why dont work this isolator?

Discussion in 'General Electronics Chat' started by mohammad2050, Jan 17, 2015.

  1. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    hi
    I use below isolator for connect pc to pc but dont work this circuit?
    [​IMG]
     
  2. MrChips

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    Oct 2, 2009
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    Because there are too many unknowns.
     
  3. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    what is unknown?
    Optocoupler is CNY17 .
     
  4. MrChips

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    What is J1 computer?
    What is J2 instrument?
    What software are you running?
    What are the COM protocols on both J1 and J2?
    What data is being transmitted from where to where?
     
  5. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    this picture is in below website
    http://www.123microcontroller.com/Hardware-Interfacing/OptoCouple-with-RS232
    perhaps J1 and J2 is a symbol !

    Hyper Terminal

    RS232

    this circuit don't work
    Can you show me a circuit for RS232 isolator?
     
  6. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    For starts, you have to use no hardware flow and/or handshaking control between ports for this device to work. Also you must make sure that your RTS signal on each of the two ports is logic high (a zero, in this case) sot that it can deliver up to +12V (+15V in some cases). And finally, whatever opto-isolator chip you're using must be sensitive enough for it to work with the meager 5ma that the RTS is normally able to deliver.
    There might be other factors playing here, depending on your hardware, software, and application. But we'd need to know far more details than the ones you've just given.
     
  7. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    Just Google "RS232 optoisolator" and you'll get plenty of answers. Some self-powered, like the one you've just given. And others powered through an external power supply.
    I'd use the latter option if I were you, since it would be far more robust and reliable.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    As Cmartinez mentions, you need to set the hardware to Null Modem, you do this by jumpering the 1-4-6 & 7-8 pins at each end.
    Is there a particular reason you are wanting isolation?
    The signal for RS232 is a ± voltage signal.
    I use a diagnostic tool such as RS232 HEX Com.
    Max.
     
  9. cmartinez

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    I had a nightmare with a ground loop two years ago while trying to interface a CNC ... that's usually the most common reason why people set up optoisolation in RS232 devices, other than special safety controls requested by the user, of course...
     
  10. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    but work properly when I connect directly two pc Together without OPTO_ISOLATOR (with 3 wire , Rx , Tx and Gnd) , so The problem is not the RTS , do I am in wrong?
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I usually overcame this by obtaining the power for the PC from the CNC machine itself, I found most problems of blown communication IC's was when a different source of power was used, Ground to ground voltage difference etc.
    Max.
     
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  12. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    I want to connect my pc to a instrument that have different power supply , of course After the success at this stage
     
  13. MaxHeadRoom

    Expert

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    I don't think you are getting the right ± (plus to minus voltage) signal transition?
    Max.
     
  14. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I have done this for many years, as long as the commons of both are connected it should not matter.
    Max.
     
  15. MrChips

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    Max nailed it.
    RS-232 has to go -V to +V.
     
  16. mohammad2050

    Thread Starter Member

    Nov 14, 2014
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    You are right , I before connect directly my pc to device and Could not create any damage but don't talk together !
    this device have a Transducer that is rs232 isolator and device easily talk with pc
    So I certainly should use of this type Transducer
     
    Last edited: Jan 17, 2015
  17. cmartinez

    AAC Fanatic!

    Jan 17, 2007
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    In my case, the PC was connected to the same 110VAC power line as the servo driver I was trying to interface to. But it didn't matter if the grounds were connected close together or not... I'd get huge error readings unless one of the sides of the shield was left unconnected on the three conductor shielded cable that I used between the two DB9 connectors. So after connecting pins 2, 3 and 5, and leaving the shield connected only on the PC side of the cable things became acceptable, though not perfect. I'd still get one transmission error every 100 characters or so, which I had to manage by introducing CRC and communications monitoring techniques.
     
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