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GND: Connecting your devices

Discussion in 'Electronic Design' started by valentin tihomirov, Jan 4, 2004.

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  1. I have a problem connecting my device to PC. The device is not grounded,
    there is 90AC between it and PC. When I link them with a rs232 cable, the
    device halts (an MCU inside device stops working). The PC goes on working.
    How do you typically prevent the problem? I power the device from an average
    220AC->10DC adapter.

    Thanks.
     
  2. scada

    scada Guest

    First off you need to see if there is a problem with either your PC or the
    Hardware device. Does the RS232 connector shell of the hardware device read
    90 VAC to earth ground? Does the PC serial connector? How much current will
    it pass, if i remember correctly the maximum amount of leakage allowed is 5
    milliamps!

    If above checks out good then....
    Get an RS232 optoisolator device. They isolate the PC from the hardware
    opticaly. Some are even powered by the PC port, others use a wall wart
    supply.
     
  3. John Smith

    John Smith Guest


    Use a 1:1 isolation transformer between the adapter and the mains.
     
  4. Whenever measuring voltages between grounds, put a 10k or so resistor in
    parallel with the test leads. Otherwise you're probably just measuring
    leakage.

    If you've still got 90V between grounds through the 10k resistor, then
    there's a real problem; for instance, the adapter might have an internal
    fault. But my bet is that with the 10k resistor there, the voltage you
    measure will only be a volt or two. In that case, the problem might be
    something else.

    Can you tell whether simply connecting the RS232 cable's ground pins to
    ground (rather than to the PC) makes the device stop working? That is, can
    you remove the PC from the equation?
     
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