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Emc issues for electronics housed in a plastic box

Discussion in 'Electronic Design' started by IanM, Oct 6, 2007.

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  1. IanM

    IanM Guest

    Hello,

    I am designing a cct that has 2 usb connectors at the bottom, 1 rs232
    connector at the top, 2 push button switches and user changeable alkaline AA
    batteries. This is all going in a plastic enclosure. I am concerned about
    the ESD part of the CE marking process and wondered if anyone had any
    experience in this area and advice to offer.

    The cct detects the presence of the USB and steals power from it and nothing
    else (ie no connection to the data lines), it also communicates with rs232
    equipment. So the cct is basically power supply, small microcontroller and
    rs232 interface.

    Thanks,

    IanM
     
  2. Gibbo

    Gibbo Guest

    Stick a CE mark on it. Copy someone else's declaration of conformity.
    That's what everyone else does. You'll be fine.

    Unless you're making a *really* screwed up circuit or a transmitter of
    some sort, the chances are it would pass tests anyway. And nobody
    bothers checking.

    This opinion is both true and worth what you paid for it.
     
  3. Paul Mathews

    Paul Mathews Guest

    Search for a thread a few weeks old which covers the basics of ESD
    protection. The thriving business in compliance engineering and
    independent test labs suggests that the poster who claims that no one
    is really making efforts to comply is exaggerating, although I agree
    that many products don't comply.
    Paul Mathews
     
  4. Robert Baer

    Robert Baer Guest

    There are some (expensive) conductive plastic boxes available,
    usually "available in any color you want, so long as it is black".
    Or, if for production quantities, have them coated inside with
    Acheson electrodag or equivalent; they have one or two that are not only
    conductive but also dissipative (Nickel Carbonyl if i remember correctly).
    Lastly, for onesies, line the inside with aluminum foil from the
    kitchen, or conductive copper sticky tape (either the 3M crinkled "RFI"
    finish or the plain flat stuff sold to get rid of garden slugs).
     
  5. Make sure the MCU is well decoupled, the power supply is current limited ( to avoid latchup
    problems) and make sure you use the watchdog - this should give reasonable protection against ESD.
    About the only major risk is when the connectors get plugged in - make sure all the shells are well
    bonded together, and tracked in such a way as to avoid coupling transient currents into your
    circuit.
     
  6. Guest

    About the only major risk is when the connectors get plugged in - make sure all the shells are well
    If you do this by bonding the ground contacts of all connectors onto a
    ground plane covering most of the board area you will also greatly
    reduce rf emissions.

    John
     
  7. IanM

    IanM Guest

    Thanks for all the replies, I have got a lot to go on this morning!

    regards

    IanM
     
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