Signal isolator

Discussion in 'General Electronics Chat' started by aris, May 5, 2010.

  1. aris

    Thread Starter Member

    May 5, 2010
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    Hi all,

    I have built a circuit that consists of a NE555 and a relay powered by a 12v power supply and with an output of 12V. The operation of it is that is triggered by pin 4 of a RS232 and cuts of power to the output for a time dependent on an RC circuit.
    What I want to do is to isolate the signal comming from the RS232 to the rest of the circuit after the relay is triggered. Does anyone have any ideas??

    thank you for you time everyone!!!!

    aris
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,647
    2,346
    Hello,

    I moved you thread to the general chat forum.

    Can you post a schematic of what you have upto now?
    You can place a line where the isolation should take place.

    You could think of an optocoupler as an isolation device.

    Bertus
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    You only want to isolate the RS232 after the relay has been triggered?

    Can you further define your task, and as bertus already asked, upload a schematic?
     
  4. aris

    Thread Starter Member

    May 5, 2010
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    thank both of you guys!
    what I want to do is to isolate the input comming from the RS232 after it has triggered the relay. This is the area in the red box in the attached schematic.
    if you have any idea please share it with me :):D

    thanks all of you!!
     
  5. retched

    AAC Fanatic!

    Dec 5, 2009
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    You can use optoisolators that will only pass a signal when there is a signal to pass, then it is no longer in the circuit.

    You can also use a DPDT relay and connect the RS232 to the NC pins. When the relay is energized, there will be no connection to the RS232. When the relay closes, it will be reconnected to the RS232.
     
  6. aris

    Thread Starter Member

    May 5, 2010
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    just a question retched!
    the 555 timer is activated by a low which gets from the rs232 when a computer is rebooted then the power is turned off (the box is powered by a 12V power supply) which means that once the existing relay is triggered it cuts the power to the box which leaves the rs232 in a low. what I want is when the existing relay is triggered to isolate at that point the low which comes from the rs232. would a DPDT relay would do that?

    thanks again.
     
  7. retched

    AAC Fanatic!

    Dec 5, 2009
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    Sure, once it is triggered, wire the relay to pull the trigger to ground. That will keep a constant LOW on the 555.

    Before energizing, the pin is getting 5v through the relay from the 232. once the relay is energized, you have the NO contact on the other site to ground.

    So not energized, trigger is connected to rs232 through the relay
    After energize, trigger is connected to ground through relay.
     
  8. aris

    Thread Starter Member

    May 5, 2010
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    can you suggest any device for a DPDT so I can buy one to have a go?
    I live in UK.
    Thank you very much!!!
     
  9. retched

    AAC Fanatic!

    Dec 5, 2009
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  10. aris

    Thread Starter Member

    May 5, 2010
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    thanks a lot retched for your help!!!
    I will get those and I will give you some feedback possibly on monday ;)
    Thanks once more!!!
     
  11. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ok. Let me know how you get on.
     
  12. aris

    Thread Starter Member

    May 5, 2010
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    Just a final question retched!!
    If I want to have a delay before passing the signal to the DPDT relay would a resistor and Capacitor do the job?
     
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