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Need help with a circuit

Discussion in 'Electronic Basics' started by Zinfari, Aug 19, 2004.

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  1. Zinfari

    Zinfari Guest

    I have a circuit that requires a 10k pot to function correctly. The problem
    that the device that has to be used has a 5k pot and it can't be changed.
    How would I go about getting this circuit to work properly? I still need
    full range so basically I need a 2x multiplier on the 5k pot. Thanks in
    advance.

    -Zinfari
     
  2. Depends on how the pot is used in your circuit.

    If the pot is used as a voltage divider (all three terminals used),
    the 5K pot will probably work OK as is.
     
  3. Zinfari

    Zinfari Guest

    No only 2 are used that's my issue. I need (roughly) 0k at start, 5k at 1/2
    turn and 10k full so a simple resistor in series or parallel won't work
    either.

    Anyone have any ideas?

    -Zinfari
     
  4. Depending on the circuit, you may not need any change at all. What is the
    circuit?
     
  5. Please don't top post...

    You can use an opamp and NPN transistor to emulate a 10k pot using a
    5k pot.

    VCC
    +
    |
    .-----.
    | Load|
    | |
    '-----'
    |
    .-------------------------o V1
    | |
    .-. |
    | | |\ |
    R | | +------|-\ |/
    '-' | | >--------| NPN
    | | +---|+/ |>
    o----+ | |/ |
    | +-----------------o V2
    | .-.
    .-. | |<---,
    R | | 5k | | |
    | | '-' |
    '-' o-----.
    | |
    '-------------------------o
    |
    |
    ===
    GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    This circuit makes V1 = 2 * V2. Thus, it acts like a 10k pot. As the
    resistance goes from 0 to 5k, the total resistance of the NPN + 5k
    goes from 0 to 10k. It'll freak out at low settings of the 5k pot,
    because it can't make the voltage across the NPN get less than a few
    tenths of a volt.

    Regards,
    Bob Monsen
     
  6. John Fields

    John Fields Guest

    ---
    You're a fucking idiot.

    Oh wait...

    Hopefully you're _just_ an idiot. That way you won't be able to
    figure out how to procreate and we won't have to deal with the issues
    of your non-fucking idiotic offspring.

    You mention nothing about about what the input looks like and you
    mention nothing about what you want the output to look like, yet you
    whine about what you'd like us to do for you when you apparently have
    no idea about what you need.

    But, this _is_ sci.electronics.basics., so I apologize for any
    aspersions I may have cast on you and I'll, instead, beg you to ask
    for what you want more clearly so that I might serve you in a fashion
    which will make you less uncomfortable...
     
  7. A solution largely depends on the circuit and the function of that pot in
    it. A universal - and impractical and expensive - solution can be to use the
    5k pot as a voltage divider, use the voltage to control a servo, which in
    turn controls a 10k pot. For a better solution we - at least I - need more
    information.

    petrus bitbyter
     
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