Backplane & Card Cage
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Backplane & card cage construction

In the fall of 2002 I'd been working seriously on this project for a year and half, without anything physical to show for it.  All of the work was design and simulation.  I was a bit tired of that, and decided to go ahead and build a backplane - even though I wasn't anywhere near being able to begin the real construction.

The pictures below show the process, and at the time I was pretty pleased with how it came together.  However, since then I've realized that my power and ground distribution is wholly inadequate.  I've thought a bit about how to fix this, and I think the route I need to go is to have some custom PCBs made.  However, to do it right I would need a 5 layer board - which would cost a bit more than I'd like to spend.  One fix possibility is to do a two-layer board that just does power & ground.  I could then just sandwitch it on top of my existing backplace.  The big problem with that is it would close things off.  If there was a single wiring mistake, I would be unable to correct it, and would have to trash the whole thing.  Another option is to trash what I've done, get the two-layer board and use it as a base.  Then, I'd redo all of my wire-wrapping to connect the signals together.

As of now (1/3/2004), my inclination is to go with the sandwitched two-layer appoach - but I'll put off that decision for awhile.

Anyway, here are the photos.  Click on a picture to get the hi-res version.


Took the cover off of the card cage to let me see the LED display on the EPROM daughter board, and after a while the posts were getting a little wobbly.  So, I cut a piece of plexiglas and installed it to make the cage more sturdy.  Here's a picture:


The backplane is complete, and I've been playing around with how the signals look.

backplane_complete.JPG (417147 bytes)


I've completed the left half of the backplane.  Lots of wires done, lots of wires to go....

left_wrapped.JPG (396460 bytes)

I'm running power and ground into the left half.  The right half will pick up ground through the chassis (as well as some dedicated traces).

left_back.JPG (403618 bytes)

Here's the back side.  A bit of overkill, but that will be a theme throughout construction.


The first real construction began this weekend.  I bought a nice card cage on eBay which will fit 5 of my wire-wrap prototype boards.  The cage was set up to take 7 boards, but I spaced it out to allow for the wire-wrap pins.  To create a backplane, I'll be wire-wrapping along the spine.  I'm backing the backplace with a copper-clad perfboard to reduce noise.  

PreWireCage.JPG (405705 bytes)

The screws were an odd size - 2.5mm, but I found some at HSG in Santa Clara.  The white strips are wire-wrap tags.  I'll be using them throughout.

PinSide.JPG (460559 bytes)

Pin side of the wire-wrap cards.  I got them from Excess Solutions in San Jose, at $15 each.

ComponentSide.JPG (437436 bytes)

The component side.

Backplane1.JPG (424765 bytes)

I had to do a little sanding to get things to fit, but it looks pretty good.  Next step is to find some more machine screws of the right side, and I also need to decide what kind of socket arrangement I'll use to connect to the power supply.  After that's done, the wire-wrapping begins.

CopperClad.JPG (425789 bytes)

Here they are after covering them with copper tape, and the cutting out holes for the mounting screws and wire-wrap sockets.

CutOuts.JPG (415026 bytes)

I didn't have perf-board big enough, but had some pad-per-hole prototype boards on hand.  It's a waste, but I cut two of them down to fit the backplane opening.  Unfortunately, 96-pin wire-wrap sockets had wide portions of the pins at the bottom, presumably to give them a tight fit.  To make them work with my boards, I had to use a Dremel tool to widen the holes.  It was a bit messy doing it free-hand, but it worked.

CardCage.JPG (417679 bytes)

The cage after re-spacing the guides.