I recently aquired a Heavy Armor (www.armorbyotter.com) case for my PDA.
It is a waterproof, crushproof, airtight case that still allows use of
the PDA. It's really fantastic, it's even large enough for me to leave
my compact flash 802.11 card in the unit, so I can use wireless while
still environmentally protected. Sweet. However, there is one downside.
When I wish to listen to some MP3s, I have to take the unit out of the
case. So, I was trying to think of a way to get stereo audio out of the
case without completely compromising the integrity of the case. Here are
a few of my ideas:
1) Mechanical - If I could come up with a watertight connector, that
might be an option. A watertight 1/8" stereo jack would be really cool,
but I don't know if such a beast exists. Anyone seen anything relatively
small (ie not mains plug sized) like this?

2) Optical - The bottom of the case is clear, so I was thinking about
multiplexing the stereo signal into one stream and transmitting it
optically through the case. This could work. I would have to make the
internal portion of the circuit rather power efficient because I can't
put D cells in there to power it. I was thinking of multiplexing into
one signal because I was worried that if I transmitted two signals, I'd
get some interchannel interference as the light travels within the
polycarbonate.

3) RF - This shouldn't be too hard. There must be thousands of little FM
transmitters online. I would get one of those small cheap autoscan
radios to receive the signal. Again, I don't know how power efficient
those little transmitters are.

4) Induction - This one is perhaps a bit more wacky. I was thinking that
with a couple of coils on the inside, and two more on the outside, I
could pass the audio inductively between the two. Is this even feasible?

An ideal solution would be bluetooth of course. Though I have yet to see
a bluetooth stereo headphone, and no doubt it would be out of my price
range. If only there was an 802.11 headset :)

Ideas, suggestions, threats, all welcome :)

Josh
--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
        -Douglas Adams

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