[Arm-netbook] Schematic and PCB layout CAD files

[Paul Boddie]

On Tuesday 21. May 2019 21.57.16 Luke Kenneth Casson Leighton wrote:
> On Tue, May 21, 2019 at 5:43 PM Paul Boddie <paul at boddie.org.uk> wrote:
> > Again, in case anyone wanted to take a closer look.
> 
>  thanks paul.

No problem! Actually, looking a bit closer at PCB-related topics, I started to 
wonder about a few things. Maybe they are actually covered in the 
specifications or on the wiki, but I didn't manage to find what I was looking 
for.

First of all, investigating the EOMA68 computer card characteristics, I didn't 
find the physical dimensions of such cards other than mentions of their 
thickness. I imagine that the dimensions would be the same as those of the 
different PC Card (PCMCIA) profiles:

https://web.archive.org/web/20080822091349/http://www.pcmcia.org/pccard.htm#03

I did find a PCB size of 85mm x 55mm in diagrams on the Engineering Board 
pages:

https://www.elinux.org/Embedded_Open_Modular_Architecture/EOMA68/EngineeringBoard
https://www.elinux.org/Embedded_Open_Modular_Architecture/EOMA68/MiniEngineeringBoard

Also, the A10 news page has mentions of these dimensions from several years 
ago:

http://rhombus-tech.net/allwinner_a10/news/

However, the PC Card documentation indicates that the actual housing of such a 
card is only 54mm wide, so I don't see how existing PC Card housings would 
accommodate such a PCB.

There is also the matter of the length of a PCB. Again, the PC Card housing is 
supposedly 85.6mm, which leaves a board length of 85mm as being plausible. 
Have these measurements been confirmed or maybe subsequently revised?

I do remember that EOMA68 cards (maybe of an earlier generation) were 
produced. Then again, looking at the A10 news page, there is a picture of a 
PCB layout from 2013 with dimensions of 78.1mm x 47.3mm, although it isn't 
completely clear what the screenshot is really showing.

Another thing that I wondered about is the width of the board when 
accommodating a board edge connector like the Amphenol 95622-004LF, which 
seems to be a low-cost and readily-available connector. It seems that the 
board edge needs to be less than 50.8mm across because such connectors enclose 
the contact area on each side.

Is that generally how these connectors work? I see that pictures of EOMA68 
computer card PCBs seem to have a narrower edge connector part, with the rest 
of the board presumably spanning the interior of a PC Card housing.

I am only really asking these questions because I have been looking at making 
some footprints and other resources, and at least the fundamental board 
dimensions should be an obvious thing to discover, but I just didn't see them 
mentioned as prominently as I had thought they would be.

Paul