Convert 12v Positive to Ground Signal

Discussion in 'Automotive Electronics' started by ChevyLT1Camaro94, Jan 17, 2016.

  1. ChevyLT1Camaro94

    Thread Starter Active Member

    Jan 9, 2009
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    Hello all, I was wondering if there is any simple way to convert a switched positive (12v) signal to a ground signal without using a relay? maybe using a transistor or something? I have limited space to put the component in which is why I'm trying to avoid relays. thanks!
     
  2. sailorjoe

    Member

    Jun 4, 2013
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    Chevy, if I take your question at face value, it looks like you want to short circuit your 12 v signal to GND, which is generally frowned upon.
    So is it really that you want to invert your signal, so that when you have 12 v in, you put out 0 volts, and when you have 0 volts in you put out 12 volts?
    Need to be very clear about this, or you'll get the wrong answer.
     
  3. crutschow

    Expert

    Mar 14, 2008
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    Also, what is the load for this signal.
     
  4. ChevyLT1Camaro94

    Thread Starter Active Member

    Jan 9, 2009
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    Essentially what you said is what I want. But it only needs to convert the power signal to ground. Essentially what I have is one device that sends 12v from its output. And another device that requires a ground trigger. And I want to make device 1 trigger device 2.
     
  5. ChevyLT1Camaro94

    Thread Starter Active Member

    Jan 9, 2009
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    The load is next to nothing. It's simply a trigger for a control module.
     
  6. sailorjoe

    Member

    Jun 4, 2013
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    OK, here's a link to a simple circuit, with an explanation.
    http://electronics.stackexchange.com/questions/30238/how-to-invert-a-digital-signal

    The other option is to use a relay. Wire the 12 volt signal to the coil, and the input to the contact. The other contact gets wired to ground. There should probably be a pull up resistor from the input signal to 12 v. When the coil is energized by the 12 volt signal, the relay connects the input signal to ground. Easy peasy.
     
  7. ChevyLT1Camaro94

    Thread Starter Active Member

    Jan 9, 2009
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    Yes I know how to use a relay to do this but my space constraints won't allow it. The thread you linked to shows some diagrams but I don't know how to calculate the resistors.
     
  8. sailorjoe

    Member

    Jun 4, 2013
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    No problem. Start with 10,000 ohm resistors. If that works, you're done. If not, then we need to know more about the signal source of 12 v, and the trigger module.
     
  9. ChevyLT1Camaro94

    Thread Starter Active Member

    Jan 9, 2009
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    so would this be the ideal way?
     
  10. sailorjoe

    Member

    Jun 4, 2013
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    Yes, exactly. Without knowing a lot more about the other circuits, this is a pretty safe way to start, and there is likely nothing simpler nor smaller. You can solder the resistors directly to the transistor leads, giving you a circuit with three leads to connect, but not much larger than a transistor. Use a 2N2222 transistor, they're quite robust and are often used in this type of circuit. With 12 V in, you should see 0.3 V out. That should be enough to trigger your module.
     
    ChevyLT1Camaro94 likes this.
  11. Brevor

    Active Member

    Apr 9, 2011
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    Deleted, Already answered by Sailorjoe.
     
  12. ChevyLT1Camaro94

    Thread Starter Active Member

    Jan 9, 2009
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    Fantastic. Just out of curiosity if this doesn't work should I increase the resistors?
     
  13. sailorjoe

    Member

    Jun 4, 2013
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    Most likely we would need to decrease the resistor values, but let's see what happens first. With a circuit in place you can make some measurements and we can decide what to change from there.
     
    ChevyLT1Camaro94 likes this.
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