how to connect Pot in series with resistor

Discussion in 'Homework Help' started by and1_hotsauce, Apr 27, 2011.

  1. and1_hotsauce

    and1_hotsauce Thread Starter New Member

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    Hi,

    I'm trying to connect the circuit pictured to the left. Both resistors are going into pin 2. How would I be able to make 5k a variable resistor?

    I have connected leg 3 of POT to resistor. But would that not also make the 10k a variable resistor??

    [​IMG]
  2. DerStrom8

    DerStrom8 Well-Known Member

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    No, if you connect it the way it is drawn, the 5K pot will work independently of the 10K fixed resistor. It appears that you have it connected correctly.
    Der Strom
  3. Adjuster

    Adjuster Well-Known Member

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    Your sketch on the left side of the picture shows one fixed resistor and one variable resistor connected to pin 2 of an IC. The breadboard seems to show two resistors connected to pin 2, one of which is a 5k variable, connected to another pot of unspecified value.

    You then ask if connecting the pot would make another resistor variable. I would think not, although the total resistance would be variable, within a limited range. Could you explain more clearly what you are trying to do?
  4. and1_hotsauce

    and1_hotsauce Thread Starter New Member

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    sorry let me be a bit more specific

    Assume I dont have a 30.6K and 510 ohm resistor(fig below). Instead I have a 28K and 500 ohm resistors instead. I want to connect TWO pots in series with each resistor in order to bring the value up to 30.k and 510 ohm respectively.

    The dilemma is, if I connect a pot in series with R1 does it not automatically make R2 a variable resistor as well?

    In the circuit above I have connecetd the pot to 30k pot to the 5k resistor FOR EXAMPLE, to bring it to 30.6 k. By twisting the knob, does it effect both resistors?

    [​IMG]
  5. and1_hotsauce

    and1_hotsauce Thread Starter New Member

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    What you mean? Both resistors are connected to pin 2 which is aht I have drawn (ms paint). How do I connect the pot to control only one of the resistors?
  6. Adjuster

    Adjuster Well-Known Member

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    If the 10kΩ is a fixed resistor, then it will not change just because another resistor connected to the same point is variable.

    If the two resistors are connected in series or parallel, then the total equivalent resistance will vary, but this is not the same thing. The 10kΩ remains 10kΩ, only an equivalent resistance changes.
  7. and1_hotsauce

    and1_hotsauce Thread Starter New Member

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    thanks for that! So can I say now that my 5K resistor is effectively a variable resistor? Is this the proper way to connect a pot to a resistor in order to make it variable??
    Last edited: Apr 27, 2011
  8. bluemarvin

    bluemarvin New Member

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    The 3 pot terminals may be confusing you...you need to use only the wiper and either of the other two terminals...this will vary the resistance across those two points from 0 to 5k or whatever the pot value is. Connect one of those two points to your fixed resistor in SERIES and you will make a variable resistor ranging from the fixed value to the fixed value plus 5k. You could also connect them in parallel but that would only get you 0 to 3.33k if the fixed is 10k and the pot is 5k.
  9. and1_hotsauce

    and1_hotsauce Thread Starter New Member

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    thanks got it now
    Last edited: Apr 27, 2011
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