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

[Gene Heskett]

On Saturday 07 March 2015 01:55:37 RETRO Innovations wrote:
> Here is a link to what I think is a finished 4 port design:
>
> http://s6.postimg.org/v09zrn6yp/PCB1_3.png
>
>   * All lines routed
>   * 3 power source options (5V coax, 5V Mini USB, 5,12,-12V PSU)
>   * Minimal IC count
>   * Uses 2 IDE cables (40 or 80 pin work equally well)
>   * On board 3V3 voltage regulator
>   * All ports have smoothing caps
>   * 4 position selector switch
>   * 4 selection LEDs
>   * Buffer board is 3" long, and main PCB is 5.75" long.
>
> Some notes/questions:
>
>   * The size will not allow a cartridge to be pulled out by grasping
> the top and bottom of the cart.  The minimal part-to-port distance
> requires inserting and removing carts by grasping at the sides.
> Thoughts? 

S/B fine. In fact that is my standard grip.

> Should I increase the distance to the amount on MPI? * To 
> ensure nothing interferes with the carts, I had to move the smoothing
> caps under the board.  Not a huge deal, but they will protrude 12.5mm
> (1/2 inch).  I know some folks were looking for a low profile unit. 
> Is 1/2" too high?

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.

However the standoff mount holes are not currently symmetric, 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.

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?

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.

>   * 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.

>   * 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. ;-)

> Jim

Cheers, Gene Heskett
-- 
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page <http://geneslinuxbox.net:6309/gene>