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Pots in parallel

  1. Oct 26, 2011 #1

    Could someone please help a noob like me understand the implications of having the 10MΩ resistor in the circuit i have uploaded. So far I've gathered it doesn't really influence the total resistance.
    I thought it could decrease the current but adding a branch should slightly increase it since it add to the number multiplying the voltage in the formula..
    And it doesn't help the pots handling the current when they go down in resistance, does it?

    Thanks a lot,


    Attached Files:

  2. jcsd
  3. Oct 26, 2011 #2


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    Staff: Mentor

    Welcome to the PF.

    What is that circuit from? It would appear to do nothing, except maybe to set voltages between 5V and ground on the "Analog Input" signals....?
  4. Oct 26, 2011 #3
    Hi berkeman,

    The voltage across the pots is read by the analogue inputs of an Arduino Mega2560 (using the Atmel Atmega2560) programmed to send MIDI messages.


  5. Oct 26, 2011 #4


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    Staff: Mentor

    Ah, then yes, the 10M resistor does nothing.
  6. Oct 27, 2011 #5
    As a side note, there should be some resistance either in series with each pot individually, or a resistor between one of the power rails and the rest of the pots.

    This would keep the power rails from seeing a short if all Pots are turned to 0.
  7. Oct 27, 2011 #6


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    Staff: Mentor

    That's not the way I interpret the diagram. It looks like the rails will always see the parallel combination of the full pot resistances, and the wipers just select up and down between the rails. The wipers are varying their output voltages, not varying any resistances, I believe.
  8. Oct 27, 2011 #7

    jim hardy

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    Gold Member

    that schematic raises more questions than it answers.

    first question is are those variable resistors potentiometers or rheostats?

    the arrow through element infers rheostats, which are just variable resistors

    but both ends of element are shown connected as in a potentiometer where wiper taps voltage partway through element
    and a rheostat is usually drawn with one end unconnected.

    i suspect the arrow should be perpendicular to element and end where arrowhead touches element, as in a potentiometer

    else the circuit makes no sense. Setting one variable resistor to zero would make all seven AN's read zero.

    I call that sloppy draftsmanship.

    if indeed they are potentiometers,,,
    i notice they're located at various wheels and knobs.

    Perhaps there's a connector and wiring harness involved?
    then the 10meg could provide a minimum load for 5V line provided it remains in circuit when that connector is unplugged.

    the picture is incomplete. my diagnosis is lazy drafting.

    EDIT oops i see Berkeman got there already.
  9. Oct 27, 2011 #8
    Berkeman, you are correct (no surprise there) - I see it drawn that way as well. I guess I shouldn't post early in the morning :-/
  10. Oct 27, 2011 #9


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    Staff: Mentor

    Yes, although I think jim hardy brings up good points about the ambiguities in the schematic as drawn.
  11. Oct 29, 2011 #10
    Since it's an Arduino schematic, which is an Italian company (if memory serves me), perhaps that's just the European convention for a pot.

    Just like, for resistors, they use a box and we use a squiggly.
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