in our office, people use air sprays that stink worse than anything.
Anyone have any experience with a 'foul air' type air quality sensor ?
is methane the primary sensor gas for 'human' odors ?
do the sensors detect aresol sprays ?
I figure that we can add a sensor and then have the Arduino turn the exhaust fan on and off when odor is present.
I'd go for sulphur compounds.
Methane is odorless. The only reason you can "smell gas" from the stove or water heaters is because they add stinky stuff to it. This is required by law, for obvious reasons.
The actual stinky compounds include sulfur-containing ones (nearly anything with a thiol functional group will reek), but there are also non-sulfur-containing compounds like skatol that smell awful - and they're present at miniscule concentrations (like, ppm concentrations). Noses, even on humans, are incredibly good at analyzing scents.
This is the second request for such a project in the past two weeks. Is there something that gives you the idea that a sensor like this exists? I doubt the existence of such a sensor.
I Googled hydrogen sulfide sensor and found several possibilities. You might check this sensor: http://pdf.directindustry.com/pdf/synkera-technologies/mikrokera-4l-hydrogen-sulfide-sensor-p-n-727/54300-609117.html#open.
Paul
Train a dog to push a button.
I figure that we can add a sensor and then have the Arduino turn the exhaust fan on and off when odor is present.
Wire the fan so it's on all the time, or put a timer on it so it's on during office hours.
Wire the fan to the light switch, maybe with a timer that holds the fan on for 10 or 15 minutes after the light is shut off.
Use a motion sensor with a timer to hold the fan on for 10-15 minutes.
Why not make is easy and have the fan turn on every time somebody uses the bathroom. No need for expensive sensors.
H2S can be identified by smell ("rotten eggs") at 0.005 ppm (5 ppb) - that's a very low concentration, and I think H2S is likely the easiest gas to detect. This gives you an idea of the sort of sensitivity involved....
Note that H2S is not the only, and probably not the dominant component of the odor of feces.
mistergreen:
Why not make is easy and have the fan turn on every time somebody uses the bathroom. No need for expensive sensors.
In fact, I think this is required by building codes (out of concern for sewer gas backing up through improperly installed plumbing) in many areas - the fan has to be tied to the light switch.
DrAzzy:
This is the second request for such a project in the past two weeks. Is there something that gives you the idea that a sensor like this exists? I doubt the existence of such a sensor.
I searched the list for bathroom and odors, no joy.
maybe I just did not do a good enought job.
back in the 90's, indoor air quality was all the rage. CO2 sensors were being put in buildings and a half educated attempt at fresh air was put into action.
I remember sensors that were VOC, broad spectrum and would pick up pretty much anything, paint drying, carpet glue, even a drunk breathing near the sensor.
The problem at hand is that some people in the office use the facilities, then spray the air freshener. probably the most toxic stuff on the planet.
people use the facilities, spray the toxic stuff, then shut off the fan and walk away thinking all is well.
a timer that holds teh fan on for 15 minuters could be added, but that does not allow for someone washing out a coffee cup or washing their hands.
my need is to over-ride the fan controls and keep it running until some arbitrary threshold is reached.
I would figure something like 2x room levels. at least to get started. tweak the settings as we go.
Well, I must admit that this is only conceptual, but when our house was built, I pre-wired it for this to be installed.
Given that the toilet is in a "niche", an IR beam passing some 10 cm directly above the toilet seat.
If this is interrupted continuously for a period of 25 seconds, the fan will be activated for ten minutes.
Contact your HR rep and ask for sick leave or workman's compensation due to the hairspray making you sick. As to regular restroom stink, just say loudly "Hey, how about a mercy flush!"
Hi,
If you google gases in flatulence (keep it nice)
methyl mercaptan is one of the main olfactory sensitive smells.
Good old MYTHBUSTERS.....
Tom..... 
program the arduino to listen to the flush, alternativly hack an automatic flush ir sensor, also go the HR route
watch the video.
many english slang terms
I think you'll have another problem if it does actually work: who wants to be seen coming out of the bathroom when the stinky fan is running? Just make it run for 5 minutes for everyone.
I guess I look for how to do a thing and not all the possible reasons to not do a thing.
running the fan 24 hours a day is a waste of energy both the fan motor and cost of air conditioning.
running the fan for 15 minutes after the last person left if not as bad.
running it just because someone washed their hands is not needed
this would just keep it running for however long it takes to clear the air.
this thread has been more about why and not about how.
I am looking for how.
guess I will just order some sensors from ebay and see what happens.
A recent article in a German magazine (c't Hacks) mentions the use of the circuitry, built into "automatic air refresh" products from your supermarket. Sorry, I don't know how to translate the German product description better.
I did see that Airwick has an air quality sensor.
I think I read the article you mentioned. the person said his wifew would not let him take it apart, until he got tired of the cost of refills.
VERY tiny MEM sensor.... very low voltage.
I just ordered an MQ135 from e-bay, let you know next month after it arrives.
Hi,
Got to Odour Detect Compact
Tom....
This Singapore-based commercial product for public toilets reportedly detects ammonia and hydrogen sulfide, then sends out SMS.
http://smarttechnologies.sg/smell.html
The system, developed in 2013, has now been licensed to Convergent Smart Technologies, a local small and medium-sized enterprise.
Its director Cedric Hoon said the system has received good reviews from cleaning contractors. It costs about $1,700 to $2,000 (2000 SGD = 1500 USD) to install a set of sensors for two toilets.
Has anyone heard of a DIY guide for doing this?
Look into the MQ family of gas sensors (do a search on this board, they’re asked about every few weeks at least - or Google of course). They can do H2S and NH3. They are not very gas specific, though, but should be good enough.