Positive and negative door switches

Discussion in 'Homework Help' started by Ringojames, Nov 29, 2013.

  1. Ringojames

    Thread Starter New Member

    Nov 27, 2013
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    0
    Hi Guys,

    I hope you can help me with this question, and I apologise if it is not suitable for this forum, but I am trying to learn about negative and positive door switching. I'm really struggling to get my head around it (how it works, how its wired, why its used, how to test it etc!)

    I've tried googling lots of different things to get help and understanding but I can't find anything!

    Thanks in advance for any help or direction.
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    I don't quite understand the question.
    Can you give us an example of situation, usage or application?
     
  3. Ringojames

    Thread Starter New Member

    Nov 27, 2013
    13
    0
    Sorry mate, ill try my best.

    Some vehicles have negative switching and some have positive, for example if I was to fit an alarm to a vehicle I would need to know if there was a negative signal when the door opened or a positive signal.

    Does that make sense?
     
  4. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,386
    496
    Active High or Active Low.

    Active High.
    Normal voltage is low (zero volt for example). If voltage goes high, do X.

    Active Low.
    Normal voltage is high (5 volts for example). If voltage goes low, do X.
     
  5. Ringojames

    Thread Starter New Member

    Nov 27, 2013
    13
    0
    Sorry???????
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,515
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    My take is it is a way of saying N.O. or N.C switch , especially in an automobile?
    Max.
     
  7. Ringojames

    Thread Starter New Member

    Nov 27, 2013
    13
    0
    Yes it is automotive im interested in
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    I think there are a couple concepts that are getting intermixed.

    In DC systems when you turn something on or off, you have a choice of whether you permanently connect the negative side of the circuit and put the switch in the positive side of the power path. Alternatively, you can permanently connect the positive side of the circuit and put the switch in the negative side of the power path. These are often called "switched-power" and "switched-ground", respectively. Both work and both are used.

    Is that what you are talking about?
     
  9. Ringojames

    Thread Starter New Member

    Nov 27, 2013
    13
    0
    Yes that's what I'm on about (sorry I didn't explain myself better but that is down to me not understanding the subject)

    Thanks for your reply, is there a more in depth explanation with maybe diagrams so I can get a full understanding of what you are explaining plans how it is wired from a battery back to earth etc?

    Thanks for your help!..... And patience !!
     
  10. shteii01

    AAC Fanatic!

    Feb 19, 2010
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    [​IMG]
     
  11. JMW

    Member

    Nov 21, 2011
    88
    8
    Door lights are typically Case #2. when you ground the wire, the dome lights turn on. There is one wire going to the N.O. switch, when the door is open a plunger presses against the frame completing a ground and lighting the lamps.
     
  12. WBahn

    Moderator

    Mar 31, 2012
    17,716
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    It's a car. There IS no "back to earth" involved. At least you hope there isn't. :eek:

    In most automative systems, you connect one side of the battery to the frame of the vehicle and call this "ground". In most cars, you "ground" the negative side of the battery. You then run the positive wire to the various places for the various purposes. For many things, you have either

    POWER->SWITCH->DEVICE->GROUND

    which is the switched-power approach. The other alternative is

    POWER->DEVICE->SWITCH-GROUND

    which is the switched-ground approach.
     
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