How to get trigger pulse when a relay is Energised and De Energised

Discussion in 'General Electronics Chat' started by kosss, Jun 29, 2015.

  1. kosss

    Thread Starter New Member

    Jun 29, 2015
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    Hi
    I have a 12 volt relay being activated by a timing circuit (so 12 volts is on the relay while it counts down the prescribed time)
    I need a trigger pulse or switch pulse when the relay is energised and one when the relay is De energised
    Thanks Shane
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    What is the nature of the system that is required to monitor the relay?
    Max.
     
  3. kosss

    Thread Starter New Member

    Jun 29, 2015
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    Hi
    just need 12v trigger to activate a 2.5v-12v input
    The input (IN) requires just a few milliamps at anywhere between 2.5v and 12v.
    Thanks
     
  4. Reloadron

    Active Member

    Jan 15, 2015
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    Since you do not mention any timing periods this will be generic. I would think about using a pair of One Shot multivibrators. Something along the lines of a 74123 simply because it is dual and allows for + or - triggering. Again, you do not mention the pulse width once triggered?

    Ron
     
  5. kosss

    Thread Starter New Member

    Jun 29, 2015
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    Hi
    the trigger has to run a relay pcb with the following specs (The input (IN) requires just a few milliamps at anywhere between 2.5v and 12v)
     
  6. Reloadron

    Active Member

    Jan 15, 2015
    963
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    You want a pulse when a relay coil is energized and you want a pulse when the coil is de energized. Call these pulses triggers or whatever you want but they need a pulse width or duration? So when 12 V is applied to the coil you want that positive transition to create a pulse and when the 12 V is removed you want to create a pulse on that negative going transitional edge. Use a pair of one-shot multivibtators. The 2.5 to 12 V isn't the issue. Additionally DC coil relays usually have a diode across the coil to snub the inductive kick when the coil field collapses, that may need some consideration. Commonly called a "flyback" diode.

    Ron
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    You want to use the relay contacts to generate the pulses, or do you want to use the voltage across the relay's coil?
     
  8. kosss

    Thread Starter New Member

    Jun 29, 2015
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    Hi
    I was going to try and use the relay contacts
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Do you have form C (NO,NC) contacts?

    So you need two outputs; 1 positive going when the relay closes, the other a positive going pulse when the relay releases?
     
    Last edited: Jun 29, 2015
  10. kosss

    Thread Starter New Member

    Jun 29, 2015
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    Yes the relay has C, NO, NC Contacts
     
  11. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    So you need two outputs; 1 positive going when the relay closes, the other a positive going pulse when the relay releases?
     
  12. kosss

    Thread Starter New Member

    Jun 29, 2015
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    yes this is correct
     
  13. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    I made some assumptions:
    You have 12Vdc available.
    Each input of the relay board looks like a resistance of ~2kΩ.

    238.gif
     
    #12 likes this.
  14. kosss

    Thread Starter New Member

    Jun 29, 2015
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    Thank you MikeML for your help I will build the circuit and give it a go
    Thanks Again for you help
     
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