Require special type of relay.

Discussion in 'The Projects Forum' started by Z2TT, Oct 7, 2010.

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  1. Z2TT

    Thread Starter New Member

    Oct 7, 2010
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    Hello,

    I have read the relay write up but have not been able to find the type of relay I need to function in a certain way. I will try to explain as simple as possible.

    I need a relay that controls continuity to 2 outputs, and they are labeled A and B, but normally does not give continuity to either. So it would be like this :

    [​IMG]

    Now Once The coil is energized, I want it to give continuity to A for ONLY 1 SECOND, and then go back to normal.

    But then, When the coil is de-energized, I want it to give Continuity to B for 1 SECOND ONLY, then go back to normal.

    Then when energized again repeat the process - Back to A for One Second.

    Is this possible and is there such a Relay?
    Any ideas welcome.

    Thankyou.
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
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    Outside a PLC (programmable logic controller), I don't think you will find "a" relay that will meet your spec's. A couple of details: What powers the coil? What voltage (AC? DC?) and current are the contacts supposed to switch?

    I think two 555s (or a 556) configured as positive and negative edge-detector monostables driving two SPST relays would work.

    Ken
     
  3. Z2TT

    Thread Starter New Member

    Oct 7, 2010
    2
    0
    DC Power, current would be pretty low.

    Coil will be powered by a wire that formerly supplies constant power to the vehicles ECU, however the immobilizer i installed cuts power to this wire, now upon the immobilizer "arming" itself and cutting power flow through this wire, I want an event to happen.

    So

    1. Immobilizer arms.. cuts power through ECU +12v wire

    2. At this time i want a certain wire on the cars system ('A' in my mspaint pic) to be grounded for 1 second, so that is why i want a relay to detect the +12v wire losing power, then ground a certain wire for 1 second.

    So sequence of actions.

    - Immobilizer arms, cuts power to ECU Wire
    - "My Relay" detects loss of power to this wire, grounds wire "A" for 1 Second

    And for disarming

    - Immobilizer disarms, power to ECU wire is given
    - "My Relay" detects power on this wire, grounds wire "B" for 1 second

    In a nutshell I need - A relay that detects presence and absence of voltage on a given wire, and upon detection of presence and absence of power to that given wire, the relay will provide ground to 2 different wires for 1 second only, the wire that is grounded out of the 2 is determined whether the relay detects presence or absence of power on it's trigger wire.
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
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    Can't think of a relay with a "center off" position but they did exist at one time.

    Chances are you're going to have to build some sort of tri-state flip-flop circuit.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
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    nope..no relays whatsoever
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Just a concept. I you're just grounding A and B, and don't need isolation, the relays could be replaced with MOSFETs or BJTs.

    Ken
     
  7. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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  8. bertus

    Administrator

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

    mcgyvr is right.
    Do not mingle with the ECU.

    Bertus
     
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