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

[Gene Heskett]

On Sunday 08 March 2015 03:22:59 RETRO Innovations wrote:
> On 3/7/2015 6:40 PM, Gene Heskett wrote:
> > Don't forget Jim that we CAN make our own cables, and that length
> > limit is purely an artifact of the much faster (relatively) speeds
> > of an ide interface.
>
> Well, they'd need to be 80 pin cables, now :-)  But, yes, I know you
> can make them.
>
> > 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.
>
> OK, switch has been moved to Buffer Board, and placed near the edge.
>
> > The idea of a mux is done in SW for linuxcnc. :)  I have at least
> > one such instance in the .hal files that configure the code to drive
> > my 2 machines.  But in practice you are right.  The flea clips are
> > relatively small so I wouldn't normally point too sharp a finger at
> > its noise radiation. Certainly nothing that a Holaday meter can
> > specifically find.
>
> I've actually never heard the term "flea clip".  TIL I what they are. 
> I think a more finished solution is a shorting jumper, like those on
> an IDE drive to set master/slave and such.

Precisely the same thing Jim. A teeny bit of metal in an equally teeny 
little black plastic molding that makes you handle them with suture 
clamps.  PITA but hey, they work. :)

> OK, attached is a link to v4 of the design:
> http://s6.postimg.org/hnbwm58g1/PCB1_4.png
>
>   * switch is moved
>   * LED footprints for 8 slots.
>   * Rearranged power jacks to front of board
>   * moved mounting holes
>   * Added "bank" selector
>   * Cleaned up bug on IDE cable pinout
>
> Still to do:
>
>   * Add more mounting holes (per slot, easy add)
>   * Add footprints for better selector switch option
>   * Determine if large PCBs with the angled "ears" will need slots cut
>     in the PCB to ensure full edge connector mating
Yes.
>   * Lots of wasted space on bufferboard.  Hmmm
>   * Add reset inhibit (and add reset button on buffer board (the
>     Commodore folks demand one be on every cart, not sure why)
>   * Add cart autostart inhibit
>
> Questions:
>
>   * Does cart inhibit need to be per slot, or just a master "inhibit"?
>     Latter is easier, of course.
>   * The dotted line on the buffer board is where the Coco case ends,
> so that should show how much will be stuffed inside the Coco.  If the
> remaining amount enough, or should I lengthen the buffer board PCB? *
> Is there a howto to pry one of these Tandy game carts apart so I can
> micrometer it?
>   * Seriously thinking about remove the angled ears.  Anyone care?

I think the only real answer there is to cut out a board with them, see 
how it is guided into the connector,  then cut them off and check again.  
I've suspected that as long as the contact pad for the clip on the 
socket to grab and ground is there on each side of the finger pattern, 
that the slanted ear out wider than that was probably optional.  As long 
as we fit the socket tightly enough that there is no chance of a finger 
bridging two lands on the board that it ought to home free.  OTOH, I 
don't want to be the guy who fumbles the card insertion, turns it on and 
blows the 63C09.  And my ancient, starting to get shaky fingers would 
make me that idiot all too easily.

The important measurement is of coarse the width of the FR-4 where the 
finger pattern is, that shouldn't allow more than 5 thou of sideways 
slop when the finger pattern has been inserted into the socket.
>
> Jim

Cheers, Gene Heskett
-- 
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