[dorkbotsea-blabber] electrical neural/muscle stimulation

[Wim Lewis]

On Jan 13, 2009, at 1:38 PM, Steve Greenfield wrote:
> "Blue screen of death" would take on a whole new meaning. ;')

"Always mount a scratch monkey."  :/

That said, electrical zappy things were around at fairs and science  
centers for some time and presumably injured few people. Heck, at the  
santarchy dorkbot a couple of months ago there was a toy designed to  
shock the players. I think this could be done with pretty small  
danger. But like everyone else, I'm not willing to put my livelihood  
or someone else's life on the line.

What effect are you trying to get? A tingling sensation, an actual  
painful sensation, muscle contractions, ... ?


My understanding of electrical dangers is that there are three basic  
ways electric shock can hurt you (*please* do actual research before  
hooking up the electrodes):

1) disrupting the heart rhythm. In the worst case this takes only a  
minuscule amount of current (tens of microamperes) in the right place  
(directly through the heart). Conservative solution: no currents  
through the torso, you don't know where they'll go.

2) muscle contractions causing you to throw yourself across the room,  
etc. (the actual injury being that you crack your skull on the floor,  
or involuntarily stab yourself with the screwdriver you're holding,  
or land on the curare-tipped spikes you keep on the other workbench,  
or whatever.) Conservative solution: no currents through larger  
muscles, like the legs and biceps.

3) Actually burning you, leaving charred regions to fester deep  
within your flesh. This takes 'way more power than you're likely to  
use on purpose, but there's always the possibility of a fault in your  
equipment.

Most injuries, I gather, are from #2. There are a whole host of  
variations on #2, like current causing your diaphragm to contract so  
you can't breathe.  AIUI muscle contractions are mostly what you see  
from 5-100s of mA.

There's a whole lot of uncertainty around the edges of all of these  
numbers. The amount of current that *might* stop your heart, for  
example, is a lot smaller than the amount that *probably* will stop  
your heart. Your skin resistance varies by orders of magnitude  
depending on circumstances, and therefore so can current (Ohm's law).  
There are other variables, like frequency, that affect things.


Wim.