I'm 90% sure that if this were possible someone would have done it
already, and that I probably would have by now seen an example on
the internet. Still, never deny the possibility of the impossible.
Also it's something that I've had vaguely in the back of my mind
since I was in my teens.
Electric arcs are really quite strange and complicated, but I'll
believe in the simple fact: that they form in air only when voltage
is sufficient for them to strike (after which said voltage can be
lowered while they continue to pass current (up to a point)).
This is basic, but hang in with me. Say I have three electrodes
(pins) in a board:
_________________
| |
| o |
| c |
| |
| o o |
| a b |
| |
|_________________|
Say 1,000V is sufficient to strike a (small) arc over the distance
between any of the pins. If "a" is a 1,000V, "b" is at 500V, and "c"
is at 0V, there should be an arc struck between "a" and "c".
Alternatively if "a" had been 500V while "b" was at 1,000V, the arc
would have been between "b" and "c". Or if "a" and "b" were both at
1,000V while "c" was 0V, then both "a" and "b" would arc to "c"
(also if "c" was at 1,000V while "a" and "b" were 0V, and
technically that's when "a" and "b" would arc _to_ "c" instead of
from "c" if talking with respect to the direction of current flow).
So you should see that by varying the voltages to each of the pins,
you could form any two sides of a triangel. So the aim is to create
an image within a grid of such triangles.
Now a couple more electrodes:
_________________
| |
|o o o|
|a c e|
| |
| o o |
| b d |
|_________________|
If we want to draw a "W":
a=0V
b=1,000V
c=0V
d=1,000V
e=0V
_________________
| |
|o o o|
|a# # c # #e|
| # # # # |
| o o |
| b d |
|_________________|
Or to draw:
___
\ /
a=1,000V
b=0V
c=0V
d=0V
e=1,000V
_________________
| |
|o ##### o ##### o|
|a # c # e|
| # # |
| o o |
| b d |
|_________________|
Now let's try to draw a bird, and run into a problem:
First problem is that I can't draw to save my life, so a bird looks
like this:
_ _
_\\_/\ This looks a bit better but needs more triangles: _\\_/\
\_ __/ \_ _/
// //
Or maybe the first one is a decent attempt at a Boeing 747, I don't
know. This is how I always felt in art class.
Anyway:
_____________________________________________
| |
|o o ##### o o o o |
|a b # c # d # e # f |
| # # # # |
| o ##### o o ##### o o o|
| g # h i j # k l|
| # # |
|o o ##### o o ##### o o |
|m n # o # p q r |
| # # |
| o o ##### o o o o|
| s t u v w x|
|_____________________________________________|
Phew, almost ran out of letters!
Well as far as I can tell, there's no way to make all the lines
purely by switching electrodes to 0/500/1,000V, without also
striking unwanted ones. One solution might be to use isolated power
supplies, so that arcs won't strike between those sets of electrodes
on a different supply because there's no voltage between them.
That would make some lines impossible to form though, so maybe
actually have multiple electrodes on each point and have them
connect to two isolated supplies, so that either supply could be
used to form any arc depending of which will prevent undesired arcs
from striking to other electrodes.
Or just have an extra electrode in the middle of each line that can
be switched from out-of-circuit to 400V just to strike the arc from
eg. a 900V electrode (not quite enough to strike the full lenth on
its own) which then carries on to a 0V electrode.
Or maybe there's some way to do it just with more combinations of
voltages.
Frankly I've spent too long on this useless idea now already today,
and it will take too long to figure out with some certainty which,
if any, of those solutions will work. Guess this is one for the
"unfinished" section then...
