EMC protection of portable electronics

Discussion in 'General Electronics Chat' started by dk-info, Mar 25, 2009.

  1. dk-info

    Thread Starter New Member

    Mar 9, 2009
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    0
    I am building a hand-held serial terminal that will connect to a battery powered data logger via RS232. The physical interface is using a standard 1/8" stereo male to male extension cable from the terminal to the data logger.

    I am worried about induced voltage transients when I connect or disconnect the serial interface from the data logger. If I place a TVS on the Tx/Rx lines to the PCB zero volt potential (Ground) on either side, will this be sufficient?

    Potential sources for EMI are GPS devices, Wireless entry key fobs, RC plane transmitters, cell phones, walki-talki's, static discharge and the general EM field noise one finds out-doors.

    If the zero volt potential on the PCB is not connected to an earth ground, how does a TVS work? Where does the shunted transient energy go? I can limit the current that does flow through the Tx/Rx pair but won't the "ground" plane reflect the potential dumped into it from the TVS?

    What is the "proper" way to manage transients in portable electronics devices? My understanding of analog electronics is limited. Any insight would be appreciated.

    David
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    The most common method is to use an opto-isolator on the lines. Interference is only bad data rather than a ruined circuit.

    Is this using 5V logic, or full RS-232 with +/- 12V signaling? There are isolators built specifically for each.
     
  3. dk-info

    Thread Starter New Member

    Mar 9, 2009
    8
    0
    I am using a 3V MAX3319, which puts out +- 4V from the charge pump. The literature claims RS232 compatible output. From a simple point of view, it works with my PC and the controller (another MAX3319) it connects to.

    David
     
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