Which Resistor for 9V Battery and 2ma Current?

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NathanielZhu

Joined Dec 5, 2011
50
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
 

Wendy

Joined Mar 24, 2008
22,170
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.
 

Adjuster

Joined Dec 26, 2010
2,148
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.
 

SgtWookie

Joined Jul 17, 2007
22,220
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.
 

tommydyhr

Joined Feb 3, 2009
39
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.
 

Audioguru

Joined Dec 20, 2007
11,249
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!
 
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joeyd999

Joined Jun 6, 2011
4,433
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:
 

bertus

Joined Apr 5, 2008
20,867
Hello,

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

Quote:
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