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SD card data storage questions

Discussion in 'Electronic Design' started by Richard Rasker, Apr 13, 2010.

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  1. Hello,

    I'm working on a stand-alone, battery-powered temperature monitoring device
    which collects a few megabytes of data over the course of a few weeks. The
    goal is to monitor the temperature of bearings and a clutch box of a heavy
    machine under varying loads, and evaluate these measurements afterwards.
    Most of this is a trival design matter, and I got almost everything running
    just fine within a few days.
    The only problem I'm still facing is data storage: I'd like to use an SD
    card (or Micro SD) to store this data, so that the user can transfer the
    data to a PC with minimal hassle.

    My questions:
    - It would appear that I need a license from the SD Card Association if I
    want to build (and sell) anything containing an SD card host circuit (see
    http://www.sdcard.org/developers/join/licensing/ "Host and Ancillary
    Products"). Now this would more than triple my development cost, in fact
    making it rather uneconomical to use SD cards -- this temperature monitor
    isn't meant to be built in any significant numbers (three, to be exact).
    Does anyone know more about these licensing requirements?
    - Does anyone have any information on how to write data to SD cards using a
    PIC controller?

    Any suggestions for a different data storage and retrieval mechanism are
    welcome too, of course, but I can't think of anything as easy to use as an
    SD card. Also, I'd rather not use a USB device, because the whole shazzam
    now runs off a 3V power source, whereas USB requires 5 volts.

    Thanks in advance for any suggestions, best regards,

    Richard Rasker
     
  2. Tim Williams

    Tim Williams Guest

    CF cards may be easier to use? Just an IDE interface I think. Not exactly
    "compact" by today's standards, of course...

    Tim
     
  3. Adrian C

    Adrian C Guest

    Is selling a SD compatible device without joining the SD Card
    association really something you can get fined for?

    What about a USB client port, and allow the use of USB thumb drives.

    Or, do ye have to forcibly join the USB association for that ...
     
  4. D Yuniskis

    D Yuniskis Guest

    Hi Adrian,

    "Technically", I think so. (practically? <shrug>)

    IANAL.

    I think at the very least they copyright the SD logo
    and your use of it in advertising your product would
    constitute an infringement. (I wonder if you could
    advertise as "uses those little postage stamp size
    memory cards commonly found in digital cameras" and
    get around this :> )

    I believe their (stated) goal is to ensure the "quality"
    of compliant products is maintained so the market's
    image of that technology isn't tarnished. (Of course,
    I suspect they also have financial motives).

    They could also want to protect IP as there are lots of
    other compact portable media that they are competing
    with for market share.

    Personally, I'd use an inboard serial/data flash and
    a USB slave interface. "Look like a mass storage device"
    so you could just plug yourself into a PC "as a thumb
    drive".

    Or, implement a USB host interface and expect the
    "data store" to be a mass storage device plugged *into*
    your device. Depending on the size/complexity of the
    product, this also opens other possibilities (e.g., you
    could attach a USB wireless device and use telemetry to
    deliver the data to a remote PC/collection device)
    Huh? Do you mean a *host* port? I.e., to allow a thumb
    drive to be plugged *into* the DATAC system? Or, do
    you want the device to LOOK LIKE a "thumb drive"?
    "Resistance is futile"
     
  5. Adrian C

    Adrian C Guest

    Er, Whoops - yeah, host.
     
  6. D Yuniskis

    D Yuniskis Guest

    <grin> Keyboard failure! :>

    I think the problem there is the number of product (MCU)
    offerings with host support. :< Though I think it a
    much "slicker" way of approaching the problem (i.e.,
    it might be diffcult to carry the logger *to* the PC
    if it was implemented as a "client/slave").
     
  7. SilverLeo

    SilverLeo Guest

    Il Tue, 13 Apr 2010 11:41:32 +0200, Richard Rasker ha scritto:
    Take a look at this:
    http://elm-chan.org/docs/mmc/mmc_e.html

    If you need a good FAT library:
    http://elm-chan.org/fsw/ff/00index_e.html
     
  8. D Yuniskis

    D Yuniskis Guest

    Use a wireless interface. Depending on bandwidth, could be
    something as "slow" as low end zigbee. You can also buy
    radio modems in the 400MHz band.
     
  9. JosephKK

    JosephKK Guest

    You might look at the design of the PICkit 2 which has a usb interface and
    can store plenty of data in serial flash.
     
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