[Arm-netbook] Schematic and PCB layout CAD files

[Paul Boddie]

On Monday 17. June 2019 08.40.22 Luke Kenneth Casson Leighton wrote:
> On Sun, Jun 16, 2019 at 5:14 PM Paul Boddie <paul at boddie.org.uk> wrote:
> > On Wednesday 12. June 2019 02.09.12 Luke Kenneth Casson Leighton wrote:
> > > added here
> > > http://rhombus-tech.net/pcmcia_sources/
> > 
> > I have updated this page with some more details and some remarks about the
> > physical constraints involved. If such remarks belong elsewhere, feel free
> > to move them.
> 
>  no, great idea.

Phew!

[...]

>  interestingly, there's nothing to stop you putting the card inside
> the PCB at a slight angle, such that whilst at the PCMCIA header end
> there is plenty of room (relatively speaking) on either side of the
> PCB, and at the other end the PCB becomes flush with the floor of the
> metal case.

I think you'd really have to be confident amount the manufacturing process to 
do this.

> > I don't know whether this would have influenced the choice of sockets in
> > the current batch of boards, but I wonder if it might be influential or
> > useful to consider for any subsequent production.
> 
>  the issue is that even if the 1.2mm PCB is flush with the 5.0mm floor
> (leaving no room for underside components for about... 35 possibly
> even as much as 40mm (half) the Card, which would hugely complicate
> the design, the connectors are still around 3.3mm in height (USB-OTG,
> Micro-HDMI Type D)
> 
>  5.0 - 0.1 (thickness of the metal) - 1.2 (PCB thickness) = 3.7mm
> 
>  3.7 - 3.3 (height of the connector) = 0.4mm
> 
>  minus another 0.1mm for the top case shield.
> 
>  so that leaves only 0.3mm clearance, which means that the connectors
> will poke out in a completely asymmetric way, which is very ugly.

I guess that the solution involving extending the board to provide connectors, 
in that classic PCMCIA/CardBus style seen with things like USB adapter cards, 
wasn't desirable because it would demand extra casework to be done at quite 
some expense. So the mid-mount connectors were a reasonable compromise.

>  the mid-mount option gave a reasonably symmetric above- and below-
> gap that doesn't look quite so ugly.
> 
>  plus, having 50% of the PCB impossible to put components on the
> BOTTOM side means that the PMIC area would need redesigning (again),
> spreading out the components to fit the ones that normally go on
> BOTTOM.

Yes, I can imagine that limiting the components to one side brings its own 
challenges. For simple cards only providing flash memory and other such things 
(Web searches yield some kind of card for Mercedes vehicles of this nature), I 
guess that it isn't a major concern.

[...]

> > P.S. I have also been working on KiCad footprints for some of the parts I
> > have found, in case anyone is still interested in such things.
> 
>  superb.  if you send me an ssh key i can arrange to add you to the
> repo that i started 6 years ago:
>  http://git.rhombus-tech.net/?p=eoma.git;a=summary

I'll send you that, trying to remember the preferred form of the exported key 
this time. ;-)

Paul