The DFD is a small handheld device with a short, wide, open-ended tube protruding from the front. Rather than simply detecting the presence of a fart (which any nose can do) or requiring the wielder to wave it around people's bums, the tube provides directional sensitivity: when it's pointed at the source, the greatest cross-section is available for diffusing H2S molecules to enter the gas chromatograph section.

It beeps when it detects H2S: the greater the concentration at the detector, the more close-spaced the beeping.

The 'Tricorder' model provides an appropriate shape as well as sound effects.
-- FlyingToaster, Mar 28 2010

Google results for "handheld gas chromatograph" http://www.google.c...=&aql=&oq=&gs_rfai=
> 5,000 links: note that the Idea is directional in nature. [FlyingToaster, Mar 28 2010, last modified Dec 21 2011]

yahbut we can't do GM so replicating your schnozz to stick on an iPod is out of the question. Besides we don't want to have to apply it to people's arses, just wave it around and have it point to the person.

So a dedicated directional gas chromatograph.

I wanted to do a "See the Wind" (though something a bit different from your link) but couldn't figure out how to make it work.
-- FlyingToaster, Mar 28 2010


//identify between eggs, beans, cabbage, etc?//
a quick check says a GC can differentiate 3 different sulphur compounds so... actually it probably could, though that'd require some software to develop and use baselines and perhaps need to detect a few more non-sulphurous compounds... all a bit more than "aha, there's the person wut dunnit" type of thing. § x1
-- FlyingToaster, Mar 28 2010


I'm pretty sure I haven't changed my original proposal except of course having to sub in "gas chromatograph" instead of "standard method" which apparently wasn't acceptable to you, and having to continue to flog the fact that it was directional which I imagine some would gather from not only the existing explanation in the post but possibly the title.

anything else I can do for you ?
-- FlyingToaster, Mar 28 2010


(-) If portable gas-chromatographs become widely used as consumer items, I sincerely hope someone comes up with something better to do than this.

To find direction, triangulating between multiple sniff-points might work a lot better than hoping for a detectably directional diffusion pattern; I don't buy that this would work as written.

// The 'Tricorder' model provides an appropriate shape as well as sound effects
You know, I thought the sound effects for this thing kind of suggested themselves...
-- jutta, Mar 28 2010


<link> for existence of a handheld gas chromatograph.

I imagine "looking at" diffusion would be similar to looking at a light source in the fog: the direction it's in will still be visible. Since the perpetrator's clothing will still be a source of H2S for awhile, pointing a tube in that direction should result in a higher amount of migrating H2S molecules than pointing it somewhere else.
-- FlyingToaster, Mar 28 2010


To me, looking at a strong light source in fog is more like looking at a light source behind a milk glass screen - every big of glass (or reflecting fog molecule) lights up (scatters light) in proportion to its proximity to the light source, so it's like you're taking in a whole bunch of electronic-nose readings all at once and compare their strength which arrives directionally tagged via direct photon-mail to your retina. There are no comparable smell-photons.

There's probably a reason that sniffing animals find direction by moving the point that they sniff with, not by changing the angle of their nostrils.
-- jutta, Mar 28 2010


sorta the opposite: no matter how thick the fog, the light will still be strongest in the direction of it's origin: assuming the perp's pants will have a greater amount of H2S on them for awhile, they'd have a greater concentration than ambient.

not looking for a great amount of shift though, but there should be some.

still better than the other options:

- a flashlight that causes H2S to flouresce (except H2S doesn't flouresce)

- a focused maser (similar to the "midge killer" system) which randomly superheats points proximal to nearby large objects, until one of them blows up. Admittedly that would have it's advantages.
-- FlyingToaster, Mar 28 2010


Flatulent odor propogation (I can't belive I'm writing about this!) seems likely to be strongly influenced by air currents, which are in turn influenced by thermal effects.

[Jutta] has it right; a moving sniffer or multiple sniffing points would be required to identify the source of the odor. Not sure this is possible with a single handheld device, which would itself influence air currents simply by moving them around. Multiple bluetooth-linked detectors could do the job.

I expect acoustical detection methods would work better. A cluster of suitably-equipped i-phones could vector the offender with great accuracy.
-- csea, Mar 29 2010


//multiple sniffing points//
<wince> the idea's for *directional* not *positional*.
-- FlyingToaster, Mar 29 2010


//*directional* not *positional*.//

It's difficult to know the direction something is coming from unless one knows the relative positions of source and receiver(s)... perhaps it's time to let it go. ;)
-- csea, Mar 29 2010


no no, I think I know where it's coming from...
-- FlyingToaster, Mar 29 2010


So a device like an umbrella, that unfurls into a 2-m wide array of detectors. Could be fun trying to deploy it in social situations...
-- pocmloc, Mar 29 2010


Must be a definition of 'fun' I haven't encountered.
-- Nelipot, Mar 29 2010


Maybe it could analyse the fart and determine what the culprit had been eating. If you know what your friends eat, you can then figure out who was responsible.
-- Bad Jim, Apr 01 2010



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