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pots in parallel

Discussion in 'General Electronics Discussion' started by CRChisholm, Oct 31, 2016.

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  1. CRChisholm

    CRChisholm

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    3
    Oct 31, 2016
    Ok, I had a simple I deal that I managed to oversimplify.

    Here's what I tried...

    upload_2016-11-1_7-14-7.png


    The idea was to have a five wire interface to allow me to read the values of three 10k pots. As it turns out, this does not work because the most it can return is 10k / 3 for any of the pots. Is there a simple way to modify this circuit to allow reading 0 to 10k from the wiper of these three pots?

    I hope the image shows up.

    [Mod fixed]
     
    Last edited by a moderator: Oct 31, 2016
  2. Kabelsalat

    Kabelsalat

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    27
    Jul 5, 2011
    So - your problem as far I understand is that the voltage out from each pot doesn't reach maximum or minimum level?

    What kind of pots are you using? Simulation or real world circuit? Is there any resistance in serie with P1 or P5 in your schematic that doesn't appear on the image?
     
  3. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    What values are you reading? Resistance or voltage? If voltage then do you have a low impedance power source connected when reading the voltages from the wiper?
    Thanks
    Adam
     
  4. CRChisholm

    CRChisholm

    4
    3
    Oct 31, 2016
    Yes this is a real world circuit.
    No, nothing else involved at this point. I am testing at the 5 pos female header (top of image). I measure between ether 1 or 5 and the wipers 2, 3, or 4. So, if the pot is turned so that the resistance between p1 and p2 is ~ 0, I expect resistance between p5 and p1 to be ~ 10k. (But to quote Mr Jagger... You don't always get what you want.)

    I tested the pots when not in the circuit and the resistance varies from 0 fo 10k as expected so the pots are good. When in circuit, the resistance varies the same on all three pots and never is more than 3.3k on any given pot. It seems like the resistance measured on any wiper is some how calculated on all three pots in parallel. (If you think that doesn't make sense, I agree...but something like that seems to be happening.)
     
  5. CRChisholm

    CRChisholm

    4
    3
    Oct 31, 2016
    i am measuring resistance. The point of this is to eventually send control values to three analog ports on an arduino nano. 5v is provided on P1 and ground on P5.
     
  6. OBW0549

    OBW0549

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    118
    Jul 5, 2016
    Your resistance measurements are exactly as I would expect them to be, given that your pots are all connected in parallel.

    Why not test your circuit the way you're actually going to be using it: simply connect a 5 volt supply across terminals P1 and P5, and check the voltage between P5 and P2, P3 or P4 as you rotate their respective pots. I suspect you'll find the circuit does exactly what you intended it to do.
     
    Arouse1973 likes this.
  7. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    The problem here is that the 'resistance' of all the pots will sum up together when they are wired like this...
    If you instead measure the 'voltage' present on the wiper you will get a better idea of where the pot is siting. If you *really* want to measure resistance, you will need to modify the circuit...

    Connect pins 2 and 3 together on each pot.
    You can then daisy chain the pots together and measure the resistance of any pot with only 4 wires ;)

    I'll attach a picture soon
     
  8. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    This will be measured differently than your diagram.
    R1 is measured with pin 1 and 2.
    R2 is measured with pin 2 and 3.
    R3 is measured with pin 3 and 4.
    pin 5 is unused.

    Depending on what is on the other side of that pin header... there may be another way, but we can guess all day.
     

    Attached Files:

  9. CRChisholm

    CRChisholm

    4
    3
    Oct 31, 2016
    Ok, so I guess the sky isn't falling after all. I was so focused on ohms law and the resistance I thought I needed, I didn't bother to check the voltage output. In fact, I AM getting exactly what I wanted in the form of voltage. Each analog pin on the m/c is getting a value beteen 0 and 1023, which is what I wanted. I kind of got focused on resistance instead of the voltage that was the end-game.

    Thanks again.
     
    Arouse1973, Gryd3 and OBW0549 like this.
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