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MattCarp
July 19th, 2008, 08:01 PM
I've been toying with the idea of creating a homebrew computer, similar to Bill Buzbee's (www.homebrewcpu.com).

First, however, I'd like to have a plan for the mechanicals - a backplane and prototyping boards. I'm looking for something like 10 slots, about 100-150 signals.

I think something like DEC's Q-bus is the right form factor, but I'm not sure about the availability of prototyping boards.

I think VME bus is a strong possibility, but I can't seem to find a good resource for prototyping boards. A lot of links I've found don't seem to have easy answers. Plus things look pretty expensive. Ideally, here is a backplane that looks perfect: http://www.twinind.com/catalog_detail.php?id=58 However, $500! Then I'd need a card cage. The Vector Electronics CCK220-6U looks pretty good, but Digikey lists that for $220. So, $720, then I'd need prototyping boards!

I don't like ISA, despite the large number of backplane and prototyping board choices. I think the ISA edge board connectors are too cheap and I don't like the size/physical layout of the board itself.

Does anyone have any suggestions?

NobodyIsHere
July 20th, 2008, 04:58 AM
Hi!

I recently built a home brew computer and am currently building a backplane for it.

Since the home brew computer is based on the Z80 and I am trying to keep it low cost, I am using the ECB bus.

Making peripheral cards is low cost since you can use off the shelf Eurocard or similar sized prototype cards ($5 or so) and a DIN 41612 connector ($3) per card.

I am designing a ECB backplane right now and am getting ready for a manufacturing order. I will sell these backplane PCBs the same way as the SBC PCBs at $20 a piece.

The backplane supports all 96 pins of the DIN 41612 to accomodate the "standard" 8 bit ECB format plus the "extended" 16 bit versions etc. The backplane will have its own power connector, switch, LED indicator, and 6 slots all in a 160x100 mm format.

I am using 2 layer PCBs to keep costs down but will specify double thickness PCB material and double weight traces. All the VCC and GND are triple wide and double layer will GND fill zones for good grounding performance.

If you are interested, you can see the backplane design at:

http://n8vem.googlegroups.com/web/Printing%20BackPlane-brd%20%282%29.pdf?gda=w0kl1lMAAADY_yIRHCNBFl-EkbXwOSdW6qEwWe2Yh3ZCxOeiM3DgQmG1qiJ7UbTIup-M2XPURDScuRfES1UkRrTEL_jZLsiTC4GJ69MH_8_j7KrPAzv-fCuGKAF9xERNAwtVA_jM0jE

Thanks and have a nice day!

Andrew Lynch

NathanAllan
July 20th, 2008, 06:33 AM
Andrew,

your link didn't work, got a scrambled screen.

Now I'm interested. Sounds like a great project, the Z80 is an interesting processor to work with.

Nathan

NobodyIsHere
July 20th, 2008, 07:55 AM
Hi Nathan,

Sorry about the screwy links. The schematic and PCB layout for the N8VEM ECB backplane is in the files section here:

http://groups.google.com/group/n8vem/files?&sort=date

They are named "Printing BackPlane-sch.pdf" and "Printing BackPlane-brd.pdf"

I don't know why the URLs got munged but they are easy enough to find if someone is looking for them.

There are 6 known successful N8VEM SBC builders in the "Hall of Fame" :-) I suspect there are may be more out there. I assume that several people who bought the PCBs are still holding them pending availability of parts, time, energy, rainy days, etc.

After the second round of PCBs for the SBC are distributed (which should be here soon and take a couple of weeks to finish) I am going to finish the design of the backplane and get it manufactured.

Now that the SBC portion of the project is basically in place I am focusing on the peripheral expansion phase. I built a prototype ECB bus last year and a "toy" ECB peripheral to test it. It worked fine but now it is time to replace the prototype with a much improved manufactured PCB.

I think the backplane design is nearly complete. I had to completely redesign it based on some comments and suggestions. The backplane now supports an optional IEI/IEO jumper per connector for use with the Zilog prioritized interrupt scheme. Also, the ECB backplane is a generic as I can make it as all 96 pins are routed from the DIN 41612 in parallel to allow for the various version of the ECB "standard" available.

The new ECB backplane design is completely manually routed as the autorouter went completely nuts trying to solve this complex problem. I did the entire design using KiCad and all the information will be published in the same fashion as the SBC material was/is.

No doubt, there are probably still issues with it and hopefully they'll flush out in the next few weeks. I am soliciting anyone with ECB experience to help me improve this design. I'd like to capture all the suggestions before I go to manufacturing.

Thanks and have a nice day!

Andrew Lynch