0

Indoor Air Quality Monitor
Moderators: adafruit_support_bill, adafruit

Please be positive and constructive with your questions and comments.

Indoor Air Quality Monitor

by UW_BME on Mon Mar 22, 2010 5:29 pm

Hey there,
I need some help with a project that I am doing for my Biomedical Engineering design class. My design team is working on a project for a client who is researching indoor air quality in third world countries and wants us to design a sensor to detect different concentrations of particulate matter. Currently, we intend to use an analog air quality sensor which detects particulate matter and provides an output voltage which we are using to feed into an analog input on an Arduino Duemilanove microcontroller, which then outputs to three separate LEDs on three different digital outputs set at different threshold levels (i.e. good, moderate, poor air quality, a sort of "stop light" design). This part is a fairly simple task, but there are some other issues that are surfacing. The client would like us to log air quality data in addition to providing a user output via the three LEDs. Thus, we need a way to log the voltage data from the analog input (via the particulate matter sensor) at a frequency of approx. once per minute (1/60 Hz). With this in mind, do you think we can use the GPS datalogging shield ( http://www.ladyada.net/make/gpsshield/logging.html ) to accomplish this? If so, do we need the additional GPS module? We aren't interested in GPS data, just periodically recording the sensor voltage on the analog input. I was looking at the GPS shield because it has the flash memory portion, which I think may be a useful way to go about the issue of datalogging (though I'm not sure if we need the GPS module since we're not tracking position)? Perhaps there is another shield or method that is simpler for logging analog input voltage data for later use (i.e. analysis of particulate matter concentration over time)? Thank you in advance for any help!!!
UW_BME
 
Posts: 2
Joined: Mon Mar 22, 2010 5:13 pm

Re: Indoor Air Quality Monitor

by didier on Mon Mar 22, 2010 6:35 pm

Before taking care about the driver for such a system, I would concentrate on the analysis process. Based on you basic requirements (I did not say simple!), I foresee the need for some chromatographic system. The process of analyzing air contaminants is as follow:
Trap air pollutants by circulating indoor across a retaining support (e.g. Tenax column). A simple membrane pump will do the job; cooling the trapping column will increase adsorption.
Then back flush the column using a carrier neutral gas having small molecules (e.g. helium -expensive - or hydrogen - cheap and dangerous - ). Heat up the trapping column (ballistic start) while circulating carrier gas and connect the column to a catharométric detector. This type of device will detect the molecules that are bigger than the carrier gas molecule based on their respective size and thermal conductivity. Then you will have to relate the signals occurring at the so called 'retention times" compared to the signals acquired using reference gases.
A more complex alternative consists in using a mass selective detector (target mass spectrometer) as a detector.
It is feasible, but requires some plumbing and additional resources such as pure carrier gas. Are you ready for that, or are you in something much simpler?

didier
 
Posts: 115
Joined: Mon Nov 17, 2008 6:14 am

Re: Indoor Air Quality Monitor

by UW_BME on Mon Mar 22, 2010 6:46 pm

Thanks for the reply! The current (simpler) setup involves using a sensor ( http://www.shinyei.co.jp/kik/optical/dust_e.html ) which is designed to collect particulate matter and output a voltage proportional to the concentration (it runs off of 5VDC input, which we are providing from the Arduino Milanove, which will be powered by a 9VDC supply). It will likely be tricky to calibrate the sensor (we ordered the parts, but we are awaiting their arrival), and indeed this will likely be a difficult task in and of itself. However, assuming that we can get this sensor to work, and it puts out some voltage in response to a concentration of particulate matter, we need to know how to store this analog voltage information (e.g. on flash memory), which is what we are trying to figure out (unfortunately we are all Biomedical Engineers and not EE's or Computer Scientists, so our knowledge of programming and electronics is limited). Hopefully that clarifies the problem?
UW_BME
 
Posts: 2
Joined: Mon Mar 22, 2010 5:13 pm

Re: Indoor Air Quality Monitor

by franklin97355 on Mon Mar 22, 2010 9:35 pm

The arduino.cc site will have help on writing to flash and maybe there are tutorials here too>

franklin97355
 
Posts: 21362
Joined: Mon Apr 21, 2008 2:33 pm
Location: Lacomb, OR.

Re: Indoor Air Quality Monitor

by zener on Mon Mar 22, 2010 10:43 pm

You will need to do some thinking about "bits and bytes" also. Each analog read puts out a 10 bit number (0 to 1023 in decimal), so, one of 1024 possible values. You might not need this much resolution, so you could just use 8 bits which gives you 256 possible values. Now you want to store one sample every minute, so if 8 bits is OK then that is one byte per minute. So the next question is how many minutes per day, how many days, etc. You need to figure out the total memory space you will need. Likely a harder problem will be how to get the data out, and where is it going?

That is a neat sensor. I am guessing it works somewhat like a smoke detector.

zener
 
Posts: 4483
Joined: Sat Feb 21, 2009 2:38 am

Re: Indoor Air Quality Monitor

by didier on Tue Mar 23, 2010 3:58 am

This is an intresting sensor. For your records, French homes shall have to be equipped with fume sensors by 2015: quite a big market! This sensor looks much more intresting than the ones using radioactive element (problems of life time, waste disposal)

Back to your specfications: the terms "air quality" (in the context of "Biomedical Engineering" - I am in since 20 years now...) and "particules concrentration" confused me. Thus my answer which was very much quality oriented. As far as I understand the evaluation of air quality, we mostly deal with gaseous compounds.
But I undertand now that you want to deal only with the concentration of particules, and the sensor that you found looks promising. I could not downlaod the data sheet fromthe site link. Do you know of any other place where to get it?

didier
 
Posts: 115
Joined: Mon Nov 17, 2008 6:14 am

Please be positive and constructive with your questions and comments.