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Pulse Stretching

Discussion in 'Automotive Electronics' started by Freddy1333, Jul 28, 2015.

  1. Freddy1333

    Freddy1333 Member

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    Yes I have a multimeter and use it lots. I'm still confused Tony, sorry. For me to understand what you are saying that I need to do, I think you will have to draw a simpler wiring diagram showing the connections which (to me) seem to be absent on the left of your pic/diagram. Is the lower component, which is earthed, an LED? Or can it just be a diode? Thanks for your tolerance.
     
  2. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    An LED is a diode as shown and yours is special with inbuilt resistor for 12V
    This was an equivalent circuit.

    If your info is correct,


    1. disconnect RED wire on LED from signal output and connect to switched 12V from ignition somewhere.

    2. disconnect BLK wire on LED from GROUND and connect to signal output.


    This will now enable LED On with active low (0V) signal and invert what I assume you have to what you indicated you need.
     
    Last edited: Aug 21, 2015
  3. Freddy1333

    Freddy1333 Member

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    Thanks Tony, yes I know that a D stands for diode. My question is, why do you recommend fitting a second LED rather than just a diode? Which LED are you referring to, the 12v one I have fitted or the second you you show? Or what am I misunderstanding? As I mentioned early on, I am a novice. :D
     
  4. dave

    Dave New Member

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  5. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I was always referring to yours unless you couldn't get access.
     
  6. Freddy1333

    Freddy1333 Member

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    So you're saying to reverse the wiring on the LED, is that it? If so, I've tried that and the LED does not illuminate at all.
     
  7. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    No that's not correct
    1. disconnect RED wire on LED from signal output and connect to switched 12V from ignition somewhere.

    2. disconnect BLK wire on LED from GROUND and connect to signal output.
     
  8. Freddy1333

    Freddy1333 Member

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    Well Tony, I understand the words but I don't understand what you mean - without a diagram of some sort. The one in your earlier post wasn't clear enough to me, as it showed resistors where I have none. You're obviously talking about a second LED I need to fit. Sorry, but it's not clear to me exactly what you are suggesting I do, but I certainly appreciate your input.
     
  9. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    upload_2015-8-23_8-55-46.png

    Disconnect LED and wire as above. If signal goes to ground from your circuit, then Lamp goes ON.
     

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  10. Freddy1333

    Freddy1333 Member

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    Thanks Tony. The thing is, that's what I've done and the LED works (flashes) but in the reverse order of what's it's supposed to as I described in post 29. What arrangement will enable it to flash when it should and be off when it should? Thanks again.
     
  11. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    I have already explained how high side verses low side inverts the light.
     
  12. Freddy1333

    Freddy1333 Member

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    I got it to work correctly by fitting a resistor to the 12v supply, then other end to the signal wire plus +ve LED wire, then the -ve LED wire to earth.
     
  13. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    Good, but totally inconsistent with the feedback you gave me with the signal being negative and working before without a resistor. But no problem
     
  14. Freddy1333

    Freddy1333 Member

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  15. Freddy1333

    Freddy1333 Member

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    Tony et al, I have one very minor issue remaining; the LED has a faint glow after the system/fault check, which is just visible in daylight, presumably caused by some resistance thru the ABS ECU. What can I do to solve this? With thanks.
     

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