Fwd: Re: Cheap Electronics Dissection Project
Kragen Javier Sitaker
kragen at pobox.com
Sun Oct 22 07:01:16 EDT 2006
[forwarded message originally from Shae Matijs Erisson on 2006-10-13.]
Kragen Javier Sitaker <kragen at pobox.com> writes:
> But the FCC doesn't rule the world.
Well, they rule the largest market...
(Or do they? What's the total market for radio using devices in Japan, etc?)
> I think the USRP is still a little pricey, and a paperback book is a heck of
> a big cell phone these days :)
Yeah, true... I guess the profile should either be backpack or pocket sized.
Nothing else is really portable. One good solution might be backpack size with
the new Marvell combo bluetooth & wifi chip (assuming they'll let people write
non-stupid drivers, see http://lwn.net/Articles/203562/ for details )
Nokia is making a stereo bluetooth headset, model BH-501. That would let you
keep your device in your backpack and use it without direct keyboard access.
> A wonderful list.
Did any of these ideas seem like good candidates for killer apps?
>> Things that come to mind are distributed detectors for nuclear explosions,
>> time/gravity distortions, radioactivity, etc
I thought I had a way to turn SDR into an ionizing radiation detector...
Don't remember what it was though, I should have written it down.
After fifteen minutes of thinking about it, I don't see how it would be
possible to use SDR to detect ionizing radiation. Neither scintillating nor
charged electrode detectors would benefit from SDR.
Still, I occasionally find an old file of ideas and wonder how the hell I ever
thought up a particular something, so maybe I had something good.
>> As for games, what about a "crack this encoding" that works like one of
>> http://www.pythonchallenge.com/ http://www.matessa.org/~mike/dutil-dumas.html
> If I get a chance I'll check out that second one when I get online.
What do you think?
>> Maybe 'social distance' could be a way to discover a good voice mesh
> What kind of encoding are you talking about? Presumably not an audio
> compression algorithm.
No, more than that.
With SDR you could easily tune the design of a signal to its intended use.
>> Cheap $50 mesh phones would be popular in places where cellphone networks
>> will never be setup due to economic or terrain problems.
> I'm not sure about this $50 thing. Maybe. I suspect it might need to cost
> less than that.
I think you're right, any ideas on how to make that happen?
> Good point, although sand dunes move pretty fast, so your node would be
> completely buried in a few weeks. You could probably just use thermocouples,
> or small solar panels.
If your entire device is the size of a pringles can you can just keep it in
your backpack or attached to your belt, and then give it a thermal gradient
when you're using it. Even half in direct sunlight half in shadow would give
> What's the appeal of liquid?
Spheres, disks, etc all force a particular shape on the component. If liquid
could flow through tubes and generate power, you'd be able to pack the
generator into most any device without affecting its overall shape.
That would also allow you to have a flexible generator.
Plus it'd look really cool to have a plasma globe that's powered by sloshing.
You could put it in your car or wear it to a club. Admittedly, it'd be in worse
taste than wearing ten kilos of gold jewelry, but it'd still be cute.
> Maybe you could have little turbines that drive a ratchet and pawl
Hm, yeah... I'll think about that.
> Yup. Also other kinds of development tools: simulation tools, perhaps
> development environments (esp. for things like the USRP where you need to
> program FPGAs.)
Yeah, it's too bad there aren't any FPGAs with publically documented
specifications. Netlists suck.
> That's a problem with radios in general. In the Wi-Fi case, my best-case
> received signal strength is something like -55dBm, or three millionths of a
> milliwatt, three nanowatts, and my card claims it can still at less than a
> picowatt. But when I'm transmitting, that same antenna emits as much as 100
> milliwatts, 11 orders of magnitude greater. It's hard to detect a signal
> when the noise is 10 orders of magnitude greater.
Nifty encodings like the one GPS uses would probably be quite popular if we had
SDR. I hope people would just try new stuff and record the results.
> So my Wi-Fi card doesn't try to send and receive at the same time, and the
> 802.11 PHY standard doesn't even try to do CSMA/CD, relying on RTS/CTS
> packets, acknowledgement, and PHY-layer retransmission instead.
And there's probably some nifty trick that will let you do CSMA/CD...
If only we had SDR so we could search for such a thing!
>> I discovered when reading about 802.11 frame injection attacks, I
>> don't think any wifi cards can listen while injecting custom frames.
> Or any other frames. Or do you mean that the time to switch back to
> listening mode is long enough that you can't see the response frames?
Yeah, switching time. Have you read "The Final Nail in WEP's Coffin" ?
>> Another important piece of infrastructure would be a library of antenna
>> designs and ways to build your own, extending on the cantenna idea.
> Possibly, especially when we have more automated fabrication. I think
> there's probably a lot you can do without it, though.
Yeah, it's not nearly as important as being able to send/receive signals in the
> Does that make it synthetic aperture radar if your GPS subtracts
> successive readings to tell you which way you're walking? :)
Right now GPS uses successive readings to get heading, but I wish for more...
>> FPGAs are good for reconfigurable hardware, but does that exist for
> Not that I know of. I wonder if it's possible.
Sure it is. At worst you could use a MEMS system like the color projectors that
have the zillion micromirrors inside them. Then you could build antennas out of
'pixels' just like anything else.
I've tried to teach people autodidactism, | ScannedInAvian.com
but it seems they always have to learn it for themselves.| Shae Matijs Erisson
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