[cleanairuk_news] Citizen science/low cost air pollution monitoring in Paris - 255 Euros

Network for Clean Air contact at cleanairuk.org
Sun Dec 9 17:26:37 GMT 2012


From: http://wiki.labocitoyen.fr/index.php?n=Hardware.Gasser

Gasser

Gasser is a self-contained mobile sensor for sensing NO2, O3, and SO2.
Currently we run it only with NO2 as that is the most present pollutant in
Paris.

Gasser has essentially three main parts:

    * The sensor (any analog or digital sensor can work) -- top left in
the main box.
    * The ADC & computer (analog to digital converter) -- main board
inside the box.
    * The communication medium (3G, ethernet, or write to an SD card) --
white dongle on the left side of the image.
    * Power -- black box on the left side of the image.

The Sensor

After testing an ensemble of various sensors and holding many long-winded
discussions with experts in the field, we have currently settled with the
Alphasense B4 series of sensors. These sensors, with their control board,
run in the ~100eur, but their precision is unmatched by anything else on
the market.

Output of the sensor is in the sub-mV range, and therefore proper
grounding and filtering of the lines to and from the sensor is essential.
Our first version of gasser (not documented here, but basically the same
idea just worse :P) was able to achieve precisions in the ~10ppb range
when tested in a laboratory setting.

*The ADC & Computer

We currently use a Raspberry Pi with a Delta-Sigma ADC. The Raspberry Pi
hardware is very nice (and cheap) for rapid prototyping, and allows us to
send sensor information to anything from a GPRS dongle to a megaphone
(both have been done). The software on the raspi is currently quite
trivial, taking in information from the open-source delta-sigma ADC's
library and simply sending it on either to the internet or to the SD card
in a file. As our software framework becomes more complex we will begin
pushing it to github or somesuch.

*The Communication / Storage Medium

We quickly fell in love with the Huawei E220 GPRS dongle, it has proven to
be extremely stable, cheap, and have rather good reception. Interfacing
with this dongle is quite easy, as it is fully supported by linux, so
simple configuration of wvdial allows the raspi to have a full internet
connection most anywhere in France. We use a SIM card from Free
(2eur/month), which comes out to be a rather good deal if you're not
sending inordinate amounts of data.
Power

We currently use an 8Ah battery often billed as something to "recharge
your iPad and iPhone" with. This works quite well as it allows for the
sensor system to stay on all the time, whether plugged in or not.
According to our calculations and trial runs, this should allow the system
in its current state to stay on for about 5-6 hours. It also allows the
system to stay on perpetually if given a 5v micro-usb input source such as
a tablet charger or other >1.5A 5v wall-wart.
Future Plans

Although there isn't much specific software to be run on the raspi, the
full system configuration has been rather thought out, and everything is
relatively foolproof (lost internet connections go back up, dead daemons
get restarted, etc.) Although it probably won't happen right away, we are
hoping to release a custom raspbian image with all the scripts and daemons
configured that would allow anyone to quickly and easily set up their own
monitoring system with this wonderfully cheap hardware.

*BOM

    * Raspi
          o ~30 eur
    * Huawei E220
          o ~35eur (amazon has them)
    * Delta-Sigma ADC for RasPi
          o ~30eur
    * AlphaSense B4-series sensors
          o ~110 eur
    * 8Ah phone charging battery (optional)
          o 30eur.
    * Wonderful plastic box
          o ~10eur

Total: 255eur for a high-precision highly-customisable mobile pollutant
sensing platform, and this is only the v2 prototype :-)






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