Which Resistor for 9V Battery and 2ma Current?

Discussion in 'General Electronics Chat' started by NathanielZhu, Dec 5, 2011.

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  1. NathanielZhu

    Thread Starter Member

    Dec 5, 2011
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    Hey, so I'm trying to make a simple device that will look similar to this:
    http://oi42.tinypic.com/wgyl8i.jpg It's just a picture I drew up.

    My Main question is for choosing the right Resistor.
    My goal is to reduce the current of the 9V battery to 2mA by the time it reaches the sponge (see picture) and pretend all the wires are insulated copper wires.

    What is the specs of the resistor I should get?
    Also, do I need to put a resistor on both the wires to the cathode AND the anode or just one of them
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Use Ohm's law.
     
  3. T.Jackson

    New Member

    Nov 22, 2011
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    What are you trying to do exactly?
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,766
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    Assuming a short, and using Ohm's Law,

    R = V / I
    R = 9 / 0.002
    R = 4500Ω ≈ 4.7KΩ


    The real current draw will be much less, since your sponge will also have resistance.
     
  5. Adjuster

    Well-Known Member

    Dec 26, 2010
    2,147
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    The link in the first post refers to "transcranial DC stimulation" aka passing electric currents through the skull (to stimulate the brain???).

    A picture shows wires terminating in what look like soldering iron tip cleaner sponges, possibly soaked in saline. Presumably these would be placed on the victim's head. This really does not sound like a good idea, in my view.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Since the resistance of the load will be an unknown, and will vary considerably, you would need an active constant current circuit to limit the current, rather than a fixed resistor.
     
  7. tommydyhr

    Active Member

    Feb 3, 2009
    39
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    2 mA wouldn't be too detrimental though. With the resistance through the skin and the skull, the current amounts to microamperes, or perhaps even just a few nanoamperes.
     
  8. Audioguru

    New Member

    Dec 20, 2007
    9,411
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    Why would anybody want to put DC current into their brain??
    EDIT: OK, I read Wikipedia about how it is used to help brain disorders, but it might trigger a seisure. ZAP!
     
    Last edited: Dec 5, 2011
  9. tommydyhr

    Active Member

    Feb 3, 2009
    39
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    Probably the same reason as why someone chose to invent this garbage: http://www.stimrx.com/abbelt.html

    Hilariously ridiculous! :D
     
  10. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,693
    2,765
    This is one of those topics I'd be wary of commenting on. Someone is going to try this at home with 120 VAC mains when they don't get the results they expect with a 9V battery... :eek:
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I am closing this thread as it violates AAC policy and/or safety issues.

    Quote:
    6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

    • Any kind of over-unity devices and systems
    • Automotive modifications
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    • LEDs to mains
    • Phone jammers
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