Instructables
This Instructable explains how to use a gas sensor with your Arduino.

This lets your Arduino smell (and hence you program responses to) overall gas levels for a variety of nasties, including ethanol, methane, formaldehyde, and a bunch of other volatile organic compounds.

My cost to make this actual device was under $100, including the full Arduino kit. Here's a video:
.
And no, I won't put a shirt on:-)

I've got kits / finished versions of this and some other projectsfor sale @ my website

The closest comparable commercial products I can find are:
-a commercial-quality detector: $2500+
-a lab monitor: $295
-a one-off test kit for volatile organic compounds: $234

I learned about this after hearing about some guys who added VOC sensors to toy dogs. Not sure where/if the docs on that project are, but here's the guide that I followed.

Links explaining what VOCs are and why you might want to care:
-Some symptoms of overexposure to VOCs
-an OSHA regulation on formaldehyde levels
-information on sick building syndrome: 'A 1984 World Health Organization Committee report suggested that up to 30 percent of new and remodeled buildings worldwide may be the subject of excessive complaints related to indoor air quality (IAQ).'
-The Inside Story: A Guide to Indoor Air Quality: "For pollutants other than radon, measurements are most appropriate when there are either health symptoms or signs of poor ventilation and specific sources or pollutants have been identified as possible causes of indoor air quality problems. Testing for many pollutants can be expensive. Before monitoring your home for pollutants besides radon, consult your state or local health department or professionals who have experience in solving indoor air quality problems in non-industrial buildings."
 
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Step 1: Gather Your Supplies

You'll need:
-an Arduino (or equivalent)
-a cable to hook the Arduino up to your computer / provide power
-a computer to read values
-a potentiometer or resistor of known value. anywhere from 500-1k ohms should work
-the gas sensor: a pain to buy in small quantities. i bought 2 and they cost like $22 each, but volume orders get way cheaper... the specific sensor i used was figaro sensors's 2620.

Here's what I used:
-the arduino kit I used
-the different sensors available from Figaro (use different sensors to 'smell' different things)

It' useful but not necessary to have a multimeter and wire stripper handy...

The pdf included with this step is the price list from the sensor manufacturer as of March 2008.
Price 01_08 USA.pdf(612x792) 191 KB

Step 2: Set Up Your Arduino

1. Get your Arduino connected to your computer and functional
This should be pretty straightforward, especially with any newer Arduino. This guide worked for me.
2. Program your Arduino to read the value from an analog input and display this on-screen. I used
-this guide for using a potentiometer with an arduino and basically just modified the frequency with which it reads input value (delay(100) = read 10 times per second) to get the following code, which works for me:

//this outputs pot value to screen in ohms

int gasSensor = 0; // select input pin for gasSensor
int val = 0; // variable to store the value coming from the sensor

void setup() {
Serial.begin(9600);
}

void loop() {
val = analogRead(gasSensor); // read the value from the pot
Serial.println( val );
delay(100);
}

If you're using this as your first excuse to play with an Arduino, you might want to try just wiring up the potentiometer and reading the value from it before adding the sensor.

Step 3: Create Your Circuit

The picture attached is an image of the circuit from above (meaning that the sensor's leads are pointing towards the ground; there's a little metal tab protruding from the sensor to let you understand which pin is which. Also, check out the figaro guide for the specific sensor you choose. Attached is the datasheet, with some example circuits, for the 2620.

For the 2620, the datasheet specifies at least 450 ohms resistance needed. I tuned my potentiometer to ~right around 450 ohms.

In plain english, here are the connections you'll want to make:
-sensor pin 1 to an outer pin of potentiometer and ground (arduino ground)
-sensor pin 2 to other outer pin of potentiometer
-sensor pin 3 to arduino +5 v and sensor pin 4
-middle pin of potentiometer to arduino analog 0 input

You can solder this (read Figaro note on which type of solder and temperature exposure of sensors), but a breadboard is good enough for my purposes.
2620pdf.pdf(612x792) 109 KB

Step 4: Test Your Newfound Sense of Smell

With everything connected, you're ready to hook the arduino up to your computer, fire up the arduino environment, and start reading values. Don't forget (like I initially did:)) to hit the 'monitor serial input' button in the arduino software.

You'll then begin to see values scrolling in the black space at the bottom of the arduino program. These values are the resistance, in ohms, being read from the circuit.

To test, blow slowly for at least a few seconds over the top of the sensor. The numbers on the screen should change. Also try holding the sensor over a high-concentration chemical that it should detect: my value jumped quite a bit doing this.

With ~4 days burn-in and ambient temperature of 63F, the values I read in my house were (which is reasonably free of chemical use):
-sitting in the open air, after sensor warms up for ~1 minute: 52
-breathing slowly over the sensor for several seconds: 73
-holding sensor directly over an open bottle of grain alcohol: 235

Step 5: Build Away!

Without burning in this circuit for a week and adding a thermistor, this is really only good for reading relative concentrations of chemicals: eg, if you want a 'lower-VOC' paint, you could hold this over different open bottles of paint (in a room of constant temperature) and reasonably feel a bit safer using the paint that registers the lowest value. Obviously, there are nasties (and probably some VOCs: I don't know) that this doesn't detect, but it's definitely a bit better than nothing:-)

Attached is a pdf Figaro Sensors provided, detailing the response of thermistors at different temperatures. Definitely not the only thermistor you can use, but may be useful as you explore your own, better version of this project.

A cool expansion I want to see is to display the approximate level in parts per million (ppm) of air pollution on my back as I ride my bike through traffic, maybe with an LED 'Mr. Yuck' sign that turns on above a certain concentration as well. Let me know what you build, and have fun!
smohamad33 months ago
Is it possible for the experiment to work well if i changed to arduino uno and use 39k resistance? -urgent-
please help me.. ^^
jknotts18 months ago
Volatile Organic Compound not content and the equipment involved in Environmental and Occupational health surveillance is a bit more complucated because of the sensitivity that is required to detect many of the toxic industrial materials osha and the EPA regulate.. To coduct a survey you would at a minimum require the use of a photo ionization mechanism calibrated by a federally certified lab. and the sensors for things like oxides of nitrogen, or iso-cyonates exposure levels on a time weighted average basis and that is why you pay $3500 for a multirae gas detector that only reads O2 levels, and 3 slots for toxic gas sensors. I am also interested in designing equipment for health surveillance as well as creating custom microenvironments this design is definitely great for monitoring and control automation if you are interested in exchanging ideas on either subject I'm game. I am new to the electrical engineering field I am half way through my BAS in EE but my background includes 13 years of experience in the Army specializing in Environmental, occupational, and public health and years of college in an environmental science program before switching to a Major in Electrical Engineering.
alavasier1 year ago
I liseman. How did you convert the values readed by the microcontroller to ppm of pollutants? did you calibrate the gas sensor, if so how did you do it? or how did you find teh R0 of the sensor?
liseman (author)  alavasier1 year ago
hi alavasier,

You can roughly calibrate the sensor by matching readings to the datasheet, eg http://www.instructables.com/files/orig/FCF/712B/FEMHW1YS/FCF712BFEMHW1YS.pdf . Putting the sensor in 100% concentration of target gas vs. 100% of a non-detected gas will let you determine min and max.
How did you set the sensor so its already have a value in ppm ( the value gas in actual condition) which read by microcontroller?
ozmel1 year ago
hi i am doing a wireless sensor network for hydrogen monitoring. i chose arduino uno and MQ-8 hydrogen sensor. i want you to help for the design. sorry for my english i am a frenchspeaker. thank you
bojanmanev3 years ago
can i buy arduino online please tell me the site for buy a want to do this but i haven't got a arduino i m from macedonia
You can buy them assorted places online, in prebuilt or kit form. Since they are from Italy, I expect they're just as easily available in Macedonia as here in the US.
The main site is www.arduino.cc , but there are assorted other sites that sell them.
colorex2 years ago
How To Smell Pollutants? Can't stop thinking bout this...
http://www.huffingtonpodst.com/huffing.jpg
transuranic3 years ago
could iit be modified to smell any chemical?
Unfortunately, no.
Cyme3 years ago
VOC stands for volatile organic content. If your fart, the methane you smell is a VOC. If you drink a beer or a scotch--ethanol--the odour you smell are all VOCs. If you cook fries, the grease you smell is again a VOC. If you paint with an oil-based paint, the solvent from the drying paint are VOCs. And yes, these are air pollutants that can contribute to smog.


skybosg3 years ago
Put a shirt on!
yeagerxp3 years ago
you should be able to buy arduino from WEB, search for it, it is available in EUROPE,
I know a better way. If you breathe something, and promptly drop dead, it's usually a sign of polluted air. So then you'll know in the future - oh wait.
Actually I've heard of this being done, with birds in cages, not people.
godscountry3 years ago
add this board and sensors,to a quad rotor,a low cost way to inspect accident sites,train wrecks,chemical spills etc. without the risk to humans or animals .Maybe a sniffer for explosives,drugs
cdousley4 years ago
haha your brothers cool! so are you.
tmort5 years ago
can this circuit be modified to add more sensors for mulitple gases and a datalogger?
liseman (author)  tmort5 years ago
hi tmort, yeah, that should be pretty easy to do. if you need accuracy in terms of actual gas concentrations, consider borrowing a fancy, professional gas sensor to calibrate your arduino-based one... hope this helps! -luke
Coffee bean5 years ago
nice! think it could recognize welding gas leaks?
http://www.nenvitech.com/gas-detection-heads/type-3-heads/?searchterm=acetylene

This is For acetylene There's all sorts of Gas sensors though
polar bear66 years ago
why dont you have a shirt on lol
weird
timmy1234s6 years ago
Here is a better place to get the sensors. http://www.futurlec.com/Gas_Sensors.shtml
Could u upload a vid of u fartin on it and the reaction on PC. lol would it go crazy or what :O LOL
I had the same idea.
Great Instructable! Wow! Well Done! I just voted even though votes don't count for this contest but this should win! Great work. I think I read that article your talking about in Make magazine. Nice instructable!!
LinuxH4x0r6 years ago
Woah! I just use a fan when in doubt! Great job!
Looks... complicated.