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I would like to build a electronic flatulence (fart) detector. I was thinking of methane because detectors are readily available, but I read http://en.wikipedia.org/wiki/Flatulence and it says:

However, not all humans produce flatus that contains methane. For example, in one study of the feces of nine adults, only five of the samples contained archaea capable of producing methane.

Oxygen, nitrogen, carbon dioxide are listed but I think they would be too common in normal air. That seems to leave:

  • Hydrogen
  • Hydrogen sulfide
  • Methyl mercaptan
  • Dimethyl sulfide
  • Dimethyl trisulfide

Does anyone know if practical sensors are available that detect those gases or have other ideas? I think somewhere around the $20 or less mark would be good, so I wasn't really seeking a full professional solution like gas chromatography that may normally be used.

The application is for under office type chairs, so maybe heat detection could be used although I'm not sure it would be posible to tell the difference between the desired event and someone just sitting down on a cold chair, although maybe a pressure sensor could be used along with some filtering to not trigger until the temperature had stabilized a bit.

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    \$\begingroup\$ Prevention is better than cure - install better ventilation \$\endgroup\$ – Andy aka Jun 8 '13 at 14:00
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    \$\begingroup\$ I kinda want to know why you feel the need to detect farts on a large scale. \$\endgroup\$ – Connor Wolf Jun 8 '13 at 14:25
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    \$\begingroup\$ I had a look and it appears CO2 in the atmosphere is still well under 500ppm, so that still might be worth considering. Pickup a CO2 sensor, some dried beans to half-cook and a six pack of beer and it should be a good initial test platform. \$\endgroup\$ – PeterJ Jun 8 '13 at 14:34
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    \$\begingroup\$ I sooo would like to see this project become a real product with a medical, FDA type approval just because all the legal issues to be solved before getting this thing into the market would be sooo much fun - starting with proper documentation of the intended use, and not leaving out the risk management process about what would happen if the gadget gave false results... \$\endgroup\$ – zebonaut Jun 8 '13 at 20:55
  • \$\begingroup\$ +1, this line gave me a good laugh: "... difference between the desired event and ..." \$\endgroup\$ – Anindo Ghosh Jun 9 '13 at 13:44
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It looks like Hydrogen is the major component: Normal Flatus. 360mL perday. How much per fart will take some closer reading.

Here is an Arduino flamable gas detector, it probably can sense Hydrogen: LM393 MQ-9, say, at 10ppm. (Some shopping legwork for a Hydrogen leak detector or flammable gas sensor is in order.) So a 36mL bolus of Hydrogen (I just guessed what volumes are emitted throughout the day to make up that 360ml, and guessed 1/10 of the total) must diffuse into a volume of 3600 Liters before it is below detection level of 10ppm. Your 10ppm sensor must be within about 100 centimeters. Looks like the under-the-seat location is the right spot.

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Methane was used by another guy used in his office chair to detect his own flatus, but if that source is real, Futurlec seems to offer dozens of gas sensors for whatever gas you like.

As an example: The Twittering Office Chair and it's Twitter account (apparently died of asphyxiation back in '09).

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Weird project. Chairs that detect farts? No thanks.

Anyway I would suggest you look at an off-the-shelf propane sensor. Propane (C3H8) and methane (CH4) are very similar. In fact many of them are described as Propane Methane sensors. They are cheap and made in the thousands for RV's and Boats. A friend of mine always said if he was too close the the sensor the alarm would go off.

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protected by clabacchio Jun 8 '13 at 16:19

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