[Diy_efi] electronic nose

[Phil Hunter]

I'll start w/ a disclaimer that my place of underemployment advertises in
the magazine below, other than that, no associations w/ this post.

Figaro makes a variety of sensors to detect various chemicals and gases.
Some are highly selective, responding only to certain gases and ignoring
most everything else, others are more general in what they detect. They
have sensors for gasoline & diesel exhaust, carbon monoxide, R-12 & R-134a,
combustible gases such as propane & hydrogen, and many others:
http://www.figarosensors.com/gaslist.html 
Prices range from about $15 to $57 USD.

The Sept. '04 issue of Nuts & Volts magazine has an article on building an
"electronic nose" using a Figaro sensor. Basically the sensor is configured
as one leg in a Wheatstone Bridge, and a PIC microcontroller is used
to measure the Bridge's imbalance and drive a speaker to give an audible
indication of gas concentration. The schematic is in the article, but
unfortunately the parts list was left out, it can be downloaded here:
http://www.nutsvolts.com/toc_Pages/TOC_Related_Info/sep04_sniffer.htm
Back issues of the magazine can be purchased.

The author cleverly laid out the PCB in a round disk the size of a MagLite
flashlight lens. A 4 D-size cell model of the flashlight provides the
case and power supply. No permanent modifications are made to the MagLite
so it can be reverted back to a flashlight. The author has made the PCB
and programmed uC available, sensors are available from Figaro, and the
rest of the electronic components are from DigiKey & Radio Shack. Smoldering
it all together is done by you.

rgds,
philh

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