[Coco] 4 Port MPI PCB artwork (so far)

[Gene Heskett]

On Saturday 07 March 2015 14:02:11 RETRO Innovations wrote:
> On 3/7/2015 6:40 AM, Gene Heskett wrote:
> > For the planned 8 port, where another 4 port is daisy chained (or
> > paralleled) to turn around and head back with the bottoms of the
> > boards facing each other, so that carts are then sticking out front
> > and rear, or left and right I'd say its ok unless the caps run into
> > each other when stacked on a set of 4, 3/4" high standoff posts.
>
> Any chance you could draw up he idea.  I think I understand, but not
> sure.
>
> > However the standoff mount holes are not currently symmetric,
>
> No, they are not.  I am crunched for space where the power connectors
> are.
>
> > and the one
> > now at the upper left corner of the main board looks to be a
> > potential short to a trace if a fiber washer is not used under the
> > screw heard.
>
> It should be fine, as there is soldermask and that trace is on the
> bottom of the PCB.

Much better then. :-)

> > So Q? Are your thoughts running along the lines of using a 3
> > connector cable lashup for the interconnect, effectively paralleling
> > the 2nd board?  If, so, then how does the cable cross-over come
> > about?
>
> If you will notice, the crossover is already the board.  SV1 matches
> up with SV3, 2 with 4, and they are transposed on the PCBs (SV1 is
> left of SV2, SV3 is right of SV4

I saw that easily enough, but cannot visualize it for two main boards in 
connectors 2 & 3 of each cable?

> > Obviously I'm having trouble visualizing it in the 8 slot
> > configuration without a huge cabling problem in the parallel mode.
> > That may just be me, and once I see it, it's likely to be a forehead
> > slapper. I can see adding two more of the 40/80 headers to the right
> > end of the main board, (If you can get all the traces there, which
> > may not, likely is not possible) so that 2 short jumpers reach the
> > 2nd board from there a whole lot easier.  Then it can be bent so as
> > to lay back with e 2nd boards bottom faceing the main boards bottom,
> > potentially saving some desk real estate.  That would need
> > symmetrical board mounting holes, which is not now the case.
>
> Think of the idea this way:
>
> Consider a set of IDE drives, with a new style 80 pin IDE cable that's
> wrapped in a sheath so the cable looks like a round cable except at
> the ends.
> The controller end of the cable plugs into the Coco PCB
> Master connector plugs into one of these boards
> Slave connector plugs into another on of these boards.
> You set the boards (IDE drives, for visualization) side by side, or
> front to back, or (if the master to slave cable length is sufficient)
> you run the master to slave portion of the cable under one of the MPI
> baords to the second one, and the 8 ports are in a single row.

Using rolled up (round) cables, that will work IF the connectors are far 
enough apart,  most aren't.  My mind is/was stuck on the much wider 
format of the flat cable.  Reverse the cable end for end, then the far 
end should reach the 2nd 4 slot board?

> >>    * The LEDS would not fit in between the slots, unless i increase
> >> the interslot distance.  They are now positioned immediately below
> >> the switch.  Thoughts?  If I increase the slot distance, I could
> >> put them back in front of the cart, but you would not be able to
> >> see them if you have the unit mounted behind the Coco with the
> >> slots parallel to the back of the Coco.
> >>    * Should the switch be behind the LEDs, or in front?
> >
> > I'd say it should be accessible from the edge of the board, similar
> > to the tandy version. In that event, I think I'd put the leds on top
> > and the switch on the bottom of the board, but that is an artistic
> > wish, no more.  It would be a bit hard to get to once a top shell
> > case is in place where its at now.
>
> Where would you suggest placement.

On the outer edge of the board, so a slider cap could be put on the 
switches stickup which is projecting past the edge of the board?  With a 
small stem on the slider/knob, basically a miniature of the tandy switch 
with the same exterior in miniature.  But I'm 200% open to whatever idea 
makes it accessible from the outside if we make cases for it while of 
coarse keeping costs as low as is practical.

> To put it where the MPI has it 
> means adding quite a bit for the PCB size, as the carts at present
> hang over the edge of the PCB by 1/4" on each end.

That board is narrower than a cartridge is wide by 1/2" now?  Yeah, I 
guess it is, just hadn't put a ruler on it.

> >>    * One of the designs had an cart autostart disable.  Is that of
> >> interest? * Another design had a reset disable.  Thoughts?
> >
> > Autostart disable yes, reset no.  But I could be convinced otherwise
> > with the right argument. ;-)
>
> jumpers or switch?

Flea clip jumpers per slot?  Accessible by suture clamps when that cart 
is removed?  I certainly would not ask for anything fancier than that, 
and certainly not when the one doing the work is doing it for free.

As it is, I feel I may actually be slowing the work, when what I am 
interested in is working hardware from the first run of boards.  The 
many eyeballs theory.  Sometimes the minutia can escape our 
consciousness, its happened to me on many occasions.  Fixing a problem 
is comparatively cheaper when fixed at the line on a screen stage. :)

IOW, I can be told to shut up anytime.  Designing by committee tends to 
get un-manageable if a halt is not called to the feature creep.

> Jim

Cheers, Gene Heskett
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