 571 hits with "nim module" in the search as of when I post this

Re: Thoughts on backplanes and card cages.

Posted: Mon Dec 18, 2017 6:27 am
by ian_krase
Wow there are a lot of front panel + backplane standards in the world.

NIM looks like it's a more about power and some kind of coax cable interchange than digital interchange. Do you use NIM yourself?

Re: Thoughts on backplanes and card cages.

Posted: Mon Dec 18, 2017 6:54 am
by John Myers
There are definitely a lot of choices for a backplane architecture.

VXI or PXI could be a good choice also.
Ones like uTCA and ATCA have lots of high speed lines on them making the chassis' and modules expensive.

Re: Thoughts on backplanes and card cages.

Posted: Mon Dec 18, 2017 7:49 am
by ian_krase
I've used a PXI system with LabVIEW once. It seemed pretty nice for what I was using it for, but it was also very much in "other peoples' money" area.

(And also expensive from a programming / support for processors perspective, unless a complete system falls into ones lap)

Basically, what I'm trying to do is come up with such a system for the "common man". (I'll be posting my specs here, of course.)

Re: Thoughts on backplanes and card cages.

Posted: Tue Dec 19, 2017 5:21 am
by Richard Hull
We have discussed NIM (nuclear Instrumentation modules) for years here and many of us use them..

Nim is a big boy's nuclear instrumentation erector set or Mechano for the Ero-pals here. In have a number of NIM bins and over 50 Nim modules accumulated over the years. I have sold many modules and bins at my yearly HEAS event.

I have built 3 or 4 solid state custom NIM modules by taking some worthless or non-functional modules, gutting them and placing my own electronics in the empty module, taking advantage of the power back plane.

I attach an image of one of my Nim bins loaded with modules. All standard NIM bins are 19 inch rack mountable.

Richard Hull

Re: Thoughts on backplanes and card cages.

Posted: Tue Dec 19, 2017 9:29 am
by ian_krase
Huh. Interesting. I wonder if I can find a NIM electrometer, filament controller, or quadrupole rf generator cheaply.


Does the NIM backplane carry any data?

Re: Thoughts on backplanes and card cages.

Posted: Tue Dec 19, 2017 7:20 pm
by Richard Hull
The NIM standard is 60+ years old. Thus, it is originally an analog system. While there are more modern types of data based rack systems, the surplus market for them is sparse. The NIM system handles all the needs of the amateur scientist's nuclear measurement needs rather inexpensively with a vast surplus of modules backing it.

NIM high frequency signals are handled via a profusion of BNC R-F jacks on each module, (front and rear), to transfer signal and data between modules. The buss did and can have data signals wired into the back plane as there are pins available. Originally, it was a power buss and limited signal buss.

There are so many junk modules, sold as is, that can be gutted and turned to more modern digital use by adroit hands.

Richard Hull