Dynamically Double Resistance?

Discussion in 'General Electronics Chat' started by 3dOptics, Apr 11, 2014.

  1. 3dOptics

    Thread Starter Member

    Mar 15, 2009
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    I have a potentiometer that has a range of 0-70ohms. I have a resistance gauge that measures 0-140ohms. Is there any way I can dynamically double the potentiometer resistance? Thanks.
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Use two in series?
     
  3. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Dynamically, you say? Look up "gyrator".
     
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Is this for a fuel gauge mod?
     
  5. 3dOptics

    Thread Starter Member

    Mar 15, 2009
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    Yes. The fuel sending unit on the tractor has a range of 0-70ohms. I thought a reproduction gauge would be the same ohm range but it is 0-140ohms. I could replace the sending unit or find an original gauge that is the correct ohm range, but I was hoping there would be another solution.
     
  6. inwo

    Well-Known Member

    Nov 7, 2013
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    Is this gauge connected directly from +12 to grounded rheostat?

    Can you measure current at full and empty range of the gauge you will be using?

    Or find more specs?
     
  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Here's one way you could effectively double the pot resistance.
    The 70 Ohm pot plus components in the dotted rectangle of the right-hand circuit behave similarly to the 140 Ohm pot in the dotted rectangle of the left-hand circuit. The graphs show that the voltages at points p1 and p2 track each other as the pot resistances are varied from min to max.
     
  8. 3dOptics

    Thread Starter Member

    Mar 15, 2009
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    0
    Thanks. Where do I hookup the gauge? I built the circuit in CircuitMaker but I can not get it to work correctly.

    What simulation software do you use?
     
  9. #12

    Expert

    Nov 30, 2010
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    How about just reducing the voltage to 6 volts?
     
  10. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    R1b represents the gauge, so the gauge connects to the collector of Q1 (point p2).
    LTspice (free download from Linear Technology).
    You don't have R1b going to 12V in your circuit.
     
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