[Arm-netbook] Interchangeable screen

[Luke Kenneth Casson Leighton]

On Mon, Sep 21, 2015 at 12:49 PM, GaCuest <gacuest at gmail.com> wrote:
> En 21 de septiembre de 2015 en 13:27:19, Hrvoje Lasic (lasich at gmail.com) escrito:
>> Maybe try to focus on one model in beginning, to make yourself easier job
>> going to market than proceed with three models. I don't know much about
>> your target audience and why you want three models (only I like your idea*,*
>> but my vision here is extremely limited) but believe me you will have more
>> then enough challenges on one model and by the time you have feedback from
>> customers you will gain some traction and have more than one good idea how
>> to improve product. Even if you have resources to make three models, maybe
>> you can direct this resources to make prepare some good game, to make
>> product more likable, playable etc something that could help your project
>> in different way...Just an thought…
>
> Well, we will not create three different models.
>
> Simply we create a base model (without display) and based on it you can add modules with different displays. The problem is that not everyone will know to put the modules, so we will sell configurations with mounted display modules.
>
> It is similar to BananaPi with different display models available. But with a case around the display-CTP to screw to the case of the game handheld games console.

  i just thought of something which you *really* really should
consider *well* before doing this type of modular design for LCDs.

 the cost of even a 4-layer prototype board vs a 2-layer prototype
board is *literally* a 5 to 10x jump in price.  $40 for 2 boards 1.5mm
thick can easily become $200 to $400 for 2 4-layer boards.

 as you have *three* such boards... no, five because you have main
PCB, power PCB, and 3 LCD modules, consider trying to make the boards
2 layer ***BEFORE*** committing any other resources to the modular
concept.

 as you have very short signals you should be ok but for goodness sake
make absolutely sure that you can route all the differential pairs
(MIPI, LVDS, whatever) on a single layer, directly from the connector,
directly to the IC, directly to the LCD connector.  make absolutely
sure that you have room to surround and separate the differential
pairs with GND-tied vias.

 take a look at this for example:

 http://hands.com/~lkcl/eoma/laptop_15in/laptop_2layer_pcb1.png

 in the bottom right, you can see the LVDS connector, and above it the
SN75LVDS83b.  there appears to be some unspoken communication between
the designers of all the parts so that the LVDS differential pairs
line up *DIRECTLY*.  i have places GND vias in between (as best i
can), i am not happy that the LVDS signals have to divert around them,
but the cost of boards if the vias are smaller goes up from $40 for 2
to over $150 for 2.

 then, look in the left corner.  that's a GL850G 4-port USB Hub IC.
those "GND" vias in between and surrounding the tracks go *all the
way* up the board, it took several days to arrange because i had to
adjust it and correct this arrangement several times.  it's by no
means perfect, but it is what it is.

 you can also see top middle, 7 wires in between GND tracks, those are
the SD/MMC lines, they're getting quite fast these days so i thought
it best to put GND guides around them.

 strictly speaking from what i gather you are supposed to actually
isolate the GND tracks at the outer edges, not let them become part of
a larger GND plane.  also you are supposed to leave a large distance
to any other components.  also you are supposed to leave a large
distance in between each differential pair.

l.