tDCS Schematic Confusing

Discussion in 'The Projects Forum' started by NathanielZhu, Dec 7, 2011.

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  1. NathanielZhu

    Thread Starter Member

    Dec 5, 2011
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    So I have no experience with circuits at all.
    I think I get the gist of how the thing is put together, but the one thing that confused me was the little box on the left side titled "Current Regulator".

    I'm guessing this current regulator gives a more detailed description of the LM317 current regulator, but I don't see how it relates to the actual circuit work.
    I've seen pictures of LM317 and doesn't look anything like the box on the left side titled "Current regulator".

    So, once I buy LM317 from Radio Shack, what do I do with it to match up with the box on the left side?

    Overall, this device is supposed to generate 1mA of electricity through the anode/cathode. Don't tell me how unsafe it is because I assure you, it has been well tested. Lab-grade equipment is sold for 3000 dollars. Someone had already developed a personal version which is this schema and released it.
     
  2. SLK001

    Well-Known Member

    Nov 29, 2011
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    Look at your "head" as the load. For 1mA of current, a resistance of 1250 ohms is needed. Your schematic accomplishes this with a series 1200 and a 51 ohm resistor pair.

    Tell me, what is this for? What does it do? And why would you do it?
     
  3. NathanielZhu

    Thread Starter Member

    Dec 5, 2011
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    Well, this device stimulates neurons with a very low amount of electricity.
    I found the schematic on http://brmlab.cz/project/brain_hacking/tdcs
    All the research I found on this showed positive results with side effects being minor. The air force according to one research found that it took students 1/2 the time to acquire the motor skills in their training program with tDCS compared to the students without it.

    Well, my question mainly was mainly about the stuff in the light blue box. It just doesn't seem relevant to the rest of the schematic.

    Here, I circled it.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    Whoever came up with that constant current regulator schematic didn't bother to read the datasheet which says that the LM317 needs a minimum of 10mA current output in order to provide guaranteed current and voltage regulation. They are attempting to regulate it at 1/10th of the minimum current, and the output current will not be regulated worth a darn. I don't know offhand what the current will be, but it'll be more than 1mA.

    Even the LM317L, the 100mA TO-92 package version, requires a minimum of 5mA to provide guaranteed regulation.
     
  5. NathanielZhu

    Thread Starter Member

    Dec 5, 2011
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    oh. Do you think it'll be more than 2mA? The 1mA ought to be the current that reaches the brain but the skull provides a lot of resistence.

    Can you help me with my previous post? I'm having trouble understanding what the box on the left corner is for (I circled it in my previous post)
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    I frankly don't know how much current you will get. The resistance between OUT and ADJ is way out of specifications. I've never tried going that far beyond the specifications.

    The box on the left is an excerpt from the datasheet.

    While R1 = ~1.25/Ireq; they omitted that 10mA <= Ireq <= 1.5A, so 0.8333 Ohms <= R1 <= 125 Ohms. They are using 1251 Ohms, or more than 10 times the maximum allowed.
     
  7. 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:
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    • Any kind of over-unity devices and systems
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