Electrical hacking (was Re: [Techtalk] [OT] charging USB devicewithout a PC)

Maria Blackmore mariab at cats.meow.at
Mon Apr 14 16:25:19 EST 2003

On Mon, 14 Apr 2003, Alvin Goats wrote:

> Ok, we have capacitors that are not connected to anything getting
> charged by static electricity in air currents. The electrons move
> without having a completed circuit.

yes, it's called "wind"

once they're in the capacitor, I think you'll find that they don't go
anywhere else though, except a little self-discharge.  However, if you
connect something across it, they will go somewhere.

> Bismuth Telluride, Anitmony Telluride and Bismuth-Antimony-Telluride are
> thermal electric materials, put a temperature difference on the two ends
> of the material and electrons will move to one end and the 'holes' will
> move to the opposite, without a closed circuit.

mmm, yes, but they won't go anywhere, will they?
the electrons and holes are only moving inside the material until you
connect something between the two ends.

> These are used for generating electricity, the only problem being that
> if the temperature difference changes sides, the DC gets reversed.

hot stuff

> Pyroelectric materials will do the same, as will piezoelectric and
> electro-optical, the first is heat, the second with mechanical stress
> and the last with light.

bash those electrons around!

It's a tough life being an electron.

> Electrons can move all over the place and in ordered directions
> WITHOUT a completed circuit.

I would like to contend that for the most part it's always a circuit, you
just may find that it's not formed by what you expect.

> Piezo-speakers (typically tweeters) and microphones will generate
> elecrical signals based on the stress on the crystal due to the
> mechanical cone or ribbond attached to them and do so whether they are
> connected to anything or not.

hmm, but it's not actually flowing, unless it's connected to something, is

You just get the electrons and holes wibbling and stuff.

> This is part of how people get hurt, they mistakenly think you have to
> have a completed circuit to have current flow.

well, electrons moving from one place to another forms electricity, you
always have the same amount, and so what goes around, comes around.  It's
not always simple, but it's there.  eg when i shuffle my feet on this
carpet, and then touch the desk, there's a spark, current has flowed.  Me
shuffling my feet is acting as the motive force of the electron movement,
because i'm rubbing electrons off one material onto another.

We should all be grateful for the poor abused and underappreciated
electron, for without them I wouldn't be able to do a billion and one
important things, like send emails to mailing lists or sit on IRC :)


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