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Planning Custom-built tablet - advice/opinions welcome

Discussion in 'Modding' started by Byron C, 9 Nov 2010.

  1. Byron C

    Byron C And now a word from our sponsor

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    Hey guys

    I'd like your honest opinion on an idea I've had for a while. It's probably completely crazy, but at this point I'm not sure whether it's just crazy enough to work!

    Sometime last year, I stripped my old laptop of all it's usable-serviceable parts, including the screen. The graphics chip had died a terrible death, and I had butchered the mainboard by constantly re-soldering the loose power socket. Now don't start about re-using laptop screens! I know that it is not easily possible to recycle a laptop screen as a monitor, but I'll get to that! ;). At the time, I salvaged the screen with the plan of selling it on - they're still selling at around £60-odd.

    Not long after, I discovered a resonably-priced kit on ebay which would allow me to use the screen through VGA - the seller has confirmed that the kit works with my panel and supports the native resolution. Woop! Modding ideas abound: a hand-built touch screen monitor, a monitor mounted in a side panel (temp readouts, CPU speed...), etc, etc. This idea fell by the wayside, because I have a habit of having great ideas and not following them through.

    Earlier this year, I discovered the BeagleBoard xM: a teeny single-board computer with a 1GHz Cortex A8 ARM processor, 512MB RAM and OpenGL-accelerated graphics. It might not sound that powerful, but running Linux it's an extremely attractive piece of kit - thanks to hardware acceleration, it also supports up to 720p HD video. I have seen demo videos of the platform running a full-blown Ubuntu install (with Gnome, not just XFCE) and playing HD video through XBMC - it is pretty damned impressive.

    The thought struck me: why don't I build my own tablet computer? None of the ones I've seen so far are really flexible enough for me. If I bought one, the first thing I'm going to want to do is slap Linux on it - I can do far more with Linux than I can with even the relatively open Android platform. I can't help it; I'd install Linux on my wristwatch, if I could. Basically, I want a computer in a screen.

    As I see it, the challenges (and solutions) I have identified in this plan are:

    Battery power: Maybe an external battery pack, but I don't quite think I'm experienced enough to have an in-built battery pack which can be monitored by the OS (if the BeagleBoard even supports this). Plus, it would consume an awful lot of space if I used commodity components - sadly, I don't have the research budget of Apple or Samsung to create thin high-capacity batteries.

    Automatic screen rotation: This should just be a matter of interfacing an accelerometer and finiding (or writing) software to automatically rotate the screen. Something like this *must* exist already.

    Touchscreen: This is an easy one. Touchscreen kits are easily obtainable. It won't be capacitive, but it will be a touch screen.

    VGA vs LVDS: I already have a usable laptop screen and can obtain a kit to convert it to VGA, but this extra board adds complexity and adds to the overall footprint.

    BeagleBoard video signal format: At present, I do not think that the BeagleBoard can output VGA over DVI. This is rather important, as I would need a DVI to VGA adapter so that I can use it with the LVDS to VGA board. The converter board does not have a DVI port, only VGA. The alternative is DVI to VGA signal conversion, but that would be crazy: DVI to VGA to LVDS.

    Native LVDS on board: The BeagleBoard does not support natively LVDS and does not have an LVDS interface board/adapter. Do I find a different SFF SBC that has LVDS native support? If so, will I still be able to control backlight levels and use the same inverter?

    Using a different SBC: There are SBCs out there that do have LVDS support built in, but I haven't yet found any that match the BeagleBoard's power, size or minimal cooling requirements. All of the ARM based ones I have seen except the BeagleBoard use older Cortex processors that go no faster than 720MHz and many (if not most) do not have hardware accelerated video decoding. This is still a consideration, but it would constrain multimedia performance somewhat.

    Using an x86 Mini ITX or similar: I have seen small form factor Jetway boards which have LVDS add-on cards, but they are larger than the BeagleBoard and some even require active cooling. Although these are x86, which is more flexible - I could potentially use Windows 7. Plus there is also the issue of the inverter and controlling backlight levels.

    Abandon the laptop LCD and use a DVI monitor: This seems like a more sensible idea, until I start considering that monitors run on mains voltage and have transformers built in - there's a reason they're thicker than laptop screens. I don't mind (carefully) messing with 5v or 12v DC, but fiddling with mains power that can supply up to 13 amps makes me rather nervous. The BeagleBoard only needs 5V DC and the LVDS to VGA kit uses a 12v wallwart to power the inverter. I would rather have one power source supplying both the LCD inverter and the BeagleBoard (with different voltage levels for each device, obviously) - I don't particularly want a fat kettle lead stuck in the back of this thing.

    Case, and size thereof: The all important question. It's safe to say that this won't be a subtle little tablet that I can pop in my jacket pocket and use on the train - I plan to use a 15.4 inch screen, after all. However I don't want to hold something that is as thick as a normal monitor when I'm browsing the web on the sofa. I'd prefer a *larger* screen than offered by current tablets, so the fact that it's 15.4 inches in widescreen doesn't bother me - I just don't want it to be too thick. I don't really think I can address this until I get my hands on some hardware and see what footprint I'm looking at and what hardware combinations are the best - once I know that, I can start thinking about how to enclose it.

    Case, and construction/planning/design thereof: This would obviously need to be designed from scratch, and would require custom fabrication. I lack the tools and skills to fabricate from metal or plastic, so I would need to commission a one-off custom job. Wood is a possibility, but it would likely be too thick (despite making an interesting aesthetic). I am also concerned that if I want to have a case custom fabricated then I am going to need to sell a kidney and maybe an eyeball to be able to afford it.

    So. Is this crazy enough to work, or am I just plain crazy? Would appreciate any thoughts/opinions/criticisms that anyone may have.
     
  2. Tangster

    Tangster Butt-kicking for goodness!

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    Do it.
     
  3. noobieocer

    noobieocer New Member

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    get a Beagle board.
     
  4. Byron C

    Byron C And now a word from our sponsor

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    I'm sorry to sound rude, but did you even read the thread? I know it's a bit of a wall of text, but it's not as if I haven't already done my homework on this - it's not easy to condense several months' worth of on-and-off research into a neat little 4-line paragraph.
     
  5. asura

    asura jack of all trades

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    That beagle board is a cute little find, as most of the small ARM boards out there are 400/600Mhz.

    I was thinking of getting one of the next generation VIA pico-itx or pico-itxe boards and using it as a low power web-browser/word-processor for when that's all I need, and have it turn on my main pc, and switch everything over via a KVM. Nothing like as ambitious as what you have planned... But then again those VIA boards have been sitting in their products page for quite a while now, and still haven't hit the market as discrete components, so it could be they're OEM only, which would suck!

    DVI->LVDS for only a few quid more than the VGA->LVDS you found

    Another thing to think about is the currently easily available VIA pico-itx px as it natively supports LVDS, yes it has a fan, but with some cleaver work with mCubed's BorgFX I'm sure it could be made passive.

    M-ITX would be (I feel) to deep, the problem being such things as the height of the ram stick, the power input, etc, many of these would cause issues. Yes there are many that are "flatter" than a standard board, but compared to the small scale embedded broads, they always just seem... clumsy.

    Power? Ask someone else, I'd imagen jury rigging a laptop and it's battery would be the way to go that way you're using the power brick that goes with the battery, minimising conflicts in that count.

    Very quick and rough sketchup of the beagle board for you
     
  6. Byron C

    Byron C And now a word from our sponsor

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    It's a fantastic little thing; especially when you consider that it can run at full power with USB as it's only power source. Remind me why we aren't using ARM for lightweight desktops/office workstations, and why Microsoft don't want to support it?

    The VIA boards are a viable backup option; I'd seen a few on the LinITX site before, but I never realised that they had LVDS support - clearly their site search engine sucks!

    Damn good spot - cheers for the link! I've contacted them to ask if it supports my panel (Samsung ltn154x1-l02). That's an ideal solution, and probably a bit more reliable than a Chinese eBay seller!

    Agreed - M-ITX is just too much like a scaled-down desktop board. There's no way they can match something like the BeagleBoard.

    That's not actually a bad idea... Although I suspect it would depend on the size of the cells, and whether I could rip out only the charging circuits. I have seen laptops that have daughterboards for charging circuits, and I have also seen laptops that just have one big board. To be honest, power is a low-priority consideration at the moment.

    Cheers for that - will come in handy when I get round to designing hardware :thumb:
     
    Last edited: 10 Nov 2010
  7. jhanlon303

    jhanlon303 The Keeper of History

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    if you want to see a size comparison of pico-ITX and mini-ITX, i have this ARTigo unit:

    [​IMG]

    john
     

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