modifiable backplane with sockets?

Backplane systems are pretty retro at this point, apart from a few things like VXI.

The last one I designed was around 1994, and that was a proof-of-concept prototype.

The cost, size, unreliability, and general clunkiness of backplane systems should be considered. I still build a lot of analog protos, but offshore PCBAs are pretty cheap, so I only hand-wire them when I’m in a hurry.

What are you building?

Cheers

Phil Hobbs

Here's a box with boards that plug into a backplane.

I remember wire-wrap. It was awful for digital busses but might be OK for the analog thing you are doing.

You could do a PCB for the bus, to hold things together and do the power and grounds, and let the connector tails poke up for wrapping.

That bus above has 10 grounds and 7 pins of +48V per module, from that kilowatt power supply.

I built small analog computer recently:

I don't like using offshore PCB printing, even though it is cheaper. I like OSHPark, but they are more expensive and have a three board minimum print for any single design.

Well, since you're using a patch panel anyway, why not just run the power and ground on the backplane?

Cheers

Phil Hobbs

I was imagining that they would be fairly small cards, something like

My original thought was to have the cables to the patch panel(s) hook directly into a socket as well, but maybe I could have a shorter cable going from that to some kind of plug in port on the chassis.

I'm working always at low frequencies, like 100 Hz or less. The simulations usually display on an oscilloscope at around 1 second per scan, or slower.

The plug would mount onto the card, unless I was using just contacts that slide in. I am open minded to ideas.

I don't really want to use printed wiring, preferring to experiment/design/build as I go. But I'm not really sure a practical way to do that outside of a breadboard. Maybe I can come up with some kind of generic printed board that gives me some flexibility on how I solder on ICs and wires.

It would just sit on my desk. I'd need to be able to slide in/out or (dis)connect the module cards without anything breaking. After assembly, I would mostly be interacting with just the patch panel, not the cards, but I'd want to be able to take cards out to tweak them, or replace them.

Ah, okay, so I could just screw that onto some support structure, then wire wrap to those long posts. Assuming the posts are strong enough to endure wire wrapping.

Perhaps I misunderstand your question. But if I connect the patch panel signal wires directly to the component modules, like I did with my current (already built) analog computer, then the wires end up taking a lot of space around the component modules, and you can't simply remove/replace modules without wiring stuff back up to the card.

The patch panel can be variously organized according to how you want various component I/Os grouped. I was wanting to be able, for example, to plug in a new patch panel without having to do anything to the cards, though maybe I would have to do some modification to the back plane wiring if the new patch panel expected more signals.

Design a motherboard with some female DIN connectors in a row and ground/power bussing and the rest of the pins poking out. Buy a bunch of cheap boards. The motherboard is the patch panel.

Pluging analog boards have a mating male DIN, which will lock in to the motherboard nicely.

Some people make standard jumper wires with crimped terminations that slide over wrap-post type pins without actually wrapping. Use those to patch the backplane connections. They are reusable.

The first analog computer used just DIP and through-hole components. I'm open-minded at this point on DIP vs SMT — but I don't really know how to prototype with SMT components and the stuff I've read scratching/drilling divides into copper boards doesn't sound very practical. But maybe I should try something new. Copper-clad perfboard sounds like it might be a practical, inexpensive approach.

This basic idea sounds appealing.

So, on the "postage stamp" board, how do you think I should do the interconnections? Wire wrap between posts? Or just do a solder bridge over to the next perfboard hole and connect a wire to that?

It's fast, fun, and works great.

Plain copperclad is better. The back side can be your ground plane.

The pictures look beautiful. Can you answer a few questions?:

- Is that "double sided copper clad laminate PCB circuit board" like available all over Amazon?

- What method/tool do you use to scratch/cut-out the divides in between the islands?

- on the raised islands, is that just another layer of copper clad laminate? Is there some special material I'm seeing underneath the blue break-out boards? What tool do you use to cut out chunks of the laminate?

Also, what glue do you use when you need to glue on pads or components?

I think the one part you are not understanding is the purpose of the patch panel. So, it would be like so:

- Fixed analog component modules — integrators, multipliers, and such like — connect to the back plane. These modules are normally not changed out except for repair, testing, and expansion.

- Cables from the patch panel(s) connect to the backplane. Wiring on the backplane connects these cables to the component modules. This wiring is not normally changed unless adding new patch panels or some fundamental redesign of a patch panel port.

- The patch panels(s) have a bunch banana jacks allowing me to quickly interconnect the inputs and outputs of the various analog components. These connections are frequently changed — every time I set up a new simulation.

This is how it works with my current analog computer I built, except that there is no backplane. Rather, the wires from the patch panel cables connect directly to terminal blocks on the analog component modules.

Yes, but I have mine gold plated. It solders great and doesn't tarnish in a few weeks like bare copper does. One of our PCB suppliers make it for me for about $100 a square foot.

A Dremel with a carbide dental burr. I draw lines with a Sharpie first and clean up with Soft Scrub. The cutting takes some practice to get good at. One can make controlled-impedance microstrip lines and do picosecond stuff.

These people Dremel their pumpkins.

"Manhattan style" is gluing little pedestals to the base board. We have a metal shear to slice up the FR4. A serious hole punch would make round ones.

I attach the purchased surface-mount adapters with double-stick foam tape.

FR4 strips used as bus bars or transmission lines are epoxied down.

Double-stick foam tape or 5-minute epoxy.

Correct. A backplane is not absolutely necessary, since I built one with out a backplane. But it is bothersome to have the wires from the patch panel hooked directly to the modules, as it is quite messy and makes it more difficult to work on the modules or to replace/modify the patch panels(s).

I like this idea of building the modules on top of FR-4 boards. However, this leaves me unclear on how I should interface the modules to the backplane. The "postage stamp" idea was appealing, but I am not sure how I would attach the pins. I know I don't want to be trying to drill very precise holes, or to be scratching out 20 little islands on the copper. Any further thoughts on this?

I don't exactly know what you want to do, but here is one posibility:

Design two double-side PC boards and order some from one of those cheap houses.

Use mating connectors, D-subs or DINs. The one on an analog board is a right-angle and the motherboard/patch panel gets straight ones with wire-wrap tails. Those are available.

The motherboard can do some power bussing. A motherboard could be short, 3 or 4 connectors, and designed so they can be bolted together into longer strings.

The baby boards will plug into the mobo and the connectors will hold them up. Include some common parts like power supply filters and LEDs and such. Maybe some opamp footprints.

Nice plated holes and ground planes and ways to prototype.

Maybe make an extender board too.

That's almost a product.