Hi Todd,
I'm well underway on rewiring the back plane. Since it's not a complicated circuit, I am foregoing the schematic and just doing the traces in manual mode. The first slot is spaced 1" from the 2nd slot. Since I want to be able to cascade them, and since the IMSAI board is wider, I moved the Termination to the side and was able to add a 9th slot. The back 8 slots are all 3/4" spaced. When you cascade the boards, the last slot will be 2.25" from the 2nd slot on the next board, ie, skip 2 standard slots and resume 3/4" spacing.
The mounting holes for IMSAI are there, and even when cascaded, they *should* all line up... I hope.
The mounting holes for ALTAIR are just the holes for the S100 connectors, but I was careful to not place components or traces along the width of the two rails. The first slot spaced 1" can be mounted into the existing holes, but new holes will need to be drilled and tapped for the last slot. I haven't removed my ALTAIR Back Plane to look (don't want to upset all the wires, I heard on another post that these wires break easily). But it appears they only drilled and tapped 4 holes on the rails anyway.
I hope to get this board done by tonight... but I recommend you give me another week to look it over for errors.
Cheers,
Josh
Date: Sat, 25 Apr 2015 16:03:29 -0400
Subject: Re: [N8VEM-S100:6825] Re: Reorder of S-100 8-slot Backplane PCB
From: tacom...@gmail.com
To: n8vem...@googlegroups.com
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I'm well underway on rewiring the back plane. Since it's not a complicated circuit, I am foregoing the schematic and just doing the traces in manual mode. The first slot is spaced 1" from the 2nd slot. Since I want to be able to cascade them, and since the IMSAI board is wider, I moved the Termination to the side and was able to add a 9th slot. The back 8 slots are all 3/4" spaced. When you cascade the boards, the last slot will be 2.25" from the 2nd slot on the next board, ie, skip 2 standard slots and resume 3/4" spacing.
The mounting holes for IMSAI are there, and even when cascaded, they *should* all line up... I hope.
The mounting holes for ALTAIR are just the holes for the S100 connectors, but I was careful to not place components or traces along the width of the two rails. The first slot spaced 1" can be mounted into the existing holes, but new holes will need to be drilled and tapped for the last slot. I haven't removed my ALTAIR Back Plane to look (don't want to upset all the wires, I heard on another post that these wires break easily). But it appears they only drilled and tapped 4 holes on the rails anyway.
I hope to get this board done by tonight... but I recommend you give me another week to look it over for errors.
Cheers,
Josh
Date: Sat, 25 Apr 2015 16:03:29 -0400
Subject: Re: [N8VEM-S100:6825] Re: Reorder of S-100 8-slot Backplane PCB
From: tacom...@gmail.com
To: n8vem...@googlegroups.com
Hi Josh,
Personally I'd prefer your #2, 8.5" with IMSAI and Altair holes.
It looks like fabricating the ALTAIR card guide mounts wouldn't be too bad?
I'm probably not understanding something but couldn't we fix issue with cascading the boards when the first slot is shifted buy ensuring there's enough bare (or with only lower profile parts than the connectors) after the last connector before the edge of the board? Or does that screw up card guides or something on some standard chassis?
Todd
On Sat, Apr 25, 2015 at 1:37 PM, Crusty OMO <crus...@hotmail.com> wrote:
Guys,
Here's our first hurdle.... the ALTAIR back plane is 11" wide. It is like this because the card slot guides are screwed in from the bottom of the board. The IMSAI back plane is only 8.5" wide.
The 8 slot board v2 is 7.25" wide.
It's not a problem to expand to 8.5", but 11" makes it interfere with the IMSAI chassis by about .25"
Option 1. Make it 11", ready for the ALTAIR... IMSAI use will require cutting the board.
Option 2. Make it 8.5", with IMSAI and ALTAIR holes, ALTAIR use will just have to sacrifice the card slot guides.
Option 3. Make it 10.75" with a 8.5" irregular width for the first slot, this will allow it to fit both systems, but only allows a single screw to hold the 5/8" wide card slot guide (otherwise needs 2 screws).
In Option 2, ALTAIR users can always create their own cross beams using 1/2" aluminum angle to support the card slot guides. Here's a picture of the first slot as pictured from the back.
Look closely, you see 2 holes for card slot guides. Now look at the rail that supports this board, it starts near the S-100 connector, this board is supported by the holes of the S-100 connector to two of these rails. New rails can easily be added, see the multiple holes available on the end of the chassis?
The NEXT hurdle involves the fact that the first slot on the IMSAI is spaced just over 1" to slot 2. This is because the first slot is meant to reach the front panel. All the other slots are the regular 0.75" spacing... This shouldn't be too much trouble, but it becomes trouble when wanting to cascade these boards to make larger back planes. There will need to be a sacrifice of one or two slots to maintain correct spacing.
Thoughts?
Regards,
Josh
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