RS232 Optical Isolation

Discussion in 'General Electronics Chat' started by mohammad2050, Dec 12, 2014.

  1. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    hi
    i have a device that use RS232 Optical Isolation Transceiver for connect to pc . Now my question is : do it will work without Transceiver ?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    No, why would you expect that it would?
     
  3. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    because this Transceiver is only for protect between pc and device , Both sides is RS232
     
  4. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    I don't understand your question. There ARE optically isolated RS232 transceivers out there, and their intention is to protect the equipment. But you need TWO transceivers to make an information transaction on RS232, whether they're optically isolated or not...
     
  5. Papabravo

    Expert

    Feb 24, 2006
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    Then I don't understand what you are asking. Do you want to remove the isolation and replace it with wires?
    If so you may get quite a surprise when you connect signals with different voltage levels together. The isolation is there for a reason, unless you think it isn't. You might as well give us a schematic so we can tell what you are talking about.
     
  6. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    YES ,I would
    why different voltage levels? Unless not both RS232
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    RS-232 is often implemented with different voltage levels. The spec says a MARK is any voltage in the range [-3V..-25V] with respect to GND, and a SPACE is in the range [3V..25V] with respect to GND. A voltage in the range [-3V..3V] represents an undefined signal. It is neither a MARK or a SPACE. The purpose of the isolation is that you have signals generated from different power supplies that do not share a common ground. In fact the grounds might have several hundred volts difference between them. Do you really want to connect the two devices together if this is the case? Only someone who didn't know what they were doing would try to do this.
     
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  8. mohammad2050

    Thread Starter Member

    Nov 14, 2014
    56
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    OK , thank you Papabravo for well information
    Now I have another question :
    still can not be done , If be close together two power supply?
    for example : power supply is 10 volt in devise side and other side is my laptop (use usb to RS232 converter) . Is it still can not be done ؟
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    It depends. Do you know what levels the PC is using from the USB to RS232 converter.
     
  10. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    no , i do not know how much is power supply in my laptop :(
    So do not do this work:) .Thank you for help
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The optical isolation for a RS232 link is not because there are different voltage levels in the signals; it is because there is likely a potential difference between the ground potential on the remote equipment chassis and the ground potential on the PC chassis. If you connect the RS232 cable without optical isolation, you create a "ground loop" between the two devices, which will screw up the signals...

    It can also be done for safety. If the remote equipment is for swimming pools, spas, medical devices, etc., then there could be a shock hazard that comes from the PC power supply along the common wire in a non-opto-isolated RS232 cable. The opto-isolation effectively lets the remote equipment operate at a different ground potential than the PC.

    If the maker of the remote equipment wants opto-isolation, it is for a reason, and you would be a fool to eliminate it...
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    I did make the ground potential argument in post #7. That said if we are talking about a laptop and another device that sits on the desktop there may not be much potential difference between the grounds. It would be helpful to know more about the TS/OPs device.
     
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