dc variable 4-9 volts to dc variable 0-5 volts

Discussion in 'The Projects Forum' started by rbpowered, Mar 23, 2014.

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  1. rbpowered

    Thread Starter New Member

    Mar 23, 2014
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    I need to build an adapter that will take a variable dc signal that ranges from 4-9 volts and cut it down to 0-5 volts proportionally. In other words, I need to knock 4 volts out of a dc signal. If the input is 4.5 volts I need the output to be .5 volts, input 6.5 volts output 2.5 volts, etc..

    Any thoughts?
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    Operational amplifier. Set one input at 4 volts and input the 4 to 9 volts in the other input. The chip will not respond to inputs below its offset voltage.
     
  3. inwo

    Well-Known Member

    Nov 7, 2013
    2,433
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    A little more info will be helpful.

    It could be as simple as a 4V zener if accuracy is not important and current is < a few hundred ma.

    Is this a power circuit or instrumentation?
     
  4. #12

    Expert

    Nov 30, 2010
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    Sorry, my sister was on the phone distracting me.:(

    TL431 is a suspect in this case, too.
     
    Last edited: Mar 23, 2014
  5. rbpowered

    Thread Starter New Member

    Mar 23, 2014
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    Accuracy is very important. My first question is only half of the project.

    The signal is coming from an automotive air meter. I'm trying to use a piggyback computer that will only recognize 0-5 volt input. The piggyback ecu will intercept the signal from the air meter to the factory ecu. The meter on the vehicle I'm working on is one of the only ones that does.not output 0-5 or 5-0 volts. It outputs 4-9 volts. It outputs around 4.4 volts on idle and climbs to around 8.6 volts at wide open throttle.

    I need to be able to drop the airflow meter signal by 4 volts so the piggyback ecu can read it. Small increases or decreases will be made inside the piggyback and will be output by the piggyback in the 0-5 range. I will then need to increase that output by the exact same 4 volts so the factory ecu will be able to read it.

    So accuracy is very important. I really appreciate any help you all can give.
     
  6. #12

    Expert

    Nov 30, 2010
    16,298
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    Oops. This site forbids automotive discussions. Please try electro-tech-online.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,442
    3,361
    The owners of All About Circuits have elected not to allow discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

    This thread is against the AAC forum rules, Chapter 6, as seen here:

    This can be found in our Terms of Service (ToS)

    Here is a site that may provide you with some assistance: Electro Tech Online

    Good luck.
     
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